(a) Absorption efficiency when ideal metasurfaces are used beneath the substrate compared to the case of simple reflector backing. (b) Relationship between PEC and PMC boundary conditions and admittance. (c) Schematic of the realistic geometry for our simulations, d_cigse is 100 nm and d_subs is 50 nm. Periodicity L and jIm[Y_z(x)] are changed for each deflection angle and frequency.