Application of tunneling magnetoresistance in electromagnetic tomography system construction

Tunneling magnetoresistance (TMR) is a magnetic sensor that measures the magnetic induction component toward a sensitive axis. It is used in electromagnetic tomography (EMT) systems for its high sensitivity, frequency independence, and small size. TMR-based EMT (TMR-EMT) system construction and performance enhancement require a more comprehensive understanding of TMR characteristics. This paper introduces the construction principle of a TMR-EMT system, studies effect of TMR quantity on imaging results, compares the difference between TMR-EMT and coil-based EMT (Coil-EMT) in imaging results, analyzes the influence of TMR characteristics on the measurements, and gives the corresponding solutions. Simulations and experiments indicate that adding more TMRs could enhance imaging quality, obtaining better results than Coil-EMT imaging quality. The experimental results show that dynamically adjusting the excitation amplitude and downward zero-crossing switching can effectively improve the problems of output saturation and deteriorating consistency of measurements caused by TMR nonlinear characteristic.