Electric Surface Research Articles

Enhanced electrochemical properties of LiMn2O4 cathode by adding halloysite nanotubes as additive

Halloysite nanotubes (HNTs) were used as an electrode additive to prepare a LiMn2O4/halloysite composite cathode to improve the cycle and rate performance of LiMn2O4–Zn batteries. The composite electrode was characterized by XRD, FTIR, SEM, and TEM. Electrochemical performance of batteries using composite electrode was evaluated by CV, EIS, rate and cycle test. SEM image revealed that the hollow halloysite nanotubes were well dispersed in the prepared cathode. The electrochemical performance test results showed that the battery with LiMn2O4/halloysite composite cathode containing 3 wt% HNTs exhibited the higher specific discharge capacity, better rate capability and cyclability than that of the battery using the conventional LiMn2O4 cathode without any HNTs additive. The improved electrochemical performance of LiMn2O4 cathode was attributed to the three-dimensional network channels formed by the hollow HNTs. Li+ could migrate rapidly in the halloysite nanotubes filled with water-based electrolytes, and the negative electric surface of halloysite could be another pathway for Li+ migration in the electric field. The efficient Li+ transmission effectively reduced the concentration polarization during the charge-discharge process and promoted the improvement of the LiMn2O4 cathode electrochemical performance.

Electric conductivity and surface potential distributions in carbon fiber reinforced composites with different ply orientations

The electric conductivity and surface potential distributions of carbon fiber laminated panels with different ply orientations have been investigated. We found that the unidirectional (UD) lamina has higher conductivity along the carbon fiber direction than the perpendicular direction, and equipotential contours also show different gradients along the two directions. The cross-ply (CP) and quasi-isotropic (QI) laminates have the mixed effects of the UD lamina electric conductivity and ply orientations, while the surface potential distributions mostly depend on the surface lamina direction. The conductivity along the thickness direction depends on each lamina and inter-laminar bonding. A finite element analysis model was also developed to show the effect of ply orientation on potential distribution. The CP and QI laminates with 0° surface ply have uniform potential distributions and isotropic electricity behaviors. The results could be used to monitor damage locations and design electric composite materials.

Synthesis of multi-functional substrate integrated tensor metasurfaces

Metasurfaces are emerging techniques to manipulate electromagnetic (EM) wave propagations. Metasurfaces are usually composed of subwavelength periodic unit cells in order to achieve effective surface electric and magnetic impedances. Conventionally, non-planar structures, e.g. metallic loops, are used to realize the required surface impedances, which are difficult to fabricate at high frequencies. In this work, we propose a metasurface synthesis method using only planar electric impedance surfaces, which are not only easy to fabricate even at very high frequencies, but also have great freedom to control EM wave propagations. Without loss of generality, the proposed method has taken into account the tensor form of the constituent planar electric surface impedance, the dielectric substrate effect as well as arbitrary incident angles. The proposed method is general so as to have a wide application scope, and is efficient so as to simplify the design procedure. It has been validated by numerical simulations, and has been applied to design two multi-functional metasurface devices as an demonstration.

Zeta potential of CO2-rich aqueous solutions in contact with intact sandstone sample at temperatures of 23 °C and 40 °C and pressures up to 10.0 MPa

Despite the broad range of interest and applications, controls on the electric surface charge and the zeta potential of silica in contact with aqueous solutions saturated with dissolved CO2 at conditions relevant to natural systems, remains unreported. There have been no published zeta potential measurements conducted in such systems at equilibrium, hence the effect of composition, pH, temperature and pressure remains unknown.We describe a novel methodology developed for the streaming potential measurements under these conditions, and report zeta potential values for the first time obtained with Fontainebleau sandstone core sample saturated with carbonated NaCl, Na2SO4, CaCl2 and MgCl2 solutions under equilibrium conditions at pressures up to 10 MPa and temperatures up to 40 °C.The results demonstrate that pH of solutions is the only control on the zeta potential, while temperature, CO2 pressure and salt type affect pH values. We report three empirical relationships that describe the pH dependence of the zeta potential for: i) dead (partial CO2 pressure of 10-3.44 atm) NaCl/Na2SO4, ii) dead CaCl2/MgCl2 solutions, and iii) for all live (fully saturated with dissolved CO2) solutions. The proposed new relationships provide essential insights into interfacial electrochemical properties of silica-water systems at conditions relevant to CO2 geological storage.

