Measurement Of Complex Dielectric Constant Research Articles

Analytical transmission line model for complex dielectric constant measurement of thin substrates using T‐resonator method

This work presents a new analytical transmission line model for microstrip T-resonator dielectric constant measurement method in order to simplify the extraction of the complex dielectric permittivity of the substrate and increase its accuracy. The proposed new formula, which is based on the T-matrix equivalent circuit of the structure, is only dependent on the propagation and attenuation constants of the stub line. Two new formulas to determine the end effect of open-ended stub and the propagation constant parameters are also presented. As an example, a T-resonator is implemented on a 31 mil RO4003C substrate, and it is simulated and measured S-parameter results in the range of 1 MHz–8 GHz are used to calculate a complex dielectric constant of the substrate at each resonance frequency. A full-wave simulation is also used to confirm the accuracy of the proposed model. The comparison between the simulated and the measured S-parameters demonstrates a relative error of <1% over the frequency range.

Modern possibilities of diagnosis of cell’s membrane-receptor complex dysfunction in the acute period of ischemic stroke

During the development of the acute phase of ischemic stroke (IS), the cytoplasmic membranes of cells and receptor complex are primarily damaged. Structural changes in brain tissue are accompanied by violations of its electric physical characteristics, which are quite qualitatively possible to record using microwave dielectrometry.The aim of the study was to learn the features of changes in the dielectric properties of peripheral blood erythrocytes of patients with IS during in vitro exposure to adrenergic drugs depending on the severity of the disease to optimize diagnosis.Material and methods of research. Measurements of complex dielectric constant (CDC) were performed by EHF dielectrometry at a fixed frequency of 39.5 × 109 Hz, which is in the region of γ-dispersion. The work was based on the materials of a comprehensive examination of 350 patients with the first in the life of IS on the 1st, 10th and 21st day of the disease.The severity of the condition and the degree of neurological deficit were determined using the stroke scale of the US National Institutes of Health (NIHSS) in the first hours of the disease, in the dynamics of treatment on the 10th and 21st day. There were 2 clinical groups: 1st (n = 183) – patients in a state of moderate severity (mean score on the NIHSS scale 11.74±0.33); 2nd (n = 167) – patients with severe IS (average score on the NIHSS scale 24.06±0.29).Results. In the control group, there was a significant decrease after exposure to adrenaline solution. The reaction to adrenaline in patients with IS was almost absent. It indicates a decreasing of erythrocytes β-adrenoceptors (β-ARs) sensitivity to stimulants due to their desensitisation. In patients with moderate severity, erythrocytes are more reactive than in patients with more severe IS.Conclusions. The deviation of CDC of erythrocytes induced by adrenergic drugs in vitro is a manifestation of a specific response of cells to biologically active substances and depends on the functional state of the sympathoadrenal system

Design of Substrate-Integrated Waveguide Loading Multiple Complementary Open Resonant Rings (CSRRs) for Dielectric Constant Measurement.

In order to solve the low-sensitivity problem of the dielectric constant with the resonant cavity method, a sensor based on a substrate-integrated waveguide structure loaded with a multi-complementary open resonant ring is proposed. With the enhanced resonance characteristics of the sensor, this design realized the measurement of complex dielectric constants in a wide range. The frequency selectivity of the sensor is improved by the high-quality factor of the substrate-integrated waveguide. By loading three complementary resonant rings with different opening directions in the ground plane, a deeper notch and better out-of-band suppression are achieved. The effect of the complex dielectric constant on both resonant frequency and quality factor is discussed by calculating the material under test with a known dielectric constant. Simulation and experimental results show that a resonance frequency offset of 102 MHz for the per unit dielectric constant is achieved. A wide frequency offset is the prerequisite for accurate measurement. The measurement results of four plates match well with the standard values, with a relative error of the real part of the dielectric constant of less than 2% and an error of less than 0.0099 for the imaginary part.

