Broadband transmission below the cutoff frequency of a waveguide loaded with resonant scatterer arrays

A computer-aided method for the design of waveguide structures loaded with the arrays of metamaterial cells is described. Broadside coupled split ring resonators and Omega scatterers are chosen as the resonant metamaterial cells. By optimisation of the resonator geometry, the bandwidth of the transmission range below the cutoff frequency of the waveguide is enlarged compared with the results reported in the literature. The modes propagated below the waveguide cutoff possess a passband of the order of 30-50% and can be of the backward as well as of the forward type. The presented optimisation approach is based on the eigensolver simulations of a metamaterial unit cell. The designed metamaterial arrays are fabricated and measured. The experimental results are compared with the simulations validating the proposed design approach     

Analysis of Metamaterial Cloaks Using Circular Split Ring Resonator Structures

A novel microwave cloak using circular split ring resonator (SRR) based metamaterial structure has been proposed in this paper. The cloak which operates at a frequency of 10.6 GHz is composed of cylindrical dielectric sheets printed with circular split ring resonators of spatially varying and anisotropic material properties. The article also focuses on the phenomenon of resonant splitting in circular SRR microwave cloak. A detailed analysis of various linear metamaterial arrays and their response has also been elucidated.     

Optimal electromechanical bandgaps in piezo-embedded mechanical metamaterials

Elastic mechanical metamaterials are the exemplar of periodic structures. These are artificially designed structures having idiosyncratic physical properties like negative mass and negative Young’s modulus in specific frequency ranges. These extreme physical properties are due to the spatial periodicity of mechanical unit cells, which exhibit local resonance. That is why scientists are researching the dynamics of these structures for decades. This unusual dynamic behavior is frequency contingent, which modulates wave propagation through these structures. Locally resonant units in the designed metamaterial facilitate bandgap formation virtually at any frequency for wavelengths much higher than the lattice length of a unit. Here, we analyze the band structure of piezo-embedded negative mass metamaterial using the generalized Bloch theorem. For a finite number of the metamaterial units coupled equation of motion of the system is deduced, considering purely resistive and shunted inductor energy harvesting circuits. Successively, the voltage and power produced by piezoelectric material along with transmissibility of the system are computed using the backward substitution method. The addition of the piezoelectric material at the resonating unit increases the complexity of the solution. The results elucidate, the insertion of the piezoelectric material in the resonating unit provides better tunability in the band structure for simultaneous energy harvesting and vibration attenuation. Non-dimensional analysis of the system gives physical parameters that govern the formation of mechanical and electromechanical bandgaps. Optimized numerical values of these system parameters are also found for maximum first attenuation bandwidth. Thus, broader bandgap generation enhances vibration attenuation, and energy harvesting can be simultaneously available, making these structures multifunctional. This exploration can be considered as a step towards the active elastic mechanical metamaterials design.

     

A d.c. magnetic metamaterial

Electromagnetic metamaterials are a class of materials that have been artificially structured on a subwavelength scale. They are currently the focus of a great deal of interest because they allow access to previously unrealizable properties such as a negative refractive index. Most metamaterial designs have so far been based on resonant elements, such as split rings, and research has concentrated on microwave frequencies and above. Here, we present the first experimental realization of a non-resonant metamaterial designed to operate at zero frequency. Our samples are based on a recently proposed template for an anisotropic magnetic metamaterial consisting of an array of superconducting plates. Magnetometry experiments show a strong, adjustable diamagnetic response when a field is applied perpendicular to the plates. We have calculated the corresponding effective permeability, which agrees well with theoretical predictions. Applications for this metamaterial may include non-intrusive screening of weak d.c. magnetic fields.     

