text:
ADVISOR Frank Fisher
Castle Point on Hudson
Hoboken, NJ 07030
May 1, 2008
The following report contains official documentation for Mechanical Engineering
Senior Design Group 11, Piezoelectric-based Energy Harvesting. Contained
within this report is a comprehensive design and analysis of a new product: a
piezoelectric based energy scavenging floor tile that harvests energy from foot
strikes and sends wireless signals for building surveillance purposes. The design
will utilize ZigBee wireless transmission for communication between the tile and a
remote computer. The tile will work in two different ways. During times in which
security monitoring is not needed and people will be walking on the floor
continuously, the tile will harvest the energy created by the piezoelectric strips.
When being used as a security sensor, any step on the tile will create energy that
is sent to a microprocessor and the microprocessor will send a short message to
the remote computer noting that there was movement in the floor. This report
includes the development, implementation, and tests conducted in the design of
the prototype of the floor tile. The group was successfully able to harvest enough
energy using piezoelectric materials in the floor tile to power a microprocessor
and send a signal.
Executive Summary
Piezoelectric Energy Harvesting is an emerging technology with many new and
exciting applications. This project was undertaken using a particularly innovative
technological breakthrough in this field from a company called Advanced
Cerametrics (ACI) out of Lambertville, NJ. They have developed flexible piezo
composites that generate nearly ten times the power of traditional ceramic piezos
through the use of PZT fibers that exhibit the piezoelectric effect. This project
utilizes the direct piezo effect, which converts mechanical to electrical energy,
aptly entitled Energy Harvesting.
Armed with this technology a design team of five mechanical and four electrical
engineers took on the challenge of developing a unique application using this
emerging technology. Several concepts were considered including a medical
device, a game or toy, a sensing/monitoring application, a buoy light or
ocean/wave application, or a sports device. However, after significant
deliberation, a design comparison matrix, and the consultation of ACI, all of these
applications were eliminated due to complexity and/or unfeasibility. The team
considered it a better approach to take on a smaller scope and develop a
complete and working prototype than to take on too much and develop a
disjointed project.
As such, the final chosen application was chosen as an energy scavenging floor
tile system. With the plethora of wasted impact energy and the relatively
simplistic design scope of a floor system, our Stevens advisors and our company
sponsor ACI were supportive of our choice. As a corollary objective we decided
to use the harvested energy for a useful purpose, namely, to serve as a
surveillance device that outputs wireless signals exclusively from its natively
generated energy source.
The initial conceptual approach involved a floor tile mounted on a foam subfloor,
as explained in Section 2 of this report. The idea was that the piezoelectric strips
would be hard mounted inside the tile, and that the whole tile would displace on
the foam subfloor. Point masses were mounted on the piezo strips. As the tile
displaced a differential inertia was exerted on the strips because of the point
masses, causing the strips to vibrate and hence for energy to be generated.
However, testing revealed that only negligible amounts of energy was generated
in this manner. There simply was not enough energy transfer between the
footstep and piezo strips. Additionally, the large point masses required caused
the strips to vibrate at very low frequencies. Since the piezo strips generate max
power at their resonant frequency, this was undesirable.
As such, the team took on a new approach as explained in Section 3 of this
report. In order to maximize energy transfer, a spring loaded actuation system
was designed to physically actuate the strips in lieu of a foam subfloor. The
physical actuation eliminates the frequency issue by vibrating the strips at their
natural frequency. The system also allowed the strip to be vibrated twice per
footstep, once on the down stroke and once on the upstroke. The superior
advantage of this system was immediately apparent as voltage output from the
strips was orders of magnitude better.
Concurrent to this development were several changes in the system's electrical
components. The first attempt at creating an energy harvesting circuit involved
the use of a transformer, a homemade rectifier using four diodes, some resistors
and a 1F capacitor. Several iterations of this circuit were attempted, but only with
minimally favorable results. At best, the most favorable homemade circuit was
5% efficient, thus nullifying most of the energy generated through foot strikes on
the tile. At the ultra low power levels of the piezo strips the circuit components
were simply not applicable.
As such, through the consultation of ACI, a commercially available Energy
Harvesting Circuit model EH301 was purchased from a company called
Advanced Linear Devices. A PCB with a footprint of an AA battery, it offered a
much more elegant and simple means of storing energy. The device was
specially designed to handle a variety of input voltage spikes and both store and
retain small amounts of energy with great efficiency. Testing with a singular
piezoelectric strip revealed an efficiency of roughly 90%, orders of magnitude
better than home grown attempts. The electrical system of this project is
summarized in Section 4 of this report.
After several iterations of the actuation system to optimize its performance, the
mechanical and electrical systems were integrated and testing was performed.
The Testing and Results are more completely documented in Section 5 of this
A multimeter was used to measure the voltage stored in the capacitor bank of the energy harvesting circuit. The powering of the microcontroller was successfully demonstrated. as was the performance of the wireless transmitter. Except for this small electrical issue. The approach was to power a microcontroller with the Energy Harvesting Circuit output. as well as a more complete list of alternate uses and recommendations for piezoelectric development are summarized in Section 6 of this report. Several suggestions to improve the design of this system. The application performance has the promise of serving many other uses in addition to its surveillance application. Then. Therefore in just 20 footsteps the floor tile generated enough power to send 5 wireless signals. These including motion monitoring throughout buildings.3mJ of useful power. This signal was regulated to the correct voltage using a voltage divider to power the Zigbee wireless transmitter. Four piezoelectric strips were mounted in the floor tile and connected to the Energy Harvesting Circuit to maximize energy output. Having shown the system's energy generating feasibility. as is explained in Section 4 of this report. light proximity sensors or any other application that requires energy input on the order of 8. 4 . Several test variables were used and iterated upon in order to optimize the energy generating capability.3mJ or below. the location monitoring of vehicles. the project achieved its desired result. However. An ultra low power Zigbee wireless system was used with an energy requirement of approximately 1. the microcontroller would execute a program to create the correct output signal (USART) to power the Zigbee transmitter. the main issue of this project involved directing this energy to send a wireless signal.44mJ per wireless signal. The results revealed that only 20 footsteps were required to generate 8. the linkage between the two was unable to be achieved.report. due to time constraints.
and they served as a valued consultant and material supplier for its duration. Kim – Advanced Cerametrics Electrical Expert Traditional ceramic piezoelectric materials are very brittle. Materials research and technology improvements have changed the perspective entirely. and life in the range of millions of cycles. R&D Director Dr.advancedcerametrics. and have low electrical energy outputs per unit strain. Some examples include active smart sporting goods. infrastructure. and the application of piezoelectrics to a multitude of new applications is becoming an achievable possibility in light of these technological breakthroughs. including several other innovative and exciting uses of this emerging technology. Mark Vizthum. Eric McCormick. wireless sensors. A company by the name of Advanced Cerametrics (ACI) in Lambertville. Michael Ivey. 5 . Additional information about the company and the PZT material can be found at www. industrial equipment. ACI's flexible PZT composite materials generate ten times the amount of power from mechanical energy as other forms of piezo materials. next generation aircraft. David Manning.Advanced Cerametrics Co. Arturo Dizon Advisors: Professor of Mechanical Engineering Frank Fisher Professor of Electrical Engineering Bruce McNair Stevens Institute of Technology Machine Shop George and Bruce Advanced Cerametrics Company: Bud Cass .com. acoustical equipment. President Farhad Mohammadi – Advanced Cerametrics Co. automobiles. apparel and more.Acknowledgements Mechanical Engineering Design Team: Jim Waterman. A working relationship with Advanced Cerametrics was established throughout the duration of this project. sports gear. Shingo Matsubara Electrical Engineering Design Team: Neil Patel. is a pioneer in this technology breakthrough. NJ. motorcycles. Scott Hamilton.
.....................3..........................................................................................................................................................................3........................................................... 33 SECTION 5..................................... 9 SECTION 1.. 16 SECTION 2............3.... 23 SECTION 3................................3: SECTION 1........................................................................................................................ 29 SECTION 4................................................................................................4: ELECTRICAL PERFORMANCE SUMMARY ................. 18 SECTION 3: TILE DEVELOPMENT....................................4: PROJECT OVERVIEW ..............................................................................................2: INITIAL SUBFLOOR DESIGN ..............................3: INITIAL DESIGN SPECIFICATIONS ............................................................. 29 SECTION 4........................................................................................ 2 EXECUTIVE SUMMARY ......................2......................2: SUMMARY OF TEST RESULTS ...........2......................................................................................... 41 APPENDICES..............2: USING MAGNETS AS POINT MASSES .....................................................................1: FLOOR TILE INSPIRATION .............................................................. 16 SECTION 2................................................. 43 6 ............... 5 PROJECT OBJECTIVES ....... 15 SECTION 2....... 24 SECTION 3..............................2: INITIAL FLOOR TILE CONCEPTS AND DESIGN CONSIDERATIONS ..................................... 20 SECTION 3...1: SUBASSEMBLIES .. 31 SECTION 5: TESTING AND RESULTS ...........................................2: TESTING OF ELECTRICAL SYSTEM ............................. 30 SECTION 4.......................... 32 SECTION 5......................................................................................1: WIRELESS RESULTS ................................................................................................................................... 23 SECTION 3...................................1: HOW THE ELECTRICAL SYSTEM WORKS ......................3: OBSTACLES AND CHANGES MADE ...... 19 SECTION 3............................................3................................................... 11 FINAL APPLICATION CHOICE ...............................................4: SUGGESTIONS FOR IMPROVEMENT ..................................................................................................................... 9 INITIAL APPLICATION IDEAS................................... 36 SECTION 6: PROJECT CONCLUSIONS ............. 24 SECTION 3.....................................................................3: PERFORMANCE OF ELECTRICAL/WIRELESS SYSTEM .4: PROTOTYPE BUILDING ...............................................1: STRUCTURAL ANALYSIS .. 16 SECTION 2................................3: WIRELESS TRANSMISSION CAPABILITY .............................................2........3: ELECTRO-MECHANICAL MODELING .........................................2.. 40 REFERENCES................................................................1: SECTION 6.................. 39 CONCLUSION ......................................... 22 SECTION 3......................................................................................................... 37 SECTION 6................ 17 SECTION 2.........................................................................................2: SECTION 6........... 39 RECOMMENDATIONS ............2: SECTION 1................................................................................. 9 MATERIAL BACKGROUND................................................... 14 SECTION 2............................................................... 24 SECTION 4: ELECTRICAL SYSTEM ...1: SECTION 1...................... 37 ALTERNATE USES AND APPLICATIONS ..................................1: DESIGN EVOLUTION ...............................................................Table of Contents ABSTRACT .......................................................4: SYSTEMS PERSPECTIVE OF INITIAL CONCEPT .......... 9 SECTION 1: PROJECT BACKGROUND ......................................................................................................2.............................................................................................................................. 14 SECTION 2............ 2 ACKNOWLEDGEMENTS ..........................3: UNEVEN DISPLACEMENT OF THE TILE ............... 26 SECTION 4................................................................ 27 SECTION 4.....................2.......................................1: SUBFLOOR DEVELOPMENT....................................... 35 SECTION 5......1: TEST RESULTS ..............................................3: SECTION 6.......................2: SPRING SELECTION ........................................................... 12 SECTION 2: INITIAL FLOOR TILE CONCEPT ................................2: ACTUATION SYSTEM .......................................... 23 SECTION 3............................................................................................................................................................................................................................................................................................. 19 SECTION 3............................
