Change In Permittivity Research Articles

Removal of Diesel Oil in Soil Microcosms and Implication for Geophysical Monitoring

Bioremediation of soils polluted with diesel oil is one of the methods already applied on a large scale. However, several questions remain open surrounding the operative conditions and biological strategies to be adopted to optimize the removal efficiency. This study aimed to investigate the environmental factors that influence geophysical properties in soil polluted with diesel oils, in particular, during the biodegradation of this contaminant by an indigenous microbial population. With this aim, aerobic degradation was performed in soil column microcosms with a high concentration of diesel oil (75 g kg−1 of soil); the dielectric permittivity and electrical conductivity were measured. In one of the microcosms, the addition of glucose was also tested. Biostimulation was performed with a Mineral Salt Medium for Bacteria. The sensitivity of the dielectric permittivity versus temperature was analyzed. A theoretical approach was adopted to estimate the changes in the bulk dielectric permittivity of a mixture of sandy soil-water-oil-gas, according to the variations in the oil content. The sensitivity of the dielectric permittivity to the temperature effects was analyzed. The results show that (1) biostimulation can give good removal efficiency; (2) the addition of glucose as a primary carbon source does not improve the diesel oil removal; (3) a limited amount of diesel oil was removed by adsorption and volatilization effects; and (4) the diesel oil efficiency removal was in the order of 70% after 200 days, with different removal percentages for oil components; the best results were obtained for molecules with a low retention time. This study is preparatory to the adoption of geophysical methods to monitor the biological process on a larger scale. Altogether, these results will be useful to apply the process on a larger scale, where geophysical methods will be adopted for monitoring.

Enhanced tunability in ferroelectric composites through local field enhancement and the effect of disorder

We investigate numerically the homogenized permittivities of composites made of low-index dielectric inclusions in a ferroelectric matrix under a static electric field. A refined model is used to take into account the coupling between the electrostatic problem and the electric field dependent permittivity of the ferroelectric material, leading to a local field enhancement and permittivity change in the ferroelectric. Periodic and pseudorandom structures in two dimensions are investigated, and we compute the effective permittivity, losses, electrically induced anisotropy, and tunability of these metamaterials. We show that the tunability of such composites might be substantially enhanced in the periodic case, whereas introducing disorder in the microstructure weakens the effect of the enhanced local permittivity change. Our results may be useful to guide the synthesis of novel composite ceramics with improved characteristics for controllable microwave devices.

Differential Microfluidic Sensors Based on Dumbbell-Shaped Defect Ground Structures in Microstrip Technology: Analysis, Optimization, and Applications.

A microstrip defect ground structure (DGS) based on a pair of dumbbell-shaped slots is used for sensing. The device is a differential sensor consisting of a pair of mirrored lines loaded with a dumbbell-shaped DGS, and the output variable is the cross-mode transmission coefficient. Such a variable is very sensitive to asymmetries in the line pair, e.g., caused by an asymmetric dielectric load in the dumbbell-shaped DGSs. Therefore, the sensor is of special interest for the dielectric characterization of solids and liquids, or for the measurement of variables related to complex permittivity changes. It is shown in this work that by adding fluidic channels on top of the dumbbell-shaped DGSs, the device is useful for liquid characterization, particularly for the measurement of solute concentration in very diluted solutions. A sensitivity analysis useful for sensor design is carried out in this paper.

The influence of temperature on elastin\u2013water dielectric properties

The main purpose of this article is the in vitro study of elastin from the bovine neck ligament using dielectric spectroscopy in the alpha electric field dispersion region in the temperature range from 22 to 200 °C. The temperature dependence of the relative permittivity of wet elastin indicates a maximum of about 50 °C due to the thermal decomposition of loosely bound water, as well as a rapid decrease in this parameter above 185 °C. For a dry elastin, the change in relative permittivity with temperature represents only one peak of high temperature around 185 °C, corresponding to the glass transition temperature (Tg). Below Tg, the activation energy of conductivity for wet and dry elastin at 50 kHz, responsible for the breaking of hydrogen bonds between bound water molecules and hydrophilic polar groups of the main elastin chains, is 27 and 11 kJ mol−1, respectively, and above Tg, corresponding activation energy values associated with relaxation of the main chain increase to 72 and 34 kJ mol−1. In this article, dielectric processes related to the glass transition temperature, especially in the case of dry elastin, can play an important role in the use of solid-state elastin as a biomaterial for various tissue engineering applications.