Dielectric and Emissive Properties of Sorghum (Jowar) Vegetation at C-Band Microwave Frequency

Abstract Microwave interaction with earth resources like soil and vegetation provides useful information for remote sensing techniques. Such interaction is mainly governed by a complex dielectric property of target material. This paper reports on laboratory measurements of complex dielectric constant of sorghum vegetation (leaves) at room temperature (30°C), at C-Band microwave frequency. Von Hippel (shorted waveguide) method is used to conduct the measurements. The measurements were performed for freshly cut sorghum leaves as a function of moisture content by using automated C-Band microwave bench set up with movable reflector. The least square fitting technique is used to calculate dielectric constant (e'), dielectric loss (e'') and errors in their measurements. Emissivity and radiometric brightness temperature is estimated from measured dielectric properties at different angle of incidence for dry and moist sorghum leaves using Fresnel equations. This study is useful for interpretation of microwave remote sensing of vegetation and applications specifically in agriculture

DIAGNOSTIC FEATURES OF DYSFUNCTION IN CYTOKINE AND SYMPATHOADRENAL SYSTEMS WITH ISCHEMIC STROKE

The aim: Was a comprehensive study of the changes in features like structural and functional parameters of brain tissue, cytokine profile and β-adrenoceptor in the acute period of ischemic stroke (IS) to optimise diagnosis and treatment. The study was conducted at the Department of Neurosurgery and Neurology at the Medical Institute of Sumy State University. Materials and methods: Measurements of complex dielectric constant (CDC) were performed by EHF dielectrometry. Determination of plasma levels of interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α) was performed by solid-phase enzyme-linked immunosorbent assay. The work was based on the materials of a comprehensive examination of 350 patients with the first in the life of IS on the 1st, 10th and 21st day of the disease. Results: Cerebral hypoxia leads to a significant increase in the CDC of erythrocyte membranes (about 15 %), which may lead to a rise in the volume fraction of water in cell suspensions due to damage of their membrane-receptor complex (MRC). The revealed connections between changes of CDC of patients with IS and decrease insensitivity of their MRC to adrenergic drugs testify in favour of damaging action of hypoxia. An imbalance in the cytokine system and their relationship to the sympathoadrenal system has been identified. Conclusions: There is a strong association of mechanisms that damage the MRC of cells during acute cerebral ischemia with functional changes in both the sympathoadrenal and cytokine systems. Identified links in the pathogenesis of IS should be used for early diagnosis of the disease.

Error reduction processes using multiple measurements and numerical analysis for complex dielectric constant measurement with monostatic horn antenna

To measure the complex dielectric constant of a material sample accurately by using the free-space reflection method using a monostatic horn antenna in the W-band, the authors of this paper have developed two processes to reduce errors and improve measurement accuracy. One of the improvement processes reduces errors caused by reflected millimeter-waves from surrounding objects. The process is carried out by averaging the reflection coefficients measured at multiple distances between the aperture of the antenna and the surface of the sample. The other improvement process reduces errors caused by the difference between the positions of the reference plane and the sample surface using numerical analysis. This paper presents overviews of our measurement setup for the complex dielectric constant and explains the two processes developed to reduce the measurement errors. The effectiveness of the developed processes is validated by measuring the complex dielectric constants of plastic plates. The result proves that the measurement errors can be reduced, and the complex dielectric constants of lossy plastic material can be measured accurately using the developed processes.

English

This study presents experimental measurements of complex dielectric constant at C-band microwave frequency of dry and moist saline soils collected from Dandi (Dist. Navsari) site of Gujarat state (India). An automated microwave set-up tuned at 5.3 GHz frequency is used for this purpose. Measured values of dielectric constant are then used to estimate the scattering coefficient by using perturbation model. Our results indicate relatively lower rate of increase in e' and order of magnitude higher values of e'' for these saline soils when their gravimetric MC is changed from 10 to 30% than that reported for non-saline soils by earlier researchers. Further, at constant value of MC, scattering coefficient of soil sample also increases with increase in the incident angle for vertical polarization, and this increase continues up to angles between 60o to 70o, at which it reaches maximum value and beyond this, it decreases sharply. Further, for vertical and horizontal polarizations, at constant value of incident angle, our results indicate relatively lower rate of increase in scattering coefficient values for saline soils than reported earlier for non-saline soils when gravimetric MC is changed from 10 to 20%. This data is very useful in understanding dielectric behaviour of saline soils and also for designing the active sensors for these soils.

