Imaginary Part Of Dielectric Permittivity Research Articles

Dielectric property measurement of human sweat using attenuated total reflection terahertz time domain spectroscopy.

Sweat is one of the essential biofluids produced by the human body, and it contains various physiological biomarkers. These biomarkers can indicate human health conditions such as disease and illness. In particular, imbalances in the concentration of electrolytes can indicate the onset of disease. These same imbalances affect the dielectric properties of sweat. In this study, we used attenuated total reflection terahertz time domain spectroscopy to obtain the frequency-dependent dielectric properties of human sweat in a frequency range from 200 GHz to 2.5 THz. We have investigated the variation of dielectric properties of sweat collected from different regions of the human body, and we have observed that the real and imaginary part of dielectric permittivity decreases with the increase in frequency. A combination of left-hand Jonscher and Havriliak-Negami processes is used to model the results and reveal the presence of relaxation processes related to sodium and calcium ions concentrations. This information may help design novel biosensors to understand the human health condition and provide a hydration assessment.

Recognition of healthy and cancerous breast cells: Sensing the differences by dielectric spectroscopy.

The response of human cells to applied electrical signals depends on the cellular health status, because it is influenced by the composition and structure of the main cellular components. Therefore, electrical impedance-based techniques can be considered as sensitive tools to investigate healthy or disease state at cellular level. The goal of this study is to show that different types of in vitro cellular lines, related to different health status, can be differentiated using impedance spectra analysis. Three different types of human breast cell line, corresponding to healthy, cancerous, and metastatic adenocarcinoma cells, were measured by means of electrical impedance spectroscopy. By modeling the investigated cells with proper resistive and capacitive circuital elements, the magnitude of the cell electrical components and spectra of real and imaginary part of dielectric permittivity were obtained. The latter were subsequently examined with a commonly adopted mathematical model, in order to estimate the values of specific dielectric parameters for the three different cellular lines. The relative variation of cellular capacitance with respect to that of the culture medium, estimated at 100Hz, has a larger value for the two types of cancerous cells with respect to the noncancerous type. Furthermore, the ratio between the real and imaginary part of the dielectric permittivity function has larger values for metastatic cells with respect to the normal and nonmetastatic ones. Therefore, the mentioned relative capacitance allows to discriminate between normal and cancerous cells, whereas the results obtained for the dielectric function can discriminate between metastatic and nonmetastatic cells. This study can be considered as an exploratory investigation of evaluating in vitro the health status of humans cells using selected electrical impedance parameters as potential markers. The obtained results highlight that a standard cultureware system, provided with interdigitated electrodes and appropriate impedance parameters, that is, cellular capacitance and the ratio between the imaginary and real part of cellular dielectric function, can be used to discriminate between healthy and cancerous breast cell lines, as well as different malignancy degrees.

Crossover from Ferroelectric to Relaxor Behavior in Ba1-xCaxTiO3 (x = 0.17) System.

The dielectric properties of Ba1−xCaxTiO3 (x = 0.17) ceramics were studied in a wide frequency range of 20 Hz–53 GHz. Diffused ferroelectric phase transition was revealed close to 339 K in the dielectric properties of ceramics. The behaviour of distributions of relaxation times in vicinity of the ferroelectric phase transition temperature is also typical for order-disorder ferroelectric phase transition. However, at lower temperatures (below 200 K), the most probable relaxation increased according to the Arrhenius law. At lower temperatures the maximum of the imaginary part of dielectric permittivity versus temperature strongly shifted to higher temperatures when the frequency increased (from 125 K at 1.21 kHz to 300 K at 33 GHz). This behaviour was attributed to the dynamics of Ti ions. The origin of the crossover from ferroelectric to relaxor behaviour of Ba1−xCaxTiO3 (x = 0.17) ceramics is discussed in the paper.

