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Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Measuring the complex permittivity of ultrathin, flexible materials with a high loss tangent poses a substantial challenge with precision using conventional methods, and verifying the accuracy of test results remains difficult. In this study, we introduce a methodology based on a back-propagation artificial neural network (ANN) to extract the complex permittivity of paper-based composites (PBCs). PBCs are ultrathin and flexible materials exhibiting considerable complex permittivity and dielectric loss tangent. Given the absence of mature measurement methods for PBCs and a lack of sufficient data for ANN training, a mapping relationship is initially established between the complex permittivity of honeycomb-structured microwave-absorbing materials (HMAMs, composed of PBCs) and that of PBCs using simulated data. Leveraging the ANN model, the complex permittivity of PBCs can be extracted from that of HMAMs obtained using standard measurement. Subsequently, two published methods are cited to illustrate the accuracy and advancement of the results obtained using the proposed approach. Additionally, specific error analysis is conducted, attributing discrepancies to the conductivity of PBCs, the homogenization of HMAMs, and differences between the simulation model and actual objects. Finally, the proposed method is applied to optimize the cell length parameters of HMAMs for enhanced absorption performance. The conclusion discusses further improvements and areas for extended research. [ABSTRACT FROM AUTHOR]

Soil pollution caused by hydrocarbons, such as diesel, poses significant risks to both human health and the ecosystem. The evaluation of soil pollution and various soil engineering applications often relies on the analysis of complex permittivity, encompassing parameters such as dielectric constant and dielectric loss. Various computational models, including theoretical physics-based models, mixture theory models, statistical empirical models, and artificial neural network (ANN) models, have been explored for computing soil complex permittivity and predicting water and pollutant content. Theoretical models require detailed data that is often unavailable, and thus have limited applicability. Mixture models tend to underestimate soil characteristics due to inaccuracies in permittivity estimation of soil phases. While empirical models are widely used, their applicability is restricted to specific soil types, datasets, and locations. ANN models offer promising predictions, accommodating nonlinear phenomena and allowing for missing information and variables. In this study, capacitive electromagnetic electrode sensors were utilized to determine the complex permittivity of soil contaminated with varying levels of diesel at different moisture levels. Theoretical mixture, empirical, and Feed Forward Neural Network (FFNN) models were employed to compute the permittivity of polluted soil based on its phases and to predict the level of diesel pollution. A comparison of these modeling approaches revealed that the FFNN model exhibited the best performance. The ANN model demonstrated superior performance metrics, including a high correlation coefficient and lower mean square error. Specifically, the correlation coefficients for the FFNN model were 0.9942 for training samples, 0.9967 for validation samples, and 0.9977 for test samples. Additionally, the ANN model yielded the lowest mean square error compared to the other three models. [ABSTRACT FROM AUTHOR]

The indoor terahertz (THz) wave reflection and transmission characteristics were clarified as essential for the construction of an integrated channel model for terahertz integrated sensing and communication (ISAC). Measurement campaigns were carried out on seven indoor materials at 130~134 GHz using a vector network analyzer-based measurement platform, and the frequency dependence and incidence angle dependence of the terahertz channel reflection and transmission characteristics were analyzed, which were compared with the measurement results at 282~290 GHz, to have the reflection loss characteristics in the two frequency bands revealed. A quantum particle swarm optimization algorithm was used to extract the material electromagnetic parameters, and a joint frequency-incidence angle model of the reflection coefficient was proposed. The results are shown to indicate that the variation rule of the reflection coefficient with frequency and incidence angle can be accurately portrayed by the model. The material propagation coefficient database of the 130~134 GHz band is supplemented by the research results, the electromagnetic parameter dataset is enriched, and the reflection coefficient model is established. The data basis and model reference for the detection, identification, and environmental reconstruction of the terahertz ISAC system are provided. [ABSTRACT FROM AUTHOR]

Ba 1– x Sr x TiO 3 (BST) ceramics are promising dielectric materials. However, their fabrication is usually laborious, requiring long preparation stages and high temperatures, which are not favorable for tuning the grain size and dielectric properties. In this study, (Ba 1– x Sr x)TiO 3 (x = 0.1, 0.3, 0.5) ceramics were produced via reactive flash sintering (RFS) of a mixture of BaCO 3 , SrCO 3 and TiO 2 powders at 900 °C and relatively short times (15–90 s). The electric field (E-field) with a strength of 400 V/cm and the current densities of 25–75 mA mm−2 were applied during RFS. Once the Sr2+ content increased, the incubation time for the RFS decreased, suggesting that the addition of Sr2+ facilitated the RFS process. At the RFS time above 15 s, a single-phase Ba 0.6 Sr 0.4 TiO 3 perovskite structure was formed. When the time and the applied current density increased, both the densities and grain sizes within the ceramics increased. This increased the real part (ε ') of the complex permittivity compared to that of the conventionally sintered (CS) ceramic. Moreover, the enhancement of mass transport by E-field-induced oxygen vacancies was considered the predominant mechanism of RFS in the production of BST ceramics. [ABSTRACT FROM AUTHOR]

The paper presents results of finite element modeling, development of and experiments with the measuring cell based on a symmetric stripline for measuring coarse-grained soil permittivity. The wave impedance of the measuring cell section intended for filling with soil, is about 80 Ω to expand the frequency range. This allows reducing the width of the central strip and increasing the critical frequency, which cause the higher-order modes. Cell sections with the transfer from SMA connectors to measuring section are filled with a solid dielectric. The distance between outer conductors and the central strip width in these sections, are linearly increased to the size of the measuring section to provide the wave impedance of 50 Ω. The wave impedance growth in the measuring section is considered in the soil complex permittivity calculations. The complex permittivity is measured for five calibration liquids with the static permittivity of 2.27 (transformer oil) to 78.5 (water) and three soil samples with different moisture. It is shown that acceptable values of measurement error can be obtained if the real part of the complex permittivity does not exceed 23–25 units at a frequency of ~1 GHz. [ABSTRACT FROM AUTHOR]

