KSEF R&D Excellence: Evaluation of Surface Patterns for In-Plane Measurement of Thin-Film Structures

Precision thin-film structures for space applications must maintain their shape in an environment full of dynamic disturbances. These structures, which resemble cellophane or Mylar, typically consist of a thin polymer base material with a very thin metal layer on the surface for reflectivity. They offer an ultra-lightweight solution to the challenge of launching large spacecraft, enabling the development of solar sails and the next generation of space telescopes. State-of-the-art approaches for modeling these novel devices require evaluation and verification. Experimental measurement of the structure's response is the core of the verification process. Both out-ofplane and in-plane displacements of these thin-film structures must be measured. While out-ofplane displacements can be measured using laser displacement sensors, in-plane measurements require more novel approaches. Although a number of well-characterized techniques for performing in-plane measurements are available, all require modifying the surface of the structure. This can be done by either depositing a pattern on the surface, in a process similar to those used for fabricating miniature circuits, or by etching a pattern into the surface. What is lacking is an understanding of the effects of these patterns on the film response. We propose to conduct parameter studies on pattern size, spacing, thickness, and geometry using the Finite Element Analysis technique. Our objectives are 1) to defme optimal patterns that minimize their influence on the dynamic response, 2) to evaluate fabrication approaches and 3) to combine the results of the fIrst two objectives to develop a precision measurement process for in-plane thinmm response. This effort is motivated by several current and recent research projects at the University of Kentucky, involving modeling, testing, and controlling the response of precision thin-film structures. Beyond space applications, precision measurement of in-plane response of thin fIlms is also applicable for inspection and control of high-speed material handling in manufacturing.