Electrical Contact Theory Research Articles

Research on the Influence of the Closing Amount of Electrical Connector Contacts on Fretting Wear under a Vibration Environment

As a key component for transmitting electrical signals, the electrical contact performance of electrical connectors is directly affected by the closing amount of the socket. It is urgent to explore the relationship between contact resistance and the closing amount of cylindrical groove electric connectors, as well as the range of the closing amount when their comprehensive performance is optimal in vibration environments. Based on Hertz contact theory, the long- and short-axis parameters of the contact elliptical surface were obtained using the Boussinesq solution and the contact deformation coordination equation. An electrical contact resistance (ECR) theoretical model was obtained using Holm’s electric contact theory and the GW contact model. According to the ECR and long- and short-axis parameters of the contact elliptical surface and the theoretical model of contact resistance, an ECR model based on changes in the initial closing amount (deflection) of the socket spring was established by introducing the cantilever beam model of the socket spring. Then, the failure mechanism of fretting wear and the change mechanism of the ECR of the electrical connectors under a vibration environment were analyzed using the sinusoidal vibration test of electric connectors. The optimal range of the initial closing amount of the cylindrical-groove-closing-type electrical connector socket spring was determined, providing a reference for the reliability designs of electrical connectors.

Research and Analysis on Contact Resistance of Wheel and Insulated Rail Joint in High-Speed Railway Stations

Insulated rail joint (IRJ) as one of the components of the track circuit will be burned once the electric arc is generated when the train wheel passes through the insulated rail joint and the track circuit occurs the red-light band fault, which has a great impact on the safety of the train. Reducing the voltage at both ends of the insulated rail joint can effectively prevent the occurrence of electric arc. Clarifying the wheel-IRJ contact resistance is the basis for analyzing the voltage of wheel-IRJ. The effective apparent contact area of the wheel-IRJ contact was derived through the mathematical relation. Considering the surface roughness parameters, based on the electrical contact theory and the Greenwood-Williamson (GW) model, the mathematical models of the wheel-IRJ contact resistance and current density were established, and their influencing factors were analyzed. The results show that the contact resistance increased first and then decreased. The influences of load, roughness of the contact interface, and electric arc heat on the contact resistance were greater. Considering the influencing factors of contact resistance and current density, corresponding protective measures were proposed to reduce the potential difference at both ends of the insulated rail joint.

Study on the Performance of Liquid-Solid Contact Resistance Based on Magnetohydrodynamic Micro-Angular Vibration Sensor

In this paper, the influence of the contact resistance between the conductive fluid and the metal electrode on the output characteristics of the magnetic fluid micro-angular vibration sensor (MHD sensor) is theoretically analyzed. The contact resistance models based on the solid-solid electric contact theory are established based on the resistivity, temperature, pressure and angular vibration of the materials between the conductive fluid and the metal electrode. The contact resistance was tested by setting up an experimental platform and making conductive fluid rings with electrode materials of Ag, Cu and Ti. The results show that the static contact resistance between the conductive fluid and the metal electrode is positively correlated with the material resistivity and temperature, and negatively correlated with the surface roughness and contact pressure of the metal electrode. The dynamic contact resistance fluctuation is proportional to the amplitude of the input voltage of the angle shaker and inversely proportional to the square of the input frequency. At the same time, reducing contact resistance can improve the MHD sensor's performance.

Study on electric spark discharge between pantograph and catenary in electrified railway

The electric spark caused by pantograph-catenary (PC) electrical contact failure happens frequently, it is a kind of arcing phenomenon which can severely affect the current collection of PC. The theoretical analysis and modelling of PC electric spark are tried. First, the contact spots between PC and their temperature rise are analysed and derived based on the classical electrical contact theory, respectively. The mechanism of spark discharge is revealed through the analysis of PC voltage difference, and the spark discharge model is proposed combining with the spot temperature rise formula and spark discharge mechanism. Then, in order to obtain some key parameters in an electric spark discharge model, such as contact force and contact current, the structure model of PC and the circuit model of vehicle-grid are established for the calculation of the spark rate in PC. Finally, the spark rate is calculated and analysed under the different parameters in PC system. The calculation results are verified by the experiment results. Through the presentation of the correlation of electric spark discharge and factors, such as contact force, contact current and material of PC, this study can support the assessment of electrical contact quality in the PC system in future study.

