Metallic Resonators Research Articles

Wideband graphene-based near-infrared solar absorber using C-shaped rectangular sawtooth metasurface

In this work, wideband graphene-based near-infrared solar absorber with rectangular sawtooth at the outer edge of the C-shaped structure is proposed. The C-shaped with rectangular sawtooth metasurface provides better absorption in the near-infrared region (NIR) from 0.81 μm to 1.07 μm. The metallic resonators made up of tungsten and graphene monolayer helps to improve the absorption in the gaps of structure with an efficiency of 91.8% at NIR region. The design is also compared with rectangular sawtooth on the outer edge and the inner edge of the C-shaped design. The numerical analysis is further investigated with the change in design parameters like the height of metasurface design (T), height of dielectric layer (S), width of C-shaped on metasurface (W), and the height of bottom layer (B) to observe the effect on absorption band. The design is also insensitive with the change in the angle of incidence such that proposed solar absorber can be used from energy harvesting.

Superradiant Ensembles of Terahertz Polaritonic Meta-Atoms

We experimentally demonstrate the robustness of strong light-matter interaction in an ensemble of terahertz cavities with variable radiation loss. Each cavity in the form of a planar metallic resonator is strongly coupled to intersubband transitions of semiconductor quantum wells. The polariton spectra, measured by time-domain spectroscopy, do not diminish when the cavity ensemble is brought to the superradiant regime with a radiative loss rate increased by a factor of three. In contrast, the splitting of the polariton frequencies gets larger, and indicates an increased vacuum Rabi frequency. We attribute the observed phenomenon to this well-known many-body effect in quantum electrodynamics, but here associated to an ensemble of otherwise independent polariton systems.

Optically Reconfigurable Graphene/Metal Metasurface on Fe:LiNbO3 for Adaptive THz Optics

We demonstrate, experimentally, nonvolatile optical control of terahertz metasurfaces composed of a metallic split-ring resonator array sandwiched between monolayer graphene and a photoconductive F...

Finite-Element Simulation of the Eigen Frequency Spectrum of the Cylindrical Resonator with Geometrical Imperfectness

The solid-state wave gyroscope belongs to the class of the so-called Coriolis vibratory gyroscopes. They are industrially produced, as a rule, in two versions: precise solid-state wave gyroscopes with expensive fused quartz resonators, and devices of low accuracy with metal resonators. The use of metal for the manufacture of a solid-state wave gyroscope resonator for inertial systems of medium and low accuracy can significantly simplify the design of the device and reduce its cost, however, the low-quality factor of the metal resonator and the instability of its dissipative characteristics limit the accuracy characteristics of the solid-state wave gyroscope. The use of high-quality precision fused quartz glass resonators in such solid-state wave gyroscopes is unacceptable because of their high cost. The purpose of the work is to study the characteristics of inexpensive quartz resonators made from industrially produced fused quartz tubes, with the aim of creating a medium-accuracy solid-state wave gyroscope. Using the finite element method, the main types of geometric heterogeneities arising from the production of such resonators and their influence on their spectral characteristics are investigated. The experimental results allow us to draw conclusions about the most significant defects affecting the performance and accuracy of the solid-state wave gyroscopes

Multifunctional Geometric Metasurfaces Based on Tri‐Spectral Meta‐Atoms with Completely Independent Phase Modulations at Three Wavelengths

