Complex Permittivity Data Research Articles

Enhancing Magnetic Material Data Analysis with Genetic Algorithm-Optimized Variational Mode Decomposition

As the application of machine learning technology in predicting and optimizing material performance continues to grow, handling the electromagnetic data of magnetic materials, especially in removing unavoidable data noise and accurately extracting resonance peaks in the imaginary part of electromagnetic information, has become a significant challenge. These steps are crucial for revealing the deep electromagnetic behavior of materials and optimizing their performance. In response to this challenge, this study introduces an innovative approach—Genetic Algorithm-Optimized Variational Mode Decomposition for Signal Enhancement (GAO-VMD-SE). This method, through the Variational Mode Decomposition (VMD) technique optimized by genetic algorithms, not only effectively reduces noise in the data, thereby improving the Signal-to-Noise Ratio (SNR) and reducing the Mean Absolute Error (MAE), but also significantly enhances the hidden resonance peak information in complex permittivity and permeability data to achieve a comprehensive improvement in key performance indicators. Experimental results prove that this method surpasses traditional analysis techniques in key performance metrics such as the peak width ratio, peak overlap ratio, and the number of peaks. Especially in identifying characteristic peaks related to the Snoek limit, GAO-VMD-SE can effectively reveal the peak features hidden in complex data, thus providing important insights for evaluating the performance of materials at specific frequencies. Moreover, the effectiveness of this method in denoising not only enhances the quality and accuracy of material data analysis but also achieves a 1% to 10% enhancement in peak information extraction. This optimized data processing capability and versatility make GAO-VMD-SE not only suitable for evaluating the performance of magnetic materials but also show significant practical application value in processing spectral data and other time series signal data applications.

Dielectric and chemical composition characterization of ground water collected from different water sources

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.

Thermal and microwave-absorbing properties of doped polyaniline–epoxy nanocomposites for stealth applications

The thermal properties of polymeric nanocomposites can be examined using TGA and DSC techniques, while dielectric properties can be examined through simulated scattering (S11, S12, S21, and S22) parameters. Polyaniline (PAni) nanopowder was synthesized using chemical oxidative polymerization techniques. Consequently, the crystallite size and morphology of the synthesized powder were examined using the XRD, TEM, and FESEM techniques. Further, a series of polymeric nanocomposites was developed via wet mixing and compressor molding techniques for various volume percentages (54.0, 57.5, 60.1, and 61.7 vol%) of synthesized powder within PAni/epoxy composites. Consequently, dielectric and absorbing properties have been measured using a vector network analyzer and its software module. The computed complex permittivity data were used to evaluate the absorption for different thicknesses of samples. A minimum reflection loss of − 22.3 dB (> 99.9% absorption) was optimized with broadband frequency ranges. The unique heterostructures of nanocomposite are responsible for the enhanced absorption and shielding performance.Graphical abstract

Dielectric Relaxation of Ion-pairs, Micelles and Hydration in Aqueous Hexyltrimethylammonium Bromide Solutions

Through dielectric measurements of aqueous n-hexyltrimethylammonium bromide solutions, the structure and dynamics of ion-pairs, micelles, and water are investigated as functions of concentration and temperature. The frequency range of the study was ∼ 0.2 ≤ν/GHz ≤ 89, and the concentrations were changed from 0.0448 to 0.8476 mol.dm−3 at 298.15 K. The effects of temperature (278.15 ≤ T/K ≤ 338.15) on two selected solutions with concentrations above and below the critical micelle concentration were examined. A summation of three Debye processes fits the complex permittivity data of solutions with concentrations below the critical micelle concentration. To fit the spectra above the critical micelle concentration, a summation of five Debye processes is needed. Below the critical micelle concentration, solutes relax due to the tumbling motion of solvent-shared ion pairs. The two micelle relaxation processes that have been seen are the result of free and bound counter ions tangentially and radially diffusing around the charged micelles. Maxwell-Wagner relaxation is equivalent to the high frequency micelle relaxation process. Both the solvent and micelle dispersion provide acceptable volume fractions. Hexyltrimethylammonium behaves like higher n-alkyltrimethylammonium micelles in the context of micelle relaxation. Before critical micelle concentration, the cations, anions, and ion pairs strongly hydrate a total of ∼18 ± 4 non-rotational water molecules. Beyond the critical micelle concentration, there are an additional ∼ 5 ± 2 non-rotational water molecules in addition to ∼ 15 ± 3 slower-moving water molecules in the hydrophobic hydration shell.

