Multi-reflection Interference Theory Research Articles

Ultra-wideband polarization- and angle-insensitive metamaterial absorber based on multilayer resistive ink

An ultra-wideband metamaterial absorber (MA) consisting of three layers of resistive ink separated by two layers of polymethacrylimide is proposed. The results of full-wave simulation show that the absorptivity is high up to 95% with a bandwidth ratio of 1:9.73 over the wide frequency range from 4.20 to 40.87 GHz, covering the whole C, X, Ku, K, and Ka bands. Moreover, the MA is insensitive to polarization and exhibits wide-angle stability, which is investigated by the full-wave simulation results as well as the analysis of multi-reflection interference theory. The fabricated prototype with a single unit cell of 0.081 g is tested using free-space measurement in an anechoic chamber, and the measured results are in good agreement with the simulation results, which prove the robustness of the design and indicates a practical application prospect of the proposed ultra-wideband MA with lightweight, simple, and compact structure.

Dual-band and polarization-independent metamaterial terahertz narrowband absorber.

A dual-band terahertz metamaterial narrowband absorber is investigated based on a single simple windmill-shaped structure. The proposed metamaterial absorber achieves near-perfect absorption at 0.371 THz and 0.464 THz. The full width at half-maximum is 0.76% and 0.31% relative to absorption frequency. The multireflection interference theory is used for analyzing the absorption mechanism at low absorption frequency. The theoretical predictions of the decoupled model have excellent agreement with simulation results. By investigating the absorber's distribution of electric field and surface current density at high absorption frequency, the absorber's near-perfect absorption at the high absorption frequency originating from the magnetic resonance formed between the top metal structure and the bottom metal plane is explained. Besides, the absorber proposed is independent of the polarization angle. It is significant to various applications such as narrowband thermal radiation, photoelectric detection, biological sensing, and other fields.

Switchable broadband metamaterial absorber/reflector based on vanadium dioxide rings.

A new broadband tunable metamaterial absorber based on different radii of vanadium dioxide (VO2) rings loaded on the dielectric layer is designed. According to the insulator-to-metal phase transition characteristics of VO2 under thermal excitation, the dynamic adjustment of the absorption by the external temperature is achieved. The simulation results demonstrate that when VO2 is in its metal phase at high temperature, an absorption greater than 90% in the bandwidth range of 2.64-7 THz can be obtained and its relative bandwidth is reached to 90.5%. However, the absorption rate in the same frequency range is always lower than 2.3% when VO2 is in the insulator phase at low temperature, which means that the absorber can be used as a perfect reflector. The maximum tunable range of the proposed absorber can be realized from below 2.3% to nearly 100%. We further analyze and discuss the equivalent impedance and electric field distribution of the absorber and clarify the adjustment mechanism of the absorption performance of the VO2 ring. In addition, a multireflection interference theory is also investigated to quantitatively explain the physical absorption mechanism. Such a tunable broadband absorber based on temperature control has great potential to be applied to sensors, thermophotovoltaics, and wireless communication.

Graphene-based single-layer elliptical pattern metamaterial absorber for adjustable broadband absorption in terahertz range

Graphene can be utilized in designing adjustable terahertz (THz) devices due to its variability of sheet conductivity. In this paper, a broadband adjustable graphene absorber operating at THz frequencies is proposed. By changing the Fermi level of the graphene from 0 eV–1 eV, the absorption relative bandwidth and absorption rate can be adjusted from 20%–90.32% and from 0–100%, respectively. The Fermi level of the graphene can be adjusted actively by adjusting the bias voltage on the graphene layer or by chemical doping, which enables us to electrically or chemically control the absorption performance flexibly. We use the multi-reflection interference theory to investigate the physical insight of the proposed absorber under normal incidence and oblique incidence. This paper is the first to interpret oblique incidence using the multi-reflection interference theory. From this, we can infer the value of effective permittivity of the absorber under oblique incidence, which provides great help for the design of an absorber. The calculated and simulated results are in excellent agreement.

Dual-Band Perfect Metamaterial Absorber Based on an Asymmetric H-Shaped Structure for Terahertz Waves.

