Dielectric Frequency Research Articles

A software tool for fabricating phantoms mimicking human tissues with designated dielectric properties and frequency.

Dielectric materials play a crucial role in assessing and refining the measurement performance of dielectric properties for specific tasks. The availability ofviable and standardized dielectric materials could greatly enhance medical applications related to dielectric properties. However, obtaining reliable phantoms with designated dielectric properties across a specified frequency range remains challenging. In this study, we propose software to easily determine the components of dielectric materials in the frequency range of 16 MHz to 3 GHz. A total of 184 phantoms were fabricated and measured using open-ended coaxial probe method. The relationship among dielectric properties, frequency, and thecomponents of dielectric materials was fitted through feedforward neural networks. Software was developed to quickly calculate the composition of dielectric materials. We performed validation experiments including blood, muscle, skin, and lung tissue phantoms at 128 MHz, 298 MHz, 915 MHz, and 2.45 GHz. Compared with literature values, the relative errors of dielectric properties are less than 15 %. This study establishes a reliable method for fabricating dielectric materials with designated dielectric properties and frequency through the development of the software. This research holds significant importance in enhancing medical research and applications that rely on tissue simulation using dielectric phantoms.

Dielectric relaxation and electrical conduction mechanism via hopping of polarons in (Pb0.3Bi0.7)(Zn0.1Nb0.2Fe0.7)O3 perovskite compound: A study based on CBH model

This work analyses the dielectric and conducting properties of the PZN-modified BF solid solution (0.3PZN-0.7BF) synthesized at 850 °C by solid-state reaction. The Rietveld refinement of 0.3PZN-0.7BF solid solution displays three phases: tetragonal Pb(Fe0.5Nb0.5)O3 (76.68 %), α-BZN (21 %), and Bi2Fe4O9 (2.32 %). Dielectric parameter frequency dispersion implies normal ferroelectricity. Thermal relaxation shifts dielectric loss, imaginary impedance (Z''), and loss modulus (M'') peaks to higher frequencies. Electrical investigation indicates electrode polarization, dipole orientation, charge ordering, oxygen vacancies, and defects. Investigations suggest p-type polarons dominate conductivity. At room temperature and 1 MHz, the compound has 117 dielectric constant and 0.009 tangent loss. Conductivity and impedance testing show semi-conductivity. UV–Vis spectrum investigation shows a 1.97 eV energy band gap, supporting its semiconductor properties. Photovoltaic and optoelectronic device applications benefit from 0.3PZN-0.7BF solid solution optical and electrical property studies.

Mercury-probe measurement of electron mobility in β-Ga2O3 using junction moderated dielectric relaxation

We demonstrate the junction-moderated dielectric relaxation method to measure the in-plane electron mobility in β-Ga2O3 epitaxial layers. Unlike the Hall technique and channel mobility measurement in field-effect transistors, this method does not require the deposition of permanent metal contacts. Rather, it measures the bias voltage and frequency dependence of the equivalent capacitance of the Mercury/β-Ga2O3/Mercury structure consisting of a Schottky contact, a quasi-neutral thin film semiconductor, and an Ohmic contact connected in series. The intrinsic dielectric relaxation of the bulk β-Ga2O3 semiconductor typically occurs at ∼1012 s−1, but when moderated by the Mercury/β-Ga2O3 Schottky junction, it manifests itself as an inflection in the capacitance-frequency characteristics at a much lower frequency of ∼106 s−1 within the range of most capacitance measuring instruments. Using carrier density and layer thickness determined from capacitance-voltage measurement, we extract the electron mobility of β-Ga2O3 from the junction-moderated dielectric relaxation frequency.