Study of Thermodynamic and Dielectric Parameters of Xylene and Its Isomers Using Time Domain Dielectric Spectroscopy

Raw complex permittivity data of pure aromatic hydrocarbons such as Xylene, O-Xylene (O-X), M-Xylene (M-X), and P-Xylene (P-X) have been measured for different temperatures in 10 MHz to 50 GHz frequency range using Time Domain Dielectric Spectroscopy (TDDS). Dielectric relaxation for above systems has been characterized by the Debye type spectral relaxation. The dielectric parameters such as static dielectric constant, relaxation time, Kirkwood correlation factor have been determined using the non-linear least square fit method. Effect of O-, M-, and P- substitution of CH3 group in xylene causes variation in static dielectric constant values and spectacle deviation in relaxation time with respect to temperature. The temperature dependent dielectric relaxation gives expected Arrhenius behavior.

Dielectric Dispersion Response of Binary Mixtures of n-Butanol and Valeronitrile

Complex permittivity spectra of various concentrations (0.0 → 1.0) of n-Butanol and its mixtures with Valeronitrile were obtained in the radio and microwave frequency range (0.2 GHz to 20 GHz) using Vector network analyzer (VNA). Complex permittivity data points were fitted into Havriliak-Negami Model. CNLS fitting using LEVMW software used to obtain dielectric parameters. Excess static dielectric constant and excess inverse relaxation time for the binary mixtures were calculated and fitted in Redlich-Kister polynomial to derive the binary coefficients and standard deviations. Variation of these parameters were discussed in terms molecular interaction between molecular species.

Broadband dielectric relaxation spectroscopy and molecular dynamics simulation study of paracetamol-propylene glycol solutions

The complex permittivity ε*(ω) = ε′(ω) - ε“(ω) was studied for a series of paracetamol (PCM) – propylene glycol (PG) solutions over the broadband frequency range of 20 Hz to 20 GHz at different temperatures ranging from 293.15 K to 323.15 K. Measurements of the complex permittivity were carried out using Agilent Precision LCR meter E4980A with Agilent 16452A liquid test fixture (for 20 Hz to 2 MHz frequency region) and Anritsu Shockline Vector Network Analyser MS46322A with DAK-3.5 probe (for 200 MHz to 20 GHz frequency region). Obtained broadband frequency dependent dielectric data were analyzed to explore the interaction mechanisms and structural behavior of PCM and PG molecules in mixed state in terms of molar PCM concentration and temperature variation. Temperature dependent dc conductivity response of all solutions exhibited Arrhenius behavior from which activation energy was calculated. Microwave complex permittivity data were fitted to the Cole-Davidson model in order to determine dipolar relaxation parameters of the solutions. Dielectric constant and dielectric loss values at a spot frequency of 2.45 GHz were utilized to determine the microwave heating parameters and analyzed in view of its suitability for the microwave dielectric heating in pharmaceuticals. Molecular dynamics simulation study for selected concentrations of PCM in PG was also conducted in order to understand the actual mechanism of H-bonding interactions in the solutions and to justify the inferences derived from the experimental results.

