Permittivity Measurements Research Articles

Performance of snow density measurement systems in snow stratigraphies

Abstract Gravimetric and dielectric permittivity measurement systems (DMS) are applied to measure snow density, but few studies have addressed differences between the two measurement systems under complex snowpack conditions. A field experiment was conducted to measure the snow density using the two measurement systems in stratigraphical layers of different densities, liquid water content (LWC), hardness, and shear strength, and the performance of the two measurement systems was analyzed and compared. The results showed that the snow density from the DMS tended to underestimate by 9% in the dry snowpack and overestimate by 3% in the wet snowpack, expressed as the percentage of the mean density from the gravimetric measurement system (GMS). Compared with the GMS, the DMS has relatively low precision and accuracy in the dry snowpack and similar precision and accuracy in the wet snowpack. The accuracy and precision of the two measurement systems increased with the increase of hardness and shear strength of snow in the dry snowpack, but the accuracy and precision measured of the DMSs increased with the decrease of hardness and shear strength of snow in wet snowpack. The results will help field operators to choose a more reasonable measurement system based on snowpack characteristics to get reliable density data and optimize field measurements.

Electromagnetic interference shielding performance enhancement of stretchable transparent conducting silver nanowire networks with graphene encapsulation

Silver nanowire (AgNW) networks are promising transparent conducting materials for electromagnetic interference (EMI) shielding and diverse optoelectronic devices. However, the poor contact between adjacent AgNWs leads to low electrical conductivity and weak mechanical stability of AgNW networks, which are limiting the practical application of these electronics. Here, we report an efficient strategy to improve the overall performance of AgNW networks, in which the AgNW networks are sandwiched between two layers of graphene films. The graphene films improve the contact of overlapped AgNWs and bridge the discrete AgNWs and thus increase the conductivity of graphene/AgNWs/graphene (GAG) films. Microwave permittivity measurements together with mechanism analyses reveal that the graphene films can enhance the EMI shielding effectiveness of AgNW networks through offering extra conduction loss, multiple dielectric polarization centers and multi-reflection processes. As a result, the GAG film with an average transmittance of 88% exhibits a sheet resistance lower than 15 Ω sq−1 and an EMI shielding effectiveness of 31 dB (in the frequency range of 8.2–12.4 GHz) after repeated stretching and release at a strain of 40%. Such a total performance is superior to that of most of as-reported transparent conductors. The GAG films therefore show application potential in the age of Internet of Things that electromagnetic radiation pollutions are everywhere.

Compact antenna based on split ring resonator as high Q-factor antenna for liquid permittivity measurements

Abstract Microwave sensing is important to measure the permittivity of the materials or detecting a material. In this current work, a compact antenna for WLAN application with circular polarization is designed. We are supposed to use it as a sensor to determine the permittivity of industrial oil. For calibration of the sensor, the gasoline and petrol are utilized based on Debye theory and also butanol is checked. This antenna is designed based on Microstrip slot antenna with bent feed line and special split-ring resonator (SRR) as a metamaterial (MTM) element for 4 GHz, it is shown that metamaterial can be considered for improving the Q-factor and matching where the return loss is reduced from −16.5 to −33.5 dB and the Q-factor is increased from 2.39 to 32.9. It covers 4–5 GHz with the bidirectional pattern with gain of 4 dBi which makes it useful for putting inside of liquids. The total dimensions of this resonator are 20 × 20 × 1.6 mm and the FR-4 low-cost substrate is used and the experimental results are confirmed the simulations results by HFSS commercial full-wave software. In fact, this method can be used for fast detecting oil condition and longevity by checking the resonances’ shift and permittivity.

Permittivity and electrical resistivity measurements and estimations during the recovery of DNAPL in saturated porous media: 2D tank experiments

Pumping experiments were performed in a 2D tank in order to estimate the recovery yield and rate of pure heavy chlorinated organic compounds (DNAPL; dense non-aqueous phase liquids). Several operating configurations were considered: permeability of the saturated zone, pumping flow rates, addition of surfactant (to reduce capillary effects), and thermal treatment (to reduce DNAPL viscosity). The experiments were monitored with permittivity (ε) and electrical resistivity (ρ) measurements. The experiments were also monitored with photography allowing, based on image interpretation, to accurately convert optical densities into water saturations (Sw) and to validate the geophysical data collected. Average Sw were determined in all detection areas from permittivities and electrical resistivities. These average Sw were used to calculate theoretical permittivities using the complex refractive index model (CRIM) and theoretical electrical resistivities using Archie's law. We found a good correlation between measured permittivities and the estimated permittivities with image. Conversely, the correlation was less accurate between measured and estimated electrical resistivities except for low electrical resistivities (i.e. high Sw). It is therefore not possible to accurately quantify water saturations using electrical resistivity monitoring alone. However, the accuracy is sufficient (especially for high values of Sw) to highlight differences between the three considered treatment technologies (i.e. without enhancement, with chemical and/or thermal enhancements). A combination of monitored electrical resistivity (which provides an integrated vision of the cone of depression) and monitored permittivity (which provides accurate but spatially limited information), and imaging allows a more accurate calibration of the relationship between resistivities and Sw and quantification of remediation rates and yields.

The features of organic soil dielectric characteristics in the Arctic region

The results of measurements of the complex dielectric permittivity of the Arctic region organic soil are presented. The trends in the change of the soil CDP with varying soil moisture and temperature are described. We compared measure data with the values calculated by the Dobson model for sandy and silty clay soil. It was found that the experimental and model data differ markedly.

Phase-Variation Microwave Sensor for Permittivity Measurements Based on a High-Impedance Half-Wavelength Transmission Line

A phase-variation microwave sensor operating in transmission and implemented by means of a high-impedance half-wavelength sensing line is reported in this paper. The sensor is useful for dielectric constant measurements and dielectric characterization of materials. By forcing the electrical length of the sensing line to be a half-wavelength when it is loaded with the so-called reference (REF) material, perfect matching is obtained regardless of the characteristic impedance of the line. This fact can be used to enhance the sensitivity for small perturbations, by merely increasing the characteristic impedance of the sensing line. An exhaustive analysis that supports such conclusion is reported in the paper. Then, two prototype sensors are designed and fabricated for validation purposes. As compared to the ordinary phase-variation permittivity sensor implemented by means of a matched ( 50-Ω) line with identical length, the sensitivity for small perturbations in the proposed sensor is 2.1 times larger. Further advantages of these sensors are low-cost, small size, implementation in planar technology, and very simple design and fabrication, derived from the fact that the sensing region is a half-wavelength transmission line.

Electrical properties and kinematic viscosity of biodiesel

Kinematic viscosity and electrical properties (permittivity and electrical conductivity) of biodiesel samples were determined in the temperature range between 298 K and 343 K. The samples were produced from sunflower, olive, canola, corn, soybean, grapeseed and jatropha vegetable oils. Electrical measurements were carried out in the frequency range from 20 Hz to 2 MHz.From the analysis of the experimental results, two models were developed to estimate the kinematic viscosity from electrical properties. The first model estimates the kinematic viscosity from relative permittivity measurements, with an RMS uncertainty below 0.4 mm2/s for all the samples. The second model allows the estimation of the kinematic viscosity from conductivity measurements, with an RMS uncertainty below 0.07 mm2/s for all the samples. The models and procedures presented in this work reduce the measuring time for kinematic viscosity from several minutes to a few seconds. The results are relevant for biodiesel characterization, on-line viscosity monitoring systems, and in measurements where time is prioritized over accuracy. Moreover, a power law scaling was found relating kinematic viscosity and electrical conductivity. This result is relevant for the study of processes that depend on these transport properties, such as flow electrification. For the samples studied, the fitted value of the power law exponent is -0.67±0.02.

