Abstract
Although literature on the calculation based on the symmetrical effective medium approximation (EMA) theory by changing the parameters is vast, an overall discussion taking into account the EMA theory is required in order to explain the dielectric properties of the composites, the temperature dependence of them, for example. Changes of dielectric properties and the temperature dependence of them of the composites made of carbon black and polyethylene below the percolation threshold (pc) for the volume fraction of carbon black have been discussed based on the EMA theory. The composite is satisfied with the universal law of conductivity above pc whereas it gives the critical exponent of s=1 for dielectric constant below pc. The rate of the decrement of both % changes of dielectric constant and dielectric loss factor for temperature becomes larger with more the volume fraction below pc. By incorporating the effect of thermal expansion into the EMA theory, the temperature dependence of dielectric properties is successfully explained.
