Electrical conductivity in granular media and
Branly's coherer: A simple experiment
E. Falcon and B. Castaing
Laboratoire de Physique, École
Normale Supérieure de Lyon,
46 allée d'Italie, 69364 Lyon cedex 07,
France
Reference:
American Journal of Physics
73, 302 - 307 (2005)
Abstract:
We show how a simple laboratory experiment can
illustrate certain electrical transport properties of metallic granular
media. At a low critical imposed voltage, a transition from an
insulating to a conductive state is observed. This transition comes
from an electro-thermal coupling in the vicinity of the microcontacts
between grains where microwelding occurs. Our apparatus allows us to
obtain an implicit determination of the microcontact temperature, which
is analogous to the use of a resistive thermometer. The experiment also
helps us explain an old problem, Branly's coherer effect,
which was used as a radio wave detector for the first wireless radio
transmission, and is based on the sensitivity of the conductivity of
metal filings to
an electromagnetic wave.
PDF file: here
(188 Ko)
See also others works by our group on
Electrical Transport in Granular Media (DC Branly
Effect, intermittency, fluctuations, ageing, Branly Prize)