Application of a dagger probe for soil dielectric permittivity measurement by TDR

The most basic parameter of soil is volumetric water content (VWC). This parameter is typically determined indirectly, based on other parameters. Currently, a widely used method for indirect VWC determination is a method which is based on soil dielectric permittivity (DP) measurement, using the well-known Topp formula. The paper presents a novel probe for soil VWC and electrical conductivity (EC) measurement employing the above method. The new probe is going to be adopted on a mobile plant-watering machines used in precise agriculture e.g. for plants watering, thus it features a robust mechanical design and allows for instantaneous readout of VWC and EC values. The design of the probe mimics a dagger with three flat conductors forming a short-circuited coplanar waveguide with the space between the conductors filled with a mineral cold-curing resin. The resin filling the space between the bars improves the mechanical stiffness of the probe and ensures constant electrical parameters, which increases the measurement accuracy. In the first step, Ansys HFSS software was used to perform electromagnetic (EM), numerical simulations for the proposed solution, in order to determine the optimal electrical parameters of the probe. Next, a probe prototype was made to carry out laboratory tests. The measurements were performed with the use of a vector network analyzer (VNA) in the frequency range (3.74 MHz − 3 GHz). The measured complex reflection coefficients were transformed into the time domain with the use of the inverse Discrete Fourier Transform (IDFT). Based on the time distance between the reflections of an electric pulse traveling along the probe's sensing element, bulk dielectric permittivity of soil surrounding the probe can be calculated. A linear relation between the square root of DP and the pulse propagation time was obtained. Also, the probe was calibrated for bulk electrical conductivity measurements.

DIELECTROMETRIC STUDY OF RADIATION PROTECTION ABILITY OF ULTRA-DISPERSED NANODIAMONDS

Radiation protection ability of the ultra-disperse nanodiamonds (UDD) is studied based on the measurements of dielectric permittivity of red blood cells (RBC) affected by cancer. Wistar rats with Guerin's carcinoma were treated by X-ray 5.8 Gy. Some rats received UDD with food during 5 days prior to the X-ray. The groups with UDD, X-ray, and both UDD and X-ray treatments were compared to the control group. The complex dielectric permittivity of the RBC was measured by microwave dielectrometry. It was shown, tumor development leads to the increase in the dielectric permittivity and relaxation frequency. The irradiation promotes further growth of the parameters, while UDD uptake leads to insignificant changes in comparison to the control group. Therefore, UDD occur the radioprotective effect promoting repair, compensation and restoration of body tissues that is demonstrated by normalization of the dielectric parameters of RBC.

Polytetrafluoroethylene Films in Rigid Polyurethane Foams' Dielectric Permittivity Measurements with a One-Side Access Capacitive Sensor.

As a non-metallic composite material, widely applied in industry, rigid polyurethane (PUR) foams require knowledge of their dielectric properties. In experimental determination of PUR foams’ dielectric properties protection of one-side capacitive sensor’s active area from adverse effects caused by the PUR foams’ test objects has to be ensured. In the given study, the impact of polytetrafluoroethylene (PTFE) films, thickness 0.20 mm and 0.04 mm, in covering or simulated coating the active area of one-side access capacitive sensor’ electrodes on the experimentally determined true dielectric permittivity spectra of rigid PUR foams is estimated. Penetration depth of the low frequency excitation field into PTFE and PUR foams is determined experimentally. Experiments are made in order to evaluate the difference between measurements on single PUR foams’ samples and on complex samples “PUR foams + PTFE film” with two calibration modes. A modification factor and a small modification criterion are defined and values of modifications are estimated in numerical calculations. Conclusions about possible practical applications of PTFE films in dielectric permittivity measurements of rigid PUR foams with one-side access capacitive sensor are made.