....................................................................................................... FOAM SUBFLOOR FIRMNESS......................... 16 FIGURE 9............................ STORED VOLTAGE VS............................... 31 FIGURE 25.............. SYSTEMS PERSPECTIVE ........................................................................... 33 FIGURE 29................................................................. 34 FIGURE 30...................... STORED ENERGY VS.... FINAL PROTOTYPE .................................................................................................................................................................. DIAGRAM OF MICROPROCESSOR & LED OUTPUT .... ACTUATION SYSTEM .......... 10 FIGURE 4.............. FINAL SYSTEM DESIGN............................. 19 FIGURE 12...................................................................................................................................................................................................................... 15 FIGURE 7...................................................... 10 FIGURE 3................. SUMMARY OF TEST RESULTS ............................................................. CROSS SECTION OF PZT FIBERS ...................................... 21 FIGURE 16............ 9 FIGURE 2... SUGGESTED IMPLEMENTATION TECHNIQUES FOR FUTURE PROJECTS ........................................................................................................................................ # OF STEPS ........................ INITIAL TILE DESIGN ......................... ENERGY HARVESTING CIRCUIT SCHEMATIC......................................................................................... 32 FIGURE 27............................... FEM ANALYSIS . 19 FIGURE 11............................................................................................................................. # OF STEPS ...... CAPACITOR LEAKAGE RATE OF ENERGY HARVESTING CIRCUIT ................ HOW THE SYSTEM WORKS .................................................. 28 FIGURE 23................................... PRINCIPLE OF OPERATION ................................................................................................... 32 FIGURE 28................................................................................................................................................................................... 15 FIGURE 6.............. 35 TABLE 1............................................. FINAL TILE DESIGN ...... 22 FIGURE 17.................................. MISSING DESIGN OBJECTIVE .............................................................. SYSTEM WIRELESS TRANSMISSION CAPABILITY ............................... STATIONARY ACTUATION BAR....... 39 8 ................................. 30 FIGURE 24.. 20 FIGURE 13........................ 26 FIGURE 21............................................................... PLACEMENT OF ELECTRICAL SYSTEMS IN TILE .Table of Figures FIGURE 1........................... TERMINAL GUI................................................. SECOND STAGE TILE DESIGN . STRIP MOUNTING BLOCK................................................ 16 FIGURE 8............................. DIRECT AND INDIRECT PIEZO EFFECT ............................................................................... 25 FIGURE 20..................... 35 TABLE 2...... 36 TABLE 3.............................................................. 14 FIGURE 5............................ ILLUSTRATION OF TEST SETUP .......................................................... TEST SCHEMATIC ........................... ELECTRICAL SYSTEMS DIAGRAM.. 22 FIGURE 19..... 26 FIGURE 22...................................... INITIAL TILE CONCEPT ...... 21 FIGURE 15.......................................................................................................................................................................... SAMPLE DANCE PAD .................... SPRING LOADED SYSTEM ......................... 20 FIGURE 14........... PIEZOELECTRIC FIBER COMPOSITE STRIP ........................ 22 FIGURE 18....................... 18 FIGURE 10....... 31 FIGURE 26........................................... INSPIRATION FOR TILE CONCEPT ............................................................................. 38 FIGURE 31......
2: Material Background The material properties described above offer three very unique ways to develop a new and exciting commercial application: 1) Signal Generation – electrical energy output of the material in response to strain is proportional. Section 1: Project Background Section 1. Typical Project: examines the solution to a given problem by evaluating several concepts This Project: takes a new form of technology (the piezoelectric material) and examines applications in order to pick the most suitable application to solve current problems Section 1. capacitor. can be used as a sensor 2) Energy Harvesting – trickle charge a battery. and therefore it is different than most senior design projects.1: Project Overview Piezoelectric materials create electrical charge when mechanically stressed. or other energy storage device from repeated strains and/or oscillation 3) Geometry Manipulation – feed varying voltages into material to create strains/oscillations 9 . The converse effect is also true for these materials. meaning application of an electrical force can cause mechanical movement. Thus. Figure 1. Use the harvested energy as the sole source of power to transmit wireless signals for building surveillance. The below diagram summarizes this unique material property. the approach is different. Direct and Indirect Piezo Effect The purpose of this project is to find a truly unique application for piezoelectric material.Project Objectives • • Utilize the unique properties of PZT (lead zirconate titanate) fiberbased piezoelectric materials developed by Advanced Cerametrics Company to design and develop a floor tile that harvests energy from a foot strike.
NJ. is a pioneer in this technology breakthrough. no longer a negligible amount like piezoelectric materials of the past. next generation aircraft. and have low electrical energy outputs per unit strain. Their piezoelectric material promises a functional amount of power. • • Advanced Cerametrics Inc. simply from the movement of the phone. that is useful and practical. o Convert up to 70% of energy from ambient vibration to electrical power o Most efficient transducer material available today. acoustical equipment. sports gear. flexible PZT composite piezo strips Features: o 10X more power than ceramic piezos o Eliminate battery replacement o Tested to over 1 billion cycles with virtually no output degradation. wireless sensors. This creates a potential difference which is carried away by a center electrode in the form of an AC wave. motorcycles. Cross Section of PZT Fibers extreme life span power in areas previously thought impossible. A company by the name of Advanced Cerametrics (ACI) in Lambertville. Harvested mechanical energy can be tapped to provide Figure 3. Piezoelectric Fiber Composite Strip The bending of the piezo fibers create dipole moments in the material. Think of one day powering a cell phone without batteries. The barriers imposed by 10 . ACI's composite materials generate ten times the amount of power from mechanical energy as other flexible forms of piezo materials. Materials research and technology improvements have changed the perspective entirely. infrastructure.Traditional ceramic piezoelectric materials are very brittle. and life in the range of billions of cycles. Some examples include active smart sporting goods. They produce a composite material with an aluminum substrate. piezoelectric active fibers Figure 2. industrial equipment. apparel and more. and the exciting nature of this material is immediately evident. and the application of piezoelectrics to a multitude of new applications is becoming an achievable possibility in light of these technological breakthroughs. automobiles. and PZT piezoelectric fibers spun into the material.
This concept would sense the over-extension of the knee using the piezoelectric material and provide additional support when needed to stabilize the patient. it may be possible to run the game solely using piezoelectric energy. low cycle life. 1. 2. 2. were investigated by the team. For additional information about the material see Appendix 1C. consultant and material supplier for the duration of this project.3: Initial Application Ideas Five different conceptual designs. 3. Medical Device Game or Toy Sensing/Monitoring Application Buoy Light or Ocean/Wave Application Sports Device These ideas are explained briefly in the following. and minute power output are things of the past with these new flexible composites. A working relationship with Advanced Cerametrics has been established. most knee braces only provide lateral support. These electronics can include flashing LED's or sounds that come from the game. The five concepts initially investigated were as follows: 1. Game or Toy Application Another application is a game or toy for younger children. and a feasibility study was conducted on each concept in order to choose the most suitable application with current knowledge and research. Section 1. and in a game that includes a significant amount of motion from its players. such features require a battery to charge the electronic system. completely different in nature. Often. 5. see Appendix 1A . and send signals to a microprocessor. As it currently stands. as well as the frequency of the material oscillation will allow for logicbased programming in the microprocessor to auto-stiffen the brace.Details of Initial Five Innovative Ideas. Medical Device – Auto-Stiffening Knee Brace One application we considered within the medical device field was to develop an auto-stiffening knee brace. This application would place the piezoelectric material on the brace joint.traditional ceramic piezoelectrics like brittleness. Sensing/Monitoring Application 11 . The amount of bend on the material. they have functioned as a partner. and throughout the semester. The use of electronics in children's toys is very common. 3. For more detailed description of each idea. 4. and a new frontier of product development is now possible.
Piezoelectric sensing is ideal to replace the current detection system designs by placing the strip of piezoelectric fibers along the edge of the door or inside the rubber cushion.4: Final Application Choice By looking at the final results. as we moved further and after extensive research.Self Sustained Navigation/Sensing Buoy System This concept involves designing a self sustained navigation or sensing buoy to utilize the immense amount of power that exists in the constant movement of our oceans. As the sport of golf continues to flourish in recent years among all age groups.This idea involves using the piezoelectric material as a door sensor for transportation modes such as trains and buses. This club will be able to be used on the driving range hitting real balls. we found that this idea was not feasible after a trip to Advanced Cerametrics based on the following criteria: -Functional specification too difficult -Scope too large 12 . We believe this to be possible by starting the design from the ground up. we moved forward with that as our desired product. or in any open area without a golf ball while shadow training. the group could see that the knee brace scored the highest rating based on this system. by creating a design comparison matrix. When an object is caught in between doors. Since the knee brace scored the highest. 5. the piezo sensor is bent and the voltage created can be used as a signal that indicates that something is jammed. effectively eliminating the need for batteries. high output LEDs and designing an extremely efficient sensing circuit. Buoy Light or Ocean/Wave Application . Utilizing low-power. Instead of charging a battery during daylight hours we would like to design a system that is generating power constantly. the group was able to judge each of the applications in different fields to see which would be most beneficial. After all the ideas were developed and presented. it will be much safer for people going through doors.Design Comparison Matrix for Different Applications for the detail of formation and evaluation of matrix. in order to effectively create a swing training aid. there is an ongoing market for golf accessories and training aids. Section 1. Sports Device – Golf Club Training Aid This product would incorporate a piezoelectric material into a golf club. See Appendix 1B . 4. However. and anywhere in between. This product will allow the golfer to modify their swing from a slice to a fade. A piezoelectric sensor which can create voltage in response to small mechanical strain will be more sensitive to detect small objects and as a result.
and it was thought that a surveillance floor tile which harvests energy and sends wireless signals by its own could be designed using similar mechanisms. and decided to pursue a more feasible project of an Energy Scavenging Surveillance Floor Tile that utilizes the unique properties of PZT developed by Advanced Cerametrics.1. our group decided to scrap the original idea of an auto-stiffening knee brace. More details of our inspiration are explained in Section 2.-Need advanced medical knowledge -Solution looking for a problem. The idea of the floor tile came into our minds after seeing a demonstration of a wireless temperature sensor exclusively powered by PZT strips inside. not a problem looking for a solution Therefore. 13 .
By holding the piezoelectric strip in hand and swinging it back and forth the device is able to send wireless signals of temperature readings to a laptop computer.1: Floor Tile Inspiration In the middle of the semester the group took a trip down to the piezoelectric material supplier. This section will start with how the floor tile idea was conceived. and end with analysis of the preliminary design.Section 2: Initial Floor Tile Concept Once the group realized that there were insufficient resources and schedule to fully develop a working knee brace product by design day the group switched gears to begin designing and developing the Self-Sufficient Wireless Surveillance Floor Tile Concept. Inspiration for Tile Concept The Harvestor Power Module on the left is a simple device that can be used to energize low-power electronics. While in a meeting with the owner of the company the group saw two working piezoelectric energy harvesting concepts seen below. The group would mount multiple 14 . Just by tapping the box on a table the device is able to power a trip computer for a bicycle. Section 2. The Fiber-Powered Wireless Sensor on the right is also a very simple device that was demonstrated for the group. Advanced Cerametrics. continue with the original conceptual designs. Section 2 highlights the beginning stages of the floor tile. Fiber-Powered Wireless Sensor Harvestor Power Module Onboard electrical energy storage in capacitor Wireless Temperature sensor powered exclusively by fiber strips + Piezoelectric Strips Capacitive Storage Circuit Figure 4. By combining these two concepts the group came up with the idea for the Energy Scavenging Surveillance Floor Tile.
2: Initial Floor Tile Concepts and Design Considerations In order to be able begin the design of the floor tile concept the group decided on the following project objectives. because it involved piecing together concepts that were observed as being feasible and using those concepts in a unique application. The power produced would be used to send a wireless signal to a computer alerting security of a breach. brainstorming began on the best way to execute the design objectives. The group was much more optimistic about the Energy Scavenging Floor Tile. It was decided to create an individual hollow tile system that was completely self-sufficient. Initial Tile Concept 15 . Development of the knee brace concept was stopped due to complexities that made the feasibility of successfully developing the device in the time given questionable. Invisible Fence for building security Sends wireless transmission upon foot strike Completely self-powered Modular (can implement one or several tiles) State of the art: others have tried creating such systems with little success (see Appendix 2D for State of the Art) Figure 5.piezoelectric strips in a floor tile that would be triggered by a footstep. To house all of the electrical components and allow the Figure 6. All components of the tile would be contained in the floor tile so that it implementation of a multiple floor tile system would be easy making the tile extremely modular. Principle of Operation Once the objectives were set. Section 2.
or polycarbonate plastic (Lexan). The group sided with Lexan because it is easy to work with and transparent. This design concept came from the idea of having the tile deflection seem very similar to the deflection experienced when walking on carpet. Based on this chart. For more detail on the Structural Analysis please see Appendix 2C. constraint locations. Section 2. Section 2. material choices. Figure 8. the group began looking for other variables that affect 16 . Foam Subfloor Firmness Section 2. making all of the components easy to see on design day. The model to the right went through multiple iterations with the different variables. With general design of the tile decided on. The group found the chart below from McMaster Carr to conceptualize the varying firmnesses of the foam products available. FEM Analysis Max Stress = 2400 psi Based on the maximum stress the group concluded any of the proposed materials could be used: Aluminum.3: Electro-Mechanical Modeling Once the structural aspects of the tile were analyzed and development of the subfloor was underway. and different casing design setups.2. the group went on to develop the material and dimensional specifications of the tile through a structural analysis.piezoelectric strips ample room to vibrate the group came up with design to the left.10 in thick walls Bottom Constrained Figure 7. Steel.1: Structural Analysis An FEM analysis was performed using ProEngineer changing variables such as loading. In order to activate the piezoelectric strips.2. The group decided to use a foam material to allow this deflection and then bring the tile back to its home position when a person steps on and off the tile. the group ordered a sampler pack of foam to test performances of the different foam materials available. The following characteristics were found to be suitable from these iterations: .2: Initial Subfloor Design The next major milestone the group conquered was the development of the subfloor. the tile would need to deflect slightly.2. PVC. wall thickness.
