Terahertz wave modulator based on optically controllable metamaterial

We demonstrated experimentally a terahertz wave modulator based on optically controlled metamaterial. The signal modulation mechanism of the presented terahertz wave modulator was based on the resonance characteristic of metamaterial controlled without or with light excitation. A modulated semiconductor laser with 808 nm wavelength was employed to light the substrate. The interaction between the metamaterial and terahertz wave was strengthened and yielded an appreciable modulation of the terahertz output beam. The modulation speed is 0.1 Kb/s and the modulation depth of the proposed terahertz modulator is about 57% at a frequency of 0.32 THz.     

Broadband and ultra-low reflection metamaterial absorber embedded with magnetic materials

In this study, we design, prepare and characterize a broadband, ultra-low reflectivity and incidence angle-insensitive metamaterial absorber. The design of this absorber not only provides a novel idea for the design of broadband absorbers, but also enhances the application prospects of metamaterial absorbers. By introducing FeSiAlp/epoxy magnetic composite and optimizing the structural parameters, the absorption performance of the metamaterial absorber has been significantly improved. The effective absorption bandwidth (bandwidth with reflectivity less than −10dB) is increased by 3.4 times from 2.19 GHz to 7.49 GHz, and the RL_min (minimum reflection loss) value reaches −38.31 dB at 17.83 GHz, that is the absorption rate reaches 99.99%. Meanwhile, the experimental results also verify the simulation design results. Therefore, the absorber not only plays the characteristics of strong absorption of metamaterial, but also absorbs the advantages of broadband of magnetic material.     

A compact square-shaped left-handed passive metamaterial with optimized quintuple resonance frequencies for satellite applications

The research aims to develop a more sophisticated novel left-handed and compact square-shaped metamaterial (SM) inspired multi-frequency bands like C-, X- and Ku-band applications. Even though the performance of existing satellite application devices are adequate, significant changes in technology over the past decades require advanced and more accurate techniques or devices. Hence, we approach the problem with a broader perspective by integrating a metamaterial structure in satellite application devices. As a general rule, the unconventional material known as metamaterial has extraordinary electromagnetic properties which are impracticable in commercially available materials. It represents an important study topic because this type of peculiar material is generally used in many field applications which encouraged us to experiment with the stated frequency bands by introducing a novel SM design. The novel SM design structure involved a 1.6 mm Epoxy Resin Fibre (FR-4) substrate material. This compact metamaterial design contains nine square rings with an altered small square ring joined in it. The numerical simulation of the SM design for satellite frequencies was performed using the Computer Simulation Technology (CST) Microwave Studio. The scattering parameters of the suggested SM design were determined by utilising Finite Integration Technique (FIT) in CST software. Several parametric studies that were analysed in this study include various design structure, types of substrate materials and SM array arrangement. Based on the adapted simulated frequency range (4 to 18 GHz), the unit cell SM exhibited five resonance frequencies at 5.49 and 7.33 GHz (in C-Band), 9.05 and 11.38 GHz (in X-Band) and 13.48 GHz (in Ku-Band). The measured resonance frequencies of the unit cell were 5.62 and 7.39 GHz (in C-Band), 9.15 and 11.32 GHz (in X-Band) and 13.51 GHz (in Ku-Band). The resonance frequencies obtained from both methods were similar. According to all three resonance frequencies, the SM design manifested a left-handed characteristic. Hence, on this basis, the proposed SM design with unique characteristics is deemed suitable for C-, X- and Ku-bands applications.     

Permeability enhancement of stratified metal dielectric metamaterial in optical regime

Magnetic response of stratified metal dielectric metamaterial (SMDM) is demonstrated numerically and experimentally. One unit cell of SMDM has a sandwich unit cell consisting of alumina (60 nm)/silver (30 nm)/alumina (60 nm). A Mach–Zehnder interferometer is used to obtain phase information of transmittance and reflectance from which effective permeability is determined. The maximum permeability amounts to 20 and 17 for calculation and experiment, respectively. This huge resonance occurs when the magnetic field is concentrated at the metal layer, while the electric field has a node at the center.     

