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A polarization independent conformal wideband metamaterial absorber has been proposed in this study. The proposed absorber unit cell consists of a circle and a slotted sector, loaded with four lumped resistors between them to improve the absorption bandwidth. Measured and simulated results exhibit more than 90% absorption in the frequency band from 3.90 GHz to 10.5 GHz under the normal incidence angle, and the fractional bandwidth is 91.6%. The proposed absorber is polarization independent due to the symmetrical nature. The absorber unit cell is compact in configuration with a unit cell size of 0.16 λo × 0.16 λo, where λo is the wavelength at 3.9 GHz and the substrate thickness is 0.098 λo. Once the proposed absorber is wrapped on the cylindrical surface, it shows good absorptivity in the absorption frequency band. The effects of many designed parameters have been studied to understand the performance of the wideband absorber. To recognize the absorption phenomenon of the absorber, normalized impedance, electric field distribution, and surface current density have been demonstrated. Finally, the proposed conformal absorber fabricated and measured the absorption for flat and curved surfaces, which exhibits good agreement between the simulated and the experimental results. [ABSTRACT FROM AUTHOR]

We present the design of a new type of irregular metamaterial structure that can achieve ultra-wideband absorption. The structure is created using 3D-printing to create a shell and contains multiple layers of water. The structure can achieve absorption levels greater than 0.9 in the 6.8–21.0 GHz range, with a relative bandwidth of 101.93%. The absorber also works in a wide range of incidence angles with different modes and is polarization insensitive. Measurement results obtained from a microwave experiment coincide well with the simulation results. The proposed metamaterial could be broadly applied in various civilian and military products in the future. [ABSTRACT FROM AUTHOR]

Diversiform hybrid-polarization surface plasmon polaritons (HSPPs) at metamaterial (MM)-dielectric interfaces have initially been predicted by theoretical considerations based on dispersion equations. Here, we discuss hybrid HSPPs at the interface between (1) transparent conducting oxide (TCO)/dielectric MMs and TCO or (2) MMs and dielectrics through a detailed numerical analysis based on a Drude-Lorentz model for the permittivity of the TCO-layer. We show that the introduction of a MM/TCO interface leads to a transformation of the traditional-like SPPs. As a consequence, the new types of surface waves are found, and we reveal the existence of a new type of surface wave which is closely related to the presence of the TCO layers in the MM structure. [ABSTRACT FROM AUTHOR]

The microwave-absorbing properties of a heterostructure consisting of an ordered monolayer of porous glassy carbon spheres were experimentally and theoretically investigated in the Ka-band (26-37GHz) frequency range. The electromagnetic response of such a "moth-eye"-like all-carbon metasurface at a normal incidence angle was modelled on the basis of long-wave approximation. Modelling parameters in the Ka-band were used to estimate and predict the absorption properties of monolayers in free space in the range 1-40 GHz. Experimental and theoretical results demonstrate that a metasurface based on porous glassy carbon spheres is an inert, lightweight, compact, and perfectly absorbing material for designing new effective microwave absorbers in various practically used frequency ranges. [ABSTRACT FROM AUTHOR]

Considering the Ohmic losses of graphene in the calculations and by obtaining exact dispersion relations of the modes, we theoretically study propagation and localization characteristics of Tamm surface plasmons supported by terminated graphene metamaterials. The metamaterials are composed of alternating layers of graphene and dielectric with subwavelength periods. We also examine the Tamm modes within the framework of long-wavelength approximation. It is shown that, in case the Ohmic losses of the graphene layers are taken into account, surface plasmons are not supported in a long-wavelength region, in which the graphene-dielectric multilayer structure behaves as a hyperbolic metamaterial. We prove that, when the metamaterial is truncated with air, by choosing sufficiently thick but still subwavelength dielectric layers, i.e., d = 300 nm, these surface waves will have a moderate propagation (localization) length that is comparable with those of a single layer of graphene. On the other hand, in case a miniaturized graphene metamaterial (10 < d(nm) < 100) is truncated by a thick cap layer (dcap = 5d) with εcap > εdielectric, it is possible to considerably improve the propagation and localization characteristics of the Tamm modes supported by the system within the 5.5-50 THz range of frequency, as compared to a single layer of graphene. [ABSTRACT FROM AUTHOR]

In this paper, we design a low-reflection coaxial tunable attenuator with a maximum attenuation of -50 dB by use of zero refractive index metamaterial. Almost no reflection is observed from input port of the proposed structure, due to the easily accessible impedance matching derived from the use of zero refractive index metamaterial. The relationship between attenuation and the air gap width can be well described by an equivalent circuit model. Interestingly, the ratio of input to output voltage is linearly related to the gap width due to the eliminated fringing capacitance by zero-refraction metamaterial, which makes it easy to achieve accurate calibration of the proposed attenuator. The low reflection and linear relationships enable the proposed attenuator to hold promising potential for practical applications. [ABSTRACT FROM AUTHOR]

