Analysis and reduction of the cross talk in micro-machined piezoelectric ultrasonic transducers

In a micro-machined ultrasonic array transducer, cross talk between array elements is one of the most important factors affecting the performance of the transducer, and there is strong need to identify the sources of the problem and to find the means to reduce the cross talk level. This paper considers a convex type piezoelectric linear array transducer working at 4.5 MHz when immersed. The transducer is composed of 64 piezoelectric plates separated by kerfs, a thick backing layer, two impedance matching front layers, and an acoustic lens. Through various analyses with two-dimensional finite element models of the transducer, we analyzed the origin and level of the cross talk between array elements, with evidence of coupling through certain waves such as a Scholte wave and a Lamb wave. For reduction of the cross talk level, the effects of attenuative polymeric acoustic walls were investigated, which were placed between array elements in the transducer. The responses investigated were cross talk pressure in water, cross talk displacement at the acoustic layers, and cross talk voltage at the piezoelectric elements. The performance of the acoustic walls was compared with that of conventional kerfs implemented in the transducer. According to the results, the material property of the kerf filler and the walls did not have much influence on the level of the cross talk. The geometry and dimension of the kerfs and the polymeric walls turned out to have much larger effects instead. Results of time domain transient analysis, frequency domain harmonic analysis, and spatial radiation pattern analysis were discussed to describe the general method to reduce the cross talk level in the transducer.