Permittivity Measurements Research Articles

Relative Permittivity Measurement of Microliter Volume Liquid Samples through Microwave Filters

This paper proposes a concept of dielectric characterization of low-volume liquid samples using the coupling coefficient of filters. The concept is validated through a two-pole substrate integrated waveguide filter in which the liquid under test is mounted on the coupling section between the two resonators. Unlike the conventional resonator perturbation method reported many times in the literature, this technique uses the coupling coefficient for sensing. The liquid sample is collected in a capillary tube and carefully positioned on the coupling section of the filter; the coupling coefficient of the two resonators varies compared to the relative permittivity of the sample; thus, an empirical model is established. The proposed sensor has been tested to compute the permittivity of different alcohols. Binary solutions of ethanol and water have also been characterized to calculate the volume ratio and relative permittivity as a proof-of-concept. The obtained results show that the proposed sensing technique is capable of characterizing a low quantity of liquids (≈44 µL) with good accuracy, and a worst case measured error of only 6.8% is noted. The ease of integration with other circuitry, low cost, reusability with no deterioration, and adaptability of the proposed sensor makes it a suitable choice for the chemical as well as for the pharmaceutical industry.

Measurement of Complex Permittivity for Rapid Detection of Liquid Concentration Using a Reusable Octagon-Shaped Resonator Sensor

Substrate-integrated waveguides (SIWs) are widely used in microwave systems owing to their low cost and ease of integration. In this study, an SIW-based resonator that reacts to the complex permittivity variation of solutions with dimensions of 79.2 mm × 59.8 mm is introduced. This octagon-shaped sensor can be installed on a preliminary monitoring system to test water quality by observing the parameter variations caused by external factors. The resonant structure was used to test different concentrations of ethanol-water and acetone-water mixtures for verification. The resonant frequency and quality factor (Q-factor) were found to vary with the relative complex permittivity of the liquid in the S-band, and the electric field distribution varied when liquid droplets were placed in the center of the substrate. The designed sensor operates at 2.45 GHz in the air, and the observed minimum resonant frequency shift with liquid was 15 MHz. The measurement error was approximately 3.1%, and the results reveal a relationship between the resonant frequency and temperature as well. Considering the observed sources of error, the measured relative permittivity is consistent with the actual values. The proposed sensor is economically convenient and suitable for various test environments.

A review of electrical properties of biodiesel and its blends: experimental data, prediction models and applications

AbstractBiodiesel is widely used pure or mixed with diesel fossil fuel in diesel engines. Standards for determining biodiesel quality establish limits for the values of several physicochemical properties. However, the procedures to determine many properties are time‐consuming and demand specialized personnel and expensive equipment. Other methods to characterize biodiesel, such as electrical methods, are particularly interesting. Measurements of electrical properties (permittivity and conductivity) give valuable information about biodiesel, its feedstocks, and its blends with fossil fuel diesel, and solve the usual cost and time drawbacks. This work aims to present a thorough and systematic review of the literature on applications of electrical properties measurements of biodiesel, its feedstocks, and mixtures with other fuels. An overview of the experimental data, typical ranges of values, prediction models, and applications is presented and analyzed in detail, emphasizing blends of biodiesel with fossil fuel diesel. Correlations with important properties (kinematic viscosity, methanol content) are reviewed. Applications include transesterification monitoring, biodiesel aging, the detection of contaminants and electromagnetic heating. This research aimed to determine whether electrical properties are a valuable tool for the biodiesel industry, and what applications may be realized in light of current scientific development. It was determined that, in the current state of research, permittivity measurements could be used to accurately determine the amount of diesel and biodiesel in mixtures. © 2023 Society of Industrial Chemistry and John Wiley & Sons Ltd.

Entropy, Heat Capacity, and Thermal Conductivity of trans-1,1,1,4,4,4-Hexafluoro-2-butene [R1336mzz(E)] Derived from the Gaseous Sound Speed Measurement

Thermophysical properties such as entropy, heat capacity, and thermal conductivity of trans-1,1,1,4,4,4-hexafluoro-2-butene, which is designated as R1336mzz(E) for refrigerant use, were derived from the sound speed measurement in the gaseous phase. The gaseous sound speed was measured by using an acoustic-microwave resonator with a cylindrical cavity, which enables simultaneous measurement of the gaseous relative dielectric permittivity. The ideal gas heat capacity was determined from the gaseous sound speed by analyzing the measurement data with the acoustic-virial equation, and the electric dipole moment was additionally determined from the gaseous relative permittivity measurements. In compliance with the fluid-property correlation models that involve parameters associated with the ideal gas heat capacity and the dipole moment under the corresponding states principle, entropies at saturated vapor and liquid, isobaric heat capacities at saturated liquid, and thermal conductivities at vapor and liquid phases were evaluated for R1336mzz(E).

