Showing papers on "Coupling published in 2021"

Ultrastrong plasmon–phonon coupling via epsilon-near-zero nanocavities

Abstract: Vibrational ultrastrong coupling, where the light–matter coupling strength is comparable to the vibrational frequency of molecules, presents new opportunities to probe the interactions between molecules and zero-point fluctuations, harness cavity-modified chemical reactions and develop novel devices in the mid-infrared spectral range. Here we use epsilon-near-zero nanocavities filled with a model polar medium (SiO2) to demonstrate ultrastrong coupling between phonons and gap plasmons. We present classical and quantum-mechanical models to quantitatively describe the observed plasmon–phonon ultrastrong coupling phenomena and demonstrate a modal splitting of up to 50% of the resonant frequency (normalized coupling strength η > 0.25). Our wafer-scale nanocavity platform will enable a broad range of vibrational transitions to be harnessed for ultrastrong coupling applications. An epsilon-near-zero medium is used to demonstrate ultrastrong coupling between phonons and gap plasmons. The approach may pave the path to exploitation of vibrational transitions.

Transient Analysis and Verification of a Magnetic Gear Integrated Permanent Magnet Brushless Machine with Halbach Arrays

Abstract: The magnetic gear integrated permanent magnet brushless machine (MG-IPMBM) is a kind of compact structure with high torque density and complex electromagnetic energy transfer In order to analyze the transient characteristics of the machine, an analysis method of field circuit coupling is proposed Both magnetic gear and permanent magnet motor are magnetized by Halbach array Combining the analytical model of the magnetic gear magnetic field with MATLAB motor simulation module, a joint simulation model of field circuit coupling double closed-loop control system based on the Simulink-analytical method is established The electromechanical transient response characteristics of machine under load starting, load mutation and overload self-protection are analyzed The simulation results show that the output speed and torque of machine can accurately follow the given value, and its unique overload self-protection ability greatly improves the safety of machine operation In addition, a prototype is made and an experimental platform is built The experimental results show that the output torque follows quickly, the torque ripple is small, and transient performance of the machine is good

A Wireless Power Method for Deeply Implanted Biomedical Devices via Capacitively Coupled Conductive Power Transfer

Abstract: Deeply implanted biomedical devices (DIBDs) are a challenging application of wireless power transfer because of the requirement for miniaturization while minimizing patient exposure to tissue heating. This article proposes a capacitively coupled conductive power transfer method for DIBDs, which allows for the safe transfer of power into the body while using minimum implant volume. The method uses parallel insulated capacitive electrodes to couple uniform current flow into the tissue and implants. Analytical analyses are presented, which result in a two-port network that describes circuit operation. The two-port network is further simplified for typical DIBD applications where coupling to the external electrodes is low. This results in a simple circuit model of power transfer for which the parameters are easily obtained by experimental measurements. The proposed circuit model has been validated using circuit coupled finite-element analysis (COMSOL) and benchtop experiments using a tissue phantom. In addition, the safety aspect of the method has been evaluated via COMSOL simulation of the specific absorption rate for various implanted receiver dimensions and implantation depths. Finally, a completed power supply, unaffected by the implantation depth, running at 6.78 MHz, delivering 10 mW deep into the body while meeting the IEEE C95.1 basic restriction is presented.

Multi-physics coupling in thermoacoustic devices: A review

Abstract: Latest developments in thermoacoustic devices have demonstrated comparable power output and efficiency, but higher reliability and lower cost when compared to conventional low-grade heat recovery technologies. A good coupling between multiple physical fields plays a pivotal role in realizing these potentials. This article provides a comprehensive review of the multi-physics coupling effects, namely, thermal-acoustic coupling, acoustic-mechanical coupling and mechanical-electric coupling, inside thermoacoustic devices including thermoacoustic engines, thermoacoustic electric generators, thermoacoustically-driven refrigerators, etc. The basic principles, operating characteristics, design strategies and future prospects are discussed individually for each coupling effect. System-level design techniques and synthetic optimization methodologies in consideration of the multi-physics coupling effects are presented. This review work gives insights into the underlying mechanisms of various coupling effects in thermoacoustic devices and provides guidelines for improvements of modern thermoacoustic technologies for low-grade thermal energy recovery, refrigeration and electric power generation purposes.

