Dielectric Characterization Research Articles

Combined transport and dielectric models and experimental characterization based on impedance spectroscopy for studying the microstructural and transport properties of electro-ceramic perovskites

Collective investigations on the electrical resistivity, complex dielectric permittivity, complex impedance, conductivity, and electric modulus properties of La0.55Ca0.45Mn0.8Nb0.2O3 (LCMNO) are conducted. The impedance spectroscopy (IS) technique is reviewed to examine the electrical and dielectric responses of the material according to the carrier displacement, including core-shell structure, grain boundary effects, dielectric relaxation (local relaxation), and long-range conduction (non-local relaxation). This technique can correlate the electrical and dielectric responses with the ceramics’ microstructural effects (grain boundary and grain (core-shell) zones). For LCMNO, the electrical resistivity study confirms the presence of a metal-semiconductor transition at TM-SC=66 K. It points towards a gradual crossover from the thermally activated Small Polaron Hopping (SPH) to the Variable Range Hopping (VRH) process at low temperatures and for T> TM-SC. The dielectric results confirm the presence of various types of polarization effects. The occurrence of a dipolar reorientation is attributed to long-range electrical conduction. In addition, the accumulation of the activated charge carriers increases the Maxwell-Wagner polarization resulting from an internal barrier layer capacitor (IBLC) microstructure. The electric modulus study confirms the existence of a correlation between the mobile charge carrier’s motions. From the complex impedance, dielectric, and electric modulus, it is possible to label a material’s conductive and dielectric natures (non-Debye-relaxation-type).

Structural and dielectric characterization of Potassium diphosphate/Hydroxyapatite ceramic biocomposite

We study the KH2PO4 (KDP) /Ca10(PO4)6(OH)2 (HA) biocomposite to evaluate its electrical conductivity. It was prepared by manual grinding on a 1:3 molar ratio. Studies by X-ray powder diffraction and Raman spectroscopy show a variation in the volume of the unit cell between KDP and HA and the disappearance of bands associated with KDP. Impedance spectroscopy was studied over a range of temperatures (25-80 ºC) and frequencies from 10 Hz to 1 MHz. It was found that the bulk resistance of the composite is higher in pure KDP. Using the Jonscher empirical expression suggest that the ionic hopping conduction mechanism is responsible for the conductivity behavior with hopping frequency of 1.21 x104 Rad at 80ºC.

Dielectric characterization of fiber‐ and nanofiller‐reinforced polymeric materials

AbstractThis review provides an in‐depth analysis of the electrical responses and relaxation behaviors of various polymeric materials including fiber‐reinforced polymer composites, polymer nanocomposites (PNC), and nanofiller‐reinforced polymeric films and coatings using dielectric spectroscopy (DS). The underlying theory of DS, corresponding instrumentation, various dielectric parameters, relevant equations, interpretations, and polarization mechanisms are thoroughly explored. The impact of synthetic and natural fibers and a diverse range of nanofillers on the dielectric responses and relaxation mechanisms of fiber‐reinforced composites, and PNC and films, respectively, are also examined. For each summarized article, we provide an overview of the composite or film preparation, followed by concise explanations of the dielectric behaviors under diverse conditions, including variations in temperature, frequency, moisture levels, fiber/filler ratios, and chemical treatment. In essence, this review contributes to a nuanced understanding of the intricate relationship between material structure, properties, and performance via DS data interpretation across a spectrum of scenarios.

Random Forest Regression Analysis for Estimating Dielectric Properties in Epoxy Composites Doped with Hybrid Nano Fillers

Bisphenol-A resin epoxy resin composites doped with various concentrations of inorganic hybrid nanofillers, TiO2 + ZnO, were thoroughly examined in the research described in this report for their microwave dielectric relaxation spectroscopy. Ultrasonic dispersion techniques were used to disperse the TiO2 + ZnO hybrid nanofiller into the Bisphenol-A resin. X-ray diffraction (XRD) was employed to ascertain the structural characteristics of the TiO2 and ZnO nanoparticles (NPs) and TiO2 + ZnO hybrid NPs doped neat epoxy (epoxy + hardener). A Vector network analyzer was used to measure the dielectric properties of the hybrid NPs doped neat epoxy in the frequency range from 200 MHz to 20 GHz. Our findings offer important new perspectives on the polarization mechanisms and structural properties of these composite materials. The complex relationship between frequency and dielectric characterization led to measurement complexities that often come with extensive time and cost requirements. This paper presents the random forest regression model as an effective method for predicting the frequency-dependent dielectric constants in composite materials. The main objective of this study was to examine the performance metrics, such as the adjusted R-squared score, root mean squared error (RMSE), and mean absolute error (MAE), across various values of the minimum node size parameter (n min). This study showcases the effectiveness of the RF regression model to accurately and efficiently predict the frequency-dependent dielectric constants in composites. As a result, it eliminates the requirement for laborious and expensive laboratory testing.