Low-temperature sintering BCZT-Dy ceramics with low strain hysteresis for actuator application

Ba(Cu0.5W0.5)O3 (BCuW)-doped [(Ba0.85Ca0.15)1-xDyx](Zr0.1Ti0.9)O3 (BCZT-xDy, x = 0.001, 0.03) ceramics were prepared by conventional ceramic processing via low-temperature sintering technique. Rather pure perovskite structure and densified morphology with irregular nearly spherical-shape grains are achieved in all ceramics due to liquid-phase sintering. All BCuW-doped BCZT-xDy ceramics present apparent dielectric frequency dispersion and relaxor ferroelectric characteristic due to ion substitution and adding BCuW. The ceramics prepared at optimized sintering temperatures have rather large strain and small strain hysteresis, showing prospect application in piezoelectric high-precision actuators.

A dielectric method for predicting pear firmness combining deep data augmentation and ensemble learning

Firmness is valuable in evaluating pear quality, as it determines ripeness and storability. This research presents a new method that combines deep data augmentation and ensemble learning for predicting firmness in three pear cultivars using dielectric spectra. Firstly, 126 sets of pear dielectric spectra and firmness data were obtained, and the characteristic dielectric frequencies were selected based on the prediction accuracy of partial least squares regression (PLSR) model established using different preprocessing methods. Then the generative adversarial networks (GAN), least squares GAN (LSGAN), and Wasserstein GAN (WGAN) models with different numbers of generated samples in the model's training set on the prediction accuracy of the PLSR model were compared. Finally, the optimal GAN model was combined with support vector regression (SVR), artificial neural networks (ANN), random forest (RF), and AdaBoost decision tree (AdaBoost-DT) to predict pear firmness. Results showed that the selected characteristic dielectric frequencies included two ε′ and eight ε" points. GAN, LSGAN, and WGAN all improved the prediction accuracy of the PLSR model, and the model accuracy improvement of GAN and LSGAN was proportional to the generated sample numbers added to the training set. GAN had the highest accuracy improvement for PLSR model, with the mean Rp2 (determination coefficient of prediction set) and RMSEP (root mean square error of prediction set) increasing up to 13.70% and −19.48% during 100–1000 epochs (added 126 sets of generated data in the GAN-PLSR model' training set), respectively. Ensemble learning models (RF, AdaBoost-DT) outperformed SVR and ANN. GAN-AdaBoost-DT model added 126 sets of generated data in the training set had the highest prediction accuracy, with average Rp2 and RMSEP of 0.90 and 3.35 N during 300–1000 epochs, respectively. This study proved the feasibility of deep data augmentation and ensemble learning methods to improve the prediction accuracy of pear firmness model without increasing the labor and time costs.

Identification of water transitions using a combination of moisture sorption characteristics and dielectric properties of different parts of jasmine rice (Oryza sativa).

In this work, water transition points (first transition: monolayer-multilayer water; and second transition: multilayer-free and solvent water) of different parts of jasmine rice including white rice, brown rice and bran were identified through the integration of sorption isotherm and dielectric properties data. Desorption isotherm data were fitted to four established models to select the optimal model for describing the sorption behaviors. Then, dielectric properties such as dielectric constant (ε') and dielectric loss factor (ε″) were measured across various moisture content levels within the frequency range of 200-20 000 MHz. A type III isotherm was observed for all samples and the Peleg model was the best fit with the experimental data. Monolayer moisture content of the samples, estimated using the GAB model, ranged from 3.25% to 4.17% dry basis. For dielectric properties, frequency and moisture dependencies were evident for all sample types. Moreover, the sorption isotherm models effectively described the relationship between water activity (aw) and dielectric properties as reflected by their goodness of fit, and their strong correlation through principal component analysis and Pearson's correlation results. The first water transition occurs at aw values of 0.11, 0.12, and 0.22, while the second transition appears at aw values of 0.9, 0.9 and 0.75-0.85 for white rice, brown rice and bran, respectively. This knowledge will be useful for food processors, providing insights into the optimization of food processing and storage conditions to extend food products' shelf life. © 2024 Society of Chemical Industry.

