Abstract
Piezoelectric micromachined ultrasonic transducers (PMUTs) with multi-frequency are appealing for ultrasonic applications, which can meet the requirements of large detection depth and high resolution simultaneously. Hence, a novel structure with series Helmholtz resonators under the PMUT membrane term as dual-cavity serial PMUT is presented, which utilizes both the piezoelectric effect and Helmholtz resonant effect to achieve multi-frequency and further widens the bandwidth. Based on the mechanism of vibration coupling between the membrane and Helmholtz resonator, a lumped model and an equivalent circuit model are formulated. Meanwhile, the finite element method (FEM) is developed to investigate the multi-resonance and make comprehensive validations. The results demonstrate that the multi-frequency is contributed by the induced acoustic impedance of the Helmholtz resonator, causing a simulated average sound pressure of up to 260 Pa/V at the resonance frequency and a 77% -6 dB frequency bandwidth in air by theoretical analysis and parameter optimization. The proposed dual-cavity serial PMUT provides a new approach for the application of high transmission power and broad bandwidth transducers.
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