This work introduces metallo-dielectric woven fabric as a metamaterial for phase-front manipulation. Dispersion diagram as well as effective medium parameters retrieved from reflection and transmission coefficients point out negative values of refractive index. By numerical simulations, it is evidenced that a pair of meandered metallic wires, arranged in a top to bottom configuration, can yield to a textile metamaterial with simultaneously negative permittivity and permeability. While the effective negative permittivity stems from the metallic grid arrangement, resonating current loop resulting from the top to bottom configuration of two meandered metallic wires in near proximity produces magnetic activity with negative permeability. By adjusting the distance between pairs of metallic wires, the electric plasma frequency can be shifted to overlap the magnetic resonance. Finally, it is shown that the woven metamaterial is insensitive to the incident angle up to around 60°. [ABSTRACT FROM AUTHOR]

In this paper, low-power and ultrafast all-optical tunable plasmon induced transparency in metal-dielectric-metal (MDM) waveguide side-coupled Fabry-Perot (FP) resonators system with nonlinear optical Kerr medium is investigated both analytically and numerically. High tunability in transparency window magnitude and phase responses is obtained when nonlinear optical Kerr material is embedded in the MDM waveguide. In order to reduce the pump intensity, traditional nonlinear optical Kerr material is replaced by graphene. A shift of 64 nm in the central wavelength of the transparency window is achieved when the FP resonators are covered with monolayer graphene with pump intensity increasing from 9.2 to 10 MW/cm2. An ultrafast response time of the order of 1 ps is reached because of ultrafast carrier relaxation dynamics of graphene. This work not only paves the way towards the realization of on-chip integrated nanophotonic devices but also opens the possibility of the construction of ultrahigh-speed information processing chips based on plasmonic circuits. [ABSTRACT FROM AUTHOR]

Metal-dielectric nanolaminates represent a class of hyperbolic metamaterials with uniaxial permittivity tensor. In this study, we critically compare permittivity extraction of nanolaminate samples using two techniques: polarized reflectometry vs. spectroscopic anisotropic ellipsometry. Both Au/MgF2 and Ag/MgF2 metal-dielectric stacks are examined. We demonstrate the applicability of the treatment of the multilayered material as a uniaxial medium and compare the derived optical parameters to those expected from the effective medium approximation. We also experimentally compare the effect of varying the material outer layer on the homogenization of the composite. Additionally, we introduce a simple empirical method of extracting the epsilon-near-zero point of the nanolaminates from normal incidence reflectance. The results of this study are useful in accurate determination of the hyperbolic material permittivity and in the ability to tune its optical properties. [ABSTRACT FROM AUTHOR]

Metamaterials are manmade structures that have attained considerable attention over the past 2 decades in the modern fields like cloaking, sensing, and imaging owing to their ability to harness electromagnetic fields. In this regard, we have inspected the dielectric properties of the hyperbolic metamaterials (HMM) made of metallic nanorods and dielectric medium at the infrared wavelength regime. The periodically arranged subwavelength-sized metallic nanorods embedded in the silicon dioxide ( SiO 2 ) substrate glass. The spacing between two adjacent nanorods is of subwavelength in size. Furthermore, effective permittivity of the metamaterial has been analyzed by employing the Maxwell Garnett effective medium theory. Moreover, different metallic nanorod inclusions (Au, W, Pt and Ti) were taken into account. Hyperbolic features of the metamaterial have been observed, and it is noticed that hyperbolic features merely depend on the type of metallic nanorods and their size. The observations reveal that the dielectric properties of the metamaterial can be tuned by altering the radii of the metallic nanorod. Apart from dispersion, reflection, transmission and absorption features of the HMM are taken into account. It is noticed that reflection, transmission and absorption of the HMM depend on the type of metallic nanorod and its dimension. Such HMMs structures with exotic dielectric features would be useful for sensing, filtering, and absorption applications. [ABSTRACT FROM AUTHOR]

This paper introduces a 340-GHz polarisation converter. The polarisation converter consists of a bilayer metamaterial, which is processed by the flexible thin film lithography method. Two-dimensional metamaterial offer such advantages over traditional quarter-wave-plates as compactness, low profile and simple fabrication process, but the insertion loss is comparably high. In order to lower the insertion loss, the 10-μm ultrathin polyimide substrate and a bilayer structure separated by a quarter wavelength air impedance match layer are adopted. After the horn antenna's far-field test by vector network analyser and the Gaussian beam test based on Terahertz time-domain spectroscopy (THz-TDS), the results show that in the band of 325-350 GHz, the transmission loss is less than 2 dB, and the axial ratio is less than 3 dB; besides, simulation and test insertion loss performance difference is less than 1 dB, which indicates that the method we adopt is effective. In addition, based on transmission line theory, we analyse its working principle and the influence from the fabrication error. [ABSTRACT FROM AUTHOR]

LiCoO2 powders are the popular active cathode material in lithium batteries, but their dielectric and microwave absorption properties were seldom reported. In this work, the LiCoO2 powders were synthesized by solid-state reaction. And in order to enhance their dielectric properties, influence of metal ions micro-dopant on the electromagnetic property of LiM0.94Co0.06O2 powders (M = Mg, Zn, Ni, Mn and Y) was investigated. The phase and composition were characterized. The dielectric properties and the microwave absorption properties were evaluated. Compared to dopant of Zn, Ni, Mn and Y ions, the results showed that both the real part (ε′) and imaginary part (ε″) of LiM0.94Co0.06O2/paraffin mixtures were obviously increased by doping Mg ions. One layer absorbent with 75 wt% LiMg0.06Co0.94O2 content of a thickness of 1.8 mm had the optimum microwave absorption properties. The lowest reflection loss was − 36.6 dB. The results indicated that LiCoO2 and LiM0.06Co0.94O2 powders would be a possible candidate for microwave absorption materials. [ABSTRACT FROM AUTHOR]

