A terahertz polarization insensitive dual band metamaterial absorber

Metamaterial absorbers with perfect absorption properties are essential in various fields. A multilayer metamaterial disc absorber has been designed and analyzed using a finite-difference time-domain method. In the wavelength range from 300 nm to 3000 nm, this metamaterial absorber absorbs more than 90%. The metamaterial absorber is polarisation-insensitive due to its symmetric structure. On the other hand, the designed absorber still provides a high absorbance (>80%) at an incidence angle of 60°. Surface plasmon resonance (SPR), cavity resonance, local surface plasmon resonance (LSPR), and inter-resonance interactions dominate the absorber for efficient absorption and extended absorption bandwidth.

The existence a problem of military vehicles at ship susceptible to noise propagation caused by a vibration of machine inside engine room. To solve interference problem that, it can be used by Radar Absorbing Material (RAM) such as metamaterial absorber in engine control room, so in this research will be proposed the design and simulation of metamaterial absorber at frequency in triple band that implemented at engine control room as reducer machine ship so it happen not interference to outside engine ship. Design of the metamaterial absorber will done with determine dimension and shape of metamaterial absorber and it will simulated with CST Microwave Studio 2012 software. The result of simulation at triple band metamaterial absorber brings S11 at frequency 2.079 GHz is −12.041 dB, so resulting the value of absorption is 99.6 %. For S11 at frequency of 2.895 GHz is −9.869 dB, so resulting the value of absorption is 98.93 % and frequency of 3.894 GHz is −15.544 dB, so resulting the value of absorption is 99.92 %. It show that the absorber has a good absorbing performance (absorption > 80 %) from three peaks frequency.

Metamaterials can freely control terahertz waves by designing the geometric shape and direction of the unit structure to obtain the desired electromagnetic characteristics, so they have been widely used in sensing, communication and radar stealth technology. The traditional design of terahertz metamaterial absorber usually requires continuous structural adjustment and a large number of simulations to meet the expected requirements. The process largely relies on the experience of researchers, and the physical modeling and simulation solution process is time-consuming and inefficient, greatly hindering the development of metamaterial absorbers. Therefore, due to its powerful learning ability, deep learning has been used to predict the structural parameters or spectra of metamaterial absorbers. However, when designing a new structure, it is necessary to prepare a large number of training samples again, which is both time-consuming and not universal. Particle swarm optimization algorithm can quickly converge to the optimal solution through the sharing and cooperation of individual information in the group, with no need for prior preparation. Therefore, a method of fast designing terahertz metamaterial absorber is proposed based on multi-objective particle swarm optimization algorithm in this work. Taking a new center symmetric absorber structure composed of four Ls for example, the structure parameters are optimized to achieve rapid and automatic design of metamaterial absorber. The multi-objective particle swarm optimization algorithm takes the absorptivity and quality factor as independent targets to design the structure parameters of the absorber, realizing the dual-objective optimization of the absorber, and overcoming the shortcoming of the multi-objective conflicts that cannot be solved by PSO. When used for refractive index sensing, the optimally-designed absorber achieves perfect absorption at 1.613 THz with a quality factor of 319.72 and a sensing sensitivity of 264.5 GHz/RIU. In addition, the reasons of absorption peaks are analyzed in detail through impedance matching, surface current, and electric field distribution. By studying the polarization characteristics of the absorber, it is found that the absorber is not sensitive to polarization, which is more stable in practical application. In summary, the multi-objective particle swarm optimization algorithm can realize the design according to the requirements, reduce the experience requirement of researchers in the design of metamaterial absorber, thereby improving design efficiency and performance, and has great potential for application in the design of terahertz functional devices.

We propose a multi-band metamaterial absorber operating at terahertz frequencies. The design, characterization, and theoretical calculation of the high performance metamaterial absorber are reported. The multi-band metamaterial absorber consists of two metallic layers separated by a dielectric spacer. Theoretical and simulated results show that the metamaterial absorber has four distinct absorption points at frequencies 0.57 THz, 1.03 THz, 1.44 THz and 1.89 THz, with the absorption rates of 99.9%, 90.3%, 83.0%, 96.1%, respectively. Two single band metamaterial absorbers and a dual band metamaterial absorber on the top layer are designed. Some multi-band absorbers can be designed by virtue of combining some single band absorbers. The multiple-reflection theory is used to explain the absorption mechanism of our investigated structures.

