1. Field of the Invention
The present invention is generally related to piezoelectric fiber composite strain actuators.
2. Description of the Related Art
Conventional piezoelectric fiber composite actuators are typically manufactured using a layer of extruded piezoelectric fibers encased in protective polymer matrix material. Interdigitated electrodes etched or deposited onto polymer film layers are placed on the top and bottom of the fibers to form a relatively thin actuator laminate. Protecting the fibers in a matrix polymer strengthens and protects the piezoelectric material. The resulting package is more flexible and conformable than actuators formed from monolithic piezoelectric wafers. These actuators can be easily embedded within or placed upon non-planar structures using conventional manufacturing techniques. In addition, the use of interdigitated electrode poling permits production of relatively large, directional in-plane actuation strains. The directional nature of this actuation is particularly useful for inducing shear (twisting) deformations in structures.
Unfortunately, the methods of manufacturing conventional piezoelectric fiber composites typically use relatively high cost, extruded, round piezoelectric fibers. Moreover, alternative methods of manufacture using square fibers, which are milled from lower cost monolithic piezoelectric wafers, have been unsuccessful due to the difficulty of aligning individual square fibers during actuator assembly without shifting and rolling. Rolled square fibers tend to expose sharp corners and edges which can sever the interdigitated electrode layers during the final process of actuator assembly. Both the round and square fiber approaches require individual handling of piezoelectric fibers during assembly, thereby resulting in relatively high manufacturing costs.
Another disadvantage of conventional piezoelectric fiber composite actuators is the requirement of relatively high operating voltages. High operating voltages are needed to produce electric fields which are sufficiently strong to propagate through the protective polymer material encasing the piezoelectric fibers. These electrode voltages are several times higher than those theoretically required to produce a given strain in the unprotected piezoelectric material. Additionally, round fibers have a low contact area with the electrode, thereby causing losses and decreased efficiency. To compensate for these losses, increased voltages are required. Conventional techniques for applying electrodes directly in contact with the piezoelectric fibers have thus far not been practical.
It is therefore an object of the present invention to provide an improved piezoelectric fiber composite strain actuator and a method for making same.
Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification.