Large Electrical Size Research Articles

Ultrabroadband terahertz-band communications with self-healing bessel beams

The large available bandwidth at sub-terahertz and terahertz frequencies has the potential to enable very high data rates for wireless communications. Moreover, given the large electrical size of terahertz antenna apertures, many future terahertz communication systems will likely operate in the near field. However, due to their reliance on highly directional beams, terahertz systems are susceptible to blockage. Here, we propose using Bessel beams to overcome issues caused by blockage due to their diffraction-free nature and self-healing properties in the near field. We compare the performance of information-bearing Bessel beams and Gaussian beams with and without an obstacle. We later discuss the use of reconfigurable intelligent surfaces to construct terahertz Bessel beams. Finally, we propose a metric to quantify the quality of imperfectly generated terahertz Bessel beams and explore their ability to self-heal. The results demonstrate that Bessel beams are an attractive option for near-field terahertz communications, especially when mitigating the effects of partial blockage.

Investigating the Scattering Characteristics of Artificial Field-Aligned Irregularities Based on T-Matrix Algorithm

The artificial field-aligned irregularity (AFAI) in ionosphere can be generated by heating the ionosphere with high-power high-frequency radio waves, and the physical structures of AFAIs are modeled as elongated multiple multilayer plasma cylinders. At relatively low frequencies, AFAIs could work as natural reflectors for long-distance communications. In order to evaluate the performance of AFAI-based communications, it is crucial to obtain the objective radar cross section (RCS) of AFAIs quickly and accurately. On account of the large electrical size of AFAIs, it would be time-consuming to calculate the objective RCS by full-wave simulations, meanwhile, the accuracies of the existing approximated methods are limited in many scenarios. In this paper, the T-matrix algorithm is used for analytically calculating the objective RCS of AFAIs after making reasonable approximations. Compared to the results obtained from full-wave simulations, the errors of objective RCS are within an acceptable range while the computation time is largely reduced. Furthermore, the scattering characteristics of AFAIs at different frequencies are investigated. The proposed method could be readily implemented for investigating and predicting the performance of AFAI-based long-wave communications.

Fast O(N log N) Algorithm for Generating Rank-Minimized H2-Representation of Electrically Large Volume Integral Equations

In this article, we propose a fast algorithm to generate a rank-minimized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathcal {H}^{2}$ </tex-math></inline-formula> -representation for solving electrically large volume integral equations (VIEs). Unlike existing methods whose complexity is as high as quadratic, the proposed algorithm has linearithmic complexity, and thus, it can handle problems with large electrical sizes. Furthermore, the algorithm is purely algebraic and kernel independent. Numerical experiments on electrically large 3-D arrays of dielectric cubes having over 33 million unknowns demonstrate the efficiency and accuracy of the proposed algorithm.

Hybrid Simulation Method for EM Wave Generation and Propagation of Streamer Discharges

The finite-difference time-domain (FDTD) method has been widely used for analyzing the EM wave propagation property of partial discharge (PD). However, many studies use Gaussian pulse as the excitation source, which shows few theoretical relations with the EM wave generation mechanism of PD. To simulate the EM wave generated by PD, the electric field distortion caused by the streamer discharges is analyzed. The finite element method (FEM) is used to calculate the fluid model to get the electric distribution alongside the charged air gap. This distorted electric field obtained from the fluid model is applicable as an excitation source of EM wave, which also explains its generation mechanism caused by the time-varying electric field. Because of the limitations of FEM, such as one frequency response and the huge computation complexity for large electric size. FDTD method is a useful tool to approximate Maxwell's curl equations and simulate the EM wave generated by the distorted electric field. In contrast to typical FDTD applications with one excitation, several excitation points should be chosen to simulate the distorted electric field, and they are evenly distributed alongside the streamer path since the EM wave is emitted by a charged gap rather than a point. Thus, this paper proposes a hybrid method that combines FEM and FDTD for the whole process simulation of the EM wave caused by PD. A positive streamer under two types of electrodes is simulated and the frequency spectrums of generated EM time-domain waveforms are also obtained. The proposed method simulates the EM radiation of PDs digitally, which provides a reference for PD monitoring.