All of these sub-systems combine to make our modular. The group performed extensive mechanical and electrical modeling which can be found in Appendix 2A: Electro-Mechanical Modeling. floor tile that transmits wireless signals upon impact.the performance of the floor tile. It was realized early on that piezoelectric material is extremely sensitive. self powered. Section 2. For our application there are four distinct sub-systems. and that the electrical performance characteristics are dependent on the frequency of the vibrations. For each of the systems the group developed analytical models to determine specifications. The electrical system will be described in detail in Section 4 of this report. Each of these sub-systems was analyzed as an individual unit with their own design specifications.4: Systems Perspective of Initial Concept The graphic below displays the breakdown of our complete system into subsystems. which were then used as guidelines for developing the finalized model. the piezoelectric composite strips. and lastly the circuitry and wireless transmission.2. the sub-floor. As you can see on the graphic the four systems are the floor tile. 17 .
3: Initial Design Specifications At this point the group had the floor tile concept completed on paper. Systems Perspective Section 2. It was time to start thinking in depth about fabrication of the tile so testing could begin. but many changes needed to be made for the final success of the project. These specifications proved to be a great starting point for the Energy Scavenging Surveillance Floor Tile system. Specification tables can be found in Appendix 2B: Initial Design Specifications. The group used all of the data and information collected from the various analyses performed to determine specifications for the tile concept. These changes are discussed in detail in Section 3: Tile Development. 18 .Systems Perspective – Analytical Models Floor Tile Dimensions Material of Construction Modularity Sub-floor Spring Modularity Foam Complete System Piezoelectric Composite Strips 3 Composite Types Length of Strip Point Mass Electrical Circuitry and Wireless Transmitting Circuit Transmitter Receiver Figure 9.
The major addition in this stage was having a new way to clamp the strips within the tile. there would be a mounting block placed in the tile that could be used to clamp the strips independently of the tile. This section discusses many of the obstacles and advancements the group faced as the project developed. 19 . The design in this phase included the strips being clamped between the tile halves to limit the number of parts. The other aspect that was added in this stage was using Lbrackets to construct the walls of the tile.1: Design Evolution The design of the tile went through several stages as our understanding of how the tile would work developed. The initial design incorporated the key components that needed to be included in the tile. the newly designed strip actuation system and the prototype building phase. The consisted of the four piezoelectric strips attached to a circuitry system.Section 3: Tile Development As the project proceeded. Section 3. The shelled exterior of the tile was also developed in this stage. the obstacles faced. Figure 10. the tile went through various changes and improvements. Figure 11. Initial Tile Design The next stage in our design incorporated several changes that can also be seen in the final design. There were many variables to the design which were not incorporated at the initial level of our development. you can see the various stages that the design went through with the key changes made at each step in the project. Below. Rather than having them between the tile halves. The key points that will be outlined in this section are the evolution of the tile design. Second Stage Tile Design This was done to add more stability to the exterior of the tile and eliminate the need for an adhesive which was the original idea for tile construction.
Section 3. Final Tile Design increased in this design because a box with a top design was desired rather than having two equal halves to the tile. we had to brainstorm new ideas for creating the vibration. Final System Design bases and the lexan side walls. This actuation system enabled the strips to be flicked rather than relying on transferring the energy from each footstep through the tile and into the strips.2: Actuation System The key development made in our project evolution was the addition of an actuation system to enhance the vibration of the piezoelectric strips. By cutting down the losses in energy and maximizing energy transfer. This was done to provide more space for the electrical components to be placed behind the strips. The key addition added in this final stage was the actuation system which is outlined in detail in the following section. The actuation system created has several key components that are detailed in this section. Because of the fact that the initial vibration design was not sufficient in exciting the strips effectively. These components consist of a spring loaded tile design. The walls of the tile were also Figure 12. The new additions in this stage include adding more brackets in the corner of the tile for increased stability as well as moving the mounting block to the center of the tile. the 20 . There are vast differences in this design from the initial design. The plan after this stage was to create the tile after this design and place it in the system with a foam subfloor to get the required strip vibration.The figure to the left shows the final design for the actual tile. a stationary actuation bar used to flick the strips. one further stage was added to the design development. Since this method was not sufficient. The side walls were created out of the same material as the tile walls to provide minimal friction during the tile displacement. This includes the finished tile design placed within an entire system that was used to enhance the vibration of the strips with each footstep. This figure outlines the final design for the entire system. Other components added into this final design are the wood block Figure 13. and threaded rods to vary the tile displacement.
by creating this system.5") Lexan Sidewalls do ¾" Wood Board (2X) Springs (4X) Figure 14. For a full scale picture see Appendix 3C. we were able to sufficiently actuate each of the strips for maximum power output. As stated above. along with an outline of several of its subassemblies can be seen below. Figure 15.controls height/spring pre-load Allowable Displacement (0<do<1. Actuation System The actuation system with each of its major components can be seen in the figure above. A description of how the system works. How the System Works 21 .group was able to achieve a much better strip vibration that could generate a functional amount of power. Aluminum Mounting Block PZT Strips Energy Harvesting Circuit (reduce friction) Actuation Bar Assembly (Stationary) Threaded Rod (4X).
This component of the actuation system is the spring load assembly. The end of the bar that the Figure 16. Figure 18. The selection of the springs was made based on the Figure 17. The block design provides several advantages over other options that the group had for strip mounting. The design of this component allows for a maximum 1. As you can see. rounded edge on top and a sharper edge on the bottom to make sure the strip returned once it passed the actuation bar. Spring Loaded System minimal force that would be exerted in a single footstep. By keeping the bar stationary. This final subassembly is crucial to the performance of our strips.2.Section 3. Strip Mounting Block 22 . This is the portion that is responsible for the displacement of the tile with each footstep.1: Subassemblies The first component that can be seen in this figure is the stationary actuation bar. The key components that can be seen in the figure are the wood base boards which contain slots for the 4 springs to be housed. This would enable this component to be completely stationary while the tile moved vertically past it. it would allow for a significant flick in the strips as they passed the bar and were deflected. More details of this selection and sizing can be found in the section on spring choice. That was done to increase the amount of power generated from each footstep. it includes the four piezoelectric strips placed onto an aluminum block and clamped down by having a small aluminum strip screwed into the bottom block. Stationary Actuation Bar strips contact was changed a few times to optimize the deflection received before the strip was released in passing. The design of this part of the system enabled a small vibration of the strips on the way down followed by a full vibration when the tile returned to its initial position.5" displacement in the tile which can be adjusted to limit the movement from a single footstep while still sufficiently actuating the strips. The final design of the bar had a smooth. The posts of this bar were designed to go through the tile and the spring system to the bottom of the system.
Also. This was the major cause for the newly designed actuation system that was detailed in the previous section. and an alternate idea was decided upon. This would allow the displacement to be small enough that the pedestrian would not notice the movement of the tile. we discovered that the tile we had created was too rigid and that the energy from each footstep was not being translated into the piezoelectric strips. we looked into several different springs to use.3. To be safe. Section 3.2: Spring Selection The selection of the springs to be used in the actuation system was crucial in the performance of our tile. We also wanted the free length of the spring to be the 3 inches needed to have the tile flush with the top surface. made of a foam pad. evenly distributed throughout the springs. Our goal was to have this amount of force displace the tile the necessary 1. but also compress a sufficient amount with even a small applied force.2. 23 .First. This provides us with ample space in front for the strip vibration and in the back for the housing of electrical components. the back ends of the piezoelectric strips where the wires come out of are able to extend from the back of the mounting block. This section will detail many of the areas which required further development as our project progressed through its timeline.3: Obstacles and Changes Made As is the case with any project. we tested its abilities using several different subfloors. The final spring selection with its specifications can be seen in Appendix 3A. However. we used a weight of about a 100 pound person. This would translate to a 25 pound force on each spring. We needed to find a spring that could support the full weight of our tile at its free length.1: Subfloor Development The initial idea for our tile displacement was to place a subfloor under the constructed tile.5" for full displacement. With the design considerations in front of us. The reasoning behind this design was to make the floor similar to that of a carpet and receive vibration in the strips from that small tile displacement. Section 3. changes were made to help improve the effectiveness of our system. From this testing. it enables us to place the strips anywhere in the tile. The power outputs achieved from these tests were minimal. At several points in the design and building of our system we realized that our initial plans for the tile would not work in effectively achieving the output power we needed. our tile system ran into many obstacles along our path. several problems were run into with this method. Throughout the course of the project. Section 3. This was due to the fact that the tile would need to displace with the footstep of any human being. Once the tile was completed. rather than constricting us to just along the sides.
the group was able to conclude that the magnets were able to increase the vibration amplitude while keeping the frequency well within the range of maximum power output. a production version would definitely be designed and constructed differently. the force on the tile would cause an equal displacement regardless of which part was stepped on.3. we were significantly reducing the frequency of vibration which is key in acquiring optimal power output. certain sides of the tile would depress more than others. Section 3. One other consideration would be to have the two 24 . Section 3.3. However. After testing several times without any mass. The tile could be molded in two separate halves that could be assembled using press-fit fittings.3: Uneven Displacement of the Tile With the initial design of the actuation system. we were sometimes receiving uneven displacement from each footstep. The main differences would be in the material and construction method used in producing the tile structure. Unless the tile was stepped on directly in its center. but a production model would most likely be made of high strength injection-molded plastic or stamped out of metal. Once this change was made.Section 3.4: Prototype Building The design of the prototype tile is ideal for optimization testing and for displaying components on design day. The inner workings of the system would remain very similar although optimized even further to reduce unit cost. the idea was to find a dense mass that would be small in size but high in weight to increase the amplitude of the strip vibration as much as possible. the group decided we still needed to optimize the vibration slightly. The final design includes two magnets placed towards the end of the strips.2: Using Magnets as Point Masses As a way to enhance vibration in our strips. the group soon realized that by doing this. After this conclusion. the group decided that the actuation of the strips was sufficient without and point mass on the strips. These are placed on each side of the strip and attached using heat shrink tubing. However. Initially. the group decided to put point masses at the end of each of the strips. To decrease the number of components and materials used the mounting of the piezoelectric strips could easily be integrated into the molding of the bottom half of the tile. The group chose Lexan for the prototype for its transparency and suitable strength. The solution decided upon was to place a gap closer on each side of the system to ensure the tile would move only directly up and down. The main cause for this was because there was a 1/8" gap included on each side of the tile to eliminate any possibility of galling from the plastics rubbing against each other. It is easily assembled and disassembled as well as being transparent. Through testing. There was also a small amount of grease placed between the two plastics to ensure smooth travel. This would prove to be material efficient as well as much labor intensive than the prototype.
For our design day prototype. we included numerous L-brackets to ensure proper support for the tile. the group had a large amount of work to do in a small amount of time. In our current design. However. Because of the fact that the actuation system was not incorporated until only a few weeks before senior design day. Final Prototype 25 . the group would limit the number of L-brackets necessary to still make the tile completely stable. To reduce this. the tile required countersunk holes and screwing processes which take up sufficient time during manufacturing. While the tile was fully constructed. with each of these supports.halves easily separable. the group wanted to make a fully usable system incorporating our tile design as well as our actuation system. the exterior box and the spring loaded system would need to be developed. A picture of the final prototype in use can be seen in the figure below. This would support maintenance and repair of the floor tiles in the field when necessary. When building the prototype. As the prototype developed. we were able to make changes as we saw them necessary to make a working prototype for our final testing. the group discovered several other areas that could make future building of such a tile much easier. The major area for improvement would be to reduce the number of screw holes necessary for the tile construction. Figure 19.
