Electric Permittivity Measurements Research Articles

Automated non-destructive 3D printing filament material properties monitoring based on electric permittivity, longitudinal encoding and diameter multi-axes real-time measurements

Rapid prototyping is an essential part of today’s research and development process. The ability to produce objects quickly, cost-effectively and on-site is critical to meeting this fundamental requirement. One of the factors that leads to inconsistencies and defects in the produced parts is the uncompensated change in material properties used in the material extrusion 3D printing manufacturing process. This creates the need for a real-time, low-cost filament quality monitor that can characterize the material properties of the filament along its length. This can be achieved by tracking the variation in measured capacitive tube capacitance and diameter of different sensor types over multiple selected axes and encoding the results to a specific fragment of filament used in material extrusion 3D printing. With such collected data it is possible to monitor factors such as material moisture, roundness, internal and external defects, component proportions, relative electrical permeability, Poisson’s ratio and material type. This work presents the first proof of concept of such a device and describes its operating principle in detail. As examples of applications, filament material type recognition is presented based on the characteristics of several types of filaments from different manufacturers, the process of moisture absorption over time for selected filaments is described, and the detection of defects of varying degrees is shown.

Effectiveness of Electrostatic Shielding in High-Frequency Electromagnetic Induction Soil Sensing.

High-frequency electromagnetic induction (HFEMI) sensors, operating in the frequency range from 300 kHz to 30 MHz, have been proposed for the measurement of soil electrical conductivity and dielectric permittivity that are related to the physical and chemical properties of soil. Because of the high-frequency operation, the capacitive coupling between the sensor transmitter and receiver coils is comparable to inductive coupling, creating the need for electrostatic shielding. The remnant capacitive coupling after the implementation of shielding can lead to significant difficulties in the sensor signal interpretation, because both coupling mechanisms are highly dependent on the geometry of the HFEMI sensor and applied shield. In this paper, we introduce the discussion on the relationship between the sensor geometry, shielding and the coupling mechanisms for HFEMI soil sensing. We theoretically and experimentally evaluate a typical HFEMI sensor and its shielding in the frequency range of up to 20 MHz and propose a method for evaluating the effectiveness of a shield configuration. In the case study, we experimentally analyze the HFEMI sensor above a saline solution for two shield configurations. The results agree well with the results of a finite element method analysis.

Self‐Poled Heteroepitaxial Bi(1−x)DyxFeO3 Films with Promising Pyroelectric Properties

AbstractPyroelectric materials are very promising for thermal energy harvesting applications. To date, lead‐based systems are the foremost studied materials in this field. A facile and simple metal organic chemical vapor deposition route is applied for the fabrication of lead‐free, high quality, epitaxial Bi(1−x)DyxFeO3 (x = 0, 0.06, 0.08, 0.11) thin films deposited on conductive SrTiO3:Nb (100) single crystal substrates. The films are studied by structural, morphological, compositional, and functional characterization. The correlation between the Dy‐doping amount and the dielectric properties is thoroughly investigated. Unipolar polarization–electric field loops and permittivity measurements show the important impact of Dy on ferroelectric, dielectric, and pyroelectric properties. Dy doping increases considerably the dielectric response, but much more the pyroelectric coefficient, up to a concentration of 8% Dy. The films are self‐poled, which is an ideal situation for pyroelectric applications. The best figure of merit for pyroelectric energy harvesting, FE, is 82 J m−3 K−2, showing a factor increase of 2.6 as compared to the undoped film of the sample series. It constitutes a factor 4.5 improvement as compared to previous results obtained on BiFeO3 based thin films.