Study of the Backscatter Radiation Pattern of a Quadrupole Antenna with a High-Impedance Ground Plane of Large Electrical Sizes

Introduction. The multipath resistance of GNSS antennas is largely determined by the gain slope of the amplitude radiation pattern at sliding angles (angles close to the horizon). The gain slope of the antenna radiation pattern is determined by the size of its ground plane. This article investigates the dependence between the gain slope and ground plane radius R of a quadrupole antenna.Aim. To analyse the impact of the radius of conventional and high-impedance ground planes on the backscatter radiation pattern of a quadrupole antenna at sliding angles.Materials and methods. Computer simulations were carried out in CAD CST Studio Suite using the methods of finite element analysis (FEM), finite difference time domain (FDTD) and template based post-processing.Results. Quadrupole antennas with a capacitive high-impedance ground plane and a conventional flat ground plane were simulated. The dependence of the average gain slope at sliding angles on the radius of the ground plane was determined at low fн and upper fв GNSS frequencies. The analysis of the down/up ratio, the rolloff gain and the multipath ratio for R= 1…20 of the wavelength of capacitive high-impedance and ground planes conventional flat was performed. It was established that higher gain slopes can be obtained using different types of ground planes; however, lower backscatter radiation values are achievable only using high-impedance structures. It was observed that the same slope of the radiation pattern (about 1 dB/°) for GNSS lower frequencies can be obtained at different R=12λ0, and, presumably, at 20λ0.Conclusion. A high-impedance ground plane with a diameter of 2R=12λ0 is preferable for a quadrupole antenna at low GNSS frequencies. A further increase in the ground plane size will insignificantly improve its characteristics.

Controlling the Most Significant Grating Lobes in Two-Dimensional Beam-Steering Systems With Phase-Gradient Metasurfaces

High-directivity antenna systems that provide 2-D beam steering by rotating a pair of phase-gradient metasurfaces (PGMs) in the near field of a fixed-beam antenna, hereafter referred to as near-field meta-steering systems, are efficient, planar, simple, short, require less power to operate, and do not require antenna tilting. However, when steering the beam, such systems generate undesirable dominant grating lobes, which substantially limit their applications. Optimizing a pair of these metasurfaces to minimize the grating lobes using standard methods is nearly impossible due to their large electrical size and thousands of small features leading to high computational costs. This article addresses this challenge as follows. First, it presents a method to efficiently reduce the strength of “offending” grating lobes by optimizing a supercell using Floquet analysis and multi-objective particle swarm optimization. Second, it investigates the effects of the transmission phase gradient of PGMs on radiation-pattern quality. It is shown that the number of dominant unwanted lobes in a 2-D beam-steering antenna system and their levels can be reduced substantially by increasing the transmission phase gradient of the two PGMs. This knowledge is then extended to 2-D beam-steering systems, where we demonstrate how to substantially reduce all grating lobes to a level below -20 dB for all beam directions, without applying any amplitude tapering to the aperture field. When steering the beam of two meta-steering systems with peak directivities of 30.5 and 31.4 dBi, within a conical volume with an apex angle of 96°, the variation in directivity is 2.4 and 3.2 dB, respectively. We also demonstrate that beam-steering systems with steeper gradient PGMs can steer the beam in a wider range of directions, require less mechanical rotation of metasurfaces to obtain a given scan range, and their beam steering is faster. The gap between the two metasurfaces in a near-field meta-steering system can be reduced to one-eighth of a wavelength with no significant effect on pattern quality.

Bifocal Planar Slotted-Waveguide Antenna Array

Abstract—A bifocal planar two-layer slotted-waveguide antenna array, consisting of a planar waveguide with one or several feed elements and an array of dielectric-filled rectangular metal waveguides with paired longitudinal slots in their wide walls has been proposed and investigated. The solution of the synthesis problem has shown that the shape of the reflector and coupling slot is elliptic, and it has made it possible to find the positions of the slots in the rectangular waveguides that can ensure the absence of phase aberrations for the two positions of the feed element in the planar waveguide. Using the phenomenological theory of slotted-waveguide arrays and the finite-element method, a numerical simulation of the beam-scanning characteristics for the feed element moved along the focal curve passing through the focuses of the ellipse has been performed. It has been shown that the scan sector of a planar bifocal array of a large electrical size and with an elliptic reflector is considerably larger than for a similar system with a parabolic reflector.