This paper proposes a high-sensitivity microstrip differential sensor for measuring the complex permittivity of liquids. The prototype of the differential sensor was formed by cascading two LC resonators on a microstrip transmission line based on stepped impedance. A strong electric field was found to be distributed in the circular patch of the LC resonator; therefore, a cylindrical micropore was set in the center of the circular LC resonator to measure the dielectric sample, which maximized the disturbance of the dielectric sample on the sensor. By optimizing the size of the circular LC resonator, a high-sensitivity sensor circuit was designed and manufactured. The complex permittivity of the test sample was calculated by measuring the transmission coefficient of different molar concentrations of ethanol–water solutions. The experimental results show that the designed differential sensor can accurately measure the complex permittivity of liquid materials with an average sensitivity of 0.76%. [ABSTRACT FROM AUTHOR]

Glyphosate‐based herbicides are the most used worldwide despite the fact that studies have shown their possible adverse effects on human health and the environment. Since the residues of these herbicides reach water bodies, their detection is considered an emergent research topic. In this work, the use of the intrinsic resonance of a microwave interdigitated capacitor fabricated on microstrip technology, is proposed for detecting the presence of glyphosate‐based herbicide in water. In addition, a sample holder is proposed to avoid the possible oxidation of the metal electrodes due to the direct contact with liquids. The proposed structure was designed to present its first intrinsic resonance at 1.95 GHz so that this resonance is shifted to 1.58 GHz when pure deionized water is used as sample. The sensor device was tested against 18 mixtures prepared with concentrations between 0% and 100% v/v of herbicide diluted in deionized water. Experimental measurements confirm that by using the intrinsic resonance parameters of the proposed structure, is possible to detect the presence of a glyphosate‐based herbicide. Finally, the results confirm the potential of the proposal as an alternative for real‐time, label‐free, and sensitive detection of glyphosate in water and they open the possibility of exploiting its use for the detection of other contaminants. [ABSTRACT FROM AUTHOR]

Polystyrene (PS) microspheres have the advantages of good stability, corrosion resistance and low density, which have a broad application prospect. In this paper, PS composite microspheres with 20% silver plating content were prepared by chemical plating method and incorporated into polydimethylsiloxane (PDMS) flexible matrix to prepare Ag@PS/PDMS flexible wave-absorbing materials. The electromagnetic parameters were adjusted to optimize the dielectric and wave-absorbing properties by varying the additional amount of Ag@PS composite microspheres in Ag@PS/PDMS composites. The X-ray diffraction (XRD) results proved the successful preparation of Ag@PS composite microspheres. The SEM and EDS images indicated that the Ag particles were attached to the external surface of PS. The presence of Ag particles in the Ag@PS composite microspheres enhances their electrical conductivity and enables the formation of a conductive network. This, in turn, improves the composites' dielectric constant. The optimal wave-absorbing capability of the composites was achieved when the Ag@PS composite microspheres were added at a weight percentage of 50%. When the sample attains a thickness of 1.8 mm, a reflection loss of at least −39.8 dB is attained at 10.4 GHz, along with a bandwidth of 1.6 GHz (9.1–10.7 GHz) for the effective absorption bandwidth (EAB). The pressure-sensitive properties of the pliable composites were investigated as well. The optimal pressure-sensitive performance of Ag@PS/PDMS composites was achieved with a 60 wt.% addition of Ag@PS composite microspheres. The resistance undergoes significant changes when subjected to pressure with a sensitivity of 9.7. The results indicate that the flexible composites' wave-absorption and pressure-sensitivity properties can be modulated by adjusting the amount of Ag@PS composite microspheres added. [ABSTRACT FROM AUTHOR]

In this work, we propose a differential complementary split-ring resonator (CSRR) sensor as the resonating element for permittivity analysis of liquid samples. In comparison to conventional non-differential sensors, differential sensors are found to be immune to environmental changes. The proposed sensor operates at 2.35 GHz of the ISM band and is built on a low-cost FR4 substrate. The sensor is thoroughly optimized and validated using Ansys High Frequency Structure Simulator software. Multiple liquid samples covering a wide dielectric range of 1–111 are used to determine the sensing performance of the sensor. The sensitivity of the sensor is found to be high and on par with recent works related to differential CSRR sensors. Based on the frequency of the transmission notch observed, a fit equation is developed to determine the dielectric constant of unknown samples. The proposed differential sensor promises to be a good alternative to traditional CSRR sensors for requirements involving noise and atmospheric fluctuations. [ABSTRACT FROM AUTHOR]

A systematic study of the effects of the binder matrix on the microwave absorption properties of functional carbon nanoparticle-impregnated rubber composites is reported herein. Flexible rubber composites were fabricated by loading of conductive carbon black (CB) in three different elastomeric binder host matrices: silicone rubber, acrylonitrile butadiene rubber (NBR) and ethylene propylene diene monomer (EPDM) rubber. The DC conductivity, morphology and complex dielectric permittivity were investigated using the four-point probe contact method, scanning electron microscopy and vector network analyzer instrumentation, respectively. The percolation threshold was found to be lowest for CB-silicone rubber composites, i.e. 6 wt.% loading of CB, followed by 12 wt.% for CB-NBR composites and 16 wt.% for CB-EPDM composites. The rheological behavior of these composites was also studied, and their correlation with the observed percolation threshold (DC conductivity) of composites is discussed. The microwave absorption properties (reflection loss [RL]) were calculated based on the measured electromagnetic parameters over a frequency range of 6–18 GHz for each composite system. The significant microwave absorption (RL > −10 dB) properties can be tuned by varying the thickness in the range of 1.7–3.0 mm in these composites. The studies presented in the paper provide a basic framework for selection of an appropriate binder matrix for the development of stealth composites, according to the desired area of application. [ABSTRACT FROM AUTHOR]