Magnetodielectric Material Characterization Using Stepped Impedance Resonators

Two resonance-based methods for magnetodielectric (MD) material characterization are presented in this article using stepped impedance resonators (SIRs). A single SIR (SSIR) is initially used to create two spatially separated sensing areas for permittivity and permeability measurements predicated on the resonance frequency variation. Next, a differential-based sensing method, based on resonance frequency splitting, is introduced for permittivity and permeability differential measurements. For this purpose, four spatially separated sensing areas are established on a single resonance structure using a double SIR (DSIR). The presented sensors provide a reliable sensing method for MD characterization and comparison. The proposed sensing methods are validated through numerical analysis based on electromagnetic (EM) simulation and experimental measurement of materials with different intrinsic EM properties.

Honey–Water Content Analysis by Mixing Models Using a Self-Calibrating Microwave Method

Microwave techniques, as an indirect approach, can be applied for analyzing water content in honey by way of permittivity measurements. However, these techniques require proper calibration to accurately perform such indirect evaluation. Improper calibration standards used in this calibration process could naturally result in a reduction in the accuracy and thus the performance of dielectric characterization using microwaves. Self-calibrating microwave techniques can reduce the effects of imprecise standards and thus improve the performance of microwave measurements by bypassing the requirement of calibration standards. In this study, we develop a self-calibrating microwave measurement technique to determine the relative permittivity of honey samples and implement binary mixing models to predict adulteration levels of water-adulterated honey. From this implementation, it is observed that the parallel-capacitance mixing model could efficiently be applied to determine the concentration of water adulteration by examining the differences between absolute values of the real parts of the measured and predicted complex permittivities of adulterated honey.

Time-domain transmission sensor system for on-site dielectric permittivity measurements in soil: A compact, low-cost and stand-alone solution

Dielectric-based measurement techniques have been shown to be very effective in determining the properties of various materials. These techniques have been widely used in a variety of fields and applications. Time Domain Transmission (TDT) techniques have grown in popularity because they are practical, non-destructive, provide measurements in real time and produce accurate measurements that are independent of multiple reflections. TDT techniques, on the other hand, are mostly performed with specialized bulky laboratory equipment, such as a Vector Network Analyzer (VNA) which makes TDT measurements prohibitively costly and unpractical. In fact, few works in the literature have reported portable on-site TDT systems. The aim of this paper is to design and implement a dedicated, compact, and low-cost microwave Time Domain Transmission (TDT) sensor for measuring superficial soil dielectric properties on-site. Our sensor uses a time-delay measurement technique over a microstrip transmission line to estimate the dielectric properties of the soil under test. Measurement results show that the computed mean absolute error (MAE) is less than 1.2 when compared to a calibrated dielectric assessment kit (DAK) with soils containing less than 20 % of water (ε′r<5.0), implying that our TDT sensor system can obtain on-site measurements in relatively dry soils with acceptable accuracy.

Triage of in vivo burn injuries and prediction of wound healing outcome using neural networks and modeling of the terahertz permittivity based on the double Debye dielectric parameters.

The initial assessment of the depth of a burn injury during triage forms the basis for determination of the course of the clinical treatment plan. However, severe skin burns are highly dynamic and hard to predict. This results in a low accuracy rate of about 60 - 75% in the diagnosis of partial-thickness burns in the acute post-burn period. Terahertz time-domain spectroscopy (THz-TDS) has demonstrated a significant potential for non-invasive and timely estimation of the burn severity. Here, we describe a methodology for the measurement and numerical modeling of the dielectric permittivity of the in vivo porcine skin burns. We use the double Debye dielectric relaxation theory to model the permittivity of the burned tissue. We further investigate the origins of dielectric contrast between the burns of various severity, as determined histologically based on the percentage of the burned dermis, using the empirical Debye parameters. We demonstrate that the five parameters of the double Debye model can form an artificial neural network classification algorithm capable of automatic diagnosis of the severity of the burn injuries, and predicting its ultimate wound healing outcome by forecasting its re-epithelialization status in 28 days. Our results demonstrate that the Debye dielectric parameters provide a physics-based approach for the extraction of the biomedical diagnostic markers from the broadband THz pulses. This method can significantly boost dimensionality reduction of THz training data in artificial intelligence models and streamline machine learning algorithms.