Selective enhancement of the QCD axion couplings

Abstract: We present a mechanism wherein the QCD axion coupling to nucleons, photons, or electrons can be enhanced selectively without increasing the axion mass. We focus in particular on the axion-nucleon couplings that are generally considered to be largely model independent, and we show how nucleophilic axion models can be constructed. We discuss the implications of a nucleophilic axion for astrophysics, cosmology, and laboratory searches. We present a model with enhanced axion couplings to nucleons and photons that can provide an excellent fit to the anomalous emission of hard x-rays recently observed from a group of nearby neutron stars, and we argue that such a scenario can be thoroughly tested in forthcoming axion-search experiments.

Sparse Nested Arrays With Spatially Spread Orthogonal Dipoles: High Accuracy Passive Direction Finding With Less Mutual Coupling

Abstract: In sensor array processing, the minimum sensor/element-spacing is usually restricted within a half-wavelength in order to avoid estimation aliasing. This would cause sensor/element mutual coupling when antenna-electromagnetics are considered. Based on the recently proposed nested array (NA) concept, we present a new type of NA called sparse nested spatially spread orthogonal dipole array (SNODA) to realize underdetermined direction finding with less mutual coupling. In SNODA, the sensor/element-spacing can be extended to be much higher than a half-wavelength so that the effect of sensor coupling will be much reduced. The direction estimation ambiguities caused by aperture extension is resolved by combining both spatial and element responses of spread orthogonal dipoles. Matlab code for reproduction of the results is available at https://github.com/jinhesjtu/SNODA-DF.git .

Memristor-Based Hyperchaotic Maps and Application in AC-GANs

Abstract: With the nonlinearity and plasticity, memristors are widely used as nonlinear devices for chaotic oscillations or as biological synapses for neuromorphic computations. But discrete memristors and their coupling maps have not received much attention, yet. Using a discrete memristor model, this paper presents a general three-dimensional discrete memristor-based (3D-DM) map model. By coupling the discrete memristor with four two-dimensional discrete maps, four examples of 3D-DM maps with no or infinitely many fixed points are generated. We simulate the coupling coefficient-depended and memristor initial-boosted bifurcation behaviors of these 3D-DM maps using numerical measures. The results demonstrate that the memristor can enhance the chaos complexity of existing discrete maps and its coupling maps can display hyperchaos. Furthermore, a hardware platform is developed to implement the 3D-DM maps and the acquired hyperchaotic sequences have high randomness. Particularly, these hyperchaotic sequences can be applied to the auxiliary classifier generative adversarial nets (AC-GANs) for greatly improving the discriminator accuracy.

Isolation Enhancement for MIMO Patch Antennas Sharing a Common Thick Substrate: Using a Dielectric Block to Control Space-Wave Coupling to Cancel Surface-Wave Coupling

Abstract: This article presents a novel and simple decoupling method to increase the isolation between two closely spaced patch antennas sharing a common thick substrate. The decoupling can be simply realized by adding a pure dielectric block (DB) above the coupled array. By means of DB to modify the space permittivity (propagation constant), the space-wave coupling can be controlled to cancel surface-wave coupling for isolation enhancement. Five benchmarks of combinations of two patch antennas with different positions or orientations are investigated to validate the decoupling concept and elaborate on the design procedure. The results show that the proposed method could provide over 20 dB isolation enhancements for patch antennas with $0.1\lambda _{0}$ or $0.027\lambda _{0}$ separation distances. Besides, wide isolation bandwidths and good radiation performances can be achieved for the DB-loaded antennas without reduction in total efficiency, front-to-back ratio (FBR), boresight gain, or polarization purity. Notably, the DB can be designed independently of the original array, making this method potential for some previously fabricated arrays without requiring modifying or replacing them with new ones.

Mutual Coupling and Unit Cell Aware Optimization for Reconfigurable Intelligent Surfaces

Abstract: We introduce algorithms for optimizing a single-input single-output reconfigurable intelligent surface (RIS) assisted system. The RIS is modeled by using an electromagnetic-compliant framework based on mutual impedances and its reconfigurability is realized through tunable lumped impedances. In the absence of mutual coupling among the scattering elements of the RIS, we derive a closed-form expression for the optimal tunable impedances, which accounts for the interplay between the amplitude and phase of the lumped loads of the RIS. In the presence of mutual coupling, we introduce an iterative algorithm for optimizing the tunable impedances of the RIS. The algorithm is proved to be convergent by showing that the objective function is non-decreasing and upper bounded. Numerical results reveal that the mutual coupling significantly affects the end-to-end received power. If the RIS is optimized by taking the mutual coupling into account, the received power can be increased.

