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Optimization of Electromagnetic Acoustic Transducers (EMATs) for Condition Assessment of Civil Infrastructure

There are more than 130,000 prestressed concrete bridges in the United States with about 37,000 bridges being more than 30 years old. Prestressing steel strands are an important construction element used in these bridges and are critical to their performance. Presently there is no effective Nondestructive Evaluation (NDE) technology for condition assessment of these prestressing strands once they are embedded in concrete. The overall goal of the research is to develop an inspection technology to detect deterioration in embedded steel strands in concrete structures. The Objective of this part of the research is to optimize the design parameters of a magnetostrictive Electromagnetic Acoustic Transducer (EMAT) to maximize the sensor efficiency. EMATs are the devices used to launch and receive acoustic waves in conductive materials such as steel prestressing strands, and the propagation characteristics of these waves can be used to study deterioration, damage and tensile stresses. EMATs working on the magnetostriction principle were designed and ultrasonic measurements were made in order to maximize the efficiency of EMAT by considering the influence of modifying three parameters; bias magnetic field, number of coil turns and the number of coils. Recommendations for the design of EMATs based on this empirical study were developed.