Design of Air-Coupled Broadband CMUT Micro-Elements and Array Configurations

To address the issues of narrow bandwidth and low sensitivity in air-coupled CMUT operating in the mid-frequency range (200 kHz−2 MHz), this study proposes a high-sensitivity broadband CMUT element and array through element structure design and array configuration optimization. The element employs a composite structure combining annular electrodes with nickel convex rings to regulate diaphragm stiffness, enabling piston-mode vibration for enhanced sensitivity. The array adopts a novel hybrid heterogeneous-homogeneous planar configuration: lateral heterogeneous design (frequency band overlap of different elements) expands bandwidth, while longitudinal homogeneous design (output superposition of identical elements) boosts overall sensitivity, achieving synergistic optimization of both parameters. Parametric optimization and performance simulation using COMSOL software demonstrate that the proposed CMUT element achieves a receiving sensitivity of 21.00 µV·Pa⁻¹/mm² and a transmitting sensitivity of 1.05 kPa·V⁻¹/mm² at the central frequency of 1.00 MHz. The array design realizes 111.75% −6 dB fractional bandwidth and 230.15 nA peak output current within the mid-frequency range. Finally, a CMUT fabrication process based on MEMS manufacturing technology has been established, delivering concrete experimental protocols for practical implementation.