Contact Resistance Distribution Research Articles

Experimental and Analytical Study on Contact Resistance and Current Distribution of NI HTS Coils in Low-Frequency AC Method

Experimental and Analytical Study on Contact Resistance and Current Distribution of NI HTS Coils in Low-Frequency AC Method

An efficient method for electro-thermo-mechanical coupling effect in electrical contact on rough surfaces

In this study, a numerical strategy based on the boundary element method (BEM) is developed to simulate the electrical contact behavior on rough surfaces. By using the Fourier transform, the solutions of the electric potential, temperature rise, and displacement fields in the Fourier space are derived with finite boundaries, in which the electro-thermo-mechanical coupling effect is considered. With the consideration of the contact condition, an iterative algorithm is proposed to seek the solutions of rough surface electrical contact under a given contact force and total electric potential drop. The contact pressure, real contact area, electrical contact resistance, electric current, and temperature rise distribution are predicted. For the validation, the electrical contact results of a spherical punch-half space contact and a rough surface-elastic substrate contact are calculated based on the finite element method. The good agreement between the results from the BEM-based method and the finite element method indicates the accuracy of the presented method. Then, the effect of the total electric potential and the thermal expansion on the electrical contact behavior, the relationship between the contact conductance and contact stiffness, and the probability density function of the contact pressure and temperature rise distributions are evaluated using the proposed method.

Predicting Loss Analysis from Luminescence Images in Si Solar Cells with Convolutional Neural Networks

In this work, deep convolutional neural networks (CNNs) are used to speed up the calculation of spatial nonuniform device parameters, voltage and fill factor (FF) losses in crystalline Si solar cells. Luminescence images on finished solar cells, specifically as‐measured electroluminescence (EL) and photoluminescence (PL) images, are used as input features to train the CNN models and losses analysis as output is from a finite‐element modeling program called Griddler. From the analysis of a small dataset of 250 commercial grade solar cells, the CNN models are able to predict the spatially nonuniform distribution of contact resistance and defect parameters of the devices under test and exhibit good performance in the inference of voltage and FF losses. As EL and PL images are widely collected in‐line production data, in the result, the possibility of deploying 2D spatial power loss analysis is implied as a fast, in‐line, and nondestructive analytic tool for solar cells manufacturing.

(Invited) From Material Discovery Towards a Prototype Hydrogen Generator

This contribution illustrates the approach that has been taken to develop a pre-commercial prototype of a water electrolyzer. The aim has been to develop and integrate novel nanostructured materials for both electrodes and membranes, demonstrating their upscaling potential by integrating them together in a water electrolysis cell with an active surface are of 50 cm² in order to proof their potential for further advancing the state of the art of green hydrogen generation.Based on industrial experience with medium flow hydrogen generators, the boundary conditions for the new electrode and membrane components were set, safeguarding their integration potential in a scalable stack. A nano-porous intrinsically conductive membrane material has been developed, that allows to drastically reduce the thickness of the separator, reducing ohmic losses without compromising gas separation quality during operation at elevated pressures (up to 20 barg). This was combined with nanostructured electrodes of 4-10 μm thickness on both sides of the membrane. Given the vast range of dimensional scales, from 10-8 to 10-1 m, special attention was needed for the interconnections of the materials to establish the required electronic and ionic coupling together with adequate mechanical robustness. Two phase fluid flow modelling was done do have an optimal reactant distribution and gas evacuation from the electrode surfaces. Aspects like contact resistance, elasticity, stiffness, and overall electric field distribution inside the cell were considered. To characterize the cell in operation, a dedicated balance of plant has been built (Fig.1). The installation is automated and takes care of the electrolyte solution conditions and of the process window settings in terms of applied current, electrolyte flow and operational temperature at a pre-set pressure. The resulting cell potential, the gas purity of both oxygen and hydrogen streams and the differential pressure between anolyte and catholyte chambers are continuously monitored. The upscaled cell demonstrates a high hydrogen generation efficiency of 85% (HHV) that outperforms currently installed alkaline systems in terms of productivity and gas purity when operated at an elevated pressure 20 bar. The cell robustness, documented over 800 hours, reveals further areas of improvement for both the internal construction of the stack and the control logic of the balance of plant. Figure 1

