Surface Conductivity Model Research Articles

Collaborative Optimization of Conductivity and Permittivity on GIL Spacer Surface for Electric Field Regulation Under DC Superimposed Impulse Voltages

The gas-solid interface electric field distortion is an essential factor leading to surface insulation failure. This study proposes the conductivity and permittivity-graded coating layer (ε/γ-layer) method, aiming at regulating surface charge and electric field distribution on GIL spacers under DC/ DC superimposed impulse voltages. The iteration optimization algorithm is developed to obtain the optimal conductivity and permittivity distribution of the ε/γ-layer. The surface charge and electric field behavior on GIL spacers with the ε/γ-layer are investigated through the numerical simulation approach. The polarity of the accumulated surface charges reverses on both the convex and concave sides as the conductivity of the ε/γ-layer increases under DC voltages, indicating the dominant mechanism changing from the bulk conductivity model to the surface conductivity model. The electric field distribution is also improved with the ε/γ-layer at the optimal permittivity and conductivity distribution. Compared with the raw spacer, the maximum electric field strength with ε/γ-layer is reduced by about 31.97% under DC, 20.56% under DC superimposed positive impulse (DC+Po.Im), 42.68% under DC superimposed negative impulse (DC+Ne.Im) on the convex surface, about 64.22% under DC, 21.37% under DC+Po.Im, 36.46% under DC+Ne.Im on the concave surface, correspondingly. It is hoped that the results of this study could spark off novel ideas for the optimal design of DC GIL spacers.

Numerical analysis of optical phase modulator operating at 2 μm wavelength using graphene/III–V hybrid metal-oxide-semiconductor capacitor

We propose an optical phase modulator with a hybrid metal-oxide-semiconductor (MOS) capacitor, consisting of single-layer graphene and III–V semiconductor waveguide. The proposed modulator is numerically analyzed in conjunction with the surface conductivity model of graphene. Since the absorption of graphene at a 2 μm wavelength can be suppressed by modulating the chemical potential of graphene with the practical gate bias, the phase modulation efficiency is predicted to be 0.051 V·cm with a total insertion loss of 0.85 dB when an n-InGaAs waveguide is used, showing the feasibility of the low-loss, high-efficiency graphene/III–V hybrid MOS optical phase modulator, which is useful in the future 2 μm optical fiber communication band.

Finite element method based modelling and analysis of serpentine electrodes for biochemical sensing

This paper discusses the finite element method (FEM) based performance analysis of serpentine electrodes (SREs) and interdigitated electrodes (IDEs) used for biochemical sensing applications. The SREs and IDEs structures were modelled for comparison with 20 µm (width, gap), length of 1 mm and 20 electrode pairs. The modelled SREs structure was analyzed with three diverse meshing techniques such as normal, fine, and adaptive mesh refinement (AMR). The skewness of 0.83 was found for AMR as against 0.64 and 0.57 of fine and normal mesh, respectively. Further, the electrical parameters such as signal strength, penetration depth, and electric field strength were considered to evaluate the performance of SREs and IDEs. Through simulation results, the signal strength of 4.92 pF was obtained for SREs as against 2.98 pF of IDEs. The penetration depth of 53.3 µm above electrode surface for SREs as against 26.7 µm of IDEs was obtained. Additionally, the FEM simulations were conducted for various substrate materials such as glass, FR4, Kapton® HN, and PET. Finally, a surface conductivity model in COMSOL® multiphysics was used to see the response from SREs and IDEs for varying conductivity between 0.0041 mS/cm to 12.9102 mS/cm. From simulation results, a decrease in impedance with increase in conductivity was observed validating the sensing mechanism. Moreover, a higher percentage change in impedance response was found for SREs as against IDEs for the same conductivity. Hence, this work demonstrates the importance of meshing while modelling complex electrode structures such as SREs. All the performance indicators suggest the usefulness of SREs over IDEs for biochemical analysis.

Do We Need "Ionosorbed" Oxygen Species? (Or, "A Surface Conductivity Model of Gas Sensitivity in Metal Oxides Based on Variable Surface Oxygen Vacancy Concentration").

The author provides an opinion on direct experimental evidence available to support the "ionosorption theory" often employed to interpret "electrophysical" measurements made during a gas sensing experiment. This article then aims to provide an alternative framework of a "surface conductivity" model based on recent advances in theoretical and experimental investigations in solid state physics, and to use this framework as a guide toward design rules for future improvement of gas sensor performance.