Electric field controlled cohesive symmetric hook-C shape inspired metamaterial for S-band application

In this paper, a split ring resonator (SRR) bounded new cohesive symmetric hook-C shaped unit cell is developed. The metamaterial has 4   ×  4-unit cell array, which is applicable for s-band application for its high bandwidth (S₂₁ < -10 dB) of 0.6 GHz and high effective medium ratio (EMR) 12.78. Commercially available electromagnetic simulator CST (Computer simulation technology) microwave studio has been utilized at 2.93 GHz resonance frequency in this investigation. The electric field of this design is also observed by modifying the design structure that shows effective results. The new developed hook-C shaped metamaterial is fabricated and measured to validate the simulation results, which is eligible for high performance in long distance communications. The proposed metamaterial is highly recommended to apply in Airport Surveillance Radar (ASR) system for its highly effective medium ratio and size miniaturization.     

Near-field light localization using subwavelength apertures incorporated with metamaterials

We report strong near-field electromagnetic localization by using subwavelength apertures and metamaterials that operate at microwave frequencies. We designed split ring resonators with distinct configurations in order to obtain extraordinary transmission results. Furthermore, we analyzed the field localization and focusing characteristics of the transmitted evanescent waves. The employed metamaterial configurations yielded an improvement on the transmission efficiency on the order of 27 dB and 50 dB for the deep subwavelength apertures. The metamaterial loaded apertures are considered as a total system that offered spot size conversion ratios as high as 7.12 and 9.11 for the corresponding metamaterial configurations. The proposed system is shown to intensify the electric fields of the source located in the near-field. It also narrows down the electromagnetic waves such that a full width at half maximum value of λ/29 is obtained.     

Microwave response of octagon-shaped parallel plates: Low-loss metamaterial

A very low-loss metamaterial formed by a pair of homogeneous octagon-shaped parallel plates separated by a dielectric substrate is presented to achieve simultaneous negative permittivity and permeability in the microwave region. The double-negative behavior with a high figure of merit (FOM=|Re(n)/Im(n)|=80 at 24.7 GHz) leads to reduced losses in this proposed metamaterial. The high quality feature of the structure can make the applications of the negative refractive index metamaterial more efficient and applicable, such as perfect- or super-lenses at microwave frequencies since FOM≈64.5, where the real part of the refractive index ≈?1 at 25.3 GHz.     

Loss compensated negative index material at optical wavelengths

We present a computational approach, allowing for a self-consistent treatment of three-dimensional (3D) fishnet metamaterial operating at 710 nm wavelength coupled to a gain material incorporated into the nanostructure. We show numerically that loss-free negative index material is achievable by incorporating gain material inside the fishnet structure. The effective gain coefficient of the combined fishnet-gain system is much larger than its bulk counterpart and the figure-of-merit (FOM = | Re(n)/Im(n) |) increases dramatically with gain. Transmission, reflection, and absorption data, as well as the retrieved effective parameters, are presented for the fishnet structure with and without gain.     

The modification of the initial susceptibility of dilute binary ferrofluids based on γ-Fe2O3/ZnFe2O4 nanoparticles

This paper presents a multi-band metamaterial absorber comprising three multi-gap split-ring resonators (SRRs) with different radii and ring widths, designed in combinatorial approach. Experiments demonstrate that it can perform absorption peaks at three resonant frequencies 7.10 GHz, 10.04 GHz, and 17.44 GHz with the absorption of 99.90%, 99.91%, and 99.68%, respectively. The physical mechanism of metamaterial absorber was explained through numerical calculation and simulation, which showed that three absorption peaks were caused respectively by the three four-gap SRRs. The absorber is insensitive to incident angles and polarization states, so it has broad prospect of application.     

Low-frequency and broad band metamaterial absorber: design, fabrication, and characterization

We report a metamaterial absorber (MA) with a broad absorption band in the frequency region of 2–4 GHz, whose thickness is not limited to the quarter-wavelength. Theoretical and experimental results show that the absorber has two adjacent absorption apexes at 2.24 and 3.46 GHz, respectively, which are both related to the electric and magnetic resonances of the metamaterial. The absorption is over 68% in the whole wave band of 2–4 GHz provided the thickness of 4 mm. The distributions of the surface currents and the power loss density indicate that the surface currents produced by the electric and magnetic resonances are strongly consumed by the resistive patches. This low-frequency absorber has potential applications in many scientific and martial fields.     

