Variation Of Relative Permittivity Research Articles

Measurement of void fraction of zeotropic refrigerant R454C using capacitance-based sensor in horizontal flow configuration

This study measures and analyzes the void fraction of R454C, a zeotropic refrigerant, using a capacitance-based sensor. Capacitance-based sensors offer an attractive method for real-time void fraction measurement. Given that zeotropic refrigerants undergo compositional changes in their gas and liquid phases during phase change, it is essential to account for variations in relative permittivity due to these compositional changes when using a capacitance-based sensor for void fraction measurement. In this study, Landau and Lifshitz’s mixing rule is employed to predict the relative permittivity based on compositional variations of a bi-component refrigerant, along with a calibration strategy for the capacitance-based sensor based on flow pattern transitions. The void fraction measurement results obtained from the capacitance-based sensor for R454C are validated by comparison with results obtained using the quick-closing valve-based (QCV) method under identical conditions. The measurement uncertainty of the developed sensor is 4.13 %, and compared to the measurement results from the QCV method, it is found to have a relative error of −0.955 % over the entire range of experimental conditions. The measurements are conducted in a smooth tube with an inner diameter of 7.1 mm, mass flow rates ranging from 100 to 400 kg m−2 s−1, pressures from 0.789 to 1.724 MPa, and inlet vapor quality from 0.025 to 0.900. The measurement results are then compared with existing prediction correlations, and those correlations offering acceptable predictions of the void fraction of R454C are presented.

Observation of magnetodielectric effects in Nd0.5Dy0.5FeO3 thin film and its utilization in microstripline based resonator circuit

Nd0.5Dy0.5FeO3 epitaxial thin film grown on LaAlO3 (001) substrate by pulsed laser deposition technique shows a significant magnetodielectric effect. At 100 K, a variation of around 13% in relative permittivity is observed at frequencies higher than 2 MHz in the presence of 5 T. This variation in relative permittivity (ε΄) increases to about 50% at 2 K. To utilize the observed magnetodielectric effect, we have designed the microstripline based resonator circuit using High-Frequency Structure Simulator (HFSS). Simulations are performed for the two values of the real part of permittivity (in the absence and presence of an external magnetic field) to observe the magnetic field tunability of the resonance frequency. A shift of 27% is observed in the resonant frequency of the microstripline based resonator on Nd0.5Dy0.5FeO3 epitaxial thin film.

Structural, dielectric, optical, and electrochemical performance of Li4Mo5O17 for ULTCC applications

Lithium molybdates are of great interest in ultra-low temperature cofired ceramics (ULTCC) technology due to their low processing temperature. In this study, a ULTCC Li4Mo5O17 was prepared via a solid state route. X-ray diffraction and Raman spectroscopy analysis revealed the formation of single phase triclinic structure. The variation in relative permittivity and dielectric loss of the sample with the change in frequency is explained using the polaron model. At the excitation of 514 nm, excitonic and deep-level (impurities, oxygen, and lithium vacancies) emissions were observed which contribute to the lossy nature of Li4Mo5O17. The experimentally calculated direct optical band gap energy of ∼ 3.1 eV is consistent with the energy gap (∼ 3.07 eV) predicted through density functional theory. The electrochemical study showed that the sample exhibits a high specific capacitance of ∼ 252.5 F/g at a low scan rate of 5 mV/s.

Effects of sintering temperature on the microstructure, electrical and magnetic characteristics of copper-zinc spinel ferrite with possibility use as humidity sensors

In this paper was investigated the effect of sintering temperature on a copper-zinc spinel ferrite, Cu0.5Zn0.5Fe2O4, synthesised by using a sol-gel self-combustion method, as material with possible to application in the field of humidity sensors. In order to highlight the influence of temperature treatment on the structure, electrical and magnetic properties, the powders of ferrite were annealed at various temperatures: 850 °C, 900 °C, 950 °C, 1000 °C and 1050 °C. For the analyzed samples, the X-ray diffraction investigations have revealed the phase composition and the average crystallite size. By using techniques scanning electron microscopy (SEM) and atomic force microscopy (AFM) were find the influence of the sintering temperature on some parameters like the porosity, homogeneity, shape and size of the crystallites. We have also investigated the temperature variation of the electrical conductivity, relative magnetic permeability and relative permittivity variation with frequency at room temperature. Finally, we analyzed the time response, variations of electrical conductivity and relative permittivity for various humidity levels and the perspectives of applicability copper-zinc spinel ferrite as humidity sensor.

