Determination Of Permittivity Research Articles

A Coaxial Line Fixture Based on a Hybrid PSO-NLR Model for in Situ Dielectric Permittivity Determination of Carasau Bread Dough

A Coaxial Line Fixture Based on a Hybrid PSO-NLR Model for in Situ Dielectric Permittivity Determination of Carasau Bread Dough

Effects of electrical conductivity on uncoated- and coated-rods of eight electromagnetic soil water content sensors

Soil water content stands as a pivotal parameter across numerous research disciplines and engineering applications. Electromagnetic (EM) sensors have gained widespread usage in monitoring soil water content. While commonly employed sensors are suitable for typical agronomic- or landscape-soil environments, they may exhibit significant deviations under conditions of high-salinity or -electrical conductivity (EC). We investigated sensing limits under the influence of increasing EC and the resulting accuracy of dielectric permittivity (ε) determinations using commercial soil water content sensors. Tests were conducted using eight commercially available EM sensors (CS655, HydraProbe II, TDR-305N, TDR-310N, TDR-315N, TEROS 12, TEROS ONE, and WET150). For these uncoated rod sensors, most were accurate within ±3 % relative permittivity errors in saline solutions within the range of 0‒4 dS m−1 while TDR-305N, TEROS ONE and WET150 maintained an accuracy of 5 % for EC values up to 9.24 dS m−1. We explored extending the working range of some sensors to high-saline environments by adding an insulating coating on sensor rods. Since the coated probe not only perceives the characteristics of the immersed medium but also interacts with the coating material itself, a calibration model was evaluated for determining the actual ε of the evaluated medium. The strong correlation between a four-point calibration and the model demonstrates the effectiveness of calibrating coated EM sensors for ε determination using only a limited number of calibration materials. The findings presented here could serve as a valuable resource when selecting EM sensors for use in high-saline environments. Results also shed light on the potential to extend the sensing range through the integration of insulating coatings.

Resonant cavity method based on RF measurement and simulation for measuring complex permittivity or permeability of RF absorbing materials

Accurate measurement of complex permittivity and/or permeability of radio-frequency (RF) absorbing materials is essential to predict the performances of higher-order-mode damping in damped accelerating cavities or in vacuum chambers. We propose an improved resonant cavity method that can be used as a complement to the widely used Nicolson–Ross–Weir method for measuring the RF characteristics of materials. The conventional resonant cavity method is based on the cavity perturbation theory. However, the measurements are inaccurate when losses in the materials are large. The improved method we propose determines the complex permittivity or permeability of materials from the measured resonant frequencies and Q factors based on eigenmode simulations. Because the reliability on the eigenmode calculation for RF cavities with lossy materials has become sufficiently reliable, determination of complex permittivity and permeability can be achieved using such a simulation software. We demonstrate this method using ferrite HF70 (TDK Corp.), which is useful for RF absorbers in damped accelerating cavities or in vacuum chambers.

Dielectric Characterization of H2O and CO2 Uptake by Polyethylenimine Films.

The absorption of CO2 by polyethylenimine polymer (PEI) materials is of great interest in connection with proposed carbon capture technologies, and the successful development of this technology requires testing methods quantifying the amount of CO2, H2O, and reaction byproducts under operating conditions. We anticipate that dielectric measurements have the potential for quantifying both the extent of CO2 and H2O absorption within the PEI matrix material as well as insights into subsequent reaction byproducts that can be expected to occur in the presence of moisture. The complexity of the chemistry involved in this reactive binding process clearly points to the need for the use of additional spectroscopic techniques to better resolve the multiple components involved and to validate the model-dependent findings from the dielectric measurements. Here, we employed noncontact resonant microwave cavity instrumentation operating at 7.435 GHz that allows for the precise determination of the complex dielectric permittivity of CO2 films exposed to atmospheres of controlled relative humidity (RH), and N2:CO2 compositions. We find that the addition of CO2 leads to a considerable increase in dielectric loss of the PEI film relative to loss measured in nitrogen (N2) atmosphere across the same RH range. We attribute this effect to a reaction between CO2 and PEI generating a charged dielectrically active species contributing to the dielectric loss in the presence of moisture. Possible reaction mechanisms accounting for these observations are discussed, including the formation of carbamate-ammonium pairs and ammonium cations stabilized by bicarbonate anions that have sufficient local mobility to be dielectrically active in the investigated microwave frequency range. Understanding of these reaction mechanisms and the development of tools to quantify the amount of reactive byproducts are expected to be critical for the design and optimization of carbon capture materials.

