Numerical characterization of mechanochromic photonic crystals for structural health monitoring

We discuss the possible use of photonic crystals as strain sensors. We demonstrate the feasible fabrication of a crystal having sub-micrometric polystyrene colloidal spheres in a PDMS matrix on a rubber substrate, and we demonstrate that the photonic properties change with substrate elongation according to theoretical prediction. The crystal's sensitivity to strain depends directly on interplanar spacing and on Poisson's ratio. To enhance the crystal strain resolution, we propose to fabricate inverse photonic structures, which exhibit a high geometrical Poisson's ratio, and we investigate their photomechanical behavior through nonlinear Finite Element analysis.