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Low Cost Multifunctional Planar RF Sensors for Dielectric Characterization and Quality Monitoring

Two planar resonant sensors for measuring permittivity and identifying adulteration in vegetable oils are presented in this paper. The sensors are designed to operate in 2.4 GHz Industrial, Scientific and Medical (ISM) band. The sensing technique is based on the change in resonance characteristics of the sensors with the variation in dielectric properties of the test sample in contact. The proposed sensors are capable of measuring the permittivity of solid as well as liquid samples. They can be easily immersed in liquids due to its single port topology and compactness. The prototypes of both the sensors are fabricated on FR4 epoxy substrate of thickness 1.6 mm. To experimentally validate their functionality, some of the commercially available dielectric materials are characterized using these fabricated sensors. The measured permittivity value of each sample showed a good match with the respective value available in the manufacturer’s data sheet. The use of solid test specimens in their commercially available thickness makes the test sample preparation simple and easier. Liquid dielectric characterization using these sensors is experimentally validated using some vegetable oil samples. Furthermore, different concentration levels of adulterant oil in pure vegetable oil are successfully detected by the proposed near field resonant sensors. The results demonstrate that the two sensors are capable for real time quality monitoring and permittivity measurement of solid and liquid materials.