Metallic Resonators Research Articles

High-Efficiency Dynamic Terahertz Deflector Utilizing a Mechanically Tunable Metasurface.

Terahertz (THz) wave manipulation, especially the beam deflection, plays an essential role in various applications, such as next-generation communication, space exploration, and high-resolution imaging. Current THz optical components and devices are hampered by their large bulk sizes and passive responses, limiting the development of high-performance, miniaturized THz microsystems. Tunable metasurfaces offer a powerful dynamic optical platform for controlling the propagation of electromagnetic waves. In this article, we presented a mechanically tunable metasurface (MTM), which can achieve terahertz beam deflection and vary the intensity of the anomalous reflected terahertz wave by changing the air gap between the metallic resonator (MR) array with phase discontinuities and Au ground plane. The absence of lossy spacer materials substantially enhances deflection efficiency. The device was fabricated by a combination of the surface and bulk-micromachining processes. The THz beam steering capability was characterized using terahertz time domain spectroscopy. When the air gap is 50 μm, the maximum deflection coefficient reaches 0.60 at 0.61 THz with a deflection angle of ~44.5°, consistent with theoretical predictions. We further established an electrically tunable miniaturized THz device for dynamic beam steering by introducing a micro voice coil motor to control the air gap continuously. It is shown that our designed MTM demonstrates a high modulation depth of deflection coefficient (~ 62.5%) in the target steered angle at the operating frequency. Our results showcase the potential of the proposed MTM as a platform for high-efficiency THz beam manipulation.

Plasmon resonance in split-ring resonator based heterostructures

We herein propose a plasmonic nanostructure that is composed of heterogeneous metallic split-ring resonator (SRR) trimers with built-in crosses. We studied its optical transmission properties by using finite difference time domain (FDTD) method. Results showed that, the resonant modes can be changed when the nanostructures are composed of different types of metals. For the heterogeneous metallic SRR trimers, the resonant modes were in the near-infrared region blue shift, but the modes remained the same when the air slit width was increased. All the dips red-shifted as dielectric constant of the SRRs medium was increased. The resonant modes in the visible region red shifted when the arms of metallic cross length were increased, but locations of resonance dips in the near-infrared region remained unchanged. Magnetic and electric field distributions for certain wavelengths were also investigated.

Fully Printed Dual-Layer Depolarizing Chipless RFID Tag for Wearable Applications

This work presents a cross-polar dual-layer chipless radio-frequency identification (RFID) tag based on a ladder-shaped resonator design. An integrated ground plane enables direct attachment to human skin without performance deterioration. Simulations show that the ladder-shaped resonator provides several advantages over traditional L-shaped and straight resonators, including a strong cross-polar radar cross section (-23.4 dBsm), third-order harmonics, orientation insensitivity, and compact size (0.062 λ2). The effects of the ground plane shape on the surface current distribution are investigated, and a circular tag of 20 mm radius is designed using ladder resonator groups and frequency shift encoding to provide an active area of 96.45 bits/λ2 and a unit frequency of 6.03 bits/GHz. The tag substrate is three-dimensionally (3D) printed with metallic resonator patterns that are subsequently screen-printed on the substrate. The maximum read range is measured at 40 mm using a cross-shaped, dual-polarized Vivaldi antenna connected to a network analyzer. The measured characteristics in free space are in good agreement with the simulation results, and practical on-body performance tests for the manufactured prototype using simulation and direct measurements indicate that the tag performance remains stable for both free space and on-body cases. The fully printed fabrication process makes the proposed tag design suitable for mass production at a low cost.

An ultrathin and flexible terahertz electromagnetically induced transparency-like metasurface based on asymmetric resonators

Terahertz (THz) electromagnetically induced transparency-like (EIT-like) metasurfaces have been extensively explored and frequently used for sensing, switching, slow light, and enhanced nonlinear effects. Reducing radiation and non-radiation losses in EIT-like systems contributes to increased electromagnetic (EM) field confinement, higher transmission peak magnitude, and Q-factor. This can be accomplished by the use of proper dielectric properties and engineering novel designs. Therefore, we fabricated a THz EIT-like metasurface based on asymmetric metallic resonators on an ultra-thin and flexible dielectric substrate. Because the quadruple mode is stimulated in a closed loop, an anti-parallel surface current forms, producing a transparency window with a transmission peak magnitude of 0.8 at 1.96 THz. To control the growing trend of EIT-like resonance, the structure was designed with four asymmetry levels. The effect of the substrate on the resonance response was also explored, and we demonstrated experimentally how the ultra-thin substrate and the metasurface asymmetric novel pattern contributed to higher transmission and lower loss.

