Determination Of Permittivity Research Articles

Improved open-ended coaxial probe for temperature-dependent permittivity measurements of foodstuff at radio frequencies

Accurate determination of permittivity is a crucial factor for successfully developing new food processing technologies at radio frequencies. An improved measurement test fixture based on an open-ended coaxial probe was developed to determine the permittivity of lossy food products at radio frequencies as a function of temperature. In order to increase the sensitivity of the permittivity measurements at these frequencies, especially when using a vector network analyzer as a measuring device, the dimensions of the coaxial cell were carefully modeled to consider the range of dielectric losses estimated for food materials. The electromagnetic model was used to retrieve permittivity values from reflection measurements where the entire geometry of the test fixture was considered assuming there was no open radiation or infinite flanges and without the need of reference materials to calibrate the probe. The new cell was validated through permittivity measurements of six saline solutions and then, employed to determine the dielectric properties of cheese sauces and commercial milk samples at 40.68 MHz up to 120 °C. The ionic content and temperature had a limited influence on the dielectric constant but highly determined the loss factor. • A test fixture was developed for improved temperature-dependent permittivity measurements of foodstuffs at radio frequencies. • It used an open-ended coaxial probe achieving more than 6 times the response of previous designs reported in the literature. • Permittivity of milk and cheese food sauces were measured at 40.68 MHz up to 120 °C.

Measurement and modeling of effective cable parameters of unshielded conductors

PurposeCables are ubiquitous in electronic-based systems. Electromagnetic emission of cables and crosstalk between wires is an important issue in electromagnetic compatibility and is to be minimized in the design phase. To facilitate the design, models of different complexity and accuracy, for instance, circuit models or finite element (FE) simulations, are used. The purpose of this study is to compare transmission line parameters obtained by measurements and simulations.Design/methodology/approachTransmission line parameters were determined by means of measurements in the frequency and time domain and by FE simulations in the frequency domain and compared. Finally, a Spice simulation with lumped elements was performed.FindingsThe determination of the effective permittivity of insulated wires seems to be a key issue in comparing measurements and simulations.Originality/valueA space decomposition technique for a guided wave on an infinite configuration with constant cross-section has been introduced, where an analytic representation in the direction of propagation is used, and the transversal fields are approximated by FEs.

Microstrip sensor and methodology for the determination of complex anisotropic permittivity using perturbation techniques

In this work, a sensor in microstrip technology and a methodology for measuring the real part and the imaginary part of the complex uniaxial permittivity of solid anisotropic samples are presented. The sensor is based on a pair of parallel lines coupled resonators and a cleft arranged in the coupling region which allows to hold the samples under test (SUTs). The proposed methodology relates the change in the even/odd resonance frequency with the real part of the permittivity in the vertical/horizontal direction, and the change in the Q factor of the even/odd mode with the imaginary part of the permittivity in the vertical/horizontal direction. The methodology was successfully verified with the characterization, at 2.43 GHz of anisotropic samples of printed PLA, Diclad 880, and RO4350B using the knowns materials: RT5870, PTFE and RO4003.

A Simplified Measurement Configuration for Evaluation of Relative Permittivity Using a Microstrip Ring Resonator with a Variational Method-Based Algorithm.

In this paper, we present a simple yet efficient method for determination of the relative permittivity of thin dielectric materials. An analysis that led to definition of the proper size and placement of a sample under test (SUT) on the surface of a microstrip ring resonator (MRR) was presented based on the full-wave simulations and measurements on benchmark materials. For completeness, the paper includes short descriptions of the design of an MRR and the variational method-based algorithm that processes the measured values. The efficiency of the proposed method is demonstrated on 12 SUT materials of different thicknesses and permittivity values, and the accuracy between 0% and 10% of the relative error was achieved for all SUTs thinner than 2 mm.

