Amirfereydoon Mansoori

Patterning the piezoelectric layer of a PMUT plate usually leads to improved performance, however modeling of such PMUT is not as straightforward as its conventional counterpart. This paper presents an electroacoustic model for conventional as well as patterned piezoelectric micromachined ultrasonic transducers (PMUTs) with square shaped membranes. Hamilton’s principle is utilized to formulate the dynamics of the patterned PMUT. The derived mode shape is used to obtain the electrical, mechanical and acoustic parameters to arrive at the complete electroacoustic model. The model is applied to 8 different designs, where 4 are of conventional type with different electrode configurations and the other 4 are patterned designs with different patterning configurations. Using the proposed model, the electrode and patterning geometry for each PMUT design is optimized. Natural frequency, mode shape, the input impedance at the electrical port and the transfer function from the electrical to the acoustic port calculated from this model are shown to be in good agreement with those obtained from finite element analysis for all the studied designs. Moreover, the patterned PMUTs are shown to have superior performance, in terms of volume velocity per unit voltage, over conventional PMUTs operating at a given resonance frequency.

Piezoelectric micromachined ultrasonic transducers (PMUTs) with multiple electrodes can be utilized as multi-frequency transducers by exciting selected vibration modes of the diaphragm providing configurability that may be beneficial in modern ultrasound imaging and therapeutic techniques. This requires judicious arrangement of the electrode configuration to excite the desired modes or combination of modes. Optimization of the electrode pattern can be done using full electroacoustic Finite Element Method (FEM) simulations, but this is computationally intensive and gives limited insight into the underlying physics. This paper presents a simple and efficient approach based on the in-vacuum strain mode shapes of the PMUT diaphragm to optimize the electrode configurations for an arbitrary PMUT cell resonating at any flexural mode. Strain mode shapes are obtained both from an analytical model as well as FEM. The proposed method is compared to and verified by full electroacoustic FEM simulations of PMUTs radiating into water. The optimal electrode patterns for the first few flexural modes are found for rectangular PMUTs with three different length-to-width aspect ratios, and examples of configurable PMUTs are given by combining the optimal electrodes at two different modes.