Popup Tunable Frequency Selective Surfaces for Strain Sensing

A 3-D popup frequency selective surface (FSS) is presented that can be tuned by the amount of strain due to mechanical loading in its elastomeric substrate. The proposed FSS structure comprises periodic 2-D crossed dipoles attached to the substrate at selective bonding sites. Strain release in the substrate induces compressive stress in the attached FSS, converting it to a 3-D periodic pattern. With the out-of-plane displacement, the interaction with the incident field and mutual interactions between the elements are altered, resulting in a resonant frequency shift and a more stable response regarding the incident angles from 0 degrees to 45 degrees. A design of popup FSS structure is introduced for strain sensing applications. The potential sensor can measure up to 50% strain in the substrate by frequency down-shift from 3.1 to 2.4 GHz. Multiphysics finite element method modeling of the mechanical and RF simulation was in good correlation with the experimental data and demonstrates the potential of these structures as sensors.