Surface charge behavior and flashover performance on epoxy-based spacers by graded conductivity coatings subjected to DC voltages

Surface charge accumulation subjected to direct current (DC) voltages poses hazardous effects on the surface insulation performance of the involved insulators. It is of great significance to investigate surface charge regulation methods applicable to industrialized spacers. In this study, we propose a graded conductivity coating method, with excellent adhesion strength consisting of TiO2/epoxy composites with different TiO2 contents, realizing a gradually decreased conductivity distribution on the spacer surface from high voltage (HV) to grounded (GND) electrodes. Surface charging behavior and flashover performance under DC voltages on this kind of spacer is obtained. A simulation model for surface charge computation is constructed for the sake of better understanding the surface charging mechanism on spacers with graded conductivity coating. The results indicate that the randomly distributed surface charges are obviously suppressed by this coating manner and the ring-shaped homo-charges adjacent to HV and GND electrode dominate surface charge patterns. The main cause lies in the fact that surface charge dominant mechanism changes from the bulk conductivity model to the surface conductivity model, where surface leakage current becomes the primary sources of surface charges, with the increase in coating conductivity. DC flashover performance is enhanced as well due to the improvement of surface charge accumulation and electric field distribution. This study supplies an important reference for designing DC gas insulated transmission line spacers of high reliability as well as inspires novel ideas in surface charge regulation.

A canopy conductance model with temporal physiological and environmental factors

Canopy conductance, one of the key variables in simulating evapotranspiration, is strongly influenced by the physiological status of a plant and environmental factors, including photosynthetically active radiation, vapor pressure deficit, air temperature, soil moisture and so on. However, the restrictive functions used to represent these factors rarely consider the dynamics of physiological and environmental factors. This study proposed an improved canopy conductance model by regarding radiation and vapor pressure deficit as the two main influencing factors, quantifying the temporal variation in stomatal responses to radiation that notably adjust stomatal behavior, parameterizing maximum stomatal conductance with plant type-specific functions and proposing a new restrictive function for the VPD. The improved canopy conductance model was incorporated in a surface conductance model for estimating surface conductance and evapotranspiration at 8 flux stations at the Heihe River Basin and the Haihe River Basin. The estimated results were the most accurate when comparing to two other models. Furthermore, the model performance was acceptable when most of the parameters were assumed to be constant across the sites except the reference canopy conductance Gc, ref and the soil evaporation parameter αs, which suggests that the improved canopy conductance model could be used as a parsimony model for improving canopy conductance predictions and water use efficiency over typical climate zones and underlying surface types in North of China.

Investigation of the effect of metallization ratio and side shift on the interdigitated electrodes performance for biochemical sensing

This paper investigates the effect of metallization ratio and side shift on the performance of interdigitated electrodes (IDEs). The IDEs were modelled using normal mesh and adaptive mesh refinement techniques to investigate the modelling error. The performance parameters such as electric field distribution, crosstalk and penetration depth of IDEs and the phenomenon of impedance biosensor based on surface conductivity model was simulated using COMSOL Multiphysics software. A detailed analysis was carried out to see the effect of metallization ratio on these performance parameters. In the simulation, the metallization ratio of IDEs was varied between 0.2–0.9, and the variation in side shift was 1–50 µm. A significant reduction in modelling error was obtained for adaptive mesh refinement (AMR) based IDEs model. The IDEs with metallization ratio 0.7 and side shift between 10–20 µm have shown higher measurement sensitivity. For validation of simulation results, experiments were conducted on fabricated IDEs with different metallization ratios. IDEs with metallization ratios 0.3, 0.5 and 0.7 were fabricated using PCB technology. The impedance spectra were obtained for a 10–100 mM KCl solution using electrochemical impedance spectroscopy (EIS). Through simulation and from experimental results, higher measurement sensitivity from IDEs was obtained at 0.7 metallization ratio. Finally, this paper demonstrates the importance of metallization ratio and side shift to ensure higher measurement sensitivity from IDEs when used for biochemical sensing applications.

A dual-carrier adsorbate-modulated surface conductance model better captures the thermal dependence of conductance in TiO2 and MoO3 powders than an inter-grain hopping model

Non-Arrhenius thermal dependence of surface conductance has previously been observed in the transition-metal oxides TiO2 and MoO3. Through the application of thermochemical modeling, kinetic modeling, and analysis of equivalent resistance networks, it is shown that a dual-charge-carrier model in which the adsorbate surface coverage is modulated by bi-Langmuir adsorption is better able to capture the thermal dependence of surface conductance in these materials than a model based on the hypothesis that conductance is governed by bottlenecks to charge hopping between grains. Adsorption energies predicted by the dual-charge-carrier model are in agreement with estimates of the same from published first-principles calculations. Particle-size dependence of the conductance likely arises from the increasing importance of surface processes to charge transport with decreasing particle size, not from an increase in the number of inter-particle contacts.