Vibration-induced dynamic characteristics modeling of electrical contact resistance for connectors

The electrical contact resistance (ECR) of connectors fluctuates periodically under vibration stress. However, a theoretical model used to explain the dynamic characteristics of ECR has not been fully proposed. The dynamic characteristics of ECR are presented after an analysis of the measured results. Moreover, according to the Greenwood-Williamson model for elastic contact and the equivalent spring model for random rough surfaces, the change in the contact pressure of electrical connectors during vibration is studied. On this basis, combining with the Holm electrical contact theory, a dynamic model of ECR under vibration conditions is established. The model can theoretically explain the phenomena of ECR found in the experiments. A good correlation between experimental and predicted ECR fluctuation is achieved.

Effects of Environmental Temperature on Passive Intermodulation in Electrical Connectors

Environmental temperatures may affect the high-frequency electrical performance of passive components, including passive intermodulation (PIM) characteristics. This work proposes a theoretical model of the third-order intermodulation distortion (IM3) signal as a function of the material properties and contact characteristics in a connector. A cross-sectional model of the inner conductor supported by finite-element analysis (FEA) simulations was used to investigate the effect of temperature on the current density distribution in different material regions and its impact on nonlinear performance. Based on electrical contact theory and temperature-dependent modeling, mathematical expressions were developed to calculate the impact of the various contact parameters, such as contact pressure, contact area, and contact resistance. Combining the effects of both material nonlinearity and contact nonlinearity, the IM3 product powers resulting from coaxial connectors associated with temperature change were predicted theoretically. A series of experiments were designed and conducted to measure the IM3 product powers of connectors for a variety of environmental temperatures. The model predictions show a good correlation with these experimental results.

Storage PoF model of electromagnetic relays based on electrical contact theory

To predict the storage life (SL) of electromagnetic relays better, effectively guide life extension project and save maintenance costs, this paper proposes a Physics of Failure (PoF) model for assessing the SL based on Holm electrical contact theory.Firstly, considering the relationship between storage environment, processing technology, material and contact resistance, the shrinkage, interface and body resistance expressions are constructed. Then the PoF model is established regarding contact resistance to the initial value ratio as an input parameter. The dimensionless parameter in the model that reflects the diffusion rate of the corrosion film on contact surface is determined from the contact resistance data measured in the Accelerated Storage Degradation Test (ASDT). By using this model to calculate SL of the samples at different stress levels and comparing results with ASDT records, the accuracy of the model is verified. It proves that the proposed storage PoF model can predict the SL of electromagnetic relays effectively and provides a theoretical reference for rapid assessment of their storage state.

Analysis of electromagnetic behaviors induced by contact failure in electrical connectors

AbstractElectrical connectors are widely used in electrical devices as an interconnect element and their reliability is a critical factor in device performance. However, there are multiple factors that may lead to poor reliability. These include contact failure induced by temperature and humidity, vibration, and atmospheric contamination, which may induce deterioration of the transmitted signal and leakage of electromagnetic energy. In the current work, the contact failure characteristics of a specific connector are investigated through measurement and analysis of high frequency parameters and spectrums. Based on transmission line theory and electrical contact theory, an equivalent model was developed to explore the effect of contact failure on high frequency parameters. Experiments were conducted using a network analyzer, signal generator, signal analyzer, and H‐field probe. The high frequency parameters were measured and compared with the calculated values, with consistent results. The leakage spectrums were measured with an H‐field probe for a variety of input signal amplitudes and frequencies and loose contact conditions. The results indicate that leakage increases with higher frequency and greater input signal amplitude.

Passive Intermodulation of Contact Nonlinearity on Microwave Connectors

For the passive intermodulation (PIM) problem of nonlinear contact on microwave connectors, an effective method is presented to improve the computational accuracy of PIM. First of all, the contact stress distribution on contact surface is analyzed by finite-element method based on the Weierstrass-Mandelbrot model. The contact stress and real area of contact are evaluated under different loading conditions. Then, the electrical parameters of physical effects of nonlinear contact are derived based on the electric contact theory and the physical effects of metal-metal microcontact. Finally, the nonlinear I-V relation is established from the microcontact equivalent circuit, and the third-order PIM power level generated by contact nonlinearity is revealed in analytic form. The analytic results are verified by the PIM test experiments. This work provides a novel way for PIM calculation of rough surface contact.