Abstract: "Herein, we consider the technologies of obtaining composite structures that can exhibit the properties of metamaterials, namely layered metal-dielectric (metal-polymer) structures and fish-net metal-polymeric structures. The dielectric and resonance properties of the synthesized structures are studied both theoretically and experimentally, and the excitation features of new types of quasi-non-diffraction plasmon-polaritons generated in them are established. Original methods and tools for characterizing the optical properties of the created composite structures (in particular, a differential polarization interferometer, a method and a device for detecting a negative refractive index) are proposed. Based on the developed and created metamaterials, a number of new devices are proposed and implemented, in particular, new configurations of flat lenses (so-called superlenses) of the near and far fields in the spectral range from ultraviolet to infrared radiation". [ABSTRACT FROM AUTHOR]

A dielectric metamaterial absorber has been proposed, which consists of fractal-like structure and conductive sheet. The fractal-like structure is made by the high permittivity dielectric and also is covered by the conductive sheet. Absorptivity of such a dielectric metamaterial absorber is 99.1%, which can be found at 10.196 GHz; meanwhile, the absorber is polarization insensitive. To enhance the bandwidth of absorber, a novel absorber also is proposed, whose bandwidth is 0.566 GHz, which ranges from 9.752 to 10.318 GHz, and relative bandwidth is 5.64%. The maximum absorptivity can reach to 99.8%, and the proposed absorber also is polarization insensitive. In the meantime, the absorber shows excellent performance which is incident angle insensitive; when the incident angle is increased to 70°, the absorptivity is larger than 75%. [ABSTRACT FROM AUTHOR]

In the visible spectral range, Mie resonance-based double negativity has still not been observed in all-dielectric metamaterials due to the lack of dielectrics with sufficiently high refractive indices. In this work, the dielectric materials containing nanospheres of gain-metal nanocomposites are proposed as double negative materials operating in the visible. They are embedded with two types of composite nanospheres: one contributes to the negative permeability via magnetic Mie resonance facilitated by gain-assisted high indices of composite nanospheres and the other one to the negative permittivity via plasmonic dipolar resonance in the same spectral range. The figure-of-merit of these materials reaches up to infinity or even can be negative, implying the gain, depending on the structural and material parameters. The proposed materials can find broad applications as loss-free negative index materials in the visible and near-infrared. [ABSTRACT FROM AUTHOR]

In this paper, a stacked structure composed of periodic arrays of one-dimensional thick slits embedded in a conventional dielectric medium is investigated in the subwavelength regime. Arrays of thick slits are known to support extraordinary transmission resonances. When periodically embedded in multilayered structures, they demonstrate band gap properties, which can produce flat passband regions in some structures, applicable to filter designs. In addition, by adjusting the parameters of the structures, they can be designed to create epsilon-near-zero and negative permittivity metamaterials. The analysis is carried out based on a simple and accurate analytical solution. The employed circuit model includes a transmission line corresponding to the slits, terminated by two surface admittances at the interfaces. The surface admittances assume the role of the diffractive modes and dominate the limitations of the usual analytical surface admittances obtained through heuristic approaches. A Π network of lumped elements equivalent to this circuit model is introduced in the present paper. This network helps to find the source of extraordinary resonances. Finally, the electromagnetic wave transmission through the stacked structure is studied and the effects of the thickness of the slits and dielectric slabs on the transmission spectra are analyzed. The results are compared to those obtained by full wave simulations, showing good agreement. [ABSTRACT FROM AUTHOR]

We propose a 3D metasurface structure with unsymmetrical metallic slices array. The tunable plasmon-induced transparency (PIT) effects and different electric field mode distributions could be realized by modulating the structure parameters and angle of incidence. The radiative and dark elements of the asymmetric metallic slices unit cell structure are analyzed. The transmission spectra and the electric fields distributions are studied by the finite element method (FEM). We demonstrate that PIT phenomena based on those metasurface array structures may have applications as tunable sensors and filters in nanophotonics and integrated optics. [ABSTRACT FROM AUTHOR]

A compact wideband coplanar waveguide (CPW)-fed antenna is designed for body implantable applications. The proposed antenna has an electrical dimension of only 0.42λ x 0.42λ x 0.0072λ at 2.3 GHz resonating frequency. Fractional bandwidth of 93.5% (1.35-3.5 GHz) is achieved with the low-profile antenna. To understand the extent of miniaturisation and bandwidth enhancement of the antenna, the characteristic modal analysis is performed. The wideband feature is achieved with the application of asymmetric complementary split-ring resonator structure through multiple mode excitations. Additional miniaturisation and impedance matching are obtained with a pair of asymmetrical arc-shaped annular ring slots within the main radiator. The substrate and radiator have been realised using silicon and gold due to their inherent property of excellent biocompatibility with the human body. Single layer, as well as multi-layers phantom model, was used to assess the performance of the antenna. Owing to the inherent wideband feature of the designed antenna, it is able to cover the desired band efficiently even after detuning in different phantom models. The designed antenna is tested in vitro with the development of proper muscle mimicking liquid and the measured results are found to be in good agreement with the simulated ones. [ABSTRACT FROM AUTHOR]

