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, Physics Department,
Université de Liège, B-4000 Liège, Belgium
2 Laboratoire de Physique, Ecole Normale Supérieure
de Lyon, CNRS, 69 007 Lyon, France
3 MSC, Université Paris Diderot - Paris 7, CNRS, 75
013 Paris, France
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.