The role of medium on the assembly of carbon nanotube by dielectrophoresis

Dielectrophoresis (DEP) is an electrode-medium process used to control the movement of Carbon nanotubes (CNTs) within a solution under nonuniform electric fields. CNTs are typically dispersed into a solvent to form a homogeneous suspension in order to prevent their aggregation and to improve solubility. This paper starts with a short review of the techniques used to improve the compatibility of CNTs with a target medium. Then, direct and indirect variations in CNTs’ velocities as a function of DEP force were investigated, under different dispersion mediums, for a rectangular electrode pair with a 10 μm gap subjected to a 500 kHz AC signal with an amplitude of 10 V. The effects of changes in permittivity, conductivity, viscosity, and density of the medium were presented and discussed. Simulation results from this study were used to further clarify the role of the medium on the motion of CNTs during alignment using a DEP process prior to an actual alignment.

Determination of complex permittivity of thin dielectric samples based on high-q microstrip resonance sensor

In this paper, a high quality factor microstrip resonator based on modified Minkowski fractal structure sensor is presented for determining the dielectric sample's complex permittivity. A high loaded quality factor value has been achieved by utilizing fractal structure, which is far greater than that of a typical rectangle microstrip antenna. Besides, the modified fractal radiation patch and the feeding section of the sensor result in a highly sensitive area to the tested materials. The sensing principle is implemented by detecting the electric fields perturbation of the resonator when different tested materials are placed over it. The complex permittivity change of the tested materials can be forecasted by transferring the acquired experimental relative resonant frequency shifts (Δf) and loaded QL values of the proposed sensor to a well-developed neural network system. To validate the proposed method, various standard dielectric samples including Teflon, PVC, and others are tested and analyzed. The experimental results are compared with published values with the maximum error of 4.9%.

Relative study between the exposures of 6MeV photons and 0.3 mT-50 Hz magnetic fields in rat's liver

Effect of 0.3mT-50Hz magnetic field exposure on rats' liver dielectric relaxation was studied. Animals were exposed similar to occupational workers 8h/day for periods from 1 to 4 weeks the exposure effects were monitored relative to the effect of exposure to high energy 6MeV standard dose of 1 rad. Dielectric relaxations in frequency range up to 8MHz carried out immediately for all animals from each group to examine bioelectrical changes in liver relative permittivity, conductivity, and dielectric loss. The results indicated significant difference in dielectric characteristics due to the counter-ion diffusion at frequency up to 1MHz, whereas frequency increased the shift unremarkably noticed. Unveil to the data of relative fraction of damage (RFD), it insight remarkable damage due to magnetic fields in a manner it should not be less important than high energy photons. Significantly, animals of 1 week magnetic field exposure showed maximum damage effect by 15%, 26% and 5% damage in relative permittivity, conductivity and dielectric loss respectively more than 6MeV photons exposure. Relative to unexposed group the samples from 1 week magnetic field exposure confirmed liver bioimpedance results and indicated significant increase in enzymatic levels by 20.6%, 17.1%, 3.32% and 13.1% for SGOT, SGPT, TP and MDA respectively. The former results may reflect the animal body self-adaptation as exposure period increased. It is worthy to mention that this work is an important one that correlates between the effects of both extremely low frequency fields and ionizing radiation.

RADIO-WAVES REFLECTION AT REMOTE SENSING OF UNDERLYING COVERS

Monitoring technologies are rapidly developing at present and allow to extract and use non-coordinate information about objects. Noncoordinate information is the information about the type and properties of an object under study. Remote sensing is the main method of solving monitoring problems where special positioning belongs to the radar methods, based on space-time processing of signals and, in particular, on methods of radio polarimetry. It is necessary to have information about the surface in order to solve the monitoring task. The slightest changes in the electrical and physical properties of such areas as salinity, humidity, soil composition, etc. will lead to a change in the basic electrodynamics of the surface, notably its complex dielectric permittivity. The article demonstrates the precise solutions to the problems of radio-waves reflection from a layered surface with various laws of changes of the complex permittivity  in depth. Media with exponential and quadratic laws of variation  for arbitrary angles of incidence of the radio wave on the surface are considered. Precise decision is obtained for layered media with the law of change in the complex permittivity the polynomial and linear characteristics. A similar problem for the parabolic layer is considered separately. The detailed analysis of radio waves reflection from the medium with a matching layer is carried out. The nature of the electromagnetic field inside the transition layer is studied in detail. The article is illustrated by the graphs showing the dependences of an electromagnetic wave reflection coefficient on the layered medium with linear and exponential laws of variation of the complex dielectric constant over depth.