We designed an ultra-thin dual-band metamaterial absorber by adjusting the side strips’ length of an H-shaped unit cell in the opposite direction to break the structural symmetry. The dual absorption peaks approximately 99.95% and 99.91% near the central resonance frequency of 4.72 THz and 5.0 THz were obtained, respectively. Meanwhile, a plasmon-induced transmission (PIT) like reflection window appears between the two absorption frequencies. In addition to theoretical explanations qualitatively, a multi-reflection interference theory is also investigated to prove the simulation results quantitatively. This work provides a way to obtain perfect dual-band absorption through an asymmetric metamaterial structure, and it may achieve potential applications in a variety of fields including filters, sensors, and some other functional metamaterial devices.

Microwave Metamaterial Absorber for Non-Destructive Sensing Applications of Grain.

In this work, we propose a metamaterial absorber at microwave frequencies with significant sensitivity and non-destructive sensing capability for grain samples. This absorber is composed of cross-resonators periodically arranged on an ultrathin substrate, a sensing layer filled with grain samples, and a metal ground. The cross-resonator array is fabricated using the printed circuit board process on an FR-4 board. The performance of the proposed metamaterial is demonstrated with both full-wave simulation and measurement results, and the working mechanism is revealed through multi-reflection interference theory. It can serve as a non-contact sensor for food quality control such as adulteration, variety, etc. by detecting shifts in the resonant frequencies. As a direct application, it is shown that the resonant frequency displays a significant blue shift from 7.11 GHz to 7.52 GHz when the mass fraction of stale rice in the mixture of fresh and stale rice is changed from 0% to 100%. In addition, the absorber shows a distinct difference in the resonant absorption frequency for different varieties of grain, which also makes it a candidate for a grain classification sensor. The presented scheme could open up opportunities for microwave metamaterial absorbers to be applied as efficient sensors in the non-destructive evaluation of agricultural and food product quality.

Design and theoretical study of a polarization-insensitive multiband terahertz metamaterial bandpass filter**Project supported by the National Natural Science Foundation of China (Grant Nos. 11504418, 11447033, and 61372048) and the Fundamental Research Funds for the Central Universities, China (Grant No. 2015XKMS075).

We report the design of a novel multiband metamaterial bandpass filter (BPF) in the terahertz (THz)-wave region. The designed BPF is composed of a metal–dielectric–metal sandwiched structure with three nested rings on the top surface and a cross structure on the bottom surface. Full-wave simulation results show that the designed BPF has three transmission peaks at frequencies of 0.42, 1.27, and 1.86 THz with transmission rates of −0.87, −1.85, and −1.83 dB, respectively. Multi-reflection interference theory is introduced to explain the transmission mechanism of the designed triple-band BPF. The theoretical transmission spectrum is in good agreement with the full-wave simulated results. The designed BPF can maintain a stable performance as the incident angle varies from 0° to 30° for both transverse electric and transverse magnetic polarizations of the incident wave. The designed BPF can be potentially used in THz devices due to its multiband transmissions, polarization insensitivity, and stable wide-angle response in the THz region.

Broadband, polarization-insensitive, and wide-angle microwave absorber based on resistive film

A simple design of broadband metamaterial absorber (MA) based on resistive film is numerically presented in this paper. The unit cell of this absorber is composed of crossed rectangular rings-shaped resistive film, dielectric substrate, and continuous metal film. The simulated results indicate that the absorber obtains a 12.82-GHz-wide absorption from about 4.75 GHz to 17.57 GHz with absorptivity over 90% at normal incidence. Distribution of surface power loss density is illustrated to understand the intrinsic absorption mechanism of the structure. The proposed structure can work at wide polarization angles and wide angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves. Finally, the multi-reflection interference theory is involved to analyze and explain the broadband absorption mechanism at both normal and oblique incidence. Moreover, the polarization-insensitive feature is also investigated by using the interference model. It is seen that the simulated and calculated absorption rates agree fairly well with each other for the absorber.

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.

