Symmetric Wire Research Articles

Paralleled multi-GaN MIS–HEMTs integrated cascode switch for power electronic applications

A cascode gallium nitride (GaN) switch integrating four paralleled GaN depletion-mode metal–insulator–semiconductor–high-electron-mobility transistors (MIS–HEMT) and a silicon MOSFET (Si-MOSFET) is presented. Each GaN chip is wire-bonded into a multi-chip power module to scale up the power rating. An optimized symmetric configuration and wire bonding of an integral package are used in the cascode switch. By utilizing an optimized packaging approach, the performance of the multi-GaN-chip cascode switch was evaluated through both static and dynamic characterizations. The constructed cascode switch provides a low-static on-state resistance of 72 mΩ and an off-state blocking capability of 400 V with a positive threshold voltage of 2 V. Analysis of dynamic switching characteristics are discussed and demonstrates stable dynamic on-state resistance (R DS-ON) in inductive load circuits with switching dependencies of voltage, frequency, time, and temperature. The extended defects from buffer caused a minimal decrease in dynamic and static R DS-ON with respect to hard switching conditions. However, there was no noticeable degradation in R DS-ON under harsh switching conditions. This study provides a complete analysis of the multi-GaN-chip cascode switch, including MIS–HEMT manufacturing, cascode packaging and static and dynamic characterizations.

Analysis of Symmetrical Wires Breaking in Unbonded Prestressed Steel Strand Considering Bending Deformation

Analysis of Symmetrical Wires Breaking in Unbonded Prestressed Steel Strand Considering Bending Deformation

Effect of Heat Treatment on the Vibration Isolation Performance of Axially Symmetric NiTi Wire Mesh Damper

In this paper, superelastic (SE) NiTi wire is used to fabricate axially symmetric wire mesh dampers (WMDs) with the expectation of a higher damping capacity. However, the phase transformation damping of the NiTi WMD could be suppressed by the cold-work-induced dislocation. Therefore, the NiTi WMDs were heat-treated and then tested by a hydraulic universal testing machine. The NiTi WMD is found to achieve higher damping capacity when heat-treated at 200 °C. However, the WMD heat-treated at 250 °C suffers from a sharp decline in the loss factor in exchange for an improvement in the stiffness. The sine sweep test was then conducted to examine the dependency of the WMD’s vibration isolation performance upon the heat treatment temperature and the excitation acceleration. The NiTi WMD outperforms the 304 stainless steel (SS 304) WMD in damping capacity only when the excitation acceleration magnitude is less than 1.5 g. The stiffness of NiTi WMD can be improved without significantly compromising its damping capacity by heat treatment at 200 °C for 30 min. The present work carries out comprehensive measurements of the NiTi WMD’s response to dynamic mechanical test and sine sweep test and addresses how heat treatment influences the stiffness and damping capacity of the SE NiTi WMD.

A Suboptimal Approach to Huygens’ Metasurfaces for Wide-Angle Refraction

Huygens’ metasurface uses boundary conditions to solve for the required electric and magnetic current densities to provide a theoretical solution for wavefront shaping. However, the physical implementation of Huygens’ metasurface often suffers from interlayer coupling, leading to the difficulty in synthesizing the desired properties. This article proposes a novel approach to suppress interlayer coupling using a symmetric wire–loop topology. The proposed unit cell is designed to induce orthogonal components of Huygens’ dipole to each face, and the multipole moments are directly calculated from current distributions induced on metallic patterns. Due to the suppressed interlayer coupling, electric and magnetic dipoles can be independently tuned to achieve the desired phase conditions without causing any distortion of electromagnetic responses in their combined structure. Furthermore, the tolerance to the phase difference between dipole moments is analyzed to extend the range of phase gradient for a transmit wave while maintaining high transmit efficiency. The proposed approach is validated by designing two metasurfaces for normally incident waves to bend toward different angles at 10 GHz, and their characteristics are demonstrated by near- and far-field measurements. The measured results confirm that a high transmittance of greater than 83% is achieved up to the maximum validation angle of 65°.