We present a comprehensive investigation of a continuously tunable metamaterial perfect absorber operating at terahertz frequencies. In particular, we investigate a three-layer absorber structure consisting of a layer of split ring resonators and a metallic ground plane, with a central layer consisting of a mechanically tunable air-spaced layer. The absorber was characterized using terahertz time-domain spectroscopy in reflection (at normal incidence) as a function of spacer thickness from 0 to 1000 μm. Our experimental measurements reveal the detailed evolution of the absorption bands as a function of spacing, in excellent agreement with analysis using interference theory and simulation. Our Fabry-Pérot-like structure provides an avenue for achieving massive tunability in metamaterial absorber devices. [ABSTRACT FROM AUTHOR]

Local electromagnetic field enhancement in resonant metamaterials is useful for efficient generation of nonlinear phenomena; however, the field enhancement is suppressed by losses of nonlinear elements in metamaterials. For overcoming this issue, we investigate the nonlinear response of an electromagnetically induced transparency-like metasurface loaded with gas as the nonlinear element. To induce nonlinearity in the gas associated with discharges, an electromagnetic wave with a modulated amplitude is incident on the metasurface. The measured waveform and spectrum of the transmitted electromagnetic wave, along with light emission from the discharge microplasma, reveal that frequency mixing can occur on the metasurface. The parameter dependence of the conversion efficiency of the frequency mixing phenomenon shows that the efficiency is determined almost entirely by the ratio of the duration of microplasma generation to the modulation period of the incident wave amplitude. This result implies that the frequency mixing is derived from a binary change in the transmittance of the metasurface caused by the generation and quenching of the microplasma. [ABSTRACT FROM AUTHOR]

Abstract: The development of ultrathin dielectrics for low power electronics operations, flexible and printed electronics, and field‐effect‐transistor‐based sensors is still a challenge. Here, monolayers of engineered lipids supported on silicon are reported presenting exceptional mechanical and dielectric properties. The lipid monolayers are stabilized using a simple procedure based on a two‐stage reticulation process in both their aliphatic chains and their head‐group. With a thickness lower than 3 nm, such layers are demonstrated to offer exceptional mechanical and dielectric stability with unprecedented low leakage current and dielectric strength. Surprisingly, the mechanical and dielectric pressures required to rupture/breakdown the monolayers are shown to be similar. These results suggest the presence of a strong correlation between mechanical and dielectric properties, as well as between the mechanisms of rupture and breakdown. [ABSTRACT FROM AUTHOR]

The authors present a triple-band metamaterial absorber operating at mm wave frequency band. The absorber is composed of periodic unit cells, which consists of a new pattern and a ground plane, placed in two sides of a dielectric substrate made of polyimide film. To best understand the absorption mechanisms, full-wave simulation results for the electric field, surface current, and power loss distributions are presented. The experimental results, for a transverse electric-polarised normal incident wave, show three distinctive absorption peaks, at frequencies 101.25, 108.75, and 129 GHz with absorptivities of 92.5, 94.9, and 88.6%, respectively. The absorber is independent of the wave polarisation, where high absorption is achieved for a wide range of oblique angles of incidence. [ABSTRACT FROM AUTHOR]

A tunable Fabry–Perot filter composed of two separated all-dielectric metamaterials is proposed and numerically investigated. Different from metallic metamaterials reflectors, the all-dielectric metamaterials are constructed by high-permittivity TiO 2 cylinder arrays and exhibit high reflection in a broadband of 2.49–3.08 THz. The high reflection is attributed to the first and second Mie resonances, by which the all-dielectric metamaterials can serve as reflectors in the Fabry–Perot filter. Both the results from phase analysis method and CST simulations reveal that the resonant frequency of the as-proposed filter appears at 2.78 THz, responding to a cavity with λ /18 wavelength thickness. Particularly, the resonant frequency can be adjusted by changing the cavity thickness. This work provides a feasible approach to design low-loss terahertz filters with a thin air cavity. [ABSTRACT FROM AUTHOR]

Abstract: Metamaterials have optical properties that are unprecedented in nature. They have opened new horizons in light manipulation, with the ability to bend, focus, completely reflect, transmit, or absorb an incident wave front. Optically active metamaterials in particular could be used for applications ranging from 3D information storage to photovoltaic cells. Silicon (Si) particles are some of the most promising building blocks for optically active metamaterials, with high scattering efficiency coupled to low light absorption for visible frequencies. However, to date ideal Si building blocks cannot be produced by bulk synthesis techniques. The key is to find a synthetic route to produce Si building blocks between 75–200 nm in diameter of uniform size and shape, that are crystalline, have few impurities, and little to no porosity. This Review provides a theoretical background on Si optical properties for metamaterials, an overview of current synthetic methods and gives direction towards the most promising routes to ideal Si particles for metamaterials. [ABSTRACT FROM AUTHOR]

We present a general numerical approach for the calculation of the non‐local macroscopic dielectric response of a binary metamaterial made of arbitrary non‐magnetic materials with any geometry. From the spatial dispersion of the permittivity, characterized by its dependence on the wavevector, we obtain the corresponding effective local macroscopic permeability of the metamaterial. We illustrate our computational approach by calculating the permeability of two‐dimensional split‐ring resonators and validate the results through comparison with those of simple models. Our scheme may be further applied to arbitrary geometries. We discuss the limitations of the local permeability approach. [ABSTRACT FROM AUTHOR]