Distributed Consensus Control of Linear Multiagent Systems With Adaptive Nonlinear Couplings

Abstract: This paper addresses the consensus problem of linear multiagent systems via nonlinear couplings. First, we show that the multiagent system can achieve consensus via nonlinear couplings provided the coupling strength surpasses a threshold, which depends on the smallest nonzero eigenvalue of the interaction graph Laplacian. Second, an adaptive coupling protocol is proposed to adjust the coupling strength without any usage of global information. Some numerical simulations are given to illustrate the effectiveness of the proposed protocols.

Design Considerations for a Self-Latching Coupling Structure of Inductive Power Transfer for Autonomous Underwater Vehicle

Abstract: Wireless charging to autonomous underwater vehicle effectively prolongs the attended time and extends the endurance mileage. As the most promising underwater power feeding technique, inductive power transfer is also faced with challenges such as the attenuation in seawater, ocean current disturbance, etc. Special concerns in terms of power quality, efficiency improvement, and mechanical fixing need to be considered when designing the underwater electromagnetic coupling structure. An attenuation model in seawater is established in this article. The optimal working frequency range is refined for a specific transmission media. Different from the wireless power transfer system in the air, the underwater WPT system features tight coupling between the transmitter and receiver. The optimal range of coupling coefficient needs to be redesigned, as high coupling coefficient incurs frequency splitting and the increase of harmonic component, while low coupling coefficient results in low efficiency. Based on the theoretical analysis, a self-latching coupling structure is proposed with lightweight design on receiver side. System parameters are optimized correspondingly and a 3-kW experiment validates the theoretical analysis.

Efficient conversion of orbital Hall current to spin current for spin-orbit torque switching

Abstract: Spin Hall effect, an electric generation of spin current, allows for efficient control of magnetization. Recent theory revealed that orbital Hall effect creates orbital current, which can be much larger than spin-Hall-induced spin current. However, orbital current cannot directly exert a torque on a ferromagnet, requiring a conversion process from orbital current to spin current. Here, we report two effective methods of the conversion through spin-orbit coupling engineering, which allows us to unambiguously demonstrate orbital-current-induced spin torque, or orbital Hall torque. We find that orbital Hall torque is greatly enhanced by introducing either a rare-earth ferromagnet Gd or a Pt interfacial layer with strong spin-orbit coupling in Cr/ferromagnet structures, indicating that the orbital current generated in Cr is efficiently converted into spin current in the Gd or Pt layer. Our results offer a pathway to utilize the orbital current to further enhance the magnetization switching efficiency in spin-orbit-torque-based spintronic devices. Manipulation of the magnetization is of major importance in spintronics. The authors demonstrate that an electric field triggers a transverse flow of orbital moment: the so-called orbital Hall effect. This enables the efficient magnetization control, holding the promise for fast and miniaturized memories and sensors.

Flexible Combination and Switching Control for Robust Wireless Power Transfer System With Hexagonal Array Coil

Abstract: Multitransmitter structure can improve the misalignment tolerance of wireless power transfer (WPT) system, but some new problems such as a sharp drop in transmission efficiency will occur when the receiver moves to the boundary situation between transmitters. It is very crucial to solve this problem for an efficient and stable WPT system. In this article, a flexible combination multitransmitter coupling structure based on hexagonal array coil and auxiliary switch is proposed, and the coupling characteristics under misalignment conditions has been deeply analyzed with mutual inductance model. Unlike using coupling coefficient, a convenient switching control strategy is proposed based on the primary current to activate the optimal coil working mode, and the experimental results favorably verified the theoretical analysis. Compared with the circular array coil and the square array coil, the proposed coupling structure and control method can greatly improve the transmission efficiency of the WPT system at the coil boundary, and has stronger robustness under different misalignment conditions.

A review of the FE2 method for composites

Abstract: Composite materials and structures are inherently inhomogeneous and anisotropic across multiple scales. Multiscale modelling offers opportunities to understand the coupling of material behaviour and characteristics from the micro- to meso- and macro-scales, critical to the optimal design of composite structures for lightweighting and mechanical performance. FE2 is an increasingly popular class of multiscale methods because of its versatility to model heterogeneous material behaviour across multiple scales. In classical FE2 analysis, two finite elements (FE) calculations are carried out in a nested manner, one at the macroscale and the other at the microscale. Unlike conventional analysis, the macroscale FE analysis does not require homogenized constitutive properties because these are derived from the microscale FE simulations at the representative volume element (RVE) level. This has exciting significance for composite mechanics because properties characterized and defined at the microscale can be directly transferable to higher scales and validated with experiments. For example, failure criteria for composites need only be formulated at the microscale level of fibers and matrix. However, FE2 analysis is computationally expensive and the generally more complex classical nested implementation of FE2 is disadvantageous. This paper presents a review of the FE2 method to model various phenomena in the mechanics of composite materials and discusses various implementations. Recently, the Direct FE2 method, a variant of the FE2 method, has been shown to be particularly easy to implement in commercial FE codes, which also means that it has the additional advantage of ready access to inbuilt constitutive models library and other advanced features of the commercial code. We conclude with future directions for multiscale modelling of composites using FE2.

