Changes In Dielectric Permittivity Research Articles

Universal measuring cell and installation for determining dielectric parameters during the transition from a liquid oligomer to a solid polymer

This paper presents the design of a new installation and a universal measuring cell that allows determining the dielectric properties of materials in various states of aggregation.The data of dielectric permittivity studies for the initial components of the oligomeric binder, ED-20 epoxy oligomer and aminetype hardener triethylenetetramine (TETA), as well as the kinetics of its curing process, established by the change in dielectric permittivity, were obtained for the first time. It is also shown that the maximum temperature of the curing reaction of the ED20+TETA system can be determined from dielectric permittivity data.

Effect of soil compaction on the measurements of complex dielectric permittivity spectrum with an open-ended antenna probe and the coaxial cell system

The paper proposes the use of dielectric spectroscopy to measure changes in dielectric permittivity for soil subjected to compression. Density-dependent dielectric permittivity characteristics of soils for the entire range of obtained density, and thus for a significant parameter of soil properties corresponding with ideal conditions for plant growth as well as those inhibiting their growth were presented. Measurements were carried out for three soil types with different moisture content using an open-ended antenna probe (OE-A), operating in the frequency range of 20 MHz–1.2 GHz and a coaxial cell system in frequency range of 20 MHz–3 GHz. Experimental results showed that an increase in bulk density and volumetric water content of soil affects the complex dielectric permittivity spectrum – a model for this relationship was proposed. Soil dielectric permittivity as a parameter reflecting soil moisture and density can be useful in assessing soil quality.

Evaluating Frequency Domain Reflectometry as a Tool for Lithium-Ion Battery Health Prognosis

Monitoring battery aging is crucial for maintaining reliability and performance. This study investigates Frequency Domain Reflectometry (FDR) as a tool for monitoring lithium-ion battery State-of-Health (SoH). While FDR has been applied in battery research, the existing literature fails to address SoH assessment and lacks studies on larger battery samples to provide more meaningful results. In this work, nineteen cells initially underwent Electrochemical Impedance Spectroscopy (EIS) to assess their degradation levels during cyclic aging. This work evaluates FDR’s effectiveness in monitoring battery health indicators, such as capacity and equivalent series resistance (ESR), by correlating these with FDR-measured impedance between 300 kHz and 1 GHz. Analytical comparison between impedance measured before and after de-embedding processes were presented. The results show FDR reactance within 300 kHz–40 MHz correlates with EIS-measured ESR, suggesting its potential as a SoH indicator. However, reduced sensitivity and accuracy, particularly after de-embedding, may limit practical applicability. Additionally, resonance-based analysis was conducted to explore the relationship between changes in circuit resonance and cell dielectric permittivity. Despite having the lowest sensitivity, the method showed that the resonance frequencies of cells remain relatively constant, mirroring behaviours associated with changes in resistive properties. Overall, this study provides insights into FDR’s potential for battery diagnostics while highlighting avenues for future research to enhance effectiveness in real-world scenarios.

Structural, morphological and electrical properties of hydrothermally synthesized cobalt disulfide (CoS2) nanoparticles

Cobalt disulfide (CoS2) is a highly sophisticated metal chalcogenide that has garnered significant attention due to its distinctive properties such as its electrical, optical, catalytic, and magnetic capabilities and potential for use in a range of applications. In this work, pure CoS2 nanoparticles were synthesized using the economical and facile hydrothermal method. The X-Ray diffraction (XRD) method was used to characterize the synthesized sample, confirming that it has a cubic crystal structure with space group P a −3. The Debye-Scherrer’s formula was implemented to determine the average crystallite size of nanoparticles and found to be 24.24 nm. Through the use of Field Emission Scanning Electron Microscopy (FESEM), the morphology and effective grain size of the obtained sample was determined. FTIR spectrophotometry was used to examine the vibrational stretching of the various bonds in CoS2. UV-Vis spectroscopy is employed to measure the optical property of the sample. The optical bandgap calculated from the Tauc Plot is around 1.90 eV reflecting the presence of photovoltaic properties in the sample. The change in dielectric permittivity and loss have been observed for the sample in the frequency range of 100 Hz to 10KHz at different temperatures between 303K and 423K. The frequency-dependent electrical conductivity of CoS2 is also explained. The observations revealed the presence of unique electrical and structural properties in the synthesized sample.