Synchrotron radiation from a charge circulating around a cylinder with negative permittivity

We investigate the radiation from a charged particle rotating around a dielectric cylinder with a negative real part of dielectric permittivity. For the general case of frequency dispersion in dielectric permittivity, expressions are derived for the electric and magnetic fields and for the angular density of the radiation intensity on a given harmonic. Compared with the case of a cylinder with a positive real part of the permittivity, new interesting features arise in the nonrelativistic limit and for the radiation at small angles with respect to the cylinder axis. Another feature is the appearance of sharp narrow peaks in the angular density of the radiation intensity for large harmonics. We analytically estimate the height, width and the location of these peaks. The influence of the imaginary part of dielectric permittivity on the characteristics of the peaks is discussed. The analytical results are illustrated by numerical examples. We show that the radiation intensity on a given harmonic, integrated over the angles, can be essentially amplified by the presence of the cylinder.

Investigation dielectric and morphological properties of fly ash collected from thermal power plant

AbstractFly ash is finely divided waste obtained during the generation of energy in thermal power plants by burning powdered coal. The recycling of fly ash has become an issue in recent years, as this industrial waste is environmentally and economically important. To utilizate this waste material, some electrical analyzes were carried out in the present study. The impedance, dielectric dissipation, dielectric permittivity and conductivity parameters of the pellet were measured as a function of temperature. Then, they were analysed how these parameters change depending on frequency and varying temperatures. Real and imaginary part of dielectric properties of the fly ash was measured in the frequency range of 100 Hz –15 MHz in the temperature range of 25–200 °C. The origins of observed anomalies have discussed. Temperature dependence of real and imaginary part of dielectric permittivity suggests that fly ash exhibits strong broadband electrical behavior. Additionally, EDX, XRD, TGA and DSC measurements have performed to determine structural properties of fly ash. SEM analysis has performed to observe the morphology of pellets. From the results obtained, fly ash can provide suitable new broadband absorption capacity. With utilization of this waste, it is possible to save energy, produce cheaper, protect ecological balance.

Dielectric relaxation studies of aqueous l-glutamine-ethanol mixtures in the microwave frequency range

A study on the dielectric properties of various molar concentration levels of aqueous l-glutamine, ethanol mixtures at microwave frequency region (0.02 < ν/GHz < 20) is carried out in the temperature range of 298 K to 323 K. Dielectric parameters such as dielectric permittivity, dielectric loss of different molar concentrations of l-glutamine in water, ethanol medium are evaluated. It is noticed that the real and imaginary part of dielectric permittivity increases with increase in molar concentration levels of l-glutamine in water and ethanol medium and decreases with increase in temperature. From these parameters, average relaxation time (τ), excessive inverse relaxation time (1/τ)E, excessive dielectric permittivity (εE) are determined and their behavior is analyzed in terms of the distribution of hydrogen bond network in the liquid medium. The theoretical dipole moments of l-glutamine in both aqueous and ethanol medium are determined by using DFT-B3LYP method with different solvation models. Mean molecular polarizability (αM) of the system is calculated from the Lippincott δ function potential model and compared with the Lefevre method. The activation entropy (ΔS*), activation enthalpy (ΔH*), Helmholtz energy (ΔFE) parameters have also been evaluated and the results are correlated.

Correlation of dielectric dispersion with distributed Curie temperature in relaxor ferroelectrics

The fascinating dielectric property of relaxor ferroelectrics is investigated on the basis of phase-transition dynamics within the mean-field theory. With a power-law distribution of the Curie temperature for the second order phase transition ferroelectrics, the complex dielectric permittivity is derived. The result shows that the modified Curie–Weiss relation in the paraelectric phase follows the power-law distribution directly. The significant conclusion is that the “rediscovered” distributed Curie temperature can describe the universal dielectric dispersion for both real part and imaginary part of dielectric permittivity with temperature and frequency in relaxor ferroelectrics, and it conforms well to experimental results.

