A comparison of model and experiment for a high frequency (35 MHz) linear ultrasonic array

In this study we evaluate the ability of a 2-D finite element model (FEM) using the PZFlex software package, as well as a 1-D PiezoCAD KLM model, to predict the performance of a fabricated high frequency array. A four element 35 MHz array prototype array was fabricated and tested and compared to both models. The array featured monolithic elements mechanically diced out of a fine grain high density PZT-5H ceramic and spaced 50 micron pitch. Electrical interconnection was made via a flexible circuit and matched to the 50 Ohm system electronics with an 85 Ohm transmission line coaxial cable. An average center frequency of 34 MHz was measured and a -6 dB bandwidth of at least 45% per element was achieved for the fabricated array. The experimental results agree well with both models. The PiezoCAD model predicted a 35.6 MHz center frequency with a 60 % -6dB bandwidth, and the FEM predicted a 34.4 MHz center frequency and a 46 % -6dB bandwidth. Because the KLM model cannot be used to simulate the response of multiple elements it should be used only to access the feasibility of an initial high frequency array design and determine the best thickness and composition of the matching, backing and piezoelectric layers. In contrast, the FEM proved to be a far more valuable tool for predicting the response of the array. With this model, kerf fillers, slotted versus continuous matching layers and variable depth dicing can be investigated further as they relate to the overall array performance.