AbstractMetasurface has drawn much attention due to its unprecedented wave‐front manipulation abilities with an ultrathin flat profile. However, the metasurface as a diffractive device usually suffers from chromatic aberrations, which greatly hinders the design freedom at different wavelengths. In this work, it is demonstrated that this limitation can be overcome by a multifunctional metasurface with completely independent phase modulations at three arbitrarily wavelengths. Specifically, a novel single‐layer tri‐spectral meta‐atom composed of three alternatively arranged slot and metallic resonators is proposed to operate at three distinct wavelengths, where 2π geometric phase modulations under the circularly polarized incidence can be achieved independently by rotating the corresponding resonators. As proof of concept demonstrations, a tri‐wavelength vortex beam generator and a meta‐hologram are designed to verify the proposed method. First, a vortex beam generator with arbitrary topological charge numbers at three wavelengths is designed and verified through theoretical calculation and full‐wave simulation. Moreover, a meta‐hologram generated by the computer‐generated holography is designed to display three frequency selective holographic images on the same image plane. The tri‐wavelength meta‐hologram is validated through theoretical calculation, full‐wave simulation, and experiment. The experimental results agree very well with the numerical ones, demonstrating the attractive capabilities of multifunctionalities at three wavelengths.

Tunable Plasmon-Induced Transparency through Bright Mode Resonator in a Metal–Graphene Terahertz Metamaterial

The combination of graphene and metamaterials is the ideal route to achieve active control of the electromagnetic wave in the terahertz (THz) regime. Here, the tunable plasmon-induced transparency (PIT) metamaterial, integrating metal resonators with tunable graphene, is numerically investigated at THz frequencies. By varying the Fermi energy of graphene, the reconfigurable coupling condition is actively modulated and continuous manipulation of the metamaterial resonance intensity is achieved. In this device structure, monolayer graphene operates as a tunable conductive film which yields actively controlled PIT behavior and the accompanied group delay. This device concept provides theoretical guidance to design compact terahertz modulation devices.

Comparison of the Goos–Hänchen Shift Induced by Surface Plasmon Resonance in Metal–MoSe2–Graphene Structure

The surface plasmon resonance (SPR) based on the two-dimensional (2D) materials is proposed to enhance the Goos–Hanchen (GH) shift. In MoSe2-graphene-coated heterostructure with different metals (Ag/Cu/Au), the GH shift is significantly enhanced. In order to realize high GH shift, the number of MoSe2 and graphene layer are optimized. Through comparative analysis, by using Ag as the metal, the best GH shift up to 434.7λ can be achieved with the MoSe2 and graphene monolayer. The optimum GH shifts of Au/Cu-MoSe2-graphene structures are 360.7λ and 190.1λ, respectively. Therefore, the highest GH shift corresponding to the sensitivity of 6.600 × 105λ/RIU is obtained by Ag–MoSe2–graphene structures. Moreover, the sensitivity of Au–MoSe2–graphene structures is 5.815 × 105λ/RIU, which is about 1000 times higher than the Au, Au–graphene, and Au–MoSe2 structure. The GH shift sensor with 2D-materialsan be extensive used in the fields of biological researches, optical sensing, and measurement.

Approaching the upper limits of the local density of states via optimized metallic cavities.

By computational optimization of air-void cavities in metallic substrates, we show that the local density of states (LDOS) can reach within a factor of ≈10 of recent theoretical upper limits and within a factor ≈4 for the single-polarization LDOS, demonstrating that the theoretical limits are nearly attainable. Optimizing the total LDOS results in a spontaneous symmetry breaking where it is preferable to couple to a specific polarization. Moreover, simple shapes such as optimized cylinders attain nearly the performance of complicated many-parameter optima, suggesting that only one or two key parameters matter in order to approach the theoretical LDOS bounds for metallic resonators.

Triple-Band Terahertz Perfect Light Absorber Using the Strong Interaction of Two Metallic Resonators

An approach to realize a multiple-band perfect light absorber is demonstrated using a simple metamaterial design featuring a composite metallic structure consisting of a closed ring and a rectangular patch atop a metallic substrate separated by an insulator. Three narrow-band and discrete resonance peaks with nearly 100% absorption rates are obtained. The first absorption peak is due to the dipole resonance of the closed ring, while the last two absorption peaks are caused by the coupling effect of the closed ring and rectangular patch. The field distribution of the three absorption peaks is given to provide additional evidence. Unlike traditional multiple-band light absorbers that eliminate (or avoid) the interaction between the metallic array structures, our design is based on the mode coupling of the composite structure. This method can obviously reduce the number of metallic resonators, simplify the structure design and reduce fabrication costs.

