Electrical conductivity in granular media and Branly's coherer: A simple experiment

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 illustrates an old problem, the explanation of Branly's coherer effect - a radio wave detector used for the first wireless radio transmission, and based on the sensitivity of the metal fillings conductivity to an electromagnetic wave.

arXiv commentaccepted for publication in American Journal of Physics (to be published between February 2005 and June 2005)

References in corpus (3)

• Nonlinear electrical conductivity in a 1D granular medium
• "Turbulent" electrical transport in Copper powders
• Breakdown patterns in Branly's coheror

Cited by in corpus (5)

• On equivalent resistance of electrical circuits
• Some aspects of electrical conduction in granular systems of various dimensions
• Effects of electromagnetic waves on the electrical properties of contacts between grains
• Bipolar electrical switching in metal-metal contacts
• Betweenness Centrality as Predictor for Forces in Granular Packings