Tunable THz Graphene Filter Based on Cross-In-Square-Shaped Resonators Metasurface

The tunable terahertz (THz) Fano-resonant filter based on hybrid metal-graphene metamaterial was proposed. The optical parameters of metasurface with unit cell in the form of a cross-shaped graphene sheet in the center of a square gold ring were simulated by the finite element method using a surface conductivity model of a graphene monolayer. The narrowband modulation of the transmission by varying the Fermi level of the graphene and the position of graphene cross inside the metal ring was demonstrated. Simulation results were well explained theoretically using a three-coupled oscillator model. The proposed device can be used as a narrowband filter in wireless THz communication systems and sensing applications.

A simple model of ac hopping surface conductivity in ionic liquids

The boundary conditions proposed to discuss the charge exchange taking place in an ionic liquid in contact with non-blocking electrodes are reconsidered in a dynamic situation. Assuming that the variation of the bulk ionic current density depends linearly on the surface value of the ionic current density, the frequency dependence of the phenomenological parameter is determined. The analysis has been performed in the framework where the relaxation times are smaller than a maximum relaxation time τM, and that the response function is independent on the value of the relaxation time. Using simple physical considerations, an expression for the surface conductivity describing the ionic charge exchange at the electrode is obtained. According to our calculations, its frequency dependence is similar to that predicted for the electric conductivity in disordered materials when the mechanism is of the hopping type. From measurements of impedance spectroscopy, by the best fit of the experimental data, the temperature dependence of the hopping time, of the dc surface conductivity, and of the diffusion coefficient are derived. They are in good agreement with the theoretical predictions obtained with the random distribution of surface energy barrier.

Comparative research on two surface conductivity models for the scattering of electromagnetic wave by the charged sphere

The surface conductivity model plays an important role in solving the electromagnetic scattering of microwave by the charged particle. We compared two models that can be used in the scattering of electromagnetic wave by the charged spherical particle. The results show that the extinction efficiency and the scattering efficiency calculated through these two models are much different in some cases, and which also affect by the particle size, refractive index, and its charged quantity. However, when the size parameter of particle is larger enough, the results from these two models became consistent with each other.

Validating GIC Models With Measurements in Austria: Evaluation of Accuracy and Sensitivity to Input Parameters

AbstractSpace weather events can cause geomagnetically induced currents (GICs) in power transmission networks. Over the past years, these currents have been measured in multiple substations in Austria, and the measurements have been tested against a model of local GIC with the aim of producing an optimized model, which can be developed through evaluation of various input parameters. We show the impact the choice of the local resistivity, in particular the surface conductivity in thin‐sheet modeling, and the source of geomagnetic variations has on GIC modeling. In addition, the sensitivity of the model to the accuracy of the network configuration is also investigated. This encompasses the inclusion of power grids outside of Austria in the model as well as the consequences of removal of a substation either through transformer failure or active disconnection. Results show that a detailed surface conductivity model brings benefits to areas with large lateral conductivity variations and that there are certain substations that lead to increases and decreases of GIC in the rest of the network when removed. The importance of regionally representative geomagnetic field measurements is also highlighted and shown to impact model accuracy. This study concentrates on regional effects, but the results are also valid for large‐scale studies elsewhere.

Regional Daily ET Estimates Based on the Gap-Filling Method of Surface Conductance

Remote sensing allows regional evapotranspiration (ET) values to be obtained. Surface conductance is a key variable in estimating ET and controls surface flux interactions between the underlying surface and atmosphere. Limited by the influence of clouds, ET can only be estimated on cloud-free days. In this study, a gap-filling method is proposed to acquire daily surface conductance, which was coupled into a Penman-Monteith (P-M) equation, to estimate the regional daily ET over the Hai River Basin. The gap-filling method is coupled with the canopy conductance, surface conductance and a simple time extension method, which provides more mechanisms and is more comprehensive. Field observations, including eddy covariance (EC) fluxes and meteorological elements from automatic weather station (AWS), were collected from two sites for calibration and validation. One site is located in Guantao County, which is cropped in a circular pattern with winter wheat and summer maize. The other site is located in Miyun County, which has orchard and summer maize crops. The P-M equation was inverted to the computed surface conductance at the field scale, and latent heat fluxes from EC were processed and converted to daily ET. The results show that the surface conductance model used in the gap-filling method performs well compared with the inverted surface conductance, which suggests that the model used here is reasonable. In addition, the relationship between the results estimated from the gap-filling method and EC measurements is more pronounced than that between the other method and the EC measurements. The R 2 values improve from 0.68 to 0.75 at the Guantao site and from 0.79 to 0.88 at the Miyun site. The improvement mainly occurs during the growing crop season, according to the temporal variations in the results.