Dependence of Salt in Water-in-Crude-Oil Emulsion System

A cylindrical-shape sample cell was prepared to investigate the dependence of salt amounts in a water-in-crude oil emulsion system by measuring the dielectric properties in the frequency range from 10 2 Hz to 10 7 Hz with an impedance analyzer. High-sensitivity complex dielectric constant measurements were obtained after calibration with several fluids having known dielectric constants. From complex dielectric spectra, we observed two regions for frequency characteristics: conduction relaxation in the low-frequency region due to diusion by charge transport caused by impurities such as resins and asphaltenes in the continuous phase, and the dielectric-relaxation mechanism in the high-frequency region due to the modified Debye type where the relaxation time was in linear proportion to the salt content in the disperse phase of the water-in-crude oil emulsion system.

Dielectric Characterisation of Plastics for Microwave Oven Applications

The materials used in microwave oven cavities must have specific dielectric properties in order to maintain the efficiency of the food heating. Plastics, by their mechanical and chemical properties and low cost, are one of those potential materials. In this study, we present the results of the measurements of complex dielectric constant, ´´ ´ * e e e í − = , in the microwave frequency region, on different plastics: polyoxymethylene (POM), polypropylene (PP) and polybutylene terephtalate (PBT), using the cavity resonant method. We measure the shift in the resonant frequency of the cavity, Df, caused by the insertion of the sample, which can be related to the real part of the complex permitivitty, e´, while the change in the inverse of the quality factor of the cavity, D(1/Q), gives the imaginary part, e´´. The relations are simple when we consider only the first order perturbation in the electric field caused by the sample.

The correlation of the complex dielectric constant and blood glucose at low frequency

A new needle-type sample cell was designed and produced to investigate the correlation between blood glucose and electrical parameters using an impedance analyzer. The characteristics of the measurement cells were optimized to give high sensitivity. High sensitivity complex dielectric constant measurements were obtained by calibration with several known fluids. It was observed that the values of the real ( ε′) and the imaginary ( ε″) dielectric constant increase with decreasing glucose contents in the water/glucose system, and that the value of ε′ in hamster tail changes according to the variation in blood glucose. It is likely that there is a correlation between blood glucose and the value of ε′, the electrical parameter.

Interlayer electrodynamics of Bi 2Sr 2CaCu 2O y from the c-axis complex dielectric constant measurements

The c-axis dielectric function ( ϵ c = ϵ 1 c +i ϵ 2 c ) measurement for the heavily underdoped Bi 2Sr 2Y 0.2Ca 0.8Cu 2O y (BSCYCO) was performed to study the dependence of the c-axis conductivity σ 1 c and the c-axis penetration depth λ c on the hole doping. We found that the behaviors of σ 1 c ( T) of the heavily underdoped BSCYCO qualitatively agreed with that of Gaifullin et al. [Phys. Rev. Lett. 83 (1999) 3928]. Comparing with our previous results for the slightly underdoped Bi 2Sr 2CaCu 2O y (BSCCO) [J. Low Temp. Phys. 117 (1999) 1241], we concluded that a large increase of σ 1 c ( T) below ∼0.9 T c for the slightly underdoped BSCCO had not an extrinsic but intrinsic origin, and that the behavior of σ 1 c ( T) strongly depended on the hole concentrations.

Novel Characterization Method of Ions in Liquid Crystal Materials by Complex Dielectric Constant Measurements

The frequency dependence of the complex dielectric constant of liquid crystal materials doped with tetra-n-butylammonium iodide (TBAI) is investigated in the low-frequency region, and the experimental results are analyzed in terms of space charge polarization. The contribution from an electric double layer is also taken into consideration in the analysis. By means of curve fitting utilizing theoretical expressions of the space charge polarization, five sets of diffusion coefficient and density values are obtained for mobile ions. It is confirmed by experiments on the temperature dependence that five kinds of ions follow Walden's rule, and verified from the viewpoint of ion radii that two of the five kinds of ions are TBA+ and I-. The frequency-dependent dielectric properties, which are characteristic of the behaviors of ions, can be well explained by this study and the analytical method introduced here is considered to be powerful for the evaluation of the attributes of mobile ions.