By using the scattering matrix formalism, it is studied the optical properties of one dimensional photonic crystals made of multiple layers of dielectric and uniaxial anisotropic single negative electric metamaterial with Drude type responses, with inclusions of graphene in between the dielectric-dielectric interfaces (DGMPC). The transmission spectra for transverse electric (TE) and magnetic (TM) polarization are presented as a function of the incidence angle, the graphene chemical potential, and the metamaterial plasma frequencies. It is found for the TM polarization the tunability of the DGMPC optical response with the graphene chemical potential, which can be observed by means of transmission or reflexion bands around the metamaterial plasmon-polariton frequency, with bandwidths depending on both the incidence angle and the metamaterial plasma frequency. Also, the transmission band is observed when losses in the metamaterial slabs are considered for finite systems. The conditions for the appearance of these bands are shown analytically. We consider this work contributes to open new possibilities to the design of photonic devices with DGMPCs. [ABSTRACT FROM AUTHOR]

A metamaterial equipment is designed and experimental verified in the near-infrared with two reflectivity dips. The metamaterial equipment shows independent of polarization. Simulated results indicate that the reflectivity dip is excited by the coupling of localized surface plasmon (LSP) modes. The metamaterial equipment can work as a refractive index detection sensor with high figure of merit (FOM) value. This proposed metamaterial sensor can be applied in detecting different biochemical liquid. [ABSTRACT FROM AUTHOR]

A patterned, plasmonic metasurface can strongly scatter incident light, functioning as an extremely low-profile lens, filter, reflector or other optical device. When the metasurface is patterned uniformly, its linear optical properties can be expressed using effective surface electric and magnetic polarizabilities obtained through a homogenization procedure. The homogenized description of a nonlinear metasurface, however, presents challenges both because of the inherent anisotropy of the medium as well as the much larger set of potential wave interactions available, making it challenging to assign effective nonlinear parameters to the otherwise inhomogeneous layer of metamaterial elements. Here we show that a homogenization procedure can be developed to describe nonlinear metasurfaces, which derive their nonlinear response from the enhanced local fields arising within the structured plasmonic elements. With the proposed homogenization procedure, we are able to assign effective nonlinear surface polarization densities to a nonlinear metasurface, and link these densities to the effective nonlinear surface susceptibilities and averaged macroscopic pumping fields across the metasurface. These effective nonlinear surface polarization densities are further linked to macroscopic nonlinear fields through the generalized sheet transition conditions (GSTCs). By inverting the GSTCs, the effective nonlinear surface susceptibilities of the metasurfaces can be solved for, leading to a generalized retrieval method for nonlinear metasurfaces. The application of the homogenization procedure and the GSTCs are demonstrated by retrieving the nonlinear susceptibilities of a SiO 2 nonlinear slab. As an example, we investigate a nonlinear metasurface which presents nonlinear magnetoelectric coupling in near infrared regime. The method is expected to apply to any patterned metasurface whose thickness is much smaller than the wavelengths of operation, with inclusions of arbitrary geometry and material composition, across the electromagnetic spectrum. [ABSTRACT FROM AUTHOR]

BiCu 3 Ti 3 FeO 12 ceramics, with similar crystal structure as ACu 3 Ti 4 O 12 , were fabricated by a standard solid-state reaction method. By tuning the sintering temperature, the samples with homogeneous grain size and low porosity were obtained. The electric responses of BiCu 3 Ti 3 FeO 12 were revealed by electric modulus and complex impedance analysis. Interestingly, unlike CCTO materials, BiCu 3 Ti 3 FeO 12 ceramics did not exhibit low-frequency giant permittivity plateau, which is induced by high grain resistivity. Due to different electronegativity of Ti 4+ and Fe 3+ , Fe 3+ is much easier to be reduced to Fe 2+ and in turn BiCu 3 Ti 3 FeO 12 ceramics show a higher Fe 2+ content. Higher activation energy for electron hopping between Fe 2+ and Fe 3+ gives rise to a higher grain resistivity in the samples. By modifying composition, low-frequency giant permittivity plateau was successfully achieved for the samples with low Fe content. [ABSTRACT FROM AUTHOR]

Self-assembled metamaterials attract considerable interest as they promise to make isotropic bulk metamaterials available at low costs. The optical response of self-assembled metamaterials is derived predominantly from the response of its individual constituents, i.e., the meta-atoms. Beyond effective properties, primary experimentally observable quantities, such as specific cross-sections, are at the focus of interest as they are frequently considered when exploiting metamaterials in specific applications. This posses the challenge of predicting these observable quantities for a diluted ensemble of randomly oriented meta-atoms. Thus far, this has been achieved by either averaging the optical response of the meta-atom across all possible incident fields or by restricting the consideration to only an electric and magnetic dipolar response. This, however, is either time-consuming or imposes an unnecessary limitation. Here, we solve this problem by deriving and presenting explicit expressions for experimentally observable quantities of metamaterials made from randomly arranged and oriented meta-atoms characterized by their T-matrix. [ABSTRACT FROM AUTHOR]

