Development of bulk wave EMAT sensors with enhanced Lorentz force through magnetic field concentration in eddy current regions

Abstract

In this paper, we propose the development of electromagnetic acoustic transducers (EMATs) to generate ultrasonic bulk waves and inspect metallic specimens at elevated temperatures. EMATs play a vital role in the NDE due to their non-contact inspection behavior; however, they are constrained by their low Signal-to-Noise Ratio (SNR), especially under high-temperature conditions. This work addresses the challenges by developing EMAT configurations that enhance the Lorentz force and ultrasonic wave generation by optimizing the magnetic field in the region of eddy current generation. The Finite Element (FE) simulations were performed in aluminum samples to study the eddy current through varying coil widths, liftoffs, and static magnetic field intensity concentration. The FE simulations on eddy current revealed that eddy current intensity is independent of the coil widths. Different EMAT configurations were designed and developed by concentrating the static magnetic field intensity in the region of the eddy current generation by considering the simulation results. Various EMAT configurations were fabricated and tested on 26 mm and 50 mm aluminum samples to measure their SNR. The configuration with the highest SNR was further tested at elevated temperatures under proper insulation techniques. These advancements have the potential to enhance the capabilities of NDE techniques in challenging industrial environments.