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This paper presents the design and analysis of a metamaterial-based wideband microwave absorber in the C- and X-band, comprised of lumped resistors, having thicknesses of the order of 0.05 λ mm. The structure was micro-machined on the FR-4 sheet in a periodically arranged array of 15 × 15 unit cells. These unit cells have a dimension of 12 × 12 mm each. The proposed absorber design presents excellent broadband absorption characteristics with relative bandwidth (RBW) of 85.05% covering a bandwidth of 8.02 GHz ranging from 5.42 to 13.44 GHz. The absorption mechanism has been explained with the help of characteristic impedance and surface current densities in the operating region. The designed absorber shows polarization angle independency and wide incidence angle stability for the incident microwaves. The results of the prototype are compared with the simulated results illustrating excellent compatibility with the simulation results. Absorber structure may find its potential use in camouflage applications during war times. [ABSTRACT FROM AUTHOR]

This research investigates the design of a nanostructured metamaterial absorber, featuring a core composition of nickel (Ni) metallic patch surrounded by an inductive grid. The proposed Ni-based nano-absorber exhibits a remarkable absorption bandwidth, spanning both visible and short-infrared wavelengths, with an impressive average absorption efficiency of 90% from 400 to 2000 nm. This study comprehensively examines the absorption characteristics of the nano-absorber across a range of incident angles and polarization states of optical light. Notably, the absorber demonstrates a polarization-insensitive response due to the inherent four-fold symmetry within its nanoresonator design and gives a sizeable absorption for various incident angles. Furthermore, the paper also investigates the surface electric field for a deeper understanding of its performance. Additionally, an equivalent circuit model has been developed for the proposed nanostructured absorber, and a comparison between the simulated and analytical absorption shows a close agreement between them. The simple and easily fabricable design of this absorber makes it a promising candidate for diverse applications, encompassing energy harvesting, solar cells, photodetectors, etc. Furthermore, the straightforward and versatile geometry of the proposed nano-absorber can be readily adapted for use in different operating frequency spectra, including microwave and terahertz ranges. [ABSTRACT FROM AUTHOR]

A flexible slotted metamaterial backed microstrip (SMBM) antenna operating at 2.45 GHz is proposed in this article for breast tumor detection. The substrate used is flexible optically transparent polydimethylsiloxane (PDMS) with 1-mm thickness, and copper is used for conducting layer. The SMBM antenna consists of partial ground and metasurface unit cells. It is noted that with the addition of metamaterial layers in the antenna the bandwidth, reflection co-efficient got improved and the specific absorption rate (SAR) value is reduced. Two different kinds of phantoms are arranged: one is a skin phantom and the other is a breast phantom; the antenna of the flat and flexible condition is placed on the phantoms and the analysis is observed. The detection of tumors can be observed by the variance in the value of E-Field, H-Field, and J-Surf between the phantom has a tumor and no tumor. A notable amount of difference is obtained which represents the existence of a tumor. The antenna has the SAR value, which is less than 1.6 W/kg as per the guidance of Federal Communications Commission (FCC) standard. Alongside SAR, by utilizing metamaterial, the gain of the SMBM antenna is likewise improved and the efficiency of the SMBM is expanded with 67% (to 92%) by the consideration of metamaterial construction. The results of the fabricated antenna are analyzed, and comparisons are made with the simulated antenna. [ABSTRACT FROM AUTHOR]

The unique ability to absorb electromagnetic radiation by metamaterial absorbers has garnered significant attention in recent periods. The proposed simulation study shows a new SRR-based metamaterial absorber design which has potential applications in biological sensing operating in the terahertz range. The proposed design incorporates four identical square ring resonators (SRR) made from Tungsten placed on top of a dielectric layer that was made by Gallium Arsenide (GaAs) semiconductor. Both the layers are formed on a Silicon substrate. The sensing regime's high field confinement results in a unity perfect absorption (i.e.,100%) at 2.75 THz, with a large quality factor of 39. According to the findings, the proposed design exhibits exceptional sensitivity while modifying the refractive index (n) of the medium. As a result, the proposed device can serve as a biomedical sensor (refractive index (n) sensor) with a sensitivity of 60 THz/RIU and a figure of merit (FoM) of 20. The researchers verified the device with refractive index (n) values ranging from 1.34 to 1.39, which covers a broad range of biomedical blood samples, including cancerous cells. As a result, this sensor design can be employed for a variety of biomedical sensing applications. [ABSTRACT FROM AUTHOR]

