Effect Of Surface Conductivity Research Articles

An Electrical Parameter Characterizing Solute Heterogeneity: The Mixing Factor M

AbstractQuantitative estimates of hydrological state variables using electrical or electromagnetic geophysical methods are systematically biased by overlooked heterogeneity below the spatial scale resolved by the method. We generalize the high‐salinity asymptotic limit of electrical conduction in porous media at the continuous (e.g., Darcy) scale, by introducing a new petrophysical parameter, the mixing factor M, which accounts for the effect of fluid conductivity heterogeneity on the equivalent electrical conductivity tensor; it is expressed in terms of the volume‐average of the product of mean‐removed fluid conductivity and electric fields. We investigate the behavior of M for static and evolving fluid conductivity scenarios. Considering 2‐D ergodic log‐normal random fields of fluid conductivity, we demonstrate, in absence of surface conductivity, that observing the components of the M‐tensor allows univocally determining the variance and anisotropy of the field. Further, time‐series of the M‐tensor under diffusion‐limited mixing allows distinguishing between different characteristic temporal scales of diffusion, which are directly related to the initial integral scales of the salinity field. Under advective‐diffusive transport and for a pulse injection, the time‐series of M have a strong dependence on the Péclet number. Since M is defined in the absence of surface conductivity, we investigate how to correct measurements for surface conductivity effects. The parameter M provides conceptual understanding about the impact of saline heterogeneity on electrical measurements. Further work will investigate how it can be incorporated into hydrogeophysical inverse formulations and interpretative frameworks.

New insights into how temperature affects the electrical conductivity of clay-free porous rocks

SUMMARY Geothermal energy is increasingly important for the global environment and for the sustainable development of our society. Electrical surveys are widely employed for the exploration of geothermal energy, because the electrical geophysical properties provide useful information about the fluids at depth. However, although quantitative interpretation of electrical survey data relies on the knowledge about the effects of temperature on the electrical properties of fluid-bearing rocks, it remains poorly understood about how temperature affects the electrical conductivity of clay-free porous rocks. We bridge this knowledge gap by measuring the electrical conductivity and porosity of five brine saturated clean Berea sandstones with temperature ranging between 25 and 140 °C, and analysing all the factors that impact the rock conductivity. We showed that the effects of surface conductivity on the temperature-dependent electrical conductivity can be negligible, whereas the temperature induced variation in the porosity and pore structure quantitatively characterized in terms of cementation exponent can be more significant. We also found that temperature affects the electrical conductivity of brine saturated Berea sandstones by impacting the brine conductivity, and the pore structure and porosity of the samples, with their importance in a descending order. The results have provided new insights into how temperature affects the electrical conductivity of clay-free porous rocks, and will help to improve the quantitative interpretation of electrical survey data for the exploration of geothermal energy.

Computational Fluid Dynamics Process for Front Windshield Mist Deposition and Its Subsequent Demisting

<div>A vehicle’s heating, ventilation, and air-conditioning system plays a dual role in passenger thermal comfort and safety. The functional aspects of safety include the front windshield demist and deicing feature of the system. The thin-film mist is a result of condensation of water vapor on the inner side of the windshield, which occurs at low ambient temperatures or high humidity. This mist deposition depends on the air saturation pressure at the front windshield. Indian regulation AIS-084 defines the experimental setup for testing, which encompasses both the mist deposition and its subsequent demist process. This regulation mandates testing, which occurs at a later stage of product development. This performance validation can be performed using a three-dimensional computational fluid dynamics approach.</div> <div>Current work summarizes the simulation process for both the mist deposition and the subsequent demisting phenomenon. The complexity of the flow physics is captured via the transient multiphase fluid flow phenomenon subjected to buoyancy effects. This phenomenon is simulated using the Eulerian wall film approach. The wall film deposition of the mist is modeled via species transport. Further, the near-wall thermal effects of surface conduction and heat transfer are simulated by modeling shell conduction layers. Vapor diffusion and relative humidity inside the cabin are modeled using a user-defined function. The process correlation is achieved for two categories of vehicles to establish the process efficacy and robustness. Moving ahead, a design of experiments (DOE) is planned to mitigate the need to simulate mist deposition. The DOE is planning to incorporate deviations in both the input airflow conditions and the imposed ambient conditions. The results from DOE point toward factors that might cause deviations in simulation results with respect to the test. Importantly, the study concludes that the uniform initial thickness assumption of the mist layer can be used for subsequent demist analysis.</div>

