ABSTRACT
Piezoelectric actuator and transducer designs are commonly fabricated with a bimorph, multilayer, or flextensional structure. New multilayer configurations or heterostructures comprising electromechanical materials and modified electrode patterns are anticipated that will be incorporated into evermore sophisticated smart systems. Flat and cylindrical shapes, for example, are preferable to cube and solid rod structures, respectively. Unimorph devices have one plate, and bimorph structures have two ceramic plates bonded onto an elastic shim. Two categories are being investigated for ultrasonic motors from a vibration characteristic viewpoint: a standing-wave type and a propagating-wave type. AlliedSignal developed ultrasonic motors similar to Shinsei's, which are utilized as mechanical switches for launching missiles. Simple disk structures are preferable to unimorphs for motors because the bending action of the unimorph cannot generate sufficient mechanical power, and its electromechanical coupling factor is generally less than 10%. Crack propagation has been investigated in a variety of multilayer systems.