Modes of a Nonlinear Fiber Containing a Parabolic Graded-Index Core with Light Induced Variable Radius

"New features of the light localization in a nonlinear and graded-index medium in the case of radial symmetry are described analytically. The model of nonlinear graded-index fiber assumes that the dielectric permittivity changes abruptly when the electric field amplitude reaches a certain level. The dielectric permittivity depends on the polar radius according to a parabolic law, in the regions where the electric field amplitude exceeds a certain level. Explicit exact solution to the wave equation is found, in terms of the Whittaker function and the modified Bessel function of the second kind, describing a new type of optical localized structure. The influence of the propagation constant and parameters of the nonlinear graded-index dielectric permittivity on the field profile over the fiber radius is analyzed. It is derived that the core radius and the dielectric permittivity of the core depend on the propagation constant. The dependence of the core radius on the propagation constant causes the appearance of local dispersion."

Composite of DNA-Stabilized Multiwalled Carbon Nanotube and Nematic Liquid Crystal for Display Performance Optimization

We have prepared composites of a nematic liquid crystal (NLC) mixture to improve display performance by doping multiwalled carbon nanotubes (MWCNTs) and single-stranded-DNA-wrapped MWCNTs. Polarized optical microscopy images indicated the uniformity of the composite. Infrared absorption spectra showed there existed an interaction between MWCNTs and 4-pentyl-4′-cyanobiphenyl (5CB, a practical solvent-type monomer NLC) due to π–π stacking and charge transfer, indicating the anchoring of 5CB molecules on the MWCNT surface. The electro-optical property proved the incorporation of MWCNTs and DNA-wrapped MWCNTs reduced the threshold voltage and response time, thus following the changed splay elastic constant and rotational viscosity coefficient of LC, reflecting that DNA can improve the stability of MWCNTs in 5CB. Moreover, dielectric measurement showed the enhanced value to dielectric anisotropy and shift in relaxation frequency, including the changes of dielectric permittivity and loss, revealing the electrically “inertness” MWCNTs at high frequencies and the DNA-induced broadened frequency range of low dielectric loss. Then electrical conductivity tests further proved the cooperative orientation of MWCNTs with 5CB under the applied voltage and the contribution of MWCNTs’ high conducting along the long axis. This study revealed that MWCNT doping could improve the physical properties of NLCs, and DNA wrapping could pave a promising way toward stabilized MWCNT/NLC composites for display performance optimization.

Minimally Invasive Implant Type Electromagnetic Biosensor for Continuous Glucose Monitoring System: In Vivo Evaluation.

Continuous glucose monitoring system (CGMS) is growing popular and preferred by diabetes over conventional methods of self-blood glucose monitoring (SBGM) systems. However, currently available commercial CGMS in the market is useful for few days to few months. This paper presents a durable, highly sensitive and minimally invasive implant type electromagnetic sensor for continuous glucose monitoring that is capable of tracking minute changes in blood glucose level (BGL). The proposed sensor utilizes strong oscillating nearfield to detect minute changes in dielectric permittivity of interstitial fluid (ISF) and blood due to changes in BGL. A biocompatible packaging material is used to cover the sensor. It helps in minimizing foreign body reactions (FBR) and improves stability of the sensor. The performance of the proposed sensor was evaluated on live rodent models (C57BL/6J mouse and Sprague Dawley rat) through intravenous glucose and insulin tolerance tests. Biocompatible polyolefin was used as the sensor packaging material, and the effect of packaging thickness on the sensitivity of sensor was examined in in-vivo test. Proposed sensor could track real-time BGL change measured with a commercial blood glucose meter. High linear correlation (R2 > 0.9) with measured BGL was observed during in vivo experiments. The experimental results demonstrate that the proposed sensor is suitable for long term CGMS applications with a high accuracy. Present work offers a new perspective towards development of long term CGM system using electromagnetic based implant sensor. The in vivo evaluation of the sensor shows excellent tracking of BGL changes.