A new scheme to achieve a simple design of triple-band metamaterial absorber at terahertz frequency is presented. In this scheme, we employ a traditional sandwich structure, which is consisted of a metallic resonator and an appropriate thickness of the dielectric layer backed with an opaque metallic board, as the research object. Three strong but discrete resonance peaks with the narrow bandwidths and high absorptivities are realized. The combination of the dipolar resonance, LC (inductor-capacitor circuit) resonance, and the surface resonance of the metallic resonator determines the triple-band absorption. Numerical results also show that the frequencies of the three absorption bands and the number of the resonance peaks can be effectively tuned by adjusting or changing the geometric parameters of the metallic resonator. Moreover, we present a simple design of five-band terahertz absorber by further optimizing the sizes of the metallic elements in the top layer of the metamaterial. The design of the unit structures will assist in designing innovative absorbing devices for spectroscopy imaging, detection, and sensing. [ABSTRACT FROM AUTHOR]

In this paper, a three-dimensional, polarization-insensitive broadband metamaterial absorber in the infrared region is proposed. And the same kind of metal is used in the whole structure. The simulated results show that the structure can achieve a broadband absorption greater than 90% from 40.3 to 70.2 THz for either transverse electric or magnetic polarization mode at normal incidence. Subsequently, due to the rotationally symmetric distributions of the structure in the z-axis, the proposed metamaterial absorber is independent for the different polarization angles. Moreover, unlike previous resistive films metamaterial absorbers which are based on the resistive film for the absorption of the electromagnetic waves, and in this structure, the absorption are not based on the metal films themselves but based on resonance. In addition, through analysis of the electromagnetic field and the surface current distributions, it can demonstrate that the absorption mechanism of the absorber which is based on the surface plasmonic and dipole resonance responses. Finally, we believe this idea also extends to other frequency regions and also can realize broadband absorption. [ABSTRACT FROM AUTHOR]

Microwave assisted pyrolysis (MWAP) is an alternative heating approach to convert biosolids into value-added products, such as biochar, biogas and bio-oil. Studying the dielectric properties of biosolids is fundamental to understand the behaviour of this material under microwave irradiation and to design microwave assisted pyrolysis systems. This study examined the dielectric properties of biosolids with changes in moisture content and applied microwave frequency. Results demonstrated that the dielectric constant decreases with decreasing moisture content and with increasing microwave frequency, but the dielectric loss factor of dry biosolids is almost zero. Simulations demonstrated that moisture content of biosolids impacts on the distribution and intensity of electromagnetic field. Because of the poor dielectric properties of dry biosolids, a microwave susceptor must be added to the biosolids to attract microwave energy so that the materials can reach temperatures required for pyrolysis. Therefore, this study also investigated the impact of four microwave susceptors (activated carbon, charcoal, biochar and glycerol) on biosolids pyrolysis and on biochar properties produced from biosolids via microwave assisted pyrolysis at 600 °C. The choice of microwave susceptor influences the heating rate of biosolids and the specific surface area of the resultant biochar. Results show that activated carbon favours the heating process, increases surface area, and the biochar produced with activated carbon has the highest carbon stability and energy value. [ABSTRACT FROM AUTHOR]

The design and performance of low-profile, multiple-feed metasurface antennas with different numbers of patch cells and different substrate thicknesses at a terahertz frequency are presented in this paper. The utilized antenna designs consist of a periodic array (N × M) metallic square-patch metasurface and a planar feeding structure, which are both patterned on an electrically thin, high-permittivity GaAs substrate. The antenna gain increased in a linear fashion with an increasing number of patch cells, which were directly fed by the slit feedline. A 3-dB gain increment was observed irrespective of the substrate thickness when the number of patch cells was doubled. However, the 3-dB gain bandwidth as well as the radiation efficiency changed significantly with varying substrate thicknesses. The described antenna structure offers useful characteristics by means of a combination of different substrate thicknesses and patch numbers. In addition, the proposed antenna design features a number of benefits, including a low profile, mechanical robustness, easy integration into circuit boards, and excellent suitability for low-cost mass production. [ABSTRACT FROM AUTHOR]

A novel magneto-electro-dielectric waveguided metamaterial (MED-WG-MTM) that the effective permeability εeff is changed obviously with the decrease of substrate's thickness is proposed. The proposed MTM can be used to simultaneously achieve the miniaturization and ultra-thin profile of overall antenna. Then, for demonstrated the characteristic, a coplanar-waveguide (CPW)-fed antenna by loading the proposed MTM is designed, fabricated, and measured. The measured result shows that the S11 less than -10 dB is from 1.48 to 5.08 GHz (109.7% bandwidth) and 72% miniaturization is achieved. The results between simulation and measurement coincide well. The thickness of the overall antenna is only 0.003λmax, which is smallest compared with the reported ones. (λmax is the wavelength at the lowest operating frequency). [ABSTRACT FROM AUTHOR]

We report a new design of triple-band electric metamaterial resonator (TBEMR) based on integration of open delta loops within square ring resonator. This metamaterial resonator has three distinct ε-negative regions (ENG) over C, X frequency bands. The transmission and reflection response of the proposed subwavelength resonator is analyzed using full-wave electromagnetic solver Ansys HFSS to demonstrate the presence of electrical resonances within frequencies 4–12 GHz. Effective medium parameters permittivity and permeability are extracted from simulated complex scattering parameters to verify existence of ENG regions. The investigations are also carried out regarding dependence of resonant frequencies on design parameters of the TBEMR unit cell. The effective medium ratio (λ0/a) for proposed subwavelength resonator is compared with various other metamaterial resonators to indicate its compact nature. [ABSTRACT FROM AUTHOR]

