Time Domain Dielectric Spectroscopy Research Articles

Upgraded Full multiple reflections method improves accuracy in Time-Domain dielectric spectroscopy

Automated measurements of the dielectric properties of matter, based on Time-Domain Dielectric Spectrometry, have been used for several decades. In this paper, we report and evaluate a novel Full Multiple Reflections algorithm for extracting the material-under-test complex dielectric permittivity, able to perform over a wide range of frequencies. The novel method is based on the analysis of multiple reflections due to non-idealities and unintended impedance mismatches in the transmission line, to extract their influence on the final result. The method is compared against two classic strategies and proves to be more accurate, while overriding the well-known drawbacks of using non-ideal transmission lines. Limitations of the method are discussed and tested through representative results using materials widely studied and researched in the literature.

Dielectric Relaxation Studies on the Hydration Dynamics of Ionic, Non-Ionic and Zwitterionic Surfactants in Aqueous Acetate Buffer Solution

Dielectric relaxation studies of acetate buffer solutions of Sodium Dodecyl Sulphate (SDS- anionic), Cetyl Trimethyl Ammonium Bromide (CTAB- cationic), Tween 80 (TW-80-non-ionic), Betaine Anhydrous (BA- zwitterionic) surfactants have been examined in the frequency region between 1GHz and 25GHz for various concentrations of surfactants at the temperatures of 283, 288, 293 and 298K using time domain dielectric spectroscopy. The obtained corrected loss spectra of all the amphiphiles except betaine anhydrous in acetate buffer solution depicted peaks near 1-2GHz and 15GHz, respectively. For betaine anhydrous, expected peak was not observed in the 1-2GHz frequency region. The peak ascertained near 15GHz, and another peak about 1-2GHz was accorded to free water relaxation and bound water reorientation of the surfactant micelles, and has acquired the reliance of temperature with concentration in detail. Single Debye and Cole-Cole function was employed to compute the relaxation times of free water and bound water, respectively. The Arrhenius plot was used to calculate the enthalpy and entropy for the micelle forming surfactants.

Study of Thermodynamic and Dielectric Parameters of Xylene and Its Isomers Using Time Domain Dielectric Spectroscopy

Raw complex permittivity data of pure aromatic hydrocarbons such as Xylene, O-Xylene (O-X), M-Xylene (M-X), and P-Xylene (P-X) have been measured for different temperatures in 10 MHz to 50 GHz frequency range using Time Domain Dielectric Spectroscopy (TDDS). Dielectric relaxation for above systems has been characterized by the Debye type spectral relaxation. The dielectric parameters such as static dielectric constant, relaxation time, Kirkwood correlation factor have been determined using the non-linear least square fit method. Effect of O-, M-, and P- substitution of CH3 group in xylene causes variation in static dielectric constant values and spectacle deviation in relaxation time with respect to temperature. The temperature dependent dielectric relaxation gives expected Arrhenius behavior.

Time and frequency domain dielectric spectroscopy for in-situ and ex-situ determination of amorphous fractions of isothermally cold-crystallized Polylactic acid

Time and frequency domain dielectric spectroscopy for in-situ and ex-situ determination of amorphous fractions of isothermally cold-crystallized Polylactic acid

Thermodynamic and Dielectric Properties of Cyclohexanol-Xylene Binary Mixtures Using Dielectric Spectroscopy

The complex permittivity spectra for cyclohexanol (CYN) with Xylene have been measured in 10 MHz to 20 GHz range using time domain dielectric spectroscopy. The complex permittivity spectra of CYN + Xylene binary mixtures were fitted to the Debye model. The dielectric relaxation parameters have been determined using the least squares fit method and are dependent on association and chain length of molecule. The experimentally obtained results were quantitatively used to know dipole-dipole interactions, nature of inter and intra molecular interaction between solute-solvent components in such a way when mixed in terms of hydrogen-bonding between CYN and Xylene. So the frequency dependent dielectric relaxation time gives the expected Arrhenius behavior, such that all concentrations of binary mixture shows linearity in plot of log (τ*T) versus 1000/T, which confirms the relaxation process as rate process according to Eyring’s theory.