The Effect of Surface Conductivity on the Accumulation and Dissipation of Static Electricity Charges on the Surface of Polymer Dielectrics

The Effect of Surface Conductivity on the Accumulation and Dissipation of Static Electricity Charges on the Surface of Polymer Dielectrics

On the behavior of sub-micrometer polystyrene particles subjected to AC insulator-based dielectrophoresis.

Polymer beads, especially polystyrene particles, have been extensively used as model species in insulator-based dielectrophoresis (iDEP) studies. Their use in alternating current iDEP (AC-iDEP) is less explored; however, an assessment in the low-frequency regime (≤10kHz) allows to link surface conduction effects with the surface properties of polymer particles. Here, we provide a case study for various experimental conditions assessing sub-micrometer polystyrene particles with AC-iDEP and link to accepted surface conduction theory to predict and experimentally verify the observed AC-iDEP trapping behavior based on apparent zeta potential and solution conductivity. We find excellent agreement with the theoretical predictions, but also the occurrence of concentration polarization electroosmotic flow under the studied conditions, which have the potential to confound acting dielectrophoresis conditions. Furthermore, we study a case relevant to the assessment of microplastics in human and animal body fluids by mimicking the protein adsorption of high abundant proteins in blood by coating polystyrene beads with bovine serum albumin, a highly abundant protein in blood. Theoretical predictions and experimental observations confirm a difference in observed AC-iDEP behavior between coated and non-coated particles, which might be exploited for future studies of microplastics in blood to assess their exposure to humans and animals.

Effect of spacecraft surface conductivity on voltage of microwave neutralizer in gridded ion thrusters

The μ10 gridded ion thruster, designed and developed at the Institute of Space and Astronautical Science, Japan, is used in the asteroid explorer Hayabusa2. In this propulsion system, the cathode is negatively biased with a power supply. The potential difference between the cathode and the system ground is regarded as an essential indicator of the cathode condition. In the operation of μ10 during the Hayabusa2 mission, it was found that the potential difference increased faster than that measured in a durability test on the ground. In this study, we performed a fault tree analysis of the on-orbit increase in the potential difference between the cathode and the system ground considering the total current balance (including electrons that flow back to the spacecraft). In addition, to understand the effect of the conductive surface around the thruster on the potential difference, we experimentally simulated the change in conductive area. It was found that the potential difference increased under a certain conductive surface condition. The results suggest that the on-orbit increase in the potential difference between the cathode and the system ground is caused by a loss of surface conductivity.

Integrated LaFeO3/rGO nanocomposite for the sensitive electrochemical detection of antibiotic drug metronidazole in urine and milk samples

Metronidazole (MTZ) is a nitroimidazole antibiotic commonly used to treat bacterial infections, but its residues in food products may pose teratogenic, mutagenic, and carcinogenic risks to human health. Hence, monitoring MTZ in food and human samples is essential. In this study, we developed a glassy carbon electrode (GCE) modified with lanthanum ferrite (LFO) integrated with reduced graphene oxide (rGO) nanocomposite for the electrochemical detection of MTZ. The engineered nanocomposite was prepared by the sonochemical treatment and then systematically characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) techniques. The modified LFO/rGO/GCE exhibits excellent electrochemical performance, which is mainly owing to the high surface areas, conductivity, and synergistic effects of LFO and rGO. Using the DPV method, the LFO/rGO/GCE sensor showed a wide linear range of 0.2–1221 µM and a low LOD of 0.048 µM for MTZ detection. The modified sensor selectivity was confirmed with biological species and metal compounds. In addition, the developed sensor demonstrated good stability, reproducibility, and repeatability toward MTZ. Satisfactory recoveries were obtained for MTZ detection in human urine and milk samples using the fabricated LFO/rGO/GCE sensor.