Dielectric Characterization of Ex-Vivo Breast Tissues: Differentiation of Tumor Types through Permittivity Measurements.

Early analysis and diagnosis of breast tumors is essential for either quickly launching a treatment or for seeing the evolution of patients who, for instance, have already undergone chemotherapy treatment. Once tissues are excised, histological analysis is the most frequent tool used to characterize benign or malignant tumors. Dielectric microwave spectroscopy makes use of an open-ended coaxial probe in the 1-8 GHz frequency range to quickly identify the type of tumor (ductal carcinoma, lobular carcinoma, mucinous carcinoma and fibroadenoma). The experiment was undertaken with data from 70 patients who had already undergone chemotherapy treatment, which helped to electrically map the histological tissues with their electric permittivity. Thus, the variations in the permittivity of different types of tumors reveal distinctive patterns: benign tumors have permittivity values lower than 35, while malignant ones range between 40 and 60. For example, at a frequency of 2 GHz, the measured permittivity was 45.6 for ductal carcinoma, 33.1 for lobular carcinoma, 59.5 for mucinous carcinoma, and 27.6 for benign tumors. This differentiation remains consistent in a frequency range of 1 to 4.5 GHz. These results highlight the effectiveness of these measurements in the classification of breast tumors, providing a valuable tool for quick and accurate diagnosis and effective treatment.

Dielectric characterization analysis of natural fiber based hybrid composite for microwave absorption in X-band frequency

Dielectric characterization analysis of natural fiber based hybrid composite for microwave absorption in X-band frequency

The Effect of Deposition Temperature on Structural, Morphological, and Dielectric Properties of Yttria-Doped Zirconia Thin Films

The aim of this study was to investigate the effect of deposition temperature on the structural, optical, morphological, and dielectric properties of yttria-stabilised zirconia (YSZ) films prepared by sol-gel spin-coating method. X-ray diffraction (XRD) measurements of YSZ films showed that the peaks of the cubic phase were prominent and the peak intensities increased with deposition temperature. The crystallite size, dislocation density, and microstrain of the thin films were identified by XRD. It was observed that the crystal size of the YSZ thin films increased from 16 nm to 22 nm with the deposition temperature. The surface roughness of the thin films was found to have changed as revealed by Atomic Force Microscopy (AFM) measurements. The roughness increased from 7.72 nm to 11.92 nm with increasing temperature. The optical transmittance of the YSZ thin films was investigated in the wavelength range 200-900 nm and was found to increase slightly with increasing deposition temperature. Metal-Oxide-Semiconductor (MOS) devices were fabricated from these YSZ materials for dielectric characterization. The dielectric properties of the Ag/YSZ/n-Si MOS structure were investigated. It was found that the capacitance, conductivity and other dielectric parameters of these structures are strongly frequency dependent.

Polyvinylpyrrolidone – KNNLST lead-free ceramic composites for dielectric applications

Piezoelectric composites offer many advantages compared to piezoelectric ceramics or polymers because of their mechanical flexibility and relatively high stress-induced voltage. In this research, high-molecular weight polyvinylpyrrolidone (PVP) and lead-free piezoelectric (K0.45Na0.51Li0.04) (Nb0.85Ta0.1Sb0.05)O3 (KNNLST) ceramics have been used to produce composites. The possible range of composites from 0 to 100 wt% has been explored. The ceramics were produced using conventional processing methods, while the composites were solution-cast after being mixed with a magnetic stirrer. The composites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and dielectric and piezoelectric characterization to determine their properties. The morphology of the composites indicates the homogeneous distribution of the ceramics in the polymer. The XRD patterns show that the dissolved amorphous PVP precipitates and the addition of KNNLST ceramics contributes substantially to the crystalline phase formation. The relative permittivity and loss tangent values increase with an increase in ceramic content. Acceptable polarization and strain hysteresis curves were obtained only for the KNNLST ceramics. The composites produced will be suitable for dielectric applications.

