Bruggemann's formula $$n=\displaystyle\frac 12\sqrt{(3p-1)n_b^2+(2-3p)n_\nu^2+\sqrt{((3p-1)n_b^2+(2-3p)n_\nu^2)^2+8n_b^2n_\nu^2}}$$, where $$n$$ is the refractive index of the composite; $$p$$ is porosity of the layer material; $$n_b$$ and $$n_\nu$$ are refractive indices of the bilk material and voids, respectively. Average Weighted Value of Permitiviteis $$n^2=pn_b^2+(1-p) n_\nu^2$$, where $$n$$ is the refractive index of the composite; $$p$$ is the volume fraction of voids; $$n_b$$ and $$n_\nu$$ are refractive indices of the bilk material and voids, respectively. Average Weighted Value of Refractive indices $$n=pn_b+(1-p) n_\nu$$, where $$n$$ is the refractive index of the composite; $$p$$ is the volume fraction of voids; $$n_b$$ and $$n_\nu$$ are refractive indices of the bilk material and voids, respectively.