Dynamic Scattering Steering with Graphene‐Based Coding Metamirror

AbstractThe recent development of metasurfaces offers a unique technique for the arbitrary control of electromagnetic waves by spatially manipulating their amplitudes and phases. However, real time control in metasurfaces typically depends solely on dynamical phase modulation, but lacks of the amplitude modulation. In this paper, the dynamical amplitude modulation is tried to combine with phase coding metasurface, for the dynamical manipulation of electromagnetic scattering at microwave frequencies. Such an active metasurface is achieved by placing a patterned graphene layer on binary metallic resonators. When applying bias voltages on the graphene layer, continuous reflection amplitude modulation can be achieved for the selected resonators while the others are not affected. By this merit, two degrees of freedom, preset phase coding and dynamical amplitude modulation, are obtained to control the electromagnetic wave. As an example, a metasurface that can dynamically and continuously control the scattering pattern from mirror reflection to diffusion scattering is shown. The above concepts and physical phenomena are confirmed by numerical simulations and experiments.

Phenomenon of Electromagnetic Field Resonance in Metal and Dielectric Gratings and Its Possible Practical Applications

Calculations of the field distribution in the structure of the dielectric substrate/buffer layer/volume phase grating/analyzed medium were performed. It is shown that in the presence of a buffer layer with a low refractive index in the dielectric waveguide leads to a shift of the maximum field at the waveguide resonance into analyzed medium. As a result, the spectral and angular sensitivity of the corresponding sensor increases. Based on the waveguide equation, analytical expressions are obtained that connect the spectral and angular sensitivity of the sensor to the sensitivity of the propagation constant change due to the refractive index change of the analyzed medium. The conditions for the excitation of the resonance of surface plasmon–polariton waves in the structure with a metal or dielectric grating on a metal substrate are also given. The fields that occur at resonance for silver and gold gratings are calculated.

Multifunctional reflective dielectric metasurface in the terahertz region.

The recent emergence of digital coding metasurfaces has significantly simplified the design of functional devices and manipulated electromagnetic waves digitally. In this paper, we propose a dielectric coding metasurface with different functions, which is implemented by a metasurface with specific coding sequences. It is composed of a three-dimensional T-shaped dielectric block placed on a metal plate. Compared with traditional metal resonators, the all-dielectric metasurface has relatively low loss and the reflection amplitude maintains a high value. Here, we demonstrate five different functions of anomalous reflection, beam splitting, diffuse scattering, line focusing, and vortex beam generation achieved under normal incidence of the linearly polarized wave. Through full-wave numerical simulation, the far-field scattering patterns and near-field electric-field intensity distribution of the proposed metasurface under various reflection conditions are obtained, which is in good agreement with the theoretical prediction. It is verified that the multifunctional dielectric coding metasurface provides a new way to control the reflection of terahertz waves.

High-Throughput and Dynamic Study of Drug and Cell Interactions Using Contrast Images in Aluminum-Based Nanoslit Arrays

High-throughput and dynamic measurement for living cell activities can benefit biological research and drug development. A low-cost metallic nanostructure-based surface plasmon resonance (SPR) imaging platform, comprising multiple aluminum nanoslit arrays and a color image device, is proposed for label-free study of cell and drug interactions. The multiple nanoslit sensing arrays were fabricated using the compression-injection molding process. These sensing chips showed a detectable depth of 600 nm and refractive index resolution of ∼5 × 10-5 refractive index unit (RIU) by using a self-referenced two-color analysis. Two examples of kinetic studies of living cells under various doses of drugs are presented. The focal adhesion kinases inhibitor (FAKi 14) and cell interactions show exponential changes of cellular adhesion and time constants for different concentrations of antiadhesion drugs. The anticancer drug (doxorubicin (DOX))-treated cells show slow increases of SPR signals in the first 2 h due to the nucleus swelling. The DOX-treated cells further process plasma membrane disruption and become floating cells and debris in the medium, resulting in rapid drops of the SPR signals.

