A method for calibrating a strip resonator used in measurements of the complex permittivity of moist soils and grounds

Abstract

A method for calibrating a microstrip microwave resonator used to measure the complex permittivity of moist soils and grounds is proposed. This method is based on the use of mixtures of a disperse solid substance and aqueous solutions of salts with known values of their complex permittivity. The resonator is composed of two segments of strip lines, the capacitive electromagnetic coupling between which occurs through a container with a moist soil sample. Sandy soil samples wetted by a sodium chloride solution were used as reference samples. The values of their complex permittivity were determined using the generalized refraction model and the reference data for the complex permittivity of a salt solution. A system of algebraic equations was set up, the solution to which, together with the formulas of the refraction model, allowed the complex permittivity of the test soil sample to be reconstructed from the measured values of the resonance frequency shifts and Q factor. The rms errors in measuring the real and imaginary parts of the complex permittivity, which varied over the ranges 4.79–11.03 and 0.39–3.15, were 0.21 and 0.03, respectively.