Variation Of Dielectric Properties Research Articles

Microwave absorption analysis on heated edible spirulina with various temperatures

This paper discusses the microwave absorption analysis of edible Spirulina by using WR62 and WR90 rectangular waveguides in conjunction with Agilent P-series Vector Network Analyzer (PNA). Heat might lead to the degradation of spirulina. This phenomenon involves the chemical and physical reaction that is associated with the variation of dielectric properties. These properties determine the propagation mechanism of microwaves within the sample or material. Hence, an assessment method to detect a nutrient change in spirulina due to heat is necessary. In this context, a microwave absorption measurement system was developed to study the reflection coefficient, transmission coefficient, and absorption coefficient of Spirulina tablets over temperature. The transmission/Reflection line method is well-known because it is non-destructive and rapid in analyzing chemical and physical properties. In this work, Spirulina tablet is used since it is a popular food supplement that is believed to be able to treat diseases is and good for health. The reflection, transmission, and absorption measurements were conducted on Spirulina from 12.4GHz to 18GHz.

Effect of manganese doping on structural, optical, morphological, and dielectric properties of Ba(Ti1-xMnx)O3 lead-free ceramics for energy storage in supercapacitors.

A supercapacitor (SC) is considered to be one of the best energy storage devices due to its high-power density, long lifespan, fast charge storage capability, and eco-friendliness. Ceramics with low-cost, nontoxic, high efficiency, and stability are the suitable and promising materials for performed supercapacitors at room temperature. As proposal, we synthesized by sol-gel method the ceramics Ba(Ti1-xMnx)O3 (where x = 0, 1, 2, or 3%) to study the effect a low rate of manganese doping on their morphological, structural, dielectric, and optical properties. The microstructure of the sintered ceramics was examined using scanning electron microscope (SEM), and the results reveal that the average grain size (AGS) of the ceramics (0.663-1.018μm) increases with increasing Mn doping content. The optical behavior was studied by UV-visible spectroscopy, and the results indicate that Mn doping reduces the band gap (Eg) from 3.27 to 2.79eV thus, the possibility of using these materials in photocatalyze applications. The dielectric properties of all studied samples were investigated at the temperature range 30-400°C and frequency range 103-106Hz. Significant modification in dielectric permittivity and an appreciable decrease in dielectric losses were observed when adding Mn2+ ions to BaTiO3 ceramics. Variations in dielectric properties and AC conductivity, as a function of frequency, reveal a relaxation mechanism related to the Maxwell-Wagner interfacial polarization. The obtained results suggest the use of prepared ceramics in capacitor and actuator applications at room temperature (RT).

Ethylcellulose-stabilized fat-tissue phantom for quality assurance in clinical hyperthermia

Background Phantoms accurately mimicking the electromagnetic and thermal properties of human tissues are essential for the development, characterization, and quality assurance (QA) of clinically used equipment for Hyperthermia Treatment (HT). Currently, a viable recipe for a fat equivalent phantom is not available, mainly due to challenges in the fabrication process and fast deterioration. Materials and methods We propose to employ a glycerol-in-oil emulsion stabilized with ethylcellulose to develop a fat-mimicking material. The dielectric, rheological, and thermal properties of the phantom have been assessed by state-of-the-art measurement techniques. The full-size phantom was then verified in compliance with QA guidelines for superficial HT, both numerically and experimentally, considering the properties variability. Results Dielectric and thermal properties were proven equivalent to fat tissue, with an acceptable variability, in the 8 MHz to 1 GHz range. The rheology measurements highlighted enhanced mechanical stability over a large temperature range. Both numerical and experimental evaluations proved the suitability of the phantom for QA procedures. The impact of the dielectric property variations on the temperature distribution has been numerically proven to be limited (around 5%), even if higher for capacitive devices (up to 20%). Conclusions The proposed fat-mimicking phantom is a good candidate for hyperthermia technology assessment processes, adequately representing both dielectric and thermal properties of the human fat tissue while maintaining structural stability even at elevated temperatures. However, further experimental investigations on capacitive heating devices are necessary to better assess the impact of the low electrical conductivity values on the thermal distribution.

