SANDWICHED PIEZOELECTRIC ULTRASONIC TRANSDUCERS OF LONGITUDINAL-TORSIONAL COMPOUND VIBRATIONAL-MODES

Sandwiched piezoelectric ultrasonic transducers of longitudinal-torsio nal compound vibrational modes were studied. The transducers consist o f coaxially segmented, longitudinally and tangentially polarized piezo electric ceramic rings, a back metal cylinder, and a front exponential solid metal horn. Based on the plane-wave approximation, the equivale nt circuits of the longitudinal and torsional vibrations in the sandwi ched transducer were obtained and the resonance frequency equations of the transducer in longitudinal and torsional vibrations were derived. By means of choosing the radius decay coefficient of the front expone ntial horn, the longitudinal and torsional vibrations are made to reso nate at the same frequency in the transducer. Sandwiched piezoelectric ultrasonic transducers of longitudinal-torsional compound modes were designed and fabricated according to the frequency equations. It is de monstrated that the measured resonance frequencies of the transducers are in good agreement with the theoretical results, and the measured r esonance frequencies of the transducers in longitudinal and torsional vibration modes are also in good agreement with each other. Theoretica l and experimental results show that this kind of transducer can be us ed in ultrasonic welding, ultrasonic machining, ultrasonic motors, and other ultrasonic applications which need large displacement amplitude s.