Improvement in the Electromechanical Properties of a Partially Diced Piezoelectric Disc Transducer

Piezoelectric discs vibrating in the thickness mode are widely used in underwater electroacoustic and electromechanical applications. It is well known and established that the first fundamental mode along the thickness of the disc determines the transducer resonant frequency and the disc diameter determines the radiation surface. For certain applications, the frequency, radiation pattern, and power requirement determine certain thickness-to-diameter (h/2a) ratio, however, at these aspect ratios, the vibrational velocity of the piezoelectric disc is non-uniform across its surface due to the combination of coupled vibration in thickness and radial directions. These higher order radial modes decrease the electromechanical and electroacoustical transformation, resulting in a performance degradation of the transducer. Previous theoretical analysis on piezoelectric cylinders as a function of thickness-to-diameter ratio under three different polarizations, namely the radial, axial, and circumferential, was published by Sarangapani et al., and the coupled vibration for piezoelectric disc of certain thickness-to-diameter ratio has been studied analytically by Aronov. This paper investigates the effect of the electromechanical performance of the transducer using piezoelectric disc of certain aspect ratios where coupled vibration in thickness and radial direction exists. We also propose a solution to overcome the limitations of a piezoelectric disc with non-ideal thickness-to-diameter ratio by a partially diced design. A finite-element model is used to calculate the dynamics of the diced disc and in comparison with a uniform disc to illustrate the reduction of coupled vibration in thickness and radial directions. The electromechanical coupling coefficient is shown to improve greatly over the uniform disc by optimizing certain dicing parameter. An equivalent circuit based on Mason's equivalent circuit model is derived for the diced disc under the assumption of a one-degree-of-freedom system. The electromechanical properties, the frequency spectrum, and the effective coupling coefficient are presented and show good agreement with the experimental results.