Characterizing dispersion due to moisture using multi-pole Debye model
Abstract: Ground penetrating radar (GPR) is a nondestructive measurement technique that utilizes electromagnetic waves to locate targets beneath the surface. The speed of EM waves is determined by dielectric permittivity, which is often assumed to be constant within a homogeneous material. However, dielectric permittivities in real materials vary with frequency. This phenomenon, called dispersion, affects the interpretation of GPR signals. Dispersion becomes stronger with increasing moisture content in materials due to the dipolar nature of water molecules. The goal of this work is to isolate the dispersion caused by water from the dispersion inherent to material. We measure the complex permittivities of samples from a massive sulphide mine under both ambient and dry conditions. The measurements are fitted to a 2-pole and a 3-pole Debye model. Results show that dry samples can be fitted well with 2-pole model while the ambient samples require an additional pole. The relaxation time of the additional pole in ambient samples does not match to that of pure water and further experimentation with higher moisture content is needed.