Design for the reconfigurable polarization rotator by inhibiting Fano resonance with graphene-metal grating structures

In this paper, the Fano resonance associated with the integrated grating-enhanced transmissive cross-polarization rotator (TCPR) superimposed via two polarization plates operating in disparate frequency bands is observed. The metal resonance frequency dramatically impacts the Fano effect, which triggers alterations in polarization conversion ratio (PCR). Through the analysis for the surface current distributions, the spring vibrator model driven by external forces in two orthogonal directions is employed to figure out the internal mechanism of the Fano line shape in the PCR curve. Subsequently, the symmetrical lateral current branches on the two gold polarization sheets are accessible. The relative bandwidth (RBW) value and the operating region of the ultimate optimized TCPR are 84.6% and 0.563 THz–1.388 THz, respectively. In other words, the PCR band is expanded successfully. Intended to obtain the fabulous polarization switching behavior to enhance the reconfigurability, the gated voltagedriven graphene is doped in grating gaps with the chemical potential fluctuating uniformly between 0.01 and 0.50 eV. The proposed optimizations with the PCR and the final TCPR are distinguished from precedented instances in the RBW and tunability, which is universally applicable in multitudinous terahertz-controlled scenarios.

Experimental investigation of the maximum quality factor axes temperature deviation in metallic Coriolis vibratory gyroscopes resonator

A metallic cylindrical resonator is a well-known base detail of the significant part of Coriolis vibratory gyroscopes (CVG) [1] including a MEMS gyro. It own parameters just after mechanical manufacture in main are determine an advisability of further utilize and the future gyroscope accuracy potential. Initial testing CVG resonators directly after their manufacture often done using the optical method [2,3] or acoustic method [4,5]. Unfortunately investigated manufacture quality of the resonators by using acoustic method not very well describe in scientific literature. A paper presents the results of some extension acoustic investigations of the metallic CVG resonators. This result describes the behavior of maximum quality factor (Q-factor) axes and own resonant frequencies axes under stabilized temperature step influences and can be used in prediction for CVG bias minimization during it works in temperature range.

The state and prospects of the development of vibration gyroscopy in Ukraine and in the world

The work analyzes the development and current state of vibration gyroscopes in Ukraine and in the world. The development of quartz and metallic resonators of various diameters for vibrating gyroscopes is presented and analyzed. In addition, for comparison with world practice, the developments of quartz and metallic resonators of advanced foreign companies, leaders in this field, are given. The block diagrams of the standing wave control system of the vibrating gyroscope in three modes of operation: as the angle rate sensor, as the rate-integrating or whole angle mode sensor and the differential mode are considered. In the perspective, the possibility of combining all three modes in one gyroscope with automatic switching from one mode to another one is shown, for maximum use of the advantages of each mode in dependence of environmental conditions and motion parameters. The test results of gyroscope with a metallic resonator made in Ukraine, on the effect of a wide range of external disturbances are presented. The development prospects of vibrating gyroscopes and systems based on them are evaluated. The paper draws conclusions about the state and prospects for the development of vibrating gyroscopy in Ukraine.

Terahertz generations of transmissive deflection, focusing, and orbital angular momentum with polarization conversion

By coding meta-atom with discrete phase, electromagnetic wavefront can be flexibly manipulated with the pre-designed coding sequence. In this work, transmissive metasurfaces are proposed to achieve wavefront reconfiguration with polarization conversion for terahertz wave. Based on composite structures of metallic resonators and polyimides, the designed meta-atoms are capable of polarization conversion and 360° phase modulation by changing notch angle and rotation angle of resonators at 2.0 THz. Then, three types of metasurfaces are designed.Firstly, transmissive wavefront of gradient metasurface is reconstructed through periodic alignment of eight meta-atoms along x axis. This metasurface realizes anomalous transmission and transforms x-polarized incidence to y-polarized wave.Secondly, two focusing lenses are implemented, and they realize single-focusing and dual-focusing under x-polarized incidence. Finally, two vortex beam generators are proposed with orbital angular momentum modes of l = 1 and l = 2 in channel of cross polarization. Our designs may be applied in the fields of terahertz communication, focusing, and encryption.