Experimental investigation of reflection characteristics of left-handed metamaterials in free space

The transmission and reflection characteristics are presented of a one-dimensional (1D) left-handed metamaterial (LHM) and its constituents, split ring resonator and thin wire arrays. A well-defined left-handed transmission band with a peak value of -7.2 dB is obtained at frequencies where effective permittivity and permeability are both negative. A sharp dip (-34.5 dB) at the reflection spectrum of 1D ordered LHM is observed. The frequency of ultra-low reflection did not change considerably for another LHM with a different thickness, meaning that the low reflection is not because of the thickness resonance but rather the impedance-matching of LHM at the surface. Disorder in LHM structures is shown to affect the reflection characteristics     

Some Applications of Metamaterial Resonators Based on Symmetry Properties

Metamaterial resonators are electrically small resonant particles useful for the implementation of effective media metamaterials. In this paper, some applications of metamaterial resonators (such as the split ring resonator -SRR-, the complementary split ring resonator -CSRR-, the folded stepped impedance resonator -SIR-, and the electric LC resonator), that exploit the symmetry properties of transmission lines loaded with such symmetric particles, are reviewed. This covers differential (balanced) lines with common mode suppression, linear and angular displacement sensors (including alignment sensors), angular velocity sensors, and radiofrequency barcodes. Advantages and drawbacks as compared to existing implementations are also discussed.     

负折射超材料响应中心频率的液晶调控

提出开口金属环加液晶的三明治超材料结构,将优化的超材料金属环线结构单元与液晶相结合,采用外加电场调节液晶的介电系数,使该结构的负折射响应中心频率可在一定范围内较方便、反复的调整.通过模拟仿真和理论分析证明这是一个可行的结构模型.     

Microstrip bandpass filters based on zeroth-order resonators with complementary split ring resonators

The zeroth-order resonant (ZOR) properties of the left-handed material (LHM) unit cells composed of complementary split ring resonators and series gaps are analysed. The method to determine the resonant frequency and susceptance slope parameter is proposed. A bandpass filter (BPF) is designed by connecting the ZORs with admittance inverters. Experimental verification is provided and a good agreement has been found between the simulation and measurement. Compared with the bandpass structure fabricated by simply cascading the same amount of LHM unit cells, the proposed BPF has much better selectivity, more symmetrical responses and controllable bandwidth.     

Three-dimensional double-negative metamaterials resonating at 13.5 GHz

A three-dimensional double-negative (DNG, ϵ< 0, μ< 0) metamaterial has been designed to operate near 13.5 GHz. The metamaterial was comprised of patterned copper split ring resonators (SRRs) and wires on a Rogers 5880 substrate. The SRRs and wires were each constructed in three orthogonal planes to give a nearisotropic response to an arbitrarily polarised EM excitation. As this material responds to radiation of arbitrary polarisation and direction, it is referred to as a 3E3H structure where all the six components of the EM tensor are present. The simulated losses in the unit cell are large (2 dB/cm), a major contribution being ohmic effects in the SRRs. For many applications, unit cells of lower dimensionality, that is, 2E2H or 1E1H, where only a restricted number of the elements of the EM tensor are needed, can perform nearly as well as 3D DNG materials, but with much lower loss, and thus may be preferred as an alternative to an isotropic 3E3H structure.     

Tunable metamaterial absorber based on resonant strontium titanate artificial atoms

Dynamic control of the absorption frequency and intensity of metamaterial absorbers has attracted considerable attention,and many kinds of tunable metamaterial absorbers have been proposed.Unfortunately,due to the integration of separate resonant unit and tunable unit,these designed metamaterial absorbers suffer from complex structure and low sensitivity.We numerically and experimentally demonstrate a tunable metamaterial absorber composed of artificial dielectric atoms as both resonant and tunable unit arrayed periodically in the background matrix on the metallic plate.Polarization insensitive and wide incident angle absorption band with simulated and experimental absorptivity of 99%and 96%at 9.65 GHz are achieved at room temperature.The absorption frequency can be gradually modulated by temperature,however,the absorption intensity at working frequency remains near unity.The dielectric atoms based tunable metamaterial absorbers with simple structure have potential applications as tempe rature sensors and frequency selective thermal emitters.     