A metamaterial resonating antenna design having a hexagonal patch is proposed for biosensing applications to work in triband resonating frequencies at 5.2GHz, 9.6GHz, and 18.5GHz. The hexagonal patch is built on a dielectric constant of 4.4 FR4 epoxy substrate with a loss tangent of 0.030. Two different antennas are designed and tested with conducting metallic patches bounded by split ring resonator (SRR) slots and closed ring resonator slots which are also hexagon-shaped. Each antenna is capable of resonating at different frequency bands with good wide band characteristics due to the presence of partial ground plane. The hex-SRR resonates at 1.9GHz and 3.1GHz and hexagonal-CRR resonates at 5.2GHz, 9.6GHz, and 18.5GHz frequency bands resulting in multiband resonance characteristics. The proposed antenna is also validated with the study of metamaterial property of hexagonal SRR at the resonant frequency of 5.2GHz hence resulting in a compact (20 × 20 × 1.6) m m 3 and more dominant design. Furthermore, the specific absorption rate (SAR) for the three-layer phantom model is confirmed, resulting in superior performance that is more appropriate for biosensing and on-body wearable devices. The testing is performed using an E5063A ENA vector network analyzer provided by Keysight Technologies. The measured and simulated results are very close, resulting in a better validation of the proposed work. [ABSTRACT FROM AUTHOR]

This article proposes a fourfold star petal–shaped nanostructure, as a broadband plasmonic metamaterial absorber applicable in the frequency band of 390 THz to 750 THz. In this range, it provides a median absorbance of over 96% regardless of all polarization angles. The proposed absorber also exhibits stable performance in both TE and TM modes. A sandwiched metal-dielectric-metal layer construction is used to form this metamaterial absorber. The upper and lower metal layers are made of ultra-thin chromium (Cr) 15 nm layers separated by a 55 nm SiO2 dielectric sheet. This absorber unit cell has a periodicity of 160 nm with a thickness of only 85 nm. The top layer is with a fourfold symmetrical arrangement, which contributes to polarization insensitivity. An analysis of absorption in TE and TM modes for several metals is also presented. This investigation shows that chromium (Cr) exhibits constant and maximum absorption across the whole visible spectrum. Furthermore, metamaterial parameter extraction, absorption study, field and current distribution, design steps, parametric variation, etc. are discussed. Due to its compact nature and high performance, the proposed structure may be a prospective contestant in energy harvesting for low-power devices, stealth technology in avionics, and biomedical sensors applications. [ABSTRACT FROM AUTHOR]

An ultra-thin terahertz (THz) perfect metamaterial (MM) absorber with multi-spectral characteristics is reported in this paper. The MM absorber has a compact geometry and is developed on a polyimide substrate supported by a silicon wafer. The conductive regions of the perfect MM absorber are created using copper. The MM absorber has a square lattice and the unit cell is patterned using concentric L-stubs connected to a central stub along one end of the L-sections. These structures are rotated and distributed along the four sides to obtain a polarization-independent absorber unit cell. The proposed absorber has six distinct frequency bands between 0.45 and 2.2 THz. The absorptivity in each of the frequency bands is greater than 90% with a peak absorption of 99% at 1 THz and 1.56 THz. The absorber is tested for angular independence and the performance is found stable up to 60°. Furthermore, the absorber as a material sensor is evaluated and the results are presented. The sensitivity of the sensor is estimated to be greater than 10.56 GHz/PU with a deviation of less than 3.12 GHz/μm. Thus, from the investigations presented, it is inferred that the proposed MM absorber meets the need for THz sensing, imaging and spectroscopy. [ABSTRACT FROM AUTHOR]

