PSpice Modelling of an Ultrasonic Setup for Materials Characterization

Transducer is the most important element in an ultrasonic device because it governs the conversion of electrical energy to acoustical one and vice versa. Therefore it's very important to predict its behaviour and to determine its optimal domain of functioning. Many approaches can be used in this study. The first one is the resolution of the piezoelectric equations using numerical methods. However this approach requires powerful computing systems and it is not appropriate for each situation. The second method is based on the equivalent electrical circuit and consists of using simulation software such as PSpice, VHDL or Cadence. This method can be easily adapted for any configuration provided that we have the suitable equivalent circuit so it offers much flexibility. We propose in this paper to use PSpice in order to model a pulse echo ultrasonic system. A piezoelectric disc is used for transmitting at 2.2 MHz and receiving the reflected wave. The simulation is based on the Leach model and its parameters are deduced from the acoustical characteristics of the transducer. A transmission line is used to represent the medium of propagation considering the plan wave case. We studied the effects of the backing and the propagating medium on the ultrasound behaviour. The transient and frequency response, the sensitivity and the electrical impedance are studied too. The results of simulation are compared to some measurements performed in distilled water and paraffin oil. Results obtained fit some much with those found in literature and show the validity of the used model.