Few-Mode Fiber Coupling Efficiency for Free-Space Optical Communication

Abstract: Few-mode fiber is a significant component of free-space optical communication at the receiver to obtain achievable high coupling efficiency. A theoretical coupling model from the free-space optical communication link to a few-mode fiber is proposed based on a scale-adapted set of Laguerre-Gaussian modes. It is found that the coupling efficiency of various modes behaves differently in the presence of atmospheric turbulence or random jitter. Based on this model, the optimal coupling geometry parameter is obtained to maximize the coupling efficiency of the selected mode of few-mode fiber. The communication performance with random jitter is investigated. It is shown that the few-mode fiber has better bit-error rate performance than single-mode fiber, especially in high signal-to-noise ratio regimes.

Loss-induced nonreciprocity.

Abstract: Nonreciprocity is important in both optical information processing and topological photonics studies Conventional principles for realizing nonreciprocity rely on magnetic fields, spatiotemporal modulation, or nonlinearity Here we propose a generic principle for generating nonreciprocity by taking advantage of energy loss, which is usually regarded as harmful The loss in a resonance mode induces a phase lag, which is independent of the energy transmission direction When multichannel lossy resonance modes are combined, the resulting interference gives rise to nonreciprocity, with different coupling strengths for the forward and backward directions, and unidirectional energy transmission This study opens a new avenue for the design of nonreciprocal devices without stringent requirements

Controlling Stationary One-Way Quantum Steering in Cavity Magnonics

Abstract: We show how to implement stationary one-way quantum steering with strong entanglement in a cavity magnonic system that consists of two magnon modes and a microwave cavity. The cavity is driven by a squeezed vacuum field generated by a flux-driven Josephson parameter amplifier and coupled to two Kittel modes via magnetic dipole interaction. We find that the steering directivity only depends on the ratio of two coupling rates (i.e., the ratio of coherent information exchange frequencies) and is barely affected by the dissipation of the system. Meanwhile, the entanglement and steering can be significantly enhanced due to the squeezed vacuum field and thus are more robust against thermal noises. This provides an active method to manipulate the steering directivity instead of adding asymmetric losses or noises to subsystems at the cost of reducing steerability.

Mutual Coupling Reduction With Dielectric Superstrate for Base Station Arrays

Abstract: This letter proposes a dielectric superstrate to reduce the couplings between copolarized and cross-polarized antenna elements in realistic base station (BS) arrays. The mutual couplings are reduced by adjusting the permittivity and profile of the dielectric superstrate to create “reflected” waves to neutralize the original coupling wave. The dielectric superstrate is a simple structure that is easy to design and manufacture. A large dielectric board and four small dielectric blocks help reduce the couplings between horizontal and vertical antenna elements, whereas a dielectric pillar is added to suppress the coupling between diagonal elements. The superior decoupling performance (>25 dB isolation) is demonstrated for dual-polarized BS arrays over the fifth generation frequency band of 3.3–3.8 GHz, without affecting the matching and radiation performances of the array elements.

Design and Analysis of a New Hybrid Wireless Power Transfer System With a Space-Saving Coupler Structure

Abstract: This article is to present the design, analysis, and verification of a new hybrid wireless power transfer (HWPT) system, which has a space-saving coupler structure. The key of the design is to simplify the two coupling capacitor plates into one single frame-shaped plate at each side. Then, the coupling coil for inductive power transfer (IPT) is embedded into the metal frame to form a compact hybrid coupler. Meanwhile, the coupling polarity between the coils is specified to realize the superposition of the inductive and capacitive coupling. As a result, the proposed HWPT system can offer a good comprise of efficiency promotion and a space-saving coupler structure simultaneously. To illustrate the system working principles, the equivalent circuit model is first derived. Then, a detailed analysis is conducted in terms of the reflected impedance. Consequently, the mechanism of the efficiency promotion can be clearly explained. Finally, a prototype is constructed with several experiments, which validate the effectiveness of the proposed HWPT system. Results show that an efficiency increase of 14% over the pure IPT is obtained at 35-cm distance. Moreover, the effects of varying the resonant frequency are also carried out to instruct the practical system design.