Section 4: Electrical System Figure 20. Electrical Systems Diagram Output Input from Piezo Strips Rectifiers Energy Harvesting Circuit Figure 21. Appendix 4B for data sheets and electrical parts list 26 . Placement of Electrical Systems in Tile *See Appendix 4A for a Full Circuit Diagram.
retain this energy and condition the voltage using regulators to power useful output. Shown above in Figure 20 is an Electrical Systems Diagram illustrating the overall concept. with the potential for major losses in power. Due to using the energy harvesting PCB. The EH301 Energy Harvesting Circuit solves these issues. programmed to wake up Zigbee Transmitter 5) Zigbee Transmitter – to send signals 6) Zigbee Receiver – to receive signals 7) PC Terminal with Graphical User Interface (GUI) to provide a "WARNING" alert The first component is the oscillating piezoelectric strips mounted inside the spring actuated floor tile. To increase output voltage 4 piezoelectric strips were incorporated into the final prototype. currents and timing waveforms and is able to accommodate such conditions with exceptional efficiency and effectiveness.Section 4. The strips output AC voltage.1 to 5. The EH301 operates in the 3. which is not easy to combine the four outputs. According to our sponsor Advanced Cerametrics. There exists the potential for the strips to be vibrating out of phase. Therefore. This commercially available product was discovered after several unsuccessful attempts of creating a homemade circuit.2 V to power the PIC16F877a Microprocessor chosen. Previous attempts were nullified by power losses in circuit components and fast capacitive discharge rates that exceeded input power. The major components include: 1) 2) 3) 4) Four piezoelectric strips mounted in the floor tile – output AC voltage Full wave bridge rectifiers – to rectify each AC output to DC ALD EH301 Energy Harvesting Circuit – to store energy PIC16F877a Microprocessor – powered by energy harvesting circuit.1: How the Electrical System Works This section will provide detailed design and functionality specifications of the main electrical components of this project. The circuit has the following characteristics: 27 . It is able to take electrical charge packets that arrive in a wide range of voltages. the energy harvesting PCB addresses the impedance matching issue. The low power output and variability of the input voltage spikes make it very difficult to store and retain power. which can cause destructive interference of the AC waves if connected together. resulting in negligible net captured energy. The second major component is the energy harvesting circuitry. the output from each strip was passed through individual rectifiers on a protoboard mounted in the tile and connected in parallel to the energy harvesting PCB. A data sheet is provided in Appendix 4B for additional information about the product. The group used an energy harvesting PCB (EH301) developed by Advanced Linear Devices (ALD). The circuit is able to store these small energy packets in a 1000uF capacitor. impedance matching was no longer a concern.
which has an operating voltage between 3.to store the captured energy for as long as possible with minimal leakage or loss 3) Energy Management . The transmitter is powered to 3.2V) Figure 22.3 and 5 Volts.3 volts using a voltage divider where R1 = 3K and R2 = 5K.condition the stored energy to provide the output necessary for the desired application (in this case the microprocessor) 4) Useful Energy Output of 8. This is reduced to 3. At that time.3 volts from the microprocessor. see the attached data sheet in Appendix 4B. The power supplied from the microprocessor is 5 volts. which receives its power from the Energy Harvesting Circuit. This program runs in a loop until the capacitor is drained beyond the necessary level to power the microprocessor. Energy Harvesting Circuit Schematic The third component is the microprocessor. Power and a USART signal are then provided to the ZigBee transmitter. The fourth and final electrical component is the ZigBee transmitter. The microprocessor is powered from the output discharge of the capacitor in the energy harvesting circuitry. the transmitter receives a USART signal from the microprocessor and it transmits a warning signal to a receiver terminal. The group used a PIC16F877a microcontroller obtained from the Stevens Engineering Design 1 Lab. For more information on the microprocessor.1) Energy Efficiency – circuit is roughly 90% efficient in order to maximize net captured energy Net captured energy = energy available – energy EH circuit consumes 2) Energy Retention . 28 .1 and 5.3mJ (1000uF capacitor b/t 3.
To do this. The microprocessor was tested to verify the USART signal was being sent properly. This was a simple test to verify the outputs. and the programmed output pin was connected to an oscilloscope.1 volts to 5. While stepping on the tile. a bridge rectifier. because it enabled us to determine the output energy available to power the microprocessor. The test setup required one piezoelectric strip. the transmission was successful.2: Testing of Electrical System The most critical test was verifying the performance of the energy harvesting circuitry. as will be elaborated upon more fully in Section 5 of this report. Also. we were able to observe an average charge of 100mV per step. After the discharge.3 volt capacitor from 3. to determine of the pins were set correctly. If a packet is received. This test was most significant. To test this. 29 . and then the energy harvesting PCB.2 volts and discharges to 3. Figure 23 shows the breadboard circuit and the LED connected to the microprocessor.1 volts. The level of voltage increase was noted as the capacitor charges after each flick.3 volts. The microprocessor sends the USART signal.3: Performance of Electrical/Wireless System The capabilities of the final design did not vary too much from the planned outcomes. This test was crucial to determine of the proper USART signal was being sent to the ZigBee Transmitter. a resistor was placed in series with an LED running to ground. Section 4.2 volts in approximately 20 steps on the tile. The positive and negative outputs of the strip were connected to the positive and negative input of the bridge rectifier. The oscilloscope was then adjusted to adequately view the signal. the process was then repeated and the amount of flicks is recorded again. The microprocessor was programmed to turn on an LED. and when it turns on. and the output at the receiver terminal was watched. the energy harvester's V+ pin. The final prototype was able to charge a 5.2 volts. the microprocessor was powered with a power supply. it would denote exactly when the harvester reached 5. A multimeter was connected to the output of the capacitor on the PCB (positive lead) and ground of the PCB (negative lead). The strip was then flicked until the capacitor reached 5. which measures the voltage on the capacitor. The ZigBee was powered with a power supply to 3. and the energy harvesting device from ALD.Section 4. The test for the ZigBee transmitter was the least complex. was measured using a multimeter.
This worked when it was powered with an independent power supply. the microprocessor would have been programmed to output one message to be transmitted then immediately go back into sleep mode.3. the ZigBee transmitter was programmed to output random messages when it turns on instead of using the input from the PIC's USART.1: Wireless Results The team was unable to successfully transmit a ZigBee signal because of microprocessor difficulties. it would not turn on. Section 4. The team first thought the PIC was outputting square waves. After looking at the USART output pin on an oscilloscope. As a last minute idea. the oscillator was deemed too slow at 45Hz for the ZigBee to read it as a USART signal. The resistor and capacitor of the RC oscillator were swapped to create a higher clock frequency but it must have made the PIC unstable as the output of the USART became only noise.9 volts of the 3.3mJ is exhausted. giving plenty of time for it to send numerous ZigBee messages. Diagram of Microprocessor & LED Output The team was able to show that the LED stayed lit for approximately 3 seconds using the output from the Energy Harvesting circuit. Figure 23. but the square waves turned out to be USART signals that were significantly slowed down. but when powered by the PIC.3 necessary volts to the transmitter. This would save the energy on the capacitor to last throughout the night. Under the current setup the microprocessor is powered until the full output capacity of 8. as the grounds were somehow shorting and only supplying 1. Ideally. 30 . There was difficulty in finding a ground for the Zigbee.
The only design objective that was incomplete was the link between the microprocessor and Zigbee transmitter. it would change to a red screen with "WARNING" written across it (Figure 24). The Energy Harvesting Circuit was connected to the microprocessor. Since the electrical system development was performed concurrently on a different project team. The transmitter was supplied 3. we would troubleshoot the USART signal to try to understand why it would not work correctly. The only missing link was the powering of the Zigbee transmitter by the microprocessor.In testing the Zigbee. Terminal GUI This was used as an easy way to distinguish if the receiver was receiving data. this problem could be eradicated. The Zigbee worked independently of the microprocessor using a power supply.4: Electrical Performance Summary In all. An LED was also connected to the ON pin to show the status of the transmitter as on or off. the integration of the two systems was slightly incomplete. Figure 24. The receiver was connected to a laptop via the supplied Maxstream board. and it was shown that the microprocessor successful ran through its programmed logic by lighting up an LED on its output pin for approximately 3 seconds. but was unable to be successfully implemented into the design. Figure 25. With additional time. and another LED connected to the transmitter that would be lit when the transmitter was communicating with the receiver.3V from a power supply and had the USART output of the PIC to the Din pin. Using this configuration. Missing Design Objective 31 . the group was able to harvest energy in a new and unique application. a GUI was designed so when the receiver received any packets of data from the transmitter. Section 4.
Illustration of Test Setup Data collection was performed using a very accurate Agilent brand multimeter pictured just above. As was discussed in Section 4 of the report. the collected voltage data allows for the calculation of harvested energy in the capacitor bank. Test Schematic The above diagram illustrates the iterative test procedure used to optimize the energy harvesting capability of the prototype system. Therefore.Section 5: Testing and Results Setup Actuation System Measure # of footstrikes to charge circuit Test Variables Judge relative feasibility of the test condition Multimeter • # of PZT strips • # of magnets • Location of triggering mechanism Choose Final Configuration • Spring pre-load • Weight of test subject Figure 26. 32 . Net harvested energy = energy available – energy consumed by harvesting circuit. the capacitive discharge rate with no load was also examined to determine the net harvested energy. Figure 27. A multimeter was used because the voltage measured is DC. Testing was performed by changing the test variables and recording the voltage output of the Energy Harvesting Circuit as function of the number of steps. The purpose of testing was to validate the effectiveness of the prototype. Since Ecap = ½*C*V^2 and the capacitance is known (1000uF).
Section 5. 1 piezo strip • 2 magnets.2V. It follows a linear trend. which was determined to be 20 33 . 4 piezo strips The conditions with only 1 piezo strip were run as an experimental control.1: Test Results *For actual test result data see Appendix 5A.2V. Voltage (mV).measured across the leads of the 1000uF capacitor in the EH301 Energy Harvesting Circuit. so a more useful metric is the number of steps to charge from 3. 1000uF cap Stored Voltage vs. 1 piezo strips • 1 magnet.1V to 5. # of steps This data allowed the group to reach some conclusions. 4 piezo strips • 1 magnet. # of steps 7000 6000 5000 4000 3000 2000 1000 0 no magnets 1 magnet 8.1V. which gives the strips some additional vibration amplitude relative to one and zero magnet conditions. 1 piezo strip • No point mass. 4 piezo strips • 2 magnets.3mJ useful output 2 magnets Upper Voltage Threshold 0 10 20 30 40 50 60 Lower Voltage Threshold # of steps Figure 28. However. From zero voltage it takes 50 footsteps to charge the circuit completely to 5. The best energy generating condition is the two magnet condition. the circuit holds its charge at 3. The following graph shows the charged voltage (mV) in the Energy Harvesting Circuit 1000uF capacitor as a function of foot steps. The energy output was considered undesirable with only 1 strip. The following test conditions were run: • No point mass. Stored Voltage vs. The results with 4 piezo strips are shown in the following diagram.
Therefore.1V.52mJ as shown above.footsteps. this data supports that 8. # of steps 18 no magnets 15 12 1 magnet 8. under the 2 magnet condition is charged in roughly 20 steps. Energy (mJ). The following graph shows the result. Also of importance is the power consumption of the energy harvesting circuit to stay in active mode. The capacitor leakage rate was determined by measuring the voltage loss across the capacitor with no load as a function of time using the multimeter.3mJ/20steps) in the operating range. Stored Energy vs.3mJ useful output 9 2 magnets 6 Upper Energy Threshold 3 0 0 10 20 30 40 50 60 Lower Energy Threshold # of steps Figure 29. At its fully charged condition of 5. # of steps As expected. At 5.3mJ of useful output can be generated in just 20 footsteps on the floor tile! Another view of the results is to look at the energy generated as a function of footsteps. The results are shown in Figure 30. The output remains active until 8.2V the charged energy is 13.3mJ of energy is dissipated and the circuit discharges to the Lower Energy Threshold when Vcap = 3. Recall that Net Harvested Energy = energy available – energy consumed by harvesting circuit. Therefore. This is easily calculated by remembering the relationship between capacitor voltage and energy. the energy storage in the capacitor is parabolic.42mJ/step (8. namely: Since Ecap = ½*C*V^2. the system charges at a rate of approximately 0.2V. 34 . in order to approximate net harvested energy. This graph clearly shows how the useful output. it takes approximately 3 days at a discharge rate of 72mV/hour to completely discharge the circuit. 1000uF cap Stored Energy vs.