Sol-gel derived cobalt doped LaCrO3: Structure and physical properties

Nanocrystalline samples of LaCr1-xCoxO3 (0 ≤ x ≤ 0.3), synthesized through the sol-gel process are characterized to investigate the effect of cobalt doping on various physical properties. The orthorhombic structure of the samples is verified by the XRD patterns. Lattice parameters are estimated using PowderX software and are found to follow the Vegard's law. Williamson Hall analysis is employed to compute the crystallite size and lattice strain. Crystallite sizes exhibit a decrease whereas lattice strain shows an overall increasing trend with the increase in Co concentration. The random dispersal of grains is recognized through scanning electron micrographs and the EDX analysis approves the purity of the samples. TEM analysis provides the particle size in the range of 10–30 nm. The presence of characteristic band in FTIR spectra confirms the formation of LaCr1-xCoxO3 (0 ≤ x ≤ 0.3) samples. UV/Visible analysis is used to calculate the energy band gap and other optical parameters and cobalt doping decreases the band gap considerably. Thermal analysis reveals the occurrence of structural transition for all the samples. Imaginary part of dielectric permittivity and loss tangent decrease with increase in the frequency and finally becomes constant at higher frequencies. The AC conductivity data obey the Jonscher's universal dynamic law and it is established that small polaron hopping is involved in the conduction mechanism. Electrical modulus increases with the rise in frequency indicating the short range mobility of charge carriers. Nyquist plots exhibit only one incomplete and distorted semi-circular plots for all the samples specifying that the relaxation process deviate from the ideal Debye type behaviour. Also, both the grains and charge carriers hopping give rise to the conduction phenomenon in these orthochromites.

Dielectric properties of Al/PVA/p-Si (MPS) Structure as a function of frequency and voltage

Abstract Metal-Polymer-Semiconductor (MPS) structure Al/PVA/p-Si was fabricated using polyvinyl alcohol (PVA) as an organic interfacial layer on a p-type silicon wafer by spin coating method. Frequency dependent dielectric properties like real and imaginary part of dielectric permittivity (dielectric constant e′ and dielectric loss e″), dissipation factor or loss tangent (tan δ), real and imaginary parts of the electric modulus (M′, M′′) of the fabricated MPS structure were investigated for various frequencies from 50 KHz to 1 MHz. Frequency dispersion has been found for all dielectric parameters. Simultaneously these were found to be a function of voltage. It was found that e′ and e″ decrease with the increase in frequency. M′ increases with frequency while M′′ shows a peak behaviour that shifts towards lower frequency with increasing applied voltage. All these changes in dielectric parameters may be attributed to surface states distribution at PVA/p-Si interface and interfacial polarization.

Concentration effect of Cadmium Selenide Sulphide/Zinc Sulphide quantum dots on electro-optic and dielectric properties in nematic liquid crystals composite

In this work, we have studied concentration effect of Cadmium Selenide Sulphide/Zinc Sulphide (CdSeS/ZnS) quantum dots (QDs) dispersed on liquid crystalline material, 4-pentyl-4′-cyanobiphenyl nematic liquid crystal (5CB NLC). We used the dielectric spectroscopy technique to obtain electrical and dielectric properties for pure 5CB and doped with QDs form. To observe the effect of CdSeS/ZnS QDs concentration, 5CB was dispersed with 0.05, 0.1 and 0.15 % wt/wt CdSeS/ZnS QDs. Some physical parameters such as real part of dielectric permittivity (ε′), imaginary part of dielectric permittivity (ε"), loss tangent (tanδ), dielectric anisotropy (Δε′) and ac conductivity (σac) of pure 5CB NLC and CdSeS/ZnS QDs doped 5CB NLC composite were measured in the frequency range of 1 kHz–10 MHz at various bias voltages by using dielectric spectroscopy technique at room temperature. In addition, the threshold voltage (Vth) and splay elastic constant (K11) parameters were calculated dependent on doping concentration. The current-voltage (I-V) characteristics of the samples were also investigated. The results showed that the electro-optic and dielectric parameters change significantly with CdSeS/ZnS QDs doping and which were explained by the molecular interaction mechanism between LC molecules and CdSeS/ZnS QDs.

