Multiple Acoustical Matching Layer Design of Ultrasonic Transducer for Medical Application

Abstract

Ultrasonic diagnostic equipment is widely used due to its merit of being a noninvasive technique as well as because it provides a clear real-time display of body tissue. Our focus is on the design of low-loss (high transmitting power) and wide-band transducers for ultrasonic diagnosis. The approach we have used consists of impedance matching the front face of the piezoelectric transducer to the propagating medium with a quarter wavelength impedance matching layer and inserting an unmatching quarter wavelength acoustical layer between the rear face and backing material. By tuning the acoustical impedance of the matching layer, transducers with wide-band characteristics and high transmitting power can be obtained. For the backing at the rear surface, a soft backing demonstrating a better impedance matching result which can improve the bandwidth, but exhibiting a longer duration impulse response should be used. A heavy backing would degrade the wide-band phenomena, but show a shorter time duration (<0.5 µS) for image application. To obtain the optimal solution to a specific design formulation, PSPICE (Personal Simulation Program with Integrated Circuit Emphasis) programming techniques can be applied. The PSPICE code of the Mason model is implemented to precisely predict the performance of the matched transducers such as impedance, insertion loss, bandwidth and duration of the impulse response. Good agreement between the simulation results and experimental results has been achieved.