The purpose of this study is to address the issues of high boundary stiffness, difficulty in releasing residual stress, and insufficient driving force of a single piezoelectric layer in conventional piezoelectric micromachined ultrasonic transducers (PMUTs), and to propose a novel bimorph cantilever-based PMUT to improve the transmitting and receiving performance under air-coupled conditions.
Slits are etched along the diagonals of a hexagonal diaphragm to form six cantilever beams connected at the center, combined with etched holes at the boundary and a dual-piezoelectric-layer synergistic actuation scheme. A 3D finite element model with layer-specific residual stress, damping and acoustic-structure coupling is developed using COMSOL Multiphysics.
Under a typical residual stress of −150 MPa and 1 Vpp driving, the BC-PMUT achieves a sound pressure level of 112 dB at 10 cm and a receiving sensitivity of 0.84 mV/Pa, which are approximately 16 dB and 5.6 times higher than those of a conventional unimorph PMUT, respectively, while exhibiting significantly lower frequency shift and displacement loss.
The study focuses on single-device performance, without considering process variations or array coupling effects. Nevertheless, the high-fidelity model provides a solid design basis for future experiments.
The proposed structure achieves high sound pressure and high sensitivity under low voltage, making it suitable for battery-powered portable air-coupled ultrasonic devices, such as short-range rangefinders, gesture recognition and high-precision nondestructive testing.
To the best of the authors’ knowledge, for the first time, the stress release capability of cantilever beams, stiffness reduction by boundary etched holes, and high driving force of bimorph actuation are systematically integrated into a hexagonal diaphragm. The central platform enables cooperative vibration, simultaneously addressing the two bottlenecks of residual stress suppression and insufficient low-voltage driving force.
