Grounded Surface Research Articles

Sub‐Micron Thickness Self‐Limiting Electrospray Deposition via Voltage Bias of Spray Target

AbstractElectrospray deposition (ESD) is a technique with emerging relevance for applications requiring micro‐/nano‐scaled coatings. Self‐limiting electrospray deposition (SLED) is a regime of ESD where upon satisfying the criteria for self‐limiting behavior, the charge buildup of the material will eventually begin to repel itself until an asymptotic thickness is achieved, based primarily on the properties of the spray solution and deposited material. This work focuses on controlling the coating thickness further to achieve sub‐micron thicknesses. By applying a voltage bias of the same polarity of the spray onto the target substrate while providing a secondary grounded surface, the thickness of a payload can be manipulated for thinner and more precise thicknesses. The magnitude of the voltage bias is varied to show the effect of voltage bias on thickness, and 2‐D and 3‐D structures are used to demonstrate the generality of this technique for complex substrates. The results show how SLED can be included as a potential alternative for conformal coatings deposited at ambient conditions at the sub‐micron scale.

Ion energy analysis of a bipolar HiPIMS discharge using a retarding field energy analyser

The time evolution of the positive ion energy distribution functions (IEDF’s) at the substrate position in an asymmetric bipolar high-power impulse magnetron sputtering (HiPIMS) system was determined using a gridded energy analyser. This was done for a range of operating conditions, namely the positive voltage U rev and ‘on-time’ negative pulse duration τ neg. The magnetron sputtering discharge was equipped with a Nb target. Based on the knowledge of the IEDF’s, the bombarding ion flux density Γi and energy flux density Q i to a grounded surface were calculated. Time-resolved IEDF measurements showed that ions with energies approaching the equivalent of the positive pulse voltage U rev were generated as the reverse positive voltage phase developed. On time-average, we observed that increasing the set U rev value (from 0 to 100 V), resulted in a marginal decrease in the ion flux density Γi to the analyser. However, this is accompanied by a five-fold increase in the ion energy flux density Q i compared to the unipolar, U rev = 0 V case. Reducing the negative HiPIMS pulse duration τ neg (from 130 to 40 μs) at a constant discharge power leads to a modest increase in Γi, but a four-fold increase in Q i. The results reveal the benefit of the bipolar HiPIMS technique, in which it is possible to control and enhance the power density of ions bombarding a grounded (or fixed bias) substrate, for potentially better tailoring of thin film properties.

Novel comparison concept between CBN and Al2O3 grinding process for eco-friendly production

Minimal Quantity of Lubrication was developed to achieve green manufacturing in machining process. In this study, parameters of cutting fluid flow, grinding wheel type and wheel cleaning system were evaluated to achieve the maximum potential of this technique in grinding process. The comparison of super abrasive (CBN) and conventional (Al2O3) grinding wheel, the cutting fluid flow (30 ml/h, 60 ml/h and 120 ml/h), and the wheel cleaning system were analyzed based on: surface roughness, roundness errors, grinding wheel wear, confocal of grounded surface, grinding power, acoustic emission and workpiece microscopy. In a novel way, this study compared the costs per piece and the carbon footprint in terms of CO2 emission for both abrasive tool application. For all the parameters analyzed, the CBN grinding with MQL outperformed the Al2O3 grinding, showing a superior performance not only in terms of surface finishing, on average, 29% lower surface roughness and dimensional deviation 9% lower but also regarding tool efficiencies, such as 127% lower diametrical wear, 42% lower acoustic emission, and 13% lower grinding power. Despite that, the cost per piece was also evaluated for the different lubri-cooling conditions and tools, and the cost per piece recorded for Al2O3 grinding was substantially lower than CBN grinding, irrespective of the lubri-cooling method employed. The cost of grinding for all MQL techniques analyzed with aluminum oxide wheel was, on average, 72% less than grinding with CBN wheel. Besides, the conventional method with the CBN wheel was 7% more expensive than the aluminum oxide wheel.

