Analysis of mechanically tunable metasurfaces for identifying multiple strains

We present design and analysis of a mechanically tunable metasurface under multiple strains, which consists of an array of low aspect ratio bilayer Si-TiO2 nanopillars embedded in a flexible substrate. Based on the generalized Snell's law, active control of the transmitted light is analyzed under uniaxial, biaxial and shear strains. A bidirectional solution between complex external strain and optical response is developed. Far-field refracted light spot coordinates are used to determine the strain state the metasurface is under and to estimate the arrangement parameters of the meta-atoms. Finite-difference time-domain simulations and preliminary proof-of-concept experiments validate the accuracy of the bidirectional solution model. Our analysis demonstrates the promise of such tunable metasurfaces for multi-strain detection, beam steering and optical sensing.