Ultrathin Metamaterial Absorber Research Articles

Ultrathin Terahertz Dual-Band Perfect Metamaterial Absorber Using Asymmetric Double-Split Rings Resonator

In this article, an ultrathin terahertz dual band metamaterial absorber made up of patterned asymmetrical double-split rings and a continuous metal layer separated by a thin FR-4 layer is designed. Simulation results show that two almost identical strong absorption peaks appear in the terahertz band. When the incident electric field is perpendicular to the ring gaps located at 11 μm asymmetrically, the absorptivity of 98.6% at 4.48 THz and 98.5% at 4.76 THz can be obtained. The absorption frequency and the absorptivity of the absorber can be modulated by the asymmetric distribution of the gaps. The perfect metamaterial absorber is expected to provide important reference for the design of terahertz modulator, filters, absorbers, and polarizers.

Angular- and Polarization-insensitive Ultrathin Double-layered Metamaterial Absorber for Ultra-wideband Application

We proposed an ultra-thin polarization-insensitive metamaterial absorber (MMA) for ultra-wideband and wide incident angle operation. The MMA is composed of double-layer symmetric split rings (SSRs) connected with two orthogonally-arranged bars and the ground metallic plane separated by two identical substrates. Multiple metallic layers and scalabilities are employed to provide broadband absorptivity based on the cooperated mechanisms of the Ohmic loss and the Fabry-Perot interference. To further broaden the absorption bandwidth, four lumped resistors are loaded with the SSRs on the top metallic layer. By this means, an ultra-wideband absorbance is achieved nearly in 4~22 GHz, two gentle slope belts with absorptivity over 60% and 80% in 4~12 GHz and 12~22 GHz, respectively. The whole structure is with an ultrathin thickness of 2.4 mm, which is 0.032λlow and 0.176λhigh corresponds to the lowest and highest absorption frequency separately. Meanwhile, the symmetric structure enables the MMA of satisfactory stability for polarization and wide incident angles. Numerical and experimental results prove the capability of the proposed MMA for ultra-wideband absorbance.

Polarization-independent wide-angle ultrathin double-layered metamaterial absorber for broadband application

In this letter, a polarization-independent broadband metamaterial absorber (MMA) for wide incidence angle is proposed. The MMA is composed of double-layer symmetric split rings connected with two orthogonally arranged bars and the ground metallic plane separated by two equal-sized substrates. The whole structure is with an ultra-thin thickness of 2.4 mm, which is 0.031 $$\lambda$$ corresponds to the lowest frequency of absorption peaks. Multiple metallic layers and multi-scalability are employed to provide broadband absorptivity based on the cooperated mechanisms of the Ohmic loss and the Fabry–Perot interference. A desirable absorption is achieved with double strong absorption peaks in 2–6 GHz and a broadband absorption in 10–24 GHz. The absorptivity can reach up to 100% with nearly all absorption peaks over 90%. The symmetry enables the MMA of satisfactory stability for polarization and incidence angles. Numerical and experimental results prove the capability of the proposed MMA for broadband absorbance.

An analysis of RCS for dual-band slotted patch antenna with a thin dielectric using shorted stubs metamaterial absorber

A dual-band slotted patch antenna with thin dielectric has been proposed for Ku–band applications. A rectangular patch with pair of bent slots at each side of center has been designed and resonant at 11.95 GHz and 14.25 GHz with respect to ITU standard. A dual resonance ultrathin metamaterial absorber (MMA) based on circular rings and shorted stubs operating at same frequency bands have been designed. Its behavior at an oblique angle of incidence and polarization sensitivity has been also observed. In this research work, it has been obtained that when dual–band slotted patch antenna is surrounded by proposed MMA structure, it significantly enhances in-band stealth capability of the antenna. The monostatic and bistatic RCS of the proposed design has been reduced significantly whilst maintaining and preserving the antenna radiation performance. This design finds its application in satellite and wireless communication.

An ultra-thin compact polarization-independent hexa-band metamaterial absorber

In this paper, an ultra-thin compact hexa-band metamaterial absorber has been presented using single layer of dielectric. The proposed design is polarization independent in nature owing to its fourfold symmetry and exhibits high angular stability up to 60° angles of incidences for both TE and TM polarizations. The structure is ultrathin in nature with 2 mm thickness, which corresponds to λ/11.4 (λ is the operating wavelength with respect to the highest frequency of absorption). Six distinct absorption frequencies are obtained from the design, which can be distributed among three regions, namely lower band, middle band and higher band; each region consists of two closely spaced frequencies. Thereafter, the dimensions of the proposed structure are adjusted in such a way that bandwidth enhancement occurs at each region separately. Simultaneous bandwidth enhancements at middle and higher bands have also been achieved by proper optimization of the geometrical parameters. The structure with simultaneous bandwidth enhancements at X- and Ku-bands is later fabricated and the experimental absorptivity response is in agreement with the simulated one.