The permittivity of a material is an important parameter to characterize the degree of polarization of a material and identify components and impurities. This paper presents a non-invasive measurement technique to characterize materials in terms of their permittivity based on a modified metamaterial unit-cell sensor. The sensor consists of a complementary split-ring resonator (C-SRR), but its fringe electric field is contained with a conductive shield to intensify the normal component of the electric field. It is shown that by tightly electromagnetically coupling opposite sides of the unit-cell sensor to the input/output microstrip feedlines, two distinct resonant modes are excited. Perturbation of the fundamental mode is exploited here for determining the permittivity of materials. The sensitivity of the modified metamaterial unit-cell sensor is enhanced four-fold by using it to construct a tri-composite split-ring resonator (TC-SRR). The measured results confirm that the proposed technique provides an accurate and inexpensive solution to determine the permittivity of materials.

This paper presents a novel capacitive sensor-based device for detecting type-2 diabetes through blood analysis. The proposed methodology measures changes in the complex permittivity of red blood cells (RBCs) caused by elevated glucose levels, affecting their rheological and electrical properties, such as viscosity, volume, relative permittivity, dielectric loss, and AC conductivity. These changes, well-documented in the literature, alter the bio-impedance signature of RBCs, serving as an indicator for type-2 diabetes. The study examines various concentrations of normal and diabetic RBCs within a frequency range of 50 kHz to 200 kHz, chosen for its relevance to bio-impedance responses. Experimental results show that healthy RBCs in a 200 μL PBS solution have a complex permittivity (ɛmix) of 65.12 and conductivity (σmix) of 0.63 S/m, while diabetic RBCs measure 73.44 and 0.68 S/m, respectively. Additionally, the complex permittivity decreases as the cell concentration increases for both normal and diabetic RBCs. At 100% cell concentration, the average bio-impedance for diabetic blood cells is 50.3 kΩ, compared to 56.7 kΩ for healthy blood cells over the entire frequency range. The standard deviation of bio-impedance (Zmix) between 50 kHz and 200 kHz highlights the difference between healthy and diabetic RBCs, with 200 kHz measurements proving more reliable. To detect these bio-impedance changes, an interdigitated electrode (IDE) capacitive sensor with 40 capacitive elements was simulated. The complex bio-impedance (Zmix) was measured within the 50 kHz–200 kHz frequency range, providing clear differentiation between healthy and diabetic blood cells. Simulation using Finite Element Method (FEM) through COMSOL® software supports these findings, showcasing the sensor’s efficacy in type-2 diabetes detection.

Microwave heating is an emerging alternative pretreatment method for road maintenance in cold seasons. The thermal behavior of asphalt pavement under microwave heating is mainly determined by the complex permittivity of the asphalt mixture. In this study, an innovative approach for calculating the complex permittivity of an asphalt mixture based on a three-dimensional meso-scale heterogeneous structure was proposed. A series of experiments was conducted to verify the accuracy of this approach. The effect of porosity, void size, moisture content and aggregate gradation on the complex permittivity for an asphalt mixture were computationally analyzed based on the validated approach. Moreover, the applicability of commonly used classical dielectric models was analyzed. The classical Lichtenecker–Rother (LR) dielectric model was modified on the basis of simulation data for various conditions. The results showed that the real part of the complex permittivity decreased with the increase in porosity. Some sudden change in the imaginary part of the complex permittivity was observed within the frequency range from 2.6 GHz to 3.9 GHz. A larger air void size would lead to a larger frequency at which sudden change occurs. The real part and imaginary part of the complex permittivity tend to be smaller when more coarse aggregates are replaced with fine aggregates. Both the real part and the imaginary part of the complex permittivity increase with higher moisture content due to the stronger dielectric property of water. Each 1% increase in moisture content would lead to about a 3~4% increase in the real part of the complex permittivity. The determination coefficients R2 for the real part and the imaginary part of the complex permittivity fitted by the modified Brown model were the maximum values, which were 0.922 and 0.980, respectively. The method presented in this study is useful for transportation agencies to optimize microwave heating during winter maintenance. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the L.N. Gumilyov Eurasian National University. Technical science & Technology series is the property of L.N. Gumilyov Eurasian National University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Dielectric characterization of water samples, of different water sources such as borewell and step well located at three different places of the Gujarat State were carried out. Complex permittivity (ε′, εʺ) of the distilled water (DW) and water samples were measured over a frequency range from 20 Hz to 2 MHz using a precision LCR meter at room temperature (T = 298.15 K). Although the spectral response of ε′ and εʺ for all samples and DW was identical, it exhibited significant shift with respect to that of distilled water. Therefore, we adopted a novel approach, in which frequency dependent ε′ and ε′′ values of all the samples were normalized with respect to those of the distilled water. When normalized ε′ and εʺ values were plotted against frequency it exhibited well defined characteristic frequencies. These frequencies were found to vary with sample types. Chemical compositional analysis of the samples was also carried out. Correlation between various parameters derived from complex permittivity data and dissolved salts in the sample (measured by chemical compositional analysis) was established. [ABSTRACT FROM AUTHOR]

