Toroidal Excitation Research Articles

Terahertz binary computing in a coupled toroidal metasurface

The applications of terahertz metamaterials are being actively explored in recent times for applications in high-speed communication devices, miniature photonic circuits, and bio-chemical devices because of their wide advantages. The toroidal resonance, a new type of metasurface resonance, has been examined with great interest to utilize its properties in terahertz metasurface applications. This study reports a proof of concept design of a toroidal metasurface that experimentally demonstrates binary computing operations in the terahertz frequency regime. The analog computing of binary operations is achieved by the passive tuning of distance between the split ring resonators comprising the meta-molecule. The amplitude modulation is utilized as a method of determining the Boolean logic outputs of the system. The proposed metasurface could be further optimized for high amplitude modulations and active logic gate operations using tunable materials including graphene and ITO. The proposed metasurface consists of three split-ring resonators, and the near-field coupling between the adjacent resonators dictates the Boolean operations. A multipole analysis of the scattered powers of terahertz radiation determines the toroidal excitation in the metasurface. The proposed metasurfaces experimentally define AND Boolean logic operation at 0.89 terahertz, and OR Boolean logic operation at 0.97 terahertz. Numerical simulations support the experimentally obtained results. Additionally, we numerically report the excitation of NAND operation at 0.87 THz. Such toroidal analog computing metasurfaces could find applications in digitized terahertz circuits and integrated photonic devices.

Hybrid-Excited Variable Reluctance Resolver With Wide Speed Range

The accuracy of the variable reluctance resolver (VR-Resolver) highly depends on the rotational speed and its rotational speed range is limited by the frequency of the excitation signal. To eliminate the mentioned performance dependency, this paper proposes a hybrid-excited VR-Resolver (HVR-Resolver) with two separate sets of excitation windings: a toroidal excitation winding for the AC excitation supply and an on-tooth one for the DC excitation supply. Similar to the conventional method, the HVR-Resolver is working with AC excitation ON and DC excitation OFF at the low-speed range. For high-speed operation, the excitation switched from AC excitation to DC. By using this technique, the proposed HVR-Resolver is able to accurately estimate the position at a wide speed range. This feature makes the HVR-Resolver an outstanding candidate for EV applications. The proposed design is simulated using time-stepping finite element analysis (TSFEA) in order to study the performance at both low-speed and high-speed ranges with different rotor pole numbers. In addition, an optimization process is conducted to find the best rotor shape factors. The experimental test on the proposed HVR-Resolver indicates a close agreement between simulation and experimental results.

Polarization independent lattice-coupled terahertz toroidal excitation

The toroidal dipole excitation is important for metamaterial research because of its low-loss attribute. In this study, we demonstrate numerically and experimentally, a unique toroidal metasurface that modulates a broad resonance into a sharp mode, independent of the polarization of the incident terahertz (THz) radiation, by coupling the inherent toroidal dipole excitation to the lattice mode of the metasurface. The advantage of polarization independence enables the excitation of ‘lattice-coupled toroidal mode’ for both the orthogonally polarized states of the incident THz radiation in the metasurface. The interaction of the two resonances results in the enhancement of the quality factor of the metasurface at the point of resonance matching. The surface current profile as well as multipole analysis of scattered powers by electric, magnetic, and toroidal dipoles confirm the domineering effect of toroidal dipole excitation for both the polarization states of incident THz radiation. Such a lattice-matched toroidal excitation-based device has the potential to impact the development of polarization-independent THz components for ultrasensitive sensors, lattice-enhanced equipment, and slow light devices for light–matter interaction.