Theoretical and Experimental Demonstrations of a Dual-Band Metamaterial Absorber at Mid-Infrared

We present the design, fabrication, and physical interpretation of an infrared dual-band metamaterial absorber. The unit cell of the metamaterial absorber consists of a cross resonator ringed by four split-ring resonators spaced a distance above a gold ground plane with a dielectric layer of SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The absorber shows two absorption peaks of 90.3% and 88.4% at 4.17 μm and 4.86 μm, respectively. The multireflection interference theory is applied to explain the absorption mechanism with the gold ground plane described by Drude model, and the theoretical calculation agrees well with the simulations and experiments. In addition, the designed absorber is insensitive to incident angle and polarization direction in a broad range, which are highly favorable features in practical applications.

Dual-band and polarization-insensitive terahertz absorber based on fractal Koch curves

We report the design, fabrication, and characterization of a dual-band and polarization-insensitive metamaterial absorber (MA), which consists of periodically arranged fractal Koch curves acting as the top resonator array and a metallic ground plane separated by a dielectric spacer. Compared with conventional MAs, a more compact size and multi-frequency operation are achieved by using fractal geometry as the unit cell of the MA. Both the effective medium theory and the multi-reflection interference theory are employed to investigate the underlying physical mechanism of the proposed terahertz MA, and results indicate that the latter theory is not suitable for explaining the absorption mechanism in our investigated structure. Two absorption peaks are observed at 0.226 THz and 0.622 THz with absorptivities of 91.3% and 95.6% respectively and good agreements between the full-wave simulation and experimental results are achieved.

Miniaturized and dual-band metamaterial absorber with fractal Sierpinski structure

We report on the design, characteristics, and measurements of a terahertz (THz) metamaterial absorber (MA) based on fractal Sierpinski curves. By applying the fractal structure as the top resonators array, a more compact unit cell with a size reduction of 42% and dual-frequency operation has been achieved as an advantage over the conventional square-shaped MA. In addition, due to the rotationally symmetric structure, the fractal absorber is polarization insensitive and can perform well at a wide range of incident angles. Both the effective medium theory and the multireflection interference theory have been employed to investigate the underlying physical mechanism of the proposed THz MA, and it is found that the latter theory is not applicable for explaining the absorption mechanism of our investigated structure. The THz MA was measured in the case of 30° oblique incidence under TE polarization, and two absorption peaks have been observed at 0.2 and 0.58 THz with absorptivities of 91% and 92.2%, respectively. A microwave MA based on the same Sierpinski structure has also been demonstrated to validate the performance of the fractal MA at various incident angles, and good agreements between the full-wave simulation and experimental results have been achieved.

Multi-band microwave metamaterial absorber based on coplanar Jerusalem crosses

The influence of the gap on the absorption performance of the conventional split ring resonator (SRR) absorber is investigated at microwave frequencies. Our simulated results reveal that the geometry of the square SRR can be equivalent to a Jerusalem cross (JC) resonator and its corresponding metamaterial absorber (MA) is changed to a JC absorber. The JC MA exhibits an experimental absorption peak of 99.1% at 8.72 GHz, which shows an excellent agreement with our simulated results. By simply assembling several JCs with slightly different geometric parameters next to each other into a unit cell, a perfect multi-band absorption can be effectively obtained. The experimental results show that the MA has four distinct and strong absorption peaks at 8.32 GHz, 9.8 GHz, 11.52 GHz and 13.24 GHz. Finally, the multi-reflection interference theory is introduced to interpret the absorption mechanism.

Triple-band terahertz metamaterial absorber: Design, experiment, and physical interpretation

We demonstrate the design, characterization, and interference-theory interpretation of a terahertz triple-band metamaterial absorber (MA). The experiments show that the fabricated MA has three distinctive absorption peaks at 0.5, 1.03, and 1.71 THz with absorption rates of 96.4%, 96.3%, and 96.7%, respectively. We use the multi-reflection interference theory to investigate the physical insight of the proposed triple-band terahertz MA, which provides a design guideline for MA of such type. The theoretical predictions of the interference model have excellent agreements with experimental results. The designed multiband absorber is easy to manufacture and insensitive to incident polarizations with high absorption, which is favorable for various applications.