Electromagnetic Metamaterials: Transmission Line Theory and Microwave Applications. By Christophe Caloz and Tatsuo Itoh.

In this paper, we present the design of cylindrical and spherical electromagnetic cloaks working at visible frequencies. The cloak design is based on the employment of layered structures consisting of alternating plasmonic and non-plasmonic materials and exhibiting the collective behavior of an effective epsilon-near-zero material at optical frequencies. The design of a cylindrical cloak to hide cylindrical objects is firstly presented. Two alternative layouts are proposed and both magnetic and non-magnetic objects are considered. Then, the design of spherical cloaks is also presented. The full-wave simulations presented throughout the paper confirm the validity of the proposed setup, and show how this technique can be used to reduce the observability of cylindrical and spherical objects. The effect of the losses is also considered.

Plasmonic metamaterial cloaking at optical frequencies

This paper presents a multi-band terahertz superabsorber with a surface structure that consists of a square metallic patch with a very small rectangular hole whose area is only 3.94% of the square patch. The introduction of a rectangular hole in the square patch plays an important role in achieving multi-band absorption. Three resonant bands with very high absorption (>95%) were observed in the terahertz range. Different from the near-field distributions of the traditional square patch with no modification, the introduction of a rectangular hole in the square patch can break the near-field distributions of the traditional square patch with no modification or can rearrange them to form some new or extra resonance modes, thereby generating multi-band absorption. Considering the fact that the introduced rectangular hole plays the key role in the rearrangement of the near-field and the introduction of some new resonance modes, the parameter changes of the rectangular hole introduced in the square patch provide considerable freedom in controlling the number of absorption peaks, and the resonant bands can be tuned to quad- or dual-band absorption. The multi-band superabsorbers given here should have potential applications in numerous areas.

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Multi-band terahertz superabsorbers based on perforated square-patch metamaterials

This paper describes a dual-band electromagnetic (EM) absorber for Cand X-band applications. The proposed structure consists of two circular ring resonators that are modified to make the absorber compact. The proposed absorber is demonstrated to be conformal, insensitive to polarization and angle of oblique incidence of incoming EM wave. To the authors' knowledge, it is the thinnest absorber reported with a thickness of λ0 /142.65 at lowest frequency of absorption. The absorption bands with absorption peaks of about 97% and 99% are observed at center frequencies of 4.19 and 9.75 GHz, respectively. The absorption frequency bandwidth (more than 90% of peak absorption) at these frequencies is 665 and 860 MHz, respectively. The double-band absorber can be extended to work at three frequencies by simply adding another ring between the two modified circular rings of dual-band absorber. The modified structure has absorption bandwidth of 610, 670, and 570 MHz with absorption peaks of 97.50%, 96.50%, and 98.85% at resonant center frequencies 4.19, 6.64, and 9.95 GHz, respectively. The temperature profile of the proposed absorber is measured by using lock-in infrared thermography and a temperature increase of 1.5°C is observed at all the absorbing frequencies with transmitted RF power of 10 dBm. The experimental results agree well with the simulation results, and the proposed structure is insensitive for the transverse magnetic/transverse electric field polarization of incident waves and also the angle of incidence. It provides wide angular stability up to 45°. Along with a flat surface, the proposed absorbers are tested on a curved surface to exhibit its conformal nature.

Dual- and Triple-Band Polarization Insensitive Ultrathin Conformal Metamaterial Absorbers With Wide Angular Stability

This article claims, an investigation on compact ultrathin triple band polarization independent metamaterial absorber for microwave frequency applications. The proposed absorber unit cell consist of two resonators named as Structure-A and Structure-B. Both the resonators are printed on the upper surface of dual side copper coated FR-4 epoxy glass substrate of thickness 0.8 mm. The proposed absorber structure offers three distinct absorption peaks of 99.67%, 99.48%, and 99.42% with FWHM bandwidth of 170 MHz (4.11-4.28 GHz), 350 MHz (9.17–9.52 GHz), and 480 MHz (11.24–11.72 GHz) at 4.19 GHz, 9.34 GHz, and 11.48 GHz, respectively, under normal incidence. In addition to above, the four fold symmetry of proposed absorber structure make it polarization independent. Proposed absorber structure also offers more than 80% absorptivity at different angle of incidence (up to 60°) under transvers electric and transvers magnetic polarization states. The designed absorber unit cell has compactness of $0.11~\lambda _{0} \times 0.11~\lambda _{0}$ with ultra-thin thickness of $0.0111~\lambda _{0}$ , where $\lambda _{0}$ is the free space wavelength with respect to the lowest absorption peak of 4.19 GHz. Absorption mechanism of proposed unit cell has been discussed with the help of normalized input impedance, electric field distribution, and surface current density plots. In order to discuss the metamaterial property of proposed absorber unit cell dispersion diagram has been shown.