Detection of hydrocarbon spills by means of a coaxial impedance dielectric sensor

Leakages from storage tanks or pipes frequently produce pollution of soils and groundwater reservoirs by hydrocarbons. Common practices for monitoring and characterising site contamination involve soil drilling, sampling and chemical analysis, complemented with geophysical surveys. This study evaluates the presence of paraffin oil inside soil pores by means of dielectric permittivity measurements, using a coaxial impedance device in laboratory-scale models. The real dielectric permittivity of unsaturated sand is measured before, during and after a contamination process. Monitoring small variations in real dielectric permittivity allows detection of the partial replacement of air (κ′ = 1) by paraffin oil (κ′ ≈ 2) in soil pores. These variations in soil dielectric properties enable pollution levels to be assessed, knowing in advance the κ′ of the soil at the initial stage and measuring the influence of oil and water content on κ′. The technique proposed can also be used for monitoring the lateral extension of a contaminant plume and can be successfully applied at the laboratory scale for oil leakage detection by periodically monitoring changes in the soil dielectric permittivity.

Experimental Study on the Variation of Soil Dielectric Permittivity under the Influence of Soil Compaction and Water Content

The dielectric permittivity of common soils is mainly controlled by water content and porosity, while the latter is closely related to the characteristics of compaction. By studying the changes in dielectric permittivity of soil samples with different soil water content and compaction levels, the influence of the controlling factors on the relationship model between soil water content and dielectric permittivity can be evaluated. In this paper, network analyzer was used to measure the dielectric permittivity of 7 groups of soil samples with gravimetric water content ranging from 8.09% to 14.52% and dry density ranging from 1.61 g/cm3 to 1.96 g/cm3. The results show that the dielectric permittivity increases with the increase of water content and dry density, and the effect of water content on permittivity is more significant for soils with higher dry density. Furthermore, when the water content is less than or equal to the optimal water content, Topp formula and the complex refractive index model (CRIM) can better predict the soil dry density. When the water content approaches the saturated state of soil, there is a deviation between the predicted value and the actual value. At last, the modified Topp formula and the complex refractive index model (CRIM) can accurately predict soil compactness. This provides an important basis for rapid detection of water content and compactness of highway subgrade soil by ground penetrating radar.

AC Conductivity of Gamma Irradiated LDPE/ZIF-8 Composite

Metal–organic frameworks (MOFs) are a class of materials that are increasingly used for the detection and separation of gases. This article presents the influence of gamma radiation on the dielectric properties of a LDPE/ZIF-8 composite that can be used for the production of gas sensors and massive gas absorbers. A low-density polyethylene (LDPE)–microsized zeolitic imidazolate framework-8 (ZIF-8) composite, obtained by melt mixing (95/5 weight ratio), was gamma-irradiated at room temperature to different absorbed doses up to 300 kGy. Infrared spectroscopy and optical microscopy confirmed the degradation of the ZIF-8 due to the gamma irradiation. The AC conductivity (admittance) of the samples was studied in the frequency range of 24 Hz − 120 kHz and a temperature range 200–350 K. The composite showed larger admittance components relative to the admittance components of pure LDPE; the conductance of the samples increased almost linearly with increasing irradiation dose. On the other hand, the change in dielectric permittivity of the LDPE and the composite due to irradiation was weak and showed nonlinear behavior with increasing radiation dose.