Evaluation of soil salinity using the dielectric sensor WET-2

Context The electrical conductivity of the soil saturated paste extract (ECe) is used to estimate the soil salinity. Aims This study aims to develop simple or multiple linear regression models to estimate the ECe using soil properties measured by a dielectric sensor in the field. Methods The measurements of bulk electrical conductivity (ECb), soil temperature (T) and dielectric permittivity (εb) in agricultural fields were conducted using the WET-2 sensor. A total of 105 soil samples were obtained from agricultural fields in three regions of Greece. Key results A very strong positive correlation between ECb and ECe (r > 0.6 and P < 0.001) was obtained by using the Spearman’s correlation coefficients. Multiple linear regression models (MLR) were developed using only the parameters εb, ECb and T measured by the WET-2 in estimating ECe. Considering that the MLR models are site specific, the ECe could be reliably estimated by applying MLR models in regions with coarse textured soils. Contrarily, in regions with finer textured soils characterised by ECb values <1 dS m−1, additional soil parameters are required to be included in MLR models to estimate of ECe more accurately. In regions with soils characterised by high salinity (4 dS m−1 < ECe < 25 dS m−1), a simple linear regression model seems to be sufficient. Conclusions and implications As the WET-2 sensor measures simultaneously three soil properties in situ, it might be a valuable tool for estimating ECe, for the first centimetres of soil, in the case that the soil is not dry with relatively low clay content.

Electric Properties of AlGaN/GaN/Si High electron Mobility Transistors

This work investigated the electrical properties in AlGaN/GaN/Si HEMTsgrown by molecular beam epitaxy. The electrical behavior have been investigated using by electric permittivity, modulus formalism and conductance measurements. As has been found from electrical conductance, dispersive behavior is related to barrier inhomogeneity and deep trap in barrier layer. On the other hand, the strain relaxation of charge transport is studied both permittivity and electric modulus formalisms.

Experimental apparatus for the determination of thermal conductivity and humidity in building materials by means of electrical permittivity measurements

The on-site measurement of the thermal properties of existing building envelopes is of utmost importance to fairly accurately calculate the thermal loss by transmission to the outside environment and so to define the building overall energy performance. This paper presents a preliminary investigation concerning the use of a new indirect method for measuring the thermal characteristics of building materials throughout the year based on the analysis of the material electrical properties. The main goal is to identify a relationship between thermal transmittance, moisture content and electrical impedance through relative electrical permittivity measurements.

Structural, thermal and dielectric behavior of two-dimensional layered Ti3C2Tx(MXene) filled ethylene–vinyl acetate (EVA) nanocomposites

Two-dimensional layered conductive material (MXene) filled polymer composite structures were prepared by implementing the solution casting technique. The polymer matrix ethylene–vinyl acetate copolymer (EVA) and for the inorganic segment MXene i.e., titanium carbide (Ti3C2) is used. The MXene i.e., Ti3C2Tx was first synthesized from its corresponding MAX phase, i.e., Ti3AlC2 by HF etching method. The different weight percentage (wt%) of 0, 1, 3, 5, 8, 10, 12 of filled Ti3C2Tx-EVA composites are synthesized by varying the amount of Ti3C2Tx by keeping EVA constant. The formation of Ti3C2Tx/EVA composites were confirmed by different characterization technique such as SEM, XRD, Raman, FTIR, TGA analysis. The electrical and dielectric permittivity measurements of the synthesized composites were carried out in the frequency range of 1 kHz–1 MHz. The 8 wt% of Ti3C2Tx filled EVA composite exhibit higher dielectric properties with low dielectric loss among all weight percentages. The high dielectric properties are due to high electrical conductivity, proper dispersion of filler and synergetic interaction between the matrix and filler.

Characterization of isooctane/AOT/water reverse micelles by dielectric spectroscopy, dynamic light scattering and acoustic methods

Reverse micelles are complex systems, where polar phase is enclosed in surfactant shell surrounded by non-polar solvent (water-in-oil microemulsion). Our previous studies proved their large sensibility to an external electric field and revealed a presence of pronounced maximum in the non-linear dielectric effect measured in function of concentration of water. The results obtained previously do not allow for an unequivocal explanation of the observed maximum. In this paper the micellar system of isooctane/sodium docusate (AOT)/water was investigated by dielectric spectroscopy, non-linear dielectric effect, dynamic light scattering and acoustic methods. The measurements were performed along pathways of constant AOT-to-isooctane ratios. The existence of maximum of the nonlinear dielectric effect investigated in function of water content was confirmed. It was shown that the maximum occurs for mixtures for which the molar ratio of water to surfactant (w0) is 10. Strong maxima were also observed in the measurements of electric permittivity and conductivity. The maxima were found for the same concentrations as those for non-linear dielectric effect. Sound velocity and dynamic light scattering studies do not evince any anomalies in the mixtures under discussion. No convincing evidence has been found that the maxima noticed in dielectric studies are related to critical phenomena. They were interpreted basing on the percolation effect, but not all the observed properties can be explained in this way.

