Observations on the Density Dependence of Dielectric Properties of Particulate Materials

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Abstract
Based on information in the published literature, the analysis reported herein indicates that linear relationships can be expected between functions of the dielectric properties of particulate materials and their densities. The linearity of the square root of the dielectric constant of the air-particle mixture with mixture density and the linearity of the cube root with density are consistent with published mixture formulae that imply the additivity of the volume-weighted square roots and cube roots, respectively, of the dielectric constants of the constituents of the mixture. Although both relationships should be valid for most practical applications, the cubic relationship predicted the dielectric constants of pulverized coal, whole-wheat flour, and whole-kernel wheat more accurately than did the quadratic relationship. Accuracy of the predictions decreased with increasing particle size. A linear relationship was also demonstrated between √ϵ″r + e and density, where √″r represents the dielectric loss factor, and e is a constant that depends on the particulate material.