Silicon-Au nanowire resonators for high-Q multiband near-infrared wave absorption

Semiconductors have been widely utilized to fabricate optoelectronic devices. Nevertheless, it is still a challenging task to achieve high-quality (Q) resonant light absorption using the high refractive index semiconductors. In this work, we propose a facile scheme for multi-band perfect absorption in the near-infrared range using an array of core–shell cylinder-shaped resonators which are composed of gold nanowires and thin silicon shells. Based on the cooperative effects between the photonic modes of the semiconductor cavity and the plasmonic resonances of the metal resonator, five sharp absorption peaks are observed with the maximal absorption close to 100% (99.98%) and a high Q factor up to 208. The multi-band sharp absorption is observed to be angle-insensitive and polarization-adjustable. Absorption efficiency can be quantitatively tuned via the polarization states following the classical Malus law. Moreover, different semiconductors such as gallium arsenide, indium arsenide, indium phosphide have been exploited to reproduce the sharp perfect absorption in this core–shell resonators platform. The remarkable features make the proposed system potential for multiple applications such as multispectral filtering, photo-detection and hot electron generation.

Ultra-broadband and wide-angle terahertz polarization converter based on symmetrical anchor-shaped metamaterial

We propose a reflective terahertz metamaterial linear polarization converter, consisting of three layers: an array of metallic symmetrical anchor-shaped resonators, poly tetra fluoroethylene (PTFE) as a low loss dielectric layer, and a metal surface ground plane. The simulation results show that the proposed metamaterial can convert the linearly polarized waves into the cross-polarized waves with a polarization conversion ratio (PCR) of above 93% in the frequency range of 1.21–2.83 THz and the relative bandwidth is as high as 80.2%. The proposed metamaterial is valid for a wide range of incident angles, and the average polarization conversion ratio remains 93% even though the incident angle reaches 45°. Additionally, we theoretically analyzed the conversion mechanism of achieving a high-efficiency linear polarization conversion in a wide frequency range by calculating the polarization angle and elliptical angle of the reflected terahertz waves. The experiment results using the terahertz time domain spectroscopy (THz-TDS) consist well with the simulation results. Our design will provide an important reference for the practical applications of the metamaterials in polarization manipulation.

A Metallic Waveguide-Integrated 35-GHz Rectenna With High Conversion Efficiency

A novel waveguide-integrated rectenna with high conversion efficiency is proposed and implemented at 35 GHz in this letter. A metallic Fabry-Perot resonator antenna is designed as the receiving antenna. Using the metallic structure instead of the microstrip structure that is widely used in the conventional rectenna design, the dielectric loss is avoided and a high radiation efficiency of 95.5% is achieved at 35 GHz. The rectifier is designed with a shielded microstrip line and fed with a rectangular waveguide to lower its radiation loss and insertion loss. At 35 GHz, a rectifying efficiency of 67% is measured for the waveguide-fed cavity rectifier. By integrating the receiving antenna and the rectifier with the rectangular waveguide, a waveguide-integrated 35-GHz rectenna is proposed for the first time. A prototype is fabricated and measured. The measured highest RF-to-dc conversion efficiency is 68.5% at 35 GHz when the power density is 39.3 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Symmetry-broken silicon disk array as an efficient terahertz switch working with ultra-low optical pump power**Project supported by the National Key R&D Program of China (Grant No. 2017YFA0701005) and the National Natural Science Foundation of China (Grant Nos. 11974221, 91750201, 61927813, and 61775229). Z. Han also acknowledges the support from the Taishan Scholar Program of Shandong Province, China (Grant No. tsqn201909079)

