Electrical parameters of soils in the frequency range from 1 kHz to 1 GHz, using lumped-circuit methods

Authors

  • Ben K. Sternberg,

  • Tsylya M. Levitskaya


Abstract

For studying electrical properties of soil samples with various compositions and water contents, we applied a lumped-circuit approach. The extension of this method up to 1GHz was made possible by using a coaxial sample holder. The complex electrical parameters of soils, such as the relative permittivity equation image, conductivity equation image, and resistivity equation image, were obtained by measuring the magnitude Z and phase ϕ of the sample impedance equation image. The experimental setup is described in our previous paper [Levitskaya and Sternberg, 2000]. The relative real permittivity ε′ and imaginary permittivity (dielectric losses) ε″ for high-loss soils from Arizona decrease with frequency and increase with water content. Regression equations, derived for the relative permittivity ε′ versus water content at a given frequency, can be used to determine the water content in soil from ε′ data. The third-degree polynomial equations, which relate the relative permittivity to the volumetric soil moisture content, are different for various frequencies. The complex electrical resistivity components ρ′ and ρ″ reveal a time-dependent polarization process at frequencies above 1 MHz, which shifts to higher frequencies with increasing water content. The propagation parameters, such as attenuation constant α, phase velocity Vp, and penetration depth P, which we calculated from the electrical parameters, also depend on soil wetness. Our comparison of the electrical and propagation parameters for different soils shows that the high-loss soil samples from Avra Valley, Arizona, have higher values ε′ and ε″, higher attenuation constant α, and lower penetration depth P than the low-loss soils from Brookhaven, New York. For example, at 500 MHz, a high-loss soil (Avra Valley) with volumetric moisture content of ∼10%, exhibits an attenuation of 43 dB/m, whereas for a low-loss soil (Brookhaven) with the same wetness the attenuation constant is only 4 dB/m. We also note that very dry, clean sand in a sheltered “sand box,” which is a favorite medium for testing ground-penetrating radar (GPR), is usually not representative of natural conditions. Therefore, GPR data from such “sand box” experiments must be used with considerable caution because they yield unrealistically large penetration depths and unnatural target responses.

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