A new method for measuring complex relative permittivity of dielectric material by reflection method

In this paper, a new lossless free space method for measuring the complex relative permittivity of dielectric material by reflection method is presented. When this method is used to measure the complex relative permittivity of dielectric material, there is no multi-value problem. The measurement system used in this method consists of a horn lens antenna and a vector network analyzer(VNA). In this paper, HFSS microwave simulation software is used to simulate the complex relative permittivity measurement method proposed in this paper. The simulation results show that this method can accurately measure the complex relative permittivity of dielectric material.

Multi-property evaluation for a gas sample based on the acoustic and electromagnetic resonances measurement in a cylindrical cavity

This study proposes a multi-property evaluation method for a gas sample on the basis of sound speed and relative permittivity measurements by using a cylindrical acoustic-electromagnetic resonator. Validity and reliability of the present apparatus were confirmed from the measurement result for Ar with the relative standard uncertainties of 2 × 10−4 for the sound speed and 4 × 10−6 for the relative permittivity. The sound speed and the relative permittivity measurements for trans-1-chloro-3,3,3-trifluoropropene, which is known as R1233zd(E), were carried out in the wide temperature and pressure ranges to demonstrate the multi-property evaluation for a polar molecular sample. Firstly, specific heat capacity and molar polarization in the ideal-gas state were derived from the sound speed and the relative permittivity data, respectively, based on the acoustic- and the dielectric-virial equations. Secondly, linear regression of the ideal-gas molar polarization and temperature data leaded information of dipole moment and molecular polarizability in accordance with Debye equation. The density-virial coefficients were deduced by use of an empirical correlation with the determined dipole moment on the basis of the corresponding states principle so that the acoustic- and the dielectric-virial coefficients were separately determined from polynomial regression analysis of the sound speed and the relative permittivity data, respectively. Finally, the relative permittivity data in combination with the determined dielectric-virial coefficients yield the value of density. The acquired multi-property data for R1233zd(E) were compared with the existing equation of state or reference model.

Review of Recent Microwave Planar Resonator-Based Sensors: Techniques of Complex Permittivity Extraction, Applications, Open Challenges and Future Research Directions.

Recent developments in the field of microwave planar sensors have led to a renewed interest in industrial, chemical, biological and medical applications that are capable of performing real-time and non-invasive measurement of material properties. Among the plausible advantages of microwave planar sensors is that they have a compact size, a low cost and the ease of fabrication and integration compared to prevailing sensors. However, some of their main drawbacks can be considered that restrict their usage and limit the range of applications such as their sensitivity and selectivity. The development of high-sensitivity microwave planar sensors is required for highly accurate complex permittivity measurements to monitor the small variations among different material samples. Therefore, the purpose of this paper is to review recent research on the development of microwave planar sensors and further challenges of their sensitivity and selectivity. Furthermore, the techniques of the complex permittivity extraction (real and imaginary parts) are discussed based on the different approaches of mathematical models. The outcomes of this review may facilitate improvements of and an alternative solution for the enhancement of microwave planar sensors’ normalized sensitivity for material characterization, especially in biochemical and beverage industry applications.

A Folded Substrate Integrated Waveguide Re-Entrant Cavity for Full Characterization of Magneto-Dielectric Powder Materials