Effects of ion doping on the dielectric and electro-optical properties of chiral nematic liquid crystal

This study presents experimental findings pertaining to the use of the cationic surfactant cetyltrimethylammonium bromide (CTAB) as a dopant dispersed in cholesteric liquid crystal. The impact of the additive on the electrical and dielectric properties was investigated by dielectric spectroscopy. Compared with that in the pure counterpart, the dielectric relaxation frequency increased due to the added ions in the cholesteric liquid crystals impregnated with 0.01–0.5-wt% CTAB. Furthermore, by analyzing the dielectric spectra in a specific frequency range, the DC conductivity, ion density, and diffusion coefficient were calculated and compared. By fitting the experimental data into the Arrhenius equation, the activation energy was obtained as well. Our experimental results illustrated that all these physical properties were strongly dependent on the CTAB concentration and the temperature. This work also involved the electro-optical measurement in combination with the observation of optical texture. The ion addition provoked electrohydrodynamic flows in a surfactant-dispersed mixture, generating a homogeneous and transparent uniform lying helix state between two low-transmission optical states—the focal conic and dynamic scattering states. The operating frequency range of the dynamic scattering state was significantly broadened by the ionic dopant.

Effect of hetero-valence ions on structural and electrical properties of La2Ni(Mn0.5Ti0.5)O6 ceramics

The study of powder X-ray diffraction of La2Ni(Mn0.5Ti0.5)O6 (0.5LNMT) confirms a multi-phasic composition. The monoclinic P21/n phase content dominates. Occurrence of minor rhombohedral R3‾c phase and precipitates of MnO2 and La2MnO4 were detected. The morphology was analyzed using a SEM test and ceramics showed a porous structure and variation in the grain size below 4 μm. Dielectric permittivity of marked magnitude varies from ∼30 to ∼100 000 when temperature increases. Dielectric loss coefficient frequency dependence exhibits well-defined dielectric relaxation peaks, which were found to obey the Arrhenius law with the activation energy of 0.29 eV, below the presumed phase transition. Two sets of relaxation peaks in the imaginary part of electric modulus spectra relate to relaxations of different activation energies of 0.28 eV and 0.38 eV. An optical gap magnitude of 0.8 eV was determined from the diffuse reflectance spectrum in the Vis-NIR range. It compares with the band gap estimated from the X-ray photoelectron spectroscopy test. We also compare the influence of doping ions on the crystal lattice of the surface and the bulk ceramics. Electrical conductivity relaxation processes were attributed to the electron hopping mechanism between multi-valence Mnk+ and Nin+ ions’ states, which were determined from XPS analysis. The dc resistivity shows thermally generated dependence. Activation energy Edc magnitude varies between 0.27 and 0.37 eV which indicates the occurrence of defects and structural disorder. Such disorder correlates to the variable range hopping of small polarons involved in electrical conductivity. The density of states near Fermi energy was estimated N(EF) = 2.1 × 1025 eV−1 m−3. The 0.5LNMT application prospects were discussed.

Investigation of Dielectric Properties of Quaternary Ceramic 0.47BNT-0.04BT-0.37PMN-0.18PT

Dielectric dispersion analysis has been carried out for the first time on a new quaternary ceramic [0.47(Bi0.5Na0.5)TiO3-0.04BaTiO3-0.31Pb(Mg1/3Nb2/3)O3-0.18PbTiO3] having a morphotropic phase boundary composition. The measurement of the dielectric parameters has been carried out in the frequency range of 200 Hz to 2 MHz and temperature range from 30 oC to 300 oC. The material showed high dielectric constant, low dielectric loss, negligible DC conductivity and high ferroelectric to paraelectric transition temperature. A clear Debye type relaxation was observed in the dielectric constant and dielectric loss data. An interesting feature of two Debye peaks has been noticed in dielectric loss versus frequency curves in the temperature range 125 oC to 175 oC. These peaks shift towards higher frequencies when temperature is increased. The extracted relaxation times of the two peaks are three orders of magnitude different and have been found to follow the Arrhenius law with significantly different activation energies.