Microscale mapping of thermal contact resistance using lock-in thermography

This paper proposes a new thermal contact resistance distribution measurement method using lock-in thermography. This method was used to evaluate a two-dimensional local thermal contact resistance distribution. To be able to measure the distribution, a uniform intensity laser heating system was developed. The developed system has a top-hat intensity distribution with a diameter of 30 mm. By combining this heat source and the lock-in thermography, a new measurement instrument was developed, which can evaluate local temperature behavior in the frequency domain, including the information of the contact interface in high spatial resolution of about 70 μm. Additionally, a new thermal contact resistance measurement principle was constructed based on a one-dimensional heat transfer equation that considers the reflected and transmitted temperature waves at the boundary and contact interface. The thermal contact resistance was acquired as a solution to the inverse problem of the temperature response done by fitting analyses. The validation of this method was performed quantitatively with two samples made of two bonded isotropic graphite plates. The one sample has an intentional defect area that has a slightly higher thermal resistance. The other sample has the known thermal contact resistance value measured with a validated method. Based on the results, the measurement value agreed with the referenced value. Also, the defect area was quantitatively detected clearly as a high thermal resistance region. Furthermore, as a practical example, the measurement method was applied for two different contact interface roughness samples consisting of aluminum alloys and thermal grease. Consequently, it was revealed and visualized that the contact interface with a rough surface has a high thermal resistance spot.

Effect of load application method on thermal contact resistance and uniformity of temperature distribution

Traditionally, the research on thermal contact resistance based on real rough surfaces is often limited to the uniform load. This study investigated the effects of the material, surface roughness, pressure load, and temperature on the thermal contact resistance and contact interface temperature distribution non-uniformity under a concentrated load. First, rough surfaces with different surface roughness degrees were generated by using a random generation method, and microscopic contact numerical models of three different materials were established. Then, the real contact area of different pressure loads under uniform and concentrated loads were calculated. Finally, heat transfer analysis was performed at different temperatures based on the microcontact state, the thermal contact resistance and the contact interface temperature distribution non-uniformity were calculated. Compared with the uniform load, the thermal contact resistance and the non-uniformity of the temperature distribution were improved under the concentrated load, and the effect was more obvious under the conditions of a large pressure load and small surface roughness degree. In addition, it was found that the uniformity of the temperature distribution on the contact surface was proportional to the real contact area and temperature instead of the thermal contact resistance except when the real contact area was very small.

Analysis of Contact resistance Distribution Effect on the Electric-Pathway and Heat Generation of Ag-Nanowire Network Based on Temperature Measurement

Analysis of Contact resistance Distribution Effect on the Electric-Pathway and Heat Generation of Ag-Nanowire Network Based on Temperature Measurement

Reinforced Metal Bipolar Plate Structure with Stiffening Rib Channel for Proton Exchange Membrane Fuel Cell

