Electrical resistance at rough surfaces in contact

Electrical Contact Resistance of Fractal Rough Surfaces 

The presence of roughness at electrical contacts tends to involve contacting asperities across multiple scales. Depending on the nature of the contact between asperities on opposing surfaces, different conduction mechanisms take place. This is shown in the figure here.

From ohmic resistance at standard Holm contacts to electron tunneling through oxide layers and voids, the multiple contact resistance mechanisms are considered here. The abstract of a recent paper on this topic, published in the Journal of Engineering Mechanics can be found below.

Zhai, Chongpu, et al. "Stress-dependent electrical contact resistance at fractal rough surfaces." Journal of Engineering Mechanics 143.3 (2015): B4015001.

https://doi.org/10.1061/(ASCE)EM.1943-7889.0000967

Abstract

The electrical contact resistance between contacting rough surfaces was studied under various compressive stresses. The samples considered here were isotropically roughened aluminium disks with upper and lower surfaces modified through polishing and sand blasting using different sized glass beads. Fractal geometry and roughness descriptors, including root mean square values of roughness and slope, were used to describe the topography of sample surfaces, based on the digitized profiles obtained from interferometry-based profilometry. The electrical contact resistances at the interfaces were obtained by applying a controlled current and measuring the resulting voltage, through the following scenarios: (1) over time for various applied testing currents, the resistance relaxation curves were measured at constant loads; (2) through voltage-current characteristics by means of a logarithmic sweeping current, the influence of the testing current on the electrical response of contacting rough surfaces was evaluated; and (3) for a given testing current, the electrical resistance through interfaces of different surface structures was measured under increasing compressive stresses. The experimental results show that the measured resistance depends closely on the measurement time, testing current, surface topology, and mechanical loading. At stresses from 0.03 to 1.18 MPa, the electrical resistance as a function of applied normal stress is found to follow a power law relation, the exponent of which is closely linked to the surface topology.