Electrical Properties at Multi-Frequencies for Analysis of Physical and Anatomical Properties of Fast-Growing Standing Teak Trees at Various Ages

Fast-growing teak trees are cultivated extensively in Indonesia to meet the growing demand for teak wood. However, it is necessary to assess the conditions of teak stands throughout their growth period. The nondestructive testing of wood utilizing dielectric spectroscopy approaches based on electrical properties is currently under development, particularly for evaluating tree stands. This study aimed to analyze the dielectric values of fast-growing teak tree stands within a frequency range of 250 kHz to 60 MHz and to understand the relationship between their physical and anatomical properties. A capacitance measurement system was employed to collect dielectric spectroscopy data directly from trees aged 4, 5, and 7 years. Simultaneously, physical and anatomical samples were obtained using a 0.5 cm diameter increment borer. The results revealed significant differences in the fiber length, lumen diameter, and wall thickness at each age. The optimal dielectric frequency for distinguishing wood properties in standing trees was identified to be within a range of 18 MHz to 23 MHz. In the linear model, a moderate relationship was observed with a correlation coefficient of (r)0.403, although the coefficient of determination (r2) was weak at 0.162 for green density. However, a robust relationship was observed in the linear model for specific gravity with r = 0.826 and r2 = 0.682. A weak but significant relationship was also identified with r = 0.2, a coefficient of determination of r2 = 0.04, and a significance level < 0.05 in the predictive model of wood anatomy properties (vessel diameter and fiber wall thickness). Models with low r2 but high significance indicate that the independent variables still noticeably contribute to explaining the dependent variable. Further analysis and data processing can be enhanced by identifying the crucial variables in the capacitance measurement system.

Uniaxially drawn poly (L-lactic acid)/ poly (vinylidene fluoride) polymer blend as a promising piezoelectric material: Hysteresis and resonance spectroscopy study

This study explores the potential for piezoelectricity in a blend of polyvinylidene fluoride (PVDF) and poly-L-lactic acid (PLLA) prepared using the solution casting method. Dielectric frequency measurements across a range of 102 to 106 Hz revealed piezoelectric resonance within a broader dielectric relaxation regime. Analysis of the resonance spectra for length and width vibrational modes enabled the determination of the piezoelectric tensor components of the PVDF/PLLA blend. The blend exhibited enhanced ferroelectric polarization reversal, remnant polarization, and coercive field compared to pristine PVDF samples. The piezoelectric constants d31 and d14 (d36 of the blend) were determined. Mechanical drawing and poling techniques were employed to generate multiple piezoelectric constants, allowing for efficient energy harvesting from various directions. This flexible blend offers promising prospects for versatile energy conversion applications.

Piezoelectric and Pyroelectric Properties of Organic MDABCO-NH4Cl3 Perovskite for Flexible Energy Harvesting

This study describes the synthesis and characterization of the lead-free organic ferroelectric perovskite N-methyl-N’-diazabicyclo [2.2.2]octonium)-ammonium trichloride (MDABCO-NH4Cl3). The electrospinning technique was employed to obtain nanofibers embedded with this perovskite in a PVC polymer for hybrid fiber production. The dielectric, piezoelectric, and pyroelectric properties of these fibers were carefully examined. Based on measurements of the dielectric permittivity temperature and frequency dependence, together with the pyroelectric results, a transition from a high temperature paraelectric to a ferroelectric phase that persisted at room temperature was found to occur at 438 K. The measured pyroelectric coefficient yielded values as high as 290 μC K−1 m−2, which is in between the values reported for MDABCO-NH4I3 and the semiorganic ferroelectric triglycine sulfate (TGS). The hybrid nanofibers exhibited good morphological characteristics and demonstrated very good piezoelectric properties. Specifically, a piezoelectric coefficient of 42 pC/N was obtained when applying a periodical force of 3 N and a piezoelectric voltage coefficient of geff = 0.65 V mN−1. The performance of these fibers is on par with that of materials discussed in the existing literature for the fabrication of nano energy-harvesting generators. Importantly, the perovskite nanocrystals within the fibers are protected from degradation by the surrounding polymer, making them a promising environmentally friendly platform for flexible mechanical energy harvesting.

