Dielectric permittivity of geologic Materials at different water contents - Measurements with an impedance analyzer

Dielectric permittivity is an important parameter for all investigations based on electromagnetic waves (e.g. GPR and TDR measurements). In combination with the electric conductivity, it is crucial for the determination of the propagation velocity, the reflection coefficient and the decay of the electromagnetic wave. The dielectric permittivity depends on several factors like water content, mineralogy, grain size, and bulk density of the material. Our laboratory measurements of dielectric permittivity show quantitative relations between these parameters and that commonly used general algorithms for moisture detection bear significant inaccuracies (up to 200% error for clay substrates). Therefore, it is crucial to determine the permittivity for every specific application. This paper provides new algorithms for some most important substrate types, which can be used to recalibrate TDR-tools for specific applications. However, measurements of the dielectric permittivity are also frequency-dependent. In this study an impedance analyzer was used, which provides a frequency range between 10MHz and 1GHz. This is inside the most common range of applications like the TDR measurement method, which has a frequency range from 20KHz up to 20GHz. Ground penetrating radar measurements operate mostly in a frequency range from 40 to 900MHz.