Wide-band gain enhancement of a pyramidal horn antenna with a 3D-printed epsilon-positive and epsilon-near-zero metamaterial lens

AbstractIn this article, we present a simple, low-cost solution for the gain enhancement of a conventional pyramidal horn antenna using additive manufacturing. A flat, metamaterial lens consisting of three-layer metallic grid wire is implemented at the aperture of the horn. The lens is separated into two regions; namely epsilon-positive and epsilon-near-zero (ENZ) regions. The structure of the ENZ region is constructed accounting the variation of relative permittivity in the metamaterial. By the phase compensation property imparted by the metamaterial lens, more focused beams are obtained. The simulated and measured results clearly demonstrate that the metamaterial lens enhances the gain over an ultra-wide frequency band (10–18 GHz) compared to the conventional horn with the same physical size. A simple fabrication process using a 3D printer is introduced, and has been successfully applied. This result represents a remarkable achievement in this field, and may enable a comprehensive solution for satellite and radar systems as a high gain, compact, light-weighted, broadband radiator.

High frequency response of grounding electrodes: effect of soil dielectric constant

paper is a postprint of a paper submitted to and accepted for publication in IET Generation, Transmission & Distibution (GTD) and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at the IET Digital Library.Abstract:Grounding electrodes have an important role in electric power transmission and distribution systems. They are used to prevent excessive hazardous voltages between metallic structures and ground in the case of system faults or lightning surges. It is important that they provide a low impedance path for the current in to the ground. The electrical properties of soil, which vary substantially with geographical location and time of year, affect the process considerably along with the properties of the grounding electrode itself, such as its dimensions.In order to have an accurate estimation of the developed overvoltages and the backflashover rate of the transmission lines due to a lightning strike, one has to take into account the effect of the value of the soil electrical parameters, such as the electrical conductivity and dielectric constant.This paper investigates the high frequency behavior of the grounding electrodes by solving a full-wave electromagnetic problem using the Finite Element Method (FEM). The focus is on taking into account the effect of the variation of soil relative permittivity which has been neglected in the previous studies of the grounding systems. This allows an evaluation of the response of grounding systems due to seasonal changes and specifically change of the water content of the soil, which would cause its electrical properties to vary significantly. This studydemonstrates the importance of considering the variation of relative permittivity of the soil especially in the modeling of electrodes buried in highly resistive soil.

Dielectric characterization of diseased human trabecular bones at microwave frequency

The objective of this study is to determine whether in vitro dielectric properties of human trabecular bones, can distinguish between osteoporotic and osteoarthritis patients’ bone samples. Specifically this study enlightens intra-patient variation of trabecular bone microarchitecture and dielectric properties, inter-disease comparison of bone dielectric properties, and finally establishes the correlation to traditional bone histomorphometry parameter (bone volume fraction) for diseased bone tissue. Bone cores were obtained from osteoporotic and osteoarthritis patients (n = 12). These were scanned using microCT to examine bone volume fraction. An open-ended coaxial probe measurement technique was employed to measure dielectric properties over the 0.5 – 8.5 GHz frequency range. The dielectric properties of osteoarthritis patients are significantly higher than osteoporotic patients; with an increase of 41% and 45% for relative permittivity and conductivity respectively. The dielectric properties within each patient vary significantly, variation in relative permittivity and conductivity was found to be greater than 25% and 1.4% respectively. A weak correlation (r = 0.5) is observed between relative permittivity and bone volume fraction. Osteoporotic and osteoarthritis bones can be differentiated based on difference of dielectric properties. Although these do not correlate strongly to bone volume fraction, it should be noted that bone volume fraction is a poor predictor of fracture risk. The dielectric properties of bones are found to be influenced by mineralization levels of bones. Therefore, dielectric properties of bones may have potential as a diagnostic measure of osteoporosis.