New insights into early-stage time-dependent dielectric characteristics coupled with frequency dependency and hydration-driven reaction of hydraulic cement pastes: Experiments and statistical modelling

In the field of cement and concrete materials engineering, a comprehensive understanding of dielectric properties is crucial for optimising hydraulic cement paste mix designs. This study examines the relationships among the dielectric constant (ε’), loss tangent (tan δ), frequency, hydration time, water content and admixture dosage in different compositions of hydraulic cement paste. A consistent pattern can be observed across the frequency spectrum, where dielectric constants decrease as frequency increases. This aligns with the expected behaviour of cementitious materials. The most notable finding is the inversely proportional relationship between the loss tangent and frequency. As the frequency increases, the loss tangent consistently decreases, indicating improved energy retention and reduced dissipation. This characteristic is of significant value for various applications, including sustainable infrastructure and smart materials. Furthermore, the interactions among hydration time, water content and admixture dosage present an opportunity for dynamic optimisation within the cement paste matrix. These factors collectively impact dielectric properties, providing insights into the potential for tailored material performance and durability, especially in applications where dielectric properties are critical, such as sensing applications and structural health monitoring of concrete structures. This study emphasises the importance of customising cementitious compositions for specific applications in cement and concrete materials engineering. It achieves this through a detailed comparative analysis of different compositions, each representing varying water content and admixture dosage levels. This approach has the potential to significantly transform the field by enabling engineers to create hydraulic cement pastes with customised dielectric properties that meet the specific requirements of construction, infrastructure and other related applications.

Atomic resolution microstructure study of Bi-doped SrTiO3

Intrinsic SrTiO3 is a quantum paraelectric, but moderately Bi-doped SrTiO3 exhibits dielectric frequency dispersion similar to relaxor ferroelectrics. In this paper, detailed electron microscopic studies of the microstructures of Bi-doped SrTiO3 samples were presented. It was found that the Sr sites were replaced by off-central Bi, resulting in tensile strain in the strontium titanate (STO) lattice. In the Bi-doped SrTiO3 samples, the valence of titanium mainly showed the Ti[Formula: see text] characteristic. According to the dielectric behavior and microstructure analysis, the polar nanoregions (PNRs) composed of strained SrTiO3 nanoclusters should be responsible for the ferroelectric relaxor behavior in samples with moderate Bi content.

Dielectric performance of nanostructured magnesium oxide and effect of cobalt substitution

Here, we examined effect of Co substitution on dielectric characteristics of MgO nanostructures at various doping concentrations with the view to finding its use as a capacitor. The grain and grain boundary have significant impact on the dielectric characteristics' temperature and frequency dependency. Pure and Co doped MgO nanostructures showed dramatic drop in their dielectric constant and dielectric loss with increasing frequency. Reverse micelle micro emulsions of water-cyclohexane-CTAB ternary oil-surfactant-water systems were used to synthesize both pure and Co doped MgO nanostructures. Energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD), dynamic light scattering based particle size analysis (DLS-PSA), photoluminescence (PL), and Raman spectroscopy were used to analyze the synthesized materials. Different frequency and temperature range were studied for the complex permittivity of dielectric characteristics (ε * = ε'-jε") and the loss tangent (tanδ) and based on the experimental data, ε', ε", tanδ decreases as frequency and temperature increase.

