Measurement Of Dielectric Properties Of Solid Inhomogeneous Complex Media In The Frequency Domain

With the application of microwave nondestructive testing used in road works in recentyears, the research on dielectric properties of inhomogeneous complex media like rock andsand for road construction has become the focus. Inhomogeneous complex media for theresearch of dielectric measurement techniques provide an important branch. The dielectricproperties of inhomogeneous complex media are mainly influenced by the interfacialpolarization and the interfacial polarization always occurs in broadband. Hence, it is crucial toresearch on the dielectric measurement technology of solid inhomogeneous complex media indifferent frequency bands.This dissertation mainly introduces the dielectric permittivity measurement methods ofsolid inhomogeneous complex materials in different frequency bands. In LF band, thecapacitance method is used to design a new plate capacitor. In the capacitor, the measuredsamples are seen as the parallel lumped circuit of the equivalent capacitance and conductance.By measuring the admittance, the sample dielectric permittivity is obtained. With theimprovement of the structure and algorithm of traditional capacitors, the capacitormeasurement accuracy is improved. In RF band, according to the analysis of field distributionbetween the electrodes and the quasi-static field, a higher order function of admittancebetween the electrodes is established, and through calculating the zero order and higher orderBesar functions, the sample permittivity is obtained. The algorithm improves the measuringprecision of capacitor and the upper limit of measurement frequency, which makes themeasurement for the broadband dielectric spectroscopy of inhomogeneous media possible.In HF band, a micro-strip ring resonator and a parallel microstrip line both based onmicro-strip transmission line are presented. The microstrip ring is based on perturbationtheory. When microstrip ring closes to the sample to composite an equivalent dielectric model,the sample permittivity differences will affect the electric field distribution of microstrip ring,which will disturb the resonant frequency and quality factor of the microstrip ring. Inaccordance with the disturbance, the sample dielectric permittivity is obtained by calculation.Parallel microstrip line is based on phase. Through calculating the phase difference of microstrip line, the sample dielectric permittivity is obtained. Parallel microstrip line isdifferent from the traditional microstrip line, and the plate ground at the bottom layer ischanged to the strip line, same with the top layer. The structure not only keeps the originaltransmission mode of microstrip line, and the edge electric field intensity is increased, butimproves the resolution and the accuracy of measurement. Compared with the traditionalparallel lines, coaxial cable, waveguide and resonant cavity methods as well, the twoproposed microstrip line probes have low requirements for mechanical dimensions of sample,and are suitable for the measurement of solid materials.In the higher frequency range, the conductivity has little impact on dielectric permittivityof inhomogeneous complex media. Therefore, with different detection methods, the sandmoisture content, and the porosity of water saturated sandstones were measured, theexperimental results are verified by using the empirical formula. In LF and RF bands, used bythe plate capacitor, the dielectric spectra of the various rocks such as oil and gas bearing rocks,water saturated rock, and shaly rock as the rock subgrade are measured and discussed, themultiple relaxation processes and the abnormal rises in relaxation intensity at low frequenciesare analyzed. The dielectric spectra of two-phase and three-phase flat capacitor materials to beused to simulate of pavement structure are analytically calculated and experimentallymeasured, and the measurement results are confirmed by the calculated values.