Numerical and theoretical studies were conducted on the plasmon induced transparency (PIT) of the symmetrical structure of Dirac semi-metal films (DSFS). The films have a parallel strip and split resonant ring structure. After analysing the surface current intensity and distribution, it was found that the electromagnetically induced transparency is as a result of destructive interference between these two structures, with the amplitude modulation depth of the frequency of the transmission window reaching as high as 99.09%. Moreover, by adjusting the Fermi level of the DSFS, the Fermi level changed from 50 to 90 meV, and the transmission window blue-shifted from 0.529 to 0.799 THz. The transmission peak frequency was found to have a linear relationship with the Fermi level. Similarly, the transmission phase and group delay under different Fermi levels was investigated. The positive group delay of the film reaches 7.026 ps, which provides a direction for new applications of terahertz, such as optical storage and slow optical devices. [ABSTRACT FROM AUTHOR]

In this paper, we investigate various sensor configurations via optical metamaterial nano-absorbers. These are designed by two disparate triangle shapes nanoparticles. By using the three-dimensional (3D) finite difference time domain (FDTD) method, we numerically examine the absorption and the reflection spectra, sensitivity, and figure of merit (FOM). The effective medium theory (EMT) is applied to investigate the simulation results. Based on the simulation consequences, the two-aligned triangles model has maximum sensitivity and FOM. In the proposed sensors, maximum sensitivity becomes 283 nm per refractive index (RI), whereas its FOM is 3.8 × 103 RI−1. By studying the absorption performance, the incident angle (0°–60°) insensitivity is confirmed. Also, to provide tunability, we investigate the sensor by vanadium dioxide (VO2) thin film. We have demonstrated an absorber comprising a thin film of VO2 that can be tuned the absorption bandwidth by varying the temperature. Because of the spectral features of the designed devices, one can use them to identify biological samples like human blood type and ethanol and water concentrations of some matters. [ABSTRACT FROM AUTHOR]

In this paper, on the basis of metamaterial, a simply single-layer and tunable reflective polarization converter has been numerically investigated, which is composed of vanadium dioxide film (VO2) component combined with two-corner-cut square patch cut by a slit and reflective ground layer. Calculated results obtained by the CST Microwave Studio show that in the frequency of 2.22–5.42 THz, high polarization conversion efficiency (polarization conversion ratio (PCR) above 90%) can be normally achieved at the temperature about 25 °C for both the linearly and circularly polarized wave incidence. At the same time, the cross-polarization converter can be analyzed and obtained from the view on qualitative variable of polarization azimuth angle (θ) and ellipticity (η). Moreover, a tunable polarization conversion property can be realized by the designed device with vanadium dioxide utilizing changing different conductivities. Even so, to be demonstrated, the physical mechanism of the merits of controllability and uniqueness has been discussed by the distributions of current densities and E-field map, respectively. According to the prior results, the designed metamaterial could be applied in the area of temperature-controlled sensing, THz wireless communication, tunable polarized devices. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a plasmonic ultrahigh narrowband perfect absorber, which realizes an absorption intensity of up to 99.99% in the near-infrared electromagnetic spectrum regime. Different dimensional effects on absorption properties are studied using computer simulation technology (CST) with finite element method (FEM) solver. For both transverse electric (TE) and magnetic (TM) polarization, the absorber shows high stability over a wide range of incident angles. This ultrahigh absorption is attributed to synergy effect of magnetic resonance and surface plasmon resonance. Furthermore, the sensitivity goes to 300 nm/RIU for various refractive indices of different analytes. Our proposed absorber working wavelength is very close to the communication window of information; therefore, except for remarkable sensing abilities, it can also be well utilized in optoelectronic applications like optical switching, amplifiers, and all-optical plasmonic modulators. [ABSTRACT FROM AUTHOR]