Experimental verification of negative refraction in a double cross metamaterial

We report on microwave experiments with a metamaterial composed of pairs of metallic crosses. The transmission properties of the structure show a left-handed transmission band at frequencies around 10.2 GHz. The validity of the negative effective index of refraction is verified by a Snell’s law refraction experiment performed on a wedge-shaped sample of the metamaterial. A second measurement of a similar wedge made from blank FR4 boards is done for reference. The results of the measurements show positive refraction over the whole measured frequency band for the FR4 wedge as well as the refraction of the incident radiation to negative angles within the designated left-handed frequency band for the metamaterial sample.     

An improved fishnet three-dimensional metamaterial with multiband left-handed characteristics at terahertz frequencies

We present the design of a multiband left-handed three-dimensional (3D) metamaterial based on improved fishnet structure at terahertz frequencies. The design realizes a three-dimensional material by mechanical stacking of multiple layers. The electromagnetic properties of the metamaterial have been investigated by numerical simulation. The results show that simultaneously negative values of permittivity, permeability and refractive index are found around the frequencies of 0.73, 0.85 and 1.12 THz for the electromagnetic wave normal incidence. The proposed metamaterial with independent polarization and compact effect offers a way to develop THz 3D materials and devices suitable for multifrequencies.     

Optimization of locally resonant acoustic metamaterials on underwater sound absorption characteristics

The study of acoustic metamaterials, also known as locally resonant sonic materials, has recently focused on the topic of underwater sound absorption. The high absorption occurs only within a narrow frequency band around the locally resonant frequency. Nevertheless, this problem can be addressed through a combination of several acoustic metamaterial layers that have different resonant frequencies. In this paper, an optimization scheme, a genetic and a general nonlinear constrained algorithm, is utilized to enhance the low-frequency underwater sound absorption of an acoustic metamaterial slab with several layers. Both the physical and structural parameters of the acoustic metamaterial slab are optimized to enlarge the absorption band. In addition, the sound absorption mechanism of the acoustic metamaterial slab is also analyzed. The result shows that each layer is found to oscillate as a nearly independent unit at its corresponding resonant frequency. The theoretical and experimental results both demonstrate that the optimized metamaterial slab can achieve a broadband (800–2500 Hz) absorption of underwater sound, which is a helpful guidance on the design of anechoic coatings.     

Two new designs of lamp-type piezoelectric metamaterials for active wave propagation control

A major limitation of current metamaterials is that they control the wave propagation depending on their structure. Active metamaterials in this paper are designed whose physical structure is fixed, yet the position where they control the wave propagation can be changed by piezoelectric conditions. Two kinds of lamp-type piezoelectric metamaterials were assembled from an aluminum base, rubber plate and steel column, the piezoelectric patches were attached on both sides of the steel column, which can change the equivalent elastic modulus of the whole structure when the pair of patches are accessed by an LC circuit. The equivalent elastic modulus becomes zero or negative when the frequency of the circuit varies between 29,000 Hz and 30,000 Hz, in this case the two kinds of lamp-type piezoelectric metamaterials behave as a wave localization and a wave guide, respectively. The advantage of the lamp-type piezoelectric metamaterials is that we can control the wave propagation actively, as long as we change the position of the piezoelectric patches or choose the kind of lamp-type piezoelectric metamaterial. This is more flexible than a traditional passive metamaterial and provides a new way for us to design some acoustic equipment, such as acoustic cloaking, an acoustic black hole, filter or wave guide.     

Applications of LIBS for determination of ionic species (NaCl) in electrical cables for investigation of electrical breakdown

The formation of water trees in high-voltage cables can wreak havoc to power systems. The water tree is produced within the high voltage cable insulator when impurities like sodium and magnesium present in the insulating material react with moist soil to form chlorides. This water tree causes electrical breakdown by short circuiting the metallic conductor and the earth. In this paper we use laser-induced breakdown spectroscopy (LIBS) to detect the potentially dangerous elements that form the water tree in the insulating cable. The LIBS system used for this work consists of the fundamental (1064 nm) of a Nd:YAG laser, four spectrometer modules that cover the visible and near-UV spectral ranges and an ICCD camera with proper delay and gating sequence. With this arrangement we were able to measure the elemental concentrations of trace metals present in the insulating cable. The concentrations measured with our LIBS system were counter checked by a standard technique like inductively coupled plasma (ICP) emission spectrometry. The maximum concentrations for ionic species such as Ba (455.40 nm), Ca (393.36 nm), Cr (267.71 nm), Fe (259.94 nm), Cl (542.3 nm), Mg (516.7 nm), Mn (257.61 nm), Na (589.59 nm) and Ti (334.18 nm) are 20.6, 43.2, 1.6, 148.4, 24.2, 22.1, 4.2, 39.56 and 4.35 ppm, respectively. The relative accuracy of our LIBS system for various elements as compared with the ICP method is in the range of 0.03–0.6 at 2.5% error confidence.     