Non-contact fruit ripening monitoring using a radiofrequency passive resonator

A high sensitivity radiofrequency (RF) passive resonator is used to investigate the feasibility of fruit ripening assessment by non-contact sensing of fruit dielectric property changes. To do so, kiwifruit samples of similar size and ripeness are monitored during 14 days using the RF resonator, used as an inductive sensor. The recording of the sensor impedance enables monitoring of the fruit complex dielectric permittivity changes induced by the ripening process. These results are compared to mechanical tests carried out on the kiwifruit samples during ripening, which validate the ability of the proposed RF sensor to monitor the ripening process. These preliminary results open the way to developing a low-cost, non-contact and non-destructive assessment of the fruit ripening process. • A non-contact RF passive resonator is used to monitor kiwifruit ripening. • RF resonator enables the monitoring of kiwifruit complex dielectric properties. • Dielectric properties of the kiwifruit feature a monotonous increase with time. • Kiwifruit dielectric monitoring is consistent with visual observations and firmness.

Evaluation of fibrinogen concentration by clot firmness using a dielectric blood coagulation test system.

To determine if fibrinogen concentration can be evaluated by dielectric permittivity changes in dielectric blood coagulation testing (DBCM) during cardiovascular surgery with cardiopulmonary bypass (CPB). We performed a single-center prospective observational study at a university hospital. One hundred patients undergoing cardiovascular surgery with CPB were enrolled. Whole-blood samples were obtained after weaning from CPB, and dielectric clot strength (DCS) was measured by intrinsic pathway testing with or without heparinase in DBCM. The FIBTEM test was performed during rotational thromboelastometry using the same samples, and maximum clot firmness (MCF) was evaluated. Spearman's correlation analysis was performed, and receiver operating characteristics (ROC) curve analyses were used to evaluate the performance of hypofibrinogenemia detection. DCS showed a strong positive correlation with plasma fibrinogen concentration (Rs = 0.76, P < 0.0001). The area under the ROC curve for evaluating plasma fibrinogen concentration < 200mg/dL was 0.91 (95% confidence interval (CI) 0.85-0.97) for DCS, compared with 0.88 (95% CI 0.81-0.94) for FIBTEM MCF. The optimal cutoff value of DCS was 17.0 (sensitivity 94%, specificity 80%). DCS variables showed a significantly strong correlation with plasma fibrinogen concentration, and the diagnostic performance for hypofibrinogenemia was comparable to that for FIBTEM MCF. This novel methodology has the potential to provide a point-of-care test with sufficient accuracy for the detection of perioperative hypofibrinogenemia during cardiovascular surgery with CPB.

Subcutaneously implantable electromagnetic biosensor system for continuous glucose monitoring

Continuous glucose monitoring systems (CGMS) are becoming increasingly popular in diabetes management compared to conventional methods of self-blood glucose monitoring systems. They help understanding physiological responses towards nutrition intake, physical activities in everyday life and glucose control. CGMS available in market are of two types based on their working principle. Needle type systems with few weeks lifespan (e.g., enzyme-based Freestyle Libre) and implant type system (e.g., fluorescence-based Senseonics) with few months of lifespan are commercially available. An alternate to both working methods, herein, we propose electromagnetic-based sensor that can be subcutaneously implanted and capable of tracking minute changes in dielectric permittivity owing to changes in blood glucose level (BGL). Proof-of-concept of proposed electromagnetic-based implant sensor has been validated in intravenous glucose tolerance test (IVGTT) conducted on swine and beagle in a controlled environment. Sensor interface modules, mobile applications, and glucose mapping algorithms are also developed for continuous measurement in a freely moving beagle during oral glucose tolerance test (OGTT). The results of the short-term (1 h, IVGTT) and long-term (52 h, OGTT) test are summarized in this work. A close trend is observed between sensor frequency and BGL during GTT experiments on both animal species.

