Extraordinary absorption by a thin dielectric slab backed with a metasurface

Abstract

The absorption of electromagnetic waves by a thin dielectric slab backed by a metasurface has been comprehensively studied and discussed at microwave frequencies. The metasurface consists of a metallic plate decorated with a periodic distribution of coaxial-or annular-type cavities. Analytical expressions for the absorbance have been obtained by using a mode-matching method. For P -polarized waves it is predicted that a low-frequency peak of perfect absorption is possible by properly choosing the lossy component of the permittivity of the dielectric slab, with the position of this peak being easily tunable by the cavity length. It is also shown that non-Bravais lattices, containing several cavities in the unit cell, and the excitation of guided waves by the periodic array of resonators are complementary absorption mechanisms in the studied structures.

Experimental verification of total absorption by a low-loss thin dielectric layer

“…The observed insensitivity of the peak position with the impinging angle supports the predictions of the model. 16 Nevertheless, the absorption amplitude changes, a maximum value is achieved for h ¼ 60 while for higher or lower angles the absorption decreases. Also, it is easy to observe that, when the incidence angle is close to normal incidence (h % 0), the absorption vanishes because the impinging wave cannot excite the resonant modes in the coaxial cavities without a phase variation across the surface.…”

“…13 Also, if the sub-wavelength thickness requirement is relaxed, performance improvements in broadband operation can be achieved. 14,15 Previously, some of the current authors proposed a strongly absorbing "metasurface" for microwave frequencies consisting of a thin layer made of a low loss dielectric material on top of a patterned metallic plate, 16 and they emphasized its ability to tune the frequency of the absorption peak. The metallic plate under consideration consisted of a square array of closely spaced (non-diffracting) air-filled coaxial cavities.…”

“…16 and present a practical demonstration of the easy tunable system theoretically proposed. In particular, a metasurface producing total absorption is designed, fabricated, and experimentally characterized, studying the influence of the angle of incidence.…”

“…Selection of the peak frequency, f , and the cavity length, h, is done using the expressions extracted from the low-frequency and monomode approximation in Ref. 16. See Sec.…”

“…The symbols represent the experimental data, while the continuous line is the calculated with the model based on the mode matching technique reported in Ref. 16. For the comprehensiveness of this work, an account of the model can be found in Sec.…”