The advancement of terahertz technology in recent years and its applications in various fields lead to an urgent need for functional terahertz components, among which a terahertz switch is one example of the most importance because it provides an effective interface between terahertz signals and information in another physical quantity. To date many types of terahertz switches have been investigated mainly in the form of metamaterials made from metallic structures and optically-active medium. However, these reported terahertz switches usually suffer from an inferior performance, e.g., requiring a high pump laser power density due to a low quality factor of the metallic metamaterial resonances. In this paper, we report and numerically investigate a symmetry-broken silicon disk based terahertz resonator array which exhibits one resonance with ultrahigh quality factor for normal incidence of the terahertz radiations. This resonance, which can never be excited for regular circular Si disks, can help to realize a superior terahertz switch with which only an ultra-low optical pump power density is required to modify the free carrier concentration in Si and its refractive index in the terahertz band. Our findings demonstrate that to realize a high terahertz transmittance change from 0 to above 50%, the required optical pump power density is more than 3 orders of magnitude smaller than that required for a split-ring resonator (SRR) based terahertz switch reported in the literature.

A Metamaterial Absorber Operating in the Visible Light Band Based on a Cascade Structure

In this paper, a broadband and polarization-insensitive metamaterial absorber (MA) operating in the visible light band based on a cascade structure is proposed, and the main structure of MA consists of three metal resonator layers (MRLs), a metal reflector at the bottom, and a dielectric substrate between them. Each MRL consists of four different resonators. The similar resonator is proportional to the size of the top view in the different MRLs. Through the different absorption effects generated by different MRLs, a MA working in the visible light band is obtained, which can cover 490–825 nm. Absorption bandwidth can be expanded by adding different MRLs and placing different resonators near the same layer. The center frequency of the absorption spectrum can be controlled by changing the layer distance between different MRLs. To better understand the physical mechanism of absorption, the electric and magnetic field intensity distributions, the power flows, and the power loss densities also are investigated. We also found that the better permanence can be obtained with the lower incident angle.

A thermally tunable terahertz three-dimensional perfect metamaterial absorber for temperature sensing application

We present a three-dimensional (3D) perfect metamaterial absorber (PMA) for temperature sensing application in terahertz region. The PMA consists of a 3D metal resonator structure array and a continuous metal film separated by an indium antimonide (InSb) layer. The numerical simulations demonstrate that the PMA can achieve perfect absorption (about 99.9%) with the high [Formula: see text]-factor of about 18.8 at 2.323 THz when the temperature is 300 K (room temperature). Further simulation results indicate that this terahertz PMA is polarization-insensitive and wide-angle for both transverse electric (TE) and transverse magnetic (TM) waves. The electric field and surface current distributions of the unit-cell structure indicate that the perfect absorption is originated from the excitation of the fundamental magnetic and electric dipole resonance mode. Since the permittivity of the InSb is sensitive to the external temperature, the resonance absorption frequency of the PMA can be dynamically adjusted. The temperature sensitivity of the PMA is about 15.24 GHz/K, which may have potential prospects in temperature sensing and detection.

Ultrathin Electromagnetic–Acoustic Amphibious Stealth Coats

AbstractRadar and sonar technologies are generally used to detect objects in air space and water. In some cases, both technologies are involved in probing waterborne objects like submarines. However, the simultaneous stealth regarding these two detection methods is not well explored due to the difficulty in satisfying material properties for two different physical systems. In this work, an artificial ultrathin amphibious stealth coat with a minimum thickness less than 0.5 mm achieving free‐space microwave and underwater acoustic absorption is proposed and demonstrated. It is realized by combining an electromagnetic metasurface and an acoustic metasurface—a flexible printed circuit with multisized metal resonators and a polydimethylsiloxane film with multisized air cavities. These two alien metasurfaces are engineered with minimized disturbance to each other by controlling the thicknesses of the resonators as thin as possible. A free‐space microwave absorptivity over 80% in the 12.38–13.7 GHz region and an underwater acoustic reflectance less than 10% in the 80–160 kHz region are obtained experimentally. The current work may shed light on advanced stealth technologies of the free‐space microwaves and underwater acoustic waves.