Based on the equivalent circuit method and the finite element method, the dimensions of the sandwich piezoelectric ultrasonic welding transducer are optimized. The effect of the lengths of the back and the front metal blocks on the vibration velocity ratio and the effective electromechanical coupling coefficient are discussed. According to the theoretical analysis results, some sandwich piezoelectric ultrasonic welding transducer are designed and fabricated, and their effective electromechanical coupling coefficient are tested by the impedance analyzer. The results show that by optimizing the dimensions of the front and back metal blocks of the transducer, the best electromechanical conversion efficiency and the maximum vibration velocity ratio can be obtained, which will provide theoretical guidance for the optimization of the performance of the sandwich piezoelectric ultrasonic welding transducers.

sandwich piezoelectric transducer; effective electro-mechanical coupling coefficient; vibration velocity ratio; optimization design