Diabetes is one of the biggest health problems in the world; in order to control blood in modern biological detection and analysis, most of them use the method of label determination to realize the detection. This method usually needs to modify and label the samples in advance. This pretreatment process is not only complex, time-consuming, and slow in response, but also has a great risk of damaging and polluting the samples to be tested, which seriously limits the detection accuracy [1-2]. In order to realize the real-time detection and analysis of biological targets without label, high precision, and high sensitivity, the design of liquid refractive index sensor based on terahertz metamaterials is carried out in this paper. Based on terahertz technology and artificial periodic structure design of metamaterials, a liquid refractive index sensor with high precision, high sensitivity, and high stability is successfully designed. Then, based on the equivalent medium theory, the absorption characteristics of the sensor are studied; it is proved that the sensor has excellent polarization-insensitive and wide-angle incident characteristics. It can complete the detection of biological targets in most polarization modes and electromagnetic wave environment with various incident angles, and maintain perfect absorption at the resonance frequency of the sensing structure. The displacement of the resonance absorption peak is 102 GHz, the displacement sensitivity is 51 GHz/RIU, and the detection accuracy is 0.0196 RIU/GHz, which can realize the detection of minimal refractive index change; the average absorption index is high, which is 99.98%, and the displacement of absorption peak has an excellent linear relationship with the change of refractive index, and the linear fitting degree is 98.788%. Through data analysis, it is found that the sensor structure also has a strong bandwidth and absorption stability, which has a certain practical application value in the detection and analysis of biological targets. It provides a new idea for the real-time detection and analysis of biological liquid analytes with no label, high precision, and high sensitivity. Finally, through the data analysis, the change law of the sensor absorption characteristics with different physical dimensions is revealed, which lays a theoretical foundation for the future sensor structure optimization and the improvement of sensing accuracy and sensitivity. [ABSTRACT FROM AUTHOR]

We proposed a dual-band polarization-insensitive metamaterial absorber consisting of merely the square metallic patch and a continuous metallic ground separated by a middle dielectric layer. Two resonance peaks derived from 'the fundamental resonance (with 97% absorbance) and the surface lattice resonance (with 99% absorbance) are realized. It is different from previous work that the dual-band response is obtained by combining two resonances of different sizes. Moreover, a first-order diffraction mode of grating predicts the resonance wavelength of the proposed absorber. The surface electromagnetic field distributions of the unit-cell structure reveal the physical origin of the dual-band absorption. Importantly, the first absorption peak results from surface lattice resonance with narrow line-width has large sensitivity perform and high-quality factor, which has significant potential in the application of the biosensors and monitoring. [ABSTRACT FROM AUTHOR]

A highly sensitive absorption-based sensor based on folded split-ring metamaterial graphene resonators (FSRMGRs) is designed, and its biomedical application in terahertz (THz) spectrum is investigated. The sensor has a nearly perfect absorption, with a spectral absorption coefficient of 99.75% at 4 THz and an average Q-factor of 13.76. The resonance peak frequency is sensitive to the refractive index (RI) of the test medium (analyte), and a fairly high sensitivity of 851 GHz/RIU has been obtained. The specifications of the sensor can be tuned by an external DC-bias voltage applied to the graphene layer. According to the obtained results, the developed absorber appears to be a good candidate bio-sensing applications. [ABSTRACT FROM AUTHOR]

A five-band polarization-insensitive perfect metamaterial absorber (PMA) is reported in this paper for THz detection and sensing applications. The proposed absorber is constructed using interconnected circular ring elements enclosed by a square loop. The ring elements are interconnected using short strip lines which increases the electrical length to offer resonance at the lower frequencies of the THz regime without increasing the electrical length. The proposed absorber has a footprint of 0.12 λeff × 0.12 λeff where λeff is the effective wavelength calculated at the lowest operating frequency. The absorber provides 92%, 84%, 90%, 100%, and 100% absorption at 0.24, 0.56, 0.65, 0.82, and 0.95 THz, respectively. The proposed structure offers structural symmetry, and hence, it is polarization-insensitive. The proposed five-band absorber has good angular stability consistent with many research works reported in the literature and has a small frequency ratio of 1:2.3:2.7:3.4:3.9. The proposed absorber can be used as a permittivity sensor and its sensitivity is estimated to vary from 5.8 GHz/permittivity unit (PU) to 23.56 GHz/PU. [ABSTRACT FROM AUTHOR]

