Characterization of Piezoelectric Transducers Used in Ultrasonic Devices Operating Above 0.1 GHz

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Abstract
Piezoelectric transducers for ultrasonic devices operating at frequencies above 100 MHz are presently being made either by thin‐film deposition techniques or by bonding thin plates to the substrate and lapping them to the required thickness. In either case the performance of the transducers cannot be evaluated separated from the device, and the evaluation is complicated by the presence of intermediate layers and spurious circuit elements. This paper uses Mason's equivalent circuit to critically appraise the validity of methods used to evaluate transducer performance from loss and admittance measurements made under these circumstances. Computed families of curves are presented, spanning the practically important range of mechanical impedances and coupling factors. Experimental data from a ZnO film and a LiNbO3 thin‐plate transducer on fused quartz substrates are presented to demonstrate the application of equivalent circuit descriptions to obtain the coupling factors.