3mJ useful power Stored Energy/step in 3.1-5.42mJ/step in the operating range. Summary of Test Results 35 . which is approximately equivalent to 100mV/step charged in the 1000uF capacitor.2V range Capacitive Discharge with no load Footstep rate for zero net energy transfer 50 20 0.2: Summary of Test Results The following table summarizes the test results of the system with four piezoelectric strips with 2 magnets mounted on each strip. Capacitor Leakage Rate (no load) Voltage (mV) 6000 5000 Upper Voltage Threshold Leakage/day Energy Harvesting Circuit holds charge for 3 days! 4000 3000 2000 Leakage Rate = 72mV/hour 1000 0 0 1 2 3 Days Figure 30. the equilibrium rate of steps/hour can be determined that matches input energy to lost energy. So as long as the tile is stepped on at least once per hour the system will not discharge on its own with no load. This result shows that the energy loss has a negligible effect on net energy transfer and that the circuit energy retention rate is extremely good.Since the discharge rate is known. Steps to charge circuit from 0-5.2V) for 8.72 steps/hour. It was shown that energy is harvested at 0. Capacitor Leakage Rate of Energy Harvesting Circuit Section 5.72 footstep/hr Table 1.1-5.2V Steps to charge circuit in operating range (3. Solving the following equation: [100mV/step * X steps/hour = 72 mV/hour] yields a result of 0.42mJ/step 72mV/hr (in 1000uF capacitor) 0.
Therefore.3).44mJ 5. 20 footsteps generate enough power to send 5 wireless signals. the power requirements for several wireless signals were successfully generated by the system.3mJ output capability of the EH301 Energy Harvesting Circuit.76 signals Table 2.44mJ per signal power requirement.3: Wireless Transmission Capability Although the full wireless functionality of the system was not fully recognized (as explained in Section 4. 5 wireless signals can be sent with a 1. 36 .Section 5.3mJ 1. System Wireless Transmission Capability The above table shows that given the 8. Useful Energy Output Energy Required/Wireless Transmission Wireless Transmission Capability 8.
along with possible solutions for each issue. One tile would be avoidable by any intruder. 37 . In addition. Problem or Flaw Suggested Solution or Improvement A displacement of 1. The tile should be installed in a network that would allow for each tile to be dropped into place and become instantly fully functional. A complicated mechanical mechanism could be used to translate a much smaller vertical displacement into a large displacement of the PZT composite strips.5 inches would be noticeable while casually walking across a network of floor tiles. Also included in this section will be any improvements or recommendations of the group's specific application for this technology. After completing the designed prototype the group had an opportunity to look at the project as a whole and compile a punch list of changes that could have been made if the timeline allowed for it. Using the piezo strips developed by ACI the group was able to prove that they could harvest power from the mechanical forces created when taking a step across an average floor tile. These suggestions would be a great starting point for future design teams if they chose to pursue a similar application using the same technology. This proof of design conceptual prototype would act as a great stepping stone for future senior design groups desiring a similar application. Section 6. In order to get a full understanding of the need for change within the prototype the group thought it was fit to populate a list of downfalls that the prototype had. the group was able to prove that the amount of energy harvested would be enough to power both a logic controller and a wireless transmitter that could be used for surveillance purposes.1: Suggestions for Improvement As a whole the group felt that they achieved the objectives that they set forth for themselves at the beginning of this design process.Section 6: Project Conclusions This section of the report will act as a culmination of all the lessons learned while completing this Senior Design process. The results of this assessment can be seen below.
If possible the metal could be stamped out of flat stock so that just the top of the tile would need to be attached. Since the tile is self sufficient there would be no need for utilities of any kind to penetrate the exterior. Table 3. The use of a microprocessor drained the capacitor quicker then anticipated. The tile is not durable enough for an application in a harsh climate. A PCB would be more efficient then the configuration currently used. After finalizing the circuitry. would be time consuming to mass produce as is. Another option might be to use a method of injection molding if the housing material was a polymer. These commercially made rectifiers have a .4 V drop currently being used. High performance. Suggested implementation techniques for future projects 38 . The charge time for EH capacitor is slightly longer then an ideal situation. Any of the sides that needed to be fastened could be done so with the use of gaskets around the union to insure water resistance. low power rectifiers could be used as an alternative. The rectifiers used had a larger voltage drop across them then originally desired. Some suggestions would include designing the exterior of the tile out of metal so that the seams could be welded rather then fastened using nuts and bolts.Tile is not designed for manufacturability. the electronics could be incorporated on a printed circuit board which would be easier to mount and mass produce. Lithium Ion batteries could be used in place of the capacitor for holding charge.4 V drop compared to that of the 1. The electrical components are mounted onto a protoboard which can cause inefficiencies in the circuitry. This would allow for a greater buffer during times of inactivity. The energy harvesting circuit could be connected directly to a wireless transmitter which would use substantially less power then when controlling with the microprocessor.
When using these ACI developed PZT composites it is important to understand the relationship between both frequency and amplitude with respect to the voltage generated. Some of the ideas that group thought of were: • • • • • Light up gaming application using the footsteps of the user to power LEDs embedded into the fabric of the dance pad. an actuation system is essential to get optimal performance. Some suggestions that the group would pass on are: • • • • Due to the nature of this material. In the case of using a discontinuous forced vibration. it is highly suggested to have ample electrical support when taking on a project of this magnitude.2: Alternate Uses and Applications When taking a step back and looking at the project as a whole the group came up with a few applications using similar concepts. 39 . The only need for frequency matching would be if there was a continuous forced vibration. This included numerous activities with repetitive foot striking.Section 6. Section 6. Discontinuous. Sample Dance Pad light timing based on traffic flow.3: Recommendations As stated previously the group felt that this project would be a great stepping stone for a future group working on an application using the same material. Location monitoring of: o Cars or other industrial equipment o Pedestrian traffic o Animals Traffic light sensors to aid in the control of traffic Figure 31. Dance floors in bars or clubs that would light up using the power of the people's movements throughout the room. The group found that frequency matching was not needed in the case of discontinuous vibration. and the unknown specifications that go along with it. An application within the sole of a shoe that might help to power small personal electronics from everyday walking. translated vibrations within a structure will not correspond to good transmission of mechanical to electrical energy without the use of such an actuation system. With this in mind the group thought that some of the lessons learned during the last two semesters would be helpful in this type of situation.
In addition.3 mJ of useful power harvested in the 1000 μF capacitor would be enough to send out five wireless signals during off hours.Section 6.4: Conclusion The group began this project with the following two objectives in mind: • • Utilize the unique properties of PZT (lead zirconate titanate) fiberbased piezoelectric materials developed by Advanced Cerametrics Company to design and develop a floor tile that harvests energy from a foot strike. The group was able to accomplish the goals that they set forth for themselves at the start of this design process. The final prototype proved to be a self-sufficient system that could be independently placed in the field and used for surveillance purposes during offhours. Use the harvested energy as the sole source of power to transmit wireless signals for building surveillance. the group found the design process to be very fulfilling and helped them to understand all the necessary steps to designing and testing a prototype. The group valued the experience and believed that it would help them throughout all of their future endeavors in the engineering field. A prototype was constructed during the spring semester whose purpose was to use the wasted mechanical forces created while walking and convert them into a useful electrical energy. 40 . Using energy harvesting circuitry and a logic controller the group was able to demonstrate that the 8.
Ed." D.com DigiKey: www.com/culture/lifestyle/commentary/imomus/2006/08/715 82 Google Patent Search: http://www. Challa. 9 Oct 2007.© 2003 MicroStrain. Websites: Supplier of Piezoelectric Material: Advanced Cerametrics Company: www. Vol.C." David Morrison. Richard Cass and Farhad Mohammadi. R. Yong Shi and Frank T. Churchill.com "Power from the People" http://www. S.References Articles: "Fiber Technology at Advanced Cerametrics. "A vibration energy harvesting device with bi-directional resonance frequency tenability.advancedcerametrics. H.W.ipdl." Henry A. Power Electronics Technology. Townsend. M. JerryRuddle and. "Modules Will Harvest Energy For Remote-Sensor Networks.mouser.jp 41 .mcmaster.J.Mohammadi.google.aldinc. Inman." F.Department of Mechanical Engineering. Inc.com Supplier of Electrical Materials: Mouser: www.L. kim.digikey. Virginia Polytechnic Institute and State University. 10.go. Cass. "Comparison of Piezoelectric Energy Harvesting Devices for Recharging Batteries. B. 86.inpit. American Ceramic Society Bulletin. Hamel. Stevens Institute of Technology "Advanced Cerametrics Harvests Clean Energy. "Vinod R. Sodano and Daniel J. "Strain Energy Harvesting for Wireless Sensor Networks.com/patents Japan Industrial Property Digital Library: http://www.P.com Supplier of Mechanical Materials: McMaster Carr: www. Arms.wired." Jerry Ruddle.com Supplier of Energy Harvesting Circuit: Advanced Linear Devices: www.G. Fisher. M. No. Prasad.
wikipedia.com/support/swing. http://www.html 42 .com/golf_training.html PJCA.practicerange.org/wiki/Piezoelectricity Strain Gauge.evisiongolf.Piezoelectricity: http://en. http://www. http://en.aspx?ID=654 Jump USA.html CVI Melles Griot: http://www.com/detail.html Practice Range.wikipedia.org/wiki/Strain_gauge Floor generation in Tokyo train station. http://www.free-golf-swing-tips.mgkk.com/ids/news/2007/q2/070529a_nr.jumpusa.narinari.com/golf-slice-fix.com Boeing New Release. http://www. http://www.com/Nd/2006106570.boeing. http://www.html Evision.
However. Since batteries are hard to dispose of properly. One way to do this is to make it so that 43 . it could help in the reduction of battery usage which has proven harmful to the environment. Hungry Hippos. Another subsystem will be installed to dampen/prevent motion should conditions become unsafe for the patient. These electronics can include flashing LED's or sounds that come from the game. With that as the targeted goal for the piezoelectric material. there is a variety of game ideas that can be branched from such an activity. This application would place the piezoelectric material of the brace joint.Appendices Appendix 1A: Details of Initial Five Innovative Ideas 1. it will be helpful for marketing to parents because they won't have to spend the extra money on batteries for the product. Medical Device – Auto-Stiffening Knee Brace One application within the medical device field for piezoelectric material is to develop an auto-stiffening knee brace. This concept would sense the overextension of the knee. In such a game. in a game that includes a significant amount of motion from its players. the best option would be to make a game that maximizes the use of the levers to obtain the most energy possible from the piezoelectric material. This is essentially an active damping system. such a feature would require a battery to charge the electronic system. This is useful for several reasons. they create a significant amount of harm to the environment. 2. and provide additional support when needed to stabilize the patient. The energy would then be used to power an electronic scoreboard or sounds that come out of the game board. Also. most knee braces only provide lateral support. First. Clearly. This concept could also use the bending of the material as an energy harvesting device. As it currently stands. The amount of bend on the material. The use of electronics in children's toys is very common in order to prove the aesthetics of the game and make it more exciting for the children playing them. If the batteries in such a system were to fail. and send signals to a microprocessor. it may be possible to run the game solely using piezoelectric energy. Constantly re-charging these batteries could serve as a fail safe to ensure the system always works as it was designed. and the device's active damping system would fail. actively controlled by the microcontroller. Often. up to four players will be repeatedly tapping a small lever responsible for applying a motion to the piezoelectric material. as well as the frequency of the material oscillation will allow for logic-based programming into the microprocessor. possibly to recharge the batteries which power the microprocessor to create a self-sustaining device that will always work. The idea we have thought of for the game would be similar to that of the current game called Hungry. making such a game environment friendly. Game or Toy Application One application that our group has looked into using piezoelectric energy for is a game or toy for younger children. the logic from the microprocessor would disappear.
