Relative Absorption Bandwidth Research Articles

Broadband terahertz metamaterial absorber based on simple multi-ring structures

Single-layer metallic rings are the effective structure cell which are widely used to design single-band and multiband perfect metamaterial absorbers owning to their electromagnetic resonance. However, the absorbers based on the single-layer metallic rings have a common shortcoming, that is the narrow absorption bandwidth. To overcome the limitations, here we proposed a single-layer, flexible and broadband terahertz metamaterial absorber, which consists of four sub-cells with multiple metal rings and a metal ground plane separated by a dielectric layer. By enhancing the coupling response between adjacent metallic rings and merging the adjacent resonant peaks of multi-resonators, we experimentally observed broadband characteristics at the terahertz band. The average absorption of 88% from 0.63 to 1.34 THz and the relative absorption bandwidth of 95% at the incident angle of 15o for TE polarization. Correspondingly, for TM polarization the absorption of more than 80% from 0.61 to 1.1 THz with the relative absorption bandwidth of 80% were also observed. The results went far beyond the previous single-layer absorbers based on metal rings and were much better than the fractal-cross structure reported recently [Kenney et al., ACS Photonics 4, 2604 (2017)]. We had reason to believe that the presented terahertz metamaterial absorber with broad absorption bandwidth and simple structure can find important applications in communication, stealth, energy harvesting systems and so on.

Thermally Tunable Ultra-wideband Metamaterial Absorbers based on Three-dimensional Water-substrate construction

Distilled water has frequency dispersive characteristic and high value of imaginary part in permittivity, which can be seen as a good candidate of broadband metamaterial absorbers(MAs) in microwave. Here, an interesting idea based on the combination of water-substrate and metallic metamaterial in the three-dimensional construction is proposed, which can achieve outstanding broadband absorption. As a proof, the distilled water is filled into the dielectric reservoir as ultra-thin water-substrate, and then the water-substrates are arranged on the metal backplane periodically as three-dimensional water-substrate array(TWA). Simulation shows that the TWA achieves broadband absorption with the efficiency more than 90% from 8.3 to 21.0 GHz. Then, the trigonal metallic fishbone structure is introduced here between the water-substrate and the dielectric reservoir periodically as three-dimensional water-substrate metamaterial absorber(TWMA). The proposed TWMA could achieve ultra-broadband absorption from 2.6 to 16.8 GHz, which has increase by 64.8% in relative absorption bandwidth. Meanwhile, due to the participation of distilled water, the thermally tunable property also deserves to be discussed here. In view of the outstanding performance, it is worth to expect a wide range of applications to emerge inspired from the proposed construction.

Broadband metamaterial absorber on a single-layer ultrathin substrate

In this article, a broadband metamaterial microwave absorber on a low-cost FR-4 Epoxy substrate is proposed. The unit cell of the absorber consists of a staircase shape metallic patch placed on the top of the metal-backed ultrathin dielectric substrate having a thickness of 1.9 mm (0.07 λ0). The absorption of more than 90% is achieved with this proposed low profile single-layer microwave absorber throughout the operation band from 8.86 to 15.5 GHz. The performance is analyzed for different values of incident angle, polarization angle, substrate height, and dielectric constant. The surface current and the power loss density at the top and bottom planes at the two absorption peaks of 9.46 and 13.90 GHz are also analyzed to elaborate the absorption mechanism of the structure. Experimental result closely follows the simulated one. The broadband characteristics of the design with relative absorption bandwidth (RAB) of 54.51% at both TE and TM polarizations of incident wave for a wide incident angles makes it versatile for applications in the X and Ku bands of microwave frequencies. The proposed work is very compact (unit cell size: 0.22 λ0) with ultrathin substrate height (0.07 λ0) and giving RAB performance of 54.51% comparable with that of others. Thus with this single-layer low-cost substrate material a broadband absorber is achieved.

Single-channel labyrinthine metasurfaces as perfect sound absorbers with tunable bandwidth

Perfect sound absorbers with a deep-subwavelength thickness are important to applications such as noise reduction and sound detection. But their absorption bandwidths are usually narrow and difficult to adjust. A recent solution for this problem relies on multiple-resonator metasurfaces, which are hard to fabricate. Here, we report on the design, fabrication, and characterization of a single-channel labyrinthine metasurface, which allows total sound absorption at resonant frequency when appropriate amounts of porous media (or critical sound losses) are introduced in the channels. The absorption bandwidth can be tuned by changing the cross-sectional areas of channels. A tradeoff is found between the absorption bandwidth and the metasurface thickness. However, large tunability in the relative absorption bandwidth (from 17% to 121%) is still attainable by such metasurfaces with a deep-subwavelength thickness (0.03–0.13λ).

