Determination Of Complex Dielectric Permittivity Research Articles

Polarization method for determination and visualization of complex permittivity in remote sensing issues

When using remote radiophysical methods in problems of monitoring the environment, the central place belongs to solving problems of determining its electrophysical characteristics, i.e. dielectric permittivity e, conductivity c (complex permittivity ek). The complex dielectric permittivity e, determined in one way or another, serves as the basis for determining the physical characteristics of the medium under study: temperature, humidity, salinity, hardness, etc. The method for remote determination of complex dielectric permittivity is proposed based on relative amplitude-phase relations in the radar receiver channels (orthogonal in polarization) (we call it determination of the polarization phasor). Knowledge of the polarization phasor makes it possible to determine uniquely both the permittivity and the conductivity of the surface under investigation. The latter is presented in the form of a series of universal graphs which allow one to directly interpret the physical characteristics of surfaces. It shows how the polarization phasor is placed on the KLL-sphere. In addition, the trajectory of the phaser on this sphere is investigated in the case when the physical characteristics of the investigated surface change. The random nature of local changes in the electrophysical properties of the surface under study leads to random fluctuations of the polarization phasor. The paper contains a two-dimensional density distribution of the permittivity and conductivity, as well as the corresponding one-dimensional densities. A graphic illustration of the relations obtained is given.

Measurement of Complex Dielectric Permittivity of Quartz Systems

The article describes the problem of the experimental determination of complex dielectric permittivity for natural, activated, and modified quartz systems. The results of determination of specific surface, complex dielectric permittivity, sands porosity are presented in this article. The authors obtained the empirical equation of complex dielectric permittivity calculation for natural, activated, and modified quartz sands, taking into account the effect of moisture, specific surface, porosity, impurities content into consideration. The modification of the sand surface by means of mechanical beneficiation and ultrasonic treatment leads to reduction of complex dielectric permittivity and specific surface, thus contributing to the increase of the active centers quantity on the sands surface. The modification of the sand surface by polyvinyl alcohol aqueous solution leads to increase of complex dielectric permittivity. Polyvinyl alcohol aqueous solution modification envisages the creation of new active centers by oligomers inoculation to the surface and blocking the clay component and authigenous film ingredients. Among the considered methods, ultrasonic treatment in aqueous solution and mechanical beneficiation are the most efficient and technologically acceptable ways of activation.

Quantitative GPR inspection of quasi-homogeneous ground layers

This work covers methods of GPR monitoring of constructions that are quasi-homogeneous ground layers. The monitoring methods include the determination of complex dielectric permittivity and moisture of the construction layers of highways and railways. In order to obtain quantitative values of these parameters the GPR method is calibrated via the measurement of these quantities using the resonance method at frequencies close to the central frequency of the microwave radiation used.

Magnetic Properties of Diluted Ferrites Near Ferromagnetic Resonance in Millimeter Waves

Magnetic permeability and dielectric permittivity characteristics of barium and strontium ferrite materials in broad band millimeter wave frequency range have been obtained. The measurements have been done using free-space quasi-optical millimeter wave spectrometer in tunable magnetic field up to 8.5 kOe. A set of backward wave oscillators have been used as sources of high power coherent radiation tunable in 34 -120 GHz frequency range. Magneto-optical approach has been successfully employed for the separation of dielectric and magnetic effects in ferrites and simultaneous determination of complex dielectric permittivity and magnetic permeability of materials. Zone of strong absorption in the transmittance through the samples due to ferromagnetic resonance in millimeter waves has been observed. Shift of the ferromagnetic resonance to higher frequencies and broadening of the zone of strong absorption in transverse magnetic field have been observed. It has been shown that a variation in the chemical composition of ferrites leads to a change in the magnetic properties as well as absorption of materials in the millimeter wave range.

Accuracy of frequency domain analysis scenarios for the determination of complex dielectric permittivity

Frequency domain analysis of time domain reflectometry waveforms has been shown to be useful for more accurate water content determination, water content determination in saline soils, and determination of such difficult to measure soil properties as specific surface area and soil solution conductivity. Earlier frequency domain analysis approaches to determine frequency‐dependent dielectric properties of soils have used a variety of methods. In this paper, these methods for the determination of dielectric permittivity were compared using the Shuffled Complex Evolution Metropolis algorithm (SCEM‐UA). SCEM‐UA is a global optimization method that allows the simultaneous determination of optimal Debye parameters, which describe the dielectric permittivity as a function of frequency, and their confidence intervals. The analysis of numerically generated measurements with added instrumental noise showed that analysis of network analyzer measurements in the frequency domain potentially has the highest accuracy for determination of dielectric permittivity. Furthermore, the analysis of time domain reflectometry waveforms in the time domain was found to be more accurate than analysis of these waveforms in the frequency domain. Analysis of real network analyzer measurements in the time and frequency domain showed that both analysis scenarios allowed reasonably accurate estimates of the Debye parameters with the SCEM‐UA algorithm, even when the true value of a parameter falls beyond the limits of the frequency bandwidth. However, frequency domain analysis of ethanol measurements showed that results were susceptible to model errors caused by nonideal probe behavior. These errors were larger for three‐wire probes than for seven‐wire probes. This study shows that the accuracy of the dielectric permittivity determination can be improved by reducing the model error. This can be achieved by the use of more accurate models, such as multiscatter functions, and by using more advanced probes, such as coaxial cells. The results also imply that future research on dielectric properties of soils should focus more on the use of network analyzers instead of cable testers, since model errors are more obvious in the frequency domain. The SCEM‐UA algorithm proved to be a valuable tool in frequency domain analysis because reported problems with parameter identification and initialization of the optimization are circumvented with this global optimization algorithm.

Determination of Complex Dielectric Permittivity of Loss Materials at Microwave Frequencies

The method of determination of complex dielectric permIttIvIty of loss materials at microwave frequencies (X-band) using measured amplitudes of reflection and transmission coefficients and numerical calculations is developed. Different numerical methods namely graphical, bisection (halving), newton, and secant, are applied in order to determine the permittivity of cement-based materials. Simulation time and errors of these methods are compared. It is shown that the fastest and most accurate method is the bisection (halving) method because it is a global method.

Application of the method of brather for the determination of complex dielectric permittivity from measurements of isothermal polarization current

AbstractSome years ago, Brather proposed a method for calculation of the real and imaginary parts of the complex dielectric permittivity starting from measurements of isothermal polarization current. This method shows some advantages over the Hamon method, which is normally used. Both methods are applied in this work to the β relaxation of poly(butyl methacrylate). It is concluded that, with the usual accuracy of measurement, a combination of the two methods is advisable; Hamon's method is taken to be a first approximation to that of Brather. Results following the two procedures are compared, and their respective advantages and disadvantages are discussed.

Measurement of Complex Permittivity of Liquids at Frequencies from 5 to 40 GHz

Computer analysis of reflected power profiles allows accurate determination of complex dielectric permittivity of low, medium, and high permittivity liquids by one single method if nonideal plunger properties are taken into account. For low loss measurements account is taken of the losses in the waveguide walls. For medium and high permittivity liquids, dumbell plunger design leads to important errors due to higher mode excitation and propagation.