Incorporation of mechanical noise in the SPICE model of a piezoelectric transducer

Abstract

SPICE models of a piezoelectric device and the ultrasound propagation medium can be used in a simulator intended for electronic circuits and IC design to make efficient system level optimizations. This paper presents the inclusion of mechanical noise in the SPICE model of an ultrasound system. The modeling of the noise is based on the mechanical thermal noise which is equivalent to electronic Johnson (thermal) noise. For a system with a high-Q piezoelectric device designed into a medium-Q transducer the main energy loss, and thus also the main noise contribution, will occur in backing and sound propagation media. Thus, the modeling of the mechanical noise is performed by including electrical noise generation in the resistors that model these media in the electrical equivalent circuit. The resulting output voltage noise follows theoretical derivations of transducer noise as published by Farlow and Hayward. Simulations of a 4 MHz Pz27 piezoelectric disc with a diameter of 8 mm give a peak spectral noise density over 1 nV / √ Hz, which is comparable to that achievable with low-noise preamplifiers.