Acoustic and rheological characterization of hollow glass microsphere composite for development of optimized air-coupled ultrasonic matching layer

An air-coupled acoustic matching layer, based on hollow glass microsphere composite, was developed for air-coupled ultrasonic transducers. The effects of the matrix, powder series, and volume fraction were systematically analyzed by acoustic and rheological characterization. The optimized hollow glass microsphere-epoxy composite showed a superior air-coupling performance, with a characteristics acoustic impedance of 1.08 MRayl and attenuation coefficient of 0.05 dB/mm, respectively. To validate the developed composite, an air-coupled ultrasonic transducer was fabricated with piezoelectric ceramic vibrator, and its feasibility for application in a gas flowmeter was demonstrated. The developed composite exhibits a suitable air-coupling performance for a high-accuracy ultrasonic gas flowmeter.