High-resistivity with PN interface passivation in 22 nm FD-SOI technology for low-loss passives at RF and millimeter-wave frequencies

In this paper, GlobalFoundries’ 22 nm fully depleted (FD) silicon-on-insulator (SOI) process is run on standard and high-resistivity wafers with a specially designed PN junctions interface passivation solution to counteract parasitic surface conduction (PSC) effects. Substrate quality is evaluated at RF and mm-wave frequencies through the on-wafer measurements of a set of passives: coplanar waveguides (CPW) lines, two inductors and a crosstalk structure. The effective resistivity (ρeff), losses and harmonics generated by the substrate are monitored based on CPW lines measurements, fabricated in either bottom or top metal layers. Several PN patterns are examined and they demonstrate effective passivation of the PSC, enabling ρeff values in the kΩ.cm range (up to ∼6 GHz) and > 100 Ω.cm up to ∼60 GHz. Patterns with intrinsic region separating the P- and N- doping regions show better performance, which can further be improved applying a reverse PN bias to widen the depletion regions. 50 Ω CPW line designed with PN interface passivation achieves 0.22 dB/mm lower propagation losses at 50 GHz than 50 Ω thin-film microstrip line in this technology. Impact of substrate quality on two spiral inductors is analyzed by comparing substrates with standard resistivity, high-resistivity with PSC and high-resistivity with PN junction solution. The high-resistivity substrate with PN junction solution shows an up to 62% and 15% increase in quality factor with respect to the standard substrates for the 5–20 GHz and 30–60 GHz inductors, respectively. Finally, measurements of a crosstalk structure show a strong isolation improvement in crosstalk through the substrate with the PN interface passivation solution.

The Effect of Defect Charge and Parasitic Surface Conductance on Aluminum Nitride RF Filter Circuit Loss

When AlN thin films are deposited directly on the high-resistance silicon (HR-Si) substrate, a conductive layer will be formed on the HR-Si surface. This phenomenon is called the parasitic surface conduction (PSC) effect. The presence of the PSC effect will increase the power consumption of electronic components. Therefore, it is necessary to reduce the PSC effect. In prior technology, the polysilicon layer is usually used as the trap-rich layer to reduce the PSC effect. Experiments show that compared to AlN films deposited directly on HR-Si, the AlN substrates with polysilicon introduced on HR-Si have less radio frequency (RF) loss. To verify the effect of polysilicon on RF loss, polysilicon films of three different thicknesses and several different roughnesses were introduced. The results show that the thickness of the polysilicon will affect the RF loss, while the roughness has almost no effect on it. The polysilicon trap-rich layer can reduce the RF loss, which gradually becomes smaller as the polysilicon thickness increases.

Effects of volume and surface conductivity on the surface charge and electric field characteristics of the tri‐post insulator in SF 6 ‐filled ± 500 kV DC‐GIL

Herein, the surface charge characteristics of a tri-post insulator in a ± 500 kV direct current gas-insulated transmission lines (DC-GIL) filled with SF6 are thoroughly studied. The influences of volume and surface conductivity of the insulator on the surface charge and consequent electric field distribution are discussed. An improved method is introduced to obtain the distribution of surface charge with considerable accuracy and efficiency for the calculation. It is found that with increasing the volume conductivity, the dominative conduction mechanism changes from surface conduction to bulk conduction, while the inverse variation appears with increasing the surface conductivity. During the variation of electric conductivity, obvious effect of surface charge accumulation is found on the electric field distribution involving the variation of peak electric field strength and its location. Besides, high charge density usually appears along with low peak field strength during this variation. It can be concluded that the surface charge accumulation should be paid special attention when analysing the insulation characteristics of tri-post insulators. The variation of volume and surface electric conductivity should be thoroughly considered.

