Active structures flexible enough to be molded in desired shapes and coupled with the ability to be controlled have been pursued for many high precision applications. Membrane-thin but extremely large (>10 m) optical mirrors and reflectors for combined RF-Optical applications are one of the important high precision applications where shape and vibration control of a structure is highly desirable. In this application the precision demands of the optical surface mitigate the combined benefit of the large aperture.
Polyvinylidene Fluoride or PVDF is a semi-crystalline piezoelectric polymer with strong orthotropic in-plane properties. This material is suitable for making large reflectors due to its availability in thin sheets and almost linear and nonhysteretic behavior at low to moderate operating voltages. Its low cost and ease of manufacture also make it suitable for shape and vibration control of large reflecting structures.
This research focuses on a three-layer laminated actuator with two layers of PVDF film bonded with a layer of epoxy. The electrodes are applied externally on the top PVDF film in a given pattern such that the applied electric field will yield the desired shape of the laminate. The bottom layer of the bimorph is the reflecting surface and acts as the ground. The actuator itself acts as the RF and optical surface and therefore requires no secondary surface.
Research has been performed by Sumali et. al. and Massad et. al. for quasi-static deflection of a PVDF bimorph with both simply supported and corner supported boundary conditions under an applied electric field. This methodology produced excellent results under ideal conditions with no disturbances. Due to lack of any kind of feedback, the methodology was an open loop technique lacking the ability to acclimatize under inclement real world conditions.
This research takes a step further and removes this demerit by dynamic modeling of a three layer PVDF laminated plate with simply supported boundary conditions and developing a Closed Loop Control Methodology which is capable of rejecting external disturbances. This will not only help in controlling the shape, but also will allow the structure to maintain it under inclement environment. The orthotropic properties of the laminate / actuator are also incorporated into the model, reducing the error due to unmodeled dynamics. Using the developed model and closed loop control methodology, the laminate can be precisely and accurately shaped to function as a satellite antenna, optical reflector or a solar reflector. Typically, these are the type of applications where a shape change is difficult once the system is installed.