Research on Acoustic Impedance Matching Method of CMUT Sensor Based on PDMS/BN Particles

In this article, we propose an improved bandwidth matching layer using boron nitride/polydimethy- lsiloxane (BN/PDMS) 0–3 composites to achieve superior electrical insulation and transmission performance for underwater capacitive micromachined ultrasonic transducer (CMUT) sensor. This innovation addresses the limitations of traditional quarter-wavelength micromechanical ultrasonic transducers (MUTs) in meeting the demanding broadband CMUT matching requirements. To effectively encapsulate CMUT sensor, we use BN/PDMS 0–3 composite material with a volume concentration of 16.9%, which closely matches the acoustic impedance of water. The properties of the 0–3 composites are analyzed using the Reuss model, followed by the preparation of composites with varying concentrations and rigorous testing of their acoustic impedance. The experimental results indicate that despite an 8-dB reduction in signal amplitude in seawater after encapsulation, the original curve trend of the CMUT sensor device remains unchanged. The bandwidth increased from 28.38% to 31.63%, representing an 11.45% increase. The −6 dB beamwidth before and after encapsulation is 5°, while the maximum sidelobe level is recorded as −15.89 dB (3°) and −22.19 dB (3°), respectively. At this volume fraction, BN/PDMS 0–3 composites effectively reduce sidelobe interference, emphasizing their importance. The outstanding matching performance of 0–3 composite materials provides CMUT sensors with a significant advantage in underwater detection systems, ensuring the reliability of ultrasonic imaging.