Clean energy has become a concern because fossil fuels are the primary cause of climate change and air pollution. A proton exchange membrane fuel cell (PEMFC) is an environmentally friendly vehicle's alternative energy source. Bipolar plates, gaskets, gas diffusion layers, and a membrane electrode assembly (MEA) constitute a PEMFC. The bipolar plate accounts for a large portion of the fuel cell stack cost. Metallic bipolar plates are utilized in vehicle fuel cell stacks because of its low fabrication cost, high manufacturability, mechanical strength, and low weight. Despite the benefits, a thin metal plate's major drawbacks are deformation and corrosion resistance.Stamping metallic plates form trapezoidal cross-section channels, whereas machined graphite bipolar plates can form rectangular cross-section channels. These trapezoidal channels make dimensional errors such as draft angle and fillet radius. Besides, the spring back effect makes shape errors in the manufacturing process. Many kinds of research are conducted to understand the impact of channel tolerances on the performance of PEMFCs. Mainly, inhomogeneous compression in the gas diffusion layer results from channel deformation caused by unevenly distributed clamping force and shape inaccuracy of the metal bipolar plates. High contact resistance and non-uniform reactant gas distribution would result from inhomogeneous compression of GDL.A reinforced metal bipolar plate structure with a stiffening rib channel is proposed in this work to reduce bipolar plate deformation and improve gas transfer. Stiffening ribs are imprinted on the top of the channel. The geometric parameters of the stiffening ribs are shown in Fig. 1. Four geometric design parameters are selected in this study, the distance between the ribs d1, length of the rib l1, height of the rib l2, width of the rib l3. The stainless steel with a thickness of 0.1mm, 50mm×50mm active area, is used. The influence of stiffening ribs on mechanical and fluid characteristics is investigated through numerical analyses and experiments. The static structural analysis illustrated the deformation of the bipolar plates and GDL under the clamping force. The stiffening rib design improves the structure's mechanical strength, lowering bipolar plate deformation. When the endplates clamp the stack, the stiffening rib supports more stress to prevent deformation. The flow distribution in the flow field channel and GDL was then visualized using computational fluid analysis. Stiffening ribs increase the velocity of the reactant. Enhanced under rib convection makes reactant gas evenly distributed. In addition, stiffening ribs causes a convective flow beneath the rib, which improves PEMFC performance. Finally, single-cell studies proved that the modeling results are valid. Under the same operating conditions with the same geometry to the model, electrochemical reactions are investigated to decouple the leading cause of the resistances. The ohmic resistance decreases with the robust structural stiffening ribs, and the mass transport resistance decreases with the well-distributed reactants flow. Figure 1

Stacked-Interconnect for Monolithic Integration of Low-Temperature Polysilicon and Amorphous Metal-Oxide Thin-Film Transistors

While offering a range of practical benefits, the monolithic integration of low-temperature polysilicon (LTPS) and amorphous metal-oxide thin-film transistors presents several incompatibility issues regarding materials and processes. Presently addressed are two critical ones arising from the back-end processes of contact treatment and metallization. Both are resolved by employing a stacked-interconnect consisting of two conductor layers, with each layer forming the preferred contact electrodes for one of the two types of transistors. At the expense of a slight increase in process complexity, a narrow distribution of low specific contact resistance ( ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> Ω·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) for both types of transistors was obtained, thus giving rise to more consistent transistor characteristics. Inverters consisting of complementary top-gate LTPS pull-up and bottom-gate indium-gallium-zinc oxide pull-down transistors were demonstrated, exhibiting a gain of 40 V/V and a rail-to-rail full swing.

Open Fermi-Hubbard model: Landauer's versus master equation approaches

We introduce a simple model for the quantum transport of Fermi particles between two contacts connected by a lead. It generalizes the Landauer formalizm by explicitly taken into account the relaxation processes in the contacts. We calculate the contact resistance and non-equilibrium quasi-momentum distribution of the carriers in the lead and show that they strongly depend on the rate of relaxation processes.

Evaluation of Thermal Contact Resistance Between Two Solid Surfaces Using Photoacoustic Technique

Thermal contact resistance is one of the factors that complicates heat transfer between the interfaces of different components. Because heat transfer is influenced by several factors, it is difficult to estimate all the influencing factors for practical applications. In this study, the thermal contact resistance between two solid surfaces was evaluated using the photoacoustic (PA) technique. The samples consisted of a metal foil and metal cylinders, which had various surface roughnesses at the contact faces measured at the same contact pressure. A one-dimensional analytical solution of the phase lag of the PA signal showed a similar trend with the experimental results. However, there were some quantitative differences between the two groups. By comparing the numerical calculation results for the developed heat conduction model of a cylindrical coordinate system with the experimental results, we found that the in-plane distribution of thermal contact resistance at the contact face contributed to the deviation between the experimental results and the numerical results. The thermal contact resistance was evaluated by considering the in-plane distribution of the thermal contact resistance, and reasonable values of thermal contact resistance were obtained.