Effect of variation of different nanofillers on structural, electrical, dielectric, and transport properties of blend polymer nanocomposites

In the present work, the effect of different nanofiller (BaTiO3, CeO2, Er2O3 or TiO2) on blend solid polymer electrolyte comprising of PEO and PVC complexed with bulky LiPF6 have been explored. The XRD analysis confirms the polymer nanocomposite formation. FTIR provides evidence of interaction among the functional groups of the polymer with the ions and the nanofiller in terms of shifting and changing peak profile. The highest ionic conductivity is ~2.3x10-5 S cm-1 with a wide electrochemical stability window of ~3.5 V for 10 wt. % Er2O3. The real and imaginary part of dielectric permittivity follows the identical trend of the decreasing value with increase in the frequency. The particle size and the dielectric constant shows an abnormal trend with different nanofiller. The ac conductivity follows the universal power law. An effective mechanism has been proposed to understand the nanofiller interaction with cation coordinated polymer in the investigated system.

Dielectric and structural characteristics of the Bi-As2S3 quasibinar chalcogenides

The results of measurements of the real and imaginary part of dielectric permittivity ε of Bi5(As2S3)95 and Bi7(As2S3)93 chalcogenides indicated their usual dispersion behavior. On the other hand, significantly higher values of these two parameters were obtained in the entire frequency measuring range (100Hz–10MHz), compared to those that generally characterize chalcogenide glasses. Very high values of dielectric function parameters of the Bi7(As2S3)93 sample was explained by charge carrier accumulation due to reduced mobility at the interface between the phases with different conductivity. The results of Raman spectroscopy have shown the complexity of the sample structure. Namely, significant number of narrow peaks observed in the Raman spectrum proved the existence of several molecular species or clusters i.e. the occurrence of the phase separation. Crystallization of the sample with lower bismuth content observed in differential scanning calorimeter (DSC) curve as a two-stage process is the reason why the significant increase of the real part of ε at higher temperatures could be attributed to the existence of two types of molecular dipoles, that is to molecular phase separation. Their identification was made by X-ray diffraction analysis of the sample, annealed at the temperature of the beginning of the first crystallization process.

Investigation of dielectric relaxation in ferroelectric composite nanocrystalline cellulose – triglycine sulfate

ABSTRACTDielectric relaxation in ferroelectric composite nanocrystalline cellulose – triglycine sulfate in the frequency range from 103 to 106 Hz in a weak measuring field (1 V·cm−1) from room temperature to the phase transition temperature of these composites (+54°C) has been investigated. Two series of nanocomposites were used: the first one with the perpendicular directions of nanochannels with respect to the sample surface and the second one – with parallel. The typical for single-crystal triglycine sulfate maximum of the imaginary part of dielectric permittivity at frequencies (105 Hz – 106 Hz) in the case of composites nanocrystalline cellulose – triglycine sulfate is shifted to the range of lower frequencies (104 Hz – 105 Hz).

Dielectric and conductivity relaxation in poly(3,4‐ethylenedioxythiophene) nanotubes

The charge carriers relaxation dynamics in synthesized poly(3,4‐ethylenedioxythiophene) nanotubes has been investigated as a function of frequency and temperature through the framework of dielectric permittivity, modulus formalism and impedance formalism. The fitting of experimental data of real part of dielectric permittivity and imaginary part of modulus with Havriliak‐Negami equation and Bergman modified Kohlrausch‐Williams‐Watts function indicates the presence of non‐Debye type relaxation process in the synthesized poly(3,4‐ethylenedioxythiophene) nanotubes. The scaling of imaginary part of modulus and impedance formalisms have been performed to understand the charge carrier relaxation dynamics in the synthesized samples, which suggests the presence of time temperature superposition principle in the nanotubes. The red shifting of the band from 1440 cm−1 to 1430 cm−1 in micro‐Raman spectra indicates the conformational transition from benzenoid to quinoid structure with increasing dopant concentration. The linear increase of imaginary part of dielectric permittivity with decreasing frequency is ascribed to the higher contribution from dc conductivity as compared to that from the electrode polarization effects. POLYM. ENG. SCI., 56:448–457, 2016. © 2016 Society of Plastics Engineers

Dielectric Properties of Cu(In0,7Cr0,3)P2S6 Crystals under High Hydrostatic Pressure

Composition and dielectric properties of Cu(In0.7Cr0.3)P2S6 crystals have been investigated in the temperature range 77 < T < 450 K under hydrostatic pressure (0,1 < p < 500 MPa). At temperatures above 300 K, we observed frequency dependent anomalies of real and imaginary part of dielectric permittivity. The (p,T) phase diagram of Cu(In0.7Cr0.3)P2S6 crystals has been constructed.