Door units recognize the object or person when the IR beam emitted vertically or horizontally is intercepted. Sensing/Monitoring Application One application of piezoelectric material proposed here is the piezoelectric door sensor for transportation modes such as trains and buses. the group could create a product which is very marketable on the toy market. the mechanisms that are currently utilized are not sensitive enough to detect small objects such as fingers. there are many areas we would need to complete further research on. Piezoelectric sensing is ideal to replace the current design of detection system by placing the strip of piezoelectric fiber along the edge of the door or inside the rubber cushion. A control unit can then reduce the force to make it easier to pull the object out or can stop the movement of the closing door until the object clears. The consequence can clearly be fatal. the most widely used design for detecting obstacle. While the object of the actual game could still be refined. When an object is caught in between doors. However. The object would be to get your piece to the center of the game board first. you have a piece that extends towards the center of the game board. several other door sensors that are currently used are described for comparison with piezoelectric sensor. Since most of the information we have tells us that the energy is in the range of milliwatts.each time you press your lever. 3. there could be some issues with such a use of the technology. is to use an infrared beam. A piezoelectric sensor which can create voltage in response to small mechanical strain will be more sensitive to detect small objects and as a result. but probably LED type lights that require small amounts of energy. in case an object is caught between the closing doors. the piezo sensor is bent and voltage created can be used as a signal that indicates that something is jammed. the idea of the technology being used would probably stay the same. while the leg of the baby stroller was stuck between doors as well as a time that a child got caught in automatic revolving door. 44 . the tip of an umbrella or things that can be compressed to a thin size such as backpacks and handbags. it will be much safer for people going through doors. However. we would need to be able to acquire it quickly and store it for usage. Also. we are unsure of the exact power output we would be able to acquire from such an application and whether or not it will be enough to power the game board. By eliminating the use of batteries. but overall. This mechanism is often used in European trains where the train does not get very crowded. At this time. the product would be useful because of its marketability. Automatic doors today that are powered by motors or compressed air often have some kind of detection system. but include an obstacle of some sort to inhibit the players from just blindly pressing their levers as fast as possible. this cannot be used for congested trains where people are standing very close to the door or overflowing because the IR beam will remain intercepted and the door will never be closed. In the following paragraphs. There have been accidents when a train has started moving. First. the electronics we use for the game would not be able to be high powered. If such an application is chosen. However.
depending on the number of IR sensors. However. 45 . Comparison of alternatives mentioned above is summarized in a matrix in Appendix 1B. voltage of the piezoelectric sensor goes up. Unlike the pressure sensor with a strain gauge inside in which electric resistance is kept high as long as the object is stuck. but this method utilizes a pressure sensor mounted in the rubber along the edge of door. as it is done with a pressure sensor. Also. It is advantageous in the way that it can sense the obstacle before the door hits the person or object. piezoelectric sensor ranks the highest except for the detection before touching or catching the object. so it may not know when the object is pulled out. In the case of a plug door where the door opens to the outside of the body. This would create a voltage as long as it stays in between the doors. and does not need extra devices for detection. At that moment. As it can be seen from the comparison matrix. A second design takes advantage of the electric motor that powers the door in which the load on the motor or torque applied is increased because of an obstacle in between the doors. This mechanism is the same as a strain gauge which measures change in electrical resistance in response to the deformation. a control unit recognizes the object being caught. The motor has to deliver more torque to close the door if there is something that blocks the movement of the door. The third design is similar to the second design. To use a piezoelectric sensor on the door. and it is still possible that the person or object slips out through the detection. a piezo sensor can be placed on the other side as well to detect human fingers getting caught when the door is opening. When the object is caught. and it is relatively cheap. the door closes almost completely leaving only a tiny space and it cannot detect an object as the motor is stopped. This mechanism is useful in the case of a crowded train described earlier where the door has to be kept closing no matter what is getting caught. piezoelectric material loses voltage in about 1 second. it is expected that an axial piezo sensor is placed in the rubber as a protection and placed along the edge of the door. the door continues to close slightly after detection because of inertia and there is some delay in responding. it still needs an outside power source to operate. To solve this problem. it is natural that the person would keep moving the object or hand until it is pulled away from the door. a control unit recognizes that the object is pulled away a few seconds after the last voltage ramp is measured because if something is stuck. A drawback of this mechanism is that if an obstacle is too small.The area of detection is limited. unlike a piezoelectric sensor that is self powered and creates voltage by itself that can be used as signal. The picture of the door showing the location of a robber can be seen in the appendix. This design is highly sensitive to a small load. A control unit then reduces the torque or stops flowing electricity to make it easier for the obstacle to be pulled out.
4. in order to effectively create a swing training aid.Self Sustained Navigation/Sensing Buoy System There is a multitude of buoys in the ocean. Utilizing low-power. Buoy Light or Ocean/Wave Application . Sports Device – Golf Club Training Aid This product would incorporate a piezoelectric material into a golf club. 5. After many cycles of charging and discharging these batteries will eventually need replacing. This product will allow the golfer to modify their swing from a slice to a fade. All buoys have one thing in common. they require navigation lighting as well as some sort of system in order to power the navigation lighting on all the buoys in the ocean. that is. We believe this to be possible by starting the design from the ground up. This mechanism would have triggers that would deflect the piezeoelectric material as the buoy travels up and down on the waves. high output LEDs and designing an extremely efficient sensing circuit. we would like to build the system's power generator using Lead Zirconate Titante (PZT) piezoelectric material. Once the circuit has been designed and the power requirements are known. Most of these buoys are for navigation or some sort of sensing application. This club will be able to 46 . and then at night the charged battery powers the navigation lighting. effectively eliminating the need for batteries. This system would have an internal mechanism that would travel up and down within the buoy. Instead of charging a battery during daylight hours we would like to design a system that is generating power constantly. and anywhere in between. As the sport of golf continuous to flourish in recent years among all age groups. once dead must. Other buoys utilize solar panel which recharges a battery during the daylight hours. this system takes advantage of power generated when the material is under axial oscillation from the mass pulling on the piezoelectric material. Another power generation system idea is to design a triggering device to deflect the piezoelectric material generating power from straining the material. Some of these systems are powered by batteries that. there is an ongoing market for golf accessories and training aids. be replaced. One idea is to design a mass-spring system where the piezoelectric material acts as the spring. The group's concept for designing a self sustained navigation or sensing buoy is to utilize the immense amount of power that exists in the constant movement of our oceans.
This golf club will be an improvement to a golf aid that is already on the market. The difference between a good and bad swing in golf is all in the approach to the ball. This product would incorporate piezoelectric fibers along the shaft of the golf club in order to recognize the stress and strain that the club is exposed to in multiple planes. This can be seen below. z-plane. 47 . The path that the club head takes as it approaches the ball dictates the action on the ball after impact. or some degree of either. The design of the existing product on the market incorporates a hinged mechanism onto the shaft of the golf club. this product can only be manufactured using a steel shaft. therefore altering the golfer's swing. Our product will use piezoelectric fibers as a sensing element. When the head of the club travels inside or outside the ball this creates a spin on the ball. or in any open area without a golf ball while shadow training. The logic of the microprocessor will then display. The moment created by the head of the club will result in a flex on the shaft in the direction of the path of the swing. The player's back and fore swing can be a deciding factor in whether the ball comes off with the intended trajectory and spin on the ball. Existing Products: While maintaining the same design criteria. The problem with this product is that in can be much heavier than a regular club. our product would improve on some of the constraints that the existing product has. and the flex of the club will be recognized in the x and y planes. Also due to material properties. whether the path of the club will create a slice or a fade.be used on the driving range hitting real balls. The shaft of the club will be used as a reference. based on direction of strain. thus sending a signal corresponding to the strain on the fibers. resulting in either a slice or a fade. A conceptual model of this product can be viewed below. even though almost every golfer uses fiberglass shafted drivers and woods. This resulting strain will be analyzed by a microprocessor to access which direction the club is being swung in. This is designed so the golfer is only able to swing the shaft of the club in parallel with the hinged mechanism without the hinge failing. and the club bending.
we were able to multiply through the importance factors and calculate a weighted average for each of the applications.12 2. Attribute Feasibility Energy Generated vs Required Budget Achievability Impact on Field Marketability Manufacturability Originality/Practicality Importance 5 4 3 2 4 3 5 Weighted Average Knee Brace 4 Game/Toy Sensing/Monitoring 2 5 Buoy Light 2 Sports Device 4 4 4 3 5 3 4 3 2 2 4 3 3 4 4 2 2 4 2 1 3 1 2 3 2 4 3 3 4 5 4 4.08 4.48 2. 48 .08 *Note: Although none of the Initial Concepts above were chosen as the final application. also from 1-5. Then. These fields were then given a specific importance rating from 1-5 based on the impact that characteristic would have on our final project.Conceptual Model: Appendix 1B: Design Comparison Matrix for Initial Applications Each field was decided on by the group based on what areas are common to any piezoelectric project we may choose. by rating each of the applications in the given fields. this chart shows the way in which we honed in on an application.88 3.
Appendix 1C: PZT Fiber-Based Piezoelectric Material Details
PZT = Lead Zirconate Titanate
The piezoelectric material used in this project is a composite strip called a PFCB
(piezoelectric fiber composite bimorph). The PFCB is a composite formed by 2 PFC's
connected in series, which is then attached to a thin center steel shim via an epoxy.
Each PFC is a flexible composite piece of fibers embedded in a laminate piece about 6
inches long, 0.5 inches wide and 0.4mm thick. The fiber direction runs longitudinally
along its length, with an electrode placed above and below the fibers. The steel shim
gives the composite strip some flexural rigidity and ability to sustain vibration. Electrical
leads are riveted to the electrodes to complete the PFCB construction. The PFC and
PFCB are pictured below.
Below is a cross section of a PFC, showing the PZT fibers.
The following picture shows the polarity of the electrodes on the PFC. The longer
electrode (L2) is the negative terminal. The coil shape shown to the left is the electrode
running perpendicular to the fiber-direction. When the material vibrates it generates an
AC voltage output.
Appendix 2A: Electro-Mechanical Modeling
Piezoelectric material develops electrical energy from mechanical input energy in
the form of vibrations. See the schematic below:
To generate electrical energy the piezoelectric material must be stimulated by
either constant input mechanical vibrations or an impulse that will cause the
material to vibrate on its own. During this oscillation the material goes through
repeated up and down displacement. The beam displacement causes changes
in mechanical stress in the material which generates an output voltage.
Before the group was able to start power calculations, the mechanical vibrations
of the system needed to characterized. Given the shape and material properties
of the piezoelectric material the group treated the system as a vibrating cantilever
beam. With the current floor tile design the material will be excited by the input
force of a foot strike. When an individual steps on the tile, it will displace slightly.
This small displacement will be enough to force the material to begin oscillating.
Because of natural damping effects inherent in a cantilever beam these
oscillations will become smaller and smaller until they eventually cease.
To begin modeling the behavior of the vibrating cantilever, the amplitude of the
oscillations needed to be analyzed. The group calculated the stiffness coefficient,
damping ratio, undamped natural frequency and damped natural frequency using
the equations in the appendices. From the equation below the group was able to
then characterize the amplitude of the tip of the beam on a time interval (t), given
an initial displacement (Xo).
A= X0 ×e(−ζ /2m)t ×cos(ωdt)
Since the power output of the piezoelectric material is dependent on changing
stress in the beam it is in the best interest of the group to maximize the amplitude
and duration of the vibrations. These parameters are dependent on the damping
ratio, which is dependent on spring stiffness and dimensions of the beam, and
mass of the system (beam with a point mass). Analysis of the spring stiffness
characteristics can be found in the material selection section of the mechanical
model. When experimenting with applying a point mass to the piezoelectric
material, the group made two observations: the lower the frequency of the
vibration the longer the duration of the vibrations; and the lower the frequency the
larger the amplitude of the vibration over the time interval. Using the frequency
equations in the appendices the group was able to generate the graph below.