An integrated flexible self-powered wearable respiration sensor

Human respiration is rich in physiological and pathological information for health assessment and illness prediction. In this work, an integrated triboelectric self-powered respiration sensor (TSRS) was developed for simultaneously monitoring human respiratory behaviors and NH3 concentration in exhaled gases. The TSRS based on Ce-doping ratio of 0.004 M exhibits a better selectivity and larger sensitivity of 20.13 ppm−1 compared with those synthesized in other doping ratios. Under the same moisture as the breathing gas (97.5%RH), the sensor holds greater sensitivity toward NH3 at low concentration (0.1–1 ppm) than that at high concentration (1–10 ppm), implying the capability in detecting trace level NH3 biomarker in human breathing gases. Furthermore, triggered by the expansion and contraction of chest during breathing, TSRS can spontaneously monitor human respiratory patterns and physiological process after physical exercise. Meanwhile, a theoretical modeling was established in terms of permittivity change under gas molecules adsorption and verified via finite element simulation to interpret the self-powered sensing behaviors. This research not only proposes a promising approach to develop an all-in-one wearable respiration monitoring system for personal health diagnosis but also sheds some light on the theoretical modeling of triboelectric self-powered gas-sensing in terms of permittivity change.

Aging behavior of flame‐retardant cross‐linked polyethylene in nuclear power plant environments

Sheets of flame‐retardant cross‐linked polyethylene (FR‐XLPE) were aged thermally at 80, 100, 135, and 155 °C for various periods from 100 to 800 h. They were also aged concurrently by heat and gamma rays at the same temperatures for the same periods at a dose rate of 100 Gy/h. For these sheets, we measured indenter modulus, elongation at break, complex permittivity, and absorption spectra at midinfrared and THz frequencies. As a result, it has become clear that the aging at 135 °C makes FR‐XLPE hard regardless of the presence of concurrent irradiation of gamma rays. This makes the transport of charge carriers difficult. Therefore, both the real and the imaginary parts of complex permittivity decrease, which is significant if the measurement frequency is low. However, this tendency becomes opposite as the samples were aged at 155 °C by heat or concurrently by heat and radiation. Using indenter modulus as an indicator, it has become clear that the aging progress is composed of two different stages, which could be a good clue to the explanation of these opposite changes in complex permittivity. On the other hand, the samples aged at 155 °C concurrently by heat and radiation show larger values in the indenter modulus and in two parts of complex permittivity than the samples aged at the same temperature only by heat. This is probably due to the oxidative degradation induced by the cooperative reaction of heat and radiation. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Magnetodielectric Response of Soft Magnetoactive Elastomers: Effects of Filler Concentration and Measurement Frequency.

The magnetodielectric response of magnetoactive elastomers (MAEs) in its dependence on filler concentration, magnetic field, and test frequency is studied experimentally. MAEs are synthesized on the basis of a silicone matrix filled with spherical carbonyl iron particles characterized by a mean diameter of 4.5 µm. The concentration of the magnetic filler within composite materials is equal to 70, 75, and 80 mass%. The effective lossless permittivity ε′ as well as the dielectric loss tanδ grow significantly when the magnetic field increases. The permittivity increases and the dielectric loss decreases with increasing filler concentration. In the measurement frequency range between 1 kHz and 200 kHz, the frequency hardly affects the values of ε′ and tanδ in the absence of a magnetic field. However, both parameters decrease considerably with the growing frequency in a constant magnetic field. The more strongly the magnetic field is applied, the larger the change in permittivity and loss tangent at the same test frequency is observed. An equivalent circuit formulation qualitatively describes the main tendencies of the magnetodielectric response.