Microwave shielding and absorbing properties of single- and multilayered structures based on two-phase filler/epoxy composites

The microwave absorbing and shielding properties of epoxy composites with multiphase filler were studied in a wide frequency range of electromagnetic radiation (EMR) (1–67) GHz. The multiphase filler consists of carbon nanotubes (CNTs) and dielectric (titanium dioxide TiO2) or ferromagnetic (carbonyl iron Fe) particles. The content of TiO2 or Fe was fixed and equal to 35 wt% and 30 wt%, respectively, while the CNT content was varied from 1 to 5 wt%. It was found that EMR shielding efficiency SET is sufficiently increased with carbon nanotubes content and thickness of the composite especially for epoxy CMs filled with carbon nanotubes and carbonyl iron. The measured complex permittivity data (and permeability for CNT/Fe/epoxy CMs) were used for simulation of the reflection loss RL for studied composites. The simulated data have shown that more pronounced reflection loss $$\left| {\text{RL}_{\min } } \right|$$ = (30–44) dB is observed for 2–3 wt% CNT content in ternary epoxy CMs (sample thickness is 0.5–0.7 mm). For the higher CNT content (4–5 wt%), especially for CNT/Fe/epoxy CMs, the reflection loss $$\left| {\text{RL}_{\min } } \right|$$ was decreased, i.e., the large contribution in EMR attenuation is provided due to EMR reflection on the first air-composite boundary. It was shown that effective bandwidth of $$\left| {\text{RL}_{\min } } \right|$$ at level 10 dB can achieve (8–12) GHz and its position and $$\left| {\text{RL}_{\min } } \right|$$ value can be manipulated by varying the composition and thickness of the composite sample. The absorbing performance of 4-layered composite structures was modeled using electromagnetic parameters of single-layer absorbers based on the three-phase composites and optimal layers composition and thickness were found.

Additive Manufacturing of PLA-Based Microwave Circuit-Analog Absorbers

Fused filament fabrication (FFF) was used to additively manufacture (3-D print) two-prototype circuit-analog (CA) absorbers. The CA absorbers consist of a lossy frequency selective surface (FSS), substrate, and ground plane. In this article, the FSS and substrate were manufactured using two different FFF materials to make a cohesive structure manufactured during a single printing procedure. To design the CA absorbers, the complex permittivity of FFF printed polylactic acid (PLA), bronze-, brass-, copper-, and iron-powder infused PLAs, and a graphite-PLA composite was measured using a free-space materials measurement system. Out of the candidate materials measured, graphite PLA and standalone PLA were selected as the FSSs and substrates, respectively. Complex permittivity data from the selected materials were input to Computer Simulation Technology Microwave Studio so that a genetic algorithm could optimize absorber dimensions. Reflectivity of the printed absorbers was measured using a free-space measurement setup. Measured reflectivity data were compared to that from simulations. A simulated-geometric tolerance study corroborated differences noted between ideal models and measured data. The results showed that FFF techniques can be used for CA-absorber designs and that 3-D printing settings can ultimately affect absorber performance.

Dielectric relaxation and co-operative dynamics of propylene glycol – Ethanol mixtures using time domain spectroscopy

The dielectric measurement of propylene glycol (PG) – ethanol (ETH) mixtures over whole composition range have been carried out using time domain technique in the frequency range of 10 MHz to 50 GHz. The measurements were carried out at temperatures 25 °C, 15 °C and 5 °C. Dielectric parameters were evaluated by fitting the complex permittivity data in Cole-Davidson model using non linear least square method. Dielectric relaxations and co-operative dynamics of PG-ETH molecules in pure and their mixtures were discussed using Kirkwood correlation factor (geff), excess permittivity (ε0E), thermodynamic parameter.

Molecular interaction in binary mixtures of 3-Bromoanisole and methanol: A microwave dielectric relaxation spectroscopy and molecular dynamic simulation study

Complex permittivity spectra for the binary mixtures of 3-bromoanisole (3-BA) and methanol (MeOH) with varying concentrations at different temperatures (T = 293.15 to 323.15 K) were obtained over a broad microwave frequency range. The complex permittivity data were fitted to different dielectric relaxation models using complex nonlinear least square fitting method. From the best fitting model dielectric relaxation parameters were extracted. Concentration dependence of the dielectric relaxation parameters were used to gain information about the molecular interaction among the constituent of the mixtures. The formation and deformation of H-bonds among the molecules of the mixture are discussed using wait-and-switch model. Temperature and concentration dependent static permittivity provided information about the alignment and cross-linkage of molecules in liquid mixtures. Molecular dynamics (MD) simulations of mixtures of 3-BA and MeOH at 293.15 K temperature have also been conducted to gain additive information regarding molecular interaction and to justify the inferences derived from the experimental microwave complex permittivity data.

