Finite element analysis on reduction of the cross talk in ultrasonic transducers

In an ultrasonic transducer, the cross talk between array elements is an important performance degrading factor, and there is strong need to identify the sources of the problem and to find the means to reduce its level. This paper considers two most representative ultrasonic transducers, capacitive micromachined ultrasonic transducer (cMUT) and piezoelectric transducer. Both are linear array immersion transducers. Two-dimensional finite element models of the transducers are constructed using the commercial code ANSYS. We analyze the origin and level of the cross talk between array elements, with evidence of coupling through certain waves such as the Stoneley wave propagating at the transducer-water interface and the Lamb wave propagating in the substrate or the impedance matching layer. For reduction of the cross talk level, the effects of various structural schemes are investigated. They are the change of wafer thickness, the installation of etched trenches of various dimension and sound absorbing materials inside, and installation of polymer walls between array elements for a cMUT as well as the change of the dimension and material of kerfs for a piezoelectric transducer. Results for the two transducers are discussed to describe the general method to reduce the cross talk level in ultrasonic transducers.