The present paper is aimed at investigating application of planar metamaterial (MM) structures for effective EMI shielding and stealth capability in X-Band. Various MM structures using FR-4 substrate and copper conductors were conceived and designed followed by simulations carried out using CST MWS Suite software. As a first step, the designs were aimed at achieving extremely high absorption for normal incidence, polarisation independence and maintaining high absorption in wide-angle performance while keeping the requirement of light weight, flexibility and environmental ruggedness in mind for deployability on platforms to achieve effective stealth capability against radars and for other EMI shielding applications. Circularly symmetric, single layer Metamaterial Microwave Absorber (MMA) design over thin FR-4 substrate in spokes and wheel structural arrangement provided these desired features. The thin FR4 substrate of 0.6 mm provides the light weight and flexibility while absorbing the EM waves. Rotational symmetry of the spoke and cut-wheel design gives it polarisation independence and 4 ring planar array concept with rings scaled to different sizes in the same plane in the unit cell provided the increase in bandwidth. Reduction in received signal level of the echo is depicted by the S-parameter at the input port. Getting values of this S-parameter less than -60 dB at resonant frequency for MMAs is highly encouraging and is not reported much in literature. Enhancement of nearly 3-8 times in operating bandwidth was achieved by changing size of rings in each quadrant in the co-planar array having four resonant rings in each unit cell. [ABSTRACT FROM AUTHOR]

This study employed single symmetry split-ring resonator (SRR) to implement biosensor applications. The behavior of the applied mechanism was observed comprehensively by altering the substrate refractive index. Also, numerical functions were evaluated using CST microwave studio, while the Maxwell's equation was resolved by finite integration technique (FIT). Furthermore, impedance of SRR metamaterial tends to reduce by increasing the refractive index for both the substrate and initial substance. These conditions consequently influenced the permittivity and the permeability. However, permittivity was presented with a significant modification for separate refractive index values, but was not the case for permeability. Meanwhile, both properties obtained varying amplitudes under distinct refracted conditions. [ABSTRACT FROM AUTHOR]

In this paper, a graphene-based tunable multi-band terahertz absorber is proposed and numerically investigated. The proposed absorber can achieve perfect absorption within both sharp and ultra-broadband absorption spectra. This wide range of absorption is gathered through a unique combination of periodically cross- and square-shaped dielectrics sandwiched between two graphene sheets; the latter enables it to offer more absorption in comparison with the traditional single-layer graphene structures. The aforementioned top layer is mounted on a gold plate separated by a Topas layer with zero volume loss. Furthermore, in our proposed approach, we investigated the possibility of changing the shapes and sizes of the dielectric layers instead of the geometry of the graphene layers to alleviate the edge effects and manufacturing complications. In numerical simulations, parameters, such as graphene Fermi energy and the dimensions of the proposed dielectric layout, have been optimally tuned to reach perfect absorption. We have verified that the performance of our dielectric layout called fishnet, with two widely investigated dielectric layouts in the literature (namely, cross-shaped and frame-and-square). Our results demonstrate two absorption bands with near-unity absorbance at frequencies of 1.6–2.3 and 4.2–4.9 THz, with absorption efficiency of 98% in 1.96 and 4.62 THz, respectively. Moreover, a broadband absorption in the 7.77–9.78 THz is observed with an absorption efficiency of 99.6% that was attained in 8.44–9.11 THz. Finally, the versatility provided by the tunability of three operation bands of the absorber makes it a great candidate for integration into terahertz optoelectronic devices. [ABSTRACT FROM AUTHOR]

This paper mainly studies the influence of multilayer hyperbolic metamaterials (HMMs) with different structural parameters on the intensity of spontaneous radiation of quantum wells, thereby improving the coupling efficiency of incident electromagnetic waves and free electrons on metal nano-surfaces. In this paper, numerical simulations of visible light bands of 450–700 nm of Ag, Au, and Cu thin films are performed. The local field enhancements of multilayer HMMs with different shapes are compared, and it is found that circle Ag/Si multilayer HMMs have stronger field enhancement effects than other structures. At the same time, Purcell analysis was performed by changing various parameters of multilayer HMMs. It is found that the thickness of the metal/dielectric layer, the distance between the dipole and the HMMs, and the length of the multilayer HMMs change the intensity of the plasmon resonance radiation and have a great impact on the position of the resonance wavelength. [ABSTRACT FROM AUTHOR]