Light-Enhanced Blue Energy Generation Using MoS2 Nanopores

Summary Blue energy relies on the chemical potential difference between solutions of high and low ionic concentrations, potentially providing an independent energy source at estuaries around the world. The energy conversion relies on reverse electrodialysis via ion-selective membranes. A novel generation of these membranes is based on nanopores in atomically thin material. Single nanopores in molybdenum disulfide (MoS2)-based membranes have shown record-high power outputs in alkaline conditions. By increasing the surface charge of MoS2 membranes by light, we can double the osmotic power generated by a single nanopore at a neutral pH. The increased surface charge at the pore rim enhances the ion selectivity and leads to a larger osmotic voltage (dominating in small pores), while the increased surface charge of the membrane enhances the surface conductance, leading to a larger osmotic current (dominating in larger pores). The combination of these effects could efficiently boost the energy generation using membranes containing arrays of nanopores of varying sizes.

Physical optics and full-wave simulations of transmission of electromagnetic fields through electrically large planar meta-sheets

Abstract. Ultra-thin metamaterials, called meta-surfaces or meta-sheets, open up new opportunities in designing microwave radomes, including an improved transmission over a broader range of antenna scan angles, tailorable and reconfigurable frequency bands, polarization transformations, one-way transmission and switching ability. The smallness of the unit cells combined with the large electrical size of microwave radomes significantly complicates full-wave numerical simulations as a very fine sampling over an electrically large area is required. Physical optics (PO) can be used to approximately describe transmission through the radome in terms of the homogenized transmission coefficient of the radome wall. This paper presents the results of numerical simulations of electromagnetic transmission through planar meta-sheets (infinite and circularly shaped) obtained by using a full-wave electromagnetic field simulator and a PO-based solution.

Coding Metasurfaces for Diffuse Scattering: Scaling Laws, Bounds, and Suboptimal Design

Coding metasurfaces, based on the combination of two basic unit cells with out‐of‐phase responses, have been the subject of many recent studies aimed at achieving diffuse scattering, with potential applications to diverse fields ranging from radar‐signature control to computational imaging. Here, via a theoretical study of the relevant scaling‐laws, the physical mechanism underlying the scattering‐signature reduction is elucidated, and some absolute and realistic bounds are analytically derived. Moreover, a simple, deterministic suboptimal design strategy is introduced that yields results comparable with those typically obtained by approaches based on brute‐force numerical optimization, at a negligible fraction of their computational burden, thereby paving the way to the design of structures with arbitrarily large electrical size. Results are corroborated by rigorous full‐wave numerical simulations and microwave experiments, and may be of interest in a variety of application fields, such as the design of low‐scattering targets and illumination apertures for computational imaging, not necessarily restricted to electromagnetic scenarios.

Full-wave simulation of optical waveguides via truncation in the method of moments using PML absorbing boundary conditions.

Full-wave simulations of optical waveguides are often intractable due to their large electrical size. Naively focussing on a smaller part of the waveguide, e.g. to study coupling, offers no solution given the non-negligible interaction with the remaining parts of the structure. Thereto, in this paper, the coordinate stretching formulation of a perfectly matched layer is integrated into a method of moments based boundary integral equation solver in order to damp the interaction between multiple parts, allowing to focus on the part of interest. The new technique is validated using the classical example of scattering by a wedge. By truncation of the simulation domain to merely ten wavelengths from the tip, the advocated method is found to be both efficient and accurate compared to a traditional, analytical solution technique. Next, the method is applied to model a silicon polarization beam splitter excited by a Gaussian beam.

Efficient and Accurate Computational Electromagnetics Approach to Precipitation Particle Scattering Analysis Based on Higher-Order Method of Moments Integral Equation Modeling

AbstractA new full-wave computational electromagnetics (CEM) approach to precipitation particle scattering analysis based primarily on a higher-order method of moments (MoM) for solving surface integral equations (SIEs) is proposed, as an alternative and addition to the conventionally used tools in this area. This is a well-established CEM approach that has not been applied, evaluated, discussed, or compared with other approaches in the scattering analysis of precipitation particles so far. Several characteristic examples of scattering from precipitation particles of various shapes demonstrate the capabilities and potential of the presented numerical methodology, and discuss its advantages over both discrete dipole approximation (DDA) and -matrix methods in cases considered. In particular, it is shown that the higher-order MoM-SIE approach is much faster, more accurate, and more robust than the DDA method, and much more general and versatile than the -matrix method. In addition, the paper illustrates problems with the convergence of the DDA method in some cases with high-contrast dielectric materials and large electrical sizes of particles and with the convergence of the -matrix method in some cases with electrically large or geometrically complex (viz., with a large aspect ratio) particles. For simulations of continuously inhomogeneous scatterers (e.g., melting ice particles), a higher-order MoM volume integral equation (VIE) technique is used, as the study’s secondary methodology. The results also indicate the necessity for numerically rigorous and computationally efficient realistic precipitation particle modeling in weather scattering applications, which is becoming even more important as the sensor frequencies of radar/radiometric systems are increasing.