Control of electromagnetic wave absorption properties in La-Co-Ti substituted M-type hexaferrite–epoxy composites

La-Co-Ti substituted Sr-hexaferrite, Sr0.906La0.094Fe11-2xCoxTixO19 (x = 0.8, 1.0, 1.2, 1.4) powder-epoxy (10 wt%) composites were fabricated for electromagnetic wave (EM) absorption application. Single M-type hexaferrite phase was confirmed by X-ray diffraction analysis for all the samples. Both saturation magnetization and coercivity of the composites decrease with increase of Co-Ti substitution x. Reflection loss (RL) of the hexaferrite powder–epoxy composites were calculated using their complex permittivity and permeability data. The EM absorbing frequency range is controlled by the substitution x because the ferromagnetic resonance (FMR) frequency of the samples is systematically varied following Snoek’s limit law. The hexaferrite sample with x = 1.2 is suitable for use as an X-band (8–12 GHz) radar absorber since RL < -10 dB is satisfied in the full X-band. Also, high EM absorbing performances in millimeter range, RL < -20 dB at 24 GHz (3 mm), and RL < -20 dB at 26.5 GHz (0.9 mm), could be achieved in the FMR-controlled La-Co-Ti substituted M-type hexaferrite-epoxy composite.

Dielectric and Radar-Absorbing Properties of Exfoliated Graphite Dispersed Epoxy Composites

Electromagnetic absorbers based on carbonaceous materials, i.e., carbon black, polyaniline, polypyrrole, carbon fiber, etc., are prominently employed to attenuate incident electromagnetic waves. In the current work, exfoliated graphite (EG) was synthesized with swollen expanded volume from graphite flake by using a simple and inexpensive method. After synthesis, a series (8.9, 22.9, 33.3, 41.4 and 44.7 volume percentage) of EG–epoxy composites were prepared using a wet mixing method. EG and the prepared composites were characterized by x-ray diffraction analysis, field-emission scanning electron microscopy, and energy-dispersive x-ray analysis. An Agilent vector network analyzer (model PNA E8364B) was employed to compute the complex permittivity (er = e′ − je″) of the prepared composites in the frequency range of 2 GHz to 18 GHz. The dielectric loss of the prepared EG–epoxy composites was quantified in terms of the loss tangent (tanδe = e″/e′). Their radar absorption properties were evaluated in terms of the return loss (RL), which in turn was calculated for varying thicknesses of the prepared composites using the computed complex permittivity data. The measured minimum RL was −26.4 dB for the absorber with thickness of 4.0 mm, and the bandwidth achieved was 5.2 GHz for RL ≤ − 10 dB in the effective frequency region of 8 GHz to 14 GHz. The matching frequency shifted towards downwards with increasing EG content in the epoxy thermosetting matrix according to both the calculated and measured data. Consequently, the prepared composites exhibited good complex permittivity, dielectric tangent loss, and microwave absorption and could be utilized in the design of electromagnetic interference shielding and absorbers for stealth applications.

