Mechanochromic response of 3D composite photonic crystals by numerical simulation

In this work, we present the possible use of 3D Photonic Crystals in Structural Health Monitoring. We show how the optical response of a colloidal photonic crystal built from sub-micrometric polystyrene spheres in a PDMS matrix on a rubber substrate varies with elongation. The optical features are analyzed by means of Finite Difference Time Domain (FDTD) three-dimensional (3D) simulations, using an in-house code that numerically solves Maxwell’s equations for a light beam impinging on the crystal. It contains different wavelengths in the visible spectrum and the wave amplitudes of the reflected and transmitted secondary beams are then observed. A change in the characteristic prominently reflected or transmitted wavelengths is produced, ascribable to changes in the spacing between the spheres due to deformation. This behavior is ultimately amenable to diffractive effects from the crystal, which are fully captured by our full wave 3D FDTD model. It uses the basic equations governing the light-matter interaction at a macroscopic level, without any simplifying approximations. Further numerical studies are in progress to compare the proposed computational model with the experimental results. Nowadays numerical investigations are a powerful and important tool in predicting and studying the behavior of a real sensor device, for which the experimental data of interest are not always clearly recognizable because of complexity.