Ultra-wideband polarization-insensitive and wide-angle thin absorber based on resistive metasurfaces with three resonant modes

In this paper, a metamaterial absorber is designed, fabricated, and experimentally demonstrated to realize ultra-wideband absorption, which is composed of three layers of square resistive metasurfaces with different dimensions. Multilayer resistive metasurfaces can not only broaden the absorption bandwidth but also adjust the impedance matching based on multi-resonant modes. The total thickness of the proposed absorber is 3.8 mm, which is only 0.09λ at the lowest frequency. The bandwidth of absorptivity more than 90% is from 7.0 GHz to 37.4 GHz, and the relative absorption bandwidth is about 137%. The proposed absorber has good polarization-insensitiveness and wide incident angle stability. The measured results agree well with the theoretical design and the numerical simulations.

An ultra-broadband metamaterial absorber based on the hybrid materials in the visible region

In this paper, an ultra-broadband metamaterial absorber is successfully designed in the visible region. The structure of the absorber is just obtained by the two-dimensional plane structure which rotate 90° along x-axis. Furthermore, the formation of the structure for the hybrid materials is based on the four U-shaped structure of the metal titanium is embedded in the semiconductor (indium antimonide). The simulated results show that the proposed metamaterial absorber can achieve an ultra-broadband absorption with greater than 90% from 252.2 to 822.3 THz, and the relative absorption bandwidth gets to 106.1%. Finally, the simulated electric field, surface current and power loss density distributions further illustrate the absorption mechanism of the metamaterial absorber. And we believe the metamaterial absorber will have many potential applications in energy harvesting and stealth devices.

Design and Characterization of an Ultrabroadband Metamaterial Microwave Absorber

This paper presents the design, simulation, fabrication, and performance of an ultrabroadband metamaterial absorber (MMA) at microwave frequencies. The unit cell of this design is composed of the combined metallic resonance structure of two overlapping squares, as well as a square split-ring at the top of an FR-4 dielectric layer and a continuous copper ground plane. The simulated results derived from CST2015 indicate that the absorption ratio of the MMA is over 83%, with a wide frequency range from 20.59 to 43.73 GHZ for a normal incidence electromagnetic (EM) wave. The proposed ultrabroadband MMA has a full width at half maximum (FWHM) absorption bandwidth of 25.64 GHZ and a relative FWHM absorption bandwidth of 79.5%. Moreover, the absorber has a thickness of 0.92 mm, which is only 0.1 λ0 at the center frequency of 32.17 GHZ. The effects on the absorption properties produced by the materials' properties and polarization angles have been investigated. The electric field and surface current distributions have been analyzed at three absorption peaks to understand the EM wave absorption mechanism. The proposed absorber has been fabricated using the laser ablation machine and tested for the normal incidence EM wave. Measured results show an agreement with the simulated results. Furthermore, the proposed design can greatly enrich the applications of MM in thermal imaging, detection, stealth technology, antenna systems, and other EM devices because of its broad frequency range, high absorption, simple fabrication, and effective cost.

Broadband and conformal metamaterial absorber

In this study, a new broadband and conformal metamaterial absorber using two flexible substrates was proposed. Simulation results showed that the proposed absorber exhibited an absorption band from 6.08 to 13.04 GHz and a high absorption of 90%, because it was planar. The absorber was broadband as its relative absorption bandwidth was 72.8%. Moreover, the proposed absorber was insensitive to the polarization of the TE and TM waves. The absorber was ultra-thin; its total thickness was only 0.07l at the lowest operating frequency. Furthermore, different regions of absorption can be adjusted by lumping and loading two resistors onto the polyimide film, respectively. Moreover, compared with the conventional microwave absorber, the absorption bandwidth of the proposed absorber can be broadened and enhanced when it was bent and conformed to the surface of objects. Experimental and simulation results were in agreement. The proposed absorber is a promising absorbing element in scientific and technical applications because of its broadband absorption, polarization insensitivity, and flexible substrates.

Broadband terahertz metamaterial absorber based on tantalum nitride.