Quantitative and qualitative parameters are essential for comprehending the intermolecular interactions in binary polar liquids. In this work, complex permittivity and excess dielectric constant of alcohol–water mixture is used for the quantitative and qualitative analysis, respectively. Aqueous solutions of methanol, ethanol, propanol and isopropyl alcohol are considered. The frequency dispersion of permittivity and the intricate structure of these liquids make the analysis a difficult task. A decision tree regression-based machine-learning model is proposed for the prediction of parameters. For quantitative analysis, the dataset is prepared by measuring the complex permittivity of the mixture using dielectric probe kit–N1501A of Keysight Technologies over a frequency range of 0.2–20 GHz at 25°C. For qualitative analysis, available standard equations are modified to calculate the excess dielectric constants in the specified frequency range. The proposed model requires only three input parameters—frequency, volume fraction of alcohol and static dielectric constant of alcohol to make the prediction. Performance comparison of the model with the measured values of complex permittivity shows minimum error. The analysis reveals the effect of the volume fraction of alcohol and frequency on complex permittivity and excess dielectric constant of the mixture. The proposed model is a novel and reliable prediction tool that can be used for both quantitative and qualitative analysis of alcohol–water mixture. [ABSTRACT FROM AUTHOR]

Polystyrene (PS) microspheres have the advantages of good stability, corrosion resistance and low density, which have a broad application prospect. In this paper, PS composite microspheres with 20% silver plating content were prepared by chemical plating method and incorporated into polydimethylsiloxane (PDMS) flexible matrix to prepare Ag@PS/PDMS flexible wave-absorbing materials. The electromagnetic parameters were adjusted to optimize the dielectric and wave-absorbing properties by varying the additional amount of Ag@PS composite microspheres in Ag@PS/PDMS composites. The X-ray diffraction (XRD) results proved the successful preparation of Ag@PS composite microspheres. The SEM and EDS images indicated that the Ag particles were attached to the external surface of PS. The presence of Ag particles in the Ag@PS composite microspheres enhances their electrical conductivity and enables the formation of a conductive network. This, in turn, improves the composites’ dielectric constant. The optimal wave-absorbing capability of the composites was achieved when the Ag@PS composite microspheres were added at a weight percentage of 50%. When the sample attains a thickness of 1.8[Formula: see text]mm, a reflection loss of at least −39.8[Formula: see text]dB is attained at 10.4[Formula: see text]GHz, along with a bandwidth of 1.6[Formula: see text]GHz (9.1–10.7[Formula: see text]GHz) for the effective absorption bandwidth (EAB). The pressure-sensitive properties of the pliable composites were investigated as well. The optimal pressure-sensitive performance of Ag@PS/PDMS composites was achieved with a 60[Formula: see text]wt.% addition of Ag@PS composite microspheres. The resistance undergoes significant changes when subjected to pressure with a sensitivity of 9.7. The results indicate that the flexible composites’ wave-absorption and pressure-sensitivity properties can be modulated by adjusting the amount of Ag@PS composite microspheres added.

The aim of the research is to develop a radar method for determining the physical and chemical parameters of subsurface soil horizons, providing rapid determination of moisture and specific conductivity in the area of the plant root system. The proposed method is based on a set of Fresnel equations which describe reflection of electromagnetic waves from the interface between dielectric media in vertical and horizontal polarization of the probing signal. For the practical implementation of the method, it is proposed to use two unmanned aerial vehicles that form a bistatic radar system which irradiates the Earth's surface obliquely in order to create the Brewster's effect and increase the fraction of the radio signal reflected from subsurface horizons. The percentage of moisture and the specific conductivity of soil are calculated from the measured values of the imaginary part of the complex permittivity. The required accuracy of moisture and conductivity measurements is achieved by two-step calibration of the measuring device. The values of the moisture content and specific conductivity of soil obtained by radar at a frequency of 469 MHz are in good agreement with the results of measuring these parameters using the soil moisture meter TDR 150 Spectrum Technologies, Inc.

Sand and dust storms present significant challenges to microwave and millimeter-wave propagation, directly impacting communication systems. Despite the existence of various theoretical and analytical models for predicting dust storm attenuation, many have overlooked the crucial factor of humidity. This study had conducted a year-long monitoring of visibility, humidity, and received signal levels for two microwave links operating at 14 GHz and 22 GHz in Khartoum, Sudan. The percentage variation in visibility during a dust storm is 95%, and the percentage variation in humidity is 78%, as the received signal level varies from −42.17 dB to −82 dB. The research unveils a notable correlation between fluctuations in humidity and the complex permittivity of sand and dust particles. Furthermore, this study proposes an empirically developed prediction model for sand and dust storm attenuation, surpassing existing models by incorporating both visibility and humidity data. In contrast to models that solely rely on measured visibility and neglect humidity, this research methodology takes into account both of these measured parameters during dust storms to predict attenuation at any desired frequency. The model’s performance is validated through measurements at 14 GHz, 22 GHz, and 40 GHz, demonstrating robust agreement with the collected data. This comprehensive model provides a more accurate representation of the complex weather conditions during sand and dust storms, enhancing the readability of microwave links design by accurate prediction and mitigation of their impact on communication systems.

