Metamaterial Absorber Structure Research Articles

Aluminum Nitride Thin Film Pyroelectric Detector Based on Metamaterial Absorber

Highly integrated pyroelectric detectors have been widely used in infrared spectrometers and gas detection. Aluminum nitride(AlN) has excellent compatibility with CMOS processes and is often used to fabricate piezoelectric and optoelectronic devices with superior performance. This study proposes a pyroelectric detector with AlN thin film as the sensitive element and integrated metamaterial absorber. Magnetron sputtering technology was used to prepare the AlN thin film as the sensitive element. To achieve narrowband specific absorption subsequently, a three-layer metamaterial absorber structure was designed and simulated. Preliminary processing of AlN pyroelectric detectors was performed based on MEMS technology. The designed narrowband absorbing structure exhibits near unity specific absorption, with a quality factor of 17.75. This study preliminarily verifies the application potential of AlN thin films in mid-infrared pyroelectric sensors, and realizes narrowband absorption through metamaterial structures, laying the foundation for the development of mid-infrared gas detection sensors.

A Wideband DNG Metamaterial Absorber with WS-Shaped Split Ring Resonator for X- and Ku- Frequency Band Applications

A novel compact microwave metamaterial absorber structure with a wide bandwidth is proposed. The absorber structure is designed on an FR4 substrate with a 2.4 mm thickness. The metamaterial absorber unit cell design consists of a combination of W and S-shaped structures in which splits are incorporated to have the effect of a split ring resonator. The proposed unit cell structure is designed to have a wide absorption band, which includes the X and Ku frequency bands. The optimized dimension of the unit cell is 0.071 λ 0 × 0.71 λ 0 where λ 0 is the wavelength of the center frequency of the absorption band. The WS-shaped structures are oriented to absorb TE and TM waves for a wide range of polarization angles. The simulation results of the unit cell have shown absorption above 95% from 10.48 to 13.28 GHz. In addition, the absorber has an efficiency above 92% for incidence angles from 0° to 60° for fixed polarization. The unit cell structure and array are fabricated, and measurements are performed. The simulation and measured results have shown good agreement. The proposed metamaterial can be used in defense and radar surveillance applications.

Analysis and characterization of structural, dielectric and magnetic properties of MgxCo(0.90−x)Zn0.10Fe2O4 nanoparticles based flexible metamaterial absorber for wireless communication

The anisotropic flexible metamaterial absorber (FMA) structure comprises a resonating layer, a ferrite-based flexible substrate layer, and a back layer. The sol-gel method is used to prepare the ferrite-based nanomaterial for enhancing absorbability. The solution prepared material is according to the formula of MgxCo(0.90−x)Zn0.10Fe2O4 and specified as X25, X50, X75 for X = 25%, 50%, and 75%, respectively. Then the proposed ferrites materials are characterized by XRD, and FESEM, respectively. Moreover, the magnetic and dielectric properties of the proposed MgxCo(0.90−x)Zn0.10Fe2O4 ferrites samples were explored for microwave applications. The dielectric constants and loss tangents of the fabricated, flexible substrates are measured at a frequency range of 3–7 GHz using the DAK 3.5. The computed relative permittivity values are 2.95 for X25, 3.55 for X50, and 4.05 for X75, respectively, while the loss tangents values are 0.00295 for X25, 0.00495 for X50, and 0.00695 for X75. Whereas the permeability and magnetic loss tangent values varied from 0.875 to 1.00 and 0.00225–0.00585, respectively. Finally, the resonators of the absorber consist of a Y-style shape, square-shaped metallic plate resonator, square ring resonator (SRR), and cross-liked shape. The proposed flexible metamaterial absorber (FMA) structure is developed on MgxCo(0.90−x)Zn0.10Fe2O4 nanomaterial-based flexible substrate with dimensions of 0.110λ x 0.110λ x 0.017λ to validate the design experimentally. The electrical dimension is calculated at a 5.5 GHz resonance frequency. The simulated results from the CST Microwave Studio simulator reveal that absorption peaks at 5.5 GHz with a 99.99% absorption that includes the C band frequency that can be used in satellite applications. The proposed FMA structure achieved a 60° incident angle response for TE and TM modes. The structure has superiority with compact dimensions, lightweight, and flexibility and can be used for C band wireless communications.