Simultaneous Determination of Levels and Complex Permittivities of Layered Liquids Using a Five-Wire Line-Based Microwave Sensor

In industrial processes, there is a great need for enhanced monitoring of layered liquids for safety and quality assurance. Here a five-wire line-based microwave sensor is presented for simultaneous determination of the levels and complex permittivities. Special design of a transition section is made for signal coupling and impedance matching. Applying the transmission line theory and the transmission matrix technique, an analytical model is proposed for the inverse calculation. Numerical simulation is performed to show that the electromagnetic fields are confined between the central rod and the other rods. The experimental results also confirm that the sensing is unaffected by surrounding metallic objects. The applicability for the common air-oil-water system is thoroughly investigated, where the errors of the levels and the permittivity are within ±5%. It is demonstrated that the permittivity of strongly frequency dispersive liquids can also be accurately evaluated using a relaxation model, offering wide applicability. The sensor developed is compact, scalable, easy to implement and desired for on-site automated assessment.

Broadband Soil Permittivity Measurements Using a Novel De-Embedding Line–Line Method

A new de-embedding line&#x2013;line method has been proposed for accurate complex relative permittivity (<inline-formula> <tex-math notation="LaTeX">$\varepsilon _{r}$ </tex-math></inline-formula>) determination of soil samples loaded into an EIA 1-5/8&#x201D; coaxial transmission line measurement system. The method has three main features. First, it bypasses the requirement of calibration of this system by using only two identical coaxial lines with different lengths. Second, it does not need any numerical technique for <inline-formula> <tex-math notation="LaTeX">$\varepsilon _{r}$ </tex-math></inline-formula> determination. Third, it does not require knowledge of electromagnetic properties and thickness information of the bead used for supporting soil samples. The method is next validated by simulations performed using a full 3-D electromagnetic simulation program (CST Microwave Studio) and by <inline-formula> <tex-math notation="LaTeX">$\varepsilon _{r}$ </tex-math></inline-formula> measurement of a polyethylene (PE) material. Finally, <inline-formula> <tex-math notation="LaTeX">$\varepsilon _{r}$ </tex-math></inline-formula> values of three air-dried and water-saturated soil samples having 90&#x0025; or more sand content with different electrical conductivities (ECs) and gathered from different areas of the city Gaziantep in Turkey, were measured.

Improved Method for Permittivity Determination of Dielectric Samples by Free-Space Measurements

A new deembedding technique is proposed for relative complex permittivity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon _{r}$ </tex-math></inline-formula> determination of dielectric materials using gated free-space measurements. Its three main features are 1) it does not require any formal calibration procedure (calibration-free); 2) it is position-insensitive; and 3) it extracts ripple-free <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon _{r}$ </tex-math></inline-formula> due to gating process. The objective function derived to determine <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon _{r}$ </tex-math></inline-formula> by the proposed method is validated by free-space measurements of three dielectric samples (polypropylene, polyethylene, and polyoxymethylene). Besides, the accuracy of our method is compared with the accuracy of other calibration-free and calibration-dependent methods in the literature.

Material Relative Permittivity Determination From the Inhomogeneous Transmission-Line Secondary Parameters

After further transmission line technique investigation, we propose a new approach to material characterization based on the combination of the propagation constant and the characteristic impedance of the transmission-line. Three main elements constitute the approach novelty’s root: the determination of the propagation constant without using the eigenvalue principle, the improved mathematical expression of the characteristic impedance, and the automatically corrected coefficient. The two-line technique is based on three required measures, where the most extended fixture is partially filled with the specimen to be tested. As a result, the discontinuities caused by the geometric change of access interfaces and the waveguide dimensions have been solved. The characteristic impedance is determined straight and amended by a third polynomial function degree. The polynomial function and the amended correction coefficient determination are the facilitation parameters of the new approach technique. This new method allows the extraction of the material’s complex relative permittivity. The procedure has been validated with the Rogers RO4003C, Alumina 99.6%, and Vinifera (based on the dielectric materials available in our laboratory) through the microstrip fixture in the scanned frequency (0.08 – 8) GHz by extracting its electric intrinsic parameters. The dielectric constants range from 1.1–10.4, where the thicknesses are 1.54 mm, 2.067 mm, and 1.078 mm have been used. Two identical microstrip test cells with the same geometric dimensions but various lengths have been manufactured. That promotes the feasibility of two measures simultaneously.