Preparation and properties of a left-handed metamaterial composite

ABSTRACTA left-handed metamaterial (a YIG/Ag composite with adjustable negative permittivity and permeability) was prepared by an in situ synthesis process, and its characterisation, microstructure, electrical conductivity, dielectric loss and magnetic properties studied. A negative permittivity behaviour with a Fano-like resonance is ascribed to plasma oscillation of delocalised electrons from silver conducting networks. As the silver content increases, the turbine loss increases, which greatly enhances the electromagnetic wave consumption capacity inside the material and leads to a stronger electromagnetic absorption and shielding performance. The dielectric loss near the percolation threshold is due to the combined effects of polarisation and conduction. The capacitive character is responsible for positive permittivity, and the inductive character leads to negative permittivity. LC resonance results in the Fano-like resonance, leading to the permittivity changing from negative to positive. Gyromagnetic spin rotation, domain wall motion and percolation characteristic of YIG/Ag composites cause frequency dispersion of the permeability. The YIG/Ag composite with double negative characteristics provides prospects for electromagnetic shielding application.

Gas Sensing by Microwave Transduction: Review of Progress and Challenges

Microwave transduction is a novel research field in gas sensing owing to its simplicity, low cost, passive, and non-contact operations that indicate a huge potential in applications for gas sensing. At present, the study of microwave gas sensors is limited to testing the macroscopic performance of materials. Although the permittivity change of materials is the reason for microwave transduction, the knowledge of the fundamental mechanism is an urgent requirement for boosting the development of microwave gas sensors. In this review, we summarized the presented progresses of microwave gas sensors, including the performance of the different materials and propagative structures, as well as their sensitive signal. We have attempted to explain the sensitive mechanism of these materials, discuss the function of the propagative structure, and analyze the sensitive signal extracted from the parameters of electromagnetic waves. Finally, the challenges in the study of sensitive materials and propagative structures used in microwave gas sensors are analyzed. It is clear from the published literatures that microwave transduction provide a new route for gas detection, and it is expected that commercial manifestation will occur. The future research on microwave gas sensors will continue to exploit their sensitive materials and propagative structure for different applications. The understanding of the microscopic polarization interactions with gases will assist in and guide the fabrication of high-performance microwave gas sensors in the future.

The effects of gamma irradiation on dielectric properties of Ag/Gd co-doped hydroxyapatites

1.0 at% Ag-containing hydroxyapatites (HAps) doped with the different amounts of Gd (e.g., 0, 0.8, 1.6 and 2.4 at%) were synthesized by a wet chemical method and their dielectric properties were investigated before and after gamma irradiation. The changes in the relative permittivity and alternating current (AC) conductivity values of the as-synthesized samples before and after irradiation were investigated using dielectric measurements. It was found that both Gd content and gamma irradiation dose significantly affect the dielectric properties and AC conductivity. It was concluded that especially due to the thermal stabilities and suitable dielectric properties, the as-synthesized Gd-doped Ag containing HAps could be used for bone healing applications.

CNT-Based Inkjet-Printed RF Gas Sensor: Modification of Substrate Properties during the Fabrication Process.

This paper presents the feasibility of a fully inkjet-printed, microwave flexible gas sensor based on a resonant electromagnetic transducer in microstrip technology and the impact of the printing process that affects the characteristics of the gas sensor. The sensor is fabricated using silver ink and multi-wall carbon nanotubes (MWCNTs) embedded in poly (3,4-ethylenedioxythiophene) polystyrene (PEDOT: PSS-MWCNTs) as sensitive material for Volatile Organic Compounds (VOCs) detection. Particular attention is paid to the characterization of the printed materials and the paper substrate. The manufacturing process results in a change in relative permittivity of the paper substrate by nearly 20%. Electrical characterization, made in the presence of gas, validates our theoretical approach and the radiofrequency (RF) gas sensor proof of concept.

Electromagnetic properties of chloroprene rubber after long-term ultraviolet ageing, oil immersion and thermal degradation

The electromagnetic properties of chloroprene rubber after long-term ultraviolet ageing, oil immersion and thermal degradation were experimentally investigated in the frequency range from 1 kHz up to 1 THz. Ageing was shown in terms of mechanical degradation and the change in the complex dielectric permittivity. Within the whole investigated frequency range decrease of dielectric permittivity was observed after thermal treatment combined with oil immersion in comparison with chloroprene rubber stored under normal conditions. In contrast, thermal and ultraviolet ageing without immersion leads to increase of rubbers dielectric permittivity in all investigated frequency ranges. A non-invasive express method of degradation detection is proposed and proofed.