Triple-Band Square Split-Ring Resonator Metamaterial Absorber Design with High Effective Medium Ratio for 5G Sub-6 GHz Applications

This article proposes a square split-ring resonator (SSRR) metamaterial absorber (MMA) for sub-6 GHz application. The unit cell of the MMA was designed and fabricated on commercially available low-cost FR-4 substrate material with a dielectric constant o 4.3. The higher effective medium ratio (EMR) of the designed unit cell shows the compactness of the MMA. The dimension of the unit cell is 9.5 × 9.5 × 1.6 mm3, which consists of two split rings and two arms with outer SSRR. The proposed MMA operates at 2.5 GHz, 4.9 GHz, and 6 GHz frequency bands with a 90% absorption peak and shows a single negative metamaterial property. The E-field, H-field, and surface current are also explored in support of absorption analysis. Moreover, the equivalent circuit model of the proposed MMA is modelled and simulated to validate the resonance behavior of the MMA structure. Finally, the proposed MMA can be used for the specific frequency bands of 5G applications such as signal absorption, crowdsensing, SAR reduction, etc.

Ultra-broadband near-perfect metamaterial absorber for photovoltaic applications.

An ingenious double-grating metamaterial-based ultrathin-broadband absorber consisting of AlGaAs-Ge-GaAs on a titanium film operating in the visible to infrared wavelength was designed in this work. This structure is capable of overcoming the Shockley-Queisser (SQ) limit and the tunneling junction effect of tandem solar cells. Our comprehensive study revealed the structure's absorption mechanism using the finite-difference time-domain (FDTD) technique, which exhibited excellent short-circuit current density and high absorption. Our proposed ultrathin structure of 410 nm thickness provided a high average absorption of 82.2% and 99.7% under unpolarized and TM-polarized light for a wavelength range of 450-2000 nm, respectively. Additionally, we observed high incidence angle tolerability under the plane wave and thermal stability over time for our proposed grating structure. The performance analysis of our proposed structure as an absorber layer of a solar cell revealed its high power conversion efficiency (PCE) of 31.7% with an excellent short-circuit current density of 47.1 mA cm-2 for AM 1.5 G solar irradiance. The double-grating metamaterial absorber structure has enormous potential for diverse applications such as solar harvesting, thermoelectric generation, and photodetection.

Remote Water Salinity Sensor Using Metamaterial Perfect Absorber

Controlling water salinity plays a key role in farming efficiency. Current sensors are mostly expensive and need regular maintenance. In addition, they require electrical connections or extra power supply that leads to difficult and costly implementation in remote-sensing scenarios. In this article, an accurate and low-profile sensor is developed using a metamaterial perfect absorber (MPA) structure. The proposed sensor works based on the level and frequency of the absorbed signals. Hence, there is no need for electrical connections, which enables remote-sensing applications. Square-shaped channels have been created in a regular FR-4 substrate to facilitate sensing of water salinity levels. A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7 \times 7$ </tex-math></inline-formula> array with a total size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$140 \,\,\text {mm} \times 160 \,\,\text {mm}$ </tex-math></inline-formula> has been fabricated that shows a resolution of 10 MHz per percentage of water salinity. The absorption frequency shifts from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f=3.12$ </tex-math></inline-formula> to 3.59 GHz for salinity level from 0% to 50%. A strong correlation between measurement and simulation results validates the design procedure.

Quad-band polarization sensitive terahertz metamaterial absorber using Gemini-shaped structure

In this article, we design a metamaterial absorber (MMA) to provide quad-band absorption characteristics in terahertz range. The proposed MMA structure comprises of a Gemini-shaped resonator, graphene, SiO2 and metallic plane demonstrating multiple peaks at 1.29, 3.32, 3.85, and 4.56 THz with absorptivities greater than 90%. The absorption mechanism can be attributed to the high-order resonances analyzed by the electric field distribution. Further, simulated results are verified using equivalent circuit model and the obtained results are in well accordance with the simulated results. The proposed absorber is further analyzed with various polarization angles suggesting that absorber is polarization sensitive due to its symmetrical shape of the resonator. The compactness and thickness of the proposed design is 0.207λ and 0.047λ, respectively, which is better than earlier reported absorbers. The Gemini shaped absorber can be utilized in various fields including sensing, detection and imaging.

