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 in the design of 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 to include 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 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 were PZ-27 crystals with diameters 6 mm and 12 mm, with a center frequency of 4 MHz. Results show that the simulated amplitude of the echo follows measured values well in both near and far fields, with an offset of about 10%