Enabling broadband efficient beam splitting based on ultra-thin reflecting metasurfaces

In this paper, we present a scheme for achieving broadband efficient beam splitting based on homogeneous ultra-thin metasurfaces, which is composed of an ultrathin dielectric spacer sandwiched between periodic arrays of identical rectangular metal resonators and an optically thick metal film. Based on this scheme, three beam splitters for incident wavelengths in the ultraviolet (UV), visible, and infrared (IR) are designed and investigated numerically. Although these beam splitters exhibit polarization-dependent optical responses, each one still has an operational band in which the conversion efficiency remains above 90 % for any polarization incidence. The operational band is respectively 250–299 nm, 478–574 nm, and 1411–1700 nm for these three metasurface-based beam splitters. Moreover, we propose a dual-band beam splitter and a four-channel beam splitter based on this metasurface with MIM configuration. The operational window of the dual-band beam splitter respectively locates in the visible and infrared regions.

Study of a solid-state vibrating gyroscope in the mode of determining the true azimuth of a given direction and the latitude of the location of the object

The accuracy of determining navigation parameters, the true azimuth of the specified direction, and the latitude of the object's location is being investigated using a Coriolis vibratory gyroscope with a cylindrical metal resonator as a sensitive element of the tactical accuracy class for stabilization systems and control of moving objects. The study used a scheme of a scanning single-component analytical gyroscope compass with the ability to provide vertical direction scanning during the input axis of the angular velocity sensor – the Coriolis vibratory gyroscope. The obtained root-mean-square value of 0,32°·secφ of the error in determining the true azimuth of the specified direction under conditions close to normal confirms the potential possibility of using a Coriolis vibratory gyroscope with a cylindrical metal resonator in orientation and attitude heading reference systems. The average error of 0,34 in determining the latitude of the object's location obtained under the same conditions, with a root-mean-square value of of it is scatter, correlates with the expected result.

Plasma Ag-loaded bandgap variational Zn1-xMgxO-enhanced charge separation for photoelectrochemical water oxidation of CuWO4 photoanodes

The recombination of photogenerated carriers and sluggish surface oxidation kinetics severely inhibited the development of copper tungstate (CuWO4) photoanode photoelectrochemical (PEC) water oxidation. Herein, the Zn1-xMgxO-modified CuWO4 photoanode ameliorated the vital matter of easy recombination of electron-hole pairs, where the transformation of the heterojunction type (type I to type II) between Zn1-xMgxO and CuWO4 played a crucial role in the extraction of carriers. Further, the effective charge separation was obtained utilizing the local surface plasmon resonance (LSPR) of plasma metal (Ag), which facilitated the PEC water oxidation reaction. Besides, the surface states trapped/stored holes and reduced charge transfer resistance, thus facilitating charge transfer. The overlap of the fillable surface states with filled redox coupled states ensured the enhancement of the water oxidation kinetics, which further promoted the charge transfer. As a result, the optimized CuWO4/Zn0.7Mg0.3O/Ag photoanode showed significant advancement in photocurrent density (1.71 mA/cm2 at 1.23 V vs. RHE), electrochemical impedance and stability. This work emphasized the interfacial structure modulation of two strategies that potentially provide more ideas and options for the design of other efficient photoanodes.

Dynamically switching the asymmetric transmission and monodirectional absorption of circularly polarized waves using cascade composite resonator-graphene meta-surfaces.

We propose a reconfigurable hybrid graphene meta-surface for modulating circularly polarized (CP) waves with dual functionalities of asymmetric transmission (AT) and monodirectional absorption. Such a meta-surface consists of three cascade dielectrics covered with identical metallic resonators and different patterned graphene sheets over the front and the back sides, respectively. The left-handed CP incidences will be transformed into right-handed CP counterparts efficiently with an AT-parameter of 0.8, and the state of transmission will be contrary when the incident CP waves are from the opposite direction. On the other hand, the proposed cascade composite resonator-graphene meta-surface can also function as a super monodirectional absorber to trap the forward incident CP waves at the same frequency range when we simply tune the Fermi energy of graphene. The proposed design should pave the way for building up more advanced meta-devices with multiple functionalities to manipulate CP waves.