Managing the micro-structure and properties of Sm-ZnO thin films by tuning the contents of Sm

The microstructural variations in zinc oxide (ZnO) nanostructures are probed caused by the incorporation of RE metal ion Sm3+ in replacement of Zn2+. Sm-doped ZnO nanostructures with Sm concentration of 6–10 wt % is synthesized via a simple sol gel-dip coating synthetic technique. The current research looks into the physical, surface morphology, dielectric, optical, and magnetic properties of Samarium doped ZnO nanostructures. Structural and morphological investigations are primarily carried out using XRD and SEM techniques. The data from XRD identified the synthesized Sm doped ZnO nanostructures crystallize in a wurtzite hexagonal structure. The Sm dopant is incorporated into the Zn matrix. After adding Sm in ZnO, a slight variation in crystallite size is noticed. The estimates of the optical energy band gap based on optical transmittance measurements show that the band gap is widened. The variation in dielectric properties of Sm-ZnO is assumed to be the result of the increase in Sm doping %. The various functional groups that appeared in the prepared nanostructures are identified using FTIR. These prepared nanostructures are highly recommended for sensing applications as well as for optoelectronic devices.

A new rare-earth orthovanadate microwave dielectric ceramic: ErVO4

A new microwave dielectric ceramic ErVO4 with a zircon structure was prepared by solid-state reaction method. The structure of ErVO4 was confirmed by X-ray diffraction and TEM diffraction, and no second phase was generated in the ceramic. At different sintering temperatures, slight changes in the lattice parameters affected microwave dielectric properties of the ErVO4 ceramic. Relative density, packing fractions, etc. Were investigated to analyze the variation of dielectric properties. Further the complex chemical bond theory revealed that the dielectric constant had a similar changing trend to the ionicity of bond, while the lattice energy had a positive impact on the quality factor. ErVO4 ceramic sintered at 1150 °C had the microwave dielectric properties of εr = 12.03, Q × f = 25,549 GHz, and τf = −52.89 ppm/°C.

Room temperature magneto-dielectric coupling in the CaMnO3 modified NBT lead-free ceramics

The sol–gel prepared (1-x)Na0.5Bi0.5TiO3-(x) CaMnO3 (x = 0, 0.03, 0.06, 0.12) compositions show a Rhombohedral (R3c) phase up to x = 0.06 while a mixed rhombohedral (R3c) and orthorhombic (Pnma) phases for the x = 0.12. The lattice volume consistently decreased with an increase in the CaMnO3 content. The phase transition temperature (Tc) decreased with an increase in the CaMnO3 compositions. The room temperature dielectric constant increased, and loss decreased for the x = 0.03 composition due to a decrease in the oxygen vacancy and Bi loss confirmed by the valence state study (XPS). All the compositions show a variation of the room temperature dielectric property with an application of magnetic field confirming a magnetodielectric coupling. The x = 0.06 composition shows the highest negative magnetodielectric coupling constant (MD%) of 3.69 at 100 kHz at an applied field of 5 kG.

Microwave Reflectometry Sensing System for Low-Cost in-vivo Skin Cancer Diagnostics

Skin cancer is one of the most commonly diffused cancers in the world and its incidence rates have constantly increased in recent years. At the current state of the art, there is a lack of objective, quick and non-invasive methods for diagnosing this condition; this, combined with hospital crowding, may lead to late diagnosis. Starting from these considerations, this paper addresses the implementation of a microwave reflectometry based-system that can be used as a non-invasive method for the in-vivo diagnosis and early detection of biological abnormalities, such as skin cancer. This system relies on the dielectric contrasts existing between normal and anomalous skin tissues at microwave frequencies (in a frequency range up to 3 GHz). In particular, a truncated open-ended coaxial probe was designed, manufactured and tested to sense (in combination with a miniaturized Vector Network Analyzer) the variations of skin dielectric properties in a group of volunteer patients. The specific data processing demonstrated the suitability of the system for discriminating malignant and benign lesions from healthy skin, ensuring simultaneously effectiveness, low cost, compactness, comfortability and high sensitivity.

