Broadband and low‐loss composite right/left‐handed transmission line based on broadside‐coupled lines

A novel composite right/left‐handed (CRLH) transmission line (TL) structure is proposed and investigated. This structure consists of a pair of broadside‐coupled lines and a shorted stub. First, its fundamental characteristics and the relation between its electrical parameters and bandwidth are studied utilizing the TL theory. Then, closed‐form design equations with flexible parameter selection are given. Finally, several microstrip implementations of the proposed structure are developed to verify our theoretical results. It is shown that the proposed structure can achieve a very wide left‐handed (LH) and right‐handed (RH) bandwidth with low insertion loss and low return loss.     

Ultrathin dual‐layer triple‐band flexible microwave metamaterial absorber for energy harvesting applications

An ultrathin dual‐layer flexible metamaterial absorber with triple‐band for RF energy harvesting applications has been reported in this article. The sub‐wavelength unit cell of the proposed absorber is composed of six distinct concentric annular having outer circumference of ring and octagonal inner circumference. The metallic resonators are constructed from copper foil self‐adhesive tape which are affixed on flexible neoprene rubber sheet terminated by metal ground plate. The proposed absorber prototype is ultrathin and compact with the thickness less than 0.037λ₀ and cell size less than 0.2λ₀ at the lower absorption frequency of 1.75 GHz. Flexible dual‐layer absorber exhibits triple absorption peaks of 96.91%, 96.41% and 90.12% at 1.75 GHz, 2.17 GHz and 2.6 GHz with full width at half maximum (FWHM) bandwidth of about ~6.5%. The RF performance of proposed absorber is numerically computed for different polarization and incidence angle variations. The absorption value is above 76% for the oblique incidence angle up to 45° in TE mode operation, whereas the absorption value is 94% for oblique incidence angle up to 60° in TM mode operation. The measured outcomes are in agreement with the numerically calculated results. The energy harvesting potential of the proposed absorber structure is numerically confirmed by the resulting improved RF absorption value in dependence to different resistive loading of the polarization insensitive unit cells.     

Wide band fractal‐based perfect energy absorber and power harvester

In this article, a novel wide band polarization and incident angle independent metamaterial absorber (MA) and energy harvesting applications which operates at C (4GHz‐8 GHz) and X (8GHz‐12 GHz) is proposed. The unit‐cell of the proposed structure based on fractal circle loop. Four lumped resistors are mounted the structure to obtain a broad band absorption characteristics. Resistors increase the absorption characteristic of proposed MA significantly at mentioned frequency ranges. In addition, under favor of the resistors proposed MA can convert absorbed energy from incident wave to appearing power.     

Broadband transparent metamaterial absorber in wireless communication band based on indium tin oxide film

In this article, a broadband optically transparent metamaterial absorber in wireless communication band is proposed. Indium tin oxide (ITO) film, a kind of resistive transparent thin film, is utilized to construct the absorber unit to realize optical transparency, and increase ohmic loss to broaden the absorption bandwidth. The proposed absorber is fabricated and measured. The measurement results are in good agreement with the simulations. It is demonstrated that the absorption rate of the proposed absorber is higher than 90% from 1.67 to 3.8 GHz. The full width at half maximum bandwidth is 5.11 GHz from 0.89 to 6 GHz. In addition, the absorption response of the absorber remains stable regardless of polarization and incidence angle of the electromagnetic waves.     

Compact ultrathin conformal metamaterial dual‐band absorber for curved surfaces

A compact, ultrathin conformal metamaterial dual‐band absorber for curved surfaces has been presented in this article. The absorber unit cell composed of circular and split ring resonators which are connected with plus‐shaped structure. The proposed absorber unit cell is compact in size (0.22λ_o × 0.22λ_o) and as well as ultrathin thickness (0.006λ_o), where λ_o is the wavelength at 5.8 GHz. The designed absorber gives two absorption tips at 5.8 and 7.7 GHz with more than 90% absorptivity. The full width at half maximum bandwidths are 220 MHz (5.67‐5.89 GHz) and 250 MHz (7.58‐7.83 GHz). The proposed conformal absorber is sensitive to the polarization angle and has a stable absorptivity over a wide range of incident electromagnetic wave. The parametric analysis and equivalent transmission line model have been investigated. The surface current and electric field distribution also discussed for understanding the absorption mechanism. To analyze the performance of proposed absorber on the curved surfaces, it is wrapped on the different radius of cylindrical surface and measured the absorptivity. Simulated and measured results have good agreement between them.     

