Measurements of the complex dielectric constant of sand and dust particles at 11 GHz

Measurements are reported of the refractive index (Δn ) and loss tangent (tan δ) of dust particles in a laboratory-simulated model of dust storms, carried out at 11 GHz utilizing a confocal microwave open-cavity resonator. Four samples were used, namely, sandy, silty, clayey silt, and clayey, for concentrations varying from 10^-4 to 4×10^-3 g/cm³. The particle-size distribution (PSD) of each sample was measured using the hydrometer technique. Dielectric-constant measurements were also conducted at bulk concentrations using the standing-wave technique for the dry samples and as a function of volumetric moisture content for up to 0.5 cm³/cm³. The complex dielectric constant of the dust particle material was evaluated by two approaches. In one the data for permittivities obtained over the whole range of measured concentrations were extrapolated to the particle densities of the samples. In the other a mixing formula was utilized for the determination of ε_s from permittivities measured at bulk concentrations