Spatial localization of stress-perturbing wave generated by an electromagnetic acoustic transducer

A new apodization of electromagnetic acoustic transducer has been proposed to generate the stress perturbing wave, which has a spatially localized magnitude distribution. According to the acoustoelastic effect, a stress perturbing wave radiated into metals gives rise to an ultrasound velocity change that corresponds to the deviation of the stress in the metal. In ultrasonic measurements, it is desirable to use a narrow beam in order to obtain a high resolution. A transducer has been constructed which has a Sinc function apodization. To compare with other types of electromagnetic acoustic transducers, including a Limited Bessel-type transducer, numerical simulations are performed. It is shown that the proposed transducer provides the optimum characteristics of the spatially localized magnitude distribution. Furthermore, experimental results are presented to confirm the numerical predictions.