Boxun Xiao

Tailoring Dual-band electromagnetically induced transparency in planar metamaterials

The transmission characteristics of a planar metamaterial, composed of two finite metal strips (with different length) and one double split-ring resonator, have been numerically and experimentally investigated in this paper. By varying the length of the two strips slightly, this structure can exhibit single-band and dual-band electromagnetically induced transparency (EIT)-like spectral response in microwave region. The dark mode can be excited because of the length difference of the two metal strips, which can lead to a very asymmetric Fano-like resonance or gradually EIT-like profile in transmission. So the dual-band EIT-like physical mechanism is characterized by two bright-dark coupling modes. Our work provides a way to obtain multiple EIT-like effect, and it may achieve potential applications in a variety of fields including filters, sensing, and some other microwave devices.

Triple-band linear and circular reflective polarizer based on E-shaped metamaterial

We present the design, analysis, and measurement of a triple-band linear and circular reflective polarizer based on an E-shaped metamaterial. Measured results show that the proposed reflective polarizer can convert a linearly polarized wave to its cross-polarized wave at the three resonant frequencies, which can also convert the linearly polarized wave to a circularly polarized wave at three other resonant frequencies. Furthermore, the reflective wave can maintain the same rational direction at the three resonant frequencies when the incident is a circularly polarized wave. The simulated and measured results are in agreement in the entire frequency range, and the polarization conversion ratio (PCR) is over 90% for both linear and circular polarizations. The mechanism of polarization conversion is interpreted by using surface current distributions.

Tunable electromagnetically induced transparency in coupled three-dimensional split-ring-resonator metamaterials

Metamaterials have recently enabled coupling induced transparency due to interference effects in coupled subwavelength resonators. In this work, we present a three dimensional (3-D) metamaterial design with six-fold rotational symmetry that shows electromagnetically induced transparency with a strong polarization dependence to the incident electromagnetic wave due to the ultra-sharp resonance line width as a result of interaction between the constituent meta-atoms. However, when the six-fold rotationally symmetric unit cell design was re-arranged into a fourfold rotational symmetry, we observed the excitation of a polarization insensitive dual-band transparency. Thus, the 3-D split-ring resonators allow new schemes to observe single and multi-band classical analogues of electromagnetically induced transparencies that has huge potential applications in slowing down light, sensing modalities, and filtering functionalities either in the passive mode or the active mode where such effects could be tuned by integrating materials with dynamic properties.

Analysis of ultra-broadband metamaterial absorber based on simplified multi-reflection interference theory

The simplified multireflection interference theory is proposed to analyze the physical insight quantitatively of the ultra-broadband metamaterial absorber (MMA) loading lumped resisters in which the resonant layer, including lumped resisters and the substrate, are equivalent to a homogeneous and isotropic effective medium. The simulated full width at half maximum (FWHM) absorption bandwidths is approximately 11.2 GHz with relative FWHM absorption bandwidths of 116.7% for a normal incidence electromagnetic wave. Microwave experiments are performed and measured results are in good agreement with the numerical results. The absorbance of the proposed MMA calculated by the simplified multi-reflection interference theory coincides well with simulated and measured results.

Multiple-band reflective polarization converter based on deformed F-shaped metamaterial

A three-layered deformed F-shaped metamaterial reflective polarization converter (RPC) is proposed to realize linear and circular polarization conversions. The proposed F-shaped RPC can convert a linearly polarized wave to its cross-polarized wave at the four resonant frequencies. It also can convert the linearly polarized wave to a circularly polarized wave at the other four resonant frequencies. In addition, the proposed F-shaped RPC can maintain the same rational direction at the five resonant frequencies when the incident is a circularly polarized wave and higher reflective coefficients can be obtained with the increase of the thickness of the dielectric layer. The simulated and measured results are in agreement in the entire frequency range, and the polarization conversion ratio is more than 85% for both linear and circular polarizations. Further simulations reveal that the polarization in the terahertz range can also be obtained by changing the thickness of the dielectric layer and the unit of the reflective polarization converter.