In this essay, a tunable metamaterial-based biosensor is proposed for simultaneous monitoring of blood components including cells, plasma, water, thrombus, and urine components as well as glucose, albumin, and urea. The proposed biosensor is based on optical sensors, and it provides real-time, label-free, and direct detection, small size, and cost-effectiveness that can be an alternative tool to other conventional methods. The influence of operating frequency, sample thickness, temperature, and radiation angle on the performance of the sensor is investigated by the finite element method (FEM). Numerical results show that the maximum sensitivity and figure of merit (FoM) in the high frequency are 500 (nm/RIU) and 2000, and for low frequency are 136 (µm/RIU) and 155, respectively. The footprint of the structure is 0.34 µm2, which is remarkably smaller than the other reported biosensing structures. The proposed biosensor has the potential to provide high sensitivity, high FoM, and a wide operating range for biomedical applications. [ABSTRACT FROM AUTHOR]

Acoustic metamaterials are introduced as the structures with the alternating elements possessing effective properties that can be tuned seeking for the dramatic control on wave propagation. Homogenization of the structure under consideration is needed aiming to calculate permittivity of metamaterial. We present theoretical outcomes studying an acoustic composite possessing negative effective parameters in the acoustic frequency range. An acoustic metamaterial with an the alternating nanowires arranged in a building block and embedded in a host material was investigated. Propagation of surface plasmon polaritons at the metamaterial interface was predicted. [ABSTRACT FROM AUTHOR]

Due to the advantage of improving the sensing performance, narrow-band metamaterial perfect absorbers (MPAs) have attracted much attention in the sensor field. Here, we propose an ultra-narrow-band infrared absorber (UNBIRA) based on localized surface plasmon resonance. The peak absorption of the UNBIRA exceeds 99% with the full width at half maximum (FWHM) of 1.94 nm and 6.32 nm for transverse electric (TE) wave and transverse magnetic (TM) wave in 1.5–1.8 μm. The corresponding Q-factors for TE wave and TM wave are 817 and 266, respectively. When used as an infrared refractive index sensor, the sensitivity of UNBIRA is as high as 1632.5 nm/RIU for TE wave and 1647.5 nm/RIU for TM wave. Accordingly, the figure of merits (FOMs) of 816.2/RIU for TE wave and 260.7/RIU for TM wave are achieved. This UNBIRA possesses a simple geometry structure and an excellent sensing performance, implying a great potential for application of ultra-narrow infrared sensing or detecting. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical study on the propagation of electromagnetic surface waves supported by the metamaterial-filled bi-layered graphene structure. The effective surface conductivity approach based upon the Kubo's formalism is used to model the atomically thick graphene layer, while the analytical modeling of the metamaterials used the framework of causality principle-based Kramers-Kroing relations. With respect to the index of refraction, the two configurations of metamaterials have been considered—i.e., double positive (DPS) and double negative (DNG). The impedance boundary conditions (IBCs) have been employed at the interface for the computation of characteristics equations of odd and even surface modes under DPS and DNG configurations. The numerical results regarding the dispersion relations, effective mode index, and phase speed for the odd and even modes of electromagnetic surface waves supported by each configuration of structure have been presented. Further, the influence of chemical potential and thickness of metamaterial filling in parallel graphene layers on the wave propagation characteristics has been analyzed. To check the accuracy of the numerical results, special conditions were employed, which converge to the published results. The proposed work may have potential applications in plasmonic based logic designs, renewable energy devices, THz surface wave guides, and near-field communication devices. [ABSTRACT FROM AUTHOR]

Three layers of periodic artificial metamaterial sensing structure (including the upper metal particles, intermediate dielectric layer, and the lower reflective layer) with ultra-narrow band absorption were designed. The resonance characteristics and sensing properties were analyzed by the finite difference time domain (FDTD) method. The effect of localized surface plasmon resonance (LSPR) was obviously observed at the resonance wavelength of 911 nm, and it achieves nearly perfect absorption of exceeding 98% with a full width at half maximum (FWHM) of 3.5 nm. In addition, a wavelength sensitivity of 542 nm/RIU with a figure of merit (FOM) of 155 was obtained in the refractive index (RI) range from 1.00 to 1.35, which has a wide range of applications. The results show that the proposed structure has high absorption and RI sensitivity, which is suitable for bioengineering and medical detection. [ABSTRACT FROM AUTHOR]

