Design of acoustic impedance gradient matching layers

This article proposes a new acoustic impedance gradient matching layer based on phononic crystal theory to further expand the bandwidth of piezoelectric ultrasonic transducers and improve their working efficiency. The matching layer is made of a composite of two different materials and its transverse structure can be regarded as a one-dimensional phononic crystal. This structure can effectively reduce the transverse vibration of the transducer and enhance the longitudinal vibration. In addition, the gradient alteration of acoustic impedance in the longitudinal direction of the matching layer improves its acoustic impedance matching performance with the medium. Through theoretical calculations and finite element simulations, we obtained the equivalent acoustic parameters of the gradient matching layer and investigated the suppression of transverse vibration by its structural properties based on the band gap theory. Finally, a sample of the transducer equipped with the gradient matching layer was prepared and its working performance was measured by pulse echo experiments, which is a significant improvement compared to the conventional & lambda;/4 matching layer transducer.