Search Results (638)

In the present research, the structure and thermal–dielectric behavior of Styrene Butadiene Rubber (SBR) and of the SBR/EPDMd composite with SiO₂ with different compositions and concentrations of EPDMd are analyzed. In this sense, interesting behaviors are observed for the DC-AC regime of the conductive behavior of the material; therefore, a very marked DC and AC regime is observed in the conductivities, showing a different dielectric behavior at low and high frequencies. On the other hand, peak relaxations due to polarization phenomena are observed in terms of the imaginary modulus. Conductively, SiO₂ does not produce significant or relevant changes, but it does produce changes in the permittivity and the electrical modulus, so it is concluded that the impact of the incorporation of SiO₂ in these compounds affects energy storage (permittivity and modulus) in these types of compounds. Compared with compounds without silica (insights—no SiO₂), it is observed that SiO₂ maintains a similar operating regime to the initial one (SBR and SBR + EPDMd + SiO₂) without SiO₂ dielectric changes occurring, so silica presence modifies the dielectric behavior, reducing polarization effects, as can be seen in the dielectric results. Conductively, SiO₂ produces more insulating compounds, that is, less conductive; this property can make it interesting as electrical insulation. Full article

Non-invasive glucose monitoring remains a significant challenge in diabetes management, with existing approaches often limited by poor accuracy, high cost, or patient discomfort. Microwave-based biosensors offer a promising label-free alternative by exploiting the dielectric contrast between glucose and water. This paper presents a compact, dual-band concentric square-shaped split-ring resonator (SRR-type) biosensor fabricated on a low-cost FR-4 substrate for aqueous glucose detection. The sensor leverages electric field confinement in inter-ring gaps to transduce glucose-induced permittivity changes into measurable shifts in resonance frequency and reflection coefficient. Experimental results demonstrate a linear, monotonic response across the clinical range up to 250 mg/dL, with a frequency-domain sensitivity of 1.964 MHz/(mg/dL) and amplitude-domain sensitivity of 0.0332 dB/(mg/dL), achieving high coefficients of determination (R² = 0.9956 and 0.9927, respectively). The design achieves a normalized size of 0.137 λ_g², combining high sensitivity and compact size within a scalable platform. Operating in the UWB-adjacent band (2.76–3.25 GHz), the proposed biosensor provides a practical, reproducible, and PCB-compatible solution for next-generation label-free glucose monitoring. Full article

The potential of graphene for electric field sensing is limited by its zero bandgap. This study employs a combined first-principles and experimental approach to enhance its response via heterojunctions with ZnO, SnO₂, and Al₂O₃. Calculations reveal spontaneous formation and interfacial charge transfer in all systems, with SnO₂/graphene exhibiting the most significant charge transfer (0.3636 e) and inducing a finite bandgap (0.017–0.064 eV). Experimentally, SnO₂-graphene/PDMS composites demonstrated the highest relative permittivity (3.19) and a 7.76% increase in normalized induced voltage over pure PDMS within 50 Hz–50 kHz. This work establishes a direct correlation between interfacial charge transfer, bandgap opening, and macroscopic dielectric enhancement, identifying SnO₂/graphene as the optimal heterojunction. The integrated multi-scale methodology provides a clear design principle for high-performance, graphene-based field-sensitive materials. Full article

This work investigated the electrical, dielectric, and magnetic properties of ferrofluids containing Fe₃O₄ nanoparticles and their composites with chitosan (30–100 cP and 100–300 cP), relevant to magnetic hyperthermia. The nanoparticles were synthesized by coprecipitation and characterized using impedance spectroscopy, X-ray diffraction, scanning microscopy with X-ray microanalysis, Mössbauer spectroscopy, and calorimetry. The study showed that the chitosan coating altered the textural properties of Fe₃O₄, reducing the specific surface area from 76.3 m²/g to 68.9–72.5 m²/g. The zeta potential and particle size showed strong pH dependence. Impedance measurements showed that the conductivity of ferrofluids was frequency- and temperature-dependent, with both metallic and dielectric conductivity observed. The complex dielectric permittivity exhibited Maxwell–Wagner–Sillars interface polarization. Calorimetry revealed that specific absorption rate (SAR) ranged from 11.4 to 23.4 W/g, depending on the chitosan concentration and type, while the chitosan coating reduced SAR by 12–40%. These results confirm that the electrical and dielectric parameters of ferrofluids significantly influence their thermal capabilities, which is important for optimizing magnetic hyperthermia therapy when energy dissipation is considered in bio-heat models. Full article

