Development of a piezoelectric unimorph using a mechanically pre-stressed substrate

Abstract

This paper proposes a novel curved shape piezoelectric unimorph called PUMPS(piezoelectric unimorph with mechanically pre-stressed substrate) that uses anew and simple fabrication method. Generally, conventional pre-stressed curvedshape unimorphs are made by using high-temperature adhesion processes andthe thermal expansion coefficient mismatch of their constituent layers. In theconventional methods, therefore, it is necessary to use materials with differentthermal expansion coefficients, high-temperature ovens or autoclaves, and specialadhesives. In addition, the conventional methods generally require the re-poling ofthe piezoceramic actuator layer due to high-temperature adhesion near or abovethe Curie temperature of the piezoceramic. The present fabrication method usesmechanically pre-stressed substrates and a room temperature adhesion processinstead of relying on a thermal coefficient mismatch. First, a substrate material isstrained in the longitudinal direction and then a piezoelectric material is attached tothe substrate. A difference of mechanical strains between the substrate and thepiezoelectric layer causes the final manufactured actuator to curve. In this way, a newtype of curved shape pre-stressed piezoelectric unimorph, PUMPS, can be easilyfabricated at room temperature and can be used as a sensor, an actuator and anenergy-harvesting element without the necessity of a re-poling process. A series ofperformance tests on the proposed PUMPS actuators was accomplished and the testresults show that the actuation capability of PUMPS is comparable to that ofconventional curved shape actuators, in spite of the much simpler manufacturing process.