Effective permittivity of porous media: a critical analysis of the complex refractive index model

Abstract

ABSTRACTThe availability of reliable constitutive models linking the bulk electric properties of porous media to their inner structure is a key requirement for useful quantitative applications of noninvasive methods. This study focuses on the use of dielectric measurements to monitor fluid saturation changes in porous materials. A number of empirical, semi‐empirical and theoretical relationships currently exists that link the bulk dielectric constant with volumetric water content. One such relationship, named complex refractive index model or Lichteneker‐Rother model has been extensively applied in recent years. Here we first analyse the characteristics of this Lichteneker‐Rother model by means of theoretical considerations. This theoretical analysis indicates that the Lichteneker‐Rother exponent is dependent upon the geometrical properties of the porous structure, as well as the permittivity contrast between the different phases. Pore‐scale modelling and experimental data further support this result. The parameter estimation robustness in presence of synthetic data error is also assessed. This demonstrates that Lichteneker‐Rother parameters cannot, in general, be independently identified on the basis of bulk dielectric constant versus moisture content data.