Data-driven sensitivity analysis of contact resistance to assembly errors for proton-exchange membrane fuel cells

The proton-exchange membrane fuel cell is a promising power source for automobile industry because of its zero pollution. However, its stack structure always faces increased contact resistance caused by assembly errors, leading to substantial energy loss during the working period. To enhance its output performance, the influence of assembly errors on contact resistance is studied for proton-exchange membrane fuel cell. The mechanical simulation model of fuel cell assembly process is established to provide contact resistance distribution with different assembly errors. An improved global sensitivity analysis method is proposed to evaluate the influence coefficient of each assembly error term on contact resistance based on a series of randomized simulation data. The case study of a single-layer fuel cell demonstrates the proposed method achieves higher efficiency than traditional sensitivity analysis methods, and finds out key assembly errors in regard to reducing contact resistance.

Reducing Contact Resistance in Two-Dimensional-Material-Based Electrical Contacts by Roughness Engineering

The engineering of efficient electrical contacts to two-dimensional (2D) layered materials represents one of the major challenges in the development of industrial-grade 2D-material-based electronics and optoelectronics. In this paper, we present a computational study of the contact resistance and current-flow distribution for electrical contacts between 2D materials and three-dimensional (3D) metals and between different 2D materials. We develop models of the electrical contact resistance for 2D/2D and 2D/3D metal/semiconductor contact interfaces based on a self-consistent transmission-line model coupled with a thermionic charge-injection model for 2D materials and first-principles simulation by density-functional theory, which explicitly includes the variation of the electrostatic potential in the contact region. We compare the results of our self-consistent calculations with existing experimental work and obtain excellent agreement. It is found that the presence of contact interface roughness, in the form of fluctuating Schottky barrier heights in the contact region, can significantly reduce the contact resistance of ${\mathrm{Mo}\mathrm{S}}_{2}$/metal Schottky 2D/3D contacts. Our findings suggest that roughness engineering may offer a possible paradigm for reducing the contact resistance of 2D-material-based electrical contacts.

Replacement strategy of medium-voltage circuit breakers based on the segmented risk estimation

In this paper, a new replacement strategy for medium-voltage circuit breakers based on the segmented risk estimation of keeping them in service is presented. The methodology is based on the condition measurements of both circuit breakers and belonging feeders, and the assessment of risk of failure in the next period. The risk is divided into different operational conditions (normal and extreme) and different failure and feeder types. Normal risk deals with the probability of reaching the maximal allowed control value during normal operating conditions and the latter with the probability of reaching the maximal allowed number of short current interruptions in the next period. The total of 427 circuit breakers has been monitored, with data gathered in the past 10 years. After having administered the statistical tests, parameters for Weibull probability distribution of contact resistance for breakers on both overhead and underground feeders were determined. The probability of maximal number of interruptions is determined using the Poisson distribution. Finally, the risk estimation and replacement priorities are presented on the whole population of 427 breakers.

Simulations on Current Distribution in Railgun Under Imperfect Contact Conditions

In the process of electromagnetic launch, the initial contact pressure distribution of armature/rail (A/R) contacts interface is uneven, and the actual contact area is obviously different from the perfect contact. The uneven contact pressure leads to uneven contact resistance distribution, affecting the magnetic diffusion process and changing the A/R interface current distribution. Therefore, it is necessary to consider the influence of contact pressure on the current distribution. In the past, the simulation studies usually considered the contact between rails and armature as the perfect contact, and the result obtained may be different from the actual situation. This paper uses the finite element software COMSOL to perform coupling simulation analysis on the electromagnetic module and solid mechanics module in the initial stage of electromagnetic launch. At the initial stage of electromagnetic launch, the contact pressure is mainly provided by the prepressure generated by the interference fit. In this paper, the influence of contact pressure on current distribution and the influence of magnitude of interference on contact position, contact pressure, and current distribution are analyzed.

