Study on Dry-Coupled Ultrasonic Transducer for Solid Rocket Motor Detection

In order to develop a dry-coupled ultrasonic transducer that can detect the internal defects of a solid rocket motor, the piezoelectric vibrator was studied by the finite element method with multiple physical field couplings. Firstly, the vibration modes and corresponding resonant frequencies of the piezoelectric vibrators at 20–300 kHz without power were solved, and it was determined that the piezoelectric vibrator can adopt the structure form of bi-laminated, series three laminated, and parallel three laminated preliminarily. Then the frequency response of the piezoelectric vibrators was analyzed according to the admittance-frequency relation. It was found that the bending vibration mode of bi-laminated and parallel three-laminated boards could be excited when the electrical load was applied to both ends. Then, it is found that the parallel three-layer laminate has a larger amplitude in the direction of thickness and a higher electromechanical conversion efficiency based on transient analysis. Therefore, the parallel three-layer laminate is finally selected as the basic form of a piezoelectric vibrator. In addition, the amplitude performance of piezoelectric vibrators with matching layers and backing is compared and analyzed, and these structures are determined not to be used in the dry coupling transducer.