Theory of magnetotransport in shaped topological insulator nanowires

We show that shaped topological insulator (TI) nanowires, i.e. such that their cross-section radius varies along the wire length, can be tuned into a number of different transport regimes when immersed in a homogeneous coaxial magnetic field. This is in contrast with widely studied tubular nanowires with constant cross-section, and is due to magnetic confinement of Dirac surface carriers. In flat 2D systems such a confinement requires non-homogeneous magnetic fields, while for shaped nanowires of standard size homogeneous fields of the order of $B\sim\,1$T are sufficient. We put recent work [Kozlovsky et al., Phys. Rev. Lett. 124, 126804 (2020)] into broader context and extend it to deal with axially symmetric wire geometries with arbitrary radial profile. A dumbbell-shaped TI nanowire is used as a paradigmatic example for transport through a constriction and shown to be tunable into five different transport regimes: (i) conductance steps, (ii) resonant transmission, (iii) current suppression, (iv) Coulomb blockade, and (v) transport through a triple quantum dot. Switching between regimes is achieved by modulating the strength of a coaxial magnetic field and does not require strict axial symmetry of the wire cross-section. As such, it should be observable in TI nanowires fabricated with available experimental techniques.

A broadband single mode single polarization metal wires-embedded hollow core anti-resonant fiber for polarization filter

Abstract A broadband single mode single polarization metal wires-embedded hollow core anti-resonant fiber for polarization filter is designed and investigated by the finite element method in this paper. When there are no metal wires, the hollow core anti-resonant fiber has a broadband single mode property by adjusting structure parameters. Then, through embedding two symmetrical metal wires into fiber, only one polarized state of fundamental mode suffers a high loss due to the selective excitation of surface plasmon resonance. The effects of three kinds of metal wires (gold, silver and aluminum) on the hollow core anti-resonant fiber are investigated in detail. Simulation results demonstrate that the hollow core anti-resonant fiber with aluminum wires has the best single polarization characteristics. Its polarization and high order mode extinction ratios are greater than 100 within a broad wavelength range from 1.26 to 1.58 μm. The low loss of the polarized fundamental mode is 0.33 dB/m and 0.99 dB/m at the wavelength of 1.31 μm and 1.55 μm, respectively. The proposed broadband single mode single polarization fiber has a potential application as a polarization filter in coherent optical systems, interferometric fiber sensors and fiber gyroscopes.

Controlling the Flow around a Circular Cylinder by Means of a Corona Discharge

The effect of electric wind produced by a positive corona discharge on the air flow around a circular cylinder at Reynolds numbers of 2400 and 3200 is investigated. The geometry of cylinder–wire electrodes is considered for two positions of the corona electrode relative to the cylinder: one wire behind the cylinder and two symmetrical wires above and below the cylinder. A direct numerical simulation of the electrohydrodynamic problem is performed using an original unipolar model of the corona discharge. The effect of a thin jet of electric wind directed from the corona electrode to the cylinder on the structure of the vortex wake behind the cylinder and the drag force is considered. It is shown that, when two corona electrodes are located above and below the cylinder, the electric wind prevents the formation of a Karman vortex street and significantly reduces the air drag of the cylinder. If the discharge electrode is located behind the cylinder, the corona discharge and the electric wind lead to the formation and development of large vortices in the wake behind the cylinder, which leads to significant fluctuations in its air drag. It is shown that a corona discharge significantly changes the characteristics of the Karman vortex street: as the voltage increases to 30 kV, the vortex shedding frequency decreases by a factor of 2.5 and the sizes of the vortices and their rotation velocity noticeably increase. The drag force is quasi-periodic and its mean value linearly depends on the corona voltage.