Terahertz band communication using plasma wave propagation in multilayer graphene heterostructures

Graphene-based heterostructures provide a viable platform to implement optoelectronic devices that can operate in the terahertz (THz) band. In this study, the authors focus on multilayer (ML) graphene as the building block to implement high-frequency and low-energy plasmonic interconnects for on-chip signalling in next-generation systems. Two specific plasmonic interconnect geometries are analysed: single waveguide (SWG) and parallel-plate waveguide (PPWG). While SWG interconnects support propagating surface plasmons that are polarised in the transverse magnetic direction, in PPWG interconnects, nearly dispersion-less quasi-transverse electromagnetic modes are supported. The dispersion characteristics are derived by solving Maxwell's equations in the device setup in which ML graphene presents an impedance boundary condition. The effects of number of layers, electrostatic screening, and Fermi level are included in the model of intra-band dynamical surface conductivity of ML graphene. The authors also develop analytical models of energy-per-bit and bandwidth density for both SWG and PPWG interconnects. The energy dissipation includes the effect of plasmon generation, detection, and modulation circuitry within a thermal- and shot-noise-limited transmission of information. They quantify optimal interconnect length scales for which plasmonic interconnects provide lower energy and higher bandwidth when compared against their electrical (copper/low- κ ) counterparts at the 2020 ITRS technology node.

基于石墨烯的光学控制窄带太赫兹开关

This paper proposes an optically controlled terahertz switcher based on cross-shaped metal resonators metasurface covered by monolayer graphene. The spectral characteristics of proposed composite structure were calculated using the surface conductivity model of graphene and the finite element method. The modeling demonstrated the appearance of a narrowband resonant dip in the transmission spectrum with a modulation depth of 36.8% and a Q-factor of 250 after the optical pump intensity achieving to 0.2 W/mm2. In addition, the modulation depth of such a dip can be slightly tuned by varying value of the pump intensity. Thus, the design of the optically tunable terahertz switcher may contribute to the development of functional components for terahertz communication applications.

Characterization of a porous transducer using a capillary bundle model: Permeability and streaming potential prediction

A capillary bundle model is used to evaluate the permeability and streaming potential coupling coefficient of a porous transducer, which is the key element of a fluid-based angular accelerometer. The capillary bundle is specified with structural parameters and a method to transform the particle size distribution into the capillary radius distribution. Together with a theoretical model of zeta potential and specific surface conductance, the model is applied to determine permeability and streaming potential prediction. Three types of transducers are fabricated and experiments validate the proposed model, which is an important part of the sensor model for engineering application.

Dielectric Constant Estimation of a Carbon Nanotube Layer on the Dielectric Rod Waveguide at Millimeter Wavelengths

A method has been developed to estimate dielectric properties of a layer containing carbon nanotubes (CNTs) randomly arranged in plane, deposited on a dielectric rod waveguide (DRW). In the framework of this method, a theoretical model of a layered DRW with extended narrow walls and perfect electric conductor walls was used to fit the experimental results. The experimental results were obtained by measuring the wave propagation characteristics ( S11 and S21) of a DRW unloaded and loaded with different CNT layers at 75-110 GHz. The developed model allows derivation of the dispersion equation of the wave excited in the loaded DRW in an analytical form. The propagation constant is then found numerically through the fitting process with measurement results. Additionally, the complex permittivity of the CNT layer can be estimated using the surface conductivity model of the CNT and mixing formulas. Both methods give reasonable and comparable results. The obtained results (ε = 1- j5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) allow full-wave simulation (e.g., HFSS) of DRW structures loaded with CNT layers with a thickness of 60 nm or more. Simulation and measurement results agree rather well.

Compilation of 3D global conductivity model of the Earth for space weather applications

We have compiled a global three-dimensional (3D) conductivity model of the Earth with an ultimate goal to be used for realistic simulation of geomagnetically induced currents (GIC), posing a potential threat to man-made electric systems. Bearing in mind the intrinsic frequency range of the most intense disturbances (magnetospheric substorms) with typical periods ranging from a few minutes to a few hours, the compiled 3D model represents the structure in depth range of 0–100 km, including seawater, sediments, earth crust, and partly the lithosphere/asthenosphere. More explicitly, the model consists of a series of spherical layers, whose vertical and lateral boundaries are established based on available data. To compile a model, global maps of bathymetry, sediment thickness, and upper and lower crust thicknesses as well as lithosphere thickness are utilized. All maps are re-interpolated on a common grid of 0.25×0.25 degree lateral spacing. Once the geometry of different structures is specified, each element of the structure is assigned either a certain conductivity value or conductivity versus depth distribution, according to available laboratory data and conversion laws. A numerical formalism developed for compilation of the model, allows for its further refinement by incorporation of regional 3D conductivity distributions inferred from the real electromagnetic data. So far we included into our model four regional conductivity models, available from recent publications, namely, surface conductance model of Russia, and 3D conductivity models of Fennoscandia, Australia, and northwest of the United States.