Simultaneous Manipulation of Electric and Magnetic Surface Waves by Topological Hyperbolic Metasurfaces

Simultaneous Manipulation of Electric and Magnetic Surface Waves by Topological Hyperbolic Metasurfaces

High-confinement ultra-wideband bandpass filter using compact folded slotline spoof surface plasmon polaritons

A novel bandpass filter (BPF) based on spoof surface plasmon polaritons (SSPPs) using a compact folded slotline structure is proposed and experimentally demonstrated. The proposed novel SSPPs structure compared with a conventional plasmonic waveguide with slot line SSPPs unit structure at the same size, the considerable advantages in much lower asymptotic frequency with tight field confinement, which enable the proposed filter to be more miniaturization. A high-efficient mode conversion structure is designed to transition from TE-mode to SSPPs-mode by gradient slotline lengths. The low-frequency stop-band can be committed with microstrip to slotline evolution on both sides of the dielectric, while the high-frequency cutoff band is realized by the proposed SSPPs structure. The influence of dispersion relation, electric field distribution, surface current, and structural parameters on the transmission characteristics of the proposed BPF are analyzed by finite difference time domain (FDTD). To validate the design concept, the prototype of the miniaturized SSPPs BPF has been manufactured and measured. The experimental results show high performance of the fabricated sample, in which the working in a range of 0.9 GHz–5.2 GHz with the relative bandwidth is 142%, the insertion loss less than 0.5 dB, the reflection coefficient less than −10 dB, and the group delay is less than one ns. This works provides a mirror for realizing the miniaturization of waveguides, and the application and development of high-confinement SSPPs functional devices in the microwave and THz regimes.

ЭКСПЕРИМЕНТАЛЬНЫЙ ПОДБОР РЕЖИМОВ ЭЛЕКТРОИСКРОВОЙ ОБРАБОТКИ ДЛЯ ЭЛЕКТРОДОВ, ПОЛУЧЕННЫХ РАЗЛИЧНЫМИ МЕТОДАМИ

Electric spark surface treatment is widely used in repair production. Its high versatility is ensured by a wide range of electrical modes and the possibility of using all conductive materials as electrodes. The selection of optimal electrical modes of the electric spark processing installation is important for obtaining high-quality coatings when using a specific electrode. This problem is especially acute for new electrode materials obtained from machine-building waste, since such electrodes are still poorly studied. (Research purpose) The research purpose is in experimentally selecting optimal modes of electric spark processing of steel parts for each of the electrodes under consideration for using the obtained data in further research. (Materials and methods) The article presents electrodes made of bronze grade BrAZh9-4 according to GOST 18175-78 and from secondary bronze powder. The coatings were applied using the Vestron AI-007 electric spark treatment unit on steel samples. The analytical scales Acculab ALC-210d4 and the micrometer MG H25 GOST 6507-90 were used. (Results and discussion) All coatings were applied to samples with an equal area in three layers under different processing modes. The increase in the thickness and mass of the electrode material on the sample surface was measured. The article presents formulas and graphs based on the results of the work. (Conclusions) For each electrode, the optimal mode of electric spark processing was chosen, which would further help to compare the electrodes by the quality of the coating formed. The performance characteristics of sintered secondary bronze powder, almost similar to the characteristics of standard materials, prove the feasibility of obtaining such powders by the energy-efficient method described above.

Dynamically switchable dual-band absorber based on electromagnetically induced reflection in metal-graphene hybrid metamaterial

In this paper, a dynamically switchable dual-band absorber based on electromagnetically induced reflection (EIR) in metal-graphene hybrid metamaterial is proposed. The unit cell of metamaterial absorber has three layers. The top layer consists of two split-ring resonators (SRRs) and two orthogonal cut-wires (CWs) with different lengths. Due to the low reflection dips in EIR structure and good absorption of graphene, two absorption bands accompanied with more than 90% absorptions are obtained under y-polarized and x-polarized incident waves, respectively. The power loss densities at the absorption points clearly reveal the absorption positions of the metamaterial absorber. In addition, the electric field, magnetic field and surface current distributions explain the reason of high absorption. According to the surface currents at four resonant points, we draw the schematic diagrams of multipole moments, which are confirmed by multipole scattering theory. The tunable absorption performance of metamaterial absorber can be observed by tuning the Fermi level of graphene. The metamaterial absorber exhibits excellent wide polarization angle behavior and shows great prospects in multi-band metamaterial absorber under oblique incidence. The proposed metamaterial absorber expands the development of metamaterial and shows great potential for multifunctional metamaterial absorber.