In this work, we propose the concept that a device based on mechanical metamaterials can be used to induce and control its own rotational motion as a result of internal deformations due to the conversion of translational degrees of freedom into rotational ones. The application of a linear force on the structural units of the system may be fine-tuned in order to obtain a desired type of rotation. In particular, we show, how it is possible to maximise the extent of rotation of the system through the alteration of the geometry of the system. We also show how a device based on this concept can be connected to an external body in order to rotate it which result may potentially prove to be very important in the case of applications such as telescopes employed in space. [ABSTRACT FROM AUTHOR]

In this paper, a high-order dielectric metasurface based on silicon nanobrick array is proposed and investigated. By controlling the length and width of the nanobricks, the metasurfaces could supply two different incremental transmission phases for the X-linear-polarized (XLP) and Y-linear-polarized (YLP) light with extremely high efficiency over 88%. Based on the designed metasurface, two polarization beam splitters working in high-order diffraction modes have been designed successfully, which demonstrated a high transmitted efficiency. In addition, we have also designed two vortex-beam generators working in high-order diffraction modes to create vortex beams with the topological charges of 2 and 3. The employment of dielectric metasurfaces operating in high-order diffraction modes could pave the way for a variety of new ultra-efficient optical devices. [ABSTRACT FROM AUTHOR]

In this work, the structural, compositional, optical, and dielectric properties of GaS thin films are investigated by means of X-ray diffraction, scanning electron microscopy, energy dispersion X-ray analysis, and ultraviolet-visible light spectrophotometry. The GaS thin films which exhibited amorphous nature in its as grown form are observed to be generally composed of 40.7 % Ga and 59.3 % S atomic content. The direct allowed transitions optical energy bandgap is found to be 2.96 eV. On the other hand, the modeling of the dielectric spectra in the frequency range of 270-1,000 THz, using the modified Drude-Lorentz model for electron-plasmon interactions revealed the electrons scattering time as 1.8 ( fs), the electron bounded plasma frequency as ~0.76-0.94 ( GHz) and the reduced resonant frequency as 2.20-4.60 ×10 ( Hz) in the range of 270-753 THz. The corresponding drift mobility of electrons to the terahertz oscillating incident electric field is found to be 7.91 ( cm / Vs). The values are promising as they nominate the GaS thin films as effective candidates in thin-film transistor and gas sensing technologies. [ABSTRACT FROM AUTHOR]

In this work, we fabricated ceramic composites based on the composite matrix SrCoNbO (SCNO)-TiO. The SCNO was synthesized by solid-state reaction, and x-ray diffraction was used for the structural characterization of this synthesis. We measured the dielectric properties in the microwave range by using the Hakki-Coleman method, as well as the thermal stability of these composites in this frequency range. We inserted TiO in an SCNO ceramic matrix in order to improve the thermal stability of SCNO. The cylindrical dielectric resonators were fabricated using concentrations of 5 wt.%, 10 wt.%, 20 wt.%, 40 wt.%, 60 wt.%, and 80 wt.%. The insertion of TiO improved the thermal stability, dielectric loss, and permittivity of the SCNO-based ceramic. These ceramic composites were evaluated as dielectric resonator antenna, and the performance of these materials presented a reflection coefficient below −10 dB, gain above 2.5 dBi, and efficiency above 60%. [ABSTRACT FROM AUTHOR]

Dielectric properties of composites near percolation threshold (fc) are often sensitive to thermal treatments, and the annealing temperature is usually associated with a polymer's rheological properties. In this study, the influences of the thermal treatment on dielectric properties are investigated for the polystyrene (PS) matrix composite reinforced by graphene nanoplatelets (GNP) fillers near fc. It can be found that the thermal treatment can not only increase the dielectric constant, but also decrease the dielectric loss for the PS/GNP composite. This interesting phenomenon possibly happens in the interfacial region of PS/GNP with the thickness about 4-6 nm according to the electron energy-loss spectroscopy (EELS) results. The free volumes around the interface can be easily altered by the movement of polymeric segments after annealing at the glass transition temperature. [ABSTRACT FROM AUTHOR]

All-dielectric metamaterials are a promising platform for the development of integrated photonics applications. In this work, we investigate themutual coupling and interaction of an ensemble of anapole states in silicon nanoparticles. Anapoles are intriguing non-radiating states originated by the superposition of internal multipole components which cancel each other in the far-field. While the properties of anapole states in single nanoparticles have been extensively studied, the mutual interaction and coupling of several anapole states have not been characterized. By combining first-principles simulations and analytical results, we demonstrate the transferring of anapole states across an ensemble of nanoparticles, opening to the development of advanced integrated devices and robust waveguides relying on non-radiating modes. [ABSTRACT FROM AUTHOR]