An Investigation on Compact Ultra-Thin Triple Band Polarization Independent Metamaterial Absorber for Microwave Frequency Applications

In this article, a compact zeroth-order resonance (ZOR) antenna with extended bandwidth is presented. The proposed antenna consists of a rectangular and semicircular patch separated by gap G which is liable for initiating ZOR mode. The semicircular patch and ground planes are connected by a thin stripline, hence, via less coplanar metamaterial structure. The proposed antenna offers measured fractional bandwidth of 23.64% at ZOR frequency (fZOR = 3.60 GHz) with an average peak gain of 2.26 dB with 95.89% radiation efficiency over entire working band. The proposed antenna shows the overall footprint area of 0.276 λ0 × 0.129 λ0, where λ0 is the free space wavelength centered at 3.60 GHz. It also offers dipole like pattern in xz-plane and omnidirectional pattern in yz-plane at ZOR frequency. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:71–75, 2016

A Miniaturized ZOR antenna with enhanced bandwidth for WiMAX applications

In this paper, an ultrathin triple-band polarization insensitive metamaterial (MTM) absorber has been presented for C-band applications. The proposed structure is explained as a combination of two absorbers, named as Absorber-I and Absorber-II. It exhibit 91%, 98.9% and 99.5% absorptivity at 4.2 GHz, 7 GHz and 7.4 GHz frequencies respectively. Absorber-I and Absorber-II are individually responsible for the origin of two separate frequency bands at 4.2 GHz and 7 GHz respectively. Further, mutual coupling between Absorber-I and Absorber-II is responsible to generate one more absorption band at the frequency of 7.4 GHz. The fourfold symmetric nature of the proposed unit cell provides polarization insensitivity phenomena. The absorbing mechanism of the designed absorber has been explained by two methods. One is by plotting input impedance of the absorber. Another one is by analyzing the EM wave propagation inside the structure. The proposed absorber has been fabricated and simulation results are experimentally verified.

Design and analysis of an ultrathin triple-band polarization independent metamaterial absorber

In this paper, a wideband circularly polarized cylindrical shaped dielectric resonator antenna (DRA) with simple microstrip feed network has been designed and investigated. The proposed design uses dual vertical microstrip lines arranged in a perpendicular fashion to excite fundamental orthogonal hybrid ${HE}_{11\delta }^{x}$ and ${HE}_{11\delta }^{y}$ modes in the cylindrical DR. The Phase quadrature relationships between orthogonal modes have been attained by varying corresponding microstrips heights. To ratify the simulation results, an antenna prototype is fabricated and measured. Measured input reflection coefficient and axial ratio bandwidth (at $\Phi =0^{\circ }$ , $\theta =0^{\circ }$ ) of 30.37% (2.82–3.83 GHz) and 24.6% (2.75–3.52 GHz) has been achieved, respectively. This antenna design achieves an average gain of 5.5 dBi and radiation efficiency of above 96% over operational frequency band. Justifiable agreement between simulated and fabricated antenna results are obtained.

Analysis of a Wideband Circularly Polarized Cylindrical Dielectric Resonator Antenna With Broadside Radiation Coupled With Simple Microstrip Feeding

This article investigates on the design and analysis of an ultrathin X-band metamaterial absorber in the microwave frequency regime. The proposed structure consist of four-fold symmetry, and it has been exhibiting 99.6% absorptivity at the frequency of 8.65 GHz with full width at half maximum (FWHM) bandwidth of 331.8 MHz (8.4777 GHz - 8.8095 GHz). The metamaterial characteristics of the proposed unit cell are verified with the help of dispersion plot. The working mechanism of the proposed absorber structure has been explained here by the E-field, H-field and the impedance plots. The absorptivity of the proposed structure have been investigated at different polarizations angles. In addition to above, MTM property is also shown by plotting permittivity and permeability plots. At the resonance frequency of 8.65 GHz, the input impedance of the designed absorber is 371.6 Ω, nearly equal to the free space impedance value. The designed absorber is of ultrathin thickness (λ0/40) with respect to center frequency fc = 8.65 GHz. The proposed structure has been fabricated and simulated results are experimentally verified for the fabricated proto-type. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2481–2485, 2016

Naveen Mishra

Papers

An Investigation on Compact Ultra-Thin Triple Band Polarization Independent Metamaterial Absorber for Microwave Frequency Applications

A Miniaturized ZOR antenna with enhanced bandwidth for WiMAX applications

Design and analysis of an ultrathin triple-band polarization independent metamaterial absorber

Analysis of a Wideband Circularly Polarized Cylindrical Dielectric Resonator Antenna With Broadside Radiation Coupled With Simple Microstrip Feeding

Design and analysis of an ultrathin X-band polarization-insensitive metamaterial absorber