An Improved Hyperbolic Method and Its Application to Property Inversion in Martian Tianwen-1 GPR Data

On 15th May 2021, the Tianwen-1 (TW-1) successfully landed on the surface of Mars within the southern Utopia Planitia. It delivered a rover named Zhurong equipped with ground penetrating radar (GPR), a device that can investigate the thickness and structure of the geological layers below the martian surface. The hyperbola method is commonly used for extracting dielectric property variations with depth from GPR data to aid the interpretation of the subsurface structure and material composition. This study analyzes the advantages and drawbacks of three hyperbola methods with different geometric models. Next, it proposes a new method aiming to use the highly precise, yet complex geometric model and address issues caused by its solving process. We also analyze the influencing factors contributing to measurement errors and design corresponding criteria for measurement point selection to mitigate errors. The average error of the proposed method is less than 5% for a depth of up to 9 m. We employed the proposed method to obtain the dielectric constant distribution in the shallow surface layer of the TW-1 landing zone to a depth of up to 16 m. The dielectric constant is mainly concentrated between 2 and 8 m and increases gradually with depth. Below 2 m, the dielectric constant is about 5.1 and the density is about 2.5 g/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The stratification and density variation can be inferred from the dielectric constant distribution diagram.

Structural, optical, magnetic and dielectric properties of Ag doped Mg nano ferrites prepared by citrate gel auto combustion method

The Silver Substituted Magnesium ferrites with the formula MgAgXFe2-XO4 (where 0 ≤ x ≤ 0.5 by step 0.1) have been prepared through the citrate gel auto combustion method. Prepared samples structural, morphological, electrical, and magnetic properties have been investigated by XRD analysis, FESEM, AC conductivity, and VSM respectively. XRD and FESEM were used to investigate the structural properties of prepared ferrite materials such as average crystalline size, lattice parameter, X-ray density, unit cell volume, and morphology. Crystalline size was measured to be between 25–30 nm. Five Raman active modes (A1g+Eg+3Tg) were observed in the Raman Spectrum, which are expected in the spinal ferrite system. The prepared sample's structure is confirmed by FTIR spectra bands appearing ∼400 and ∼600 cm−1 wave number region indicates that stretching frequency of tetrahedral (A-site) and octahedral (B-site) respectively. The optical band gap energy of the material observed ranged from 3.44 to 3.51 eV. The variation of dielectric properties has been studied with regard to temperature variation as a function of frequency. All the samples dielectric constant decreases with increasing frequency and temperature, which is the nature of ferrites. It obeys the Maxwell-Wagner type of dispersion because of interfacial polarization. The magnetic properties investigated by room temperature VSM, low coercivity values observed indicate that the sample is of soft magnetic nature.

Understanding the variations in dielectric properties of mustard (Brassica nigra L.) and argemone (Argemone mexicana) oil blends at different temperatures.

Mustard oil is the most commonly adulterated edibleoil, invariably with argemone oil. This study was aimed to develop a parallel plate capacitive sensor for measurement of dielectric properties of pure mustard oil, pure argemone oil and their blends (25, 50 and 75%) at five levels of varying temperature (10 to 50°C). The effect of blend ratio and temperature on the selected dielectric properties of oil-capacitance (C), dielectric loss tangent (tanδ), dielectric constant ( ), dielectric loss factor ( ) and electrical conductivity (σ) were investigated. It was observed that composition of the individual oils in terms of moisture and fatty acids influenced the physical and dielectric properties. The sensor was used to relate the dielectric properties of oil samples with blend ratio and temperature by means of statistically significant (p < 0.05) and robust (R 2 > 0.8) multiple linear regression model. The effect of temperature on C and was negative, while it was otherwise for tanδ, and σ. Increase in argemone oil content in the blends, increased the dielectric measures due to the associated changes in the physical and chemical properties. The capacitive sensor could distinctly identify mustard oil, argemone oil and its blends on the basis of dielectric properties.

