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

This paper proposes a novel curved shape piezoelectric unimorph called PUMPS (piezoelectric unimorph with mechanically pre-stressed substrate) that uses a new and simple fabrication method. Generally, conventional pre-stressed curved shape unimorphs are made by using high-temperature adhesion processes and the thermal expansion coefficient mismatch of their constituent layers. In the conventional methods, therefore, it is necessary to use materials with different thermal expansion coefficients, high-temperature ovens or autoclaves, and special adhesives. In addition, the conventional methods generally require the re-poling of the piezoceramic actuator layer due to high-temperature adhesion near or above the Curie temperature of the piezoceramic. The present fabrication method uses mechanically pre-stressed substrates and a room temperature adhesion process instead of relying on a thermal coefficient mismatch. First, a substrate material is strained in the longitudinal direction and then a piezoelectric material is attached to the substrate. A difference of mechanical strains between the substrate and the piezoelectric layer causes the final manufactured actuator to curve. In this way, a new type of curved shape pre-stressed piezoelectric unimorph, PUMPS, can be easily fabricated at room temperature and can be used as a sensor, an actuator and an energy-harvesting element without the necessity of a re-poling process. A series of performance tests on the proposed PUMPS actuators was accomplished and the test results show that the actuation capability of PUMPS is comparable to that of conventional curved shape actuators, inspite of the much simpler manufacturing process.