Mechanism of electromagnetic interference shielding conductive rubber

Conduction mechanism

Conductive rubber is a composite conductive polymer material, and its conductive mechanism mainly includes macroscopic percolation theory (conductive pathway mechanism), microscopic quantum mechanical tunneling effect and microscopic quantum mechanical field emission effect.

(1) Conductive path mechanism When the amount of conductive filler in rubber increases to a certain critical value, a more complete conductive path network is formed inside the rubber, and the resistivity of the rubber will drop sharply. In the relationship between the resistivity and the amount of conductive filler, there is a narrow mutation region, in which any small change in the amount of conductive filler will lead to a significant change in the rubber resistivity, this phenomenon is called the percolation phenomenon, and the critical amount of conductive filler is usually called the percolation value.

(2) Tunnel effect When the amount of conductive filler is small, the distance between conductive particles in the rubber matrix is large, and the conductive path network has not been formed in the microstructure of the composite material, at this time there may still be conductive phenomenon, which is caused by the migration of thermal vibration electrons between conductive particles, and the conductive current is an exponential function of the width of the conductive particle gap. The tunneling effect almost only occurs between conductive particles that are close to each other, and there is no current conduction between conductive particles with large gaps.

(3) Field emission effect
When the amount of conductive filler is small and the distance between conductive particles inside the rubber matrix is large, if the electric field inside the conductive particles is strong, the electrons will have a great chance to leap over the polymer interface barrier, jump to the adjacent conductive particles, generate field emission current, and form a conductive network.

Conductive pathway mechanism, tunnel effect and field emission effect exist in conductive rubber at the same time, which may be dominated by one or two mechanisms under different conditions. When the conductive filler is above the critical amount, the conductive path is the main conduction mode, that is, the conductive path mechanism is the main one. When the amount of conductive filler is small or the applied voltage is small, the gap of isolated electrons or their aggregates is large and can not participate in conduction, and the excited electrons of thermal vibration transition and form a large tunnel current, which is mainly tunnel effect. When the amount of filler is small and the internal electric field between particles is strong, the matrix layer is equivalent to the internal distribution capacitance, and the field emission effect is more significant.