Development and Evaluation of Physico-Chemical Properties of Functionalized Cannabis indica Fibers Reinforced Bio-Polymer Composites

ABSTRACT The objective of this research work is to evaluate the variation in mechanical, thermal, dielectric and physico-chemical properties of Cannabis indica fibers fortified unsaturated polyester composites with respect to fiber proportions and type of surface functionalization techniques employed. The various surface functionalization techniques utilized were mercerization and silane, benzoyl chloride and acrylic acid/acrylonitrile graft copolymerization. To optimize fibers proportions, portrayal of polymer composites has been done by considering their mechanical properties like tensile, compressive and flexural strength, and the optimized values have been noted to be 22.66, 51.7 and 53.27 MPa, respectively, when stacked with 30% benzoylated fibers. These composite materials have additionally been assessed for their water absorbance, chemical strength and dampness absorbance behavior, and best properties were observed in case of benzoyl chloride and acrylonitrile grafted fibers. The optimized samples were then characterized by scanning electron microscopy and thermal gravimetric analysis techniques. Additionally, these composites have likewise been assessed for their dielectric properties and combustibility. Furthermore, the ability of magnesium hydroxide and zinc borate fire retardant fillers on the fire resistance properties of Cannabis indica fibers fortified polyester composites has also been examined and was noticed to increase the limiting oxygen index values of polymer composites from 20 to 23%.

Detection of hydrocarbon spills by means of a coaxial impedance dielectric sensor

Leakages from storage tanks or pipes frequently produce pollution of soils and groundwater reservoirs by hydrocarbons. Common practices for monitoring and characterising site contamination involve soil drilling, sampling and chemical analysis, complemented with geophysical surveys. This study evaluates the presence of paraffin oil inside soil pores by means of dielectric permittivity measurements, using a coaxial impedance device in laboratory-scale models. The real dielectric permittivity of unsaturated sand is measured before, during and after a contamination process. Monitoring small variations in real dielectric permittivity allows detection of the partial replacement of air (κ′ = 1) by paraffin oil (κ′ ≈ 2) in soil pores. These variations in soil dielectric properties enable pollution levels to be assessed, knowing in advance the κ′ of the soil at the initial stage and measuring the influence of oil and water content on κ′. The technique proposed can also be used for monitoring the lateral extension of a contaminant plume and can be successfully applied at the laboratory scale for oil leakage detection by periodically monitoring changes in the soil dielectric permittivity.

Comparing the Dielectric Properties of Papaya Oil with Mineral Insulating Liquid under Temperature Variation

Abstract: The world’s energy requisite has been controlled by petroleum oil for a long time in transportation, household and power sectors. Mineral Transformation Oil (MTO), being an essential insulating material in transformers, has been used for over fifteen decades. MTO application in the power sector could be hazardous to the environment, especially during a transformer explosion which may cause a spill of oil to the soil or water stream. Owing to the threat of MTO to environment aspects, alternative insulating oil with biodegradable characteristics has attracted a lot of devotions in recent studies. To validate the aptness of using Purified Papaya Seed Oil (PPSO) as an insulating fluid in an electric transformer, it is vital to compare dielectric properties of PPSO with that of MTO insulating liquid. This study presents a comparison of temperature effect on dielectric properties of PPSO with the MTO insulating liquid. Breakdown voltage, dissipation factor (tan δ) and dielectric constant were measured by existing established testing standards. The breakdown voltage was determined by IEC 156 standard test method, whereas the dissipation factor and dielectric constant were determined based on IEC 60247 standard test method. The results revealed that the variation of dielectric properties of PPSO due to temperature change was similar to that of MTO. However, the dissipation factors and breakdown voltages of dielectric properties of PPSO were better when compared with those of MTO at higher temperatures, but with a slight decrease in dielectric constants with the increase in temperature. Keywords: Papaya seed oil, Dissipation factor, Dielectric constant, Breakdown voltage, Temperature, Transformer. PACS: 77.84. Nh, 88.05. Lg.

Investigation of Morphological, Optical, and Dielectric Properties of RF Sputtered WOx Thin Films for Optoelectronic Applications.