Tunability in Graphene Based Metamaterial Absorber Structures in Mid-Infrared Region

Tunable conductivity of graphene, makes it a promising material for metamaterials. There are various graphene tunable metamaterial absorbers in the mid-infrared region, whose absorption spectrum can be dynamically tuned by varying the Fermi potential of graphene. However, graphene absorbers working in the low mid-infrared region (4–7 μm) has limited tuning. In this work, the spectral tuning efficiency of a graphene based metal disc pattern and a graphene ribbon pattern metamaterial absorber is studied using FDTD simulation. The tunability in absorption spectrum achieved by metal disc absorber is 2–4%, which increased to 5–20% for graphene ribbon absorber with more than 85% absorption rate. Thus, the graphene pattern absorber significantly improves the tunability and provides broad tuning in 4–7 μm wavelength range. However, the graphene ribbon absorber is polarization dependent due to its non-symmetric shape. Hence, a new type of nano square hole (NSH) graphene absorber is proposed, which can easily be externally biased and provide polarization independent absorption. The NSH graphene absorber has wide tunability of 5–20% and high absorption rate of 85% similar to the graphene ribbon absorber. These results are very helpful to design tunable sensors and multispectral devices for gas sensor and biosensor applications.

Design of 2.5D Miniaturized Broadband Absorber for Ultrahigh-Frequency Band

A broadband metamaterial absorber (MA) structure for Ultrahigh-Frequency (UHF) band was proposed, and the miniaturization of the unit was realized by combining the method of bending metal wires and loading metal vias. The size of the unit cell is 0.040 λL × 0.040 λL × 0.075 λL (λL is the wavelength corresponding to the lowest frequency of 0.5 GHz). The simulation results show that the bandwidth of the MA is from 0.50 GHz to 1.33 GHz, and the relative bandwidth is 90.7%. Polarization insensitivity of the MA was realized through assembling a 2 × 2 orthogonal array. TE and TM polarizations maintain more than 80% of the absorptance in the range of 40° at oblique incidence. The consistency of full-wave simulation, circuit simulation and measured results is high, which verifies the broadband absorption characteristics of the proposed MA.

Polarization Independent Metamaterial Absorber with Anti-Reflection Coating Nanoarchitectonics for Visible and Infrared Window Applications.

The visible and infrared wavelengths are the most frequently used electromagnetic (EM) waves in the frequency spectrum; able to penetrate the atmosphere and reach Earth’s surface. These wavelengths have attracted much attention in solar energy harvesting; thermography; and infrared imaging applications for the detection of electrical failures; faults; or thermal leakage hot spots and inspection of tapped live energized components. This paper presents a numerical analysis of a compact cubic cross-shaped four-layer metamaterial absorber (MA) structure by using a simple metal-dielectric-metal-dielectric configuration for wideband visible and infrared applications. The proposed MA achieved above 80% absorption in both visible and near-infrared regions of the spectrum from 350 to 1250 nm wavelength with an overall unit cell size of 0.57λ × 0.57λ × 0.59λ. The SiO2 based anti-reflection coating of sandwiched tungsten facilitates to achieve the wide high absorption bandwidth. The perceptible novelty of the proposed metamaterial is to achieve an average absorptivity of 95.3% for both visible and infrared wavelengths with a maximum absorptivity of 98% from 400 nm to 900 nm. Furthermore, the proposed structure provides polarization insensitivity with a higher oblique incidence angle tolerance up to 45°.