Current Issues Regarding the Analysis of the Physico-Chemical and Electrical Properties of Transformer Oil

Researchers and practitioners interested in the operation, monitoring and diagnosis of electrical equipment (such as: transformers, motors and generators, circuit breakers, etc.) know that in order to ensure a safe operation of such equipment it is necessary to know, among other things, the condition of the insulation system. This is one of the essential information to know because about 40% of failures which occur in the operation of the electrical equipment are due to insulation breakdown; in some cases they can reach even close to 100%. In this context this pa-per proposes the presentation of several modern methods and equipment for the study and analysis of physical and chemical properties (namely: analysis of water content, density and interfacial tension, dissolved gas analysis and furan components determination) and electrical parameters (namely: determination of loss factor and relative permittivity) of transformer oil. Samples of transformer oil type MOL TO 30.01 (uninhibited electrical insulator, non-additive), new StaSo Transformer Oil I (high quality inhib-ited insulating oil) and TR 30 oil were studied. Two samples were collected directly from the original barrel, two samples were collected from the transformer tank after dielectric tests at the transformer’s manufacturer and also two samples of used TR 30 oil were collected from two transformers. The tests were carried out in an accredited laboratory with calibrated equipment. The results highlighted the properties of each analyzed sampled. The interpretation of the results emphasized the qualities and defects of each analyzed oil sample and whether or not they fit the standards in the field.

In Situ Determination of Dry and Wet Snow Permittivity: Improving Equations for Low Frequency Radar Applications

Extensive efforts have been made to observe the accumulation and melting of seasonal snow. However, making accurate observations of snow water equivalent (SWE) at global scales is challenging. Active radar systems show promise, provided the dielectric properties of the snowpack are accurately constrained. The dielectric constant (k) determines the velocity of a radar wave through snow, which is a critical component of time-of-flight radar techniques such as ground penetrating radar and interferometric synthetic aperture radar (InSAR). However, equations used to estimate k have been validated only for specific conditions with limited in situ validation for seasonal snow applications. The goal of this work was to further understand the dielectric permittivity of seasonal snow under both dry and wet conditions. We utilized extensive direct field observations of k, along with corresponding snow density and liquid water content (LWC) measurements. Data were collected in the Jemez Mountains, NM; Sandia Mountains, NM; Grand Mesa, CO; and Cameron Pass, CO from February 2020 to May 2021. We present empirical relationships based on 146 snow pits for dry snow conditions and 92 independent LWC observations in naturally melting snowpacks. Regression results had r2 values of 0.57 and 0.37 for dry and wet snow conditions, respectively. Our results in dry snow showed large differences between our in situ observations and commonly applied equations. We attribute these differences to assumptions in the shape of the snow grains that may not hold true for seasonal snow applications. Different assumptions, and thus different equations, may be necessary for varying snowpack conditions in different climates, suggesting that further testing is necessary. When considering wet snow, large differences were found between commonly applied equations and our in situ measurements. Many previous equations assume a background (dry snow) k that we found to be inaccurate, as previously stated, and is the primary driver of resulting uncertainty. Our results suggest large errors in SWE (10–15%) or LWC (0.05–0.07 volumetric LWC) estimates based on current equations. The work presented here could prove useful for making accurate observations of changes in SWE using future InSAR opportunities such as NISAR and ROSE-L.

Effective Relative Permittivity Determination of 3D Printed Artificial Dielectric Substrates Based on a Cross Unit Cell

Effective Relative Permittivity Determination of 3D Printed Artificial Dielectric Substrates Based on a Cross Unit Cell

Dielectric properties of asphalt pavement materials based on the temperature field