High-speed density measurement for LNG and other cryogenic fluids using electrical capacitance tomography

The global custody transfer market for liquefied natural gas (LNG) has grown at a strong pace in the last decade and use of LNG as transport fuel has considerable environmental benefits. The quantity of LNG is traded on the basis of energy transferred, calculated from volume, density and gross calorific value. High-speed, accurate density measurement is therefore of significant commercial value.The electrical capacitance tomography (ECT) device described in this paper has the potential to measure the LNG density rapidly, on-line at a moderate cost. Continuous monitoring of variation in LNG density during dynamic LNG flow measurement also gives a good indication of change in fluid quality and thus onset of boiling which is known to affect measurement accuracy. ECT is a leading candidate to be explored for online density measurements through measurement of electrical permittivity, as in addition to average value, it offers the image of permittivity across the whole flow conduit, allowing localised bubbles, boiling or other variations to be identified and measured.We report here experiments to explore the use of ECT in cryogenic applications. An 8-electrode test ECT sensor was designed, built and tested in laboratory conditions and then in liquid nitrogen. The resolution and imaging capability in cryogenic conditions are shown to be comparable to that under laboratory conditions. The experiments reported here use liquid nitrogen as an analogue fluid, but the results presented are believed to be representative of many cryogenic fluids. Although the use of ECT has been widely reported in the literature for multiphase flows in general, its use has not previously been reported for cryogenic flows. This paper offers proof of principle for ECT cryogenic multi-phase density and flow measurement.Dielectric constant is strongly linked to fluid density, and the ECT sensor design tested here shows an estimated measurement of the relative permittivity of liquid nitrogen of 1.45 with a standard measurement error of 0.034. Measurement stability at cryogenic conditions gave an rms variation of output under static conditions of better than 0.001 relative permittivity units even though it was unguarded and only a single electrode ring. The primary errors are associated with the unguarded nature of the test sensor, which was primarily designed as a proof of concept and material demonstrator.In addition, such an ECT sensor would provide clear images of any gas in the liquid and give a good estimation of the concentration and velocity of the gas bubbles. The scope of this work is to provide a proof of concept of the cryogenic ECT sensor.

Development of RGO/BaFe12O19-based composite medium for improved microwave absorption applications

Microwave absorbing composite containing barium hexaferrite (BaFe12O19) and reduced graphene oxide (RGO) has been synthesized for X-band (8–12 GHz). Barium hexaferrite particles are synthesized by auto-combustion reaction using citrate precursors. The synthesis process of RGO is carried out by using improved hummer’s method. Different composites consisting of barium hexaferrite and RGO are fabricated by mixing of RGO and barium hexaferrite in different weight percentages followed by heat treatment. The developed composites are characterized for electric permittivity, magnetic permeability and reflection loss measurements. Three composites, namely RGO2, RGO4 and RGO6, are developed by varying weight percentage of RGO in barium hexaferrite. The saturation magnetization of barium hexaferrite is observed to decrease from 47.02 to 16.253 emu/g, with the increase in RGO content in the composite. The composite containing 6% RGO (RGO6) shows maximum value of complex permittivity. When RGO6 composite is casted into a pellet of thickness 2.1 mm, the maximum reflection loss of − 52.21 dB is achieved at frequency 10.72 GHz. Also, the − 10 dB bandwidth of RGO6 composite reached to 2.92 GHz, i.e., covering about 70% of X-band.