Natural Frequency vs. Mass
Natural Freaquency (Hz)
Length 1 -> .15m
Length 2 -> .18 m
Length 3 -> .22 m
Mass (kg)
This graph demonstrates two relationships: as the point mass increases the
natural frequency decreases; and as the length of the beam increases the natural
frequency decreases. Increasing the length of the beam both changes the
dimension of the beam (affecting the damping ratio) and increases the length
between the mounting point of the beam and the location of the point mass. This
confirmed the group's initial conceptions that the beam should be as long as the
physical dimension of the tile allow and that the point mass should be placed on
the end of the beam.
Next the group decided to explore the relationship between the mass of the point
mass and amplitude of the vibrations. For this analysis we used the longest
piece of material available from our supplier and varied the magnitude of the
point mass at the end. The amplitude equation above was used to generate this
following graph.
Beam Deflection vs. Time (point mass)
Tip Deflection (m)
Mass -> 0.0015
Mass -> 0.011
Mass -> 0.025
Time (sec)
The reason that this was difficult was because of the application for these piezoelectric composites. that increasing the point mass yields larger amplitude and a longer sustaining of vibration. This modeling begins with using the amplitude data to calculate the stress in the beam. the relationship between deflection. The next step for the group was to develop a data acquisition set-up to begin doing there own performance testing on the material. After this analysis the group was ready to move forward in developing the test set-up and verification of material performance. The challenging part began when the group tried to take the derived stress into units of usable power. the longest piece of piezoelectric material and the largest point mass possible should be used. This test set-up is explained later in the report. The power analysis needed to incorporate the effects of logarithmic decrement and sinusoidal propagation on the composites. In this equation. 52 . and stress can be easily understood. Both of the graphs in this section helped the group to realize the design considerations when developing the final model of the floor tile. Once the mechanical characteristics of the cantilever beam were characterized and design considerations were determined the group turned the modeling focus to calculating expected voltage and power. Power Generation From the above analysis. The specifications from the material supplier allowed the group to determine that the piezoelectric strips chosen would indeed produce enough power for the wireless transmission. using this graph. while considering the physical dimensions of the floor tile. the Force and Moment Area were calculated using equations that can be found in the appendices. The following equation is used to calculate output voltage. The equations for these calculations can be found in the appendices. frequency. This can be seen in the graph just above. the g33 term is the piezoelectric constant which was provided by the group's material supplier ACI.The group confirmed. It was confirmed that. The specifications supplied by the material supplier predicted roughly 140 mW of power at 50 Volts.
3 V S ta n d b y P o w e r 1 mW 53 .5 in E le c t r ic a l / W ir e le s s T r a n s m it t io n R e q u ir e d P o w e r f o r T r a n s m ittio n 4 5 m W @ 3 .0 2 5 g P o in t M a s s L o c a tio n @ 4 .1 1 1 3 lb s ft ft in F lo o r T ile L e n g th W id th H e ig h t M a te r ia l o f C o n s tr u c tio n M a te r ia l T h ic k n e s s 1 ft 1 ft 2 in Lexan .Appendix 2B: Initial Design Specifications D e s ig n S p e c if ic a t io n s C o m p le t e A s s e m b ly W e ig h t L e n g th W id th H e ig h t 2 .1 in S u b F lo o r M a te r ia l o f C o n s tr u c tio n L e n g th W i d th H e ig h t M o d u la r ity W o o d /F o a m ? ! ? 1 ft 1 ft 1 in Yes P ie z o e le c t r ic C o m p o s i t e S t r ip s L e n g th 5 in P o in t M a s s .
Once the tile setup was designed in ProEngineer. From the picture above.Appendix 2C: Finite Element Analysis of Floor Tile The design of the floor tile as well as the setting up of the stress test was set up using ProEngineer. ANSYS was used to solve the system and evaluate the results. 54 . one can see that a 300 pound distributed load was placed on the tile. These results let us evaluate which areas of the tile would be affected most by the weight of a person being applied to it.
1 inch thick wall. Comparing this with the material with the smallest yield strength (PVC) of 7500 psi. split-shell design and bottom only constraint. the maximum stress achieved was about 2400 psi.These scales show the impact that a change in wall thickness had on the test results. while the bottom shows the scale for the tile with a . This was with minimal wall thickness. This variable was the only one that had a major effect on the results we received. 55 . The top scale shows the results for a tile with . After testing several variables.2 inch thick walls. we receive a factor of safety of at least 3 in any scenario we present.
These projects above prove that it is possible to convert previously-wasted mechanical energy from the movement of individuals into electrical energy through the use of piezoelectrics. However. Most of MIT's projects utilize piezoelectric polymers. not the power generation characteristics. The floor tile in the picture is designed to sense the pressure of a person's foot to track people movement. This material is able to generate ten times the amount of power of materials used in previous systems giving us a much higher potential for success. The search returned no existing US patents for any form of power generating or energy scavenging floor or floor components with piezoelectrics. A small collection of these research projects can be found below.Appendix 2D: State of the Art The group used Google patent search to try to find piezoelectric floor tiles that have been patented. ACI is in the process of building a high production facility for manufacturing PZT fiber-based piezoelectrics which should greatly reduce the cost of this material. It is known that the piezoelectric concept and piezoelectric materials have been used for several years so the group decided to then expand the search to include prior research and prototyping of an energy scavenging floor utilizing piezoelectrics. This Sensate Floor is similar to ours in that it tracks people movement. these prior endeavors have had very limited success with regards to an appreciable amount of power generated and cost-effectiveness of the energy harvesting system. A major advantage our project has over priors is the utilization of PZT fiber-based composite materials produced by ACI. East Japan Railway Company The East Japan Railway company has installed ticket gates that use piezoelectric material to harness pressure and vibration caused by the foot traffic of passengers to power the gates themselves. What was found is that there are a number of universities and institutions that have experimented with using various piezoelectric materials to produce prototype models of energy scavenging floor surfaces and floor mats. but at this point they have not proven that it is cost effective to use this same technology elsewhere in the station to power lights or other electrical power draws. This is why the group has chosen to use ultra-low power wireless transmission for our application. 56 . this project included. This project has been successful in producing enough power to energize the ticket gates. nor is it self-powering. MIT's projects also use the sensing capabilities of piezoelectrics. MIT Sensate Floor MIT has done a lot of development with piezoelectric materials. but it does not send the signal wirelessly. At this point in the project the group has also fully recognized that special attention needs to be paid to choosing the right application to utilize the low power characteristics of the material. increasing the cost-effectiveness of the project.
Appendix 3A: Spring Specifications 57 .
30 Metal Shim Stock Assortment 1 $43.50 1 ft x 1 ft Lexan plastic 2 $23.50 58 .25 Corner Brackets Epoxy Repair Cement Machine Screws Total $504.52 Piezoelectric Strips 4 $240.56 Ceramic Disc Magnets 20 $1.00 7/8" Springs 4 $9.02 1 $11.06 Flexible Magnet Disks 20 $7.00 Steel Nuts 100 $1.13 Quick Recovery Foam 1 $14.Appendix 3B: Mechanical Components Bill of Materials Description Quantity Price 2 ft x 4 ft Lexan Plastic 1 $57.72 6" Heat Shrink Tubing 1 $2.69 Polyurethane Foam 5 $19.41 100 $8.22 Foam Selector Pack 1 $41.36 Aluminum Shim Stock 1 $4.25 50 $17.51 Steel Washers 100 $2.
controls height/spring pre-load Allowable Displacement (0<do<1.Appendix 3C: Full Page Model of Final Design Aluminum Mounting Block PZT Strips Energy Harvesting Circuit (reduce friction) Actuation Bar Assembly (Stationary) Threaded Rod (4X).5") Lexan Sidewalls do ¾" Wood Board (2X) Springs (4X) 59 .
2V Range The microcontroller creates a USART signal reduced to 3.3V using resistors and fed into XBee transmitter The XBee receiver receives the data packet from the transmitter and outputs a "warning" sign using GUI on computer 60 . The bottom left shows the combination of the piezoelectric outputs fed into the Energy Harvesting Module The output of the Energy Harvesting Module is fed into a PIC16F877a microcontroller in the 3.1 – 5.Appendix 4A: Full Circuit Diagram The top row shows the four piezoelectric strips which are passed through individual rectifiers.
Appendix 4B: Electrical Parts/Data Sheets/References Datasheet for PIC16F877A Microcontroller: http://ww1.jsp?productId=2062324&cp 9 http://www.pdf Brochure for EH301 Energy Harvesting Module: http://www.jsp 61 .digikey.radioshack.asp?number=4447+TE 5http://www.radioshack.com/pages/energy_harvesting_components/ 2 http://www.com/product/index.com/prodinfo.radioshack.com/products/wireless/zigbee-mesh/xbee-series2-module.pdf Based on the final prototype the team has concluded the following electrical parts list necessary to completely build a working prototype.aldinc. Electrical Parts List Reference: 1 http://www.com/product/index.digi.dll?Detail?name=923252-ND 4 http://www.com/Search/ProductDetail.com/pdf/EH300Brochure.com/pdf/EH300ds.microchip.aspx?qs=NoieiqYAh1CVRGGWkRFRmg%3d%3d 6 http://microcontrollershop.aldinc.php?cPath=112_184&products_id=992 7 http://www.com/product/index.mouser.jsp?productId=2062324&cp 8 http://www.com/downloads/en/DeviceDoc/30292c.com/product_info.jsp?productId=2062581&cp 3 http://search.advancedcerametrics. The cost of piezoelectric materials was graciously donated by the material supplier Advanced Cerametrics.pdf Datasheet for EH301 Energy Harvesting Module: http://www.mpja.com/scripts/DkSearch/dksus.
786 2.444 0.186 1.293 7.035 0.808 2.449 0.147 9.530 10.960 1.634 13.23 Step 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 mJ/Step 4 Piezoelectric Strips Energy in 1000uF Cap (mJ) no magnets 1 magnet 2 magnets 0.47 95.975 8.057 8.242 5.856 6.966 1.174 0.898 0.253 0.462 1.894 16.856 2.941 5.354 8.616 0.673 0.429 0.76 104.357 8.832 0.595 8.279 11.464 2.638 7.691 2.008 1.958 7.896 10.104 0.051 6.508 9.361 1.572 5.365 4.567 3.345 1.275 13.008 0.880 3.320 3.747 8.145 13.869 4.082 0.198 0.144 12.073 0.497 0.355 3.005 0.345 1.968 3.726 9.632 6.420 5.926 4.068 0.485 13.022 0.607 4.263 0.014 10.226 2.722 11.200 6.267 3.537 6.205 0.898 4.648 4.665 12.162 0.107 9.030 13.704 7.201 1.363 0.602 7.973 10.901 1.911 0.050 3.194 12.786 1.238 7.903 15.595 11.044 0.226 2.230 4.856 13.448 6.316 5.274 7.090 4.305 11.656 1.835 11.163 2.952 3.037 1.140 4.217 1.406 2.583 0.704 12.490 0.824 3.330 0.142 0.057 11.883 6.016 0.259 0.991 8.665 5.014 9.620 1.553 5.149 12.110 1.299 62 .399 10.298 0.101 1.661 0.004 0.Appendix 5A: Detailed Test Results Step 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 mV/Step 4 Piezoelectric Strips Voltage in 1000uF Cap (mV) no magnets 1 magnet 2 magnets 97 94 126 180 199 210 286 265 295 405 370 382 455 466 533 590 569 640 725 630 772 813 720 852 926 872 942 997 990 1080 1080 1110 1150 1160 1220 1230 1240 1290 1350 1340 1390 1420 1440 1490 1540 1550 1560 1640 1640 1650 1780 1710 1710 1890 1820 1800 1980 1950 1890 2110 2050 1980 2210 2110 2080 2320 2210 2220 2390 2260 2300 2500 2370 2400 2610 2430 2470 2710 2577 2590 2817 2671 2686 2921 2766 2782 3026 2860 2878 3130 2955 2973 3234 3049 3069 3338 3143 3165 3443 3238 3261 3547 3332 3356 3651 3427 3452 3755 3521 3548 3859 3616 3644 3964 3710 3739 4068 3805 3835 4172 3899 3931 4276 3994 4027 4381 4088 4122 4485 4183 4218 4589 4277 4314 4693 4372 4410 4798 4466 4505 4902 4561 4601 5006 4655 4697 5110 4749 4793 5214 4844 4888 5319 4938 4984 5423 5033 5080 5527 5127 5176 5631 5222 5271 5736 94.380 0.530 9.645 3.020 0.554 2.394 15.109 0.948 14.041 0.756 0.577 4.732 11.584 1.248 0.462 1.497 10.744 0.872 5.585 12.442 2.008 6.960 2.556 9.709 5.290 5.672 3.125 2.583 0.769 0.144 7.442 2.421 14.