Surface plasmon polaritons enhanced magnetic plasmon resonance for high-quality sensing

We investigate the metamaterials consisting of top layer U-shaped metallic split-ring resonators, the middle thin dielectric layer, and the bottom thick metal film, which can realize high-quality refractive index sensing. When propagating surface plasmon polaritons are introduced, two ultra-narrow-band hybridized modes will appear, whose full width at half maximum can reach up to 2.5 nm. Because of the ultra-narrow linewidth and huge magnetic field enhancement at hybridized modes, the metamaterials display very high sensitivity (S = 912 nm RIU−1, S* = 95.64 RIU−1) and large figure of merit (FOM = 364.8, FOM*= 160 740.34), which has great potential in label-free biomedical sensing.

Simple terahertz metasurface with broadband and efficient functionality.

Pancharatnam-Berry (PB) metasurfaces have demonstrated mighty capability to manipulate electromagnetic (EM) waves, and exhibited potential applications for devices with broadband and efficient functionality. However, it remains a challenge to simultaneously achieve broadband and efficient wavefront manipulation for terahertz (THz) components with simple profiles. Herein, we introduce a simple ultra-thin PB metasurface with superior properties in the THz region. The structure is composed of a simple metallic C-Shaped Split Ring Resonator (CSRR) patterned on a flexible polyimide support layer. It is verified that the circular transmission efficiency is close to the theoretical limit of the single-layer metasurface in the range of 0.6 - 1.2 THz. Furthermore, we design metasurfaces based on the PB meta-atoms with spatially rotated orientation to achieve beam steering and superposition of vortex waves. The results are basically in line with expectations, validating the good performances of our proposal. This simple and easily deployable metasurface will give rise to more possibilities for the design of THz functional devices.

Mid-Infrared Hollow-Core Fiber Based Flexible Longitudinal Photoacoustic Resonator for Photoacoustic Spectroscopy Gas Sensing

Photoacoustic spectroscopy (PAS) has received extensive attention in optical gas sensing due to the advantages of high sensitivity, gas selectivity, and online detection. Here, a mid-infrared hollow-core fiber (HCF) based flexible longitudinal photoacoustic resonator for PAS-based gas sensing is proposed and theoretically demonstrated. A mid-infrared anti-resonant HCF is designed to innovatively replace the traditional metallic acoustic resonator and obtain a flexible photoacoustic cell in PAS. Optical transmission characteristics of the HCF are analyzed and discussed, achieving single mode operation with below 1 dB/m confinement loss between 3 and 8 μm and covering strong absorptions of some hydrocarbons and carbon oxides. With varied bending radii from 10 mm to 200 mm, the optical mode could be maintained in the hollow core. Based on the photoacoustic effect, generated acoustic mode distributions in the HCF-based flexible photoacoustic resonator are analyzed and compared. Results show that the PAS-based sensor has a stable and converged acoustic profile at the resonant frequency of around 16,787 Hz and a favorable linear response to light source power and gas concentration. The proposed novel photoacoustic resonator using HCF presents bring potential for advanced flexible PAS-based gas detection.

Optically controlled and polarized sensitivity adjustable terahertz metamaterial absorber

A photoactive terahertz (THz) absorber is designed based on the quadruple rotational symmetrical metamaterial structure combined with the GaAs bars. For the bare metallic metamaterial structure, the THz absorber shows a polarization insensitive property with two perfect absorption peaks at 0.62 THz and 0.84 THz, and the absorption rates are 98.80 % and 99.97 %, respectively. For the GaAs functionalized metamaterial structure, the hybrid THz absorber is equivalent to the metallic resonator in the absence of the pump light since the GaAs bars are in an insulated state with the conductivity of 100 S/m. Further, the GaAs bars turn into a metallic state as the conductivity increases to 5 × 105 S/m under pump light. The hybrid THz absorber becomes an axisymmetric structure with a polarization sensitive property, which could excite two new perfect absorption frequencies at 0.71 THz and 2.24 THz, and the corresponding absorptivity are 99.80 % and 99.90 %. The simulated electronic field distribution and surface current distribution indicate that the perfect absorption is due to the dipole resonant modes. The proposed optically controlled and polarization tunable THz metamaterial absorber provides potential applications in the related fields of THz switches, detectors, and imaging.

