In power ultrasonic and underwater acoustic fields, the ultrasonic treatment efficiency of vibration system can be improved significantly when vibration system is driven by the multi-frequency longitudinal transducer, and the performance of vibration system is determined by the multi-frequency characteristics of transducer. In this paper, using electromechanical equivalent circuit method, the multi-frequency characteristics of a longitudinal ultrasonic transducer with a stepped horn are studied for the ultrasonic vibration system optimal design. The expressions of the input impedance and the velocity amplification ratio of the transducer are obtained. The relationships between the electromechanical coupling coefficients, the velocity amplification of the multi-frequency transducer and the excitation position of the piezoelectric stack, the size of the stepped horn are analyzed. Combined with the finite element analysis of the transducer's key performance, the optimal design parameters of the multi-frequency transducer are given. Finally, the electromechanical properties of the multi-frequency transducer are tested experimentally, the theoretical analysis and finite element results are verified well.
Keywords: Electromechanical coupling coefficient; Electromechanical equivalent circuit; Longitudinal transducer; Multi-frequency; Velocity amplification ratio.
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