Semi-Analytical Calculation of Lamb Wave Signals Generated by EMATs in Multilayer Metal Specimens

Ultrasonic Lamb waves are one of the most commonly used guided waves in nondestructive testing (NDT). The calculation of Lamb wave signals considering transducer structures often relies on finite element methods (FEMs), which are computationally slow and make it difficult to quantify the sensitivity of reception signals to each processing stage. A theoretical modeling for Lamb wave signals generated and received by electromagnetic acoustic transducers (EMATs) is proposed. The entire EMAT-based Lamb wave excitation and reception process is equivalently modeled as a single-input–single-output system. The received Lamb wave signal can be obtained by multiplying the excitation signal with the system transfer function, which is the combination of transfer functions of the excitation, propagation and reception processes. The transfer functions for the EMAT-based Lamb wave excitation, propagation, and reception processes were calculated, respectively. Experimental results on both single-layer and multilayer specimens demonstrate that the proposed analytical calculation method can accurately compute the received Lamb wave signals in these structures.