A wideband wide‐angle ultrathin low profile metamaterial microwave absorber

AbstractIn the recent article, Sood and Tripathi (Microwave Opt Technol Lett., 58: 1131–1135. doi:10.1002/mop.29741) proposed metamaterial absorber structure composed of inclined hexagonal patch printed on grounded dielectric substrate. The reported structure was shown to have wideband absorptivity having 10‐dB bandwidth of 5.02 GHz from 8.81 GHz to 13.83 GHz. In this report, we claim that the reported structure is not a metamaterial absorber. We find that for reported structure peak absorptivity is less than 13%. The low value of absorption in our opinion is caused due to crosspolarization effect rather than absorption.

Polarization-maintaining reflection-mode THz time-domain spectroscopy of a polyimide based ultra-thin narrow-band metamaterial absorber

This paper reports the design, the microfabrication and the experimental characterization of an ultra-thin narrow-band metamaterial absorber at terahertz frequencies. The metamaterial device is composed of a highly flexible polyimide spacer included between a top electric ring resonator with a four-fold rotational symmetry and a bottom ground plane that avoids misalignment problems. Its performance has been experimentally demonstrated by a custom polarization-maintaining reflection-mode terahertz time-domain spectroscopy system properly designed in order to reach a collimated configuration of the terahertz beam. The dependence of the spectral characteristics of this metamaterial absorber has been evaluated on the azimuthal angle under oblique incidence. The obtained absorbance levels are comprised between 67% and 74% at 1.092 THz and the polarization insensitivity has been verified in transverse electric polarization. This offers potential prospects in terahertz imaging, in terahertz stealth technology, in substance identification, and in non-planar applications. The proposed compact experimental set-up can be applied to investigate arbitrary polarization-sensitive terahertz devices under oblique incidence, allowing for a wide reproducibility of the measurements.

Ultra-thin and broadband tunable metamaterial graphene absorber.

A broadband tunable metamaterial graphene absorber is investigated in this paper. The unit cell of the proposed metamaterial graphene absorber is composed of four patch resonators. By tuning the chemical potential of graphene and the geometric size of each patch, the simulated total reflectivity is less than -10 dB from 22.02 to 36.61 THz and with the total thickness of 0.76 um (only 0.09λ at the lowest frequency). The analysis of the surface current, magnetic field and power flow distributions has been performed to better understand the absorption mechanism. Moreover, this proposed absorber achieves its bandwidth tunable characteristics through a voltage biasing of the graphene's Fremi level. This proposed metamaterial graphene absorber (MGA) could be used as smart absorbers, photovoltaic devices and tunable sensors.

Experimental demonstration of the performance of flexible metamaterial absorber on planar and cylindrical surface

In this paper, an ultrathin polarization independent conformal metamaterial absorber for planar and cylindrical surface is presented. The proposed structure consists of a periodic array of truncated square patch element in the center with rectangular strips coupled to the edges. It is fabricated on low cost commercially available FR-4 substrate by photolithographic method and the performance of structure is studied for both planar and cylindrical surface configurations. The absorbing structure having a thickness of λ/128, displays angular stability up to 40° for TE polarization and 60° for TM polarization in the planar configuration. In the cylindrical configuration, the performance depends on the radius of curvature, since different elements are illuminated at different angles. This aspect is also studied and reported with experimental results.

Ultra-Thin Multi-Band Polarization-Insensitive Microwave Metamaterial Absorber Based on Multiple-Order Responses Using a Single Resonator Structure.

We design an ultra-thin multi-band polarization-insensitive metamaterial absorber (MMA) using a single circular sector resonator (CSR) structure in the microwave region. Simulated results show that the proposed MMA has three distinctive absorption peaks at 3.35 GHz, 8.65 GHz, and 12.44 GHz, with absorbance of 98.8%, 99.7%, and 98.3%, respectively, which agree well with an experiment. Simulated surface current distributions of the unit-cell structure reveal that the triple-band absorption mainly originates from multiple-harmonic magnetic resonance. The proposed triple-band MMA can remain at a high absorption level for all polarization of both transverse-electric (TE) and transverse-magnetic (TM) modes under normal incidence. Moreover, by further optimizing the geometric parameters of the CSRs, four-band and five-band MMAs can also be obtained. Thus, our design will have potential application in detection, sensing, and stealth technology.