Analysis of laser radiation performance of fingerprint-texture cholesteric liquid crystal device

Low-cost tunable lasers have broad application prospects in optoelectronics. In this paper, a laser device based on fingerprint-textured cholesteric liquid crystal (CLC) was designed and fabricated, in which a narrow linewidth single-mode laser output on the side of the device was realized. The planar helical structure of the “fingerprint-texture” of CLC was obtained by the combined effect of externally applied electric field and substrate surface anchoring. Under the pumping light of a Nd:YAG solid-state pulsed second harmonic laser with the wavelength of 532 nm, the lasing emission wavelength of our CLC device changes non-monotonically with gradually increasing electric field, which first shifting from 568.5 nm to 609.2 nm and then shifting from 609.2 nm to 586.2 nm. And the observed spectral tuning of the lasing emission was reproducible and reversible. The analysis shows that the output laser radiation was the result of the Bragg reflection feedback provided by the fingerprint-texture.

Light focusing in linear arranged symmetric nanoparticle trimer on metal film system

Benefiting from the induced image charge on film surface, the nanoparticle aggregating on metal exhibits interesting optical properties. In this work, a linear metal nanoparticle trimer on metal film system has been investigated to explore the novel optical phenomenon. Both the electric field and surface charge distributions demonstrate the light is focused on film greatly by the nanoparticles at two sides, which could be strongly modulated by the wavelength of incident light. And the influence of nanoparticle in middle on this light focusing ability has also been studied here, which is explained by the plasmon hybridization theory. Our finding about light focusing in nanoparticle aggregating on metal film not only enlarges the novel phenomenon of surface plasmon but also has great application prospect in the field of surface-enhanced spectra, surface catalysis, solar cells, water splitting, etc.

Surface Phonon Polariton Modes in Suspended Monolayer Hexagonal Boron Nitrides

Dispersion properties and characteristics of transverse magnetic (TM) and transverse electric (TE) surface phonon polaritons (SPhP) in suspended monolayer hexagonal boron nitrides (hBN) was studied extensively. The analytical results show that the hBN based TM (TE) phonon polaritons exist in restsrahlen bands when imaginary surface conductivity is positive. The effective mode index of TM phonon polaritons is much higher than that of TE phonon polaritons with respective values of ~3000 and ~1.0002 which makes TM SPhP more promising in the practical realization. In addition, the propagation length of TE SPhP is less lossy and surpass that of TM SPhP by factor of 104. This study compares these important properties and sheds more insight into their applications in optical communications, photonics and optoelectronics devices.

Analysis of discharge channel characteristics based on three-phase flow dielectric characteristics in USV-MF assisted WEDM-LS

In this paper, considering the effects of the characteristics of the three-phase flow dielectric in the discharge gap flow field on the discharge channels in the ultrasonic vibration and magnetic field assisted low speed WEDM (USV-MF assisted WEDM-LS), the model of discharge channel including discharge position and size of discharge channel is established. Firstly, a mechanism of bubble-particle bridging breakdown was proposed under working condition of cutting workpieces with large thickness. Then a prediction model of the discharge point position in USV-MF assisted WEDM-LS under three-phase flow dielectric characteristics based on the breakdown mechanism was performed, and FEM software COMSOL was used to simulate and analyze this model. By comparing with the experimental results of discharge point position captured by high-speed camera, the accuracy of the prediction results of discharge point position in USV-MF assisted WEDM-LS was verified, it showed that the model can explain the dielectric breakdown more accurately. Next, the model of radius of discharge channel including magnetic field intensity, electric field intensity, medium pressure, and surface tension of discharge channel was established, and the influence of USV and MF on the size of discharge channel was analyzed theoretically. The radius of discharge channel in USV-MF assisted WEDM-LS was obtained by solving the partial differential equation in MATLAB. According to discharge point position and radius of the plasma discharge channel, surface morphology of workpiece was simulated by COMSOL. Finally, the experiment of photographing the discharge channel in USV-MF assisted WEDM-LS was carried out to verify the above model. It showed that the trend of the simulated results of discharge channel position is the same as that of the experimental results, and the error of peak height value between simulated and experimental results is within 6%.

Numerical Studies on Electrostatic Interaction Forces and the Free Energy between Parallel Colloidal Rods of Finite Size in Skewed Configurations.