Nondestructive testing equipment evaluates the quality of asphalt pavements and identifies different distresses based on the difference in the relative permittivity of asphalt pavement materials at different positions of the asphalt pavement structural layers. Thus, the accurate determination of the relative permittivity of asphalt pavement materials is essential for the quality evaluation of asphalt pavements. However, the dynamic temperature field inside the asphalt pavement will affect the performance and dielectric properties of each layer mixture and therefore affect the detection accuracy of nondestructive testing equipment.In order to analyze the influence of the temperature field on dielectric properties of asphalt pavement materials, the relative permittivity of each structural layer of the actual core specimen was measured at different temperatures by using the Dielectric Constant Test Platform, and a temperature-based dielectric composite model was developed. Meantime, the temperature field simulation of the typical asphalt pavement structures and distresses were carried out based on COMSOL finite element simulation, and the heat radiation, heat conduction, and heat convection were theoretically analyzed. On this basis, the relative permittivity and the relative permittivity correction rate of each structural layer was calculated to quantify the influence of the temperature field on the dielectric properties of asphalt pavement materials.This study confirmed that a crucial correlation exists between the temperature and relative permittivity of asphalt pavement mixtures. The temperature field distribution of distresses, namely, top-down cracks, reflective cracks, and road cavity, were simulated, and then the measured dielectric permittivity of each asphalt pavement structural layer was corrected. These findings can provide a theoretical basis for the temperature correction of detection data of nondestructive testing equipment and lay the foundation for the accurate identification of typical distresses in asphalt pavement.

Determination of Permittivity of Homogeneous Dielectric Medium Using Rectangular Patch Antenna

In this article, a design guide line is proposed to determine the permittivity of homogeneous dielectric medium using rectangular patch antenna. The numerical values obtained with present model are compared with experimental results. The very close correlation is seen between the computed and measured values.

Quantitative Determination of Relative Permittivity Based on the Fluorescence Property of Pyrene Derivatives: An Interpretation of Hydrophobicity in Self-Assembled Aggregates of Nonionic Amphiphiles.

Aggregates in aqueous solutions can embed hydrophobic molecules, and their interactions depend on the properties of the aggregates. The electric surface potential, molecular mobility, and gradual hydrophobicity are the properties that regulate the interactions, and it is essential to understand these to quantify the properties. Electric surface potential and molecular mobility are quantified using the zeta potential and NMR measurements. In this study, the quantification of gradual hydrophobicity within the aggregate based on the relative permittivity, also called the dielectric constant, has been estimated from fluorescence spectra of pyrene-dicarboxylic acid conjugates. The localization of the pyrene moiety was modified by conjugation with succinic acid, suberic acid, or dodecanedioic acid, and the conjugates were evaluated in the shallow, middle, and deep regions of the aggregates. Span and Tween surfactants have been employed to prepare these aggregates, because they form various kinds of aggregates such as micelles and vesicles. It was realized that the hydrophobicity gradually increased from the interface to the hydrophobic core. Alternatively, a comparison of hydrophobicity within the aggregates showed no remarkable difference. Moreover, the analyses suggested that there are a few water molecules in the deep region. These results support the idea of the localization of embedded molecules in aggregates.

Determination of the permittivity of materials in a volume resonator with allowance for the surface roughness

The accuracy of determining the permittivity of the material depends on the thickness of the intermediate layer with variable dielectric characteristics formed on the surface of the sample upon manufacturing. We present the results of studying the influence of the surface roughness of the test sample on the accuracy of determining the permittivity using the resonator method. An algorithm for calculating the permittivity in a volumetric cylindrical resonator is proposed, taking into account the roughness value and the residual gap. Using the matrix method for calculating the wave transmitted through the plate, a model for determination of the dielectric permittivity of a multilayer sample using a measuring resonator is developed. The results obtained can be used to improve the accuracy of the permittivity determination in a volume resonator when testing the samples with a roughness exceeding the required standard.