Monostatic Free-Space Method for Relative Permittivity Determination Using Horn Antenna Near-Field Measurements

Monostatic Free-Space Method for Relative Permittivity Determination Using Horn Antenna Near-Field Measurements

Extraction Method for Unique Determination of Complex Permittivity From Graphical Analysis of Natural Frequencies

A time-domain free-space extraction procedure is proposed to uniquely determine the relative complex permittivity ϵr(ω) based on two-sets of natural frequencies of a metal- and air-backed dielectric sample. A graphical analysis is applied for evaluating whether unique ϵr(ω) can be extracted by using such natural frequencies. The method is numerically validated by using two dielectric samples with different ϵ(ω) for the ideal case (no noise) and under the influence of noise with different signal-to-noise ratios.

A symmetric bar chart-shape microwave sensor with high Q-factor for permittivity determination of fluidics

AbstractThis paper introduces a symmetric bar chart-shape (SBCS) microwave sensor for measuring permittivity of fluidic samples. For designing purposes, the introduced sensor was used based on the field changes between the SBCS and rectangular loop microstrip (RLM) structure. When a sample is placed on the sensing location, interaction between SBCS and RLM varies the field intensity. The vinegar samples were combined with water and then they are placed on the sensor. The change in field intensity changes the resonance frequency. However, there is a relationship between the permittivity of samples and the resonance frequencies. The proposed sensor is implemented on the substrate of RO4003C. The relative permittivity of samples changed from 59 to 77 and the resonance frequencies changed from 2.3 to 1.4 GHz. The quality factor is 3544 and the sensitivity is 2.2%.

Determination of Internal Erosion and Permittivity of Biopolymer-Added Geosynthetic Clay Liners

Geosentetik kil örtü (GKÖ), düşük hidrolik iletkenliği sayesinde tatlı su rezervuarlarında kaplama malzemesi olarak kullanılabilmektedir. GKÖ üzerinde birikebilecek yüksek seviyedeki su, GKÖ içerisindeki bentonitin geotekstillerin arasından sıyrılarak ani hidrolik iletkenlik artışıyla malzemenin kullanılamaz hale gelmesine neden olabilir. Bu etkileşime içsel erozyon denilmektedir. Bu çalışmada GKÖ’nün bentonit bileşenine sırasıyla ağırlıkça %0.25, 0.5, 1, 2, 5 ve 10 oranlarında kitosan ile Na karboksimetil selüloz biyopolimerleri eklenerek üç eksenli hidrolik iletkenlik deneyleri yapılmıştır. GKÖ içerisinde Na ve Ca içerikli iki farklı bentonit kullanılmış olup içsel erozyonu gözlemleyebilmek için GKÖ’ler, dane boyutu 37.5 mm olan iri daneli yuvarlak çakılların üzerine serilerek yüksek hidrolik yükler altında test edilmişlerdir. Bu koşul, karşılaşılabilecek en kötü senaryolardan birini temsil etmektedir. Deney sonuçlarına göre 10 m’lik hidrolik yük altında test edilen bütün GKÖ’lerde içsel erozyon gözlemlenmiştir. Ayrıca içsel erozyondan hemen önce ölçülen permitivite değerleri karşılaştırılarak kullanılan biyopolimerlerin, GKÖ’lerin hidrolik performansını ne ölçüde değiştirdiği araştırılmıştır. Sonuçlara göre GKÖ’lerdeki bentonite %1 kitosan ve %2 selüloz eklenmesi, GKÖ’lerin permitivitesini 2 mertebeden daha yüksek oranda azaltmıştır. Böylelikle çevre dostu, organik katkı malzemesi olan iki farklı biyopolimerin çevre geotekniği uygulamalarında kaplama malzemesinin hidrolik iletkenliğini azaltmasına bağlı olarak bariyer amaçlı kullanımı teşvik edilebilecektir.