Thin Dielectric Layers Evaluation Using Tunable Split-Ring Resonator Based Metasurface in THz Frequency Range

The paper presents the evaluation of thin dielectric layers using a tunable split-ring resonator-based metasurface in the THz frequency range. Tunable unit cells of a metasurface allow its resonant frequency variation using some external excitation. This can be done in various ways. In this work, the behavior of such a metasurface is investigated by monitoring the resonant frequency value when the unit cell geometry is changed. Such behavior is utilized for the quality evaluation of a thin dielectric layer placed in vicinity of a metasurface. A change in dielectric permittivity noticeably affects the resonant frequency of a metasurface. In order to examine the state of the material under test, finite element method simulations were made for a 15 µm thin layer. As a result, the approximation-based relations between resonant frequencies (obtained for various geometries of structural element—in tunability range) and dielectric parameters of the examined material were derived. These relations carry more information than in the case of just one resonant frequency (the case of a non-tunable metasurface) and can be utilized for permittivity evaluation.

Effect of Dielectric Saturation on Ion Activity Coefficients in Ion Exchange Membranes.

Polymeric ion exchange membranes are used in water purification processes to separate ions from water. The distribution and transport of ionic species through these membranes depend on a variety of factors, including membrane charge density, morphology, chemical structure, and the specific ionic species present in the fluid. The electrical potential distribution between membranes and solutions is typically described using models based on Donnan theory. An extension of the original theory is proposed to account for the nonideal behavior of ions both in the fluid and in the membrane as well to provide a more robust description of interactions of solutes with fixed charge groups on the polymer backbone. In this study, the variation in dielectric permittivity in the membrane medium with electric field strength is taken into account in a model based on Gouy–Chapman double-layer theory to provide a more accurate description of ion activity coefficients in an ion exchange membrane. A semianalytical model is presented that accounts for the variation in dielectric permittivity of water in a charged polymer membrane. A comparison of this model with Manning’s counterion condensation model clearly demonstrates that by incorporating changes in water dielectric permittivity with electric field strength, much better agreement with experiments can be obtained over a range of salt concentrations for different ions.

Enhanced magnetic and magnetodielectric behavior in morphologically distinct BTFO and LSMO composites

In this work, sol–gel modified technique is used to synthesize the (1-x)BTFO-(x)LSMO composites (x = 0, 0.1, 0.2, 0.3, and 0.4). The composite's dual (BTFO and LSMO) phases are verified using X-ray diffraction analysis. A scanning and transmission electron microscope is used to analyze the distinct morphology of the two phases that demonstrated the plate-like grains and quasi-spherical particles of BTFO and LSMO phases in the composites, respectively. The magnetic studies reveal that the saturation magnetization (Ms ∼ 7.0 emu/g) and coercive field (Hc ∼ 1660 Oe) increased by nearly-three and 66 times for 40 % LSMO contained composite. The enhanced magnetic behavior is due to the interaction between the multiple magnetic ordering (AFM/FM) present in the prepared composites. The estimated values of squareness ratio (Mr/Ms) are lower than 0.5, illustrating the multi-domain nature of the composites. The switching field distribution (SFD) plot indicates that strong exchange coupling exists in the x = 0.4 composite compared to others. The change in dielectric permittivity at different magnetic fields is due to the magnetodielectric (MD) coupling in the composites. The field-dependent MD studies reveal that maximum MD strength (∼0.34 %) and minimum magnetoloss (ML) (∼0.02 %) are observed in x = 0.2 and 0.1 composites at 100 kHz, respectively. It is due to the non-collinear alignment of magnetic Mn ions at RT, which leads to the inverse Dzyalonskii-Moriya interaction. Additionally, the maximum MD coupling strength γ (-16.87 (emu/g)2) is observed in the x = 0.2 composite. The observed MD response in the composites is due to the dominating grain capacitive effect rather than the resistive effect, which is ascertained by the frequency-dependent magnetoresistance measurement. Hence, the composite's enhanced magnetic and magnetodielectric behavior makes it a suitable candidate for multifunctional device applications.

