Effects of electromagnetic waves on the electrical properties of contacts between grains

TL;DR

This study investigates how electromagnetic waves influence the electrical resistance of metallic bead contacts, revealing that sparks can reduce resistance and induce microweldings, affecting the medium's conductivity.

Contribution

It demonstrates that electromagnetic sparks can alter contact resistances and induce microweldings in granular metals, explaining their sensitivity to electromagnetic disturbances.

Findings

Electromagnetic sparks lower resistance in resistive contacts.

High current sparks induce microweldings between beads.

Resistance distribution shifts from log-normal to Gaussian with current.

Abstract

A DC electrical current is injected through a chain of metallic beads. The electrical resistances of each bead-bead contacts are measured. At low current, the distribution of these resistances is large and log-normal. At high enough current, the resistance distribution becomes sharp and Gaussian due to the creation of microweldings between some beads. The action of nearby electromagnetic waves (sparks) on the electrical conductivity of the chain is also studied. The spark effect is to lower the resistance values of the more resistive contacts, the best conductive ones remaining unaffected by the spark production. The spark is able to induce through the chain a current enough to create microweldings between some beads. This explains why the electrical resistance of a granular medium is so sensitive to the electromagnetic waves produced in its vicinity.