Admittance Spectroscopy Study of Defects in β-Ga2O3

We present a comprehensive investigation of electrically active defects and transport properties in commercial (2¯01) edge-defined film-fed growth β-Ga2O3 using admittance spectroscopy measurements from 14 K up to 450 K. Isothermal capacitance-frequency measurements were conducted from 410 to 450 K to resolve a defect ∼0.8 eV below the conduction band edge and compared with deep-level transient spectroscopy and isothermal capacitance transient spectroscopy measurements. We report significant non-Arrhenius behavior of a defect ∼100 meV below the conduction band and apply the Arrhenius transformation matching method to extract its temperature-dependent activation energy and capture cross-section in the temperature range of 75 to 195 K. At low temperatures (<50 K), we use bias-dependent admittance spectroscopy to extract the electron mobility in β-Ga2O3 from the modified dielectric relaxation frequency. Finally, we discuss the potential of admittance spectroscopy for defect characterization in wide bandgap semiconductors in terms of the defect detection range, instrument requirements, and the frequency-temperature experiment space.

Machine Learning for Detecting Fertilizer Solution Information Based on Dielectric Frequency Response

Machine Learning for Detecting Fertilizer Solution Information Based on Dielectric Frequency Response

Investigation of Dielectric Properties of Potato, Tomato and Onion Juices at Microwave Frequencies

The dielectric properties of fresh juices of Solanum tuberosum (potato), Solanum lycopersicum (tomato) and Allium cepa (onion) were measured in terms of the dielectric constant and dielectric loss factor, over a frequency range from 1 to 50 GHz and at temperatures ranging from 30 to 60 °C, by using the PNA network analyzer model E8364C and open-ended coaxial probe 85070E. A prediction of relaxation frequencies of molecules for the three different juices was done and their molecular behavior was then studied by plotting dielectric constant vs. frequency and dielectric loss factor vs. frequency curves in the frequency range from 1 to 50 GHz at four different temperatures from 30 to 60 °C. The dielectric properties of food products play a crucial role in determining their heating behavior when subjected to an electromagnetic field. Understanding these properties is essential for the development of microwave pasteurization and sterilization processes tailored to various food products.

Terahertz ferroelectric soft mode in weakly doped SrTiO3: M thin films (M=Mn, Ni, Fe, Co)

Systematic study of the terahertz soft-mode in SrTiO3: M thin (150 nm) films doped (2 at%) with transition metals M = Mn, Fe, Ni, Co is performed at frequencies 7–1000 cm−1 and temperatures 5–300 K. The soft mode dielectric strength and frequency follow the Barrett-like temperature behaviours with unusually high quantum temperatures and large in magnitude negative Curie temperatures, indicating strong destabilization of the ferroelectric state due to a combined effect of quantum fluctuations, dead layers at the boundaries of crystallites, misfit strains within crystallites and disorder induced by doping. Dopant-dependent variation in the asymmetry of the Fano resonance describing coupling of the TO2 phonon and continuum states of polarization fluctuations is observed suggesting presence of polar nanoregions in the films. Clear correlation between the asymmetry parameter and the Barrett quantum temperature is observed that highlights the complex character of the local structure-dielectric properties relationships in the films.

Optical studies on thermally evaporated Ge–Se/Ge-Sb-Se chalcogenide glass films by spectroscopic ellipsometry

The GexSb30-xSe70: x = 30, 25, 15, 10 glass films were prepared by thermal evaporation technique. The surface morphology of glass films was studied by atomic force microscopy. The samples exhibited surface roughness with a root mean square value falling within the 0.89–1.47 nm range. The optical properties were precisely characterized by spectroscopic ellipsometry in the 4.13–0.77 eV spectral range. The Cody-Lorentz dispersion model was used to fit the data across the entire spectral range and extract the optical functions of glass films. It has been observed that the refractive index, n values rise with increasing energy, reaching a peak, and then experience a subsequent decline. The refractive index values exhibit a rising trend with an increase in Sb content. The optical bandgap, Egopt was found to follow a decreasing pattern with a decrease in Ge content. The refractive index dispersion curve was analyzed using the Wemple and DiDomenico single oscillator model in the lower absorption spectral region. It has been observed the values of oscillator energy, Eo, and static refractive index, n0, exhibit a pattern consistent with that of Egopt , and n, respectively. The optical properties, such as the high-frequency dielectric constant, carrier concentration, plasma frequency, and optical conductivity were analyzed.