Defects evolution and temperature stability of low-loss magnesium titanate stannate - calcium strontium titanate microwave dielectric ceramics

Magnesium titanate stannate - calcium strontium titanate (MgTi0.95Sn0.05O3-xCa0.8Sr0.2TiO3; abbreviated as MTS-xCST, x = 0.02, 0.04, 0.06, 0.08) microwave dielectric ceramics were synthesized via the conventional solid-state reaction. The optimum densities corresponded to higher sintering temperatures than the optimum quality factor, so the ceramics were classified as MTS-xCST-D and MTS-xCST-Q. All compositions exhibited a composite phase consisting of the rhombohedral structure MTS and the orthorhombic structure CST. As the sintering temperature rose, the relative densities of the ceramics increased significantly, while the formation of oxygen vacancies and titanium reduction were intensified. Finally, the x = 0.06 compositions sintered at 1425 °C (MTS-0.06CST-D) and 1375 °C (MTS-0.06CST-Q) had excellent temperature stability and low loss. At low frequency, the change of dielectric permittivity at 25–150 °C did not exceed 0.1, and the loss tangent was less than 0.003. In addition, microwave dielectric properties of MTS-0.06CST-D (εr = 20.4, Qf = 63,770 GHz, τf = −1.8 ppm/°C) and MTS-0.06CST-Q (εr = 18.4, Qf = 74,740 GHz, τf = −4.3 ppm/°C) compositions were obtained. These results suggest that MST-0.6CST ceramics could be a candidate material for 5 G microwave communication devices.

DATA PROCESSING SEQUENCE FOR GPR INVESTIGATION OF ANTHROPOGENIC SEDIMENTS IN URBANIZED AREAS

The article presents a historical overview of the ground penetrating research (GPR) development. Although the theoretical foundations of the GPR method was formulated many years ago, it has been possible to practically implement this method only in recent years. Nowadays there are difficulties with GPR data analysis because the change in dielectric permittivity depends on a lot of factors. The aim of this study was to develop an effective GPR data processing sequence and interpretation of GPR profiles obtained on the basis of geophysical surveys in urbanized areas. The survey was conducted on the right bank of the Dnieper River in Mogilev (the Republic of Belarus), where previously residential quarters were located (according to architectural data). The developed GPR data processing sequence is based on a combination of the following methods: amplification of individual signals, the method of subtracting the average, a bandpass filter. The proposed data processing sequence is based on dielectric permeability. Information about the shape and depth of the objects buried in the cultural layer was obtained by using the proposed sequence.

Local strain distribution imaging using terahertz time‐domain spectroscopy

AbstractIn this work, terahertz time‐domain spectroscopy (THz TDS) was applied to monitor strain distribution as a function of mechanical loading through a passive composite sensor. The composite sensor was made up of strontium titanate (STO) particles. Strain distribution was measured by analysing the change in THz pulse amplitude while it passes through the composite sensor. The change in THz pulse amplitude is related to change in dielectric permittivity. The change in dielectric permittivity induced in the STO composite layer due to deformation leads to a change in the time of arrival (ToA) of the electromagnetic pulse (EMP) in THz band. This change in the sub‐millimetre domain is correlated to the strain and can be mapped for reproducing strain distribution around different geometries. The measurements of strain mapping are compared with finite element simulations and digital image correlation (DIC) measurements, showing similar strain contours.

Experimental Verification of Dielectric Models with a Capacitive Wheatstone Bridge Biosensor for Living Cells: E. coli.

Detection of bioparticles is of great importance in electrophoresis, identification of biomass sources, food and water safety, and other areas. It requires a proper model to describe bioparticles’ electromagnetic characteristics. A numerical study of Escherichia coli bacteria during their functional activity was carried out by using two different geometrical models for the cells that considered the bacteria as layered ellipsoids and layered spheres. It was concluded that during cell duplication, the change in the dielectric permittivity of the cell is high enough to be measured at radio frequencies of the order of 50 kHz. An experimental setup based on the capacitive Wheatstone bridge was designed to measure relative changes in permittivity during cell division. In this way, the theoretical model was validated by measuring the dielectric permittivity changes in a cell culture of Escherichia coli ATTC 8739 from WDCM 00012 Vitroids. The spheroidal model was confirmed to be more accurate.