The electrophoretic mobility of montmorillonite. Zeta potential and surface conductivity effects

Clay minerals have remarkable adsorption properties because of their high specific surface area and surface charge density, which give rise to high electrochemical properties. These electrochemical properties cannot be directly measured, and models must be developed to estimate the electrostatic potential at the vicinity of clay mineral surfaces. In this context, an important model prediction is the zeta potential, which is thought to be representative of the electrostatic potential at the plane of shear. The zeta potential is usually deduced from electrophoretic measurements but for clay minerals, high surface conductivity decreases their mobility, thereby impeding straightforward interpretation of these measurements. By combining a surface complexation, conductivity and electrophoretic mobility model, we were able to reconcile zeta potential predictions with electrophoretic measurements on montmorillonite immersed in NaCl aqueous solutions. The electrochemical properties of the Stern and diffuse layers of the basal surfaces were computed by a triple-layer model. Computed zeta potentials have considerably higher amplitudes than measured zeta potentials calculated with the Smoluchowski equation. Our model successfully reproduced measured electrophoretic mobilities. This confirmed our assumptions that surface conductivity may be responsible for montmorillonite’s low electrophoretic mobility and that the zeta potential may be located at the beginning of the diffuse layer.

基于遥感和Penman-Monteith模型的内陆河流域不同生态系统蒸散发估算

The terrestrial water cycle is of critical importance to a wide array of earth systems. Evapotranspiration( ET) is an important component of the terrestrial water cycle,which controls the distribution of plant communities and the net primary production of ecosystems. Considerable efforts have been made by scientists to use remotely sensed data to estimate the spatial and temporal distribution of evaporation rates. Compared with other methods of estimation based on remotely sensed data,the Penman-Monteith equation has proven effective at both the point scale and the kilometer scale but the effectiveness of the surface conductance model in some specific areas such as arid regions still requires validation.Evaporation processes are complex in arid regions and the processes and patterns of ET under different vegetation types in arid regions are poorly researched. Therefore the Heihe River Basin was chosen as a study area because it is a typical arid area in China. The aim of this study was to evaluate the Penman-Monteith equation for estimating daily evaporation fluxes in arid regions using MODIS LAI data and meteorological data. A simple biophysical model using leaf area index( LAI) from remotely sensed data and the Penman-Monteith equation was used to calculate the daily ET of grassland and farmland at various sites in the middle and upper reaches of the Heihe River. The Penman-Monteith equation is a biophysically basedequation for calculating land surface evaporation and has been used extensively. The model for computing the surface conductance contains six parameters requiring local calibration. The shuffled complex evolution( SCE) algorithm was used to optimize the parameters in the surface conductance model for each site. The Nash-Sutcliffe efficiency( NSE) was selected as the optimized objective function. Optimal parameters in the surface conductance model were obtained by minimizing the cost function NSE with the SCE algorithm. Excellent agreement was obtained between the measured mean daily evaporation rates and those calculated using remotely sensed LAI data and the Penman-Monteith equation. The NSE at the A' rou( grassland) and Yingke( farmland) sites were 0.84 and 0.85,respectively and the root mean square error( RMSE) were1.25 and 1.66 MJ m-2d-1,respectively. With regard to grassland and farmland ecosystems in this study,the transpiration was much stronger than the soil evaporation during the growing seasons,however,the opposite situation was found during the non-growing seasons. From this study it can be concluded that the Penman-Monteith equation combined with LAI data can provide reliable estimates of ET at daily time scales in different ecosystems of arid and cold regions. However,there are still some uncertainties in ET estimations of the ecosystems in this study area,especially the cropland at the Yingke station.These biases are possibly because the model cannot simulate the impact of the extreme soil moisture changes caused by irrigation on ET. The soil evaporation factor is a constant in this study,whereas in reality it is a variable that depends on the moisture status of the soil near the surface. Thus,the effect of soil moisture variation on surface conductance was considered,and it improved the precision of the equation in the simulation of farmland ET.