OS02W0013 A functional electromagnetic acoustic transducer for optimum Lamb wave modes with multi-wavelengths

Lamb waves are normally utilized for inspecting thin metal sheets. Wheel-type probes using piezoelectric oscillators have generally been used as the sensors for Lamb waves. Recently, an electromagnetic acoustic transducer (EMAT) has been developed and is beginning to be used as a Lamb wave detector. The EMAT offers the advantage of inspection without using a couplant. The EMAT generates Lamb waves with fixed wavelengths determined by the interval between the meander lines in the sensor coil that constitutes the EMAT. We have studied an EMAT consisting of a meander line coil with intervals from 1mm to 4mm and having a paired structure symmetrically embraced with a thin steel sheet on opposite sides. The EMATs generate S_0, A_0, S_1, A_1-mode Lamb waves with different wavelengths corresponding to the resonance frequency range from approximately 0.5MH to 2MHz. We confirmed how to properly generate a symmetrical or anti-symmetrical Lamb wave.