Experimental Study on Intermediate Layer Made of (0–3) Composite Materials for Use in Air-Coupled Ultrasonic Transducers

The (0–3) composite materials for the intermediate layer of a MHz-range air-coupled ultrasonic transducer were studied experimentally. The optimal value of the characteristic acoustic impedance for this intermediate layer was calculated using a transmission line model. The (0–3) composite materials were formed from a mixture of silicone rubber and hollow thermoplastic microspheres at various weight ratios, and their acoustic properties were measured, and compared with those of a Reuss model. The measured values of the acoustic properties of the composite materials agreed well with the theoretical estimation. The transmission and reception of an air-coupled ultrasonic waves of 1 MHz using a piezoceramic transducer fitted with the intermediate layer was demonstrated with a pulse–echo system, and the sensitivity was improved by 20 dB by using the optimal composite material.