Determination of the Permittivity of Transmission Lines at Milli-Kelvin Temperatures

Many quantum technologies rely heavily on propagation of RF and microwave signals through devices at cryogenic temperatures, and detailed understanding of materials and signal propagation is therefore key to improving the performance of quantum circuits. The properties of dielectric substrate materials used for transmission lines (TLs) such as their permittivity need to be precisely determined to design high performance quantum integrated circuits. In this paper, we discuss a measurement technique for determining the effective permittivity of a TL at mK temperatures. The technique utilizes S-parameter measurements of multiple TLs to reliably extract the effective permittivity of the TL implemented in a substrate material. The technique is demonstrated using measured S-parameters of grounded co-planar waveguide (GCPW) at 296 K and 15 mK. The effective permittivity of the TL at 296 K and 15 mK are determined from measurements and compared. We observed the effective permittivity determinations at 15 mK to be approximately frequency independent and calculated the relative permittivity of Rogers RO4350B material at 15 mK to be 3.64. There is no significant deviation from this relative permittivity value with respect to manufacturer data and from measured data at 296 K.

Square Waveguide Cavity for Complex Permittivity and Permeability Measurement by Perturbation Method Without Repositioning

This article presents a novel configuration for the simultaneous complex permittivity and permeability determination with only a single sample placement inside the resonant cavity. The proposed structure incorporates two waveguide orthomode transducers (OMTs) and a square cavity. The square cavity is designed to overcome the limitation of permeability measurement by the rectangular cavity perturbation method. These components allow the product of two orthogonal transverse electric (TE) resonant modes (TE10L and TE01L) with the same cutoff frequencies. Based on Maxwell equations and perturbation theory, new relations are developed to characterize the complex permeability of specimens at TE01L modes. The proposed structure eliminates the main drawbacks of previous studies such as depolarization effect of partial-height samples, radiation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${H}$ </tex-math></inline-formula> -plane sample hole, need to apply the sample holder and precision positioner, multistate positioning, iterative calculations, extra calibration process, and employing complicated mathematical equations. The proposed configuration was designed using CST Microwave Studio (MWS) and ANSYS high-frequency structural simulator (HFSS) and then manufactured and measured. The operating frequency has been selected from 7.5 to 12.5 GHz. Good agreement is achieved between measurement and simulation. The performance of the developed structure was verified by measuring the material characteristics of bar-shaped dielectric and magneto-dielectric specimens and compared with other studies.

A review of new TDR applications for measuring non-aqueous phase liquids (NAPLs) in soils

• NAPL monitoring in soils is performed by using invasive techniques. • Many studies demonstrated that TDR offers the possibility to detect NAPL in soils. • NAPL tests were conducted in different soils, under variable saturated conditions. The time domain reflectometry (TDR) technique is a geophysical method that allows, in a time-varying electric field, the determination of dielectric permittivity and electrical conductivity of a wide class of porous materials. Measurements of the volumetric water content (θ w ) in soils is the most frequent application of TDR in Soil Science and Soil Hydrology. In last four decades several studies have sought to explore potential applications of TDR. Such studies (except those conducted on θ w estimation) mainly focused on monitoring soil solute transport. In more recent times, innovative TDR approaches have also been implemented to extend current TDR fields of application to the problem of monitoring non-aqueous phase liquids (NAPLs) in variable saturated soils. NAPLs are organic compounds with low solubility in water and are characterised by a high mobility in the vadose zone. Due to their high toxicity, NAPLs constitute a severe geo-environmental problem, thus making detection and observation of such substances in soils an increasingly important issue. The present paper deals with these studies and aims to provide an up-to-date review of the main NAPL-TDR studies. To date, the literature has focused on TDR applications in three main fields: (i) NAPL monitoring in homogeneous, variable saturated soils, (ii) NAPL monitoring in layered variable saturated soils, and (iii) NAPL monitoring during soil decontamination processes. For an exhaustive and complete overview of TDR research in this field, we also recall the basic principles of TDR signal propagation, the functioning of a typical TDR device, and the dielectric mixing models that are widely used to interpret the dielectric response of NAPL-contaminated soils.