Terahertz high-Q magnetic dipole resonance induced by coherent Fano interactions

High Q-factor resonance holds great promise for bio-chemical sensing and enhanced light–matter interaction. However, terahertz (THz) magnetic resonances usually demonstrate low Q-factors, resulting in huge energy radiation loss particularly in high frequency bands. Here, we show that high Q-factor magnetic dipole resonance at THz frequencies can be achieved by exploiting the coherent Fano interactions with strong field enhancements in an array composed of single metallic split-ring resonators, working at Wood–Rayleigh anomalies. It can give rise to ultrahigh Q-factor beyond 104 in the THz regime. Experimentally, the measured Q-factor of dominant magnetic dipole resonance can achieve no less than a level of ∼261 by Lorentzian fitting to the experimental data. In addition, a high Q-factor of the fundamental-order magnetic dipole resonance is demonstrated beyond 30. High-Q magnetic dipole resonance is closely associated with ultralow-damping and negative permeability in the THz band. The measurements of magnetic dipole resonances are in good agreement with the theoretical analyses. Our scheme suggests a feasible route to suppress radiative loss for enhanced THz field-matter interaction.

Ultra-broadband nanowire metamaterial absorber

Broadband absorbers generally consist of plasmonic cavities coupled to metallic resonators separated by a dielectric film, and they are vertically stacking configurations. In this work, we propose an ultra-broadband nanowire metamaterial absorber composed of an array of vertically aligned dielectric nanowires with coaxial metallic rings. The absorber shows strong absorption from 0.2 to 7 μm with an average absorption larger than 91% due to the excitation of gap surface plasmon polariton modes in Fabry–Perot-like resonators. Moreover, a refractory dielectric cladding can be added to improve the thermal stability of the absorber, showing a negligible impact on its absorption performance. The proposed absorber may find potential applications in solar energy harvesting, infrared imaging and spectroscopy, and optoelectronic devices.

Tunable metamaterial absorber based on VO2-graphene

In this paper, a tunable multilayer metamaterial absorber is proposed, which is composed of VO2-graphene mixed structure layer, PDMS dielectric layer, VO2 layer, PDMS dielectric layer and bottom metal film layer. The simulation results show that when VO2 is in the insulating phase and the Fermi level of graphene is 0.9 eV, the absorption peak of 0.75–1.15 THz is generated by the interaction resonance of graphene and bottom metal. When VO2 is in metal phase and the Fermi level of graphene is 0 eV, the absorption peak of 2.5–4.5 THz is generated by the resonance of vanadium dioxide. Therefore, the tunable switching between two different frequency bands can be realized. Moreover, the dual regulation of both vanadium dioxide conductivity and graphene Fermi energy level can also modulate the absorption amplitude and broaden absorption band. In order to explain the mechanism of VO2-graphene on the absorption performance, the electric field distribution and equivalent impedance of the absorber are discussed and analyzed in this paper. In addition, the absorption performances at variable incidence angles for both TE and TM polarizations are investigated and the absorber is insensitive to polarization. Therefore, the absorber has potential application value in the terahertz field.

Engineering Heterostructures of Layered Double Hydroxides and Metal Nanoparticles for Plasmon-Enhanced Catalysis

Artificially designed heterostructures formed by close conjunctions of plasmonic metal nanoparticles (PNPs) and non-plasmonic (2D) lamellar nanostructures are receiving extensive interest. The synergistic interactions of the nanounits induce the manifestation of localized surface plasmon resonance (LSPR) in plasmonic metals in the specific environment of the 2D-light absorbing matrix, impacting their potential in plasmon enhanced catalysis. Specifically, layered double hydroxides (LDH) with the advantages of their unique 2D-layered structure, tuned optical absorption, ease of preparation, composition diversity, and high surface area, have emerged as very promising candidates for obtaining versatile and robust catalysts. In this review, we cover the available PNPs/LDH heterostructures, from the most used noble-metals plasmonic of Au and Ag to the novel non-noble-metals plasmonic of Cu and Ni, mainly focusing on their synthesis strategies toward establishing a synergistic response in the coupled nanounits and relevant applications in plasmonic catalysis. First, the structure–properties relationship in LDH, establishing the desirable features of the 2D-layered matrix facilitating photocatalysis, is shortly described. Then, we address the recent research interests toward fabrication strategies for PNPs/support heterostructures as plasmonic catalysts. Next, we highlight the synthesis strategies for available PNPs/LDH heterostructures, how these are entangled with characteristics that enable the manifestation of the plasmon-induced charge separation effect (PICS), co-catalytic effect, or nanoantenna effect in plasmonic catalysis with applications in energy related and environmental photocatalysis. Finally, some perspectives on the challenges and future directions of PNPs/LDHs heterostructures to improve their performance as plasmonic catalysts are discussed.