Non-Contact Time Domain Ultra Wide Band Milk Spectroscopy

Recently, wideband dielectric spectroscopy (WBDS) has been applied for material characterization. Milk spectroscopy is usually done with high-cost contact-based methods using a vector network analyzer (VNA). Non-contact WBDS of milk is a novel and convenient technique, which can be utilized for milk qualification. In this paper, an ultra-wideband time domain dielectric spectroscopy system for milk characterization is presented. The proposed setup is a quasi-monostatic free space dielectric spectroscopy in which all measurements are done with Xethru X4 sensor. Material under test is located in the far-field of Xethru sensor. The Fast Fourier Transform (FFT) of received time domain signals is computed and the permittivity of low-fat pasteurized cow milk and mixture of untreated raw cow milk and water have been estimated by mapping phase and amplitude differences of calibration materials. Mean squared error (MSE) of permittivity for low-fat milk and milk with different water content are 0.29% and below 0.056%, respectively.

Electrical and Mechanical Condition Assessment of Low Voltage Unshielded Nuclear Power Cables Under Simultaneous Thermal and Mechanical Stresses: Application of Non-Destructive Test Techniques

Low voltage cables play a crucial role in the safe and reliable operation of nuclear power plants. This paper discusses the effect of simultaneous combined thermal and mechanical stresses on the overall insulation of unshielded low voltage power cables used in nuclear power plants. Cable samples based on XLPE/CSPE insulation were exposed to thermal-mechanical combined accelerated aging tests for an extended period lasted to 907 hours. Time and frequency domain dielectric spectroscopy were applied to reveal the degradation level of the core insulation and jacket due to combined stresses. The former technique was conducted through the measurement of the decay and return voltage slopes, while the latter technique was based on the measurement of the complex permittivity. Moreover, the mechanical properties of the cable insulation were investigated by applying the measurement of the Shore D hardness. The results showed that the combined aging affects both the electrical and mechanical properties of the overall insulation. The complex permittivity at 100 Hz, the decay voltage slope, and the hardness had an upward trend with aging, while the return voltage slope showed an inverse trend. In addition, the results of the electrical and mechanical measurements showed strong correlation with aging time and further correlation was observed between the dielectric and mechanical properties. The correlation between aging time and test results suggests that the presented test methods are promising tools for in situ condition monitoring of low voltage unshielded cables in nuclear power plants.

The dielectric spectroscopy of human red blood cells during 37-day storage: β-dispersion parameterization

This study exploits dielectric spectroscopy to monitor the kinetics of red blood cells (RBC) storage lesions, focusing on those processes linked to cellular membrane interface known as β-dispersion. The dielectric response of RBC suspensions, exposed to blood-bank cold storage for 37 days, was studied using time-domain dielectric spectroscopy in the frequency range 500 kHz to 200 MHz. The measured dielectric processes are characterized by their dielectric strength (Δε) and their relaxation times (τ). Changes in the dielectric properties of the RBC suspensions, due to storage-related biophysical changes, were evaluated. For a quantitative characterization of RBC vitality, we characterized the shape of fresh and stored RBC and measured their deformability as expressed by their average elongation ratio, which was achieved under a shear stress of 3.0 Pa. During the second week of storage, an increment in the evolution of the relaxation times and in the dielectric permittivity strength of about 25% was observed. We propose that the characteristic increment of ATP, during the second and third weeks of storage, is responsible for the raise of the specific capacitance of cell membrane, which in turn explains the changes observed in the dielectric response when combined with the influence of the shape changes.

Dielectric relaxation behaviour of ethyl acetate-xylene mixtures using time domain reflectometry

ABSTRACT Complex permittivity spectra were measured for the binary mixtures of Ethyl Acetate (EA) with Xylene using Time Domain Dielectric Spectroscopy (TDDS) for 11 concentrations at different temperatures in the frequency range from 10 MHz to 30 GHz. The values of static dielectric permittivity and relaxation time have been obtained by fitting complex permittivity spectra using least square fit method in Debye model. The observation of excess permittivity, excess relaxation time and Kirkwood correlation factor has been undertaken to study the behaviour of molecular structure in EA and Xylene using dielectric relaxation parameters.