Tungsten oxide (WOx) thin films were synthesized through the RF magnetron sputtering method by varying the sputtering power from 30 W to 80 W. Different investigations have been conducted to evaluate the variation in different morphological, optical, and dielectric properties with the sputtering power and prove the possibility of using WOx in optoelectronic applications. An Energy Dispersive X-ray (EDX), stylus profilometer, and atomic force microscope (AFM) have been used to investigate the dependency of morphological properties on sputtering power. Transmittance, absorbance, and reflectance of the films, investigated by Ultraviolet-Visible (UV-Vis) spectroscopy, have allowed for further determination of some necessary parameters, such as absorption coefficient, penetration depth, optical band energy gap, refractive index, extinction coefficient, dielectric parameters, a few types of loss parameters, etc. Variations in these parameters with the incident light spectrum have been closely analyzed. Some important parameters such as transmittance (above 80%), optical band energy gap (~3.7 eV), and refractive index (~2) ensure that as-grown WOx films can be used in some optoelectronic applications, mainly in photovoltaic research. Furthermore, strong dependencies of all evaluated parameters on the sputtering power were found, which are to be of great use for developing the films with the required properties.

Dielectric dispersion characteristics of the phospholipid bilayer with subnanometer resolution from terahertz to mid-infrared.

There is growing interest in whether the myelinated nerve fiber acts as a dielectric waveguide to propagate terahertz to mid-infrared electromagnetic waves, which are presumed stable signal carrier for neurotransmission. The myelin sheath is formed as a multilamellar biomembrane structure, hence insights into the dielectric properties of the phospholipid bilayer is essential for a complete understanding of the myelinated fiber functioning. In this work, by means of atomistic molecular dynamics simulations of the dimyristoylphosphatidylcholine (DMPC) bilayer in water and numerical calculations of carefully layered molecules along with calibration of optical dielectric constants, we for the first time demonstrate the spatially resolved (in sub-nm) dielectric spectrum of the phospholipid bilayer in a remarkably wide range from terahertz to mid-infrared. More specifically, the membrane head regions exhibit both larger real and imaginary permittivities than that of the tail counterparts in the majority of the 1–100 THz band. In addition, the spatial variation of dielectric properties suggests advantageous propagation characteristics of the phospholipid bilayer in a relatively wide band of 55–85 THz, where the electromagnetic waves are well confined within the head regions.

Comparative studies on electric properties of 85% BaTiO3 + 15% Ni0.95-xCoxMn0.05Fe2O4 magnetoelectric composites

The magnetoelectric (ME) composites with varying ferromagnetic phase: 15% Ni0.95-xCoxMn0.05Fe2O4 (x = 0.01, 0.02 and 0.03) and ferroelectric phase: 85 % BaTiO3 are prepared. In XRD studies, two phases: piezomagnetic cubic phase and perovskite piezoelectric tetragonal phase are detected in resultant ME composites. The dielectric constant (έ) versus frequencies (10 Hz to 1 MHz) measurements for resultant ME composites at room temperature showed dispersion owing to the interfacial polarization of Maxwell-Wagner type. The temperature-dependent changes in dielectric constant (έ) and loss tangent (tan δ) are recorded at constant frequency. As a function of magnetic field intensity, the ME- conversion factor dc (ME)H is investigated. With varied molar ratios of the ME components, variations in dielectric properties and ME effect are observed. The highest value dc(ME)H = 0.610 mV/cm.Oe for ME- conversion factor is obtained in a ME composite consisting of 15% Ni0.95-xCoxMn0.05Fe2O4 + 85% BaTiO3 with x = 0.01.

Dielectric property measurement of human sweat using attenuated total reflection terahertz time domain spectroscopy.

Sweat is one of the essential biofluids produced by the human body, and it contains various physiological biomarkers. These biomarkers can indicate human health conditions such as disease and illness. In particular, imbalances in the concentration of electrolytes can indicate the onset of disease. These same imbalances affect the dielectric properties of sweat. In this study, we used attenuated total reflection terahertz time domain spectroscopy to obtain the frequency-dependent dielectric properties of human sweat in a frequency range from 200 GHz to 2.5 THz. We have investigated the variation of dielectric properties of sweat collected from different regions of the human body, and we have observed that the real and imaginary part of dielectric permittivity decreases with the increase in frequency. A combination of left-hand Jonscher and Havriliak-Negami processes is used to model the results and reveal the presence of relaxation processes related to sodium and calcium ions concentrations. This information may help design novel biosensors to understand the human health condition and provide a hydration assessment.

