Micro Mechanical Piezoelectric Ultrasonic Transducer Dynamic Performance Research

In this paper the dynamic characteristics of a piezoelectric micromachined ultrasonic transducer (pMUT) was studied using couple stress theory and Rayleigh-Ritz method. When the transducer receives an ultrasonic wave, the dynamic response of the transducer and the electrical output of the transducer are given. Moreover, the optimal diameter ratio of top electrode to transducer membrane for maximizing output electric charge is determined through theoretical analysis, and the bending rigidity of a micro-scale plate is also determined.The piezoelectric micromachined ultrasonic transducer is a new transducer based on Micro-Electro-Mechanical System(MEMS). Compared with the conventional ultrasound transducers, the pMUT has the advantage of light weight, small size, low power consumption, high reliability, low cost, implement intelligent and easy with the integrated circuit.The piezoelectric micromachined ultrasonic transducer in this paper is a multilayered disc, which includes a piezoelectric layer, an elastic layer and two electrode layers. Since the whole thickness of the transducer membrane is in micro-scale, and the mechanical properties of micro structures have been experimentally shown to be quite different from that of the macro structures, the size dependence of the dynamic deformation behavior was evaluated using couple stress theory. The response of the transducer to ultrasonic wave was analyzed using modal decomposition and Bessel function, and was implemented by Matlab software. The results show that the non-dimensional rigidity of the transducer membrane increases obviously when the thickness of the membrane is in micro-scale, and this results in a shift of the resonant frequency of the transducer. Moreover the output electric charge and voltage for the first mode of the transducer are reduced accordingly because of the increase of non-dimensional rigidity. Further analysis shows that the optimal diameter ratio of top electrode to transducer membrane for a maximal output of electric charge obtained by the first mode is around0.674. However this diameter ratio is not applicable to the output voltage for an open-circuit system.