Applicability of point-dipoles approximation to all-dielectric metamaterials

All-dielectric metamaterials consisting of high-dielectric inclusions in a low-dielectric matrix are considered as a low-loss alternative to resonant metal-based metamaterials. In this paper we investigate the applicability of the point electric and magnetic dipoles approximation to dielectric meta-atoms on the example of a dielectric ring metamaterial. Despite the large electrical size of high-dielectric meta-atoms, the dipole approximation allows for accurate prediction of the metamaterials properties for the rings with diameters up to $\ensuremath{\approx}0.8$ of the lattice constant. The results provide important guidelines for design and optimization of all-dielectric metamaterials.

On fractal FSS suitable for WLAN and WiMAX communication

ABSTRACTMultiband properties of three different types of fractals namely Sierpinski Carpet, Koch Snowflake, and Sierpinski Gasket have been exploited. It is seen that all three fractal frequency selective surfaces (FSSs) on suitable optimization of their fractal geometry exhibit dual band properties of wireless local area network (WLAN), IEEE 802.11b standard, but at the fatal cost of large electrical size. In an attempt of making their size less, the Sierpinski Carpet and Koch Snowflake fractal looses their resonance properties partially at WLAN frequencies; however, the newly designed, modified Sierpinski Gasket FSS, marvelously exhibits stable resonance at WLAN frequencies with an additional resonance at WiMAX frequency, IEEE 802.16e standard. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1546–1550, 2015

A Multilevel Numerical Approach with Application in Time-Domain Electromagnetics

AbstractAn algebraic multilevel method is proposed for efficiently simulating linear wave propagation using higher-order numerical schemes. This method is used in conjunction with the Finite Volume Time Domain (FVTD) technique for the numerical solution of the time-domain Maxwell’s equations in electromagnetic scattering problems. In the multilevel method the solution is cycled through spatial operators of varying orders of accuracy, while maintaining highest-order accuracy at coarser approximation levels through the use of the relative truncation error as a forcing function. Higher-order spatial accuracy can be enforced using the multilevel method at a fraction of the computational cost incurred in a conventional higher-order implementation. The multilevel method is targeted towards electromagnetic scattering problems at large electrical sizes which usually require long simulation times due to the use of very fine meshes dictated by point-per-wavelength requirements to accurately model wave propagation over long distances.

Simulation Methodology for the Assessment of Field Uniformity in a Large Anechoic Chamber

The paper presents a simulation methodology for assessing the properties of a generic anechoic chamber, taking into account wall and floor coatings, measurement table, and antenna. Unlike previous approaches, the absorbing walls of the chamber are modeled as infinitely thin sheets. This leads to considerable improvement of the simulation performance. To this aim, a technique for extracting equivalent surface impedance material parameters from wall reflectivity measurements is presented. The large electrical size of the problem, its multiscale character, given by the large dimensions of a typical chamber on one hand and the fine details of the antenna on the other hand, and the complicated material parameters represent the challenges of such a simulation.

Characterizing and modeling mechanical properties and onset of short circuit for three types of lithium-ion pouch cells

Three types of lithium ion pouch cells ranging from small consumer electric cells with LiCoO2 cathode to large (electric vehicle size) cells with nanophosphate chemistry were tested under several local and global compression scenarios, including compression between two flat plates and local indentation with a flat cylindrical punch, a conical punch, and three hemispherical punches. Load, displacement, temperature, and voltage were recorded in all tests. The punch displacements were stopped when a drop in force and voltage of the cell, as well as a rise in temperature indicated a short circuit in the cell. Finite element models were developed for each cell type. Two tests were used for calibration of the constitutive properties of each type of cell, and the remaining tests served for the validation of the computational model. The models successfully predicted the load displacement relation and contour of deformations in the cells. Additionally, the models closely predict the force and punch displacement corresponding to the onset of short circuit in the cell. The current results are building confidence in robustness and accuracy of the present calibration and modeling approach.