Minkowski-like fractal resonator-based dielectric sensor for estimating the complex permittivity of binary mixtures of ethanol, methanol and water

A microwave dielectric sensor with defected ground structure including a Minkowski-like fractal resonator is proposed for estimating the complex permittivity of ethanol-water, methanol-water and ethanol-methanol mixtures. Positioned glass capillary tubes at the center of the metamaterial normal to the sensor surface, it is possible to see the fast impact of the shift of the transmission response for different liquid mixtures. The dimension of the proposed sensor is as small as 0.17λ0 × 0.17λ0 × 0.010λ0, where λ0 indicates the resonance wavelength in free-space. Complex permittivity of the liquid mixtures are estimated based on the shift of the resonance frequency and the magnitude of the S21 values by using a first-order model incorporating in characteristic matrix formulation. Estimated values indicated a very good agreement with the values in the reported studies. The sensitivity of the proposed sensor related to 0.07 μL effective sample volume is obtained to be 0.52 MHz/εr. The attractive features of the sensor, such as being label-free, reusable, easy to fabricate, practical, non-invasive and real-time, assure accurate determination of the complex permittivity of unknown liquid mixtures for applications in chemistry and medicine.

Errors in Broadband Permittivity Determination Due to Liquid Surface Distortions in Semi-Open Test Cell

We study how surface distortions of liquid samples due to a meniscus and a tilt of a semi-open coaxial test cell affect errors in a broadband permittivity determination. The study is based on the scattering parameters, obtained using the electromagnetic simulations of samples with flat and distorted surfaces in a broad frequency range up to 18 GHz. The parameters are processed with the classic Nicolson–Ross–Weir (NRW) method and our new meniscus removal technique. We analyze the errors for several samples of different properties, such as distilled water and propan-2-ol. The results show that the meniscus removal technique is more robust and provides smaller errors in the permittivity determination compared to the classic NRW method. The effect of the cell tilt, to our best knowledge, has not been considered in the literature yet.

Direct Broadband Dielectric Spectroscopy of Liquid Chemicals Using Microwave-Fluidic Two-Wire Transmission Line Sensor

A novel robust approach for permittivity measurements of liquid materials in a wide frequency range is proposed. A high-sensitivity microwave-fluidic sensor is developed enabling direct determination of liquid samples' permittivity from the measured sensor's propagation constant. Importantly, neither sensor calibration using liquid standards nor sensor's geometry (except length) information is required, which is very advantageous for industrial applications. This is achieved through the sensor's geometry, which is a two-wire transmission line (TWL) encapsulated in a 3-D printed container, and thus, the liquid-under-test fully encloses the propagating electromagnetic waves. The measurement setup comprises the sensor cascaded between two microstrip-to-TWL transitions for which a simplified de-embedding procedure is proposed using only a THRU standard. For demonstration, a setup was developed with transitions operating within 1-10 GHz and tested up to 18 GHz by measurement of a set of alcohols to produce useful data within the transition bandwidth, which can be extended at the cost of increased uncertainty by postprocessing. Finally, the measurement error study has shown that a relatively low uncertainty and error with respect to the reference is obtained, verifying the usability of the developed measurement technique.

The Determination of Mega Permittivity in PEDOT-PSS Films

The Determination of Mega Permittivity in PEDOT-PSS Films

Dielectric Properties Characterization Based on Complementary Split-Ring Resonator

Material characterization method based on radio frequency and microwave measurements is highly demanded. The dielectric properties are very important for electronic circuit design, food industry, and medicine and health care. In this work, a complementary split-ring resonator (CSRR)-based sensor employed in the ground plane is proposed for dielectric measurement. This method enables the determination of both relative permittivity and relative permeability at the same time as well as simple sample preparation process. This project focuses on the design, simulation and the prediction formulae of the CSRR. This CSRR is resonating at 2.477 GHz with a quality factor of 128.91 in unloaded condition. Basically, there are shifting in the resonance frequency and the change of the quality factor when dielectric material is placed at the sensing area in separate zones. Four prediction formulas are proposed, which they are depend on the dielectric constant, real permeability, normalized resonance frequency, inverse normalized quality factor, electric loss tangent and magnetic loss tangent of the materials. These formulae are used to measure the permittivity and permeability of FR-4, Polyimide, and self-defined material. Based on the comparison, the percentage error between calculated result and reference data are 10% and 4.1% for electric and magnetic loss tangent respectively. The maximum percentage error in dielectric constant and real permeability are 4.5% and 4.29% respectively. Based on the percentage of error, it is convincing that the prediction formulas are reliable for dielectric measurement. Future work of this project should focus on verification of its actual performance through experimental measurement.