Broadband Impedance Matching for Immersed CMUTs: An End-to-End Design-to-Measurement Validation Framework

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Abstract
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.

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