Second Harmonic Generation in the Polar A′SmNb2O7 (A′ = Rb, Cs) Dion–Jacobson Layered Perovskites

Members belonging to the Dion–Jacobson (DJ) family of layered perovskites have time and again proven to be the preferred materials of choice for the exploration and identification of polar structures. We report two noncentrosymmetric n = 2 DJ members, A′SmNb2O7 (A′ = Rb, Cs), prepared by high-temperature solid-state reactions, thus expanding the polar n = 2, DJ series as A′ANb2O7 (A′ = Rb, Cs; A = La, Pr, Nd, Sm, Bi). Optical second harmonic generation measurements utilizing 1064 nm substantiated the existence of Type I phase matchable compounds, and the efficiencies were 4 to 6 times higher than the standard KDP. Structural refinements by the Rietveld method confirm the polar orthorhombic space groups of I2cm and P21am, respectively, for RbSmNb2O7 [a = 5.4368(3) Å, b = 5.3944(3) Å, c = 21.9051(1) Å] and CsSmNb2O7 [a = 5.4669(5) Å, b = 5.4158(4) Å, c = 11.1437(1) Å]. The orthorhombic distortions and symmetry lowering were further supported by the Raman spectroscopy measurements. The difference in the orthorhombic a and b parameters (∼0.05 Å) possibly originates from the chemical pressure induced by the smaller ionic size of Sm3+ (1.24 Å, XII) as compared to other Ln3+ (La, Pr, Nd) ions. Ferroelectric switching of A′SmNb2O7 (A′ = Rb, Cs) oxides is demonstrated by the polarization hysteresis loops observed at room temperature with remanent polarization values of 5.3 and 2.0 μC/cm2 corresponding to the Rb and Cs analogues. Variable-temperature powder X-ray diffraction measurements confirmed the phase transition from polar to anti-polar transitions around temperatures ∼1273 and ∼1173 K, respectively, for the Rb and Cs analogues. Structural analysis results in the identification of prototype tetragonal (a ∼ 3.88 Å, c ∼ 11.20 Å) centrosymmetric structures relating the transition temperatures to potential Curie temperatures. The transitions coincide with the observed Curie point of 1113 K for CsSmNb2O7, from the temperature-dependent relative permittivity measurements, and a much higher temperature is expected for the Rb analogue.

Detection of physiological concentrations of GABA using dielectric spectroscopy - A pilot study.

Gamma-aminobutyric acid (GABA) is a major inhibitory neurotransmitter that is present at a relatively low level throughout the normal adult human brain. Abnormal GABA levels are found in people with neurodegenerative disorders such as Parkinson's disease, epilepsy, schizophrenia, depression, and others. Being able to measure the GABA concentration would be beneficial for patient groups with fluctuating GABA levels for better diagnosis and treatment. In this study, we explore the feasibility of using dielectric relaxation spectroscopy for the detection of GABA concentrations within a physiological range, with the perspective of miniaturization and use during implantation. Utilizing machine learning techniques, we were able to differentiate GABA concentrations down to 5 μm. This work investigates a novel use of dielectric relaxation spectroscopy, to assess if physiological GABA concentrations can be detected through permittivity measurements.

Dielectric Properties of Graphite Oxide Polymeric Composites Based on N-Vinylpirrolidone Copolymers with Different Topologies

The dielectric properties of graphite oxide composite materials based on a biocompatible branched copolymer of N-vinylpyrrolidone with 1,6-hexanediol dimethacrylate and a cross-linked copolymer of N‑vinylpyrrolidone with triethylene glycol dimethacrylate are studied. High-frequency (9.8 GHz) and low-frequency (25 Hz–1 MHz) measurements of the complex permittivity and electrical conductivity of polymer composites are carried out and their dependences on the polymer matrix topology and formation conditions are analyzed. Copolymers and composites based on them are characterized by IR, UV, and visible spectroscopy, dynamic light scattering, and the surface morphology of nanocomposite polymer matrices is characterized by optical microscopy. It is shown that the proposed electrophysical approach makes it possible to additionally characterize polymer matrices with carbon nanofillers.

Nonlinear background corrections to dielectric permittivity of ferroics and multiferroics

Temperature measurements of dielectric permittivity are performed for nonstoichiometric ferroelectric lead germanate Pb4.95Ge3O11 and multiferroic solid solution [N(C2H5)4]2CoClBr3. Unlike the heat capacity data, the analysis of the dielectric permittivity of ferroics is usually performed at the assumption that the dielectric `background' is negligible compared with its critical part. In this work we quantitatively interpret the dielectric properties of the single crystals mentioned above and the appropriate literature data for multiferroic Sr2IrO4 crystals, using generalized Curie-Weiss formulas that combine corrections due to a nonlinear temperature-dependent dielectric background, a modified critical index of electric susceptibility, and a diffuse character of phase transition. We argue that taking account of the temperature dependent dielectric background can improve notably the quantitative analysis of PTs for a number of classes of the ferroic materials.