Large Apparent Electric Size of Solid-State Nanopores Due to Spatially Extended Surface Conduction

Ion transport through nanopores drilled in thin membranes is central to numerous applications, including biosensing and ion selective membranes. This paper reports experiments, numerical calculations, and theoretical predictions demonstrating an unexpectedly large ionic conduction in solid-state nanopores, taking its origin in anomalous entrance effects. In contrast to naive expectations based on analogies with electric circuits, the surface conductance inside the nanopore is shown to perturb the three-dimensional electric current streamlines far outside the nanopore in order to meet charge conservation at the pore entrance. This unexpected contribution to the ionic conductance can be interpreted in terms of an apparent electric size of the solid-state nanopore, which is much larger than its geometric counterpart whenever the number of charges carried by the nanopore surface exceeds its bulk counterpart. This apparent electric size, which can reach hundreds of nanometers, can have a major impact on the electrical detection of translocation events through nanopores, as well as for ionic transport in biological nanopores.

광대역 위상 배열 안테나의 빔 편이(Beam-Squint) 현상 제거를 위한 4-Bit 시간 지연기 설계

본 논문에서는 전기적으로 크기가 큰 능동 위상 배열 안테나에서 발생하는 빔-편이(beam-squint)현상을 해결할 수 있는 시간 지연기를 설계 및 제작하고, 측정 결과를 고찰한다. 시간 지연기는 4-bit 스위치로 제어되는 마이크로스트립 라인으로 설계되었으며, 시간 지연 구조의 손실을 보상해 주기 위해 송수신 경로에 MMIC 증폭기 모듈을 추가하였다. 시간 지연기의 측정을 통해 지연 상태별 이득 및 위상, P1dB, 수신 잡음 지수 등의 전기적 성능 규격을 만족함을 확인하였다. 또한, 제작된 시간 지연기의 성능 검증을 위해 측정 결과를 광대역 능동위상 배열 안테나에 적용하여 빔 패턴 보정 효과를 확인하였다. X 밴드 대역에서 800 MHz 대역차를 갖는 675.8 mm 크기의 안테나에 대해 빔 편이 현상을 보정해 본 결과 <TEX>${\pm}0.1^{\circ}$</TEX>이던 주파수에 따른 조향각 오차가 <TEX>${\pm}0.1^{\circ}$</TEX> 이내로 줄어드는 효과를 확인하였으며, 향후 광대역 능동 위상 배열 안테나 시스템에 적용 가능성을 확인하였다. In this paper, we have designed TDL(True-time Delay Line) for eliminating beam-squint occurring in active phased array antenna with large electrical size operated in wide bandwidth, and have tested its electrical performance. The proposed TDL device is composed of 4-bit microstrip delay line structure and MMIC amplifier for compensation of the delay-line loss. The measured results of gain and phase versus delay state satisfy the electrical requirements, also P1dB output power and noise figure meet the requirement. To verify the performance of fabricated TDL, we have simulated the beam patterns of wide-band active phased array antenna using the measured results and have certified the beam pattern compensation performance. As a result of simulated beam pattern compensation with respect to the 675.8 mm size antenna which is operated in X-band, 800 MHz bandwidth, we have reduced the beam squint error of <TEX>${\pm}1^{\circ}$</TEX> with <TEX>${\pm}0.1^{\circ}$</TEX>. So this TDL module is able to be applied to active phase array antenna system.

Fiber density of the motor units recruited at high and low force output

Motor units (MUs) are recruited according to the size principle. At low force output, macro-motor unit potentials (macro-MUPs) with small amplitude and area are recorded; MUs with large electrical size fire at high force output. Our objective was to elucidate whether this difference is caused by a higher fiber density (FD) of the MUs recruited at high force output. We measured the FD and respectively the amplitude and the area of the macro-MUPs via single-fiber macro electromyography (EMG) recorded at low and high force output in 48 healthy subjects. The macro-MUPs were significantly larger at high force output than at low force. The FD did not differ at the two force levels. Our findings suggest that the larger electrical size of the high recruitment threshold MUs is due not to a higher FD, but to a larger territory. FD is a robust EMG parameter, independent of the level of the force output.