Terahertz properties of bacterial cellulose films and its composite with conducting polymer PEDOT/PSS

Terahertz response of free standing films of bacterial cellulose and its composites with conducting polymer complex PEDOT/PSS has been studied by terahertz time domain spectroscopy. Spectra of refractive index, extinction coefficient and complex dielectric permittivity are obtained in spectral range of 0.3–2.8THz for both types of cellulose films. Considerable increase in the imaginary part of dielectric permittivity of bacterial cellulose films modified with a conductive polymer complex PEDOT/PSS as compared to that of pristine bacterial cellulose film was found out.

Surface polaritons on the interface between an enhanced dielectric and a nanocomposite media

The features of the surface polaritons propagation are studied at the interface of an enhanced isotropic dielectric and a nanocomposite media with spherical metal inclusions. For each media, the frequency dependences of the propagation constant and the wave vector transverse components, group velocity and path length, penetration depth and longitudinal energy flow have been obtained and represented by diagrams. A significant impact of the imaginary part of dielectric permittivity on the wave characteristics of surface polaritons has been shown.

Phase Behavior and Dynamics of the Liquid Crystal 4'-butyl-4-(2-methylbutoxy)azoxybenzene (4ABO5*).

The results of dielectric relaxation spectroscopy and polarizing microscope observation of the 4'-butyl-4-(2-methylbutoxy)azoxybenzene (abbreviated as 4ABO5*) are presented. Numerical analysis of the dielectric spectra results points to complex dynamics of 4ABO5* molecules in isotropic, cholesteric, and crystalline phases. Two well-separated maxima on the imaginary part of dielectric permittivity and the third low frequency relaxation process, hidden in the conductivity region, were detected and described in cholesteric and crystalline phases. Temperature dependence of mean relaxation times characterizing flip-flop motions and rotation around long axes, observed in all phases, is of the Arrhenius type.

Mechanical, electrical and tribological properties of graphite filled polyamide-6 composite materials

Abstract In this study, the influence of adding graphite filler, on the mechanical, electrical and tribological properties of nylon-6 composites, is studied. Graphite fillers with different percentages, varying between 5 and 15 wt% were added to nylon-6 polymer material. Nylon-6 composite samples were prepared by the injection molding process. Tensile, impact, electrical and tribological tests were carried out and the dielectric permittivity tangent loss factor, tensile strength, modulus of elasticity, elongation at break, impact strength, specific wear rate and coefficient of friction properties were obtained. The results showed that the tensile strength, elongation at break, impact strength, and specific wear rate of nylon-6 composites, decrease with the increase in graphite filler weight ratio, while the modulus of elasticity, hardness, real part of dielectric permittivity, imaginary part of dielectric permittivity and dielectric loss, increase with increase in the filler weight ratio. Furthermore, it is observed that a rise in the relaxation time of ionic polarization is proportional to the increase in the amount of graphite in the medium and the dielectric conductivity and loss decrease proportionally after approximately 10 KHz. Finally, the maximum improvement in properties, in total, is recorded following the addition of 5 to 10 wt% graphite filler.

Analytic description of microcylindrical cavity for surface plasmon polariton

We consider the formation of the surface plasmon polariton (SPP) mode in the microcylinder cavity. Developed theoretical model allows to analytically calculate the closed-form expressions for the mode field distributions, resonant frequency, as well as the radiation and dissipative parts of quality factor of the structure in a broad wavelength range. For the conditions when a radius of a metallic cylinder is in order of SPP's wavelength, the highest value of Q-factor is achieved in infrared region of the spectrum where the absolute value of the real part of dielectric permittivity of the metal is much more than both the imaginary part of dielectric permittivity of the metal and the dielectric permittivity of surrounding media. Also, the radiation losses decrease with increasing of radius of cylinder. The obtained results give opportunity to find optimal conditions for having efficient emission in microcylinder cavity and it can serve as practical guidelines to design SPP microcavity for stimulated emission.