In this study, a folded substrate integrated waveguide (FSIW) re-entrant cavity sensor (RECS) is proposed for full characterization of magnetic-dielectric powder materials. In the re-entrant cavity, the electric field (E-field) and magnetic field (H-field) are localized at two different regions for detecting complex permittivity and complex permeability independently. Due to the extremely weak H-field in the high-intensity E-field region of the re-entrant cavity, the impact of the high magnetic loss of magneto-dielectric (MD) materials on the permittivity measurement is ignored, which simplifies the algorithm for extracting the complex permittivity. The simulated results demonstrate a good electromagnetic separation performance of the FSIW RECS, characterized by the very low cross-sensitivity-ratios ${S}_{\textit {fm}2}{/}{S}_{\textit {fe}}$ of 0.0289 and ${S}_{\textit {Qm}2}{/}{S}_{\textit {Qe}}$ of 0.0035. Folding technology is used to enhance the sensitivity for extracting the complex permittivity and realize the miniaturization of the designed sensor. To accurately characterize the MD materials with the high magnetic loss tangent up to 0.7, the weak-coupling feeding method is employed to improve the Q-factor of this sensor, and magnetic loss tangent is taken into account in the extraction of the real part of the permeability. The prototype of the FSIW RECS was fabricated and experimentally verified by measuring the complex permittivity and permeability of several powder materials. The measured relative permittivity and permeability of powder samples are in good agreement with the referred ones, and the corresponding maximum relative errors are 3.79% and 4.44%, respectively.

Soil dielectric characterization during freeze–thaw transitions using L-band coaxial and soil moisture probes

Abstract. Soil microwave permittivity is a crucial parameter in passive microwave retrieval algorithms but remains a challenging variable to measure. To validate and improve satellite microwave data products, precise and reliable estimations of the relative permittivity (εr=ε/ε0=ε′-jε′′; unitless) of soils are required, particularly for frozen soils. In this study, permittivity measurements were acquired using two different instruments: the newly designed open-ended coaxial probe (OECP) and the conventional Stevens HydraProbe. Both instruments were used to characterize the permittivity of soil samples undergoing several freeze–thaw cycles in a laboratory environment. The measurements were compared to soil permittivity models. The OECP measured frozen (εfrozen′=[3.5; 6.0], εfrozen′′=[0.46; 1.2]) and thawed (εthawed′=[6.5; 22.8], εthawed′′=[1.43; 5.7]) soil microwave permittivity. We also demonstrate that cheaper and widespread soil permittivity probes operating at lower frequencies (i.e., Stevens HydraProbe) can be used to estimate microwave permittivity given proper calibration relative to an L-band (1–2 GHz) probe. This study also highlighted the need to improve dielectric soil models, particularly during freeze–thaw transitions. There are still important discrepancies between in situ and modeled estimates and no current model accounts for the hysteresis effect shown between freezing and thawing processes, which could have a significant impact on freeze–thaw detection from satellites.

Enhanced microwave absorption properties of Y‐Co2Z/PANI hexaferrites composites in the frequency range of 0.1–18 GHz

AbstractWe prepared Ba3−xYxCo2Fe24O41 (Y‐Co2Z, x = 0, 0.2, and 0.4) by the solid‐state reaction method. Y‐Co2Z and polyaniline (PANI) composites (named as Y‐P0, Y‐P2, and Y‐P4) were prepared by using the in‐situ polymerization method. The Y‐doping played an important role in the variation of lattice parameters, a and c. The combination of Y‐doping and PANI modified the magnetic properties of the composites, which could be observed by the changing of the saturation magnetization and coercivity. This combination had also affected the electromagnetic properties of composites through the measurements of complex permittivity and permeability. Using the transmission line theory, we calculated refection loss (RL) of composites with the variation thickness of 1.00–2.50 mm. Our composites tuned the minimum RL from the X band (RL = −29.6 dB at 11.4 GHz for Y‐P2) to Ku band (RL = −16.3 dB at 15.7 GHz for Y‐P4 and RL = −26.4 dB at 16.6 GHz for Y‐P4). For maximum effective bandwidth, our composites covered a huge range from the S and C bands (Y‐P0 with 3.9 GHz in the range of 3.4–7.3 GHz) through the X band (Y‐P2 with 3.9 GHz in the range of 9.0–12.9 GHz) to the Ku band (Y‐P4 with 4.0 GHz in the range of 13.8–17.8 GHz). Those properties proved that the composites could act as promising absorbers in the S, C, X, and Ku bands.

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.

