Figure 7: 3D calculated PBS for a 3D structure based on alternating Psi layers of 40 and 80% porosity and 0 . 5 𝑎 thickness each. Bands are plotted along main symmetry lines of the Brillouin zone, where frequency is given in normalized units ( 𝑎 / 𝜆 ). Left inset, the schematic representation of 3D structure used in the simulations is represented. In dark blue the low-porosity Psi layers and in light blue the high-porosity Psi layers are shown. Right inset, the representation of 3D Brillouin zone is shown.