Manipulating linearly polarized electromagnetic waves using the asymmetric transmission effect of planar chiral metamaterials

In this work, a kind of bilayered chiral metamaterial with double-T-shape combined structure is proposed to exhibit dual-band asymmetric transmission (AT) of linear polarization when the electromagnetic waves propagate forward and backward. Simulated and measured results demonstrate that the proposed metamaterial can rigorously satisfy the AT theorem. The cross-polarized conversion for the measurement reaches a maximum of 95%. In addition, a conspicuous broadband AT effect with the bandwidth of 2.32 GHz can be obtained by simply adjusting the thickness of the dielectric layer. Such a bilayered approach and adjustable property can be generalized to a wide variety of meta-dielectric metamaterial geometries, and the proposed metamaterial can effectually manipulate the linearly polarized electromagnetic waves.

A Dual-Band Low-Profile Metasurface-Enabled Wearable Antenna for WLAN Devices

This paper presents a compact, low-profile, wearable dual-band antenna operating in the Wireless WLAN band of 5.15 ∼ 5.25 GHz and 5.72 ∼ 5.83 GHz. The proposed antenna is composed of a planar monopole and underneath three by three array arrangement of Jerusalem Cross (JC) structure metasurface. The simulated results show that the integrated antenna express 4.09% and 4.14% impendence bandwidths, increased gain up to 7.9 dB and 8.2 dB, front to back (FB) ratio achieved to 20 dB and 18 dB at the two frequencies, respectively. The measured results agree well with simulations. In addition, the metasurface not only is equivalent to a ground plane for isolation, but also acts as the main radiator, which enables a great reduction in the specific absorption rate (SAR). Furthermore, because of a compact solution, the proposed integrated antenna can be a promising device for various wearable systems.

A high-gain and frequency-tunable bow tie antenna with epsilon-negative metasurface

Various wireless communication systems require simple and high-gain radiating element operating in different working frequency bands. In this paper, an epsilon-negative metasurface antenna (ENG-MS antenna) with high-gain and frequency-tunable properties is proposed, fabricated and studied. This antenna is composed of an original double-sided printed bow tie antenna (source antenna) and an ENG-MS frequency selecting reflection layer. The strong electric interaction between ENG-MS (allowing evanescent wave only) and source antenna exhibits a significant effect on antenna’s radiation pattern and gain. Antenna’s gain can be selectively enhanced over the source antenna’s working frequency band. It is demonstrated that the resonant frequencies of this ENG-MS antenna can be continuously tuned by changing the distance between source antenna and ENG-MS. The proposed ENG-MS antenna in this paper shows a promising result to introduce metamaterials/metasurfaces in microwave device to realize high-gain and frequency-tunable functionality.

A broadband bow-tie antenna used in UHF with metal reflection plane

There are many kinds of antennas used in UWB system. Double-side printed bow-tie antenna is one of them which has the advantages of light weight, planar structure, low cost and broad bandwidth. In this paper, a double-side printed bow-tie antenna used in UHF band is proposed first. Then a metal reflection plane is added on the back of this antenna to increase its gain and inhibit backward radiation. Return loss of -10dB or better is located in the band of 0.95-2.7 GHz and the relative bandwidth is 95.9%. They have the similar VSWR quality. Besides, the reflection plane has a strong influence on radiation pattern and antenna gain. Gain in dB of former antenna has been raised from around 2.5dB to 7.5dB due to the metal reflection plane. Hence, it has a great prospect in the application of double-side printed bow-tie antenna with metal reflection plane.

EM scattering by conductor plate coated with multilayered medium having metamaterials

The electromagnetic scattering of conductor plate coated with multilayer medium is investigated based on the physical optics (PO) theory and the principle of equivalent impedance boundary condition (IBC). Compared with the multilayered plate coated with right-handed medium, the radar cross section (RCS) of plate composed of metamaterial and right-handed medium has a reduction of 5.76dBsm in the mirror direction. It shows that metamaterials can become a candidate of the radar absorbing material (RAM), which offers a new idea for the development of stealth technology.