Highly efficient smoothing of Inconel 718 via electrochemical-based isotropic etching polishing

For the highly efficient and versatile polishing of metals, isotropic etching polishing (IEP), which is based on the merging of isotropic etching holes, has been developed. In this study, the feasibility and mechanism of isotropic etching polishing of nickel-based superalloy Inconel 718 (IN718) and the polishing characteristics have been studied. The potentiodynamic experiments revealed similar trends of the cathodic, passive, second passivation, and transpassive regions in all the electrolytes, while the corrosion susceptibility of IN718 successively decreased with the increasing H2SO4 concentration in the electrolyte. The etching anisotropy of the IN718 precipitated with different phases can be experimentally transmuted to isotropic etching by modulating the electrolyte concentration and keeping electrolyte temperature equal or above the room temperature. Because of the positive correlation of the etching current with isotropic holes density and diameter, etching at higher currents is promoted for the rapid and proficient polishing. The surface evolution mechanism during IEP has been confirmed. The surface roughness initially increased due to the formation of etching holes, then decreased abruptly owing to the rapid merging of etching holes and finally achieved a smooth surface. The wet grounded surface of IN718 with a roughness of Sa 62.7 nm has been transformed into a mirror-like smooth surface with a roughness of Sa 0.86 nm within 300 s of IEP at optimized conditions and a high MRR of 2.73 mm3/min has been achieved.

Single-phase ion trap with cylindrical zero-potential surface

In the present article, we discuss an electrostatic field around four-bar trap, where in-phase AC voltage is applied to all electrodes. We consider shielding effect on trap’s field distribution. The ideal octupole field is obtained using a cylindrical grounded surface. Single-phase trap gives an opportunity to form an n-order multipole field within n + 1 number of electrodes. This approach reduces the number of electrodes in comparison with the classical case.

Studying Resonant Frequencies of a Helical Spring with and Without Axial Loads

This paper presents the resonant frequencies of a helical spring manually calculated in compliance with SAE-11 and also via numerical simulation. In both calculations, a damper rate of zero was utilized to make modeling simpler. Two numerical simulations were run, ranging in frequency from 90 to 590 Hz. The first simulation applied frequencies with no load on the spring, while a second simulation had an axial load on the spring grounded surface, perpendicular to spring centerline. In addition, the second simulation had a constraint added to the opposite grounded surface of the spring and was opposite to the load. Likewise, manual calculation and numerical simulation via COMSOL??? Multiphysics presented very similar results. But, when comparing only the simulations, both revealed high stresses for the same frequencies. However, the second simulation (spring with load applied) had very high stresses, which indicates a high risk of premature failure of the spring.

SIW Horn Antenna with a Special Coplanar Transition and Dielectric Lens for Feeding a Leaky-Wave Antenna

The paper describes the main phases and features in designing a feeder for a leaky-wave antenna in the Ka-band. The problem of feeding can be effectively solved using a horn antenna SIW technology-based and single substrate-integrated with the radiating aperture of the leaky-wave antenna. Unlike most similar studies, where an aperture exciting from a closed-type structure is analyzed, in our work the open-type antenna feeder is synthesized.In the paper, we give a brief overview of the main achievements in designing traditional SIW-structures and present relations for their calculation. Basing on results of electromagnetic modeling, determine the influence of the substrate permittivity on the efficiency of SIW transmission line by the method of finite Weiland integrals. Consider the most popular types of the waveguide transitions to SIW, including micro-strip lines and grounded coplanar waveguides (GCPW). Depending on the required bandwidth and substrate dimensions specify conditions for selecting a design type of the waveguide transition.A special attention is paid to the non-standard coplanar transition with an elevated grounded surface (EGCPW), which is worth using if the substrates are thick. It was used as a basis for designing a new, more efficient EGCPW transition with the elevated grounded surface, which contains specially made slots (SEGCPW). Recommendations for its adjustment are given.The dependences of the gain on the aperture width for the H-plane SIW horn antenna, which are used to select its optimal size, are obtained basing on simulation. It was found that for matching the feeder with the leaky-wave antenna and decreasing the side lobes level, a dielectric lens with through holes worth using. Basing on the simulation of the unit cell of the lens the dependence of the effective permittivity on the diameter of the through hole is obtained. An influence of the non-uniformity degree of the lens with the holes of different diameters on the radiation efficiency of a horn antenna is determined. The complete design of the synthesized feeder and its radiation pattern is presented to prove the antenna efficiency in the wide frequency band.

