Broadband reflectionless metasheets: Frequency-selective transmission and perfect absorption

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.Comment: 9 pages, 10 figure

Метаматериал на основе планарных спиралей как преобразователь поляризации электромагнитных волн

The design and modeling of a metasurface is carried out, which makes it possible to transform an incident linearly polarized electromagnetic wave into a transmitted wave with elliptical polarization close to circular. At the same time, the reflection coefficient of the wave is close to zero at the resonant frequency, since the metasurface is similar to the free space in its wave resistance. The resonant elements of the meta-surface (meta-atoms) are two-turn planar spirals with balanced dielectric and magnetic properties. Such spirals exhibit radically different properties with respect to waves with right and left circular polarization. The metasurface as a polarization converter has strong chiral properties, since it contains planar spirals of only one direction of twisting, and can be manufactured within the framework of printed circuit board technologies.Проведено проектирование и моделирование метаповерхности, позволяющей преобразовать падающую линейно поляризованную электромагнитную волну в прошедшую волну с эллиптической поляризацией, близкой к циркулярной. При этом коэффициент отражения волны близок к нулю на резонансной частоте, поскольку метаповерхность аналогична свободному пространству по своему волновому сопротивлению. Резонансными элементами метаповерхности (метаатомами) являются двухвитковые планарные спирали, обладающие сбалансированными диэлектрическими и магнитными свойствами. Такие спирали проявляют кардинально различные свойства по отношению к волнам с правой и левой циркулярной поляризацией. Метаповерхность как преобразователь поляризации обладает сильными хиральными свойствами, поскольку содержит планарные спирали только одного направления закручивания, и может быть изготовлена в рамках технологий печатных плат

Photoactive Properties of Transport Sol-Gel Layers Based on Strontium Titanate for Perovskite Solar Cells

In this work, we have investigated the photocurrent and spectral sensitivity of the silicon/SrTiO3:xNb/perovskite structures. The sol–gel method carried out the deposition of undoped SrTiO3 layers as well as niobium-doped (SrTiO3:Nb) layers at atomic concentrations of 3 and 6% Nb. The perovskite layer, CH3NH3PbI3_xClx, has been deposited by the vacuum co-evaporation technique. The layers have been characterized by scanning electron microscopy and X-ray diffraction measurements. The volt–ampere characteristics and spectral sensitivity of the fabricated samples have been measured under illumination with selective wavelengths of 405, 450, 520, 660, 780, 808, 905, 980, and 1064 nm of laser diodes. We have shown that for different configurations of applied voltage between silicon, SrTiO3:xNb, and CH3NH3PbI3_xClx, the structures are photosensitive ones with a variation of photocurrent from microamperes to milliamperes depending on Nb concentration in SrTiO3, and the highest photocurrent and spectral sensitivity values are observed when a SrTiO3:Nb layer with 3 at.% of Nb is used. A possible application of the proposed structure with a SrTiO3:Nb layer for perovskite solar cells and photodetectors is being discussed

Stored and absorbed energy of fields in lossy chiral single-component metamaterials

Here we present theoretical results for estimation of electromagnetic field energy density and absorbed energy in dispersive lossy chiral single-component metamaterials which consist of an ensemble of identical helical resonators as inclusions. The shape of the helical resonator can vary over a wide range, from a straight wire to a flat split ring. An interaction of the inclusions with harmonic circularly polarized electromagnetic plane waves is studied. We focus on how the inclusion shape influences the mentioned metamaterial properties. The derived general solution for the problem is in good agreement with previous partial and alternative solutions obtained for split ring resonators, straight wires, and helices. The study reveals the optimal geometry of helical lossy resonators for their strongest selectivity of interaction with circularly polarized radiation.Peer reviewe

Acoustic waves in ceramics with the electroinduced anisotropy

The effects related with formation of induced anisotropy in natural-isotropic media, have been studied already for a long time. These phenomena interest scientists first of all due to a rare opportunity of control of artificial anisotropy of media, and also due to an opportunity of the energy transfer to a propagating acoustic or an electromagnetic wave. The idea of the nonlinear interaction of an acoustic and rotating electric field for the observation of parametrical electro-acoustic effects in crystals belongs to V.N Belyi and B.B. Sevruk, and has been ascertained more than 20 years ago [1], [2]. Then this idea has being developed by physicists of the Gomel State University [3]-[8] where F.I. Fedorov, B.V. Bokut', and A.N. Serdyukov [9]-[10] created a scientific school in the field of optics and acoustics. Until the present time the opportunity of suppression of absorption of ultrasound by rotating an electric field and amplification of ultrasonic waves in a crystal in conditions of resonant interaction of an electric field with ultrasound [11]-[14] has been predicted. In this case, media with the induced rotating spatially homogeneous acoustic anisotropy represent an acoustic analogue of spatially periodic media, showing the effects characteristic for the last

Helices of optimal shape for nonreflecting covering

In this paper we study helical inclusions of a certain shape (called the “optimal shape”), such that the electric, magnetic, and magneto-electric polarizabilities are equal, and discuss unusual reflection properties of artificial materials based on such inclusions. We study helical particles with optimized design parameters, which can make the realization of media with equal dielectric and magnetic susceptibilities possible. Not canonical helix, which consists of a split loop with two straight-wire sections, but the true helix, which is obtained by bending a wire with a constant pitch angle is investigated. The geometry of the helices makes it possible to create a composite material with equal permittivity and permeability. In such material optimal helices are located in pairs and each pair consists of the right-handed and left-handed helix. Thus compensation of chiral properties of a material as a whole is achieved

Chiral metamaterial with unit negative refraction index

In this article we study helical inclusions of a certain shape (called the “optimal shape”), such that the electric, magnetic, and magneto-electric polarizabilities are equal, and discuss unusual refractive and absorptive properties of artificial chiral materials based on such inclusions. We propose a new method of analytical calculation of resonant susceptibility of non-canonical, but true three-dimensional spirals. This method takes into account spiral trajectories and effective concentration of conduction electrons

Effect of maximum interaction of circularly polarized electromagnetic waves with the molecule of DNA

Investigation of polarizing properties of DNA is chosen as one of primary importance due to mirror asymmetry of the shape of DNA. Preliminary theoretical calculation has shown that the form of DNA is optimum for radiation of a circular electromagnetic wave under the resonance condition (~10 nm). This conclusion has been proved for the metal DNA-like helices in a microwave range in accordance with the principle of scaling. In the given work it is experimentally confirmed the presence of the effect of polarization selectivity in double reflection of microwave waves from DNA-like helical elements depending on their sign (the right-handed and left-handed helices). It is shown that the circular polarization of waves plays an important role in case of interaction of microwaves reflected from the artificial DNA-like structures. Probably, the identical effect takes place in some processes that involve DNA in biological organisms' cells, but in the range of far ultraviolet radiation and the "soft" X-ray range. These results are also interesting in connection with an opportunity of creation of artificial 2D and 3D structures on the basis of branches of a molecule of DNA. Such structures can be into a basis of new type metamaterials