Complex dielectric constant measurement of samples of various cross sections using a microwave impedance bridge

A microwave impedance bridge covering from 8.2 to 12.4 GHz used for measuring complex dielectric constants over a wide temperature range is described. This apparatus is suited for materials formed into solid posts having different cross sections. The effective diameters for use in the analysis of circular, elliptical, or rectangular cross-section posts are presented. The effective diameters are applied to determine the complex dielectric constant of rectangular-shaped conducting polymer film. The frequency and temperature dependence of the dielectric constant and conductivity are presented, and compared with those obtained using a microwave cavity perturbation technique at 6.5 GHz. The bridge results are well suited for independent determination of the depolarization factor of a rectangular post for use in analysis of results of the cavity perturbation method.

Study of conducting polypyrrole films in the microwave region

Dielectric properties of the electrochemically synthesised polymer polypyrrole with a wide range of doping levels are presented. Methods for determining the complex dielectric constant in the microwave regime are discussed. The variation of the complex dielectric constant as a function of polymer dopant concentration at room temperature using cylindrical and rectangular cavity perturbation methods at frequencies of 2.45 GHz and 10 GHz is presented. Measurements indicate that the real and imaginary parts of the dielectric constant increase in magnitude with increasing polymer doping level. Complex dielectric constant measurements were continued on semiconducting polypyrrole films with a dc conductivity range of 1×10 −3−5×10 −2 S/cm for the temperature range 90K–300K. The real part ε′ of the complex dielectric constant increased slightly with increase of temperature whereas the imaginary part ε″ increased significantly with temperature. The rate of change of the dielectric loss increased with temperature and the magnitude of the loss at a given temperature increased with increasing polymer doping levels. Reflection, transmission and absorption behaviour of polypyrrole films with dc conductivities ranging from 0.001 S/cm to 50 S/cm are also presented. Results indicate that conductivity of the doped polypyrrole films have a significant effect on transmission, reflection and absorption of microwaves. Samples with low conductivity (low dopant concentration) exhibited high transmission whereas highly conducting films were reflective. Significant absorption of microwave radiation was only observed for samples of intermediate conductivity. Solutions by theoretical methods were in good agreement with the experimentally measured results from the polypyrrole films and hence confirm the dependability of the dielectric measurement method used.

Accurate variational analysis for measurement of complex dielectric constant of the sample rod inserted in a cavity

This paper derives the Lindell formula based on the generalized variational principle. For the complex dielectric constant measurement of a small lossy dielectric rod with Rayleigh-Ritz method, an accurate variational analysis is given. The concept of complex frequency\(\tilde \omega \) is introduced in general, and the stability of the solution is discussed. Comparing with the result of perturbation method, it is concluded that the deviation, of perturbation algorithm should be taken into consideration.

The accurate variational analysis for the measurement of the complex dielectric constant of a sample rod inserted in a cavity

AbstractThis article derives a Lindell formulation based on a generalized variational principle. A complex dielectric constant measurement of a small‐loss dielectric rod using the Rayleigh—Ritz method gives accurate variational analysis. The concept of complex frequency ω is introduced in general, and the stability of the solution is discussed. When compared with the results of perturbation, it is concluded that the deviation of the algorithm is worthy of more attention.

Nontraditional antennas in complex dielectric-constant measurement

Nontraditional antennas in complex dielectric-constant measurement

Microwave measurement of complex dielectric constant

In this paper, the formula given by S. Roberts and A. Von Hippel (1946) has been extended. We make a program for calculating the phase transmission constant of the tested material which is put into the waveguide and for obtaining the multi-value solutions. The method for determing ɛ r and tanδ of a tested material does not need special equipments, but it can meet the accuracy requirement for testing ordinary materials.

Using six-port reflectometer measurement of complex dielectric constant

This paper presented the measuring principle of complex dielectric constant using six-port reflectometer and the mathematical model of computer software to perform this measurement. The experiment results of measuring Teflon material using six-port reflectometer at X-band are given. The complex dielectric constant of the same material is measured using the resonant cavity technique. The agreement of two results provides evidence of the validity of this theory.

Measurement of complex dielectric constant of inhomogeneous materials in the range 102?107 Hz

A method of measuring the complex dielectric constant of a mixture composed of a disperse substance and water by insertion of dielectric spacers between the electrodes and the investigated substance is discussed. This system exhibits relaxation of the Maxwell-Wagner type in the conductivity range 10−8–10−2 Ω−1·m−1. By constructing and analyzing Cole-Cole diagrams it is possible to determine the complex dielectric constant of mixtures with a water content of 1–100 wt.% in the frequency range 102–107 Hz.