Low frequency dielectric dispersion and microwave permittivities of Indian granites

Abstract

The complex dielectric permittivity ɛ*(ω) = ɛ<i>'- j</i>ɛ<i>" </i>of 20 Indian granite samples from various localities in India were studied in the low frequency range 0.10-100 kHz and also at microwave frequency, i.e. 10.1 GHz at room temperature. All the studied dry samples showed the dielectric dispersion in the low frequency range. These are characterized by principal relaxation time with Cole-Cole dielectric dispersion model. The values of static dielectric constant ɛ_o, high frequency limiting dielectric constant ɛ_∞, distribution parameter α<i>, </i>and relaxation time τ of these samples were determined from their Cole-Cole plots. The frequency dependent ac conductivity of these granite samples were also determined and discussed. The real part of dielectric constant ɛ<i>' </i>of dry granite samples at 10.1 GHz was found to be in the range 4.5-8.3. Clear convincing correlation was observed between the microwave frequency ɛ<i>'</i> values with the samples bulk density. The plot of ɛ<i>'</i> values versus bulk density of the studied granite samples were represented by two straight lines of different slopes. The density reduced microwave permittivity values ɛ<i>'</i>_dr of granite samples were found to be in the range 1.81-1.99. For all the studied granite samples dielectric loss ɛ<i>"</i> was found to be less than 0.5 at microwave frequency. Microwave permittivities of porous samples with water saturation were also measured and these values were compared with the permittivity values computed from the dielectric mixing equation, complex refractive index model and the self-similar model using the microwave permittivities of dry samples and water.