Development of a Superconducting Wire for the Central Solenoid of a Tokamak with Reactor Technologies (TRT)

The article presents the results of the preliminary development of a superconducting wire based on the VS type design and parallel tape packages for the central solenoid of a compact tokamak with reactor technologies (TRT). One of the main problems that must be solved for successfully implementing such projects is to develop high-current high-temperature superconducting (HTS) conductors for toroidal excitation coils and central solenoid sections. The magnetic system compactness entails the need to develop a conductor with a high engineering current density up to 90 A/mm2. The operating current in the windings should be at a level of 60 kA at 15 K in a magnetic field of 15 T. The wire in the central solenoid experiences significant mechanical loads caused by Lorentz forces. In addition, in view of a significant energy stored in the magnet, there is a need to have elements in the conductor able to perform emergency evacuation of energy with an acceptable voltage across the winding and its heating that will not entail damage to its elements. The conductor structure should have enough space to accommodate stabilizing and strengthening materials, as well as cooling channels. Two design versions of the VS type conductor based on radially arranged second-generation HTS tapes and based on parallel packages are considered. The design characteristics of the proposed conductors are analyzed for various operating modes of the tokamak electromagnetic system. The results of FEM-based calculations of the magnetic field distribution in a conductor, its current carrying capacity and energy loss estimation in a varying magnetic field are presented.

Sharp Fano resonance in a water-based toroidal dipole metamaterial

The toroidal dipole is implemented by abundant and bio-friendly water with a high dielectric constant in the microwave range. A Fano resonance, with high Q-factor up to 152, resulting from enhanced fancy toroidal dipole could be stimulated at 1.65 GHz. Analysis of the induced current and near- and far-field shows that energy can be concentrated in distilled water, and the intriguing toroidal dipole plays a decisive role in resonance. Under different size parameters and conductivity of water-based metamaterial, the toroidal excitation and its influence on transmission characteristics are discussed. The toroidal dipole excited in distilled water might be of great significance for designing ultra-sensitive sensors, absorbers, and slow-light devices.

Toroidal dipole resonances by a sub-wavelength all-dielectric torus

Electromagnetic toroidal excitations open up a new avenue for strong light-matter interactions. Although toroidal dipole resonances (TDRs) based on artificial meta-molecules were reported intensely, the TDRs supported in a single dielectric particle remain largely unknown. In this work, we show that an all-dielectric sub-wavelength torus can support a dominant TDR. The magnetic field can be enhanced greatly, and it shows a "vortex-like" configuration in the torus, confirming the toroidal excitation. The evolutions of the TDRs due to the geometrical parameters, dielectric permittivity, and polarization are discussed. It is found that the toroidal excitation is achieved mainly for TM polarization, while the anapole state is uncovered for TE polarization. This work suggests a new strategy for toroidal excitations based on a simple dielectric resonator.

Multiband transparency effect induced by toroidal excitation in a strongly coupled planar terahertz metamaterial

The multiband transparency effect in terahertz (THz) domain has intrigued the scientific community due to its significance in developing THz multiband devices. In this article, we have proposed a planar metamaterial geometry comprised of a toroidal split ring resonator (TSRR) flanked by two asymmetric C resonators. The proposed geometry results in multi-band transparency windows in the THz region via strong near field coupling of the toroidal excitation with the dipolar C-resonators of the meta molecule. The geometry displays dominant toroidal excitation as demonstrated by a multipolar analysis of scattered radiation. High Q factor resonances of the metamaterial configuration is reported which can find significance in sensing applications. We report the frequency modulation of transparency windows by changing the separation between TSRR and the C resonators. The numerically simulated findings have been interpreted and validated using an equivalent theoretical model based upon three coupled oscillators system. Such modeling of toroidal resonances may be utilized in future studies on toroidal excitation based EIT responses in metamaterials. Our study has the potential to impact the development of terahertz photonic components useful in building next generation devices.