In this paper, two composites ZrB₂/Al₂O₃ and FeSiAl/Al₂O₃ were characterized using the Transmission/Reflection characterization technique. The volume contents of ZrB₂ and FeSiAl inclusions in these composites vary between 0 and 15%. The results obtained indicate that the percentage of the inclusions in the composites effectively improves the dielectric property. The comparison of the effect of ZrB₂ and FeSiAl inclusions on the dielectric properties of these composites confirms that reinforcing these composites with FeSiAl particles results in better dielectric properties. Furthermore, these results indicate that the dielectric property of the two composites studied decreases progressively with increasing frequency in the X band. This frequency dependence of the dielectric property of the composites studied is very important and shows that the composites studied are good candidates for microwave absorption applications in the X-band and for antenna design. Additionally, a comparison between the numerical results obtained in this work and the experimental results published in the literature reveals a close agreement, validating the reliability of the study's findings.

Despite the significant number of studies published on the measurements of complex permittivity of biological tissues in the last thirty years, implementing a successful measurement program for dielectric measurements can still present a challenge for researchers. Most problems are not theoretical but of methodological or practical nature. In this article, lessons learned from experiences with goal-oriented measurements are presented by structuring them into practical guidelines for efficient and useful measurements of dielectric properties of biological tissues, aimed at addressing gaps in knowledge. Issues related to calibration, validation of the measurement system and data collection procedures are addressed from a practical perspective. This will help support reproducibility of measurements. In addition, guidelines for data analysis and data reporting are provided. The latter is also supported by a data analysis tool developed in MATLAB, made available as open source. This facilitates the harmonisation and merging of different datasets, ease of interpreting and re-using of data and comparison of data across studies. Additionally, a data repository is presented for uploading of dielectric data of biological tissues, along with the corresponding meta-data describing the experiments. These guidelines are the result of the work carried out by a dedicated working group in the project COST Action MyWAVE.

This article introduces the incorporationapproach with synthetic aperture radar (SAR) and contrast source inversion (CSI) based nonlinear inverse scattering (NIS) approach for quantitative permittivity imaging for buried object under multilayered heterogeneous ground media. It is challenging issue to retrieve a complex permittivity from ground-penetrating radar (GPR) data, since the NIS problem considerably suffers from inaccuracy due to severe ill-posed condition. To overcome this limitation, this article introduces the SAR image-based region of interest (ROI) limitation in the CSI optimization scheme, where the number of unknowns are massively reduced. Furthermore, the SAR image is also upgraded by the pre-CSI optimization, where the Green's function and background clutter for heterogeneous background (e.g., multilayered medium) are accurately generated. The FDTD-based numerical tests, assuming GPR observation model, show that our proposed scheme effectively reconstructs a dielectric property of buried object, even in severe condition.

We have analyzed the complex permittivity of a porous (10 volume % of pores) sodium-lithium niobate ceramic with the results of computer simulation. The calculation was based on the Cole–Cole formula, which took into account the presence of various mechanisms of relaxation processes in the low-frequency (linear dispersion) and mid-frequency regions, an additional term from the Debye formula was added to take into account the mixed polarization, and a term taking into account the damping factor was added for resonant-type polarization. The simulation was carried out with and without the conductivity taken into account. To take into account the contribution of conductivity to the dynamic dielectric response, the expression σ* = (ε″ + iε′)ε0ω was used. It is shown that the linear part of the frequency dependence in the range from 50 Hz to 1 MHz is equally well described both with and without conductivity. At the same time, the behavior of the dielectric response of piezoelectric ceramics in the high-frequency region, where resonance effects are observed, and the low-frequency region, where volume-charge polarization predominates, is much better described taking into account the contribution of conductivity to the dielectric response of the system.

The composite material based on multi-walled carbon nanotubes and a water-dispersed paint has been obtained. Low-frequency spectroscopy showed that ultrasonic dispersion of the multi-walled carbon nanotubes (MWCNTs) in the water-dispersion paint leads to a non-monotonic dependences of the complex dielectric constant and electrical conductivity of the composite on the processing time. This behavior is associated with the deagglomeration of MWCNT bundles, the destruction of the MWCNTs at defect sites, and the appearance of extended conductive structures in the bulk composite. [ABSTRACT FROM AUTHOR]

This paper presents the synthesis of hematite Fe2O3 nanofiller from mill scales and its application in polytetrafluoroethylene (PTFE) composites for enhanced dielectric and microwave-absorbing properties. The nanofiller was obtained through 9 hours of highenergy ball milling, resulting in a particle size reduction 43.6 to 11.05 nm. The PTFE/Fe2O3 composites were fabricated by dispersing different concentration of Fe2O3 nanofillers using the dry powder processing technique. The structural and morphological characterization of the nanofiller and PTFE/Fe2O3 composites was carried out using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. The composites' microwave absorption properties were analyzed utilizing vector network analyzer (VNA) measurements in the 8-12 GHz frequency range. Based on the findings from the results, as the percentage of filler increased from 5 to 15%wt, the composites' loss tangent and dielectric constant increased from 0.0272 to 0.0478 and 2.12 to 3.25, respectively, while their reduced signal transmission speed was between 2.21 and 2.07 x 108 m/s at 8 GHz and from 2.24 to 2.11 x 108 m/s at 12 GHz. These findings demonstrate that Fe2O3 nanoparticles are a suitable material for developing microwave-absorbing polymer composites within the 8-12 GHz frequency range. [ABSTRACT FROM AUTHOR]