Surface-Acoustic-Wave Devices Based on Lithium Niobate and Amorphous Silicon Thin Films on a Silicon Substrate

This work presents an acoustic platform using solidly mounted thin-oriented lithium niobate (LiNbO3) film on silicon (Si). A thin layer of amorphous Si eliminates a conductive layer generated in the thin-film bonding processes and contributes to acoustic energy confinement and thermal frequency stability. The gigahertz operating frequency is achieved by resorting to the guided acoustic wave shear-horizontal wave (SH0) in a 400-nm-thick X-cut LiNbO3 thin film. Due to the elimination of the parasitic surface conduction (PSC) effect, the electromechanical coupling of the guide acoustic wave is maximized in the Si-based heterogeneous wafer. Due to the minimized acoustic impedance mismatch between surface material and substrate, longitudinal and higher order spurious modes are suppressed. Due to the stiff substrate with a small temperature expansion coefficient (TEC), the solidly mounted structure features a reduced temperature coefficient of frequency (TCF) and improved power handling. The fabricated resonator shows an extracted electromechanical coupling coefficient of 22.8%, a high loaded <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> of 1208 at 1.6 GHz, and a TCF of −36 p/min/K. The compressed filter is demonstrated with a minimum insertion loss (IL) of 0.6 dB, a fractional bandwidth (FBW) of 8%, an out-of-band rejection of 30 dB, a TCF of −38.5 p/min/K at roll-off, and a miniaturized footprint of 0.4 mm2. The performance has shown the strong potential of the LiNbO3–Si platform for front-end applications in 5G.

Effect of surface conductivity on electromagnetic shielding of multi-walled carbon nanotubes/Poly(ε-caprolactone) composites

Herein, the effect of surface conductivity on microwave shielding effectiveness (SE) is discussed in the sandwiched multi-walled carbon nanotubes/poly(ε-caprolactone) (MWCNT/PCL) composites. The electrical conductivity on single or double-side surface of the composites is regulated by controlling different MWCNT loadings on the surface. The electromagnetic SE values of the MWCNT/PCL composites decrease with decreasing surface conductivity, and decline acutely when the surface becomes non-conductive. The shielding mechanism is investigated by a simulation and experimental study for the composites having different surface conductivity. The results indicate that the microwave reflection is very important to contribute the shielding performance of the composites. In addition, the effect of dielectric properties of surface layers on electromagnetic shielding performance was discussed for the composites with insulation surface. The composites with different polymers as insulting surface layers exhibit the close SE values, suggesting that the microwave shielding performance of the In/Con/In composites is irrelevant to the different polymer with different dielectric constant on the surface layers. Furthermore, the conductive network on surface exerts a great influence on microwave attenuation because of the enhancement on surface conduction loss and polarization loss. Therefore, the surface conductivity is a non-negligible factor for designing materials with excellent microwave shielding performance.

Localized Backside Etching Structure of SOI Substrates on Total Ionizing Dose Effect Hardening for RF Applications

In this work, the localized backside etching (LBE) structure is introduced as a strategy for total ionizing dose (TID) irradiation hardening. Immunity to TID-irradiation-induced radio frequency (RF) property degradation is observed for the first time in SOI substrates with the LBE structure. Identical co-planar waveguide transmission lines (CPW TLines), crosstalk characterization structures, and planar spiral inductors are designed and fabricated on different 8-in SOI wafers to characterize the RF properties of substrates. Electrical characterization in the frequency ranges from 100 MHz to 40 GHz reveals that the LBE structure is beneficial to suppressing the parasitic surface conduction (PSC) effect, which will lead to better RF properties of SOI substrate. It is shown that under <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sup> Co <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula> -ray irradiation, RF losses are significantly increased in the case of conventional substrates. In contrast, LBE substrates are almost insensitive to TID irradiation due to suppression of PSC. A developed physical model is proposed to characterize the behavior of inductors under PSC and TID effects, and the improvement by LBE structure on RF TID tolerance is separated through model parameter extraction.

