Asymmetric Electric Field Distributions Research Articles

Study and analysis of high-power coupler failure due to asymmetric electric field distribution

Microwave vacuum electronics play a vital role in numerous applications, and high-power couplers are a critical component. However, coupler failure is a common problem in high-energy accelerators, especially in situations involving high continuous wave (CW) power operation, leading to costly downtime and reduced performance. This paper focuses on addressing the issue of coupler failure in high-power scenarios by studying the specific case of the Circular Electron-Positron Collider (CEPC) 650 MHz high-efficiency klystron, designed for a power of 800 kW and tested up to 700 kW. The failure was attributed to the cracking of the coupler ceramics due to asymmetric electric field distribution, a previously unnoticed issue. Consequently, this study describes the coupler testing process, analyzes the problem, and proposes corresponding solutions to achieve symmetrical electric field distribution and reduce thermal stress. After evaluating three approaches, we recommend the T-bar coupler with water cooling and forced air cooling as the most viable option. This research is significant for the future development of high-power couplers, as it offers references for overcoming technical challenges and optimizing structural designs. As a result, other high-power coupler designers may find inspiration in the suggested solutions as they strive for increased dependability and performance.

Asymmetric electric field distribution enhanced hierarchical metamaterials for radar-infrared compatible camouflage

Metamaterials are widely used in electromagnetic radiation and camouflage for their flexible wavefront manipulation and polarization over a broad spectrum ranging from microwaves to optics. However, multispectral compatible camouflage faces significant challenges due to tremendous scale differences of unit cells and desired radiative properties in various spectral regimes. This study assembles a micron-scale infrared emitter, a millimeter-scale microwave absorber, and a metal reflector to propose a hierarchical metamaterial that reduces microwave scattering and reflects low-infrared waves. As a proof of concept, laser etching micro-manufactures an upper infrared shielding layer with a periodic metal pattern. At the same time, bottom square frustum metastructure composites are fabricated and optimized based on genetic algorithms. Under the normal incidence transverse electromagnetic wave with a 90° azimuth angle, the hierarchical strategy and infrared unit create an asymmetric electric field distribution of local near-field coupling, which is conducive to generating additional resonance for broadening the absorption bandwidth. Experiments verify the multispectral camouflage, which shows a high absorption efficiency of more than 90%, ranging from 3.6 to 6.2 and from 8.4 to 18 GHz with a total thickness of 4.05 mm (0.049λmax). Due to the non-reflection of surrounding thermal signals in the infrared 2-22 μm region, low-infrared emissivity (0.29) metamaterials can adapt to various thermal backgrounds. This methodology can provide a novel route for fabricating multispectral camouflage devices.

Potential sources of compositional inaccuracy in the atom probe tomography of InxGa1-xAs

With the objective of applying laser-assisted atom probe tomography to compositional analysis within nanoscale InGaAs devices, experimental conditions that may provide an accurate composition estimate were sought by extensively studying an InGaAs blanket film. Overall, the determined arsenic atomic fraction was found to exhibit an electric field dependent deficiency, which was more pronounced at low field conditions. Although the determined group III site-fraction also showed a (weak) field-dependent deficiency at low field conditions, it remained invariant with analysis conditions and in close agreement with the nominal value at higher field. In this study, we investigate and discuss the mechanisms that could potentially contribute to As underestimation. Given the field dependence observed, the phenomena occurring between low and high field conditions are compared. At low field, the tendency of As to field evaporate in significant amounts as multiply charged cluster ions (Asni+ with n as large as 9 and i = 1,2,3) is shown to be a significant source of compositional inaccuracy. These clusters may lead to peak overlap in the mass spectrum (e.g. the peak at 150 Da may represent As42+ or As2+ or both), thereby creating an uncertainty in the quantification. Emitted clusters may also dissociate with the likelihood of neutral generation and multi-hit losses being non-negligible. Experimental studies and density functional theory calculations are presented to characterize cluster stability and its contribution to measurement uncertainty. Under high field conditions, although fewer clusters are detected and the composition appears more accurate, the emergence of two additional mechanisms, i.e., multi-hits and DC evaporation, may degrade the data quality. The challenges in evaluating the impact of all these loss mechanisms are examined in detail. Finally, we show that for InGaAs under UV illumination, due to the laser-tip interaction, the resulting asymmetric electric field distribution across the apex introduces local atomic fraction variations.