A broadband metamaterial absorber with a single layer of tantalum nitride (Ta2N3) frequency selective surface layer, printed on a foam substrate, is presented. The proposed design has been numerically examined at the terahertz region. The results have shown that a wideband absorption with absorptivity greater than 90% was achieved in the frequency range 1.17-2.99 THz, and the relative absorption bandwidth was up to 112.97%, which is significantly better than previously reported results. Moreover, the absorber was independent of wave polarization, and a high absorption for a wide range of oblique incidence was achieved. The surface current distribution, the electric field distributions, and the power loss analyses were used to explain the physical mechanism of a wideband absorption. However, the tantalum nitride layer has an important role in the energy absorption. According to the obtained results, the proposed absorber, which is compact and simple to design, has a potential application in evolving broadband terahertz absorbers and sensors.

Three-Dimensional Single-Port Labyrinthine Acoustic Metamaterial: Perfect Absorption with Large Bandwidth and Tunability

In this paper, we report on the design, fabrication, and experimental characterization of a 3D single-port labyrinthine acoustic metamaterial. By using curled perforations with one end closed and with appropriate loss inside, the proposed metamaterial can perfectly absorb airborne sounds in a low frequency band. Both the position and width of the band can be tuned flexibly. A tradeoff is uncovered between the relative absorption bandwidth and thickness of the metamaterial. When the relative absorption bandwidth is as high as 51%, the requirement of deep subwavelength thickness (0.07{\lambda}) can still be satisfied.

Ultra-broadband metamaterial absorber based on the structure of resistive films

This paper presents a three-dimensional structure of metamaterial absorber, and the unit of the absorber is composed of six different size resistive films which are placed on the metal plane ground. The simulated results show that the absorber can realize ultra-broadband absorption, which is from 38 to 142 GHz when the absorption is larger than 90%. And the relative absorption bandwidth can achieve 115.5%. In addition, the proposed metamaterial absorber is polarization-insensitive, which has the same absorption spectra for TE and TM polarization waves. And the absorber has large incident and polarization angles. In the end, the power loss density is analyzed. Through observing the distribution of power loss density, a polarization-controlled metamaterial absorber can be implemented if subtract the resistance film of the horizontal direction or the vertical direction subtracted. And the polarization-controlled metamaterial absorber also has ultra-broadband absorption effect. We believe that the absorber will have many potential applications.

A bandwidth-enhanced metamaterial absorber based on dual-band sub-cells

In this paper, a coplanar bandwidth-enhanced metamaterial absorber is presented based on the combination of three dual-band sub-cells. The simulated results show that the absorber is polarization insensitive and adaptive for wide angles of oblique incidence. The simulated FWHM absorption bandwidth is 1.09GHz (6.04–7.13GHz), with the relative FWHM absorption bandwidth of 16.6%. A sample is fabricated. The experimental results verified that FWHM absorption bandwidth is 1GHz (6–7GHz), with the relative FWHM absorption bandwidth of 15.4%, and the absorption peak of 77.5% is obtained.

A Polarization-Insensitive Broadband Metamaterial Absorber at the Optical Regime**Supported by the National Innovative Projects for College Students, the National Natural Science Foundation of China under Grant Nos 12ssjcxdd01, 61401182 and 61372057, and the Priority Academic Program Development of Jiangsu Higher Education Institutions.

We present a polarization-insensitive broadband absorber which has a feature of metal-insulator-metal structures. The top metal layer consists of four-fan-rings-shaped gold. Simulations show that the absorber exhibits an absorption of nearly unity at the wavelength of 386.1 nm and a relative absorption bandwidth of 0.548, which refers to the ratio of the full absorption bandwidth over an absorption of 0.9 to the central wavelength. Meanwhile, the absorption is nearly independent of the polarized direction of the incident wave. This absorption bandwidth with insensitive polarization is widely reported to date for such metal-insulator-metal structures. Such a structure offers a way of realization of a polarization-insensitive broadband absorber ranging in ultraviolet-to-visible wavelengths.

A novel ultrathin and broadband microwave metamaterial absorber

In this paper, the design, simulation, fabrication, and measurement of an ultrathin and broadband microwave metamaterial absorber (MMA) based on a double-layer structure are presented. Compared with the prior work, our structure is simple and polarization insensitive. The broadband MMA presents good absorption above 90% between 8.85 GHz and 14.17 GHz, with a full width at half maximum (FWHM) absorption bandwidth of 6.77 GHz and a relative FWHM absorption bandwidth of 57.3%. Moreover, the structure has a thickness of 1.60 mm (only λ/20 at the lowest frequencies). The experimental results show excellent absorption rates which are in good correspondence with the simulated results. The broadband absorber is promising candidates as absorbing elements in scientific and technical applications because of its broadband absorption and polarization insensitive.