Dielectric relaxation studies of collagen – surfactant complexes in aqueous buffer solution

Dielectric relaxation studies of rat tail tendon collagen with anionic sodium dodecyl sulphate (SDS), cationic cetyltrimethyl ammonium bromide (CTAB) and nonionic Tween 80 in aqueous buffer solutions at four different temperatures have been carried out in the frequency range 1 GHz to 25 GHz using time domain dielectric spectroscopy. The frequency dependent normalized dielectric modulus function P of the collagen and surfactant solutions show up as peaks around 1–2 GHz which is due to the bound water around collagen macromolecule and surfactant micelles. For the collagen – surfactant complexes, the peak in normalized dielectric modulus function P is shifted towards high frequency side near 2–3 GHz upon addition of surfactants to collagen in buffer solution. The water structure around collagen is altered in the presence of micelle forming surfactant additives and this change may affect the degrees of freedom of their motion. Hence the significant changes are observed in the relaxation time of bound water around collagen macromolecule in the presence of surfactants. Further, it was observed that no considerable change in relaxation time of hydration water of the complexes with respect to change in temperature within the studied temperature range. The activation enthalpy and activation entropy for the dipolar orientation corresponding to the free water for the surfactants and their complexes with collagen have been calculated from the Arrhenius plot. Our thermodynamic results suggest that the two‑hydrogen-bonded model may be possible in SDS and Tween 80 environments, whereas the one‑hydrogen-bonded model is likely to be possible in buffer and CTAB environments.

Hydration dynamics of collagen in aqueous buffer solution as studied by time domain dielectric spectroscopy

Dielectric relaxation studies of collagen in aqueous buffer solution (pH 3.7) have been carried out at four different temperatures 283, 288, 293 and 298 K as a function of collagen concentration between 0.033 μM and 0.2 μM in the frequency range of 1 GHz to 25 GHz using time domain dielectric spectroscopy technique. Apart from the dominant mode at high frequency around 14 GHz which is assigned to the free water relaxation; we have detected one more pronounced peak close to 1.8 GHz in the δ-dispersion range of the loss spectrum of collagen in aqueous buffer solution. The peak around 1.8 GHz is attributed to hydration water reorientation of the collagen macromolecules and has obtained detailed information on its temperature and concentration dependence. The retardation imposed on the hydration water by collagen is found to be ≈4.7, since collagen can cause long range perturbations beyond the first hydration shell. The activation enthalpy and activation entropy for the dipolar orientation for collagen at different concentrations have been calculated from the Arrhenius plot and is found to be 32 kJ/mol and 4.2 J/mol K respectively. The increase of thermodynamic activation enthalpy and decrease of activation entropy of collagen in buffer in the present study compared to the water have supported the idea that the water associated with collagen is highly ordered.

Time Domain Dielectric Spectroscopic Studies of Potassium Oleate and Cetyl Pyridinium Chloride in Acetate Buffer Solution

Dielectric relaxation studies of acetate buffer solutions of anionic potassium oleate (PO) and cationic cetyl pyridinium chloride (CPC) surfactants at four different temperatures 283, 288, 293 and 298 K as a function of surfactant concentrations have been carried out in the 10 MHz to 30 GHz frequency range using time domain dielectric spectroscopy. Both the surfactants exhibit a significant rise of dielectric constant with increasing concentration. The corrected loss spectra of both the surfactants in aqueous buffer solution show up as peaks close to 1.4 GHz, and 14.5 GHz respectively. In agreement with the standard interpretation, we assigned the dominant mode at high frequency around 14.5 GHz to bulk water relaxation. The other peak around 1.4 GHz is attributed to hydration water reorientation of the surfactant micelles and has obtained detailed information on their temperature and concentration dependence. The relaxation times of bulk water and hydration water were calculated using Single Debye and Cole‐Cole method respectively. The activation enthalpy and activation entropy for the dipolar orientation for the surfactants at different concentrations have been calculated from the Arrhenius plot.

