(a) Resonant wavelength λr as a function to the pitch d for a 1D absorber. The bold line corresponds to the theoretical scaling law λr = 33 d and the dots to the exact electromagnetic computations. The inset represents the absorbance spectrum with a total absorption in the microwave range for λr = 11.2 mm when d = 350 μm. (b) Ratio λr/d with respect to the slit width, the dashed and solid curves are respectively obtained with the RCWA simulations and with Eq. (9) for d = 1 μm. (c) Ratio of the spacer over the wavelength with respect to the pitch. g/λ remains constant for a period larger than 8 μm.