Copyright of FME Transactions is the property of University of Belgrade, Faculty of Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Using the Time Domain Reflectometry technique in the frequency range of 10 MHz to 50 GHz, the complex permittivity spectra of Glycine (Gly) with water combination have been determined over the complete concentration range of mole fractions and in temperature range of 10–25 °C. The Cole-Davidson model was used to fit the intricate permittivity spectra for Gly and water. The non-linear least square fit method has been used to compute the static dielectric constant (ε0), relaxation time (τ), effective Kirkwood correlation factor (geff), excess permittivity ( ε 0 E ), (1/τ)E excess inverse relaxation time (1/τ)E and Bruggeman factor (fB). An automated density and sound velocity meter, the Anton Paar DSA 5000 M and viscosity with Lovis 2000 M/ME, was used to measure the density, sound velocity, and viscosity of aqueous solutions. FT-IR spectra are used to identify the conformation assessments of hydrogen bonding development between complicated mixtures. [ABSTRACT FROM AUTHOR]

The application of magnetic nanocrystalline powders as radar absorption materials is increasingly attracting R&D interest. Severe agglomeration and mass production, however, are critical issues for practical application of magnetic nanoparticles. In the present study, iron nanowires with varying amounts of nickel addition (0, 1, 10, 30, and 50 wt%) were synthesized via direct reduction of iron salts with the aid of strong NdFeB magnets. The yield rate of these Ni-added iron nanowires (NiFe NWs) exceeded 1 g/min, making them suitable and was feasible for mass production. The characteristics of the so-obtained NiFe NWs were confirmed using field emission scanning electron microscopy, X-ray diffraction, and high-resolution transmission electron microscopy. Composite resins with NiFe NWs additions (3, 5, and 10 wt%) were prepared and examined using the coaxial line method to reveal their microwave absorption characteristics. Experimental results showed that composite resins with 10 wt% NiFe NWs additions possessed superior microwave absorbing properties, with the Ni1Fe99 NWs-added product exhibiting the best performance. When produced with a thickness of 1.7 mm, the reflection loss of the composites reached −39.28 dB at 12.53 GHz. Additionally, the efficient maximum absorption bandwidth was 3.33 GHz, ranging from 14.27 to 17.60 GHz.

This paper presents some microwave circuits, designed for characterization of materials’ permittivity. These include single and multiple-resonant types, transmission line approaches, radiation structures and planar circuits. They have either theoretical analysis, simulations, behavior analysis, or fabrication results. A simple half-wavelength coaxial system is used for measuring velocity factor or dielectric constant of the cable. This method presents very accurate results. A planar multi-dielectric antenna structure is proposed whose layers comprise the dielectric under test. The near field as well as the radiation performances are influenced by the permittivity, which is the basis for determining this parameter. Also, a planar resonant cavity is designed and optimized to give enhanced coupling performance and gets higher quality factors. It has a small size and its sensitivity is improved employing a chamfer. The values of dielectric constants are extracted from scattering parameters. In another method, a three-section microstrip line is used whose time domain response is employed to retrieve the dielectric constant. This method can be generalized to other planar lines. At last, a simple method for measuring complex conductivity of lossy planar conductors is studied and it is employed for characterization of a graphene oxide layer.

This paper proposes a high-sensitivity microstrip differential sensor for measuring the complex permittivity of liquids. The prototype of the differential sensor was formed by cascading two LC resonators on a microstrip transmission line based on stepped impedance. A strong electric field was found to be distributed in the circular patch of the LC resonator; therefore, a cylindrical micropore was set in the center of the circular LC resonator to measure the dielectric sample, which maximized the disturbance of the dielectric sample on the sensor. By optimizing the size of the circular LC resonator, a high-sensitivity sensor circuit was designed and manufactured. The complex permittivity of the test sample was calculated by measuring the transmission coefficient of different molar concentrations of ethanol–water solutions. The experimental results show that the designed differential sensor can accurately measure the complex permittivity of liquid materials with an average sensitivity of 0.76%.

The paper focuses on the mutual influence of moisture, salinity, and particle-size distribution on soil permittivity. The Agilent E8663B Analog Signal Generator is used for measurements in the frequency range of 8 to 18 GHz using the coaxial method. It is found that the maximum amount of bound water in soil depends on the soil type and is 15.9 and 13.7% for CuSO4 and NiSO4 35 mg/kg each, respectively. A 12% growth in the silt and clay content provides a 1.3% increase in the maximum amount of bound water in soil. [ABSTRACT FROM AUTHOR]

The knowledge of dielectric properties of organic materials at microwave frequencies is important for different applications in agriculture, food, or other similar research areas. The method of the low-cost disturbed cylindrical cavity resonator is a common measurement technique that considers resonant frequency shift when inserting samples of materials inside the cavity. Frequency shifts together with the knowledge of the complex permittivity of a reference material allow the estimation of the permittivity of a material under test. In this paper, the complex permittivity, and the loss tangent of dried and powdered agricultural wastes from the state of Colima in Mexico are obtained at 1.2853. The materials under test are coir and skins of rice, banana, lemon, watermelon, pineapple, and papaya since they are one of the most abundant agricultural wastes in the state of Colima in Mexico. [ABSTRACT FROM AUTHOR]

Transition-metal phosphides have been investigated for microwave absorption applications owing to their excellent conduction loss and magnetic property. In this study, novel composites comprised of porous Al 2 O 3 matrix loaded with Fe x Co y P (Fe x Co y P/Al 2 O 3) were prepared by vacuum impregnation, hydrothermal, and low-temperature phosphatizing methods. The experimental results show that Fe x Co y P is uniformly deposited on the surface of porous Al 2 O 3 ceramic, and the Fe x Co y P transforms from needle-like to particle-like structures as the Fe/Co ratio increases from 1:3 to 3:1. The minimum reflection loss (RL min) of FeCo 3 P/Al 2 O 3 composite reaches −26.19 dB at 12.4 GHz with a matching thickness of 2.6 mm, and the maximum effective absorption bandwidth (EAB) achieves 4.2 GHz in the whole X-band at 3.2 mm thicknesses. This study confirmed that the porous Fe x Co y P/Al 2 O 3 composites are potential candidates for microwave absorption applications, and their microwave absorption properties can be enhanced by adjusting the ratio of Fe to Co. [ABSTRACT FROM AUTHOR]