A simple design of a broadband, polarization-insensitive, and low-conductivity alloy metamaterial absorber

We present a simple method for significantly broadening the bandwidth of a metamaterial absorber formed using only a low-conductivity alloy ring and an alloy ground plane separated by a dielectric layer. The >80% relative absorption bandwidth of the device is improved to 101.2%, which is much higher than previously reported values. The absorption mechanism for the broadband alloy absorber involves the overlapping of two different resonance frequencies. In particular, the electromagnetic energy is entirely dissipated in the alloy layer, which makes it insensitive to the loss of the dielectric layer and widens the range of choices for potential dielectric materials.

Metamaterial-Based Low-Conductivity Alloy Perfect Absorber

We propose a simple way to enormously broaden the bandwidth of the metamaterial absorber formed by a low-conductivity square alloy patch and a dielectric layer on top of an alloy ground plane. The FWHM of the device can be up to 38.8%, which is 3.6 times larger than that of the high-conductivity (Au) absorber. Moreover, we demonstrate an ultra-broadband and polarization insensitive absorber by simply stacking three different-sized square alloy patches. Greater than 90% absorption is obtained across a frequency range of 1.34 THz with the central frequency around 1.90 THz. The relative absorption bandwidth of the device is greatly improved to 70.4%, which is much larger than previous results. The mechanism for the ultra-broadband absorption is attributed to the overlapping of four different but closely positioned resonance frequencies. The results of the proposed alloy metamaterial absorber appear to be very promising for solar cells, detection, and imaging applications.

A broadband omnidirectional absorber based on a hetero-structure composed of epsilon-negative material and mu-negative material

A broadband omnidirectional absorber which is realized by heterostructures containing a collision plasma layer and a zero − n mirror is theoretically investigated. A collision plasma layer and an appropriate dielectric layer are put on the top of the PC. It is shown to absorb roughly 70% of all available electromagnetic wave in a relative omnidirectional absorption band width 244 MHz. The absorption band edge of the PC is influenced by the range of the reflection band gap. Meanwhile, the absorption range for the transverse magnetic (TM) wave decreases at large incident angle. Compared with some previous designs, our proposed structure has a relative flatter total absorption spectrum over a broad microwave frequency range and using a zero − n gap as a mirror is insensitive to the incident angle. This kind of heterostructure offers additional opportunities to design novel optoelectronic devices.

A BROADBAND METAMATERIAL ABSORBER USING FRACTAL TREE STRUCTURE

A novel broadband absorber using the fractal tree structure is presented in this paper, which consists of three metallic layers separated by two dielectric substrates. Five metallic vias connect these three layers which make the whole structure like a two order fractal tree. Simulated and measured results show that this absorber can provide a high absorptivity level from 4.98 to 12.58 GHz, equivalent to a relative absorption bandwidth about 87%. Further investigations show that this wideband absorption can be attributed to the multi-eigenmodes and lower quality factor of the fractal tree structure.

Theoretical Limitations for TM Surface Wave Attenuation by Lossy Coatings on Conducting Surfaces

In this work, we theoretically analyze the limitations for TM surface wave attenuation on lossy coated conducting surfaces containing electric and/or magnetic loss. We use both an analytical approach as well as numerical simulations, and find excellent agreement between them. We also find that the loss can be described by a simple approximate expression for a wide range of material properties. Furthermore, we analyze lossy slabs with simple equivalent circuit boundaries on top, such as may be provided by frequency selective surfaces or other patterned structures. We find that such composite lossy coating can exceed the attenuation of a simple lossy slab, but with limited bandwidth. We also find that only by increasing permeability, and not permittivity, can the peak absorption frequency be lowered for a given thickness without reducing the relative absorption bandwidth.

A simple design of ultra-broadband and polarization insensitive terahertz metamaterial absorber

Ultra-broadband metamaterial absorbers have attracted considerable attention due to their great prospect for practical applications. These absorbers are usually stacked by many (no. <20) different shaped or sized subunits in a unit cell, making it quite troublesome to be fabricated. Simple design for ultra-broadband absorber is urgently necessary. Herein, we propose a simple design of ultra-broadband and polarization insensitive terahertz metamaterial absorber based on a double-layered composite structure on a metallic board, and each layer consists of two sets of different sized square metallic plates. Greater than 90 % absorption is obtained across a frequency range of 0.85 THz with the central frequency around 1.60 THz. The relative absorption bandwidth of the device is greatly improved to 53.3 %, which is much larger than previous results. The mechanism of the ultra-broadband absorber is attributed to the overlapping of four closely resonance frequencies. The proposed metamaterial absorber has potential applications in detection, imaging and stealth technology.