Formulas for interaction forces F(s) and the free energy G(s) between two parallel charged prismatic rods of various scaled values of d, ψs, and L in skewed configurations are obtained, where s is the lengthwise positional difference between the front-end faces of the respective rods, and d is the minimal distance between the opposing faces of the rods, ψs is the electric surface potential, L is the length of the rods. To obtain the free-energy function G(s), (i) 3D spatial distributions of the electric potential ψ around two rods were determined by numerically solving the nonlinear Poisson-Boltzmann equation with a finite element method, (ii) with the ψ distributions so determined, the lengthwise interaction electrostatic Maxwell stress tangential to the midplane between the rods was calculated to obtain the (discrete) s dependence of the stress, and (iii) by introducing two different fitting functions, the discrete s dependence was transformed into a continuous force function, F(s), which was then lengthwise integrated to derive G(s). It was found that the curves of G(s) linearly decreased with increasing s between 1 and L + 1 due to a localization of the stress. Although natural, it is of interest that the values of G(0) calculated for rods of various values of d, ψs, and L were in good agreement with those of the interaction free energy obtained in our preceding work by the widthwise integration of repulsive electrostatic forces normal to the midplane between the parallel rods in nonskewed configurations.

Design and Analysis of a Triple-band Non-zonal Polarization Electromagnetic Metamaterial Absorber

A facile design of a novel triple-band electromagnetic metamaterial absorber (MMA) with polarization insensitive property is proposed in this paper. Each unit of the MMA consists of upper copper resonator and bottom copper plate with middle dielectric FR-4 between them. The MMA performs three absorption peaks at 16.919 GHz, 21.084 GHz and 25.266 GHz with absorption rates 99.90%, 97.76% and 99.18%, respectively. The influence of the main structural parameters on the frequencies and absorption rates is analyzed. The absorption mechanism of the absorber is explained by electric field, magnetic field and surface current distributions, which is supported by the electromagnetic parameters, affected with magnetic resonance. The polarization-insensitivity of TE wave is verified by observing the effects of the polarization angle change from 0-90º. The MMA can be applied in radiation, spectrum imaging detector, electromagnetic wave modulator, and so on.

X-band RF photoinjector design for the CompactLight project

RF photoinjectors have been under development for several decades to provide the high-brightness electron beams required for X-ray Free Electron Lasers. This paper proposes a photoinjector design that meets the Horizon 2020 CompactLight design study requirements. It consists of a 5.6-cell, X-band (12 GHz) RF gun, an emittance-compensating solenoid and two X-band traveling-wave structures that accelerate the beam out of the space-charge-dominated regime. The RF gun is intended to operate with a cathode gradient of 200 MV/m, and the TW structures at a gradient of 65 MV/m. The shape of the gun cavity cells was optimized to reduce the peak electric surface field. An assessment of the gun RF breakdown likelihood is presented as is a multipacting analysis for the gun coaxial coupler. RF pulse heating on the gun inner surfaces is also evaluated and beam dynamics simulations of the 100MeV photoinjector are summarized.

Invisibility Utilizing Huygens’ Metasurface Based on Mantle Cloak and Scattering Suppression Phenomen

This communication presents the design of a Huygens' metasurface (HMS) coating aiming to achieve strongly enhanced invisibility. An analytical formulation for obtaining the required electric surface admittance and magnetic surface impedance is presented. The proposed unit cell consists of a pair of split-rin resonators in the top layer and a metal capacitor in the bottom layer of the same substrate. The geometries are properly designed to provide the required electric surface admittance and magnetic surface impedance for maximum scattering reduction at the operational frequency of 4 GHz. The designed HMS is optimized to realize the required electric surface admittance and magnetic surface impedance for remarkable cloaking purposes. Scattering-cross section (SCS) of uncloaked and cloaked conducting cylinders is obtained with CST Microwave Studio simulation which matches the analytical results. The results show robust scattering reduction with considerable bandwidth for the covered cylinder by the HMS. Furthermore, the obtained results with HMS are compared with the results presented in the literature for cloaking with ordinary metasurface. This comparison emphasizes a much better cloaking performance of the HMS. Considerable cloaking obtained in this communication can be applied for invisibility purposes, sensing applications, antenna isolation, radiation blockage reduction in antennas, etc.