Design and analysis of an ultrathin triple-band polarization independent metamaterial absorber

In this paper, an ultrathin triple-band polarization insensitive metamaterial (MTM) absorber has been presented for C-band applications. The proposed structure is explained as a combination of two absorbers, named as Absorber-I and Absorber-II. It exhibit 91%, 98.9% and 99.5% absorptivity at 4.2 GHz, 7 GHz and 7.4 GHz frequencies respectively. Absorber-I and Absorber-II are individually responsible for the origin of two separate frequency bands at 4.2 GHz and 7 GHz respectively. Further, mutual coupling between Absorber-I and Absorber-II is responsible to generate one more absorption band at the frequency of 7.4 GHz. The fourfold symmetric nature of the proposed unit cell provides polarization insensitivity phenomena. The absorbing mechanism of the designed absorber has been explained by two methods. One is by plotting input impedance of the absorber. Another one is by analyzing the EM wave propagation inside the structure. The proposed absorber has been fabricated and simulation results are experimentally verified.

An ultrathin microwave metamaterial absorber with enhanced bandwidth and angular stability

A very thin metamaterial absorber with enhanced bandwidth and angular stability is designed and its application in radar cross section (RCS) reduction of antenna is discussed in this paper. First, a wideband absorber element consisting of an unconnected square loop and unconnected printed cross on a metal backed FR-4 dielectric is designed. This structure has full width half maximum bandwidth of 0.41 GHz and exhibits polarization independent JPCOcharacteristics. It also shows good absorption characteristics for incident angles up to 40° for TE and TM polarized wave. Further enhancement in bandwidth up to 0.574 GHz is achieved by arranging the structures with overlapping resonances as a 2 × 2 array. This 2 × 2 array is used as the unit cell for the larger array. This structure also exhibits polarization independent characteristics and good angular stability up to 60°. The values of effective permittivity and permeability are retrieved from the reflection and transmission parameters of the structure. These parameters also validates the absorption characteristics of the structure. The performance of the fabricated structure for different polarization and angle of incidence is measured and the results are in good agreement with simulation. Finally, the use of this structure to reduce the RCS of a patch antenna is demonstrated.

Ultrathin Six-Band Polarization-Insensitive Perfect Metamaterial Absorber Based on a Cross-Cave Patch Resonator for Terahertz Waves.

A simple design of an ultrathin six-band polarization-insensitive terahertz perfect metamaterial absorber (PMMA), composed of a metal cross-cave patch resonator (CCPR) placed over a ground plane, was proposed and investigated numerically. The numerical simulation results demonstrate that the average absorption peaks are up to 95% at six resonance frequencies. Owing to the ultra-narrow band resonance absorption of the structure, the designed PMMA also exhibits a higher Q factor (>65). In addition, the absorption properties can be kept stable for both normal incident transverse magnetic (TM) and transverse electric (TE) waves. The physical mechanism behind the observed high-level absorption is illustrated by the electric and power loss density distributions. The perfect absorption originates mainly from the higher-order multipolar plasmon resonance of the structure, which differs sharply from most previous studies of PMMAs. Furthermore, the resonance absorption properties of the PMMA can be modified and adjusted easily by varying the geometric parameters of the unit cell.

Broad-band terahertz metamaterial absorber with stacked electric ring resonators

In this paper, we propose an ultra-thin broad-band metamaterial absorber composed of a periodic array of three-layered electric ring resonators (ERRs) within a dielectric spacer and backed by a metallic ground plane for THz applications. The overlapping of the resonance peaks relevant to the ERRs leads to a broad spectral absorption bandwidth over a wide range of incidence angles under both transverse electric and transverse magnetic polarizations. We analyze the effect of different physical properties on the absorption spectra in order to estimate the dielectric and Ohmic losses in the metamaterial structure. In addition, the Nicolson, Ross, and Weir algorithm is adopted as homogenization technique to retrieve the effective electromagnetic parameters, while the interference theory is employed to compare the simulated and analytical results for the multi-layered absorber.

A Compact Ultrathin Ultra-wideband Metamaterial Microwave Absorber

A simple design of compact ultra-wideband, ultra-thin metamaterial microwave absorber has been presented. The unit cell of the proposed design is composed of diagonally placed microstrip bend' like patches printed on grounded dielectric substrate. The simulation results demonstrate the 10-dB absorption bandwidth of 7.19 GHz from 10.45 GHz to 17.64 GHz and FWHM (full width at half maximum) bandwidth of 11.43 GHz from 9.61 GHz to 21.04 GHz. The proposed design presents more than 90% absorption for a bandwidth of 1.02 GHz at wide angle of incidence up to 60 0 . The absorption mechanism has been analyzed through surface current and electromagnetic field distributions. The proposed design has been fabricated and experimentally tested for its 10-dB absorption bandwidth under different polarization and oblique angles of incidence of electromagnetic wave. The designed absorber is low profile (unit cell size is ~0.257 I» 0 at the center frequency corresponding to 10-dB absorption bandwidth), ultrathin (~I» 0 /14 thick at the center frequency) and provides a novel design of wideband absorber for many useful applications.

