Exploiting Mechanical Flexure as a Means of Tuning the Responses of Large-Scale Periodic Structures

We present techniques for designing large-scale, mechanically tunable periodic structures (PSs). Overlapping combined with relative movement, stretching/compression, and flexure are the three mechanical tuning techniques studied in this paper. We demonstrate that all of these mechanical movements may be used to tune the capacitance and inductance of elementary periodic structures with capacitive and inductive surface impedances over wide ranges of values. Analytic formulas for calculating the variable inductance and capacitance of these tunable PSs are also provided. These elementary PSs are the building blocks of a wide range of other PSs with more complicated unit cells and response types. One such structure-a frequency selective surface (FSS) composed of series combination of these inductive and capacitive structures-is also examined to demonstrate the application of the proposed tuning and analysis concepts. The FSS is fabricated on an accordion-like substrate that can be contracted or stretched to change its frequency of operation. The response and tuning properties of this structure are experimentally characterized using a free-space measurement system. A very good agreement between theory and experiment is obtained. This demonstrates that the behavior of such complex mechanically tunable PSs can be analyzed by examining the behavior of their constitutive inductive and capacitive elements.