Complex permittivity measurement technique using metamaterial broadside coupled split ring resonator

A simple and effective method for the determination of complex permittivity of dielectric materials at microwave frequencies using a Broadside Coupled Split Ring Resonator (BCSRR) metamaterial structure is presented. A single BCSRR unit cell placed between the transmitting and receiving probes of a Vector Network Analyzer (VNA) is used as the test probe. Resonance frequencies and bandwidths of transmission curves, measured with and without the sample placed over the BCSRR test probe, are used to determine the real and imaginary parts of the complex permittivity by treating the BCSRR as an LC resonant circuit. Relevant equations connecting equivalent capacitance and resonance frequencies are derived from the basic equivalent circuit parameters of the BCSRR through a quasi-static analysis by considering the fringing fields in its vicinity, especially on the top and bottom. Accuracy of the theoretical formula derived for determining the complex permittivity using the BCSRR is verified through experiments and simulations.

Correction: Webb et al. In Situ Determination of Dry and Wet Snow Permittivity: Improving Equations for Low Frequency Radar Applications. Remote Sens. 2021, 13, 4617

In the original article [...]

Determination of the Complex Permittivity of Materials by a Modified Resonator Method Based on the Theory of Small Perturbations Using a Resonator of the Reflective Type

Determination of the Complex Permittivity of Materials by a Modified Resonator Method Based on the Theory of Small Perturbations Using a Resonator of the Reflective Type

Improved description of the potential energy surface in BaTiO3 by anharmonic phonon coupling

Barium titanate (BT) based materials are at the forefront of materials being searched as possible candidates for the replacement of lead-based compositions in applications ranging from piezoelectrics to energy storage devices. Computational methods are very promising to increase the efficiency of materials discovery, provided that finite temperature properties can be realistically computed using, for example, molecular dynamics (MD). In this work, we present a systematic increase of the quality of MD simulations via an alternative way to calculate anharmonic contributions to the potential energy surface (PES) of barium titanate. A large number of first-principles calculations are performed, which are subsequently used to parametrize an effective Hamiltonian. To test the effects on various physical properties, MD simulations for the determination of transition temperatures, hysteresis, and permittivity of BT are shown. Furthermore, measurements were performed on BT single crystals to compare them directly with the MD simulations. It is observed that by incorporating a large number of anharmonic couplings, the description of the local minima in the PES becomes more accurate than in previous simulations. This leads to a better prediction of phase transition temperatures and shows the importance of anharmonic couplings in barium titanate. The presented approach can be directly adapted for other perovskite structures.

Determining dielectric properties of nematic liquid crystals at microwave frequencies using inverted microstrip lines

ABSTRACT In this paper, we have investigated the dielectric properties of nematic liquid crystals (NLCs) by measuring the resonant frequencies of inverted microstrip lines (IMSLs) of NLC being the substrate material at the microwave frequency band. The designed IMSL devices consist of a cavity for NLC mixture between the inverted microstrip line and the ground plane. The anisotropy values of the NLCs were determined by observing the change of the resonant frequency when the strength of external electric fields applied on the NLCs varied. The experiments demonstrated that the effective dielectric constant of the NLC can be manipulated by the proposed devices via external bias voltage for tuning. The accuracy of the method for determining the dielectric constants of JC-M-LC-E7 (JC-E7) and QYPD-036 LCs was analysed with several prototypes based on two separate designs. The high accuracy of 91% in permittivity determination was demonstrated, and the design and fabrication techniques are beneficial for making microwave components of high tunability.