A Dielectric Loaded Resonator for the Measurement of the Complex Permittivity of Dielectric Substrates

A new configuration of dielectric-loaded resonator (DR), particularly versatile for the complex permittivity measurement of substrates for microwave circuits, even in the presence of back metal plates, is shown here. To test this technique in a wide interval of the values of the complex permittivity, the versatility of 3-D printing is exploited to print samples with different densities, thus artificially changing the effective permittivity in the interval (1.7–3.1) for the real part and (0.02–0.06) for the imaginary part. The designed resonator, tuned at ~12 GHz, is experimentally validated by the comparison of measurements obtained on these samples with a split ring resonator (SRR) and standard transmission/reflection waveguide methods. Then, the versatility of the designed resonator is shown in the characterization of FR4-fiberglass and Kapton polyimide samples.

Design of 3-slot loaded with T-edge rectangular patch sensor for measurement of relative permittivity

Design of 3-slot loaded with T-edge rectangular patch sensor for measurement of relative permittivity

A novel approach to measuring pore fluid sediment concentrations of debris flows in a volcanic torrent

Pore fluid in a debris flow is not fully understood, despite its contribution to the fluidity of the debris flow. To observe sediment concentrations of the pore fluids in debris flows, we established a novel monitoring system in a volcanic catchment, in southern Japan. An observation culvert, 1.0 m in width, 1.5 m in height and 2.0 m in length, was placed along the stream bank. An intake covered by a grating was equipped on the side of the culvert so that only pore fluid of debris flows was led inside. Measurements of dielectric permittivities were conducted within the culvert and used for the calculation of sediment concentrations of the fluid. The sediment concentrations of the pore fluid were successfully measured for natural debris flows. The preliminary observation revealed that the volumetric sediment concentration of pore fluid varied from approximately 5 to 69 %, which were slightly smaller or similar to those of the entire debris flows. Successive occurrences of debris flow caused decreases in the sediment concentration of the pore fluids with each surge.

A Novel Time Domain Model for Permittivity and Thickness Measurement

Motivated by the necessity of acquiring wall parameters for through-the-wall radar, a novel and general time domain model is proposed to measure the thickness and permittivity of single-layered slab-shaped materials, by exploiting the delays of the two surface reflections in the bistatic radar scheme. First, the two surface delays are formulated as functions of the unknown permittivity and thickness, as well as the accessible incident angle, and a nonlinear equation set is formed. Then based on a geometric analysis, in two separate bistatic delay tests with different antenna separations and standoff distances, the condition of identical incident angle is established. As such, the intra-wall delay is the same for the two delay tests, leading to a significant simplification and a closed-form solution to the equation set. Finally, a three-antenna test setup is constructed, with which the desired parameters can be acquired conveniently and accurately by performing bistatic tests at a set of standoff distances. Simulation and experiment show that our method can achieve high accuracy and strong robustness against noise.

Ferroelectricity in oxygen-deficient perovskite-type oxide Sr10Ga6Sc4O25

We have investigated the physical properties of an oxygen-deficient perovskite-type Sr10Ga6Sc4O25 by means of dielectric permittivity, pyroelectric current, and X-ray diffraction (XRD) measurements using a polycrystalline sample.

Balanced Microwave Transmission Lines, Circuits, and Sensors

This paper provides an overview of balanced (or differential-mode) structures operating at microwaves, including common-mode suppression filters, balanced filters and circuits with intrinsic common-mode suppression, and differential-mode sensors. The increasing interest for balanced structures within the framework of communication circuits and sensors, related to their major robustness against electromagnetic interference (EMI), noise, and environmental factors, is duly justified. Then the paper reports various approaches for the implementation of common-mode suppression filters, balanced filters and circuits (including narrowband and wideband filters, multi-band filters, power dividers, couplers and phase shifters), and differential-mode sensors (mainly devoted to the measurement of permittivity and related variables). Rather than providing a detailed analysis of the different considered implementations/approaches, the main goal of this review paper is to discuss, and compare in some cases, the main proposed strategies (pointed out in the up-to-date state-of-the-art) for optimizing the performance of the various differential-mode devices under study.

Complex Permittivity Measurement Utilizing Multiple Modes of a Rectangular Cavity

A novel method for measuring the dielectric constant and loss tangent of dielectric substrates is presented in this article. Four resonant modes of the rectangular resonant cavity, TE101, TE105, TE109, and TE1015, are utilized to realize the multiband measurement from 0.9 to 10 GHz. The introduction of additional slots cuts down the quality factor of some miscellaneous modes, making the working modes more obvious and convenient for extraction. Based on the traditional perturbation formulas, considering the sinusoidal field distribution in the sample, modified formulas are deduced to obtain more accurate results. An experimental resonant cavity is fabricated and measured to demonstrate the effectivity of the proposed method.

Highly Sensitive Miniaturized Octagonal DS-CSRR Sensor for Permittivity Measurement of Liquid Samples

Highly Sensitive Miniaturized Octagonal DS-CSRR Sensor for Permittivity Measurement of Liquid Samples