Measurement and analysis of a model dual-conductivity medium using a generalised effective-medium theory

The construction and the measurement of the conductivity of a series of two dimensional dual media is described. The conductivity results are shown to obey both the defining relationship for dual media and a recently proposed general effective-media equation, with two morphology parameters, throughout the entire (0-100%) composition range. The two parameters, a critical volume fraction f c and an exponent t, are shown to be related to the morphology of the media and in particular the effective demagnetisation coefficients of the 'grain structure' of the two components. The relationship between these and previous experimental results is also discussed.