A Miniaturized Contactless UWB Microwave System for Time-Domain Dielectric Spectroscopy

A miniaturized time-domain (TD) dielectric spectroscopy system for contactless material characterization over the ultra-wideband (UWB) microwave range is presented in this paper. The proposed system includes a transmitter, a compact contactless sensing unit, and a receiver. A picosecond pulse generator unit in the transmitter delivers a quasi-monocycle pulse with 3.5-GHz 10-dB bandwidth to an up-converter and then an amplifier. The generated pulse provides the capability to perform the material characterization in a fast pure TD fashion. The transmitter unit provides the 3–10-GHz excitation pulse based on utilizing a direct up-conversion architecture. The excitation pulse is transmitted to the receiver through the sensing unit. Two Vivaldi antennas are coupled to each other in their radiative near field to construct the sensing unit, while the material-under-test (MUT) is placed in between. A custom-designed Quartz-Glass cuvette is utilized with optimized MUT volume of ~5 mL. The TD data are captured for each MUT using DSA91304A infiniium oscilloscope as the receiver, and finally the fast Fourier transform of the measured data is extracted in MATLAB. A calibration procedure is discussed to achieve a behavioral model of the system using seven calibration MUTs. From there, the $\epsilon '$ and $\epsilon ''$ characterization of three unknown MUTs are carried out. The system shows the worst case mean-squared error (MSE) of 1.92% for $\epsilon '$ and 3.84% for $\epsilon ''$ characterization. Furthermore, binary mixture detection based on $\epsilon '$ accomplished with the MSE of 2.74%.

The dielectric spectroscopy of human red blood cells: the differentiation of old from fresh cells

Objective: The objective of the study was to gauge the effect of storage lesions on the dielectric response of red blood cells (RBC), in particular those processes linked to deformations of the cellular membrane known as the β-dispersion. Approach: The dielectric response of RBC suspensions, exposed to blood-bank cold storage, was studied using time-domain dielectric spectroscopy (TDDS) in the frequency range of 500 kHz up to 1 GHz. The measured dielectric processes are characterized by their dielectric strength (Δε) and relaxation time (τ). Changes in the dielectric properties of the RBC suspensions due to storage-related lesions were evaluated. For a quantitative characterization of RBC lesions, we measured the deformability of fresh and stored RBC as expressed by their elongation ratio (ER), which was achieved under a shear stress of 3.0 Pa. Main Result: The results show that the storage of RBC induced a statistically significant decrease of dielectric relaxation times. In addition, a sound correlation between the mean values of ER and the relaxation times was observed (Spearman’s correlation coefficient ρ = 0.847). We draw the conclusion that those alterations in the relaxation time are induced by changes in the shape of the RBC that happen during cold-storage. Significance: The evolution of the β-dispersion of RBC opens new possibilities in the blood bank inventory management.

Direct Current Conductivity of Thin-Film Ionic Conductors from Analysis of Dielectric Spectroscopic Measurements in Time and Frequency Domains

A method is developed for extracting the direct current conductivity (σdc) of ion-conducting materials from frequency- and time-domain dielectric spectroscopy measurements. This method exploits the electrode polarization effects arising from the charging of an ion-blocking capacitor and provides a useful way of obtaining σdc for ionic conductors that do not exhibit a frequency- (time-) independent conductivity plateau; the latter absence of plateau is often encountered in the case of thin-film materials. It allows, by proper design of the test cells, the estimation of σdc independently of the specimen thickness, as demonstrated herein for SiO2 blocking layers and electrolyte systems made of a polyoxometalate (POM) molecule embedded in poly(methyl methacrylate) (PMMA) polymeric matrices. For different postpreparation and measurement conditions, the σdc values obtained for thick (8 μm) POM–PMMA layers are in good agreement not only with the observed conductivity plateaus but also with the values determined ...