Graphene-Based Plasmonic Metamaterial Perfect Absorber for Biosensing Applications

Graphene as a mono-atomic sheet has recently grabbed attention as a material with enormous properties. It has also been examined for enhancing absorbance in the current plasmonic structure. This has led to an increment in the sensitivity of the plasmonic sensors. In this paper, we present theoretical investigation of the novel graphene-based plasmonic metamaterial perfect absorber for biosensing applications. The simulation study performs the analysis of the novel plasmonic metamaterial absorber structure by adding coatings of graphene sheets. Each sheet of graphene enhances absorbance of the structure. In this study, we demonstrate three layers of graphene sheets lead to perfect absorbance (100%) for multiple bands in the visible and near-infrared regions. Furthermore, we also computed the sensitivity of the graphene-based proposed structure by varying the refractive index (RI) of the sensing region from 1.33–1.36 with RI change of 0.01. Proposed fabrication steps for realization of the device are also discussed.

Rapid customized design of a conformal optical transparent metamaterial absorber based on the circuit analog optimization method.

In this paper, a conformal optical transparent metamaterial absorber (COTMA) is proposed based on the circuit analog optimization method (CAOM), which can effectively enhance the optimization speed in the metamaterial absorber structure design by quantifying the equivalent circuit parameters. The operating frequency band can be customized at any band through CAOM, such as microwave, terahertz, and near-infrared frequencies. Here, a five-square-patch structure absorber with transparency and flexible properties is achieved. The simulated and measured incident electromagnetic (EM) wave absorptions of COTMA can reach above 90% in 15.77 - 38.69 GHz band. Meanwhile, COTMA exhibits excellent conformal EM absorption, a thinner substrate (0.078 wavelength at 15.77 GHz), lower structure complexity and polarization independence, and it can also be adapted to the EM absorption of different curved screens. This design is expected to have potential applications for wearable electronics, curved surface screens and OLED displays.

Concentric tubes silicon-based metamaterial structure for mid-IR broadband absorption

In this work, we are proposing a silicon (Si) based concentric tube broadband absorber. The proposed broadband absorber is composed of consecutive concentric tubes of intrinsic Si and doped-Si (D-Si) layers. The structure exhibits a broadband performance within a wide range of mid-IR wavelength spectrum extending from 3 to 7 µm with an absorption peak that varies between 0.88 and 0.97 in the case of S-polarized incident light. We report that light coupling to the proposed concentric tube metamaterial absorber structure over a broad wavelength range is a result of exhibiting multiple resonance mechanisms at different wavelengths. We further show that bulk plasmon polaritons are excited within the layers leading to this noticeable absorption. We demonstrate CMOS compatible metamaterial absorber that is less dependent on polarization and angle. Furthermore, this proposed design reveals new avenues to realize silicon-based broadband absorption for mid-IR photo detection and mid-IR thermal harvesting applications.

A Theoretical Terahertz Metamaterial Absorber Structure with a High Quality Factor Using Two Circular Ring Resonators for Biomedical Sensing

Metamaterial absorbers, on account of their inherent property of electromagnetic radiation absorption, have become a center of attraction for many researchers in recent times. This paper proposes a unique design of a terahertz metamaterial absorber that can be used to sense biomedical samples. The proposed design consists of two identical circular ring resonators (CRRs) made of aluminum on top of a gallium arsenide (GaAs) substrate. On account of its high field confinement in the sensing regime, a near-to-perfect absorption rate of 99.50% is achieved at a frequency of 2.64 THz, along with a large quality factor (Q-Factor) of 44. The design is highly sensitive to the refractive index changes in the encompassing medium. Hence, the proposed absorber can be used as a refractive index sensor exhibiting a reasonable sensitivity of 1500 GHz/RIU and a figure of merit (FoM) of 25. The refractive index range has been varied in the range of 1.34 to 1.39. As many biomedical samples, including cancerous cells, reside within this range, the proposed sensor can be used for biomedical sensing applications.