Both transversal negative permeability and backward‐wave propagation in X‐Band waveguide with double‐side SRR metamaterials

In this article X‐band rectangular waveguides partially filled with the double‐side single ring resonator (DSRR) array are investigated for miniaturization, stop‐band, and multi‐band filters applications. Several rectangular waveguides loaded with the DSRR array in 2–10 GHz frequency band have been studied and optimized. We observe both the transversal negative permeability presented above the cutoff frequency and the backward‐wave located below the cutoff frequency with the DSRR array in X‐band waveguide. Both simulation and measurement results of DSRR array are with good agreement. The DSRR array provides better performance of the transversal negative permeability and the backward‐wave than the split‐ring resonator array. The physical explanation of backward‐wave is presented. The power loss distributions are clearly presented for the negative permeability attenuation and the backward‐wave propagation. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:240–246, 2016.     

High performance resonant cavity antenna with non‐uniform metamaterial inspired superstrate

The resonant cavity antenna (RCA) is a class of widely used high gain antennas, but usually suffers from narrow impedance bandwidth owing to its strong resonant property, as well as relatively low aperture efficiency because of its non‐uniform electromagnetic (EM) field distribution on the aperture. This article explores enhancing the RCA's impedance bandwidth and aperture efficiency by designing a non‐uniform metamaterial inspired superstrate, on which the metal patches vary their sizes with respect to their distances to the superstrate's center. After optimized by the Genetic Algorithm, the proposed RCA is designed, fabricated and tested. Measured results agree well with simulated ones and show that in comparison with a RCA with a uniform metamaterial inspired superstrate, this work significantly improves the |S ₁₁| < ?10 dB impedance bandwidth from 2.1% to 6.1%, the gain at the working frequency 10 GHz from 19.07 dBi to 20.55 dBi, and correspondingly the aperture efficiency from 50.5% to 71%. A further analysis estimates that due to the non‐uniform metamaterial inspired superstrate, a more homogeneous distribution for both the amplitude and phase of the EM field is observed on the superstrate's aperture.     

Gain enhancement of slot antenna using zero‐index metamaterial superstrate

This article presents a technique to enhance the broadside gain of a CPW fed slot antenna using a single layer metamaterial (MTM) superstrate. A finite array of 3 3 ring unit cell has been designed on both sides of a dielectric substrate to form the MTM superstrate. The gain enhancement is obtained using the zero‐index property of the metamaterial. The broadside gain enhancement for the proposed antenna is 7.4 dB more in comparison to that of the reference slot antenna. The proposed MTM superstrate loaded antenna provides a minimum overall thickness in the context of using ZIM superstrate for gain enhancement of antennas reported in earlier literatures. The overall thickness of the MTM loaded antenna is 0.13λ₀, where λ₀ is the free‐space wavelength at the resonance frequency of the antenna. Also, a high efficiency of about 93.2% is obtained in this case. The loading of the MTM superstrate produces a minimal effect on the cross polarization performance of the proposed slot antenna.     

基于SRR的超材料太赫兹调制器结构设计与调制深度仿真

电磁超材料可用于构建具有控制太赫兹辐射通断功能的太赫兹强度调制器.利用COMSOL仿真软件,通过模拟仿真,研究了基于开口谐振环(SRR)“工字型”超材料太赫兹调制器关键功能结构对器件透射光谱的影响规律,并以此完成了高调制深度器件的结构优化设计.仿真结果表明:优化后器件调制深度达到了74％.     

Plasmon-induced transparency in terahertz metamaterials

The quantum phenomena of electromagneticalty induced transparency （EIT） or plasmonic ana- logue of electromagnetically induced transparency （PIT） can be mimicked in the classical resonators, leading to a unique way to explore the coherent coupling mechanism in metamaterial systems. Various metamaterial structures have been proposed to excite and manipulate the PIT effect with flexibility and performance with geometry-controllable, polarizatiomindependent, broadband-transparency and active-modulated characteristics. These in turn promise the fascinating functionalities and applications of the PIT effects, such as slow-light com- ponents, nonlinear devices and high-sensitivity sensors. Here, we present a review on the progress in developing the PIT effect in terahertz metamaterials over the past few years.