Correlation between Molecular Mobility and Physical Stability in Pharmaceutical Glasses.

We investigated a possible correlation between molecular mobility and physical stability in glassy celecoxib and indomethacin and identified the specific mobility mode responsible for physical instability (crystallization). In the glassy state, because the structural relaxation times are very long, the measurement was enabled by time domain dielectric spectroscopy. However, the local motions in the glassy state were characterized by frequency domain dielectric spectroscopy. Isothermal crystallization was monitored by powder X-ray diffractometry using either a laboratory source (supercooled state) or synchrotron source (glassy state). Structural (α) relaxation time correlated well with characteristic crystallization time in the supercooled state. On the other hand, a stronger correlation was observed between the Johari-Goldstein (β) relaxation time and physical instability in the glassy state but not with structural relaxation time. These results suggest that Johari-Goldstein relaxation is a potential predictor of physical instability in the glassy state of these model systems.

Time domain dielectric spectroscopy of nanosecond pulsed electric field induced changes in dielectric properties of pig whole blood

The dielectric spectra of fresh pig whole blood in the β-dispersion range after exposure to 300–nanosecond pulsed electric fields (nsPEFs) with amplitude higher than the supra-electroporation threshold for erythrocytes were recorded by time domain reflectometry dielectric spectroscopy. The implications of the dielectric parameters on the dynamics of post-pulse pore development were discussed in light of the Cole–Cole relaxation model. The temporal development of the Cole–Cole parameters indicates that nsPEFs induced significant poration and swelling of erythrocytes within the first 5min. The results also show that the majority of erythrocytes could not fully recover from supra-electroporation up to 30min. The findings of this study suggest that time domain dielectric spectroscopy is a promising label-free and real-time physiological measuring technique for nsPEF-blood related biomedical applications, capable of following the conformational and morphological changes of cells.

Dielectric analysis of hydrated mannitol by time-domain dielectric spectroscopy

Dielectric analysis of hydrated mannitol by time-domain dielectric spectroscopy

D-Glucose-Induced Second Harmonic Generation Response in Human Erythrocytes

The first experimental results of the nonresonant second harmonic generation (SHG) studies of human erythrocytes membrane exposed to various glucose concentrations in phosphate buffered saline (PBS solution) are presented in this article. It is shown that the SHG signal from the membrane can be altered as a function of glucose concentration. The link between the variation of the SHG intensity and the membrane dielectric permittivity with glucose is established both theoretically and experimentally by comparison with time domain dielectric spectroscopy (TDDS) measurement data.

From the editor's desk

In this issue we have three articles. The first, "Dielectric Spectroscopy Techniques as Quality Control Tool: A Feasibility Study", by Bouaicha , Fofana and Farzaneh from the Universite du Quebec a Chicoutimi, and some German and French collaborators, is concerned with the feasibility of using time and frequency domain dielectric spectroscopy to monitor the fabrication of oil-impregnated-paper (OIP) condenser bushings. So what is time domain dielectric spectroscopy? It involves measuring the current flowing in an insulator following application and removal of a dc voltage step. Following voltage application the current decays with time, typically as t <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-n</sup> , where 0 < n < 1, and the measurement is continued until the current reaches a nearly constant value, or, more likely, the experimenter runs out of patience and opts to take the current flowing at a specific time as the nearly constant value. Measurements may extend over several hours, depending on temperature and applied field strength. A value for the dc conductivity of the sample can be estimated from the nearly constant current. The long decay leading to quasiequilibrium yields the dielectric response function, about which much has been written and upon which several scientific careers have been based! Theoretically, the current flowing after the voltage is removed, that is, after the sample is short-circuited, should be identical with that flowing during voltage application, after the appropriate shift of t = 0, subtraction of the quasi-equilibrium current, and polarity reversal. The related frequency domain spectroscopy involves the study of ac currents as a function of frequency, the analysis leading to values for the real and imaginary components of the relative permittivity, ε;.