A new approach for the design of ultrasono-therapy transducers.

In this paper we describe a new approach for the design of ultrasono-therapy transducers. Usually, in this kind of transducer, a lambda/2 front plate is inserted only in order to ensure a good mechanical protection of the active crystal from the surrounding medium. However, with an accurate design, the plate can also be used to match the piezoelectric element to the load both in terms of gain and bandwidth. To this end we apply the technique normally used in acoustical imaging and nondestructive testing, and, by means of a distributed matrix model, we optimize the thickness and impedance of the plate in order to obtain a strong response and a large bandwidth at the working frequency. Using a front plate of thickness about lambda/3, the model predicts better performances than the ones obtained with the classical design, also in terms of efficiency. An experimental comparison between a transducer realized according to the proposed design and a commercial half wave transducer shows better performances the former and therefore validates the new design criterion.

PSpice modeling of capacitive microfabricated ultrasonic transducers.

Capacitive microfabricated ultrasonic transducers (cMUTs) are the newest and potentially the most promising devices to convert electrical into acoustic signals and vice-versa. These devices are based on the capacitance modulation of a microcondenser which is obtained by microfabrication onto a silicon substrate. The aim of this paper is to describe a PSpice model of the cMUT, based on an analytical distributed model previously reported (IEEE Trans. UFFC 49 (2) (2002) 159-168), which can be used to simulate the performances of a general ultrasound system, either in frequency or time domain. The PSpice model consists of a capacitor with a parallel resistor, which represent the static capacitance and the loss and bias resistances of the transducer, respectively, plus two quadrupoles (GLAPLACE) modeling the mechanical impedance of the membranes and the radiation impedance of the medium. The usefulness of a PSpice model is the possibility to simulate and optimize the cMUT transducers in transmission and reception, along with driving and receiving electronics, in a general ultrasound system. Experimental measurements on a 5 MHz cMUT operating in pulse-echo are in good agreement with model predictions.