Accurate Technique for Electrical Permittivity Measurement of Biological Tissue Specimens at Low Frequencies

This paper proposes a technique aimed at accurate measurement of electrical permittivity (EP) of small tissue specimens at low frequencies. Accurate measurement of EP of healthy and pathological tissues can facilitate the establishment of many medical applications such as electrical impedance imaging. The proposed novel technique employs hardware with high precision for impedance measurement of capacitive structures formed by the tissue specimen as its dielectric combined with two conductive plates placed at two ends of the specimen. To determine the EP of the tissue specimen, the capacitance part of the measured impedance is processed using an inverse finite-element framework. In this framework, accurate geometry and boundary conditions of the specimen are considered. The proposed technique was validated before it was employed to measure EP of several tissue specimens including bovine heart, liver, and bone. Results obtained in this investigation indicate that the proposed technique is reliable as it provides improved EP measurement accuracy and repeatability of homogeneous or multilayered tissue specimens, especially at low-frequency range.

The Effects of Silica on the Properties of Vitreous Enamels.

Ground coat enamels for low carbon steel that contain silica as a mill addition have been developed to study the changes of their properties. Acid-resistant commercial enamel where silica addition was varied from 0 to 10.0 wt % was used for this investigation. The effects of the addition on the corrosion resistance, thermal properties, electrical properties, and mechanical adherence of the enamel to low carbon steel were studied. The corrosion resistance of the steel enameled coupons was tested using a salt spray (fog) apparatus for time periods reaching 168 h at room temperature. It was found that, although the density was not affected, the adherence decreased with an increase in silica content. As expected, the silica addition decreased the coefficient of thermal expansion, which is directly related to the increasing stress between the glass and steel in accordance with the adherence results. A mill addition of 7.5 wt% of silica to the samples was sufficient to obtain adequate enamel adherence and good corrosion resistance. Furthermore, the addition of silica influenced the electrical conductivity and dielectric permittivity measurements at room temperature and the conductivity measured in a wide frequency range (1 Hz–1 MHz). The dielectric permittivity measured at 1 MHz showed decrease after the addition of up to 7.5 wt% of silica.

Thermomechanical and Electrical Properties of Fabric Reinforced Laminates with Filled Stratified Epoxy Matrix

The thermal coefficient of linear expansion, the electrical conductivity and dielectric permittivity of fabric reinforced hybrid composites with filled stratified epoxy matrix were investigated. The measurements of electrical conductivity and dielectric permittivity had been performed, using standard method regarding electrical resistance and electrical capacity. In order to point out the effect of filler and of the spatial distribution of reinforcement layers, the medial layer of fabric was especially prepared by introducing copper wires in the woven. So, the medial layer is made of different types of tows (carbon, aramid, glass). This attempt is made in order to design a composite able to provide information about its state during various loading. The results showed that the fillers did not improve the electrical parameters of epoxy matrix, but they led to reduce the thermal coefficient of linear expansion. The thermal and electrical behavior of hybrid composites varied in dependence of number of carbon layers and fiber orientation.

Morphological, electromagnetic and absorbing properties of pani/epoxy resin samples

This work deals with the study of radar absorbing materials (RAM) based on conductive samples obtained with polyaniline (PAni) (5-20 wt%) inserted in epoxy resin matrix. SEM analyses show that the PAni presents granular morphology, with an average diameter of 5 µm, with structures evenly distributed. DRX and FT-IR analyses show that the PAni polymer was successfully obtained in its conductive form. Electrical permittivity and magnetic permeability measurements of PAni/epoxy samples were performed in the frequency range of 8.2 to 12.4 GHz (X-band). Microwave attenuation values showed that the PAni-20wt%/epoxy resin sample presented a maximum attenuation of -24 dB, i.e. ~99.6% attenuation of the incident radiation. It was also observed that the amount of attenuated energy varies according to the incident frequency and the specimen thickness.

