Linyan Guo

Broadband metamaterial absorber based on a multi-layer structure

In this paper, a broadband metamaterial absorber (MA) based on a multi-layer structure is presented. The advantages of this MA are the small periodic unit size, they are thin, have excellent polarization characteristics and are adaptive for wide angles of oblique incident electromagnetic waves. The unit cell of the broadband MA is composed of three dual-band sub-cells; each presents two resonant frequencies so as to form a wide absorptive spectrum when stacked. The sandwiched dual-band sub-cell is composed of one metallic annular patch and one metallic circular patch each etched on a lossy substrate. The radii of the metallic patches forming each sub-cell are different so as to appear to have different resonant frequencies. In the design of the unit cell there are metallic circular patches and an air layer at the bottom of each sub-cell to form magnetic coupling and avoid coupling between sub-cells. The broadband MA presents good absorptivity above 80% between 8.8 and 10.8 GHz, with a full width at half maximum (FWHM) absorption bandwidth of 2.3 GHz and a relative FWHM absorption bandwidth of 23%.

Electric toroidal metamaterial for resonant transparency and circular cross-polarization conversion

Electric toroidal dipolar response has been achieved by metamaterial based on sun-like aperture element at microwave frequency. It is confirmed numerically by scattered powers that the electric toroidal dipolar moment dominates over other moments at the corresponding resonance. This proposed metamaterial exhibits resonant transparency under linearly polarized incidence caused by destructive interference between magnetic dipole and electric toroidal dipole. Notably, it also provides circular cross-polarization conversions between left-handed circularly polarized wave and right-handed circularly polarized wave at the same frequency. These properties associated with elusive electric toroidal dipolar moment offer an avenue for various potential applications in microwave devices.

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.

Ultra-broadband electromagnetically induced transparency using tunable self-asymmetric planar metamaterials

We numerically and experimentally demonstrate a tunable electromagnetically induced transparency (EIT)-like spectral response in a self-asymmetric planar metamaterial in microwave region. This EIT-like physical mechanism is characterized by magnetic dipole coupling induced transparency, which is different from classical properties of EIT-like phenomenon. Our proposed system can be better explained by making an analogy to three-level Λ-type system. Further study also revealed that an ultra-broadband transparency window with the maximum bandwidth up to 7.8 GHz, extending from 6.1 GHz to 13.9 GHz, could be realized by simply adjusting the depth of the structure.

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.

Toroidal dipolar responses in a planar metamaterial

Both the magnetic toroidal dipolar (MTD) response and electric toroidal dipolar (ETD) response have been achieved and studied in the microwave region by designing a feasible planar metamaterial. By changing the polarized direction of a normally incident wave, two different coupling modes are observed, and therefore MTD and ETD responses can be achieved accordingly. It is also confirmed by scattered powers for various multipole moments and field distributions that they dominate over other traditional multipole responses at 5.69 GHz and 11.69 GHz, respectively. In view of the design feasibility of planar metamaterial, these resonance-enhanced MTD and ETD responses could provide an avenue for various interesting phenomena associated with the elusive toroidal moments.

Resonant transparency in planar metamaterial with toroidal moment

A magnetic toroidal dipole is constructed using a kind of planar metamaterial, on the basis of four asymmetry split ring resonators. Traditional electric and magnetic multipoles have been suppressed, and therefore, the toroidal moment can be enhanced by the resonant plasmonic response with rational arrangements of meta-atoms. In particular, the magnetic toroidal dipole is weakly coupled to external excitation, and unit transmittance has been achieved as a result of the enhanced toroidal response. This superior performance, with little effect of the dielectric loss, offers a new mechanism in the design of low-loss or electromagnetically induced transparent materials.

An X-band parabolic antenna based on gradient metasurface

We present a novel parabolic antenna by employing reflection gradient metasurface which is composed of a series of circle patches on a grounded dielectric substrate. Similar to the traditional parabolic antenna, the proposed antenna take the metasurface as a “parabolic reflector” and a patch antenna was placed at the focal point of the metasurface as a feed source, then the quasi-spherical wave emitted by the source is reflected and transformed to plane wave with high efficiency. Due to the focus effect of reflection, the beam width of the antenna has been decreased from 85.9° to 13° and the gain has been increased from 6.5 dB to 20.8 dB. Simulation and measurement results of both near and far-field plots demonstrate good focusing properties of the proposed parabolic antenna.

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.