Time Dependences of Dielectric and Acoustic Properties in PbFe0.5Nb0.5O3 and PbFe0.5Nb0.5O3–7PbTiO3 Single Crystals

The time changes of permittivity, damping and velocity of sound are studied for PbFe0.5Nb0.5O3 and PbFe0.5Nb0.5O3–7PbTiO3 single crystals in the electric fields of 0 < E < 6 kV/cm. The room-temperature local symmetry of these compounds is shown to be rather more monoclinic than rhombohedral, which is typical of other similar systems. No abrupt sound attenuation anomalies are observed upon the phase transition into the ferroelectric phase in the electric field. The effects seem to be far from the crystal symmetry changes and are attributed to the gradual transition of near-range monoclinic domains into long-range monoclinic domains, as well as to the emergence of the ferroelectric phase. The polarized phase induced in the electric field is only partially stable.

A study of the possibility of using 3D modelling and 3D printing for electrical capacitance tomography sensor

Nowadays, the optimization of energy consumption and resources is one of the most urgent topics in worldwide industry. The energy consumption monitoring and control in various multiphase flow industrial applications, where a proper flow characteristic and an optimal phase mixture control is crucial, is hard to perform due to the physical and chemical complexity of the processes. The Electrical Capacitance Tomography (ECT) is one of the relatively cheap non-invasive measurement methods that can help in the monitoring and control of optimal energy and resources dozing in industrial processes. ECT diagnostics systems use unique sensors that can non-intrusively detect spatial capacitance changes caused by spatial changes in the electrical permittivity of industrial process components. One of the latest ECT extensions is a three-dimensional measurement strategy that uses a multilayer structure of the capacitance sensor. In this paper, the authors propose a novel approach to the 3D ECT sensors fabrication process that uses 3D computer modelling and 3D printing to easily get any sensor shape, electrode layout, scale and shielding strategy. This study compares the measurement abilities of a 3D ECT sensor fabricated using a traditional hand-made technique with the 3D printed device. The results have proven the potential of the new 3D print-based sensor regarding its significant fabrication time reduction as well as the improvement of the overall 3D ECT sensor measurement accuracy and stability.

Simulation of Magnetodielectric Effect in Magnetorheological Elastomers.

We present the results of numerical simulation of magnetodielectric effect (MDE) in magnetorheological elastomers (MRE)—the change of effective permittivity of elastomer placed under the external magnetic field. The computer model of effect is based on an assumption about the displacement of magnetic particles inside the elastic matrix under the external magnetic field and the formation of chain-like structures. Such displacement of metallic particles between the planes of capacitor leads to the change of capacity, which can be considered as a change of effective permittivity of elastomer caused by magnetic field (magnetodielectric effect). In the literature, mainly the 2D approach is used to model similar effects. In this paper, we present a new approach of magnetorheological elastomers simulation—a 3D-model of the magnetodielectric effect with ability to simulate systems of particles. Within the framework of the model, three types of particle size distributions were simulated, which gives an advantage over previously reported approaches. Lognormal size distribution was shown to give better qualitative match of the modeling and experimental results than monosized type. The developed model resulted in a good qualitative agreement with all experimental data obtained earlier for Fe-based elastomers. The proposed model is useful to study these novel functional materials, analyze the features of magnetodielectric effect and predict the optimal composition of magnetorheological elastomers for further profound experimental study.

Optical stimulated transfer from glass state to polar phase in relaxors

We measured the time dependences of the dielectric permittivity of a single crystal lead magnoniobate in [110] orientation from the moment of the field application at the certain temperatures after the zero-field cooled regime. The delay time of the phase transition from the glasslike to the field-induced ferroelectric state was determined for the sharp change in the dielectric permittivity at the several temperatures. The phase transition to the ferroelectric state was confirmed by measuring the pyroelectric current. Then the same experiment was repeated in illumination condition. The effect of illumination on the delay time of the phase transition was investigated. In the case of ultraviolet illumination, the delay time became few times shorter.