Electrically induced bearing failure is a reoccurring problem in modern drive train designs. To predict this damage, electrical models of bearings are required. In these models, the permittivity of lubricants is often assumed to be constant. However, the permittivity is dependent on pressure and temperature. For operating temperatures and pressures of journal bearings, no investigation of the permittivity of the lubricant exists. For this purpose, this study investigates the pressure and temperature dependence of lubricant permittivity using specially fabricated model bodies with layered structures of steel, ceramic insulating layers and copper in a parallel plate capacitor setup. Tests were performed applying temperatures between 20 °C and 100 °C and pressures between 1 and 250 bar. A mineral oil and a polyalkylene glycol (PAG) oil were examined. Results show a clear dependence of the permittivity on pressure and temperature. The mineral oil exhibits stronger pressure sensitivity, while the PAG oil shows more pronounced temperature dependence. Empirical equations to describe the permittivity as a function of temperature and pressure are derived. These findings provide relevant input for the selection of lubricants used in electrical environments. They also support the development of predictive models for modern electrical and tribological systems. Full article

The paper presents measurements of frequency dependence of conductivity and real components of complex permittivity of a nanocomposite consisting of electrical pressboard, bio-insulating oil and water nanodroplets with moisture content ranging from 0.6 wt.% to 5 wt.%. Bio-oil meets high environmental requirements—it is fully biodegradable, and its combustion products are significantly less harmful than those of mineral oil. In addition, the use of bio-oil reduces the carbon footprint of power transformer production. The quantum mechanical phenomenon of electron tunnelling between potential wells created by water nanodroplets was used to analyze the experimental results obtained. The study determined the effect of moisture content on the relative relaxation time values. On this basis, the number of water molecules in nanodroplets, their diameters and the concentration of nanodroplets depending on moisture content were determined. The distances over which electrons tunnel in moist pressboard impregnated with bio-oil were determined. These values are the expected values of the probability distribution of the distance between neighbouring nanodroplets. The values of the number of water molecules in nanodroplets are also the expected values of the probability distribution of the number of molecules in nanodroplets. It has been established that during many years of transformer life, several parallel processes occur as the moisture content in bio-oil-impregnated pressboard increases. One of them involves the accumulation of water molecules collected in the pressboard in nanodroplets. The second is an increase in the concentration of nanodroplets. The third is an increase in the average number of water molecules in nanodroplets. Full article

This work presents the results of a theoretical investigation of the electronic and optical properties of van der Waals Janus nanoheterostructures MoS₂/SeMoS and MoSe₂/SMoSe, carried out within the framework of density functional theory (DFT) using the generalized gradient approximation (GGA-PBE) together with the Grimme-D3 dispersion correction. The calculated band structures show that both heterostructures possess an indirect bandgap whose magnitude is highly sensitive to an external electric field. In the MoS₂–SeMoS system, increasing the applied field leads to a gradual narrowing of the bandgap and a transition to a metallic state at approximately 75 V, whereas in MoSe₂–SMoSe, the bandgap first increases (up to 20 V) and then decreases, indicating a nonlinear field-dependent behavior. Analysis of the dielectric function reveals an enhancement of the static dielectric permittivity and a red shift in the absorption spectra with increasing field strength, which can be attributed to charge redistribution and an increased contribution from ionic polarizability. These results demonstrate the possibility of effectively controlling the bandgap width, polarizability, and optical response of Janus nanoheterostructures using an external electric field. This opens up promising prospects for their application in tunable photodetectors, light modulators, valleytronic components, and next-generation optoelectronic systems. Full article