Effect of symmetrical broken wires damage on mechanical characteristics of stay cable

Broken wires are a common damage in stay cables due to aging and harsh environment. However, the analytical method to study the effect of broken wires on the mechanical characteristics of stay cables is still limited. Therefore, based on the microstructural mechanical model of damaged multi-wire cable, this paper proposes an analytical method for the static and dynamic characteristics of cables with broken wires. The broken wire damage is equalised to the axial stiffness reduction in the end-sliding region and recovery region of the broken wire. Governing equations for static configuration and in-plane free vibration of damaged multi-wire cable are then established. Cables with different physical parameters are studied to research the effect of broken wire damage on the static and dynamic characteristics. The results reveal that an increase in the number of symmetrical broken wires linearly decreases the horizontal component of cable tension in piecewise, linearly increases the sag and decreases the in-plane natural vibration frequency in piecewise. Besides, the cable sag is sensitive to the location of broken wire damage, while the horizontal component of cable tension and natural frequency are not sensitive to the location of the broken wire damage. Under the same broken wire damage, the closer the damage is to the support, the greater the sag is. When the broken wire percentage reaches 18.9% at the mid-span, the relative reduction in horizontal component of cable tension is 1.7%, the relative increase in sag is 1.7% and the relative decrease in the in-plane natural vibration frequency is about 0.85% for 100 m long cable. Meanwhile, broken wire damage hardly alters the static characteristics of the initial slack cable with an aspect ratio greater than 1.002. However, the effect of the broken wire on the static characteristics of the initial taut cable nonlinearly increases with a decreasing aspect ratio. Moreover, the effect of broken wire damage on this cable's static characteristics nonlinearly decreases when the cable length increases. Hence, broken wire damage remarkably influences the static characteristics of short cable.

Управление обтеканием круглого цилиндра с помощью коронного разряда

In the paper an influence of ion wind caused by positive corona discharge on a bulk motion near a circular cylinder at Reynolds numbers 2400, 3200 was studied. The geometry of the cylinder-wire electrodes was considered for two positions of the active electrode relative to the cylinder: behind the cylinder and two symmetrical wires above and below the cylinder. A direct numerical simulation of electrohydrodynamic problem was performed. The original unipolar model of the corona discharge was used. The impact of a thin jet of ion wind directed from the active electrode to the cylinder on vortex wake behind the cylinder and the drag force was considered. It was shown that when two active electrodes are placed above and below cylinder, the electric wind prevents the formation of the Karman vortex street and also significantly reduces the aerodynamic resistance of cylinder. When the active electrode is located behind the cylinder, the corona discharge and the ion wind lead to the formation and development of large vortices in the wake of the cylinder, which leads to significant fluctuations in the aerodynamic drag. It was shown that corona discharge significantly changes Karman vortex street properties. Specifically with an increase in the voltage to 30 kV, the vortex detachment frequency decreases by 2.5 times, the size of the vortices and the speed of their rotation dramatically grow. The drag force is quasi-periodic, its average value linearly depends on the applied voltage.

Paralleled GaN DHEMTs integrated cascode GaN switch for high‐current applications

A high-current cascode gallium nitride (GaN) switch integrating a silicon-MOSFET (Si-MOSFET) and paralleled GaN depletion-mode high-electron-mobility transistors (DHEMT) is presented. The proposed switch can withstand twice or more the current than existing cascode GaN transistors by using only one Si-MOSFET and requiring a single gate driver, which evidently augments the power density, improves the system efficiency and reduces the cost. The causes and treatments of potential unbalanced current sharing among the paralleled GaN DHEMTs are further discussed and an optimised symmetric configuration and wire bonding of integral package are proposed. An effective solution is also introduced for avoiding an Si-MOSFET avalanche. The validity of proposed cascode GaN switch in the optimised package and the effectiveness of avalanche-suppressed method are both verified by simulations.

Observation of the topological Anderson insulator in disordered atomic wires.