Device Parameter Extraction for Loss Analysis of Silicon Solar Cells Based on Intelligent Model Fitting

A fully automated and rigorous loss analysis routine that provides a breakdown of the loss components occurring in silicon solar cells is presented in this work. The routine combines large-area two-dimensional modeling and smart auto-fitting routines with luminescence imaging. This allows the spatially resolved information in luminescence images to be analyzed to extract recombination parameters partitioned by regions (e.g. wafer edge, under metal contacts, over passivated areas), as well as the spatial distribution of contact resistance. After these cell parameters have been extracted, a loss analysis of open-circuit voltage can be performed by simulating the open-circuit condition and examining the various recombination currents, and a loss analysis of fill factor can be performed by successively turning off the effects of factors that degrade it in simulation. The technique is demonstrated on a multicrystalline silicon PERC solar cell.

Measurement of effective bulk and contact resistance of gas diffusion layer under inhomogeneous compression – Part I: Electrical conductivity

This paper describes a measurement technique developed for the determination of the effective electrical bulk resistance of the gas diffusion layer (GDL) and the contact resistance distribution at the interface of the GDL and the bipolar plate (BPP). The novelty of this study is the measurement and separation of the bulk and contact resistance under inhomogeneous compression, occurring in an actual fuel cell assembly due to the presence of the channels and ribs on the bipolar plates. The measurement of the electrical contact resistance, contributing to nearly two-third of the ohmic losses in the fuel cell assembly, shows a non-linear distribution along the GDL/BPP interface. The effective bulk resistance of the GDL under inhomogeneous compression showed a decrease of nearly 40% compared to that estimated for homogeneous compression at different compression pressures. Such a decrease in the effective bulk resistance under inhomogeneous compression could be due to the non-uniform distribution of pressure under the ribs and the channels. This measurement technique can be used to identify optimum GDL, BPP and channel-rib structures based on minimum bulk and contact resistances measured under inhomogeneous compression.

The effect of molecular mobility on electronic transport in carbon nanotube-polymer composites and networks

A multiscale modeling approach to the prediction of electrical conductivity in carbon nanotube (CNT)–polymer composite materials is developed, which takes into account thermally activated molecular mobility of the matrix and the CNTs. On molecular level, a tight-binding density functional theory and non-equilibrium Green's function method are used to calculate the static electron transmission function in the contact between two metallic carbon nanotubes that corresponds to electron transport at 0 K. For higher temperatures, the statistical distribution of effective contact resistances is considered that originates from thermal fluctuations of intermolecular distances caused by molecular mobility of carbon nanotube and the polymer matrix. Based on this distribution and using effective medium theory, the temperature dependence of macroscopic electrical resistivity for CNT-polymer composites and CNT mats is calculated. The predicted data indicate that the electrical conductivity of the CNT-polymer composites increases linearly with temperature above 50 K, which is in a quantitative agreement with the experiments. Our model predicts a slight nonlinearity in temperature dependence of electric conductivity at low temperatures for percolated composites with small CNT loading. The model also explains the effect of glass transition and other molecular relaxation processes in the polymer matrix on the composite electrical conductivity. The developed multiscale approach integrates the atomistic charge transport mechanisms in percolated CNT-polymer composites with the macroscopic response and thus enables direct comparison of the prediction with the measurements of macroscopic material properties.

Contact Resistance Distribution on Anode Surfaces Eroded by Break Arcs in a DC48V Resistive Circuit

Contact Resistance Distribution on Anode Surfaces Eroded by Break Arcs in a DC48V Resistive Circuit

Electromechanical properties of carbon nanotube networks under compression

The network of entangled multiwall carbon nanotubes and the composite consisting of a polystyrene filter-supported nanotube are introduced as conductors whose conductivity is sensitive to compressive stress both in the course of monotonic stress growth and when loading/unloading cycles are imposed. The testing has shown as much as a 100% network conductivity increase at the maximum applied stress. It indicates the favorable properties of the multiwall carbon nanotube network for its use as a stress-electric signal transducer. To model the conductivity–stress dependence, it is hypothesized that compression increases local contact forces between the nanotubes, which in turn leads to a decrease in the contact resistance between them. The lack of detailed knowledge of the mechanism as well as an unclear shift from individual contacts to the whole network conductance behavior is circumvented with a statistical approach. In this respect, the conductivity/compression data were fitted well using the Weibull distribution for the description of the nanotube contact resistance distribution.