Dual-Frequency Miniaturized Substrate Integrated Waveguide Quarter-Mode Cavity-Backed Antenna Based on Minkowski Fractal Gap with Orthogonal Polarization Radiation Characteristics

A novel quarter-mode substrate integrated waveguide miniaturized cavity-backed antenna loading Minkowski fractal gap is presented in this paper. Firstly, the resonant frequency of the rectangular substrate integrated waveguide resonator is reduced by etching the fractal gap in the resonator to achieve miniaturization. In addition, because of the symmetry of electric field distribution in second and third order resonant modes, the cavity can be segmented into a quarter-mode and the other order resonance modes with asymmetric electric field distribution can be suppressed according to the cavity model theory. Hence, the cavity size is further reduced. The dimension of designed antenna is 0.26λ0×0.26λ0 (λ0 is the wavelength in free space; in this paper, the corresponding wavelength is 3.6 GHz). Moreover, the orthogonal polarization of the proposed antenna in two frequency bands is achieved because the electric field is orthogonal in second and third order resonant modes. This dual-frequency orthogonal polarization characteristic enables antenna to communicate in two working bands and has good channel isolation. The simulated and measured results are consistent. The antenna gain is 4.67dBi and 3.4dBi, respectively, at 3.7GHz and 4.6GHz.

Exploiting the Wall-Induced Non-inertial Lift in Electrokinetic Flow for a Continuous Particle Separation by Size

Separating particles from a heterogeneous mixture is important and necessary in many engineering and biomedical applications. Electrokinetic flow-based continuous particle separation has thus far been realized primarily by the use of particle dielectrophoresis induced in constricted and/or curved microchannels. We develop in this work a new electrokinetic method that exploits the wall-induced non-inertial lift in a straight uniform microchannel to continuously separate particles by intrinsic properties (e.g., size and surface charge). Such an electrically originated lift force arises from the asymmetric electric field distribution around a particle nearby a planar dielectric wall. We demonstrate this method through separating both a binary and ternary mixture of dispersed polystyrene microspheres by size in a T-shaped microchannel. A semi-analytical model is also developed to simulate and understand the particle separation process. The predicted particle trajectories in the entire microchannel agree reasonably well with the experimental measurements.

Semiempirical Thrust Model of Dielectric Barrier Plasma Actuator for Flow Control

AbstractAsymmetric dielectric barrier discharge plasma generating a wall-bounded jet without mechanical moving parts was studied as a flow control device. A reliable model providing thrust value of the plasma actuator is difficult to develop without incurring a heavy calculation cost attributable to its unsteady characteristic and asymmetric electric field distribution. In this paper, a new semiempirical thrust prediction model was developed based on the one-dimensional electrohydrodynamic effect. It is implemented in a computational fluid dynamics solver as a body force term. We determined that the thrust of the plasma actuator is proportional to the energy consumed in the actuator, which is regarded as a capacitor in the alternating current (AC) circuit. An analytic estimation of the capacitance of the actuator is performed, and the sensitive design parameters dielectric constant, thickness and the upper electrode thickness are considered in the capacitance value. The thrust value from the model is inse...

Suspended and localized single nanostructure growth across a nanogap by an electricfield

Direct growth of a suspended single nanostructure (SSN) at a specific location is presented.The SSN is grown across a metallic nanoscale gap by migration in air at room temperature.The nanogap is fabricated by industrial standard optical lithography and anisotropic wetchemical silicon etching. A DC current bias, 1 nA, is applied across the metallic gap toinduce nanoscale migration of Zn or ZnO. The history of the voltage drop across the gap asa function of time clearly indicates the moment when migration begins. The shape of SSNsgrown across the nanogap by the migration is asymmetric at each electrode due tothe asymmetric electric field distribution within the nanogap. An SSN can beused as the platform for two-terminal active or passive nanoscale electronics inoptoelectronics, radio frequency (RF) resonators, and chemical/biological sensors.

Magnetic-field tunable transmittance in a ferrofluid-filled silicon nitride photonic crystal slab

A numerical simulation was performed to demonstrate the active manipulation of the transmittance spectra in a ferrofluid-filled silicon nitride (SiN) photonic crystal slab (PCS) with magnetic field applied perpendicularly to the plane. Many sharp transmittance resonances were found to be correlated with the modes extracted from band structure calculations, where they show red-shift and mutual approach as the external magnetic field increases. By changing the angle of the incident light, we found strong coupling modes because of their asymmetric electric field distributions. This in situ control of transmittance properties of ferrofluid-filled SiN PCS should open up new applications for designing filters, mirrors and displacement sensors in compact optical devices.