Controlling the mixing quality of 2K adhesives by means of electrical capacitance tomography – Part I: necessary polymer characteristics

ABSTRACT To ensure the desired mechanical properties of adhesively bonded components, maintaining the prescribed mixing quality, i.e. mixing ratio and evenness, of two-component (2K) adhesives is essential. Although different studies proved that mixing errors may exert a negative impact on the bonding result, there are currently no methods available that would allow for continuous monitoring thereof during inline dosing processes. A way out of associated issues is offered by the Electrical Capacitance Tomography (ECT), which enables practitioners to map spatial material distributions and mixing ratios by measuring the capacitances of different media, including adhesives. Therefore, the aim of the study was to investigate the ECT’s potential to be used for 2K mixture quality control. Due to the complexity of the matter, the presentation is split into two papers. In this 1st part, all preliminary experimental and analytical work aiming to determine polymer characteristics, above all permittivity, ε, needed to evaluate whether a respective 2K adhesive may be ECT-monitored is presented. For that, a permittivity measurement device (PMD) was developed, which allows for a fast and efficient determination of adhesive permittivities. Subsequently, the PMD was validated with reference dielectrics and then used to determine the permittivities of the components of 16 commercially available 2K adhesives (epoxies and polyurethanes). Finally, the relationship between permittivity and mixing ratio was investigated for a sub-set of four representative ECT-suitable adhesives. It was found that a wide variety of 2K polymers may principally be controlled by ECT and that the relationship between mixing ratio and mixture permittivity can be described by general analytical theories from the literature. As a result, preliminary experimental effort aiming to assess the adhesive suitability for inline ECT-monitoring could be significantly reduced. The latter experiments will be the topic of the 2nd part of the study.

Microwave Split Ring Resonator Sensor for Determination of the Fluids Permittivity With Measurement of Human Milk Samples

AbstractIn this paper, the human milk dielectric constant by a microwave sensor has been evaluated. The proposed sensor is result of coupling between a simple microstrip line and a split ring resonator and its resonance frequency is 6 GHz. When up to 30 μl of milk are placed on the sensing area on the sensor, it causes the resonance frequency to shift. Six samples of human milk were measured by a network analyzer, then the dielectric constant of the samples were determined, and three similar samples were measured by the built‐in sensor. The proposed microwave sensor has Q‐factor of 38 and its sensitivity is 0.17%. The implemented sensor has acceptable performance compared to previous sensors and it can be used to determine the normal behavior of human milk with a simple method and for this work, it requires to small value of sample for measurement.

Compact Multifunctional Five-Wire Line-Based Microwave Sensor for Volumetric Characterization of Liquids

A new microwave sensor system with a five-wire line configuration is developed for volumetric characterization of liquids. Compared with the existing permittivity-based evaluation methods, the sensor is low profile, low-cost, submersible, easy to fabricate and implement (can be inserted into a container through a small access). An analytical model is proposed for accurate permittivity determination, and the effects of the line length and frequency range on the signals are thoroughly studied for optimal setting. The accuracy of the sensor is verified with standard liquids of known permittivity. From the measurement of honey and alcoholic drinks, explicit relationships are found between the permittivity and the constituent content, thereby facilitating liquid discrimination. The potential for the detection of liquid stacking and level change is well demonstrated in the evaluation of oil samples. The sensor offers an alternative solution to assessment of a wide range of liquids in food, oil, agricultural and bio-sensing applications.

Permittivity Determination Method for Multilayer Automotive Coatings for Radar Applications at 77 GHz

For highly automated driving functions, up to ten radar sensors must be installed without affecting the vehicle design. This is only possible if they are placed behind painted bumpers. In order to understand the effects of automotive coatings on radar, it is crucial to determine the relative permittivity of each coating layer. A holistic approach to achieve high precision when determining the relative permittivities of multilayer automotive coatings for radars operating at 76&#x2013;77 GHz is presented. The method is applied to two different types of measurement setups utilizing a vector network analyzer (VNA) with corrugated horn antennas and an all-in-one quasi-optical free-space measurement solution.