Incorporation of Diffraction Effects in Simulations of Ultrasonic Systems using PSpice models

The use of PSpice models for piezoelectric devices and ultrasonic transmission media is of major importance when designing electronics for ultrasonic systems. Today, these models include viscoelastic loss but disregard loss due to diffraction, i.e. beam spreading. This paper presents a method for the inclusion of diffraction loss in PSpice simulations of ultrasonic systems. The conductive loss in the transmission line that models the propagation media of the ultrasound pulse is used to model the loss due to diffraction. Parameter variations for the piezoelectric device can affect the result greatly. Thus, a sensitivity analysis for the simulation model is also presented. Measurements and simulations have been performed using a pulse echo system in water. Maximum distance to the reflector was 200 mm. The piezoelectric devices used are PZ-27 crystals with diameters 6 mm and 12mm, with a center frequency of 4 MHz. Results show that the simulated amplitude of the returned echo differs less than 10% from measured values.