This paper presents the design, simulation and parametric analysis of a concentric continuous and split rings resonator (CCRR, CSRR) structure for a dual broadband metamaterial (MM) absorber. The MM structure unit cell consists of concentric circular split rings of same width and different radii and concentric continuous rings of different width and different radii arranged in four different quadrants. The three layered proposed MM absorber design has upper layer comprising of concentric continuous and split rings structured sub-cells separated by bottom laminated copper layer of FR-4 substrate. The proposed MM absorber is insensitive to any polarization state of incident EM waves due to highly symmetrical circular and split ring structures. The scattering parameter and absorption coefficient are obtained for the present MM absorber. The magnetic and electric fields are monitored to realize the behavior of MM structure. The dual broadband MM absorber has absorbance of 99% from 7.785 GHz - 8.475 GHz and absorbance of 98% from 11.835 GHz - 12.81 GHz. The absorption peaks for this MM absorber are obtained as 99.5%, 99.6%, 98.4% and 98.8% at 7.785 GHz, 8.475 GHz, 11.835 GHz and 12.81 GHz frequencies respectively for the normal incidence of EM waves. The high absorbance makes this MM absorber suitable for various microwave applications including airborne and radar signal absorption.

The metamaterial perfect absorber (MPA) is a new type of electromagnetic wave absorber first proposed by Landy. Compared with the traditional electromagnetic wave absorber, MPA has many advantages, including ultra-high absorption efficiency, ultra-thin, compact structure, easily tunable resonances, etc. so it is gradually applied to ultra-sensitive sensing, imaging, detection and other fields. Nowadays, the MPA research focuses on two areas. One area focuses on the absorption efficiency modulation and absorption wavelength tuning, and the other area is to broaden the absorption bandwidth and achieve high absorptions at different optical frequencies. Previously, the MPA absorption efficiency modulation or absorption wavelength tuning was realized by changing the device structure or the surrounding medium material. But these methods can increase the difficulty in processing and increase the device volume. In order to achieve the control of absorption wavelength and absorption efficiency without increasing the difficulty in processing or the device volume. We propose to use vanadium dioxide and graphene as the materials of MPA, which has high absorption efficiency in the infrared band. It is found that the absorption efficiency of MPA at 9.66 μm wavelength can reach 96% when the temperature of vanadium dioxide is 5 ℃ by using finite difference time domain (FDTD) method. However, when the vanadium dioxide temperature rises to 68 ℃, the absorption efficiency of MPA suddenly drops to 2.8%. The modulation depth of absorption efficiency can reach 97.08%. We propose that the MPA be able to control not only the absorption efficiency, but also the absorption wavelength. By changing the voltage of graphene, the chemical potential <i>E</i><sub>f</sub> of graphene can be controlled and the absorption wavelength of MPA can be tuned. When <i>E</i><sub>f</sub> increases from 0.1 eV to 3 eV, the absorption wavelength of MPA will be blue-shifted from 9.66 μm to 6.46 μm. The magnetic field distribution of MPA at the absorption wavelength shows that the MPA has a high absorption efficiency because of the Fabry-Pérot (FP) cavity resonance is formed in MPA. Therefore, the change of structure parameters of MPA will affect its absorption characteristics. It is found by the FDTD method that the absorption wavelength of MPA will be redshifted, when the radius, thickness, period and thickness of the nanocolumn array increase. This study can provide theoretical guidance for designing and preparing the controllable MPA, which has compact structure and low process difficulty merits.

We designed a metamaterial far-infrared absorber based on an MDM (metal–dielectric–metal) structure. We made a hollow crossed Ti microstructure at the top of the absorber. It is known that the coupling effect of equipartitional exciton resonance and intrinsic absorption at the surface of the depleting material has a strong influence on the absorber. Based on this, we investigated the absorption characteristics of the absorber using the Finite Difference in Time Domain (FDTD) theory. The results show that the absorber absorbed more than 90% of the light within a bandwidth of 12.01 μm. The absorber has an average absorption of 94.08% in the longwave infrared (LWIR) to ultra-longwave infrared (UWIR) bands (10.90–22.91 μm). The polarization insensitivity of the designed absorber is demonstrated by analyzing the absorption spectra of the absorber at different polarization angles. By adjusting the relevant geometric parameters, the absorption spectrum can be independently adjusted. Furthermore, the absorber exhibits good incidence angle insensitivity in both transverse electric (TE) and transverse magnetic (TM) modes. The absorbers are simple and easy to configure for applications such as optical cloaking, infrared heat emitters, and photodetectors. These advantages will greatly benefit the application of absorbers in practice.

In this paper, a dual-band metamaterial absorber in the terahertz frequencies is proposed and its refractive index sensing characteristics is analyzed. The metamaterial structure is designed using a square metal ring with four T-shaped strips loaded outside of the ring, where the metal periodic array is on top of a silicon wafer backed with a metal ground plane. The resonant frequencies of the absorber are at 0.89 and 1.36 THz, whose absorption rates are both over 99% under normal TE and TM polarized incidences. The full widths at half maximum of them are 4.4 and 11.2 GHz, respectively, resulting in high quality factors (Q-factors) for these two frequency bands. The absorption rate of the absorber remains stable as the incident and polarized angles are changed. Several proposed metamaterial absorbers are experimentally fabricated and electron beam lithography (EBL) technology is employed. Good measurement results of the dual-band absorption performance are obtained using a terahertz time-domain spectroscopy system based on photoconductive antennas. Furthermore, the metamaterial absorber also shows sensing properties for analytes with different refractive indices or thicknesses. This work provides a new choice for the design of high-Q dual-band terahertz metamaterial absorbers and their application to refractive index sensing.

