Abstract
Energy of propagating electromagnetic waves can be fully absorbed in a thin lossy layer, but only in a narrow frequency band, as follows from the causality principle. On the other hand, it appears that there are no fundamental limitations on broadband matching of thin absorbing layers. However, known thin absorbers produce significant reflections outside of the resonant absorption band. In this paper we explore possibilities to realize a thin absorbing layer which produces no reflected waves in a very wide frequency range, while the transmission coefficient has a narrow peak of full absorption. Here we show, both theoretically and experimentally, that a wide-band-matched thin resonant absorber, invisible in reflection, can be realized if one and the same resonant mode of the absorbing array unit cells is utilized to create both electric and magnetic responses. We test this concept using chiral particles in each unit cells, arranged in a periodic planar racemic array, utilizing chirality coupling in each unit cell but compensating the field coupling at the macroscopic level. We prove that the concept and the proposed realization approach also can be used to create non-reflecting layers for full control of transmitted fields. Our results can have a broad range of potential applications over the entire electromagnetic spectrum including, for example, perfect ultra-compact wave filters and selective multi-frequency sensors.
Highlights
Total absorption of electromagnetic radiation requires elimination of all wave propagation channels: reflection, transmission, and scattering
We explore possibilities to realize a thin absorbing layer that produces no reflected waves in a very wide frequency range, while the transmission coefficient has a narrow peak of full absorption
In our previous work [22], we demonstrated that total symmetric absorption in an electrically thin layer can be achieved only if the layer is not bianisotropic
Summary
Total absorption of electromagnetic radiation requires elimination of all wave propagation channels: reflection, transmission, and scattering. Several topologies of absorbers have been proposed based on cut wire arrays separated by a dielectric layer [16,17,18,19,20] In all these structures, the Huygens’ balance between the electric and magnetic responses (which is necessary for cancellation of the reflected waves) holds only inside a narrow-frequency band for which the dimensions have been optimized. We examine the physical requirements for full and symmetric (from either of the sides) absorption of incident waves and show that the ideal performance can be accomplished in a single-layer array of designed helical inclusions We show, both theoretically and experimentally, that an array of these inclusions truly operates as a Huygens’ surface in a very wide frequency range, exhibiting zero reflectivity even far from the absorption band. This design would allow one to build extremely thin absorbers
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