The adulteration in alcoholic beverage has costed thousands of lives and malnutrition's specifically in developing countries. The existing characterization methods such as Gas Chromatography (GC) and Bioassay and Spectroscopy (NMR) offer insights into the chemical composition but the techniques are costlier and bulkier, hence the testing is evitable in a limited number of cases. This paper discloses the novel radio frequency (RF) technology based sensors and integrated into a device to detect the presence of ethanol in beverages. The proposed sensor is two phase flow sensor as the liquid can continuously move while being sensed by the sensor. The conducting patch of the RF sensing antenna is zig–zag shaped sensor. The sensor sends the signals at RF frequencies to the liquid. The RF signal gets scattered from liquid and receive back by transceiver with a specific time and phase delay. The proposed zig–zag sensor is portable as it is smaller in size (radiating structure has dimensions of 12 mm × 40 mm ). The substrates have a running polysiloxane microfluidic channel where the samples of alcoholic beverages are applied. The device operates at frequencies of 4.592 GHz and 6.458 GHz. The ethanol concentration is detected with the help of a radio frequency spectroscopy. The results are validated with characterization with nuclear magnetic resonance (NMR). [ABSTRACT FROM AUTHOR]

This study focuses on the measurement and analysis of the complex permittivities of polymer blends using the field enhancement method (FEM). The blends, consisting of air-powder or solvent–solute mixtures, are placed in a Teflon holder and inserted into the FEM cavity to determine the complex permittivity. The resonant frequency and quality factor of the FEM cavity coupled with the samples provide information on the blends' dielectric constant and loss tangents. To extract the complex permittivities of three specific samples of DC-840, MCL-805, and MCL-Siloxane, we employ effective medium theories and the high-frequency structure simulator (HFSS) together with the measured data. The results reveal that when the volume fraction of the DC-840 solute in the xylene solvent surpasses a specific threshold, the dielectric constants and the loss tangents experience a notable increase. This phenomenon, known as percolation, strongly correlates with the viscosity of polymer blends. The observed percolation effect on the dielectric behavior is further elucidated using the generalized dielectric constant and the Debye model. By employing these models, the percolation effect and its impact on the dielectric properties of the blends can be explained. [ABSTRACT FROM AUTHOR]

The results of a study of an electromagnetic response and dielectric properties of multicomponent composite materials based on epoxy, ferroelectric BaTiO3 nanoparticles and multiwalled carbon nanotubes for operation in the 0.1–1.1 THz frequency range are presented. The influence of the MWCNT concentration in a ferroelectric composite on its complex permittivity is shown. [ABSTRACT FROM AUTHOR]

Electromagnetic pollution has become a major problem affecting human health, which requires the scientific community to characterise materials that can solve this problem. In the present work, we studied the microwave absorption properties and complex permittivity of ZrB2/Al2O3 ceramic composites in the X-band by simulation. The composites studied are based on alumina and reinforced with ZrB2 particles. The concentration of ZrB2 particles by volume in these composites are 0%, 5%, 10% and 15%. The results obtained show, on the one hand, that the complex permittivity depends on the frequency, and on the other hand, the high content of ZrB2 remarkably increases the complex permittivity and improves the microwave absorption properties. The ZrB2/Al2O3 composite with 5% by volume of ZrB2 particles has better microwave absorption property than others. In this case, the minimum reflection loss is −26.36 dB at 11.5 GHz. For this composite, the RL bandwidth of less than −10 dB is 1.72 GHz, and it is obtained in the frequency range from 9.4 GHz to 10.5 GHz. The simulation results are in good agreement with the published experimental results. In addition, they indicate that the composites studied are favourable for microwave absorption applications in the X band. [ABSTRACT FROM AUTHOR]

Porous SiC–Si 3 N 4 ceramics with various pore structures were prepared by adding different amounts and sizes of pore-forming agents (Polymethyl methacrylate, PMMA). The dielectric and wave absorption properties of porous ceramics were investigated over a wide temperature and frequency range. Increasing the porosity reduced the frequency dependence of complex permittivity. When the porosity increased from 50.97% to 54.59%, the loss tangent was slightly enhanced due to pore-induced polarization. An optimal pore size range enhanced the dielectric properties, beyond which a lower loss tangent was exhibited. Increasing the porosity reduced the temperature dependence of the loss tangent, and the peak of the change rate of the loss tangent moved to a higher temperature. The minimum reflection loss at room temperature can reach - 49.61 dB at 11.91 GHz for a 1.9 mm-thick sample. The minimum reflection loss at 9.72 GHz for 25 vol% PMMA-added porous ceramic with a 2.1 mm-thick material can be as low as - 65.92 dB at 300 °C. The porosity can be changed to achieve selective electromagnetic wave absorption at different temperatures. [ABSTRACT FROM AUTHOR]

Based on our previous work on the propagation of electromagnetic waves in a layered medium placed in a rectangular waveguide, we present the theory of using the TE10 and TM11 modes to determine the complex parameters of isotropic and anisotropic media. The Nicolson–Ross–Weir method was used. The cases of isotropic, uniaxial, and biaxial materials were considered. It has been shown that the TM11 mode can be used to extract parameters of non-magnetic uniaxial anisotropy media by a single measurement, without changing the sample position. This is not possible with the previously used TE10 mode. It is also possible to use the TM11 mode to quickly determine whether a material is isotropic or not. Experimental results are presented for some isotropic materials. [ABSTRACT FROM AUTHOR]