Photoresponse, thermal and electrical behaviors of MXene-based polysulfone nanocomposite

The Ti3C2Tx MXene nanosheet was prepared by 40% (v/v) hydrofluoric acid etching at 20 °C for 48 h and delamination of bulk MAX Ti3AlC2 precursor material. A 2D nanomaterial MXene Ti3C2Tx as a nanofiller was introduced to polysulfone (PSulfone) matrix. MXene and PSulfone/MXene nanocomposite systems were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscope, Fourier-transform infrared and thermogravimetric analysis instruments. Dielectric and electrical characterization of PSulfone/MXene nanocomposite was carried out. The electrical resistance of Ti3C2Tx MXene from measurement current (I)–voltage (V) was measured as 116 Ω. Pure PSulfone matrix exhibits typical insulator behavior, and MXene exhibits a good conductor behavior. But, when MXene was added to the pure PSulfone matrix, the resistance of the MXene/PSulfone nanocomposite increased moderately compared to that of pure MXene. In spite of the excess of surface functional groups, MXene showed surprisingly good electron transport across the surface, while in the case of PSulfone/MXene nanocomposite, the insulating behavior of PSulfone significantly reduced the electron transport of MXene. The semiconductor behavior of PSulfone/Ti3C2Tx MXene nanocomposite indicates that MXene provides efficient charge carrier transfer in the nanocomposite system. By comparing the TGA results between the PSulfone and different weight ratios of PSulfone/Ti3C2Tx MXene nanocomposites, it was determined that MXene nanosheets had a significant effect in slightly accelerating the thermal degradation of PSulfone. Optical conductivity was investigated by preparing a film of PSulfone/MXene nanocomposite on an interdigital contact. It was observed that the optical current values changed depending on the increasing illumination intensity. Considering current–voltage measurements, the photocurrent generation potential of PSulfone/MXene nanocomposite shows that it can be used in photodevice production.

Microwave dielectric characterization studies of PVDF-TrFE-Nafion blended films

The solution-based casting method fabricates the free-standing pure PVDF-TrFE, PVDF-TrFE-Nafion blended films and tests them for structural, morphological, and microwave studies. The X-ray diffraction pattern and FTIR spectrum confirmed the formation of the ferroelectric β-phase of PVDF-TrFE. The surface morphology of blended films is studied by scanning electron microscope (SEM), and noticeable changes in the morphological features are observed in the blended films resulting from the differences in the nucleation process in these films. Then using the open-ended coaxial probe method, the complex permittivity measurements were carried out over a large frequency range, from 0.5 GHz to 50 GHz. These results were verified with the Transmission-Reflection method using a rectangular waveguide in the X-band and Ku-band frequency range. The microwave absorption properties of the blends are also studied in the same frequency range. The stability of the dielectric properties and low microwave absorption indicates that the blending of PVDF-TrFE with Nafion results in a new potential material for high frequency flexible capacitor applications.

Dielectric Characterization of Dispersive Head Tissue for Detection and Classification of Tumour Using Microwave Imaging Technique and Deep Learning Model

Dielectric Characterization of Dispersive Head Tissue for Detection and Classification of Tumour Using Microwave Imaging Technique and Deep Learning Model

Varactor-Based Tunable Sensor for Dielectric Measurements of Solid and Liquid Materials

In this article, a tunable RF sensor is presented for the measurement of dielectric materials (liquids and solids) based on a metamaterial resonator. The proposed novel configuration sensor has a microstrip line-loaded metamaterial resonator with tunable characteristics by utilizing a single varactor diode in the series of the resonator. CST Microwave studio is employed for 3D simulations of the tunable sensor, and the desired performance is attained by optimizing various structural parameters to enhance the transmission coefficient (S21 magnitude) notch depth performance. The proposed RF sensor can be tuned in L and S-bands using the varactor diode biasing voltage range of 0–20 V. To validate the performance of the sensor, the proposed design has been simulated, fabricated, and tested for the dielectric characterization of different solid and liquid materials. Material testing is performed in the bandwidth of 1354 MHz by incorporating a single metamaterial resonator-based sensor. Agilent’s Network Analyzer is used for measuring the S-parameters of the proposed sensor topology under loaded and unloaded conditions. Simulated and measured S-parameter results correspond substantially in the 1.79 to 3.15 GHz frequency band during the testing of the fabricated sensor. This novel tunable resonator design has various applications in modulators, phase shifters, and filters as well as in biosensors for liquid materials.