Electrostriction is an intriguing behaviour of dielectric materials, characterized by stable electrostrain with minimal hysteresis. (Na_0.5Bi_0.5)TiO₃-based ceramics show promising electrostrictive behaviour, particularly the 0.90(Na_0.5Bi_0.5)TiO₃-0.08KNbO₃-0.02SrTiO₃ composition located near the morphotropic phase boundary between ferroelectric rhombohedral and relaxor pseudocubic phases. The templated grain growth method has been effectively used to control the grain orientation of NBT-based systems, thereby enhancing their electrical properties. In this study, texturing was introduced to 0.90(Na_0.5Bi_0.5)TiO₃-0.08KNbO₃-0.02SrTiO₃ ceramics through homoepitaxial NBT platelets prepared via a three-step molten salt/topochemical microcrystal conversion method. By adding 4 wt% of NBT platelets combined with optimized sintering conditions, textured ceramics were prepared exhibiting a high Lotgering factor of 83% with enhancement of strain (0.02%) and polarization (3 µC/cm²) at an electric field of 40 kV/cm, as well as stable dielectric permittivity between 130 and 300 °C. Moreover, the electrostrictive coefficient of textured ceramics increased by ~0.004 C²m⁻⁴ compared to that of untextured ceramics, confirming the improvement of the electrostrictive response. These results demonstrate that homoepitaxial templating effectively improves the electrical properties of NBT-KN-ST ceramics while preserving their electrostrictive nature, which offers a viable route for designing lead-free electrostrictive materials. Full article

We determined the reference characteristics of the loss tangent and the real component of the complex permittivity of the cellulose-insulating oil–water nanodroplet nanocomposite with a moisture content of 5.17% by weight in pressboard. Such a high moisture content was selected because a value close to 5% by weight is critical, and reaching it may lead to catastrophic transformer failure as well as contamination of the natural environment with poorly biodegradable mineral oil and products of its incomplete combustion. Based on the measurement results, the values of the loss tangent and the real and imaginary components of the complex permittivity of the power transformer insulation system, consisting of moistened pressboard and insulating oil, were determined according to CIGRE. These values were obtained for both factory-new and moistened mineral oil. It was found that oil moisture content has a significant impact on the tanδ characteristics of strongly moistened liquid–solid insulation in the lowest frequency range. In the intermediate frequency range, this effect gradually decreases and then practically disappears. In the frequency range above 50 Hz, the tanδ values depend on the moisture content in cellulose and on the geometrical parameters of the insulation components in the CIGRE system, and do not depend on the oil moisture content. The influence of oil moisture on the estimation of cellulose moisture content becomes noticeable starting from a water content of 2% in pressboard. This should be taken into account in insulation condition analysis and in moisture level estimation in order to detect a critical state threatening catastrophic failure of a power transformer. It was also determined that the real component of the complex permittivity depends only weakly on oil moisture, and only in the low-temperature and low-frequency ranges. In contrast, the imaginary component of the complex permittivity depends on oil moisture practically in the same way as the loss tangent of the power transformer insulation system. Full article