Hydrocarbon saturation in Bakken Petroleum System based on joint inversion of resistivity and dielectric dispersion logs

Bakken Petroleum System (BPS) is composed of both conventional and unconventional units, which exhibits significant variations in lithology, rock texture, clay content, total organic carbon, accompanied by high connate water salinity, presence of disseminated pyrite grains, and low values of porosity. These petrophysical attributes of the BPS lead to inconsistency in the oil-in-place estimates for those obtained from Electromagnetic (EM) induction log, Nuclear Magnetic Resonance (NMR) log, dielectric dispersion log measured by Array Dielectric Tool (ADT), and Dean-Stark core measurements. For purposes of improved hydrocarbon saturation estimation and petrophysical characterization in the BPS, a joint-inversion-based interpretation was performed on dispersive electrical conductivity and dielectric permittivity measurements at 4 dielectric-log-acquisition frequencies and 1 induction resistivity acquired at 20 kHz. This analysis was performed across a 350-ft depth interval in one of the science wells intersecting the BPS. Three geo-electromagnetic mixing models, namely Complex Refractive Index model, Stroud-Milton-De model, and Waxman Smits model are integrated and coupled to the inversion scheme to simultaneously estimate water saturation, formation brine conductivity, cementation exponent and saturation exponent in BPS.Water saturation estimates obtained using the proposed interpretation method were compared against those obtained from NMR log, Dean-Stark core measurements and service company’s dielectric inversion. In Middle Bakken from depth XX720 to XX750 ft, our estimates of water saturation are in better agreement with those estimated by service company’s mineral inversion method and service company’s dielectric interpretation as compared to those obtained from NMR interpretation and Dean Stark core measurement. Water saturation and formation brine conductivity estimates in Middle Bakken are in the ranges of 0.5–1 and 25–45 S/m, respectively. Inversion-derived brine conductivity and saturation exponent estimates are most uncertain in Lodgepole and Three Forks 2 formations, which exhibit a wide range of pore size distribution. Average relative errors in matching the 1 induction resistivity and 8 dielectric dispersion logs using the inversion-derived estimates are 33% and 20%, respectively, in the 350-ft depth interval of BPS. The proposed inversion achieves high certainty for the estimates when the formation has low clay content, low electrical anisotropy, and high porosity.

Performance Prediction of Microwave Absorbers Based on POMA/Carbon Black Composites in the Frequency Range of 8.2 to 20 GHz

This paper presents a comparative study involving experimental and numerical behaviors of radar absorbing materials (RAM), based on conducting composites of poly(o-methoxyaniline) (POMA) and carbon black (CB). Samples of POMA/CB in epoxy resin matrix were prepared. First, these samples were experimentally characterized by electric permittivity and magnetic permeability measurements in the frequency range of 8.2 to 12.4 GHz. Afterwards, a linear extrapolation of these electromagnetic parameters until 20 GHz was carried out. These amounts were used as parameters for a set of simulations, developed from numerical implementation of theoretical predictions. The main advantage of the performed simulations is to know the behavior of the POMA/CB/epoxy resin as RAM in a wide range of frequencies (8.2-20 GHz), previously to the experimental work. The validation of the simulations with experimental refl ection loss measurements showed a good fit and allowed predicting the material behavior as RAM. The results show that the studied RAM presents good return loss values in different frequencies, for example, –32 dB (~99.95% of absorption) at 14.6 GHz and –18 dB at 19.2 GHz, for samples with 7 and 9 mm-thickness values, respectively. The simulation tool used in this study was adequate to optimize the RAM production, contributing to the reduction of development costs and processing time of this kind of material.

Effect of PANI on Thermal, Mechanical and Electromagnetic Properties of HDPE/LLDPE/PANI Composites