Palladium doped α-MnO2 nanorods on graphene as an electrochemical sensor for simultaneous determination of dopamine and paracetamol

Defect engineering at the atomic level has been one of the most prevalent research topics in the field of catalysis because defects act as superior active sites. However, defects are difficult to create, recognize, and fully comprehend. In this study, for the first time, we demonstrate that the defects creation by palladium atom on the surface of α-MnO2 nanorods supported graphene (Pd@α-MnO2/G). These defects significantly altered the electronic and crystalline structures of the as-prepared material, as well as improving the surface/interface properties for biomolecule determination. As a result, Pd@α-MnO2/G exhibited a higher electroactive surface area, conductivity, and synergistic effect in the simultaneous detection of dopamine (DA) and paracetamol (PA) owing to its defective nature. For instance, it showed wide detection ranges from 0.2 to 425 µM and from 0.1 to 375 µM with lower limits of detection of 0.086 and 0.059 µM for DA and PA, respectively. It also showed high sensitivity (0.0591 and 0.0854 µA µM−1 for DA and PA, respectively) and experienced no interference from the presence of a 100-fold excess of interferents. Importantly, we discussed the 2H+/2e– reaction mechanism of DA and PA oxidation on the Pd@α-MnO2/G surface, for an in-depth understanding of the process.

Modeling of Semiconductor Substrates for RF Applications: Part I—Static and Dynamic Physics of Carriers and Traps

This article aims to provide deep insight into the physics of substrates for RF applications under large-amplitude signal excitations. The impact of physical parameters on substrate-induced harmonic distortion is modeled and well understood, from a theoretical and quantitative standpoint. This article formulates the interplay between applied voltage signal (dc or RF), interface fixed charge, and trapped charge in a charge-balance analysis for high-resistivity and trap-rich (TR) substrates. A TCAD approach gives strong insight into the impact of such semiconductor material and interface properties on the RF substrate's effective resistivity and linearity. First, a static analysis reveals how TR interface passivation overcomes the parasitic surface conduction effect using the concept of deep Fermi-level pinning. Next, substrates are analyzed in response to dynamic excitation signals. Using step functions to pulse an MOS structure from strong negative to strong positive applied charge sheds light on carrier dynamics. The characteristic time constants associated with variations in trap occupancy and in free carrier densities are discussed. Finally, sinusoidal large-amplitude signals are considered to analyze harmonic distortion from several types of substrates at various RF frequencies.

Critical thickness for the emergence of Weyl features in Co3Sn2S2 thin films

Magnetic Weyl semimetals are quantum phases of matter arising from the interplay of linearly dispersive bands, spin-orbit coupling, and time reversal symmetry breaking. This can be realised, for example, in Co3Sn2S2, based on a cobalt kagome lattice and characterised by intriguing phenomena such as large anomalous Hall effect, Nernst effect, and water oxidation. Here, we attempt to determine the robustness of the twofold necessary conditions for the emergence of the magnetic Weyl semimetal phase in Co3Sn2S2 ultrathin films. Except for two-dimensional layered materials, a reduction of thickness generally makes it difficult to develop topological character and ferromagnetic long-range order. In Co3Sn2S2 films, while ferromagnetic ordering appears robustly even in average thicknesses of one or two unit cells with island-like polycrystalline domains, the anomalous Hall conductivity appears only above a critical thickness of approximately 10 nm. The emergence of surface conduction and large anomalous Hall effect implies the distinct contribution of Weyl nodes and their Berry curvature. These findings reveal an exotic feature of Weyl physics in thin-film based superstructures as well as a potential for future applications in electronic devices.