Hybrid-polarization surface plasmon polaritons (HSPPs) at the interface between an isotropic medium and a one-dimensional metal-dielectric metamaterial (MM) were discussed, where the metal-layer permittivity was described with the improved Drude model. From the obtained dispersion equations, we predicated five types of HSPPs. One type is the Dyakonov-like surface polariton and another type is the tradition-like surface polarton. The others are new types of HSPPs. We establish a numerical simulation method of the attenuated total reflection (ATR) measurement to examine these HSPPs. The results from the ATR spectra are consistent with those from the dispersion equations and indicate the different polarization features of these HSPPs. The numerical results also demonstrate that the observation of each type of HSPPs requires different conditions dictated by the material parameters and the polarization direction of incident light used in the ATR spectra. These results may further widen the space of potential applications of surface plasmon polaritons. [ABSTRACT FROM AUTHOR]

We report anomalous dispersion properties of hybrid guided modes (HGMs) and their group velocity in a subwavelength uniaxial metamaterial waveguide with metal cladding. We derive exact dispersion relations and modal fields of HGMs by solving eigenvalue equation based on basic electromagnetic field theory in detail. Numerical results show that two fundamental HGMs and two types of high-order HGMs can be excited, and their exciting conditions are clarified. In addition, such HGMs can be engineered to belong to normal dispersion or anomalous dispersion. Importantly, the HGMs may be controlled to be forward or backward, and their group velocities may be very small in a certain frequency band. These properties make such metamaterial waveguides have many potential applications in integrated optics, information storage and biosensing. [ABSTRACT FROM AUTHOR]

A new simple design of a triple-band microstrip antenna using metamaterial concept is presented in this paper. Multi-unit cell was the key of the multi resonance response that was obtained by etching two circular and one rectangular split ring resonator (SRR) unit cells in the ground plane of a conventional patch operating at 3.56 GHz. The circular unit cells are resonating at 5.6 GHz for the upper band of Wi-MAX, while the rectangular cell is designed to produce a resonance at 2.45 GHz for the lower band of WLAN. WiMAX's/WLAN's operating bands are covered by the triple resonances which are achieved by the proposed antenna with quite enhanced performance. A detailed parametric study of the placement for the metamaterial unit cells is introduced and the most suitable positions are chosen to be the place of the unit cells for enhanced performance. A good consistency between simulation and measurement confirms the ability of the proposed antenna to achieve an improved gain at the three different frequencies. [ABSTRACT FROM AUTHOR]

Passive radiative cooling draws heat from surfaces and radiates it into space as infrared radiation to which the atmosphere is transparent. However, the energy density mismatch between solar irradiance and the low infrared radiation flux from a near-ambient-temperature surface requires materials that strongly emit thermal energy and barely absorb sunlight. We embedded resonant polar dielectric microspheres randomly in a polymeric matrix, resulting in a metamaterial that is fully transparent to the solar spectrum while having an infrared emissivity greater than 0.93 across the atmospheric window. When backed with a silver coating, the metamaterial shows a noontime radiative cooling power of 93 watts per square meter under direct sunshine. More critically, we demonstrated high-throughput, economical roll-to-roll manufacturing of the metamaterial, which is vital for promoting radiative cooling as a viable energy technology. [ABSTRACT FROM AUTHOR]

We theoretically study macroscopic dielectric properties of hyperbolic metamaterials proceeding from microscopic description. The theory constructed gives the answer to the question 'what properties should microscopic elements have in order to macroscopic system consisting of these elements would be a hyperbolic metamaterial.' Generalized Clausius-Mossotti relation as well as existing conditions for such metamaterials is obtained with help of the local field theory. The perpendicular and parallel components of the dielectric permittivity are found as functions of microscopic parameters of a single particle and a dielectric matrix. [ABSTRACT FROM AUTHOR]

Metamaterial behavior of polymer nanocomposites (NCs) based on isotactic polypropylene (iPP) and multi-walled carbon nanotubes (MWCNTs) was investigated based on the observation of a negative dielectric constant (ε'). It is demonstrated that as the dielectric constant switches from negative to positive, the plasma frequency (!p) depends strongly on the ultrasound-assisted fabrication method, as well as on the melt flow index of the iPP. NCs were fabricated using ultrasound-assisted extrusion methods with 10 wt % loadings of MWCNTs in iPPs with different melt flow indices (MFI). AC electrical conductivity (σ(AC)) as a function of frequency was determined to complement the electrical classification of the NCs, which were previously designated as insulating (I), static-dissipative (SD), and conductive (C) materials. It was found that the SD and C materials can also be classified as metamaterials (M). This type of behavior emerges from the negative dielectric constant observed at low frequencies although, at certain frequencies, the dielectric constant becomes positive. Our method of fabrication allows for the preparation of metamaterials with tunable !p. iPP pure samples show only positive dielectric constants. Electrical conductivity increases in all cases with the addition of MWCNTs with the largest increases observed for samples with the highest MFI. A relationship between MFI and the fabrication method, with respect to electrical properties, is reported. [ABSTRACT FROM AUTHOR]

The characterization results of a typical electrically controlled metamaterial terahertz (THz) modulator obtained by the dynamic measurement method are presented and are in good agreement with the theoretical results predicted by a first-order model. The dynamic measurement method can characterize the modulation depth and modulation speed simultaneously. The reliability of the method is verified by terahertz time-domain spectroscopy (THz-TDS), and the current response method, which show that the more intuitive and comprehensive dynamic measurement method, can be used to characterize the electrically controlled metamaterial THz modulator accurately. [ABSTRACT FROM AUTHOR]