Focusing type high power transducer using burst drive for ultrasonic welding

In order to operate ultrasonic welding tools more efficiently at high frequency over 100 kHz to MHz order, a focusing type transducer is proposed. The transducer is constructed with metal bodies. A disk PZT element is glued on the back surface of one metal. The PZT is driven by burst waves with an electric source. The metal bodies consist two kinds of materials for transmission medium. The intermediate boundary of the two metals is formed spherical so that the plain wave from the PZT element concentrates with refraction due to the difference of the propagation velocity of the dilatational wave. At this concentrated region, the transducer has the output mechanical port so that a work is placed here. A driving frequency of the PZT is a resonance frequency of the thickness mode of the element. A transduce efficiency from electricity to acoustic power is about 90% calculated from a simple model. For designing this transducer, numerical simulation using FEM and Newmark-β method is carried out. This simulation shows that the transform gain of the vibration velocity is about four times and amplitude distribution at the output surface is almost uniform at 570 kHz. The experiment has supported this result. It is available to obtain 1.2 m/s vibration velocity at the output.