Design of a type of broadband metamaterial absorber based on metal and graphene

In this paper, we demonstrate a kind of broadband metamaterial perfect absorber using both graphene and metal resonator elements. Through step by step design and simulation, wider absorption band from about 4.22 THz to 7.48 THz with average absorption rate up to 98.21% is achieved in the absorption spectrum. In addition, the absorber has characteristics of polarization insensitivity and wide incident angle due to its inherent rotational symmetry. Moreover, the absorption band can be adjusted by changing the chemical potential of the graphene. The superiorities of broadband, high absorption rate, polarization independent and wide-angle characteristics make it have potential application prospects in electromagnetic wave absorbing, signal sensing and detection, and other optoelectronic devices.     

Perfect metamaterial absorber based on a split-ring-cross resonator

In this paper, we present a polarization-insensitive metamaterial (MM) absorber which is composed of the dielectric substrate sandwiched with split-ring-cross resonator (SRCR) and continuous metal film. The MM absorber is not limited by the quarter-wavelength thickness and can achieve near-unity absorbance by properly assembling the sandwiched structure. Microwave experiments demonstrate the maximum absorptivity to be about 99% around 10.91 GHz for incident wave with different polarizations. The surface currents distributions of the resonance structure are discussed to look into the resonance mechanism. Importantly, our absorber is only 0.4 mm thick, and numerical simulations confirm that the MM absorber could achieve very high absorptivity at wide angles of incidence for both transverse electric (TE) wave and transverse magnetic (TM) wave. The sandwiched structure is also suitable for designing of a THz and even higher frequency MM absorber, and simulations demonstrate the absorption of 99% at 1.105 THz.     

Theoretical and experimental investigations of easy made fishnet metamaterials at microwave frequencies

In this work, we demonstrate theoretically and experimentally a left handed behaviour of a planar fishnet type metamaterial in the microwave regime. The fabrication procedure based on printed circuit board technology and mechanical micromachining technique is easy, unique and doesn’t involve optical lithography. The effective parameters have been extracted using the S parameter retrieval method and show a very good agreement between simulation and experiment. Using finite-element method based simulations and W-band (75 GHz–110 GHz) experiments. We measured a negative index of refraction of −4 at 85 GHz. The demonstrated left handed materials represent a step towards the easy fabrication of metamaterials with a negative refractive index that open a new path for the active manipulation of millimetre wavelengths.     

Designing polarization insensitive negative index metamaterial for operation in near infrared

Hexagonal arrays of gold nanoelements with C₃ symmetry are studied as a metamaterial slab of reduced anisotropy. Tri-dimensional (3D) finite-difference time domain (FDTD) simulations are used to calculate the reflected and transmitted electromagnetic field for two waves normally incident to the slab with mutually perpendicular polarizations. S-parameter method is used to retrieve the constitutive parameters for each polarization. While dipolar plasmonic resonance in the case of one layer metamaterial slab leads only to negative values of permittivity, using two layers of asymmetric nanoelements leads to a negative refractive index metamaterial in the near infrared range (158–172 THz) as a result of hybridized plasmonic states inversion.     

Infrared response of a metamaterial made of gold wires and split ring resonators deposited on silicon

Periodic arrays of gold wires and split ring resonators (SRR) with a minimum feature size of 50 nm are fabricated on low-doped silicon. To our knowledge, the periodic arrangement of SRRs and wires considered in this work has not been studied in the near-infrared domain yet. For normal-incidence conditions, this metamaterial structure exhibits resonances at 70 and 170 THz (i.e., at λ ≈ 4.3 and 1.75 μm), which are identified as LC- and Mie resonances, respectively. These resonances are also observed for the SRRs alone, but the amplitude of the Mie resonance is reinforced due to the coupling between the SRRs and wires. The structure is simulated using finite-element software, while transmission and reflection measurements are performed with a Fourier transform infrared spectrometer. Numerical simulations are found to be in very good agreement with experimental characterizations, thereby showing that the Drude model used in calculations is well suited to simulate gold structures at near-infrared frequencies. Theoretical calculations predict that the metamaterial has a negative permittivity and a negative permeability near each resonance.