Magnetotunneling measurement of space-charge accumulation inδ-doped quantum wells

Resonant tunneling wells with approximately V-shaped profiles have been fabricated by \ensuremath{\delta}-doping ${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As tunnel barriers. The structures show strong resonances in their current-voltage characteristics in qualitative agreement with the expected subband structure. Magnetotunneling experiments are shown to measure the electron density in the lowest subband which displays a strong asymmetry as a function of the bias voltage. This is indicative of an extremely asymmetric electric field distribution within the structure and is explained by a consideration of the dynamics of the electrons tunneling into, or out of, a slightly asymmetric well. The implications for asymmetries in other semiconductor structures are pointed out.

Kerr effect tomography for nonintrusive spatially resolved measurements of asymmetric electric field distributions

An optical method for nonintrusive spatially resolved measurements of asymmetric electric field distributions in dielectric liquids is presented. Using multiangular Kerr effect measurements the electric field distributions are reconstructed with mathematical techniques known from computer-assisted tomography. The method is applicable to all high voltage devices containing liquids showing Kerr effect, allowing multiangular optical access, and having a relatively uniform electric field direction in the plane where the measurements are performed. The measurement technique is demonstrated experimentally with nitrobenzene. Comparisons between experimentally determined electric field distributions and theoretically calculated distributions show good agreement.

Description and detection of moving sample zones in zone electrophoresis: Zone spreading due to the sample as a necessary discontinuous element

AbstractThis paper deals with the description and detection of moving sample zones in free zone electrophoresis. It is shown that the shape of a sample zone never reaches a steady‐state. However, either the front or the rear boundary of the sample zones, but not both, can represent steady‐state concentration distributions with decreasing peak heights. This results in an unsymmetrical broadening of the moving zones. With a multichannel detection device, consisting of 255 equidistant detectors along the separation trough, asymmetric electric field distributions of the sample components are measured. These are shown to agree with theoretical predictions, made by a model based on migration only. This clarifies the fact that in zone electrophoresis migrational dispersion due to the applied electric field is usually much larger than diffusional spreading.

A comparison of model predictions for plasma convection in the northern and southern polar regions

We have presented model calculations to show how the plasma flow distributions in the northern and southern polar regions differ when viewed from a geographic inertial frame. This reference frame was selected because it is the natural frame for geophysical plasma flow measurements, there being well‐known velocity corrections for either satellite or ground‐based observations. Although the magnetic invariant latitude, magnetic local time reference frame is better suited to studying magnetospheric processes, a transformation from the geographic inertial frame to this magnetic frame requires both a spatial and velocity transformation, and since the latter correction has generally been neglected, we prefer to present our results in the geographic inertial frame. However, we also present some of our results in the magnetic frame, taking account of the complete transformation. Our convection model includes the offset between the geographic and geomagnetic poles, the tendency of plasma to corotate about the geographic poles, and a dawn/dusk magnetospheric electric field mapped to a circle about a center offset by 5° in the antisunward direction from the magnetic pole. We considered both uniform and asymmetric magnetospheric electric field configurations. Our asymmetric electric field distribution contained an enhanced field in the dawnside northern hemisphere in conjunction with an enhanced field in the duskside southern hemisphere. From our study we have found the following: (1) In the geographic inertial frame the plasma flow patterns in both hemispheres exhibit significant variations with universal time because of the relative motion of the geomagnetic and geographic poles. (2) This universal time variation is greater in the southern polar region than in the northern polar region because of the greater displacement between the geomagnetic and geographic poles. (3) For the case of a uniform magnetospheric electric field the universal time dependence of the plasma flow distributions in the two hemispheres is similar, but there is a phase shift of about half a day between them. (4) For the case of an asymmetric magnetospheric electric field this half‐day phase shift is still noticeable, but there are significant differences between northern and southern hemisphere convection patterns. (5) The transformation of plasma convection patterns from the geographic inertial to the geomagnetic quasi‐inertial frame results in the same convection pattern for both hemispheres for the case of a uniform magnetospheric electric field, but results in different convection patterns for the two hemispheres for the more common case of an asymmetric electric field configuration. (6) Because the magnetospheric electric field distributions in the northern and southern polar regions are generally asymmetric, erroneous conclusions can be drawn about plasma convection patterns if data taken along satellite tracks from the northern and southern polar regions are overlaid. This is true whether the overlaying is done in the geomagnetic quasi‐inertial frame or the geographic inertial frame.