The characteristics of hybrid surface plasmon modes in a double-layer graphene cylindrical waveguide filled with metamaterials are theoretically investigated. The dispersion relation for different configurations of metamaterials (double positive (DPS)-graphene-double negative (DNG)-graphene-DPS and DNG-graphene-DPS-graphene-DNG) is derived by solving Maxwell's equations for cylindrical symmetry and implementing impedance boundary conditions at the interface. The Kubo formalism is used for the modeling of the electromagnetic response of graphene. The influence of the interlayer distance of graphene, chemical potential of graphene, and permittivity of interlayer metamaterials on the dispersion curve, effective mode index, propagation length, and phase velocity are presented. It is observed that the existence of double layers of graphene along with metamaterials provides better control and tuning of the propagation of the surface waves. The coupled surface plasmon polariton (SPP) and surface phonon polariton (SPhP) in the optical regime are observed due to the coupling of electromagnetic waves between graphene layers. The forward- and backward-propagating surface waves for the fundamental mode are studied for different waveguide configurations. The active trapping of light and tunable fast and ultraslow plasmon modes for both forward and backward propagation modes for the proposed design may enable the realization of potential optoelectronic applications, such as modulators, fast forward-wave amplifiers, frequency selectors, back wave contra couplers, thermal sensors, circular polarizers, slow light devices, infrared (IR) and molecular spectroscopy, on-chip buffers, communication switches, and energy devices. [ABSTRACT FROM AUTHOR]

We propose dynamically switchable multispectral plasmon-induced transparency (PIT) with high modulation depth in a three-dimensional metamaterial standing on a flexible substrate. The proposed metamaterial is composed of a pair of metal–insulator–metal (MIM) nano-cut-wires and a pair of insulator–metal–insulator (IMI) nano-cut-wires. Results show that two PIT windows can be achieved because of the near-field coupling between the dipole supported by the IMI nano-cut-wire and two quadrupoles supported by the MIM structures. These two PIT windows can be blue-shifted or even flipped over by stretching the substrate along one direction, or be switched off by stretching along the other direction. A classical coupled oscillator model is developed to quantitatively describe and explain these results. We expect this work will find promising applications in multispectral sensors, slow light devices and nonlinear optical devices. [ABSTRACT FROM AUTHOR]

In this paper, an equivalent circuit model of swastika-like structure metamaterial is investigated. Mutual inductance between adjacent swastikas ring arrays is taken into consideration in the proposed equivalent circuit model. The analytical expression for calculating the effective permeability of the windmill structure is derived. By the derived expressions, the physical mechanisms of the magnetic resonance frequency versus structural parameters are well explained. Based on the equivalent circuit model, some strategies for the fast and efficient optimization metamaterial structures can be used to achieve a better target performance in the future. [ABSTRACT FROM AUTHOR]

Flat nanophotonic devices hold a great potential to process diffractive optical information within ultra-thin submicron thickness. In particular, optical filtering of transmissive angular spectrum in the free space is an essential functionality in diffractive optics. Here, we propose a novel configuration and theoretical study of an ultrathin transmissive angular filtering metamaterial for the first time to the best of our knowledge. Based on the adiabatically tapered plasmonic waveguide metamaterial in the visible regime, full color angle-selective transmission is achieved near the optic axis including the representative blue (473 nm), green (532 nm), and red (633 nm) colors. By providing further analysis on bandwidth extension, we envision that the proposed flat angular filtering mechanism in the visible range promises practical value and potential for a variety of metamaterial-assisted compact diffractive imaging and sensing applications such as augmented or virtual reality displays and biomedical optical sensors. [ABSTRACT FROM AUTHOR]

We present enhancement of operational bandwidths of planar terahertz metasurfaces by incorporating a complex unit cell that consists of a pair of concentric ring resonators. The inner resonator is a closed ring, while the outer resonator contains a pair of split gaps introduced symmetrically into the two opposite arms. The enhancement of the bandwidth is attributed to the spectral overlapping of the resonant responses arising from both the resonators. A total of five metasurface samples (MM1 to MM5) have been designed, fabricated, and characterized using terahertz time domain spectroscopy (THz-TDS). Resonance broadening along with the blue shifting of higher order resonance mode is being observed while introducing the split gaps in the outer ring and increasing the split gap length (MM1 to MM5) successively. We have further performed detailed numerical investigations in order to explain the experimental observations which support the experimental results. Such metasurfaces can pave the way to realize versatile photonic applications including broadband modulators and band stop filters in the comparatively lesser explored yet technologically relevant terahertz region. [ABSTRACT FROM AUTHOR]