Multi-controlled broadband terahertz absorber engineered with VO2-integrated borophene metamaterials

We demonstrated a dynamically controlled broadband terahertz (THz) metamaterials absorber, which composed of continuous vanadium dioxide (VO2) film, a silicon dioxide (SiO2) layer, and a structured borophene layer. When VO2 is in its metallic state and the armchair direction of borophene along x axis, the proposed absorber realizes an absorptivity peak value of 100% at 7.2 THz for y polarized normal incidence, and an absorptivity peak value of 79% at 8.9 THz for x polarized normal incidence. It is the anisotropic property of borophene that results in the absorptivity difference for x and y polarization in the whole frequency range. Simulated electric field distribution and surface current oscillation has been extracted to explain the physical mechanism of THz wave absorption. Through modifying the geometric parameters of metamaterials microstructure, the broadband absorption performance can be tailored passively. Additionally, the proposed metamaterials absorber has been actively controlled by manipulating the carrier density of borophene and the conductivity of VO2, respectively. The absorptivity can be switched from 45% to 100% at 7.2 THz by changing the carrier density of borophene, and from 22% to 100% at 7.2 THz by changing the conductivity of VO2. Moreover, the proposed absorber exhibits an excellent operation tolerance for oblique TE and TE polarized incidence from 0° to 60°. This work provides a novel approach to design dynamically controlled broadband THz absorbers, which reveals promising applications in the devices of optoelectronic switches, cloakings, filters, and sensors, etc.

Microscopic Volta potential difference on metallic surface promotes the osteogenic differentiation and proliferation of human mesenchymal stem cells

Endogenous microscopic electric cues play an essential role in bone's remodeling and self-repair. Modulating the extracellular electrical environment, by means of external electric stimulation or changing surface potential of implants, was manifested to facilitate the osteointegration. The microscopic potential difference, originating from heterogeneous microstructures of materials, may mimic the endogenous electric signals to stimulate surrounding cells. In this study, the spark-plasma sintered Ti/Ta hybrid metal was fabricated and utilized to realize a surface microscopic potential difference at the same magnitude as endogenous potentials. Activated by the electric stimulation, the mesenchymal stem cells exhibited the anisotropic and polygonal cellular morphology on the Ti/Ta hybrid metal. The microscopic electric potential difference coordinated the cells proliferation on the subsequent days. Moreover, the results showed that the osteo-lineage differentiation on Ti/Ta hybrid metal were in vitro boosted over the control groups. Tailoring microstructures of material to obtain a reasonable electric microenvironment may be a necessary principle to achieve more favorable cell responses to implants, suggesting an extra degree of freedom in bone-repairing material design.

Near-to-Far Field Transformation in FDTD: A Comparative Study of Different Interpolation Approaches

Equivalence theorems in electromagnetic field theory stipulate that farfield radiation pattern/scattering profile of a source/scatterer can be evaluated from fictitious electric and magnetic surface currents on an equivalent imaginary surface enclosing the source/scatterer. These surface currents are in turn calculated from tangential (to the equivalent surface) magnetic and electric fields, respectively. However, due to the staggered-in-space placement of electric and magnetic fields in FDTD Yee cell, selection of a single equivalent surface harboring both tangential electric and magnetic fields is not feasible. The work-around is to select a closed surface with tangential electric (or magnetic) fields and interpolate the neighboring magnetic (or electric) fields to bring approximate magnetic (or electric) fields onto the same surface. Interpolation schemes available in the literature include averaging, geometric mean and the mixed-surface approach. In this work, we compare FDTD farfield scattering profiles of a dielectric cube calculated from surface currents that are obtained using various interpolation techniques. The results are benchmarked with those obtained from integral equation solvers available in the commercial packages FEKO and HFSS.

Electromechanical coupling mechanisms at a plasma–liquid interface

The direct interaction between a non-equilibrium gas discharge and a liquid volume leads to the generation of a plasma activated liquid. This interaction induces a flow in both the gas above the liquid and within the liquid volume. The physical mechanisms behind the induced flows are complex. In this work, a two-dimensional experimentally validated numerical model was developed to determine the dominant mechanism driving the liquid flow at the plasma–liquid interface. The model followed the evolution of the plasma and the flow fields in both phases, describing a pin-water discharge configuration operating in air, which was used to treat a de-ionized water sample and a tap water sample. Two potential physical mechanism were investigated, the electrohydrodynamic (EHD) flow induced in the gas phase and the electric surface stresses across the interface. It was found that the dominant mechanism driving the liquid flow is correlated with the charge relaxation time of the liquid. For liquids with a charge relaxation time longer than the characteristic time of the plasma, such as de-ionized water, the liquid behaves as a dielectric, and the electric surface stresses dominate the flow in the liquid phase. For liquids with a charge relaxation time shorter or in the same order of the plasma’s characteristic time, such as tap water, the liquid behaves as a conductor, and the EHD flow induced in the gas phase dominates the flow in the liquid phase.