Volume 79, Number 5, September 2007
Article Number 54001
Number of page(s) 5
Section Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics, and Fluid Dynamics
Published online 27 July 2007
EPL, 79 (2007) 54001
DOI: 10.1209/0295-5075/79/54001

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

S. Dorbolo1, A. Merlen2, M. Creyssels2, N. Vandewalle1, B. Castaing2 and E. Falcon3

1  GRASP-Photopôle, Physics Department, University of Liège - B-4000 Liège, Belgium
2  Laboratoire de Physique, Ecole Normale Supérieure de Lyon - 46 allée d'Italie, 69 007 Lyon, France
3  Matière et Systèmes Complexes, Université Paris-Diderot - Paris 7, CNRS - Paris, France

received 1 June 2007; accepted in final form 5 July 2007; published September 2007
published online 27 July 2007

A DC electrical current is injected through a chain of metallic beads. The electrical resistance of each bead-bead contacts is 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.

45.70.-n - Granular systems.
72.80.-r - Conductivity of specific materials.
81.05.Rm - Porous materials; granular materials.

© Europhysics Letters Association 2007