Artificial electromagnetic metamaterial produces exotic resonance, extra ordinary characteristics not available in nature, but engineers can inherit the characteristics by controlling and manipulating their structure. This research primarily the design and realization of dual-band, polarization, and incident angle insensitive metamaterial absorber (MA) is presented. By controlling and manipulating the electromagnetic design shape, artificial structure, periodic array pattern, and dielectric layer thickness a significant way to realize high absorption. In order to achieve high absorption a new shape of an octagonal ring (OR), cross-wires (CWs), and cut-off circle (CC) artificial structure have been sensibly selected. The special characteristics of this structure produce a dual resonance and its bandwidth rises compared that of classical absorber. The proposed artificial structure operation suits the Ku-band application, but possible to enhance in $C$ -band. The numerical and experimental results display a dual-band 99.8% at 12.2 GHz and 99.9% at 15.5 GHz resonance is an excellent agreement in theory and numerical analysis. The effects of the constitutive property parameters: dielectric constant ( $\varepsilon $ ), magnetic permeability ( $\mu$ ), and negative refractive index ( $n$ ) are also investigated. The investigation of symmetric design structure shows the polarization-insensitivity and high absorption initiated even in changing the incident angle. Numerical and experimental results confirmed the destructive interference of multiple penetrations are responsible for the near-unity absorption. An excellent agreement in the absorptivity rates that touches near perfection which is prominent for solar cells, detection, and imaging applications.

Multi-mode tunable absorber based on graphene metamaterial

This paper presents a compact metamaterial absorber (MMA) based on double-layer ITO resistive film for suppression of electromagnetic interference (EMI) to improve signal quality and signal integrity (SI). In the design of MMA, based on the classic Jerusalem cross, circular and fan-shaped structures are combined to increase its equivalent capacitance to achieve frequency shift, and an equivalent circuit model is established to analyze the key factors affecting its absorption rate. At the same time, the full-wave simulation results show that more than 90&#x0025; absorption rate is achieved in the frequency range of 8.9 GHz-14.0 GHz, and the measurement results show that the absorption rate of MMA at different incident angles is consistent with the simulation. Moreover, microstrip antenna and differential microstrip transmission line are also designed as equivalent radiation sources. The co-simulation results show that the 3 m field radiation of the patch antenna is reduced by 10 <inline-formula> <tex-math notation="LaTeX">$dB\mu V$ </tex-math></inline-formula> at 10 GHz. At the same time, the eye height of the differential microstrip transmission line has increased from 68 mV to 340 mV, indicating that the signal integrity problem has been significantly improved. The size of the unit is only about 0.065 <inline-formula> <tex-math notation="LaTeX">$\lambda _{L}\times 0.065\,\,\lambda _{L}$ </tex-math></inline-formula> where <inline-formula> <tex-math notation="LaTeX">$\lambda _{L}$ </tex-math></inline-formula> is the wavelength of the lowest frequency, and the total thickness of the absorber is only 0.047 <inline-formula> <tex-math notation="LaTeX">$\lambda _{L}$ </tex-math></inline-formula>. The proposed MMA has the characteristics of miniaturization, ultra-wideband, high absorption rate, and polarization insensitivity, which provides a new suppression method for the radiation problem of gradually miniaturized electronic equipment.

Attaining broadband absorption with a simple-designed photonic absorber is still considered a complex and daunting task. The Hadamard matrix has been a well-known concept for designing quantum gates in quantum mechanics and computing. Despite a series of noteworthy works being done with regard to the design of metamaterial absorbers, very few works exist in literature where a quantum-inspired design has been employed to design a metamaterial-based photonic absorber. In this work, we have demonstrated a polarization-insensitive ultrathin and wideband metamaterial (MM) absorber based on the pattern distribution of the Hadamard matrix. Within the optical domain, the demonstrated MM absorber showcases absorption of over 91% for both transverse electric (TE) mode and transverse magnetic (TM) mode. To explore the angular dependence on absorption features of our Hadamard matrix meta-absorber (HMMA), both TE and TM modes have been used at numerous incident-angles. Finite integration technique has been utilized to simulate the demonstrated MM absorber design and validated using the interference theory model to assure the simulated data. Moreover, electric and magnetic field characteristics, current distributions, and a plethora of parametric sweeps have also been investigated in order to better understand the suggested HMMA absorption mechanism. Because of its wideband absorption and polarization-insensitive characteristic, this MM absorber based on the Hadamard matrix arrangement permits a variety of applications such as light detectors, optical-sensors, magnetic resonance imaging, plasmonic-sensors, and thermal imaging applications.