RESEARCH OF A CAPACITIVE DISTANCE SENSOR TO GROUNDED SURFACE

In this paper, a review and analysis of capacitive sensors with flat concentric electrodes for measuring distances to grounded surfaces has been present. A simplified calculation model to determine the transformation function of a capacitive distance sensor with concentric coplanar electrodes has been created. The optimal relationship between the dimensions of the sensor and the measuring range has been determined. The working informative capacity of the sensor for the given sizes has been calculated. Approximating dependencies for the function "sensor working capacity – distance to grounded surface" have been determined. The graphs of the approximating functional dependence for the linear model and for the third-order polynomial model have been drawn. It is established that the use of third-order polynomials ensures the smallest approximation error. A formula for calculating the parasitic capacitance of the sensor through the dielectric of the substrate has been obtained and its value for the given sizes has been calculated. The proposals of this type sensors use are given.

Mobilization of tungsten dust by electric forces and its bearing on tritiated particles in the ITER tokamak

Experimental investigations on the electric field strength required to overcome the adhesion forces of micron size tungsten metallic dust as well as silver and aluminum oxide in powdery form deposited on a conductive surface are presented. The results reveal a strong influence of particulate surface properties on the detachment threshold, especially for tungsten particles which exhibit a thin surface oxide layer that screens their electrical conductivity. Such tungsten particles makes possible that electrostatic self-charging occurs when tritiated because of their dielectric properties even if there are deposited on a conductive grounded surface.

Numerical model of the electro-gas-dynamics of a gas–particle system based on the equations of motion of a two-velocity two-temperature gas–particle mixture

A mathematical model of the electro-gas-dynamics of a gas–particle system is described. A numerical method for solving the system of equations is proposed, and an analysis is made of the motion of charged solid aerosol particles in gas–particle flow in the electric field produced by the corona electrode of the atomizer, the grounded surface on which deposition is performed, and the charge of the aerosol particles in the interelectrode space. The solution is based on the two-velocity two-temperature model of a monodisperse medium without phase transitions and coagulation assuming that only the carrier medium, described by the Navier–Stokes equations for a compressible gas, has viscosity. The dispersed phase is defined by the equation of conservation of mass, the equations of conservation of momentum components taking into account the Coulomb force and aerodynamic friction, and the equation of conservation of internal energy. The system is written in generalized coordinates in dimensionless form and solved using the explicit McCormack method with splitting over the spatial coordinates and a conservative correction scheme. The velocity and density fields of the gas–particle mixture were investigated in the interelectrode space and near the surface on which solid aerosol particles in the gas–particle flow are deposited.

An Ultrathin Electromagnetic Absorber Comprising Resistive Resonance Loops

In this letter, we propose a novel ultrathin polarization-independent electromagnetic absorber and provide numerical simulation and experimental verification of the absorbing properties. The proposed absorber takes the form of periodic resistive resonance loops. The resonance loops, as a sort of effective loss magnetic currents, are placed in close proximity to the grounded surface. Numerical simulated and experimental results show that the overall thickness of the proposed structure is much less than centesimal wavelength, and the absorptivity at different incidences is kept well.