Dielectric spectroscopic study of solutions of amino silicone oil in the polar solvent mixtures of methyl ethyl ketone and methyl iso butyl ketone

The complex permittivity, complex modulus, alternating current electrical conductivity and complex impedance of the ternary mixtures of amino silicone oil in methyl ethyl ketone and methyl iso butyl ketone have been investigated at 303.15 K temperature over the frequency regime 200 Hz to 2 MHz. Complex permittivity and complex impedance data have been fitted to the Coelho model and Nyquist plot respectively. The Coelho model of complex permittivity data provides the electrode polarization relaxation time related to electric double layer relaxation processes. Nyquist plot of complex impedance data exhibits Debye type dispersion corresponding to conduction relaxation processes and electric double layer relaxation processes. Electrode polarization relaxation time (τEP), relaxation time (τEP′), ionic conductivity relaxation time (τσ), geometric relaxation time (τg) and double layer relaxation time (τdl) have been calculated using the different formalism. Static permittivity (ε0), DC conductivity (σdc) and refractive index (nD) have also been determined for all the ternary mixtures. Solvent effect interaction in amino silicone oil with methyl ethyl ketone, methyl iso butyl ketone and with their mixtures is also discussed in the paper. Systematic variation is observed in all the parameters with change in concentration of amino silicone oil in methyl ethyl ketone and methyl iso butyl ketone.

Temperature Sensibility of Complex Permittivity in Ni–Zn Ferrite at Different Temperatures in the 700 MHz–1 GHz Range

This paper presents a study on the behavior of complex permeability and permittivity of a Ni-Zn ferrite, at temperatures between -40 °C and 50 °C, in frequencies from 1 MHz to 3 GHz. Complex permeability and permittivity data are presented for this frequency range. We observed that the real part of permittivity (e' ) has low-temperature sensibility from 700 MHz up to 1 GHz, caused by the overlapping of two different relaxation processes, and the definition of a thermal coefficient of e' corroborated these results. Outside this frequency range, temperature variations have a greater influence in permittivity. Havriliak-Negami functions were used to describe e behavior for each measured temperature. The measurements of the real and imaginary parts of magnetic permeability μ' and μ'' showed that they decrease with frequency, which is the typical behavior for this ferrite, and that lower temperatures have higher values for both μ' and μ'' after 50 MHz.

Microwaves absorbing characteristics of metal ferrite/multiwall carbon nanotubes nanocomposites in X-band

Abstract The ferrite nanoparticles and ferrite/multiwall carbon nanotubes (Cu0.25Ni0.25Zn0.5Fe2O4/MWCNTs) nanocomposites with different concentrations of MWCNTs as filler are synthesized using co-precipitation and solution-mixing techniques. In brief, the MWCNTs were first purified for their quick dispersion and then acid functionalized to introduce carboxylic groups for effectively attaching ferrite nanoparticles and epoxy. These nanocomposites were examined for permittivity and permeability which revealed a strong dependency on filler concentration. In addition, we explored the microwave absorbing behavior of nanocomposites using network analyzer from 8.2 to 12.2 GHz frequency range. The reflection loss (RL) was calculated from complex permittivity and permeability data and maximum RL of −37.7 dB at 10.2 GHz with a sample thickness of 2.5 mm and bandwidth of 0.53 dB. The excellent microwave absorption with wide bandwidth is attributed to interfacial electric polarization, electromagnetic impedance matching, and multiple scattering network structure of Cu0.25Ni0.25Zn0.5Fe2O4/MWCNTs nanocomposites. This work indicates that the Cu0.25Ni0.25Zn0.5Fe2O4/0.16%-MWCNTs could be a promising microwave absorption material for application in X-band.

A large-scale measurement of dielectric properties of normal and malignant colorectal tissues obtained from cancer surgeries at Larmor frequencies.

Knowledge of dielectric properties of malignant human tissues is necessary for the recently developed magnetic resonance (MR) technique called MR electrical property tomography. This technique may be used in early tumor detection based on the obvious differentiation of the dielectric properties between normal and malignant tissues. However, the dielectric properties of malignant human tissues in the scale of the Larmor frequencies are not completely available in the literature. In this study, the authors focused only on the dielectric properties of colorectal tumor tissue. The dielectric properties of 504 colorectal malignant samples excised from 85 patients in the scale of the Larmor frequencies were measured using the precision open-ended coaxial probe method. The obtained complex-permittivity data were fitted to the single-pole Cole-Cole model. The median permittivity and conductivity for the malignant tissue sample were 79.3 and 0.881 S/m at 128 MHz, which were 14.6% and 17.0% higher, respectively, than those of normal tissue samples. Significant differences between normal and malignant tissues were found for the dielectric properties (p < 0.05). Experimental results indicated that the dielectric properties were significantly different between normal and malignant tissues for colorectal tissue. This large-scale clinical measurement provides more subtle base data to validate the technique of MR electrical property tomography.