Surface conductivity effects during shock wave reflection off curved surfaces

Previous work has shown that heat transfer into a plane conducting surface affects shock wave reflection properties. In the more complex reflection case of a curved surface the situation would be different because of the increased number of reflection patterns, with a rapid change in reflection geometry as the wave propagates up the surface. Test pieces of different thermal conductivities (0.19 W/mK and 401 W/mK) and hydraulically smooth surfaces are used on both convex and concave cylindrical surfaces. The test pieces are placed in identical positions on either side of a plane of symmetry and at the same incident angles in a shock tube. Tests are performed at incident shock Mach numbers of 1.22< M <1.5 and imaged using high-speed shadowgraph photography. The images are analyzed both quantitatively through reflection angle measurements and qualitatively by searching for asymmetry. Both the qualitative and quantitative measurements clearly indicate that the thermal conductivity of the surface affects the reflection patterns due to the complex transient thermal environment. Asymmetry in the reflection patterns is found at all Mach numbers. In contrast to the plane wall case the lack of theory limits comparison, where in that case it was shown that the lower the thermal conductivity the closer the experimental results approached the ideal adiabatic case. Similar comparisons in the relationship of reflection types between different materials are found in the current case. The findings could be refined by using higher imaging frame rates and spatial resolution, and sophisticated numerical modeling.

Two models for determination of the effective conductivity of concentrated suspensions of ellipsoidal particles with surface phenomena

Many multicomponent materials such as rocks or nanofluids are characterized by the presence of conductive surface layers at the interface. These conductive layers can change effective physical properties (for example, effective thermal or electrical conductivities) of such materials. A suspension of ellipsoidal particles with surface conductivity is considered. Two theoretical models are presented for the solution of the so-called one-particle problem that can be used then in any homogenization scheme for determination of the effective conductivity of such suspension. The first model is based on the modification of the boundary conditions for the electric current density (the jump boundary conditions). The second model is based on the confocal ellipsoids. The effect of surface conductivity is obtained for this model by limiting transition to the infinitely thin external ellipsoidal shell.For the calculation of the effective conductivity of the medium containing the ellipsoidal particles with the surface phenomena one of the popular homogenization scheme named by Differential Effective Medium (DEM) method is used. Comparison of numerical results obtained by this method for two different solution of the one-particle problem show that these results are rather close even for very large values of the surface conductivity.

Effects of surface conductivity on surface charging behavior of DC-GIL spacers

In this study, a simulation model is established to study the effect of surface conductivity on the accumulation of surface charge. The simulation shows that hetero-charges increase on areas away from the high voltage electrode and the electric field distribution along the surface becomes more uniform with increased surface conductivity. The dominant surface charging mechanism changes from conduction through the bulk of the insulation to surface conduction with increased surface conductivity. When the surface conductivity ranges from 1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-15</sup> to 5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-14</sup> S for a convex spacer surface, an optimal surface charge suppression and electric field homogeneity can be realized.

A novel sight for understanding surface charging phenomena on downsized HVDC GIL spacers with non-uniform conductivity

Surface charging phenomena on DC GIL spacers is a complicated process affected by lots of factors, among which surface conductivity is an important dielectrics parameter. In this study, experimental and theoretical research are carried out to investigate the effects of non-uniform surface conductivity on surface charge accumulation behaviours of downsized HVDC GIL spacers. A SiC/epoxy layer is partially coated on alumina/epoxy spacers to form a non-uniform surface conductivity. The coating manners include sector-shaped coating and ring-shaped coating. The accumulated surface charges show a rising first and then decreasing trend with the increase of SiC contents in coated area. When surface conductivity is high enough, there is almost no charge accumulation. Bipolar charges, which are generally observed on raw alumina/epoxy spacers, are found to be preferable to accumulate at interface region between high and low surface conductivity. The orientation of bipolar charges is determined by the distribution of inhomogeneous surface conductivity. The formation mechanism of bipolar charges at the interface is revealed based on the experiment and simulation results. Besides, a uniform surface conductivity contributes to suppressing randomly distributed surface charges including bipolar charges, which can provide guidance for designing and optimizing highly reliable and stable HVDC GIL.