Recently, metamaterial absorber has attracted considerable attention because of a broad range potential application to electromagnetic stealth, electromagnetic detectors, and electromagnetic communication. In this paper, a multifunctional metamaterial absorber based on the electro-optic properties of grapheme is presented. The absorber was consisted of graphene microstructure, PDMS media layer and a single layer ITO film. These components made the absorber is optically transparent because all of the components are optically transparent. At first, we optimized the structural parameters to get a satisfactory absorption rate by the finite element method when the Fermi level of graphene was 0.5 eV. In this process, we found the resonance frequency of the absorber will have a red shift phenomenon with the increase of the dielectric layer thickness. When the dielectric layer thickness increases from 1.3 to 1.6 mm, the resonance frequency of the absorber is red-shifted from 84 to 67 GHz. And the absorption rate was almost unchanged in this process. Secondly, we mainly simulated the influence of Fermi level of graphene on the absorption characteristics of absorber by the same method when the dielectric layer thickness was 1.5 mm. The research indicated that the absorber possessed a amplitude tunable characteristic resulting from the change of grapheme Fermi level by altering the applied voltage. When the graphene Fermi level increased from 0 to 0.5 eV, the absorption rate of the absorber would from 50% to 97%. And the simulation results showed that the bandwidth achieves 8.2 GHz for the absorption beyond 90%, and the maximum absorption is up to 97% when the graphene Fermi level is 0.5 eV and the dielectric layer thickness was 1.5 mm. In addition, we proved the absorber is insensitive to the polarization and the wide-angle. The absorption rate would not change when we changed the polarization direction or changed the incident angle within 45°. Finally, we studied the distribution of the surface current and the electric field to explore the physical mechanism of electromagnetic wave absorption and amplitude adjustment by simulation method. In summary, the research indicated the absorber not only has the ultra-high electromagnetic wave absorptivity of traditional metamaterial absorbers, but also has the functions of optically transparency and amplitude adjustable. And it had potential application value in the fields of electromagnetic stealth, electromagnetic detectors, and electromagnetic communication.

We propose an absorber design method based on the equivalent circuit model and impedance matching theory, and verify its capability by designing an ultra-wideband fractal disc metamaterial absorber. In this paper, we calculated the absorption characteristics and electromagnetic field distribution by using the finite-difference time-domain method. The numerical results show that the absorption band of the absorber ranges from 300 nm to 6000 nm with an average absorption rate of 97.4%. The proposed absorber has a bandwidth of 5700 nm with an absorption rate greater than 90%, and the analysis of the arbitrary polarization angle shows that the absorption rate is insensitive to the polarization angle. For TM and TE waves with large angular oblique incidence, the average absorption still exceeds 85%. The wideband and high absorption is mainly attributed to surface plasmon resonance, localized surface plasmon resonance, slow-wave effects, and their interactions. An absorber with ultra-wide absorption band, high absorbance, insensitivity to polarization, and wide-angle absorption has potential applications in solar energy harvesting, optical communication, and invisibility devices.

In response to the current challenges of narrow absorption bandwidth, weak load-bearing capacity, and low design efficiency in absorbing structures, this study focuses on the reverse design of load-bearing broadband metamaterial absorber. A parameterized model of load-bearing metamaterial absorber was developed by integrating the composite sandwich structure with the electromagnetic resonant layers. The resonant layer was constructed using the combination of Vicsek-fractal and circular rings, with resistive films employed to broaden the absorption bandwidth. A deep learning-based forward prediction model was established to accurately predict the absorbance of the metamaterial absorber. The shapley additive explanations (SHAP) framework was utilized to analyze the forward prediction network, revealing the influence of various design parameters on the absorbance at center frequencies across the L to K band spectrum. Additionally, the group teaching optimization algorithm (GTOA) was introduced into the design process, leading to the development of an automated reverse design method for metamaterial absorber that can achieve specific design objectives. Using the GTOA-based reverse design method, a metamaterial absorber capable of effectively absorbing vertically incident electromagnetic waves within the 3–20 GHz frequency range was designed. The designed absorbing structure was fabricated, and its absorption performance was measured using the arch method. The measurement results were found to be in good agreement with the simulation data. The absorbing mechanism of the designed metamaterial absorber was analyzed based on the calculation of equivalent electromagnetic parameters and the electromagnetic resonance observed at the resonant frequency. It was determined that the primary absorbing effect is induced by electric resonance triggered by electromagnetic waves. The proposed metamaterial absorber can be applied to radar stealth design for military targets such as naval vessels. The research methodology and approach demonstrate significant generalizability and engineering applicability.