In this paper, we present a simple metasurface based multiband reflective polarization converter for both linear and circular polarizations. We show that, on one hand, the proposed structure can convert the polarization of linearly polarized waves to the orthogonal direction at four frequency bands — 4.3 GHz, 7.2 GHz, 12.3 GHz, and 15.15 GHz. On the other hand, this metasurface can achieve linear to circular or circular to linear polarization conversion at 4 GHz, 4.75–5.95 GHz, 8.35–8.8 GHz and 14.35–14.6 GHz frequency bands. Such multiband operation originates from multiple resonances occurring in the structure based on meandered square ring and diagonal split strip resonator. Moreover, the polarization transforming capability is stable for oblique incident angle up to 15°, for both transverse electric (TE) and transverse-magnetic (TM) polarizations. Furthermore, the proposed structure acts as a meta-reflector that maintains the handedness of the circular polarization upon reflection. Finally, a prototype of the proposed meta-structure is fabricated and measured for both normal and oblique incidence of electromagnetic waves. All the results present excellent resonant stability with respect to the different polarization and incident angles. In addition, we have also performed the tolerance analysis of different material parameters to understand the robustness of the structure. Due to the ability of the structure to perform three functionalities through a single layout, the proposed design can pave its way in different microwave applications such as satellite, radar, and 5G communications.

In this letter, a switchable frequency selective surface (FSS) is designed that can operate between rasorber and absorber having a wide passband characteristics. The structure has an extra advantage of being built on a single dielectric layer having lossy and lossless layer on the two opposite sides. The lossy layer comprises of lumped resistors which assists in wide band absorption from 4.8-15 GHz. PIN diodes are mounted in the lossless layer to equip the structure with rasorber/absorber operation. Under the rasorber operation, a wide transmission bandwidth in between the absorption band from 9-11 GHz is obtained. The system is also simplified with the help of an equivalent circuit model (ECM). The structure is carefully designed so that it is immuned to polarization and angle sensitivity. Finally, the prototype is fabricated and measured and the results are found to be in good agreement with the simulated ones. The proposed design is expected to find its application in all airborne technologies.

In this paper, a flexible, ultra-thin, miniaturized broadband frequency selective surface (FSS) is demonstrated for wideband electromagnetic shielding application. The unit cell of the proposed FSS structure consists of cross dipoles loaded with the metallic circular strip. The proposed miniaturized FSS structure has an extremely low profile with a thickness of $0.0009{\lambda }_o$ and a unit cell size of $0.045{\lambda }_o\times 0.045{\lambda }_o$. This FSS structure provides wideband shielding of more than 20 dB from 1.1 to 2.6 GHz frequency region. Besides this wide stopband, the FSS structure acts as a transparent window in the $n78$ frequency band which can be used for the 5G communication purpose. Moreover, by comprehending the interaction between the incident electromagnetic wave and unit cell, a conceptual equivalent circuit model is developed that helps to interpret the mechanism of the miniaturization as well as the broadband response of FSS structure. We also compared the proposed FSS with other recently reported structures and observed more than 55% improvement in size reduction with several other miniaturized flexible FSS structure. Furthermore, this FSS structure exhibits 20 dB attenuation over a wide frequency region with a fractional bandwidth of 111%. Moreover, excellent resonant stability is achieved in regards to different polarization and incident angle up to ${60}^o$.

We use a classical, microscopic model of pointlike dipolarizable entities (a model that is standard in the case of positive polarizability) and investigate its behavior for simple cubic (sc), body-centered cubic (bcc), and face-centered cubic (fcc) crystals with one entity per primitive cell when the static polarizability of the entities is negative and the mutual electrostatic interaction between the entities is taken into account. We find that the static electric susceptibility is bounded below due to an instability towards self-polarization but negative values are possible in each case. The usual Clausius-Mossotti relation between the static polarizability and the static electric susceptibility remains valid in the case of negative parameters but is truncated at the lower bound; the value of the bound depends on the crystal structure and is always unrelated to the asymptote of the Clausius-Mossotti curve. The lower bounds of the static electric susceptibility are found to be $-0.906$ for sc and $-1.00$ for bcc and fcc. These results confirm that, although the magnitude of the static electric susceptibility does not diverge in the negative case (as it can in the positive case), the magnitudes attainable in the negative case for condensed media may, nevertheless, be many orders of magnitude greater than those predicted previously for inverted vapors and gases. This is a promising result in relation to the development of potential new technologies that exploit the phenomenon.

In this paper, an ultrathin, compact, hepta-band metamaterial absorber (MMA) is proposed for the first time. The MMA absorber is realized integrating two multiband MMA structures nested one inside the other. The novelty of the proposed structure lies in its four-fold symmetric nature which allows it to be polarization-insensitive absorber. The absorption mechanism at the seven resonating peaks has been explained with the help of simulated surface current distribution plots. The proposed work is expected to find its applications in various domains such as radar absorbing material (RAM), remote sensing, electromagnetic interference (EMI)/electromagnetic compatibility (EMC), and thermal imaging.