Royal Crown Shaped Polarization Insensitive Perfect Metamaterial Absorber for C-, X-, and Ku-Band Applications

This study proposed a new royal crown-shaped polarisation insensitive double negative triple band microwave range electromagnetic metamaterial absorber (MA). The primary purpose of this study is to utilise the exotic characteristics of this perfect metamaterial absorber (PMA) for microwave wireless communications. The fundamental unit cell of the proposed MA consists of two pentagonal-shaped resonators and two inverse C-shaped metallic components surrounded by a split ring resonator (SRR). The bottom thin copper deposit and upper metallic resonator surface are disjoined by an FR-4 dielectric substrate with 1.6 mm thickness. The CST MW studio, a high-frequency electromagnetic simulator has been deployed for numerical simulation of the unit cell in the frequency range of 4 to 14 GHz. In the TE mode, the offered MA structure demonstrated three different absorption peaks at 6.85 GHz (C-band), 8.87 GHz (X-band), and 12.03 GHz (Ku-band), with 96.82%, 99.24%, and 99.43% absorptivity, respectively. The electric field, magnetic field, and surface current distribution were analysed using Maxwell’s-Curl equations, whereas the angle sensitivity was investigated to comprehend the absorption mechanism of the proposed absorber. The numerical results were verified using the Ansys HFSS (high-frequency structure simulator) and ADS (advanced design system) for equivalent circuit models. Moreover, the proposed MA is polarisation and incident angle independent. Hence, the application of this MA can be extended to a great extent, including airborne radar applications, defence, and stealth-coating technology.     

Field-assisted diffusion bonding and bond characterization of glass to aluminum

The bonding of glass wafers to aluminum foils in multi-layer assemblies was investigated by the field-assisted diffusion bonding process. Bonding was effected at temperatures in the range 350–450 °C and with an applied voltage in the range 400–700 V under a pressure of 0.05 MPa. The experimental parameters of voltage and temperature were the main factors in influencing the ionic current leading to the formation of the depleted layer. The peak current in three-layer samples (glass/aluminum/glass) during bonding is twice that for the case of the two-layer samples (aluminum/glass). SEM and EDS analyses showed the presence of transition layers near the glass/aluminum interface, and XRD data demonstrated the phase structure of the glass/aluminum interface. The tensile strength of the bonded material increased markedly with increasing temperature and applied voltage. Fracture occurred in the glass phase near the interface with the aluminum. Finite element analysis showed the residual deformation in three-layer samples to be significantly lower than in two-layer samples. The symmetry in three-layer samples resulted in the absence of strain, an important advantage in MEMS fabrication.     

Square-tooth split ring resonator – a novel metamaterial for bandwidth and radiation improvement in microstrip-based radiating structure design

A square multiband truncated microstrip patch antenna was investigated using a square-tooth split ring resonator for multiband applications in both S- and C-bands. The square-tooth split ring resonator is formed from metallic inclusions in a substrate to create a metamaterial. We introduce a new square-tooth split ring resonator which increases the radiation of the antenna as well as the bandwidth. This new design creates a slow wave structure. The square-tooth addition to the split ring resonator works like a slow wave structure. The square-tooth split ring resonator design is compared with the simple split ring resonator design. The square-tooth design has four bands with center frequencies of 3.88, 4.81, 5.4, and 5.62 GHz, whereas design with the simple split ring resonator has just three bands with center frequencies of 3.88, 4.74, and 5.50 GHz. The bandwidth is increased by 20% to 30% using the square-tooth split ring resonator compared to the simple split ring resonator.     

Phase‐Modulated Scattering Manipulation for Exterior Cloaking in Metal–Dielectric Hybrid Metamaterials

Artificially structured metamaterials with metallic or dielectric inclusions are extensively studied for exotic light manipulations via controlling the local‐resonant modes in the microstructures. The coupling between these resonant modes has drawn growing interest in recent years due to the advanced functional metamaterial making the microstructures more and more complex. Here, the suppression of magnetic resonance of a dielectric cuboid, an analogue to the scattering cancellation effect or radiation control system, realized with an exterior cloaking in a hybrid metamaterial system, is demonstrated. Furthermore, the significant modulation of the absorption of the dielectric resonator in the hybrid metamaterial is also demonstrated. The physical insight of the experimental results is well illuminated with a classical double‐harmonic‐oscillator model, from which it is revealed that the complex coupling, i.e., the phase of coupling coefficient, plays a crucial role in the overall response of the metal–dielectric hybrid system. The proposed design strategy is anticipated to form a more straightforward and efficient paradigm for practical applications based on radiation control via versatile mode couplings.     