Modern electronic information technology has led social life into inevitable electromagnetic pollution, making microwave absorbing materials more and more important. Herein, dielectric-conductive ZnO/C hybrid composite absorbents were prepared by two-step carbonization with ZnO powders and glucose as critical materials. The electrical conductivity, complex permittivity, and reflection loss were analyzed to study the dielectric and microwave absorption properties. Results show that the prepared ZnO/C composite absorbents exist in the form of rod-like ZnO dispersed in the irregular block carbon, and the complex permittivity of the composite absorbents can be adjusted via varying the carbonization temperature. The minimum reflection loss of −25.64 dB is achieved at 1.8 mm thickness for the composite absorbent with 50 wt.% absorbent content as the final carbonization temperature is 750 °C, and the optimum effective absorption bandwidth is 2.21 GHz at 9.64–11.85 GHz. The excellent microwave absorption properties of ZnO/C composite absorbents are attributed to the combination actions of dipole polarization, conductance loss, and interface polarization, which is significant for the purposeful design of superior microwave-absorbing materials with dielectric and conductive absorbents. [ABSTRACT FROM AUTHOR]

This paper presents some microwave circuits, designed for characterization of materials’ permittivity. These include single and multiple-resonant types, transmission line approaches, radiation structures and planar circuits. They have either theoretical analysis, simulations, behavior analysis, or fabrication results. A simple half-wavelength coaxial system is used for measuring velocity factor or dielectric constant of the cable. This method presents very accurate results. A planar multi-dielectric antenna structure is proposed whose layers comprise the dielectric under test. The near field as well as the radiation performances are influenced by the permittivity, which is the basis for determining this parameter. Also, a planar resonant cavity is designed and optimized to give enhanced coupling performance and gets higher quality factors. It has a small size and its sensitivity is improved employing a chamfer. The values of dielectric constants are extracted from scattering parameters. In another method, a three-section microstrip line is used whose time domain response is employed to retrieve the dielectric constant. This method can be generalized to other planar lines. At last, a simple method for measuring complex conductivity of lossy planar conductors is studied and it is employed for characterization of a graphene oxide layer. [ABSTRACT FROM AUTHOR]

We present a novel broadband permittivity characterization method for liquids measured in a semi-open vertically oriented test cell with an uncalibrated vector network analyzer. For this goal, we utilize three scattering matrices measured at different levels of liquid in the cell. With mathematical operations, we remove the effects of systematic measurement errors caused by both the vector network analyzer and a meniscus shaping the top of the liquid samples in such a type of test cell. To the best authors' knowledge, this is the first of such a calibration-independent method dealing with meniscus. We verify its validity by comparing our results with the data available in the literature and with the outcomes of our previously published calibration-dependent meniscus removal method (MR) for propan-2-ol (IPA), a 50% aqueous solution of IPA and distilled water. The new method yields results comparable with the MR method, at least for IPA and the IPA solution, revealing, however some problems when testing high-loss water samples. Nevertheless, it allows one to cut down on expenditures in the system calibration engaging skilled labor and expensive standards. [ABSTRACT FROM AUTHOR]

We present the broadband transmission-reflection meniscus-removal method for liquid characterization in a semi-open rectangular waveguide. The algorithm utilizes 2-port scattering parameters measured with a calibrated vector network analyzer for three states of the measurement cell: empty and filled with two liquid levels. The method enables the mathematical de-embedding of a symmetrical sample of a liquid, not distorted with a meniscus, and provision of its permittivity and permeability, as well as its height. We validate the method for propan-2-ol (IPA), a 50% aqueous solution of IPA, and distilled water in the Q-band (33–50 GHz). We investigate typical problems for in-waveguide measurements, such as phase ambiguity. [ABSTRACT FROM AUTHOR]

In this letter, a new microwave sensor of the coaxial resonant cavity with a single-open-ended circuit loaded capacitor is proposed and used to detect the liquids' complex permittivity. The improved cavity has a higher internal electric field and smaller size when compared with the cylindrical cavity, which gives the sensor a high sensitivity in measuring liquids' complex permittivity. A coaxial resonant cavity operating in 1.9 GHz was designed in this work. The silicone hose used for the test is inserted vertically from the center of the cavity, and the liquids under test (LUTs) are guaranteed to be 2 ml each time. The dielectric properties of LUTs will cause perturbation to the internal electric field of the cavity. By analyzing the measured data, the sensitivity of the cavity is 0.12%, and the relative errors of the real part of the measured value and the reference value are 3.67%. which shows the measured value has a good agreement with the reference value. [ABSTRACT FROM AUTHOR]

The complex permittivity of 8-mol yttria-stabilized zirconia (8-YSZ) in powder and sintered (i.e., solid) forms were measured from 32 to 40 GHz using a circular waveguide probe. This probe is suitable for measuring both the powder and solid forms of materials. Comparative completely filled rectangular waveguide measurements of the powder were performed at three frequency bands to verify these results and also to extend the measured complex permittivity estimation frequency range. The results indicated good agreement between the two different measurement techniques. The complex permittivity of the 8-YSZ powder was measured to be $(\epsilon _{r} = 2.45 - j0.04)$ . Conductor-backed solid 8-YSZ, representative of an in-service ceramic coating, was also measured using the circular waveguide probe. Complex permittivity was measured to be significantly higher $(\epsilon _{r} = 29.28 - j0.07)$ when the 8-YSZ was sintered into a solid form. This was attributed to densification and other effects occurring during the sintering process.