Analytic Passive Intermodulation Model for Flange Connection Based on Metallic Contact Nonlinearity Approximation

Passive intermodulation (PIM) is one of the major reliability problems in microwave communication systems. In this paper, the PIM interference generated by the metal–insulator–metal (MIM) contact nonlinearity was analytically modeled and experimentally verified. The pressure-dependent nonlinear $I$ – $V$ equations of the MIM contact were derived based on electrical contact theory and verified using a manufactured MIM contact structure. Then a point source model for the PIM product based on the metallic contact nonlinearity was proposed. The PIM product is mainly determined by the contact resistance, surface current density, and nonlinear current coefficient from the model, and in the small contact resistance region, the PIM level decreasing rates are 60, 60, and 20 dB/decade by decreasing the contact resistance, surface current density, and the nonlinear current coefficient, respectively. A designated PIM current source was utilized to verify the relationship. In the end, the PIM equation for the rectangular waveguide connection was derived based on the point source model. This model will provide guidance on low PIM system design.

Contact resistance between two REBCO tapes under load and load cycles

No-insulation (NI) REBCO magnets have many advantages. They are self-protecting, and therefore do not need quench detection and protection, which can be very challenging to implement in a high Tc superconducting magnet. Moreover, by removing the insulation and allowing thinner copper stabilizers, NI REBCO magnets have significantly higher engineering current density and higher mechanical strength. On the other hand, NI REBCO magnets have the drawbacks of long magnet charging time and high field ramp loss. In principle, these drawbacks can be mitigated by managing the turn-to-turn contact resistivity (Rc). Evidently, the first step toward managing Rc is to establish a reliable method of accurate Rc measurement. In this paper, we present experimental Rc measurements for REBCO tapes as a function of mechanical load up to 144 MPa and load cycles up to 14. We find that Rc is in the range of 26–100 μΩ·cm2, and that it decreases with increasing pressure, and gradually increases with the number of load cycles. The results are discussed in the framework of Holm’s electric contact theory.

Effects of frequency on the intermittent failure phenomena of gold-plated electrical contact materials under fretting conditions

The typical characteristics of the change in contact resistance and tangential force with fretting cycles are compared with different fretting frequencies. Intermittent phenomena or short duration discontinuities during each fretting cycle are recorded explicitly. The instantaneous higher contact resistance values that appeared at the contact zones continuously corresponded to the distorted tangential force between contacts. Fretting frequency was determined as the crucial parameter that influenced the intermittent contact resistance. Subsequently, the contact failure mechanism of frictionally heated electrical contacts during high-frequency fretting was explained by introducing the electrical contact theory and thermoelastic instability model.

Electromechanical properties of knitted wearable sensors: part 1 – theory

This paper reports the development of a hexagon resistance model, based on the loop structure of a plain weft knitted fabric. This model is capable of describing the electromechanical properties of conductive knitted elastic fabrics. Based on the relationship between the resistance and the load on the fabric under biaxial extension, the equivalent resistance of the fabric was obtained by solving the circuit network equations. It was found that the circuit network is a multiple circuit parallel to the wale direction whereas it is in series along the course direction. And Holm’s electrical contact theory is used to calculate the relationship between the contact resistance and the contact force in an elastic fabric sensor. The contact load and deformation between two knitting loops are calculated using the classical knitted fabric mechanics model of Kawabata and Popper.

The influence of premolding load on the electrical behavior in the initial stage of electric current activated sintering of carbonyl iron powders

This paper reports the premolding load effect on the electrical behavior in the initial stage of electric current activated sintering of carbonyl iron powders. An electrical network model is put forward to estimate the uniformity of electric current in a powder compact subjected to different premolding loads in the initial stage. The improvement in current uniformity can be reflected from a simultaneous increase in the number N and the mass fraction θ of conductive particle chains in the compact. Both N and θ are found to follow a power law with the premolding load F for different exponent values. When θ is equal to 1, a critical load is reached, at which point the current flows through all particles during sintering. Using the results of the model and the electrical contact theory, it is also found that only an increased temperature of less than 20 K across the particle contacts. The distribution of temperature is uniform in particles. This is clearly different from the general acceptance that local high temperature is created at contact during electric current activated sintering. The neck formation and growth are thought to be mainly due to heat bonding and electromigration, of which effects on mass transport are pronouncedly enhanced by increasing the bulk temperature. Because of the poor current uniformity and relatively large power dissipation, a soft thermal breakdown is observed in the sample with high initial resistance. A reduction in premolding load may cause an increase in the initial electrical resistance of the compact. Owing to the unique voltage-current characteristic of electric current activated sintering, a higher initial resistance of compact means more thermal energy is involved, consequently producing a higher bulk temperature and getting a better quality of sintering. This also provides theoretical explanation for the experimental results from Inoue and Istomina.