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Toroidal excitation in metamaterial is emerging as a novel platform for the localization of optical field in both spatial and time domain. In the article, the authors (DOI: 10.1002/inf2.12174) highlight the recent progresses of toroidal excitations based subwavelength optical localization in various plasmonic and Mie (all‐dielectric) metamaterials, and discuss the toroidal excitation related promising applications for advanced optical field manipulation or information processing in e.g. spaser, sensitive sensing and active nanophotonics. image

Toroidal dipole excitation in cylindrically arranged dogbone metallic inclusions

AbstractA significant excitation of toroidal moments in cylindrically arranged dogbone metallic inclusions is validated and presented in this paper. The antiparallel poloidal currents excited on the front and back faces of the proposed cylindrical dogbone inclusions create strong magnetic field confinement at the center generating intense toroidal moments on the structure. The significant excitation of toroidal dipole moment causes an improvement in the scattering cross-section from the resonant system. The resonant mechanism is analyzed using the multipole scattering theory, and we used the scattering measurement techniques to characterize the structure experimentally in the microwave regime.

Experimental realization of electromagnetic toroidal excitation for microwave applications

An experimental realization of resonant toroidal dipole excitation in the microwave regime is presented in this paper. The metasurface proposed herewith is an asymmetric double split-ring resonator exhibiting Fano-like resonance profile. One could observe that cascading the metasurface results in near-field transverse and longitudinal coupling creating dual-band toroidal moments on the structure. This planar scheme will simulate the development of enhanced light–matter interaction, electromagnetic wave slowdown and sensor design. Here we report the experimental realization of the phenomenon in the S-band frequencies, and the results are verified using multipole scattering analysis.

Design and Analysis of a New Brushless Electrically Excited Claw-Pole Generator for Hybrid Electric Vehicle

This paper presents a new brushless electrically excited claw-pole generator (EECPG) for vehicle power generation. The proposed design uses a toroidal excitation coil to magnetize all the stator poles and then generate effective power by complementary saliency effect of dual rotors. One salient advantage of this new design is its good excitation ability with minimized excitation copper loss as well as improved energy conversion efficiency. Meanwhile, the brush and slip rings are eliminated compared to the conventional rotor-EECPG. The generator structure is introduced, with its operating principle illustrated by 3-D finite-element predicated flux distribution. Rotor configurations using interlaced and non-interlaced types are both elaborated in terms of back electromotive force harmonic distribution and cogging effect. Load characteristic is predicted by the field-circuit coupled analysis, which proves the proposed brushless claw-pole generator could serve as a high-efficiency cost-effective candidate for vehicle power generation.

Bio-field array: a dielectrophoretic electromagnetic toroidal excitation to restore and maintain the golden ratio in human erythrocytes.

Erythrocytes must maintain a biconcave discoid shape in order to efficiently deliver oxygen (O2) molecules and to recycle carbon dioxide (CO 2) molecules. The erythrocyte is a small toroidal dielectrophoretic (DEP) electromagnetic field (EMF) driven cell that maintains its zeta potential (ζ) with a dielectric constant (ԑ) between a negatively charged plasma membrane surface and the positively charged adjacent Stern layer. Here, we propose that zeta potential is also driven by both ferroelectric influences (chloride ion) and ferromagnetic influences (serum iron driven). The Golden Ratio, a function of Phi φ, offers a geometrical mathematical measure within the distinct and desired curvature of the red blood cell that is governed by this zeta potential and is required for the efficient recycling of CO 2 in our bodies. The Bio‐Field Array (BFA) shows potential to both drive/fuel the zeta potential and restore the Golden Ratio in human erythrocytes thereby leading to more efficient recycling of CO 2. Live Blood Analyses and serum CO 2 levels from twenty human subjects that participated in immersion therapy sessions with the BFA for 2 weeks (six sessions) were analyzed. Live Blood Analyses (LBA) and serum blood analyses performed before and after the BFA immersion therapy sessions in the BFA pilot study participants showed reversal of erythrocyte rheological alterations (per RBC metric; P = 0.00000075), a morphological return to the Golden Ratio and a significant decrease in serum CO 2 (P = 0.017) in these participants. Immersion therapy sessions with the BFA show potential to modulate zeta potential, restore this newly defined Golden Ratio and reduce rheological alterations in human erythrocytes.

