Detection of Sloped Aluminum Plate Based on Electromagnetic Acoustic Resonance

During the service process, the thickness of the sheet metal is unevenly changed due to uneven pressure or abrasion. The inner and outer surfaces are in two nonparallel planes, which causes the reflection path of the ultrasonic wave inside the specimen to shift and brings a challenge to electromagnetic ultrasonic thickness measurement. In this work, we used the detection scheme of electromagnetic acoustic resonance (EMAR) combined with the multiplication of n- times compression (MNC) data processing to detect the thickness of the sloped specimens through a fixed-point rotating racetrack coil. A power spectral density (PSD) analysis is performed on the spectrum signals obtained under different rotation angles $\alpha $ to achieve the judgment of the inclination direction of the specimen. The simulation results show that the measured thickness increases with the increase of the inclined angle $\theta $ of the specimen. Within a certain range, the change in the width of the racetrack coil will not have a significant influence on the thickness measurement results of the sloped specimen. The PSD of the resonance signal increases first and then decreases with the increase of the rotation angle $\alpha $ , and the PSD reaches its peak when $\alpha $ is 90°. Experimental results show that when the coil rotation angle $\alpha $ is between 50° and 70°, the scheme can accurately measure the thickness of the sloped specimen, and the direction perpendicular to the rotation angle of the maximum PSD is the inclination direction of the sloped specimen.