The phase-pure cubic pyrochlore of the Bi₂Cr_0.5Co_0.5Nb₂O_9+Δ composition can be successfully synthesized by a modified sol–gel method (Pecini method-PM) and a traditional solid-phase method (SPM). A feature of the solid-phase synthesis method is the formation of bismuth(VI) chromates as intermediate synthesis products, which is confirmed by X-ray spectroscopy data (NEXAFS). During the sol–gel synthesis method, bismuth chromates are not formed due to the formation of the Bi₂₈O₃₂(SO₄)₁₀ salt, which is thermally stable up to 880 °C, preventing the interaction of bismuth(III) and chromium(III) oxides. The temperature of the final pyrochlore calcination during sol–gel synthesis is reduced by 100 °C (950 °C) compared to the solid-phase method. The crystal structure of pyrochlore (sp. gr. Fd-3m, PM, a = 10.49360(5) Å, Z = 4) was refined by the Rietveld method based on X-ray powder diffraction (XRD) data. NEXAFS Cr2p and Co2p spectra of ceramics synthesized at 1050 °C correspond to the charge states of Cr(III), Co(II) and Co(III) ions. The thermal expansion coefficient of the cell was calculated from high-temperature X-ray diffraction measurements in the range of 20–1200 °C. The thermal expansion coefficient (TEC) monotonically increases from 3.92 × 10⁻⁶ °C⁻¹ (20 °C) to 9.89 × 10⁻⁶ °C⁻¹ (1020 °C). Above 1110 °C, TEC decreases due to thermal dissociation of Bi₂Cr_0.5Co_0.5Nb₂O_9+Δ with the formation of CoNb₂O₆, Bi₂O₃. The mixed pyrochlore (PM) exhibits a moderately high permittivity of ∼97, and low dielectric losses of ∼2 × 10⁻³ at 1 MHz and ∼30 °C. The activation energy of conductivity of the high-temperature region is 0.89 eV. The electrical properties of pyrochlore were synthesized by the ceramic (SPM) and Pechini methods (PM) were analyzed. The electrical properties of the samples up to 400 °C were modeled using equivalent electrical circuits Full article

This study investigated the effect of nanofiller on the structural properties of thermally aged polyvinyl chloride (PVC)/Aluminum oxide (Al₂O₃) nanocomposites prepared with different amounts of nanoparticles (2.5, 5.0, and 7.5 wt%) using various techniques. Experimental studies were designed to monitor structural changes in PVC/Al₂O₃ nanocomposites by means of dielectric characterization, charging and discharging currents measurements, SEM and FTIR analyses, and visual observations as a function of nanofiller amount and aging time. The results obtained demonstrated that the dielectric permittivity of PVC was increased for unaged samples with the addition of 2.5% and 7.5% Al₂O₃ nanoparticles. An increase in dielectric losses is also observed at the same level of filler content, attributable to interfacial polarization driven by improved charge transport and dipole relaxation. A decrease in charging and discharging currents with higher Al₂O₃ content is attributed to an increase in matrix rigidity, which restricts charge carrier mobility. The charging and discharging currents progressively increased during thermal aging, as polar aging products were formed during this process, which could improve charge mobility and conductivity. FTIR and SEM analyses indicated that with thermal aging, polar groups formation was more likely due to structural decomposition of the matrix and mild dehydrochlorination. The changes in color were indicative of surface degradation. These results provide new insight into the electrical and aging behaviors in PVC/Al₂O₃ nanocomposites. Full article

This paper presents a dual-polarized millimeter-wave filtering antenna based on a broadband partially reflective surface lens for gain improvement. It consists of a magneto-electric dipole (M-E dipole) as the source and a partially reflective surface (PRS) as the lens. The M-E dipole source antenna employs a dual-layer substrate structure, and its working principle is investigated by the circuit analysis method. A stub-loaded transmission line network is used to study the radiation characteristics of the source antenna, and the simulation results reveal that it has intrinsic integrated bandpass-type filtering response. The PRS lens is realized by designing a square high permittivity superstrate. By combining the source antenna and the lens, a wideband dual-polarized high gain cavity antenna is developed. The fabricated prototype has a measured impedance bandwidth of 33.3% (25–35 GHz), and a maximum in-band gain of 12.3 dBi. Above features make the proposed antenna a good candidate for 5G millimeter-wave sensor applications. Full article