TiO2 containing hybrid nanocomposites with active–passive oxygen scavenging capability

Ladder-like silsesquioxanes (SSQs) and TiO2 have been functionalized with methacryloyloxypropyl chains and embedded in a polybutadiene (PB) matrix giving rise to hybrid (organic–inorganic) nanocomposites (NCs) capable of acting as oxygen scavenging materials. The joint use of infrared spectroscopy, small-angle X-ray scattering, and permittivity measurements highlighted that the presence of TiO2, regardless of its modification, does not significantly alter the structure of the NCs, but just reduces the crosslinking degree and induces a local disorganization of the ladder-like SSQ stacks. The introduction of an optimum amount (0.5 wt%) of modified TiO2 within the polymeric matrix enhanced the oxygen uptake rate of ca. 70% with respect to the sole polymeric material. Moreover, the uptake kinetics changes from the first to second order with respect to the PB amount, clearly indicating different oxidation mechanisms. NCs containing modified TiO2 showed an oxygen uptake rate ranging from 30 to 60% higher than that achievable in the presence of bare TiO2. The superior activity of the materials containing modified TiO2 has been related to mechanistic aspects. Fluorescence and electron spin resonance spectroscopies allowed to underline the role of singlet oxygen within the polymeric matrix, although the known photochemical oxidation of PB and the TiO2 induced hydroxyl radical mediated oxidation cannot be excluded. These results open the route to highly efficient flexible oxygen scavenging materials for the protection of electronic devices such as organic based light emitting diodes, solar cells, and liquid crystal displays, which require high targets of protection from oxygen and water.

Relative permittivity of bioethanol, gasoline and blends as a function of temperature and composition

The dependence of the real part of the relative permittivity of bioethanol, gasoline, and their blends was determined. Measurements were performed in the temperature range between 298 K and 323 K, at a frequency of 100 kHz. Temperature was stabilized within ±0.1K and the uncertainty in the relative permittivity was ±0.01.In all the studied blends, the real part of the relative permittivity decreases as a function of temperature with a very good fit to a linear function. At each temperature, the real part of the relative permittivity increases with the bioethanol content in the sample.The permittivity as a function of blends composition fits very satisfactorily to a fourth - order polynomial. In all cases, the mean square error (ΔRMS) of the permittivity estimation was less than 0.09. Furthermore, for bioethanol concentrations lower than 25%, a second - order polynomial fits with an ΔRMS error below 0.04. At higher bioethanol concentrations, a linear function fits with an ΔRMS error below 0.13.The bioethanol concentration in the blends is estimated from permittivity and temperature measurements, with a mean square error in the estimation of the composition lower than 0.5% in all cases.This work shows that measurements of electrical properties can be very effective in the characterization of gasoline - ethanol blends for laboratory and industrial applications.

Material Design Strategy for Enhancement of Readback Signal Intensity in Ferroelectric Probe Data Storage.

Ferroelectric probe data storage (FPDS) based on scanning nonlinear dielectric microscopy is expected as a next-generation data storage method with its large potential for improvement of the recording density. However, this novel method has a problem of low reading speed. To overcome this problem, a novel ferroelectric recording medium with large nonlinear permittivity is required because this data storage method uses the nonlinear dielectric response induced by small-amplitude ac bias to detect the bit data recorded in the form of polarization direction. Therefore, this article discusses nonlinear permittivity enhancement from the viewpoint of data storage application in the framework of the phenomenological theory. We reveal that the Curie-point control is one of the key techniques in material design for FPDS because nonlinear permittivity increases precipitously as the Curie temperature is approached, as with the linear permittivity and piezoelectric constants. A similar conclusion is also obtained through actual measurements of nonlinear permittivity in LiTaO3 single crystals. On the other hand, we also reveal that there is a tradeoff relationship between nonlinear permittivity and polarization stability. To avoid this undesirable situation in data storage applications, pinning-site control will also be important. We also propose to employ a double-layer structure in the ferroelectric recording media for further improvement.