Achieving a high- Q response in metamaterials by manipulating the toroidal excitations

The excitation of toroidal multipoles in metamaterials is investigated for a high-$Q$ response at a subwavelength scale. In this paper, we explore the optimization of toroidal excitations in a planar metamaterial comprised of asymmetric split ring resonators (ASRRs). It is found that the scattering power of a toroidal dipole can be remarkably strengthened by adjusting the characteristic parameter of ASRRs: an asymmetric factor. Interestingly, the improvement in toroidal excitation accompanies an increment of the $Q$ factor of the toroidal metamaterial; it is shown that both the scattering power of the toroidal dipole and the $Q$ factor increase more than one order by changing the asymmetric factor of ASRRs. The optimization in the excitation of a toroidal multipole provides an opportunity to further increase the $Q$ factor of the metamaterial and boost light-matter interactions at the subwavelength scale for potential applications in low-power nonlinear processing and sensitive photonic applications.

Toroidal and magnetic Fano resonances in planar THz metamaterials

The toroidal dipole moment, a localized electromagnetic excitation of torus magnetic fields, has been observed experimentally in metamaterials. However, the metamaterial based toroidal moment was restricted at higher frequencies by the complex three-dimensional structure. Recently, it has been shown that toroidal moment could also be excited in a planar metamaterial structure. Here, we use asymmetric Fano resonators to illustrate theoretically and experimentally the underlying physics of the toroidal coupling in an array of planar metamaterials. It is observed that the anti-parallel magnetic moment configuration shows toroidal excitation with higher quality (Q) factor Fano resonance, while the parallel magnetic moment shows relatively lower Q factor resonance. Moreover, the electric and toroidal dipole interferes destructively to give rise to an anapole excitation. The magnetic dipole-dipole interaction is employed to understand the differences between the toroidal and magnetic Fano resonances. We further study the impact of intra unit-cell coupling between the Fano resonator pairs in the mirrored and non-mirrored arrangements. The numerical and theoretical approach for modelling the near-field effects and experimental demonstration of toroidal and magnetic Fano resonances in planar systems are particularly promising for tailoring the loss in metamaterials across a broad range of the electromagnetic spectrum.

Metamaterials: High‐Quality‐Factor Mid‐Infrared Toroidal Excitation in Folded 3D Metamaterials (Adv. Mater. 17/2017)

Metamaterials: High‐Quality‐Factor Mid‐Infrared Toroidal Excitation in Folded 3D Metamaterials (Adv. Mater. 17/2017)

Blueshift and phase tunability in planar THz metamaterials: the role of losses and toroidal dipole contribution.

We propose a model of tunable THz metamaterials. The main advantage is the blueshift of resonance and phase tunability due to inductive coupling in planar metallic metamolecules with incorporated silicon wires. We discuss the role of losses and toroidal dipole contribution to metamaterial response.

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.

On the development of a turbulent jet subjected to aerodynamic excitation in the helical mode

Aerodynamic excitation has been used to introduce energy into the free shear layer at the outer edges of an axisymmetric free jet by injecting a pulsating secondary jet through a thin annular nozzle that surrounds and is concentric with the primary nozzle. In the present study, it has been found that the rate of mixing can be increased if the pulsations are applied in a sequential fashion around the circumference of the jet, so as to create helical vortices in the region close to the nozzle exit plane. Flow visualisation confirms the helical nature of the vortices and shows how these vortices are convected downstream with the main flow, strongly influencing the development of the primary jet. Two-component laser Doppler anemometry (LDA) was used to make measurements of the flow distributions in the developing jet for a number of flow conditions. These results have been analysed to extract various measures of the turbulent mixing, including the time averaged velocity distributions, and the higher order moments and spectral distributions of the turbulent velocity fluctuations. The present data confirm that introducing the excitation in a helical mode leads to an increased rate of entrainment and more rapid mixing, when compared with the toroidal excitation used in previous studies. These changes significantly increase the rate of development of the jet in the axial direction.