Gantt Charts Phases I – III 63 .
After the stage one prototype was built the group began to develop a testing setup for the prototype. write the progress report 1. '08 Feb 10. S M Thu 2/21/08 Mon 1/21/08 Wed 1/23/08 1 day Wed 1/23/08 Wed 1/23/08 3 days Wed 1/23/08 Fri 1/25/08 5 days Mon 1/28/08 15 days Mon 1/21/08 Fri 2/8/08 Updated Nugget Chart 1 day Tue 2/12/08 Tue 2/12/08 8 Write Written Report 1 5 days Fri 2/8/08 Thu 2/14/08 9 Prepare and Deliver Oral Report 1 5 days Fri 2/15/08 Thu 2/21/08 1/23 Fri 2/1/08 2/12 2/14 2/21 During phase IV of the design process the group progressed greatly. the group was able to update their Nugget Chart. one group member will act as a project manager. If these tasks are not completed in the scheduled time frame it will create a domino effect that will holdup the project as a whole. The Gantt Chart for the spring semester can be seen below. Without a well thought out plan for all aspects of the project it will become hard to complete all of the tasks in a timely and efficient manner. and thus delegate tasks and follow up upon completion to ensure good utilization of both time and resources. the group used MS Project to create a Gantt chart that outlines each task that is required for completion of this stage of the project. '08 F S S M T W T Jan 27. In order to hold true to this schedule. The group was able to finalize the design.Phases IV – VI One of the most important aspects of this project will be to have an effective and well defined project management plan. '08 S S M T W T F S S M T W T F S S M T W T F S Feb 24. In order to define this schedule. '08 Feb 17. select components. Phase IV ID 1 Task Name Phase IV 2 Choose Components 3 Place Order 4 Finalize Design Draw ings 5 Build Initial Prototype in Machine Shop 6 Develop Test Setup 7 Duration Start 24 days Mon 1/21/08 3 days Finish Jan 20. Since this is the case. from the New Year until the present numerous key tasks were completed. '08 F S S M T W T F Feb 3. and create fabrication drawings for the machinist. and finally prepare for the progress presentation. Within this time period. it is very important to hold true to the schedule for each task within this plan. There are many tasks throughout this project that will be dependent on other tasks in the project. The group then spent numerous days in the machine shop to help the machinist fabricate the necessary parts needed for the complete manufacturing of the product. Lastly. order parts. 64 . This chart acts as an outline for the entire semester's work that is due for completion.
'08 S S M T W T F Mar 16. Phase VI ID Task Name 23 Phase VI Duration Start Finish 32 days Fr i 3/28/08 Mon 5/12/08 11 days Fri 3/28/08 Fri 4/11/08 1 day Fri 4/11/08 Fri 4/11/08 24 Testing Period 3 (Final Test) 25 Finalize Specifications 26 Assemble Final Prototype 5 days Mon 4/14/08 Fri 4/18/08 27 Tw eak Prototype for Senior Design Day 2 days Mon 4/21/08 Tue 4/22/08 28 Poster for Design Project Exhibition 5 days Mon 4/14/08 Fri 4/18/08 29 Senior Design Day 1 day Wed 4/23/08 Wed 4/23/08 30 Upload Project onto ME w ebsite 1 day Mon 4/28/08 Mon 4/28/08 31 Share Prototype w ith Advanced Cerametric 5 days Thu 4/24/08 Wed 4/30/08 32 Update Nugget Chart 1 day Wed 4/30/08 Wed 4/30/08 33 Prepare and Deliver Final Report 4 days Mon 4/28/08 Thu 5/1/08 34 Prepare and Deliver Final Presentation 5 days Fri 5/2/08 Thu 5/8/08 35 Return Prototype to Senior Design Lab 1 day Mon 5/12/08 Mon 5/12/08 '08 Mar 30. A general overview of these tasks can be seen in the above Gantt Chart. but the main goals and tasks will remain the same. S M Thu 3/27/08 3/1 3/19 Thu 3/27/08 3/27 Looking ahead to phase V. 65 . the group plans to begin to work more in collaboration with the electrical engineering team in order to assist them in any development of specifications or sizing of components that might be needed. '08 S S M T W T F S S M T W 4/11 4/18 4/23 4/28 4/30 5/1 5/8 5/12 Phase VI tasks will be dependent on the progress made during the previous phases.5 days Wed 3/5/08 Fri 3/7/08 15 Integrate Electrical Components 15 days Mon 2/18/08 Thu 3/6/08 16 Aid Electrical Team w ith Electrical Design 10 days Tue 2/26/08 Fri 3/7/08 17 Place Final Orders 1 day Sat 3/1/08 Sat 3/1/08 18 Testing Period 2 5 days Tue 3/11/08 Mon 3/17/08 19 Redesign Cycle 2 4 days Tue 3/18/08 Fri 3/21/08 20 Design Website and upload E-Poster 2 days Thu 3/6/08 Fri 3/7/08 21 Update Nugget Chart 1 day Wed 3/19/08 Wed 3/19/08 22 Prepare and Deliver Oral Report 2 4 days Mon 3/24/08 S Feb 17. '08 S M T W T Apr 20.Phase V ID Task Name 10 Phase V Duration Start Finish F 30 days Mon 2/18/08 11 Develop Test Variables 2 days Fri 2/22/08 Mon 2/25/08 12 Testing Period 1 4 days Tue 2/26/08 Fri 2/29/08 13 Re-design cycle 1 3 days Sat 3/1/08 Tue 3/4/08 14 Build Improved Prototype 2. '08 S M T W T F S Apr 13. Most of these tasks can be found in the section of the report which outlines the technical emphasis for this phase V. the group will require input from the EE team to efficiently select a pressure sensor for the monitoring application of the product. '08 S M T W T F S Feb 24. '08 F S S M T W T Apr 27. '08 S M T W T F Mar 2. In addition. as this project will be an ongoing design process. '08 S M T W T F S Mar 30. Some of these tasks include multiple testing and redesigning periods. '08 May 11. '08 S S M T W T F Mar 9. '08 T W T F S S M T W T F S Apr 6. thus some of these tasks may change over time. '08 F S S M T W T F May 4. Also. '08 S S M T W T F S Mar 23. the group was able to set realistic goals for milestone accomplishments to be completed during this phase of the project.
Nugget Charts The following charts summarize the progress obtained during the six phases of project development which consist of the following: Phase I: Conceptual Design Phase II: Technical Analysis Phase III: Engineering Design Phase IV: Prototyping Phase V: Experiment Design Phase VI: Performance Testing 66 .
and also fatigue characteristics 3. 5. 3. proving the worthiness of this concept in new product markets.g. 4. In general. Determine functional specification for auto-stiffening and auto-powered knee brace 4. 2. not PZT fiber based materials • do not utilize energy harvesting characteristics of piezoelectrics • require energy input (e. Look into damping / range limiting assembly 67 . Acquire an analog to digital data acquisition system 2. • Medical Device Game or Toy Sensing/Monitoring Application Buoy Light or Ocean/Wave Application Sports Device Drawing and Illustration of Promising Concepts Concept 1 Piezoelectric strips -Sensing -Energy Harvesting Key Issues/Problems to Solve 1. many products in the current market: • use piezoelectric transducers. Use Labview to determine the consistency of electrical output. • Why This Project and State-of-the-art This project is intended to expand the use of advanced.Phase I Nugget Chart • Project Objectives • Utilize the unique properties of PZT fiber-based piezoelectric materials to design and develop a unique commercial application. fiberbased piezoelectric materials. Determine a means of attaching material to knee brace 5. internal battery) • do nothing with waste energy • Conceptual Designs and Highlights 1.
Mass will be added to end of the strip to increase amplitude and create more power 68 . Tile will have to hold the weight of a person and must be hollow to hold the piezoelectric components 4. The following areas were used in technical analysis: • Electromechanical Model • Piezoelectric Material Selection • Expected Power Output • FEM Analysis of Mechanical Model • • Longer strips and larger larger point mass result in higher resulting amplitude Group will use PZT 5A composite as material for piezoelectric strips Thickness of tile wall has greatest impact on structural integrity of the tile Drawing and Illustration of Promising Concepts Design Specifications 1.Phase II Nugget Chart • Project Objectives • Results Obtained at This Point • Utilize the unique properties of PZT fiber-based piezoelectric materials to design and develop an energy harvesting floor tile for surveillance purposes • • • Focus Areas for Technical Analysis The areas of technical analysis for this application were used to help us better understand what requirements we had. Required to provide enough energy to power a wireless signal to be sent for surveillance purposes 3. Uses the impulse of a step to vibrate the piezo strips 2.
Optimize the current design based on testing results in an iterative design process. Piezoelectrics Strips. Subfloor. • From Technical Analysis to Engineering Design • Design Specifications were derived from the Technical Analysis in Phase II for the entire system: o Floor Tile. these design specifications will be finalize during Phase IV • Prototype Plan and Purchase Requisition 1. 3. Finalize energy harvesting circuitry Major Results Obtained this Semester • • • Strategic Partnerships with ACI and EE Team Finalized Design.Phase III Nugget Chart • Project Objectives • • • • • Utilize the unique properties of PZT (lead zirconate titanate) fiber-based piezoelectric materials developed by Advanced Cerametrics Company to design and develop a floor tile that harvests energy from a foot strike. Use the harvested energy as the sole source of power to transmit wireless signals for building surveillance. Co-assemble floor tile prototype and testing apparatus. 5. and Manufacturing Assembly Plan for floor tile concept Completion of an A/D data acquisition system with interface to Labview via DAQ Card Finalized Design of Testing Apparatus Drawing and Illustration of Final Design 69 . 6. Perform extensive testing on prototype according to test variables. FEM Analysis. 4. Custom fabricate parts in machine shop. Program wireless controller using Zigbee Development Kit 7. Electrical Circuit. Purchase budgeted items from industrial suppliers (McMaster) 2. Wireless Transmission • Through testing and an iterative design process. Purchase wireless transmitter and receiver 8.
Calculate energy per footstrike 6.Phase IV Nugget Chart • • • Project Objectives • Utilize the unique properties of PZT (lead zirconate titanate) fiber-based piezoelectric materials developed by Advanced Cerametrics Company to design and develop a floor tile that harvests energy from a foot strike.25 to 0. Judge the feasibility of the test condition • • Major Results Obtained this Semester • Protototype tile has been fabricated • Piezoelectric Strip Fabrication process developed • Subfloor materials limited to Silicone.33 to back-calculate actual voltage (because of voltage divider network.5 Farad) 7. Calculate the logarithmic decrement 4. Time graph in Labview Signal Express 2. From Engineering Design to Prototype Development • Perform extensive testing on prototype according to test variables. Export data to Excel for post-processing 3. • Program wireless controller using Zigbee Development Kit • Finalize energy harvesting circuitry Prototype Testing / Optimization 1. EVA. 5. Generate Voltage vs. Calculate # footstrikes to charge capacitive network (values not yet determined but is estimated to be roughly 0. Polyurethane • Completion of an A/D data acquisition system with interface to Labview via DAQ Card • Test and Data Processing Plan developed Drawing and Illustration of Final Design/Prototype 70 . Multiply the Voltage values by 8. • Optimize the current design based on testing results in an iterative design process. • Use the harvested energy as the sole source of power to transmit wireless signals for building surveillance.
controls height/spring pre-load Allowable Displacement (0<do<1.3mJ useful ener gy 10 20 30 40 50 60 Lower Voltage Threshold # of steps 71 .Phase VI Nugget Chart Piezoelectric Surveil lance Floor Tile illance Aluminum Mounting Block PZT Strips Lexan Sidewalls (reduce friction) Energy Harvesting Circuit Actuation Bar Assembly (Stationary) Threaded Rod (4X). 1000uF cap Stored Voltage vs. # of steps 7000 6000 5000 4000 3000 2000 1000 0 no magnets 2 magnets Upper Voltage Threshold 0 Springs (4X) 1 magnet 8.5") do ¾" Wood Board (2X) Voltage (mV).