Topology and disorder have a rich combined influence on quantum transport. To probe their interplay, we synthesized one-dimensional chiral symmetric wires with controllable disorder via spectroscopic Hamiltonian engineering, based on the laser-driven coupling of discrete momentum states of ultracold atoms. Measuring the bulk evolution of a topological indicator after a sudden quench, we observed the topological Anderson insulator phase, in which added disorder drives the band structure of a wire from topologically trivial to nontrivial. In addition, we observed the robustness of topologically nontrivial wires to weak disorder and measured the transition to a trivial phase in the presence of strong disorder. Atomic interactions in this quantum simulation platform may enable realizations of strongly interacting topological fluids.

Analysis of axially symmetric wire antennas by the use of exact kernel of electric field integral equation

The paper presents a new method for the analysis of wire antennas with axial symmetry. Truncated cones have been applied to precisely model antenna geometry, while the exact kernel of the electric field integral equation has been used for computation. Accuracy and efficiency of the method has been further increased by the use of higher order basis functions for current expansion, and by selecting integration methods based on singularity cancelation techniques for the calculation of potential and impedance integrals. The method has been applied to the analysis of a typical dipole antenna, thick dipole antenna and a coaxial line. The obtained results verify the high accuracy of the method.

Analysis of curvature and width of the contact area in asymmetrical rolling of wire

In this paper, an investigation into the asymmetrical wire rolling is presented using experimental tests, finite element simulation, and some analytical formulations. Moreover, the effects of the roll speed ratio, roll diameter ratio, and reduction in height on the curvature radius, and width of the contact area of a rolled wire are investigated. In addition, possibility of applying a theoretical formula for calculating the width of the contact area in the symmetrical wire rolling for the asymmetrical wire rolling is also studied. A very good agreement is shown to exist between the results predicted by the FEM simulation and the experimental results.

Nonlinear analytical modeling and characteristic analysis of symmetrical wire beam based composite compliant parallel modules for planar motion

This paper mainly deals with the nonlinear analytical modeling and characteristic analysis of two types of composite multi-beam modules for planar motion to enable rapid analysis and design synthesis. Each type of composite multi-beam module consists of identical, uniform and parallel wire beams, distributing uniformly along circle(s), with symmetrical cross sections. Analytical models of basic multi-beam modules with all beams uniformly spaced around a circle are firstly revisited. Analytical and nonlinear load–displacement equations are derived for the composite multi-beam modules, each of which is composed of two basic multi-beam modules with the same type connected either serially or parallelly. Finite element analysis (FEA) is carried out to compare and verify the analytical models. Detailed characteristic analysis and comparisons are conducted to compare three types of compliant six-beam modules whose twisting rotations are well constrained. These analytical results are capable of capturing some key quantitative nonlinear characteristics, such as kinematic effects, load-stiffening effect and nonlinear twisting stiffness (torsional stiffness), and can promote the design and analytical modeling of compliant parallel manipulators composed of the compliant multi-beam modules. In addition, the nonlinear analytical models of other variations of parallel double multi-beam modules are derived.

A structural study of a three-membered linear metal chain compound at elevated pressure

Single crystal X-ray diffraction studies of the symmetrical molecular wire compound Co3(dpa)4Cl2·(dcm) have been performed up to a pressure of 3.6 GPa using both synchrotron and conventional sources. It is found that the terminal Co-Cl bond distance initially increases by 0.013(4) Å at 0.32 GPa after which it continuously decreases. Extensive theoretical calculations show that population of a thermally excited state containing increased Co-Cl anti-bonding character is a possibility at 0.32 GPa. The relative occupancy of the disordered dcm solvent molecule changes significantly with pressure and this is explained by the analysis of void spaces and Hirshfeld surfaces at different pressures. At 3.2 GPa, fingerprint plots derived from Hirshfeld surfaces indicate that neighbouring metal chain compounds approach each other such that short H···H interactions appear.