Effect of shot peening on rolling contact fatigue and lubricant film thickness within mixed lubricated non-conformal rolling/sliding contacts

The effect of shot peening on rolling contact fatigue (RCF) and lubricant film thickness within non-conformal rolling/sliding contacts operated under mixed lubrication conditions was observed in this study. Rolling contact fatigue tests and film thickness measurements were carried out using specimens with modified surface topography by shot peening process using glass beads having diameter between 0.07 and 0.11 mm. It has been shown that the effect of shot peening on RCF has no positive effect even if shot peened surface of the roller exhibited somewhat higher hardness in contrast to the grounded surface. The reduction of RCF may be caused due to asperities interactions because after shot peening the surface roughness of the roller was increased. Film thickness measurements confirmed that the contact is realized actually only between asperity peaks of shot peened ball and smooth disc. Conversely, no negative effect on RCF was observed when the shot peened surface of the roller was polished. The polish of asperity peaks causes the creation of lands and micro-cavities, which may be employed as lubricant micro-reservoirs. From film thickness measurements it has been observed that lubricant emitted by shallow micro-cavities can provide the local increase in lubrication film thickness, which thereby reduces asperities interactions. Similar results were obtained for start-up conditions where the squeeze lubricant enlarges film thickness and reduces surface interactions. From the obtained results, it can be suggested that properly designed surface topography modification could help to increase the efficiency of lubrication films leading to the enhancement of contact fatigue life of non-conformal mixed lubricated rolling/sliding contacts.

Periodicity Perturbed Grounded Frequency Selective Surface Arrays as Millimeter Wave Random Phase Coherence Destroying Diffusers

This paper presents the design, construction and testing of perturbed periodicity slot type grounded Frequency Selective Surface (FSS) array as millimeter wave (mm-wave) random phase diffusers to eliminate speckle in active mm-wave imaging. To create a random phase diffuser for destroying the coherence of mm-wave sources we proposed FSS based diffusers arrays where the periodicities between the elements are different thought the slot of the cells are similar. The impacts of periodicity variations of both TM and TE field directions have been investigated. The periodicity of an FSS is the main design parameter used to optimize the phase shifting properties of the arrays. The critical parameters of the diffuser arrays design, such as phase relation with periodicity and optimum designed consideration are discussed. We designed the FSS arrays with Finite Integral Technique, fabricated by using etching technique and characterized the S-parameters with a free space Millimeter Wave Vector Network Analyzer (MVNA).

Experimental verification of the suppression of spatial dispersion in artificial plasma

In this paper, we verify experimentally the recently proposed theory on suppression of the spatial dispersion in an artificial plasma. We make use of the image principle and assume effectively local material parameters of the artificial plasma, in which the spatial dispersion has been suppressed, and measure the reflection from an impenetrable grounded surface. The plasma resonance can be clearly distinguished from the measurement results at the plasma frequency independently from the incidence angle. The agreement between the measurement results and the theory and simulations is very good.

Effect of inter‐element spacings variation on the performance of linear grounded frequency selective surface arrays in W‐band

AbstractThis article examines the issue of extending the inter‐element spacing between slots of equally‐spaced linear grounded frequency selective surface (FSS) arrays with spacing beyond half a wavelength in W‐band (75–110 GHz). We present the design, processing, and testing of W‐band grounded FSS arrays with different inter‐element spacings along transverse electric (TE) and transverse magnetic (TM) field directions separately. The comparison of periodicity changing effects along TE and TM field directions has been reported. The inter‐element spacing versus phase curves demonstrate that in some extent the inter‐element spacing can be a phase optimization parameter for complex array design. We fabricated the corresponding FSS arrays on quartz substrate with photolithographic etching technique, and characterized the vector S‐parameters with a free space MVNA. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 155–160, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24848

W-Band Characterization of Grounded Frequency Selective Surface Arrays Composed of Nonequal Slot Length Subarrays

We present the design and construction of Frequency Selective Surface arrays composed of two subarrays of different slot lengths. We investigated their response variations with the variation of slot length differences of the elementary sub-arrays. Such nonhomogeneous arrays cannot be simulated with Computer Aided Design (CAD) programs because the boundary conditions are not fulfilled by the simulator. In infinite array simulation, the periodic boundary conditions are prescribed on the walls of the unit cell, whereas in the case of sub-arrays of unequal slot length such boundary conditions are not applicable. The CAD simulation of such combined array gives incorrect values of amplitude and phase responses. In this work, we investigate the characteristics of such complex arrays by using heuristic experimental approach. The results of the experimental approach demonstrate that the resultant reflection amplitude and phase of such complex array depend on the difference of slot lengths (ΔL) of the two sub-arrays.