In this work, polyaniline (PANI) in emeraldine-base form, synthesized by chemical oxidation polymerization, was protonated with hydrochloric acid (HCl). Composites based on high-density polyethylene (HDPE) and linear-low density polyethylene (LLDPE) blends with PANI were prepared in molten condition using a torque rheometer. The effect of compatibilizer agent (maleic anhydride-grafted high density polyethylene, HDPE-g-MA) and different contents of PANI on the blends-based composites was also investigated. Thermal, mechanical, and electromagnetic (electric permittivity) measurements and morphological aspects of the composites were evaluated. The addition of PANI content in the composites decreases the degree of crystallinity of HDPE and LLDPE blends, which implies that PANI particles make it difficult for co-crystallization to occur in the HDPE and LLDPE, respectively. On the other hand, the addition of compatibilizer agent in the HDPE and LLDPE blends increased the degree of crystallinity. The complex parameters of permittivity in the frequency range of 8.2 to 12.4 GHz varied as a function of the PANI content in the blend. It was also observed that the compatibilizer agent increased the composite stiffness and decreased the electric permittivity values. This result shows that the increasing rigidity of the molecular structure of the polyethylene matrix hindered the dissipation of the electromagnetic energy in the sample.

Magnetic compensation-induced sign reversal of exchange bias in a multi-glass perovskite SmFeO3

We report an unusual sign reversal of exchange bias (EB) across a magnetic compensation point in an orthorhombic perovskite SmFeO3. A conventional negative EB with a positive vertical magnetization shift is observed below a cluster-glass freezing temperature (Tg ∼ 150 K). Upon further lowering of the temperature, the EB disappears at the magnetic compensation point before reversing its sign to a positive exchange bias below 4 K. The EB effect originates from an interfacial exchange interaction within a cluster glass phase, whereas its sign reversal arises from the reversal of the direction of the net magnetic moment as a result of dominance of Sm3+ over Fe3+ below the compensation temperature. The existence of a multi-glass state is demonstrated by ac-susceptibility and electrical permittivity measurements. A phenomenological model is presented to understand the EB effect and its sign reversal across the compensation point.

The influence of the relative thermal expansion and electric permittivity on phase transitions in the perovskite-type bidimensional layered NH3(CH2)3NH3CdBr4 compound

Hydrothermal method has been used to synthesized the layered hybrid compound NH3(CH2)3NH3CdBr4 of perovskite architecture. Structural, dielectric and dilatometric properties of the compound have been analyzed. Negative thermal expansion (NTE) effect in the direction perpendicular to the perovskite plane as well as an unusual phase sequence have been reported based on X-ray diffraction analysis. Electric permittivity measurements evidenced the phase transitions at Tc1=326/328K and Tc2=368/369K. Relative linear expansion measurements almost confirmed these temperatures of phase transitions. Anomalies of electric permittivity and expansion behavior connected with the phase transitions are detected at practically the same temperatures as those observed earlier in differential scanning calorimetry (DSC), infrared (IR), far infrared (FIR) and Raman spectroscopy studies. Mechanism of the phase transitions is explained. Relative linear expansion study was prototype to estimate critical exponent value β for continuous phase transition at Tc1. It has been inferred that there is a strong interplay between the distortion of the inorganic network, those hydrogen bonds and the intermolecular interactions of the organic component.

Thermal, mechanical and electromagnetic properties of LLDPE/PANI composites

Conducting polymers have attracted a great scientific and technological interest due to their interesting properties, particularly its high electrical conductivity. The polyanilines stand out because of the ease of doping with protonic acids and their chemical stability in the doped form. The processability of conducting polymers is a crucial factor in the use of their electrical and electrochemical properties in technological applications. In this work, the processability of linear low-density polyethylene (LLDPE) and polyaniline (PANI) composites was evaluated using a torque rheometer. Composites with different contents of PANI were processed in a torque rheometer and characterized using thermal analysis (DSC), mechanical properties (uniaxial tension), electromagnetic (electrical permittivity, magnetic permeability and reflection loss) measurements and scanning electron microscopy observations. The addition of PANI decreased the crystallinity degree of the LLDPE. On the other hand, the elastic modulus increased. The complex parameters of permittivity and permeability (8.2–12.4 GHz) varied as function of the PANI content in the LLDPE. Reflection loss simulations in the frequency range of 8.2–12.4 GHz showed that the 2.0-mm-LLDPE/PANI sample (60/40 wt%) behaved as a good microwave absorber attenuating the incident electromagnetic wave up to 92%.