Titanium dioxide is attractive for energy storage due to its abundance, stability, non-toxicity, low cost, and favorable electronic/optical properties. Colossal permittivity (CP) in co-doped TiO₂ is mainly linked to defect structures rather than intrinsic bulk behavior. This work studies the dielectric properties of TiO₂ co-doped with niobium and magnesium, synthesized by solid-state reaction. Grain size effects were examined by varying ball milling parameters of (½Mg½Nb)_0.05Ti_0.95O₂ and then were correlated with structure, morphology, and dielectric response. X-ray diffraction (XRD), infrared spectroscopy (FTIR), scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and impedance spectroscopy (IS) (40 Hz–10⁶ Hz, 150–370 K) were employed for structural, morphological, and electrical characterization. XRD confirmed the rutile phase. For co-doped samples, larger grains yielded higher dielectric constants, reaching high permittivity (ε′ = 429, T = 300 K, f = 10 kHz at 500 rpm for 2 h). Lower loss tangent (tan δ = 0.11, T = 300 K, f = 10 kHz at 200 rpm for 2 h) is linked to Mg segregation at grain boundaries. The most conductive sample showed the highest dielectric constant, suggesting an IBLC polarization mechanism driven by grain boundary effects. XPS confirmed Nb and Mg incorporation, with Ti⁴⁺ dominant and minor Ti³⁺ from oxygen vacancies and surface hydroxylation/defects. Full article

The results of the effect of the three Ba:Ti molar ratios (MR) (1:1, 2:1, 4:1) and four sintering temperatures (1250, 1275, 1300, 1325 °C) on the structural and electrical properties of BaTiO₃ (BT)-type ceramics synthesized by the hydrothermal method are shown. The BT phase formed was analyzed by x-ray diffraction (XRD), Raman spectroscopy (RS), dielectric and ferroelectric measurements and high-resolution scanning electron microscopy (HRSEM). For the samples synthesized using a Ba:Ti MR of 4:1 and at all sintering temperatures analyzed, XRD results confirmed the presence of the tetragonal ferroelectric phase, BT. In the same way, these results corroborated the results obtained by the RS technique. Dielectric properties measured at 100 kHz and 1 MHz over a temperature range of 30 °C–200 °C indicated a relative permittivity value of 4280 at 1 MHz and 4200 at 100 KHz at a Curie temperature of 110 °C in both cases for the sample synthesized at with a Ba:Ti MR ratio of 4:1 and sintered at 1300 °C. Ferroelectric measurements for the samples showed a best remnant polarization (Pr) of 3.5 µC/cm² for the sample synthesized with a Ba:Ti MR ratio of 4:1 and sintered at 1325 °C. The HRSEM results showed grains composed of Ba, Ti, and O homogeneously distributed in the BT structure, and a trend of increasing average grain size with increasing sintering temperature was observed. Full article

Dielectric characterization offers valuable insights into fruit structure, ripening, and storage stability. However, systematic studies on apples are still limited. This work elucidates the electrical and physicochemical properties of a specific variety of apples, Malus domestica, using Electrochemical Impedance Spectroscopy (EIS), a non-destructive, fast and cost-effective technique, suitable for real-time quality assessments. The apple samples were analyzed over the frequency range of 20 Hz–120 MHz at 25 °C, and impedance data were modeled using equivalent circuits and dielectric relaxation models. Physicochemical analyses confirmed a high moisture content (84%, wwb), pH 4.81, TSS 14.58 °Brix, and acidity 0.64%, which is typical of fresh Red Delicious apples. Impedance spectra revealed semicircular and Warburg elements in Nyquist plots, indicating resistive, capacitive, and diffusive processes. Equivalent circuit fitting with the proposed R-C-Warburg impedance model outperformed (R² = 0.9946 and RMSE = 6.610) the classical Cole and Double-Shell models. The complex permittivity (ε) represented a frequency-dependent ionic diffusion, space-charge polarization, and dipolar relaxation decay, while electrical modulus analysis highlighted polarization and charge carrier dynamics. The translational hopping of charge carriers was confirmed through AC conductivity following Jonscher’s power law with an exponent of ƞ = 0.627. These findings establish a comprehensive dielectric profile and advanced circuit fitting for biological tissues, highlighting a promising non-invasive approach using EIS for real-time monitoring of fruit quality, with direct applications in post-harvest storage, supply chain management, and non-destructive quality assurance in the food industry. Full article