Analysis and experimental validation of longitudinally composite ultrasonic transducers

The longitudinally cascaded piezoelectric ultrasonic transducer is studied which is composed of two longitudinally sandwiched piezoelectric transducers connected together mechanically in series and electrically in parallel. When the losses and load are taken into account, the electromechanical equivalent circuit of the transducer is obtained; the input electric impedance is analyzed and the resonance/anti-resonance frequency equations are obtained assuming one dimensional longitudinal vibrational theory. The relationship among the resonance/anti-resonance frequency, the effective electromechanical coupling coefficient, the mechanical quality factor and the electro-acoustic efficiency with the geometrical dimension, the losses, and the load is analyzed. Two longitudinally composite transducers are designed, made, and measured. It is shown that the theoretical resonance/anti-resonance frequencies, the effective electromechanical coupling coefficient, and the mechanical quality factor are in good agreement with the experimental results. It is expected that this kind of composite transducer can be used in large power and high intensity ultrasonic applications, such as ultrasonic liquid processing, ultrasonic metal machining, and ultrasonic welding and soldering.