Gabriel Guerreiro

Capacitive micromachined ultrasonic transducers (CMUTs) are a promising alternative to conventional piezoelectric transducers, offering superior design flexibility and broadband operational characteristics. However, their clinical and practical deployment is constrained by elevated driving voltages and limited acoustic power output, particularly when producing CMUTs based on polymers. This paper presents an end-to-end, measurement-driven experimental validation strategy for designing passive broadband impedance-matching networks that enhance transmitted acoustic power in immersed CMUT arrays while preserving bandwidth. Matching topologies are synthesized to operate near the theoretical Bode–Fano limit, and robustness to component tolerances is quantified through Monte Carlo yield analysis using realistic off-the-shelf component variations. The matching networks are then implemented and experimentally validated under representative unipolar pulse excitation, with far-field acoustic pressure characterized in both time and frequency domains and compared against numerical predictions. The results show that the optimized impedance matching increases transmit power by a factor of 2.1 at the cost of a 40% fractional-bandwidth reduction. These findings establish a directly applicable, validated framework for broadband impedance matching in polymer CMUT arrays and support its use as a cost-effective approach for ultrasound imaging and therapeutic systems.

The Classical Kirchhoff—Love plate theory is widely used to model capacitive micromachined ultrasonic transducer (CMUT) cells, assuming thin plates with negligible shear deformation and rigid boundaries. However, thicker polymer-based CMUTs operate beyond the limits of these assumptions, where the shear and boundary effects become significant. These factors alter the displacement profile, lowering the resonant frequency and the static pull-in voltage. Existing analytical models do not consider these effects alone or in combination. This study introduces the softly-clamped displacement equation, which accounts for both shear deformation and compliant boundary behavior using only two fitting constants for a single cell. The aspects investigated include the plate deflection, pull-in voltage, and electromechanical coupling coefficient. The model was validated against finite element model (FEM) simulations across various thickness-to-radius ratios, applied pressures, and voltages. The proposed reduced-order model was implemented in SPICE for both large- and small-signal operating regimes and showed excellent agreement with the FEM results: pull-in displacement (error < 0.5%), pull-in voltage (error < 2.3%), and resonance frequency (error < 4.2%). The softly-clamped model bridges a critical gap in CMUT modeling and offers a scalable framework for designing thick-plate, polymer-based transducers under realistic boundary conditions.