Photo-excited broadband tunable terahertz metamaterial absorber

We demonstrate a photo-excited broadband tunable metamaterial absorber for use in the terahertz region. The metamaterial absorber consists of a hybrid metal-semiconductor square split ring and a metallic ground plane that are separated by a dielectric resonator spacer. The conductivity of the silicon used to fill the gap in the metallic resonator is tuned actively as a function of the incident pump power, which results in frequency modulation of the resonance absorption peak. Broadband tunable metamaterial absorbers are produced by suitable placement of the photoconductive silicon in different critical regions of the metallic resonator. In addition, the proposed method is applicable to a concentric rings-based metallic resonator. The proposed photo-excited broadband tunable metamaterial absorber has numerous potential applications, including uses as terahertz modulators and switches.     

Continuum model of two-dimensional crystal lattice of metamaterials

The continuum models of two-dimensional crystal lattice of metamaterial are investigated in this paper. The equivalent classical continuum requires the introduction of frequency-dependent mass density that becomes negative or infinite near the resonance frequency. In order to avoid the frequency-dependent mass density and make the dispersive characteristic of the elastic waves propagating in the equivalent continuum approximating that of lattice wave in two-dimensional crystal lattice of metamaterial, three kinds of continuum models, namely, the multiple displacements continuum model, the strain gradient continuum model and the nonlocal strain gradient continuum model, are investigated. It is found that the nonlocal gradient continuum model may better represent the dispersive relation and the bandgap characteristics of the metamaterial by the appropriate selection of nonlocal parameters.     

Metamaterials with gradient negative index of refraction

We propose a new metamaterial with a gradient negative index of refraction, which can focus a collimated beam of light coming from a distant object. A slab of the negative refractive index metamaterial has a focal length that can be tuned by changing the gradient of the negative refractive index. A thin metal film pierced with holes of appropriate size or spacing between them can be used as a metamaterial with the gradient negative index of refraction. We use finite-difference time-domain calculations to show the focusing of a plane electromagnetic wave passing through a system of equidistantly spaced holes in a metal slab with decreasing diameters toward the edges of the slab.     

Periodic Large‐Area Metallic Split‐Ring Resonator Metamaterial Fabrication Based on Shadow Nanosphere Lithography

A fast and cheap, large‐area (>1 cm²), high‐coverage fabrication technique for periodic metallic split‐ring resonator metamaterials is presented, which allows control of inner‐ and outer‐ring diameters, gap angles, as well as thickness and periodicity. This method, based on shadow nanosphere lithography, uses tilted‐angle‐rotation thermal evaporation onto Langmuir–Blodgett‐type monolayers of close‐packed polystyrene nanospheres. Excellent agreement of the process parameters with a simplified model is demonstrated. Pronounced, tunable optical metamaterial resonances in the range of 100 THz are consistent with simulations.     

Utilization of a triple hexagonal split ring resonator (SRR) based metamaterial sensor for the improved detection of fuel adulteration

Journal of Materials Science: Materials in Electronics - In this work, a triple hexagonal split ring resonator incorporated metamaterial sensor is proposed for the improved detection of fuel...     

High‐Quality‐Factor Mid‐Infrared Toroidal Excitation in Folded 3D Metamaterials

With unusual electromagnetic radiation properties and great application potentials, optical toroidal moments have received increasing interest in recent years. 3D metamaterials composed of split ring resonators with specific orientations in micro‐/nanoscale are a perfect choice for toroidal moment realization in optical frequency considering the excellent magnetic confinement and quality factor, which, unfortunately, are currently beyond the reach of existing micro‐/nanofabrication techniques. Here, a 3D toroidal metamaterial operating in mid‐infrared region constructed by metal patterns and dielectric frameworks is designed, by which high‐quality‐factor toroidal resonance is observed experimentally. The toroidal dipole excitation is confirmed numerically and further demonstrated by phase analysis. Furthermore, the far‐field radiation intensity of the excited toroidal dipoles can be adjusted to be predominant among other multipoles by just tuning the incident angle. The related processing method expands the capability of focused ion beam folding technologies greatly, especially in 3D metamaterial fabrication, showing great flexibility and nanoscale controllability on structure size, position, and orientation.