Understanding the Branly effect

Abstract

At the end of the nineteenth century \'{E}douard Branly discovered that the electrical resistance of a granular metallic conductor could drop by several orders of magnitude when excited by the electromagnetic field emitted by an electrical spark. Despite the fact that this effect has been used to detect radio waves in the early times of wireless telegraphy and more recently studied in the field of granular materials, no satisfactory explanation of the physical origin of the effect has been given yet. In this contribution we propose to relate the Branly effect to the induced tunnelling effect first described by Fran\c{c}ois Bardou and Dominique Boos\'{e}.