Angle of Incidence and Polarization Insensitive Ultra-Thin Ultra Wide-Band Metamaterial Absorber based on Novel Non-Linearity in Unit Cell Design

A new design of an ultra wide-band metamaterial absorber (MMA), with appreciable high absorptance insensitive to angle of incidence and polarization angle is presented in the manuscript. The MMA structure consists of three concentric rings with non-linear variation in the spacing and the thickness of the rings is controlled by a single parameter. The idea of utilizing nonlinear variation based unit cell resulted in high absorptance ultra wide-band frequency spectrum in X -band. The proposed MMA design is three layered structure. The metamaterial nature of the proposed device is explained by simulated values of Z eff( f ), μ eff( f ), ε eff( f ), and η eff( f ). The FWHM bandwidth of proposed MMA is 6.32 GHz (7.36 GHz-13.68 GHz). The fabricated MMA is ultra-thin with thickness of λo/15.3 at centre frequency 9.8 GHz. The experimental results show absorptance greater than 99% at 7.9 GHz and 11.7 GHz, covering entire X -band range makes this MMA appropriate for providing stealth technology for defense equipments by reducing radar cross section (RCS).

Multiband tunable perfect metamaterial absorber realized by different graphene patterns

In this paper, the absorption performance of a proposed metamaterial (MM) absorber based on a three-layer graphene structure working in the terahertz (THz) frequency band is studied. By using different types of combined graphene patterns, dual-band, tri-band, and quad-band absorption can be achieved. In the case of tri-band absorption, three absorption peaks with absorption rates of 99.7%, 99.9%, and 99.9% can be found at frequencies of 4.64 THz, 6.45 THz, and 9.71 THz, respectively. In addition, the proposed structure is polarization independent and has the absorption characteristic of wide incident angles. The frequency and the intensity of the absorption peaks can be adjusted by changing the chemical potential and the relaxation time of the graphene and the structural parameters. Therefore, we believe that the proposed graphene MM absorber structure provides flexible design ideas for a multibandwidth MM perfect absorber, and the proposed absorber also can be applied to subwavelength integrated sensors and optoelectronic devices in the terahertz range.

Optically transparent terahertz triple-band and dual-band metamaterial absorber

PurposeThe proposed metamaterial absorber (MMA) has the following advantages: first, the structure of the MMA consists of one planar metallic resonator, which presents a new design approach to obtain a multiband absorption response, rather than using multiple unit-cells in the one large unit cell or stacking different layers. Second, the simultaneous realization of triple-band and dual-band absorption (or bi-functional absorption) at five different frequencies can integrate the respective advantages of the triple functions of the triple-band MMA and double-band MMA, and therefore, the bi-functional MMA will find more application prospects than multiple-functional devices of triple-band and dual-band. Third, the authors simulated the three combinations of MMA here, which is indium tin oxide (ITO)-Polyimide-ITO, ITO-Teflon-ITO and ITO-polyethylene terephthalate (PET)-ITO for the same planar structure and achieve a high absorption rate. Finally, the proposed structure is polarization and angle independent in nature.Design/methodology/approachThis absorption device consists of the top circular resonator, the middle insulating SiO2 medium layer and the bottom metallic copper ground plane placed on a substrate. The conductivity of the copper metal is s = 5.8 × 107 s/m. As the transmission of the MMA structure is zero, the substrate materials can be selected randomly. Totally four combinations of terahertz MMA are designed and simulated here which are ITO- SiO2 –ITO, ITO-Polyimide-ITO, ITO-Teflon-ITO and ITO- PET-ITO for the same planar structure.FindingsCompared with previous MMAs, the proposed MMA has the following advantages: First, the structure of the MMA consists of one planar metallic resonator, which presents a new design approach to obtain a multiband absorption response, rather than using multiple unit-cells in the one large unit cell or stacking different layers. Second, the simultaneous realization of triple-band and dual-band absorption (or bi-functional absorption) at five different frequencies can integrate the respective advantages of the triple functions of the triple-band MMA and double-band MMA, and therefore, the bi-functional MMA will find more application prospects than multiple-functional devices of triple-band and dual-band. Third, the authors simulated the three combinations of MMA here, which is ITO-polyimide-ITO, ITO-Teflon-ITO and ITO- PET-ITO for the same planar structure and achieve a high absorption rate. Finally, the proposed structure is polarization and angle independent in nature.Originality/valueFirst, the structure of the MMA consists of one planar metallic resonator, which presents a new design approach to obtain a multiband absorption response, rather than using multiple unit-cells in the one large unit cell or stacking different layers. Second, the simultaneous realization of triple-band and dual-band absorption (or bi-functional absorption) at five different frequencies can integrate the respective advantages of the triple functions of the triple-band MMA and double-band MMA, and therefore, the bi-functional MMA will find more application prospects than multiple-functional devices of triple-band and dual-band. Third, the authors simulated the three combinations of MMA here, which is ITO-polyimide-ITO, ITO-Teflon-ITO and ITO-PET-ITO for the same planar structure and achieve a high absorption rate. Finally, the proposed structure is polarization and angle independent in nature.

