Dynamic characteristics of 2-2 piezoelectric composite transducers

Lateral resonant modes associated with specific lateral structures in piezoceramic-polymer composites are the main drawback that interferes with performance of ultrasonic transducers utilizing the composites as driving elements. This paper presents a field solution to characterize dynamic behavior of lateral modes in composite transducers with 2-2 connectivity. The solution is derived based on a concept of Lamb wave propagation along piezoceramic and polymer layers in the thickness direction of the composite transducers. The behavior of 2-2 composite is investigated over a broad spectrum ranging from quasi-static stage up to mode transition zones. Dispersion curves for various modes were calculated and compared with experimental results. A safe zone can be identified from the dispersion curves where the interference of lateral modes to thickness oscillation is negligible. Strong interactions between thickness modes and lateral modes are observed in the transition zones where two modes merge together in the frequency domain. Electromechanical thickness coupling coefficient, k/sub t/, is calculated for the first time to include the effect of aspect ratio of the composite. Results show that the coupling coefficient, k/sub t/, varies dramatically as a function of both ceramic volume fraction and the aspect ratio. As k/sub t/ reaches its maximum value, the vibration of the ceramic phase is completely decoupled from that of the polymer phase.