Analysis of causes of the melting of contact devices in the current leads of rotors in TVF turbogenerators

Results of analysis of the melting of rotor leads in turbogenerators during the period from 2001 through 2005 are presented. A distribution of the number of damages sustained by generators with respect to type, time, type of studs, active and reactive loads at the time of failure, etc. is given. It is established on the basis of electric-contact theory that one of the basic causes of the melting of the contact components of rotor leads is misalignment of the head slots of the contact stud and its skewness in the threaded hole of the contact rod. Recommendations are given for prevention of misalignment of current leads.

Electrical Conduction Through Small Contact Spots

Earlier literature has reported that the voltage-temperature (V-T) relation for electrical contacts, and classical electrical contact theory in general, are invalid where the a-spots are on the order of nanometers. This paper reviews earlier literature dealing with the breakdown of the V-T relation and presents quantitative arguments to propose that this breakdown stems from the ballistic motion of electrons through nanometer-sized constrictions. Earlier literature also suggested that the breakdown of classical theory stems in part from thermal losses from a-spots to contaminant layers in an electrical interface. Through the use of a simple a-spot model, this paper shows that this cooling mechanism is not sufficiently important to affect the validity of the classical V-T relation and classical electrical contact theory in general

Improved physical understanding of intermittent failure in continuous monitoring method

Accelerated reliability tests are used to evaluate product life and to ensure a good fit with mission profile. Adequate detecting failure methods and criteria are fundamental to ensure the validity of the test results. In electronic interconnect reliability tests, several types of in-situ electrical continuity methods or manual resistance measurements with crack length analyses are used as failure indicator. Continuous monitoring at high sampling rate shows intermittent signals before permanent failure. In this paper we present a new test approach to improving physical understanding of these intermittent failures. Two different test benches are used to monitor BGA component solder joints under stress. Cross-section analysis, electrical circuit models and signal analysis are used to highlight the relationship between crack propagation and electrical continuity. Finally, basic electric contact theory is applied to explain resistance value fluctuations before permanent failure. The results suggest that high sampling rate in-situ monitoring methods have to be used in order to have an appropriate failure criterion and consequently be more representative of reliability results for electronic interconnects in the field.

Influence of The Sticking Effect on The Contact Resistance of a MEMS DC-Contact Switch

An improved model of the contact resistance in a MEMS DC-contact switch is presented and the sticking effect is included. In this model, the JKR theory is used to determine the sizes of contact spots and the electrical contact theory is used to estimate the contact resistance. The relationship between the contact resistance and the applied force has been investigated in different cases for a common Au-Au contact. The results suggest that the contact resistance is related to the applied force, the number of asperities, and the surface energies of contact materials. However, the height distribution of asperities has little influence on the contact resistance. The comparison between the improved model and the measurements that have been reported suggests the sticking contact model is more reasonable than the elastic contact model especially at low applied forces.

Effect of misalignment on electrical characteristics of ACF joints for flip chip on flex applications

The effect of misalignment on the electrical properties of anisotropic conductive film (ACF) joints is investigated in this work. It is found that along with the increase of misalignment, the connection resistance of ACF joints increases. When the misalignment in x-direction is less than 5 μm, the increase rate of connection resistance is quite large. Then, along with the severity of misalignment, the increase rate becomes smaller. Finally, when the misalignment is close to 20 μm, the increase rate rises again. The Holm's electric contact theory is used for understanding the connection resistance variation. On the other hand, with the increase of misalignment in x-direction, the insulation resistance between ACF joints decreases. If the misalignment exceeded 10 μm, the decrease is prominent for the Ni particle ACF joints. This phenomenon can be explained by the effect of dielectric damage of the epoxy. Computer programs are also developed to calculate the variation of the probability of open and shorting after misalignment and predicate the maximum misalignment tolerance. The results show that the open and shorting probability increase abruptly after misalignment. On the view of pad parameters, the open probability is mainly related to the pad area, while the pads gap is critical to the shorting probability. Large pads gap (small pad width) can reduce the shorting probability obviously. On the other hand, enlarging the pad area by increasing pad length decreases the open probability significantly. So comparing to square shape pad, rectangle shape pad can reduce the failure probability greatly.

Electrical contact resistance: properties of stationary interfaces

The paper reviews the dependence of electrical constriction resistance on the shape and dimensions of /spl alpha/-spots and on the magnitude of the mechanical contact load. The range of validity of the classical voltage-temperature relation for electrical contacts is also examined. The paper describes experimental evidence of breakdown of the classical electrical contact theory when /spl alpha/-spots become too small. One of the interesting and useful properties of relatively small /spl alpha/-spots is that they are subject to large surface stresses. These stresses induce /spl alpha/-spot growth.