Miniaturization for ultrathin metamaterial perfect absorber in the VHF band

An efficient resolution for ultrathin metamaterial perfect absorber (MPA) is proposed and demonstrated in the VHF radio band (30–300 MHz). By adjusting the lumped capacitors and the through vertical interconnects, the absorber is miniaturized to be only λ/816 and λ/84 for its thickness and periodicity with respect to the operating wavelength (at 102 MHz), respectively. The detailed simulation and calculation show that the MPA can maintain an absorption rate over 90% in a certain range of incident angle and with a wide variation of capacitance. Additionally, we utilized the advantages of the initial single-band structure to realize a nearly perfect dual-band absorber in the same range. The results were confirmed by both simulation and experiment at oblique incidence angles up to 50°. Our work is expected to contribute to the actualization of future metamaterial-based devices working at radio frequency.

A sextuple-band ultra-thin metamaterial absorber with perfect absorption

This paper presents the design, simulation and measurement of a sextuple-band ultra-thin metamaterial absorber (MA). The unit cell of this proposed structure is composed of triangular spiral-shaped complementary structures imprinted on the dielectric substrate backed by a metal ground. The measured results are in good agreement with simulations with high absorptivities of more than 90% at all six absorption frequencies. In addition, this proposed absorber has good performances of ultra-thin, polarization insensitivity and a wide-angle oblique incidence, which can easily be used in many potential applications such as detection, imaging and sensing.

A polarization insensitive compact ultrathin wide-angle penta-band metamaterial absorber

In this paper, the design, fabrication, and measurements of a compact ultrathin five-band metamaterial absorber with wide-angle stability have been presented. The unit cell of the absorber consists of five concentric metallic circular rings printed as the top layer of a grounded dielectric substrate of thickness 1 mm. The radii and the intermediate gap between the rings are optimized such that the proposed absorber exhibits five distinct absorption peaks at frequencies of 5.28, 7.36, 9.52, 12.64, and 16.32 GHz with absorptivities of 92.03, 90.46, 95.10, 91.65, and 91.10%, respectively. The proposed absorber is polarization insensitive for both TE and TM incident wave and results high absorption for wide incidence angle up to 60°. The proposed structure is compact with its unit cell size of 0.54 λ0 and ultrathin with thickness of ~λ0/19 corresponding to the highest frequency of absorption. Surface current and field distributions are studied to understand the absorption mechanism. A prototype of the proposed absorber is fabricated and experimentally tested for different polarization and incident angles. The measured results are observed to be in agreement with the simulated ones. The proposed absorber is suitable for potential applications due to its multi-band absorption.

Broadband, ultrathin and polarization-insensitive metamaterial absorber based on a new mixing material in infrared and visible regions

In this paper, we proposed a broadband, ultrathin and polarization-insensitive metamaterial absorber which consists of three layers in the infrared and optical regions. Compared with the traditional three layers absorber, the most remarkable difference is that the metal Sn and InSb are used on the top layer at the same time. Numerical results reveal that a broadband absorption spectrum more than 90% can be achieved from the 97.0THz to 115THz. In addition, the perfect absorption character (484.4THz–603.6THz) also can be applied in the optical region by adjusting the structure parameters. The impedance matching theory and surface current distributions are investigated to explain the physical mechanism of the perfect absorption performance.

An Investigation on Compact Ultra-Thin Triple Band Polarization Independent Metamaterial Absorber for Microwave Frequency Applications

This article claims, an investigation on compact ultrathin triple band polarization independent metamaterial absorber for microwave frequency applications. The proposed absorber unit cell consist of two resonators named as Structure-A and Structure-B. Both the resonators are printed on the upper surface of dual side copper coated FR-4 epoxy glass substrate of thickness 0.8 mm. The proposed absorber structure offers three distinct absorption peaks of 99.67%, 99.48%, and 99.42% with FWHM bandwidth of 170 MHz (4.11-4.28 GHz), 350 MHz (9.17–9.52 GHz), and 480 MHz (11.24–11.72 GHz) at 4.19 GHz, 9.34 GHz, and 11.48 GHz, respectively, under normal incidence. In addition to above, the four fold symmetry of proposed absorber structure make it polarization independent. Proposed absorber structure also offers more than 80% absorptivity at different angle of incidence (up to 60°) under transvers electric and transvers magnetic polarization states. The designed absorber unit cell has compactness of $0.11~\lambda _{0} \times 0.11~\lambda _{0}$ with ultra-thin thickness of $0.0111~\lambda _{0}$ , where $\lambda _{0}$ is the free space wavelength with respect to the lowest absorption peak of 4.19 GHz. Absorption mechanism of proposed unit cell has been discussed with the help of normalized input impedance, electric field distribution, and surface current density plots. In order to discuss the metamaterial property of proposed absorber unit cell dispersion diagram has been shown.