A metamaterial-based absorber with metal–dielectric–metal (MDM) structure design strategy is proposed and verified in terahertz the band. An absorption peak (amplitude is 92%) is obtained at the resonance frequency point 4.2 THz. Simulation results show that this absorption peak originates from the resonance of localized surface plasmon modes. The measured FWHM of this absorption peak is 0.07 THz, and the quality factor Q is 60. In the first sets of experiments, the lattice constant P is reduced from 8 to 6 μm, which leads to this absorption amplitude enhance from 92 to 97.4%, and the resonance frequency point move from 4.2 to 4.08 THz. Similarly, when the diameter D is increased in the second sets of experiments, the absorption amplitude is also enhanced. In the third set of experiments, samples are covered with different liquid layers (acetonitrile, acetone, methanol, or benzene layers). Four measured maximum absorption values are achieved: 97%, 98%, 99%, and 99.4%, respectively. The resonance frequency point is also moved to lower frequency point. The feasibility of this absorber for liquid refractive index sensing is proven. In the fourth groups of experiments, samples are covered with an ethanol layer or a chloroform layer; the absorption peaks are both reduced and moved to higher frequency points with the measured temperature increasing. The feasibility of this absorber for temperature sensing is also verified. [ABSTRACT FROM AUTHOR]

In this paper, a non-structured graphene sheet loaded with a sinusoidal-patterned dielectric is introduced as an ultra-wideband metamaterial absorber in terahertz regime. Regardless of conventional structures with multilayered-graphene, a single layer sheet of non-structured graphene is used whereas the proposed structure benefits from dielectric width modulation and cavity method in order to excite continuous graphene plasmon resonances. The structure comprises four layers that two Fabry-Perot cavity mirrors are constructed by upper sinusoidal-patterned dielectric and a gold film. Full wave simulation results demonstrate that a broadband over 90% absorption with absolute bandwidth of 6.58 THz and central frequency of 3.97 THz is achieved under normal TE/TM incident plane wave. The designed structure yields 166% relative bandwidth. According to the symmetric configuration, the absorption spectra of mentioned polarizations are thoroughly close to each other resulting to a polarization insensitive structure. The stability of bandwidth and absorbance of the structure versus angle of incidence, θ, up to 35°/65° for TM/TE polarizations, respectively, and azimuth angle, φ, shows an interesting capability for utilization as detectors and sensors. The simple geometry of utilized graphene layer results in easy fabrication. The designed structure has wideband absorption in THz regime. Moreover, it is more compact than conventional broadband THz absorbers. [ABSTRACT FROM AUTHOR]

A broadband nanostructure metamaterial absorber (MA) based on tri-layer metallic-optical-thin film molded shape is proposed for visible spectrum solar energy scavenging. This MA is investigated for photon mobility to achieve significant photon conversion and absorption to integrate into solar cell technology, IoT components, or energy harvesting. Design and analysis of the proposed MA were performed using the "Yee's Finite-Difference Time-Domain (FDTD)" method based on commercially available CST microwave studio simulation software. Numerical computational tools depict an absorptivity of higher than 80%, which covered nearly the visible region 430~627 THz. This significant absorptivity can be maintained with both transverse electric and transverse magnetic polarizations. Furthermore, molded shape with two-dimensional split and nano-square window expedites the unit cell to exhibit single negative (SNG) metamaterial characteristics and photon conversion acceleration. Compared with related previously reported broadband absorbers, the proposed MA has promising application, in conventional solar cell efficiency improvement and emitter. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel gravity-tailored absorber to achieve two different absorption peaks at two different frequencies, whose improvement is based on the traditional sandwich structure. It is unusual that two dug grooves inside are filled with the liquid dielectrics. Since existing the gravity field, rotating this absorber in the xy plane will make the absorption peak change. In addition, this gravity-tailored absorber has a good stability of the incidence angle. The discussion of the power flow, the electric field, and structure parameters are also given to explain the physical mechanism. Compared with the existing manners of regulation, this regulation of presented absorber might be more convenient to achieve. [ABSTRACT FROM AUTHOR]