Overcoming the Electrostatic Discharge in Hydraulic, Lubricating and Fuel-Filtration Applications by Incorporating Novel Synthetic Filter Media

Electrostatic charge generation occurs in fluid systems as a result of friction between the fluid and system components. The magnitude of charge generated by each component will depend on many interrelated factors, including environmental ones. It can occur during filtration of hydraulic and lubricating oils as well as diesel and gasoline fuels. This effect manifests itself in several ways, the most noticeable effect being an audible noise (clicking sound) as the discharge of electrostatic charge accumulation causes sparking internally within the system. Less-apparent effects involve migration of the electrical charge downstream of the filter, causing damage to system components and the filter itself when the charge dissipates by discharging itself to a grounded surface. Several methods have been investigated to overcome the aforementioned behavior and prevent the damage that can occur if the electrostatic discharge continues to operate unchecked. One of these methods involved adding an antistatic additive to the liquid, but this is restricted to fuel applications. Other methods involved surface modifications carried out directly on the filter media or the use of conducting materials such as meshes made from suitably selected conducting materials that can be incorporated into the construction of filter cartridges. The main aim of these modifications is to affect a discharge from the filter cartridge, before a hazardous potential accrues on the filter media, by lowering the voltage gap. Although this approach eliminates direct damage to the filter cartridge, it does not prevent charge migration into the oil where it subsequently accumulates. The approach we took involves designing the filter material to be electrostatic dissipative, which offers the advantage of eliminating filter damage entirely and significantly reducing migration of charge into the fluid.

Microarcing instability in RF PECVD plasma system

Microarcing at the chamber wall in RF plasma is studied in PECVD type system. A Langmuir probe is used to measure the plasma potential. This system and procedure allows us to create reproducibly microarcings by increasing the plasma potential. The wall arcing threshold of the plasma potential in this system is in the vicinity of 50 V. In this system, the charging process, which is about a few tens of milliseconds or more, is much slower compared to the microsecond discharge. The time constant for sheath charging can be reduced if less sheath area is responsible for the potential recovery. The arcing frequency strongly depends on the plasma potential, the grounded surface area of sheath, and the pressure. This work demonstrated that the microarcing in the RF deposition and reactive etching plasmas depends on plasma potential, gas pressure, surface area of grounded wall, and chamber conditions.

Influence of Discharge Geometry on Power Dissipation and Sheath Impedances in Silane Discharges

The influence of the interelectrode distance on the power consumed in rf silane glow discharges, for two different electrode sizes and at two different silane pressures is reported. The effect of the increasing grounded surface area in contact with the discharge is analysed by using a simplified calculation of the rf and grounded sheath impedances. At all cases the power consumed in the discharge increases with interelectrode distance and is higher for higher pressures, for a constant excitation voltage. The sheath impedances are always higher for lower pressures except for the case of the ground sheath when using the large electrode set.

Nitrogen ion dynamics in low-pressure nitrogen plasma and plasma sheath

Laser-induced fluorescence (LIF) excitation and time-resolved LIF spectroscopy have been used to explore the interaction of a nitrogen plasma with a metal surface. The rotational temperature, the concentration of N+2, and the lifetime of N+2(B2Σ+u)υ=0 were measured as a function of distance from the metal surface. It was observed that the lifetime of the excited ion decreases sharply in the plasma sheath which is created in front of the metal surface. The concentration of N+2(X 2Σ+g), which was measured simultaneously with the lifetime of excited N+2, indicates a quasilinear decrease from the cathode to the grounded surface. Trot undergoes a gradual reduction from the bulk plasma up to the surface where its value is a good approximation of the surface temperature. An interpretation of these phenomena including a numerical simulation of the lifetime decrease is proposed here. The calculated values are in good agreement with experimental results. The dependence of lifetime decrease on the sheath potential as well as on other important parameters (cross section, profile of the electric field) is further discussed.