Multi-band (9,4) chiral single-walled carbon nanotube based metamaterial absorber for solar cells

A novel multiband (9,4) polarization insensitive metamaterial (MTM) absorber structure based on the vertical nanotubes composited with the silicon dielectric material is proposed in this research. Multiband polarization insensitivity is achieved through the unique geometrical configuration of the design, which provides almost unity absorption in the visible and ultraviolet regions from 300 THz to 1000 THz. The proposed design is selected due to the simplicity of the construction, ease of fabrication and the ability to absorb almost perfectly under changing geometrical parameters. The electromagnetic response of the design is simulated for four maximum absorption peaks at 394.3 THz, 514.9 THz, 632.8 THz, and 773.2 THz with the corresponding absorption rates of 99.8%, 98.35%, 96.66%, and 80.60%, respectively. The sensitivity of the polarization angle of the MTM absorber has also been investigated, which verifies that the current design is insensitive to the different polarization angles. The flexibility of the proposed design has also been investigated by altering the geometrical components, materials, and the dimensions, and it is confirmed that the proposed MTM absorber design provides high absorption rates under all considered circumstances. The MTM absorber designs is found to be capable of improving the efficiency of the solar cell. The implementation of these MTM absorbers in the solar cells can significantly improve the absorption rate by reducing the reflection and transmission. MTM is validated by both prior art investigation and the different solver such as FEM and FIT. Results of interface theory model and simulations are compared against one another, which show good agreement yielding reliable and accurate estimations.

Multi-layered Graphene Silica-Based Tunable Absorber for Infrared Wavelength Based on Circuit Theory Approach

Graphene can be utilized as a tunable material for a wide range of infrared wavelength regions due to its tunable conductivity property. In this paper, we use Y-shaped silver material resonator placed over the top of multiple graphene silica-layered structures to realize the perfect absorption over the infrared wavelength region. We propose four different designs by placing the graphene sheet over silica. The absorption and reflectance performance of the structures have been explored for 1500- to 1600-nm wavelength range. The proposed design also explores the absorption tunability of the structure for the different values of graphene chemical potential. We have reported the negative impedance for the perfect absorption for proposed metamaterial absorber structures. All the metamaterial absorbers have reported 99% of its absorption peaks in the infrared wavelength region. These designs can be used as a tunable absorber for narrowband and wideband applications. The proposed designs will become the basic building block of large photonics design which will be applicable for polariser, sensor, and solar applications.

Ink-jet printed metamaterial microwave absorber using reactive inks

Ink-jet printing technology is one of the most promising printing techniques enabling fabrication of metamaterial absorber (MMA) in a one-step and direct process. In this study and for the first time the metamaterial microwave absorbing structure is proposed using water-based reactive inks and ink-jet printing technique. The MMA based on Unite-Ring-Swastika Cross Resonator (URSCR) is printed on a copy paper. The printed MMA structure is flexible and includes an ink-jet printed silver unit cell, a dielectric layer (copy paper), and an ink-jet printed silver ground plate was formed underneath the substrate. The working principles of the unit cell of MMA and its parametric simulations are evaluated. The performance of MMA with the full-wave simulation at the microwave frequency band is assessed as well, showing great agreement with the results obtained from the measurements. The experimental results indicate that the amount of measured flexible MMA absorption based on URSCR at resonance frequency on a planar surface at 0° to 40° incident angles and on a cylindrical surface at a 0° incident angle stays over 99%.