Enhanced high-temperature dielectric performances of polyetherimide-based composites via surface functionalized silicon carbide whiskers

In this work, 3-aminopropyltriethoxysilane (AMEO)/polyurea (PUA)-modified silicon carbide whiskers (SiCw) were firstly fabricated and then incorporated into polyetherimide (PEI) to prepare the dielectric composites toward high temperature application. The results show that the introduction of amino/urea polar groups can effectively promote dielectric constant and suppress the dielectric loss of composites at room and high temperatures owing to the strong interfacial adhesion and deep trap effect of polar groups. Specifically, the variations of dielectric properties are also greatly dependent upon the surface functionalization of SiCw. SiCw-PUA endows the composites with relatively better comprehensive dielectric performances (dielectric constant of 18.3 and dielectric loss of 0.020) at room temperature while SiCw-AMEO has more apparent role in maintaining the dielectric performances (dielectric constant of 17.0 and dielectric loss of 0.029) at high temperature of 150 ℃. Furthermore, the composites also exhibit high thermal conductivity with the maximum thermal conductivities of 1.41 and 1.37 W m−1 K−1 for the SiCw-AMEO/PEI and SiCw-PUA/PEI at filler loading of 15 wt%, respectively. The excellent reinforcement effect of the surface functionalized SiCw also endows the composites with more application probability. This work on functionalization of SiCw could be applicable for integration of dielectric, thermally conductive and mechanical properties.

Spinel M0.5Zn0.5Fe2O4 (M = Ni, Co, and Cu) ferrites for energy storage applications: Dielectric, magnetic and electrochemical properties

Spinel structured M0.5Zn0.5Fe2O4 (M = Ni, Co, Cu) were synthesized through a solid state route. Phase analysis of the samples showed the formation of a single phase spinel structure. Fourier transform infrared spectroscopy also confirm the presence of tetrahedral and octahedral sites belonging to spinel structure. The microstructural analysis of the samples revealed a grain size ranging from 0.5 to 3.7 μm. The photoluminescence spectroscopy indicated the generation of oxygen vacancies and structural defects in the lattice of the samples. The obtained dielectric constant and loss values (at 1 MHz) varied between 11 and 35, and 0.006 to 1.2, respectively. The variation in dielectric properties was dependent on polarization species, crystallite size, defects and oxidation states. The samples showed a ferromagnetic behavior at room temperature. The electrochemical performance of Cu0.5Zn0.5Fe2O4 showed the most favorable results such as the lowest overpotential of 490 mV, the highest specific capacitance of 462 F/g, and the lowest charge-transfer resistance of 876 Ω, suggesting its potential for energy storage applications.

Role of oxygen partial pressure of synthesis environment in tuning the dielectric properties of Nd2CuTiO6

Dielectric studies were carried out on Nd2CuTiO6 samples prepared by high temperature solid-state reaction followed by annealing under different oxygen partial pressures. X-ray diffraction studies revealed that the orthorhombic (Pnma) structure of Nd2CuTiO6 is retained in all the samples. The room temperature permittivity at 100Hz was found to be about 200 in the air-annealed sample, and it increased considerably to about 3000 upon annealing in argon atmosphere. The electrical conductivity in the argon-annealed compound was found to be an order of magnitude higher than that for the air-annealed sample. On annealing in oxygen, both permittivity and electrical conductivity of the sample were found to be significantly reduced. The variation in dielectric properties could be attributed to the induction or annihilation of mixed valence state of copper and oxygen vacancies, which was supported by X-ray photoelectron and diffuse reflectance spectroscopy data. The analysis of temperature and frequency dependent conductivity and dielectric data showed that the overlapping large polaron tunnelling (OLPT) mechanism is responsible for the observed dielectric relaxations and conduction. The observed systematic dependence of properties on the oxygen partial pressure of the annealing environment suggests a simple method to tune the electrical properties of Nd2CuTiO6.