A study of the nanocomposite sandwich structures for broadband microwave absorption and flexural strength

Composite sandwich structures are devised to work in a wide frequency of the microwave band. The microwave absorbing properties of composite sandwich structures are studied in 2–18 GHz frequency band. The sandwich structures were manufactured from E-glass fiber/epoxy composites filled with carbon nano-materials and para-aramid honeycomb cores. The complex permittivity of E-glass/epoxy nanocomposites and adhesive films are determined in 8–12 GHz frequency range using free-space measurement setup. The complex permittivity data were used to design the sandwich structures by varying composition and thickness of nanocomposite sheets using a simulation tool Computer Simulation Technology Microwave Studio. In the designing process, the thickness of honeycomb sheets was also varied to get best spacer thickness for the cancellation of reflected and transmitted microwaves. The simulated and measured results have shown that the designed structure can be used for −10 dB Reflection coefficient over a wide frequency ranges in the microwave region. The results of flexural strength of the sandwich structure and tensile strength of facing sheets are also presented.

A new method for the precise multiband microwave dielectric measurement using stepped impedance stub

This article presents a new method of wideband dielectric measurement at microwave frequencies. This method can be used to determine the complex dielectric properties of solid and semisolid materials from 0.9 GHz to 4.5 GHz, including the ISM bands of 915 MHz and 2450 MHz. The new method is based on the scattering parameter measurement of a stepped impedance open circuited micro-strip stub, partly loaded with dielectric test material. Current microwave wideband spectroscopy techniques generally measure dielectric materials over a wide range of frequencies but their accuracy is limited. In contrast, narrowband techniques generally measure dielectric properties to a high accuracy but only at a single frequency. This new technique is capable of measuring dielectric properties over a wide range of frequencies to a high accuracy. The technique has been verified by the empirical characterisation of the dielectric properties of Teflon and Duroid 5880 materials. Empirical results were in good agreement with values in the manufacturer’s Data Sheets. The complex permittivity data will be useful for further microwave processing of the materials.

Dielectric relaxation studies of binary mixture of β-picoline and methanol using time domain reflectometry at different temperatures

Complex permittivity spectra of binary mixtures of varying concentrations of [Formula: see text]-picoline and Methanol (MeOH) have been obtained using time domain reflectometry (TDR) technique over frequency range 10 MHz to 25 GHz at 283.15, 288.15, 293.15 and 298.15 K temperatures. The dielectric relaxation parameters namely static permittivity ([Formula: see text]), high frequency limit permittivity ([Formula: see text]) and the relaxation time ([Formula: see text]) were determined by fitting complex permittivity data to the single Debye/Cole-Davidson model. Complex nonlinear least square (CNLS) fitting procedure was carried out using LEVMW software. The excess permittivity ([Formula: see text]) and the excess inverse relaxation time (1/[Formula: see text] which contain information regarding molecular structure and interaction between polar–polar liquids were also determined. From the experimental data, parameters such as effective Kirkwood correlation factor (geff), Bruggeman factor (fB) and some thermo dynamical parameters have been calculated. Excess parameters were fitted to the Redlich–Kister polynomial equation. The values of static permittivity and relaxation time increase nonlinearly with increase in the mol–fraction of MeOH at all temperatures. The values of excess static permittivity ([Formula: see text]E) and the excess inverse relaxation time (1/[Formula: see text] are negative for the studied [Formula: see text]-picoline — MeOH system at all temperatures.