Development of air-coupled ultrasonic transducer for material surface defect detection

In order to solve the huge impedance mismatch problem between the piezoelectric ceramic material and the air in the development of air-coupled ultrasonic transducer for material surface defect detection, this paper selected hollow glass beads and epoxy resin for compounding. A type of low acoustic impedance and low attenuation matching layer material with its density of 550 kg·m^-3, sound velocity of 2 300 m·s^-1, acoustic impedance of 1.3 MRayl, and acoustic attenuation coefficient of 344 dB·m^-1 at 2. 25 MHz was prepared, and the quarter-wavelength matching principle was used for transducer design. On this basis, an air-coupled ultrasonic transducer was fabricated, and the admittance spectrum test and echo signal test analysis were performed on it. The results show that so developed air-coupled transducer has a center frequency of 204 kHz and relative bandwidth of -6 dB is 21.0% with better sensitivity and bandwidth.