The input electrical impedance behaves as a capacitive when a piezoelectric transducer is excited near its resonance frequency. In order to increase the energy transmission efficiency, a series or parallel inductor should be used to compensate the capacitive impedance of the piezoelectric transducer. In this paper, the effect of the series matching inductor on the electromechanical characteristics of the piezoelectric transducer is analyzed. The dependency of the resonance/anti-resonance frequency, the effective electromechanical coupling coefficient, the electrical quality factor and the electro-acoustical efficiency on the matching inductor is obtained. It is shown that apart from compensating the capacitive impedance of the piezoelectric transducer, the series matching inductor can also change the electromechanical characteristics of the piezoelectric transducer. When series matching inductor is increased, the resonance frequency is decreased and the anti-resonance unchanged; the effective electromechanical coupling coefficient is increased. For the electrical quality factor and the electroacoustic efficiency, the dependency on the matching inductor is different when the transducer is operated at the resonance and the anti-resonance frequency. The electromechanical characteristics of the piezoelectric transducer with series matching inductor are measured. It is shown that the theoretically predicted relationship between the electromechanical characteristics and the series matching inductor is in good agreement with the experimental results.

Three-dimensional coupled vibration of the composite cylindrical piezoelectric transducer is analyzed. The composite cylindrical piezoelectric transducer consists of an inner axially polarized piezoelectric ceramic cylinder and an outer metal cylinder with the same height. Coupled vibration of the composite cylindrical piezoelectric transducer is analyzed by equivalent elasticity method, which is an approximate analytical approach. According to this method, coupled vibration of the cylindrical transducer is regarded as an interaction between a plane radial vibration and a longitudinal vibration. The radial and longitudinal electromechanical equivalent circuits of the piezoelectric transducer are acquired. Input impedances as functions of the resonance frequency and the mechanical coupling coefficient are derived to obtain resonance frequency equations. The analytical results are supported by experimental and numerical simulated results of two prototypes of the piezoelectric transducer. The composite cylindrical piezoelectric transducer presented in this paper is superior to single cylindrical piezoelectric transducers, composite ring-type, and tube-type transducers in the field of high output power and efficiency.