Transient Electromagnetic and Heat Transfer Characteristics of the MgB2 Superconductor in Liquid Helium

A transient current density analysis is carried out for the type II superconductor (SC) material MgB2 in liquid Helium. Variable magnetic fields are used as the unknown in solving the curl-curl relations of the electromagnetic fields applying the finite element method (FEM) for 2D axis symmetric cylindrical wires. Assuming an exponential current rise, the magnetic flux, current density and temperature distribution in the SC and He are calculated. This study gives the limiting current values to avoid the normal state, the temperature distribution profile with time as well as the changes in the magnitude of the current and time constant. Oscillations and non-uniform temperature distributions are observed in He and in the SC respectively if one varies the parameters which are related to the different heat transfer mechanisms. A slight instability in the current distribution is also observed which might transfer to a thermal instability, i.e. could signal He boiling.

Atomic Structure of Mn Wires on Si(001) Resolved by Scanning Tunneling Microscopy

At submonolayer coverage, Mn forms atomic wires on the Si(001) surface oriented perpendicular to the underlying Si dimer rows. While many other elements form symmetric dimer wires at room temperature, we show that Mn wires have an asymmetric appearance and pin the Si dimers nearby. We find that an atomic configuration with a Mn trimer unit cell can explain these observations as due to the interplay between the Si dimer buckling phase near the wire and the orientation of the Mn trimer. We study the resulting four wire configurations in detail using high-resolution scanning tunneling microscopy (STM) imaging and compare our findings with the STM images simulated by density functional theory.

Vortex Domain Wall Formation in Permalloy Nanowires with Geometric Pinning Sites

An optimal geometric pinning site on Permalloy nanowires of varying widths has been investigated and applied in a magnetic memory scenario using micromagnetic simulations. Minimal limits on two key factors; the applied field length and the domain wall formation length are established such that vortex domain walls are reliably formed in the structures to facilitate lower powered domain wall movement using spin-polarised current. The symmetric wires with the nanoconstrictions at both sides have been found to favour the formation of the vortex domain wall compared with the asymmetric wires with the nanoconstrictions at only one side of the wires. The detailed micromagnetic simulations show that the domain wall formation length and the applied field length are optimal to form the vortex domain walls when they are equal to the nanowire width.

Implosion characteristics of conical wirearray Z pinches on Qiangguang1 facility

Implosion and radiation characteristics of conical wire array in different regimes of implosion are investigated at the 1 MA Qiangguang-1 facility by X-ray self-emission diagnostics. Experimental results show that the shape of precursor plasma is also conical. The initial implosion takes place near the cathode by a stronger Lorenz force, forming a triangle-like structure that produces harder X ray. The current crossing the bubble in the front of the wire array near the anode persists in persist ablating, thereby leading to a zippered stagnation. The initial implosion of a bubble near the cathode is followed by the implosion zippering upwards as the zipper implosion speed is 2.59 107 cm/s. The results shows that the conical array has a broader X-ray power pulse than cylinderical wire array due to the zippered stagnation and zippered implosion of the array. The study of implosion characteristics of specialized axis symmetric wire array Z-pinch-like conical wire array can provide a valuable test bed for understanding the regime of implosion as well as theoretical model and magneto-hydrodynamic (MHD) codes, both of which primarily develop for the modeling of cylindrical wire array Z pinches.

The Relation Between Helical Spring Compliances With Free and Fixed End Rotations

A helical spring that is constrained to no rotation has a compliance that is typically more than 95% of the compliance of springs constrained to free rotation when restricted to symmetric wires made from materials with Poisson’s ratio between 0 and 1/2. It is shown that the shape of the spring wire can be designed so the spring will not twist when it is extended nor extend when it is twisted. The constrained spring versus a freely rotating spring with the helix angle equal to π/4 has the largest reduction in compliance in the limits of beam theory. Spring compliances for torsion and extension with quite complex helical spring geometries are found to be related by a dimensionless ratio of compliances in a very simple equation that only depends on Poisson’s ratio and the helical, spring angle, ψ. Springs made from materials with negative Poisson’s ratio, however, can have a very substantial reduction in compliance; the no rotation compliance is zero when Poisson’s ratio is −1. There are large changes in spring compliances for springs with geometric coils that are elongated rectangles or flattened ellipses.