Jieqiu Zhang

Mechanically tunable metamaterials for larger incident absorption

We demonstrated that the three-dimensional metamaterial absorbers, consisting of the resistive patches and metallic backboard, can exhibit ultra-broadband and highly efficient absorption for a certain larger incidence of the transverse magnetic wave. The three-dimensional unit cell is constructed by bending the resistive patches, which is arranged at a certain period on the metal plate. Comparing with the conventional metamaterial absorbers based on the resistive frequency selective surface, our designs have the mechanical tunability which can adjust the folded angle of the resistive patches to get near-unit and ultra-broadband absorption for the larger-incident transverse magnetic wave. By studying the power loss density distributions and the electric field response excited in the proposed structure, it is revealed that there exits electric response of two direction on the resistive patches contributed the desired larger incident absorption. As a proof, we realize the idea experimentally. It is expected that the angular selectivity and ultra-broadband absorption would have various application in the field of electromagnetic emitters and detectors.

All-dielectric metamaterial band stop frequency selective surface via high-permittivity ceramics

In this paper, a band stop all-dielectric metamaterial frequency selective surface (FSS) is designed based on effective medium theory and dielectric resonator theory. The FSS is made of high-permittivity ceramics without using any metallic parts. The stop band FSS is composed of 2D arrays of Jerusalem cross-shaped ceramic resonators. Solid-state sintering method is adopted to prepare the high-permittivity ceramics, which is made of 0.7Ba0.6Sr0.4TiO3-0.3La(Mg0.5Ti0.5)O3. The permittivity of this ceramics is about 110. The simulation results show that the FSS can achieve a stop band at 6.91-9.25 GHz. The relative effective permittivity, permeability and the normalized impedance of the structure are retrieved, showing that the first resonant is a magnetic resonant and the second resonant is an electric resonant. Due to the magnetic and electric resonant, the impedance matching becomes worse, so the normalized impedance is close to 0 and the stop band forms. The electric fields and magnetic fields of the resonant points are observed to further analysis the FSS. At the first resonant point, the electric field loop is formed, equivalent to a magnetic dipole. At the second resonant point, the magnetic field loop is formed, equivalent to an electric dipole. The magnetic and electric fields are accordance with the retrieved parameters. Since such FSSs are made of high-permittivity ceramics, they have potential engineering application in high-power or high-temperature.

WLAN band-notched planar UWB antenna loaded by CSRR

With the rapid development of communication capacity, the demand for ultra-wideband (UWB, 3.1-10.6 GHz, allocated by the Federal Communications Commission of the United States, FCC) antenna has been increasing in wireless communication system. However, some other narrow band such as WLAN band (5.15-5.825 GHz), WiMAX band (3.4-3.6 GHz) and C-band satellite communication system (3.7-4.2 GHz) will inevitably disturb the operation signal. Consequently, band-notched antennas have attracted more and more attentions. In this paper, we present a 5.5 GHz band-notched ultra-wideband planar antenna loaded by complementary split ring resonator (CSRR) to reject unwanted WLAN band. The CSRR etched on the radiation patch is used to achieve band-notched performance. The VSWR, band-notch behavior and radiation pattern are analyzed by full wave simulation software High Frequency Structure Simulator (HFSS) version 12.0. This proposed UWB antenna works from 3.301 GHz to 10.695 GHz, with a band-notch from 5.064 GHz to 5.706 GHz band.

Antenna beam steering using phase gradient metasurface radome

Summary form only given. Phase gradient metasurfaces (PGMs) are the two-dimensional metamaterial. It can manipulate the propagation direction, wave front and polarization of the reflected/transmitted waves with more freedom. In this paper, the phase gradient metasurfaces are used as the radomes to manipulate the direction of the main lobe or to improve the directivity of the patch antenna. Based on the transmissive polarization conversion metasurface (PCM), two PGM radomes are achieved. One can alter the main lobe direction of the patch antenna, and the other one can highly improve the directivity and gain of the patch antenna. The simulated directional diagrams and gain of the patch antennas with and without the PGM radomes indicate that the covered PGM radomes have good performance on antenna main lobe direction manipulation and antenna directivity and gain improvement.

Design of the infrared selective thermal radiation based on metamaterials

In this paper, we propose a polarization-independent and broadband perfect metamaterial absorber operating in mid-infrared region. The proposed absorber is a periodic meta-atom array consisting of metal-dielectric-multilayer truncated cones, which can control gray- or black-body thermal signatures. The simulation is implemented using CST Microwave Studio. The simulated results show that the proposed absorber has high reflectivity in two atmospheric windows denoted as 3.0 ~ 5.0 μm and 8.0 ~ 14.0 μm for normal incidence wave, and the reflectivity completely exceeds 0.9. In the non-atmospheric window of 5.0 ~ 8.0 μm, there is a broad absorption band which leads to a high efficiency of heat radiation and good stealth for objects.

Design and study miniaturized-element wideband frequency selective surface

In this letter, we propose a miniaturized-element frequency selective surface (MEFSS) by using the LC coupling mechanisms between three metal arrays cascade by two layers substrates, so this unit cell size will not be restricted by wavelength. In order to improve resonance stability performance with respect to different polarizations and incidence angles, according to the traditional FSS hexagonal element, we create periodic elements of capacitive surface and inductive surface with hexagonal shape and hexagonal element array is in the form of equilateral triangle. An equivalent circuit model for the operating principle of MEFSS was proposed. On the basis of the transmission lines theory, the approximation formulas of the inductance and capacitance were provided. In order to the optimal parameters of wideband performance, the grid array and the effects of the parameteristice of hexagonal element on the frequency response characteristics of MEFSS are simulated using the full-wave analysis software. With PCB technology, the hexagonal metal arrays between F4B-2 are produced and a prototype MEFSS using freedom space method is examined. Both simulated and measured results obtained show that the MEFSS constructed by using hexagonal element array has much better frequency resonance stability performance with respect to different polarizations and 60° incidence angles, and the -0.5 dB bandwidth reaches up to 5 GHz. We present a theoretical and experimental reference of MEFSS for the applications in large-angle incidence curved streamlined radome.

Frequency modulation and magnetic resonance in electric resonators

Most reported negative index of materials (NIMs) have combined conducting split ring resonators (SRRs) to realize the magnetic response and nonresonant wires to realize the electric response. But wire media has some disadvantages in common practice. Therefore, electric resonators were introduced by researchers to replace the wire media recently. Electric resonators are convenient to control and can be made relatively insensitive to the cell-to-cell coupling. The electric resonance frequency of the resonators is related to the lattice constant of the structure. Then, using finite element simulation and making magnetic field is perpendicular to the plane of metamaterial, the results can be obtained for varying lattice constant. In each case, the permittivity is retrieved from the simulated S parameters. The electric-resonance frequency increases and the frequency range of negative permittivity cut short when the lattice constant decrease. In addition, there is magnetic resonance in some electric resonators, which can be used to realize the negative permeability.