Microwave dielectric characterization and loss mechanism of biowaste during pyrolysis

The effectiveness of microwave heating of biomass depends on the changes in dielectric properties. This study systematically investigated the microwave dielectric properties and loss mechanism of biowaste at different frequencies (915 and 2,450 MHz) and temperatures (25–800 °C) using the cavity perturbation method. The gas emissions and properties of the biochar produced during pyrolysis were characterised by SEM, XRD, and TG-FTIR. The findings revealed that the dielectric properties and penetration depth of the biomass and biochar changed significantly during microwave pyrolysis. The dielectric constant and dielectric loss coefficient first increased and then decreased during the drying stage, and they decreased continuously with the volatile’s generation in the pyrolysis stage, while the formation and high conductivity of biochar promoted a sharp increase in dielectric properties during the carbonisation stage. The loss tangent angle is 0.01–0.05 in the first two stages, while it increased to 0.10–0.25 in the carbonization stage, demonstrated that the biowaste is a low-loss material. However, the microwave absorption capacity was enhanced for pyrolyzed biochar. The loss mechanism revealed that dipole polarisation primarily contributes to the dielectric loss during the drying and pyrolysis stages, whereas interfacial polarisation plays an important role during the carbonisation stage. The data provided in this paper contribute to the evaluation of microwave penetration depth in biomass and the design of large-scale microwave-based heating systems. Furthermore, this study offers a theoretical basis for modelling and simulating the microwave heating of biomass and achieving efficient energy conversion.

Dielectric characterisation of chitosan-based composite membranes containing fractionated kraft and organosolv lignin

Chitosan-based composite membranes with fractionated kraft and organosolv lignin were prepared by solvent casting. A small lignin fraction (1%) was added to the neat chitosan to obtain a good distribution. The influence of lignin extraction with ethyl acetate and consequently ethanol on the dielectric and conductive properties of the composites was investigated by dielectric thermal analysis (DETA). Overall, the chitosan-lignin composites exhibit three relaxation mechanisms (β, βwet, and α) and two conductivity phenomena (σ and MWS). FTIR analysis showed that the composites with organosolv lignin fractions have fewer hydroxyl groups than those with kraft lignin, which decreases slightly further for both after ethanol extraction. The lignin fractions with lower molecular weight and higher OH content show stronger interactions with chitosan, due to hydrogen bonding. These interactions affect the thermal activation and cooperativity of the β-, βwet, and α-relaxation. Furthermore, the kraft lignin fractions with many polar groups are very compatible with the chitosan matrix, resulting in a more compact structure and higher fragility. The membranes CS OLEA and CS KLE have a lower electron conductivity and a higher proton conductivity. Thus, they have promising conductivity properties for fuel cell applications.

Thickness‐dependent glass transition temperature of hydroxyethyl cellulose thin films based on dielectric properties

AbstractHydroxyethyl cellulose (HEC) thin films with a molecular weight of 720,000 g/mol deposited by thermal evaporation in a thickness range of 250, 500, and 750 nm were measured in a frequency range of 1–105 Hz and a temperature range of 233–373 K for dielectric characterization with increments of 10 K. Dielectric results were used to derive and evaluate the glass transition temperature and ductility, which are essential parameters for structural analysis. Results showed that the thickness of HEC thin films was an effective parameter on dielectric and structural properties. Because of the increasing thickness, the dielectric constant has values between 22 and 143 at 1 kHz, and glass transition temperature and ductility change between 211–175 K and 15–20, respectively. Based on the literature and the compatible results, the main effect of these variations could be dead layers and voids in structure. The effect of the dead layer gave an important idea about the adjustability of mechanical properties of HEC thin films depending on the thickness. In this way, it would be possible to use these thin films deposited from HEC with 720,000 g/mol molecular weight, especially in drug delivery, electrophoresis technologies, biomedical devices, and coverage 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.

Dielectric Characterization Using Reflected Group Delay of a Partially-Filled Coaxial Resonator

Dielectric Characterization Using Reflected Group Delay of a Partially-Filled Coaxial Resonator

Stack Dual-band EBG Based Sensor for Dielectric Characterization of Liquids

Stack Dual-band EBG Based Sensor for Dielectric Characterization of Liquids

Novel Complementary Resonator for Dielectric Characterization of Substrates Based on Permittivity and Thickness

Novel Complementary Resonator for Dielectric Characterization of Substrates Based on Permittivity and Thickness

Millimeter-wave dielectric characterization of liquids-in-flow using spherical cavity resonator

Millimeter-wave dielectric characterization of liquids-in-flow using spherical cavity resonator