Effect of Relative Permittivity with Strain in Dielectric Elastomer Peristaltic Actuator

This article, exemplify the deformation behaviour of dielectric elastomer peristaltic actuator with variation in relative permittivity as a function of voltage induced strain. Modified model is proposed to predict the behaviour of peristaltic actuators, best suited for biomedical applications to transport incompressible fluids. Transportation is accomplished by a series of radially expanding and axially inextensible tubular modules, made up of dielectric elastomer. Consecutive equations are derived using the hypothesis of linear elasticity. The static electromechanical actuation performance is estimated and compared well with existing experimental as well as modelling data. Results indicate an efficient model is attained by considering crucial material parameters that significantly influence electromechanical performance. In the highlight, many other behaviours like viscoelasticity, dielectric loss, breakdown strength, etc. need attention to realize a reliable model for dielectric elastomer actuator towards commercial applications.

Structure and microwave dielectric behaviour of low-temperature-fired Li2Zn1−xCoxTi3O8 (x = 0–0.07) ceramics for low temperature co-fired ceramic applications

Low-temperature-fired Li2Zn1−xCoxTi3O8 (x = 0, 0.03, 0.04, 0.05, 0.06, 0.07) ceramics with 1.5 wt% Li2O–B2O3–SiO2–CaO–Al2O3 (LBSCA) glass as sintering aid were attained through a traditional solid-state-reaction method, and the relationship between their structures and microwave dielectric properties were thoroughly investigated. X-ray diffraction patterns revealed that the solid solutions composed of Li2ZnTi3O8 and Li2CoTi3O8 were produced. The main peaks were identified with the cubic spinel phase of the Li2(Zn,Co)Ti3O8. Co substitution successfully lowered the sintering temperature of Li2ZnTi3O8 to approximately 900 °C and accelerated its densification when LBSCA glass was used as the sintering aid. The cobalt content considerably influenced grain homogeneity, grain size and dielectric polarizability, as well as the variation in relative permittivity (er) and quality factor (Q × f). When x = 0.04, Li2Zn0.96Co0.04Ti3O8 ceramic sintered at 900 °C had the most uniform grain size and exhibited optimum microwave dielectric properties, having a relative permittivity of 21.61, Q × f of 79,100 GHz and temperature coefficient of resonance frequency (τf) of − 12.3 ppm/°C. Thus, it showed potential for low temperature co-fired ceramic applications.

Investigation of ferroelectric, piezoelectric and mechanically coupled properties of lead-free (Ba0.85Ca0.15) (Zr0.1Ti0.9)O3 ceramics

ABSTRACTLead-free piezoelectric ceramic (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) has been synthesised by solid-state sintering method and the effect of grain size on ferroelectric, piezoelectric, dielectric, mechanical and piezo-electro-mechanical properties was systematically studied. The compacted powders were sintered at three temperatures i.e. 1450°°C, 1500°C and 1550°C for an optimised duration of 5 h and they have exhibited well resolved morphotropic phase boundary with an average grain size ranging from 10 to 25 µm. Enhanced piezoelectric charge, d33 ∼ 560 pC/N and voltage, g33 ∼ 14.3 mV m/N coefficients were obtained for the 1450°C sintered BCZT sample. A maximum strain of around ∼0.14% was obtained which is comparable to that of lead-based piezoelectrics. Variation of relative permittivity with temperature revealed that the curves are independent of frequency, indicating the typical relaxor ferroelectric nature of the samples. A systematic study on cyclic loading was performed to evaluate piezo-electro-mechanical coefficients at different loads which showed hysteresis behaviour. High value of elastic modulus (E) and hardness (H) i.e. 262.7 ± 38.1 GPa and 13.7 ± 1.7 GPa were exhibited by samples sintered at 1450°C, which is higher than that of BCZT synthesised by wet-chemical methods. The results are discussed.

Hacking a soil water content reflectometer to measure liquid level

A method for converting a soil water reflectometer to a water level sensor is presented. The sensor essentially records the time of travel of an electromagnetic pulse along two parallel rods, which is then used to infer the relative permittivity (dielectric constant) of the medium around these two rods. While the sensor is designed to capture the relative permittivity variation of soil with its moisture content, the immersion depth of the rods in water (or potentially other dielectric liquids) also influences the average dielectric constant of the air-water medium between the rods (consequently affecting its permittivity). Here we show how this change in permittivity can be calibrated to measure small liquid depths. An empirical calibration equation is developed; it accounts for the impact of water salinity, whereas the temperature effect on the measurements is shown to be negligible.

The Effect of Using Microwave Synthesized ZnNb2O6 Powders on the Dielectric Properties of Sintered Products

In this study ZnNb2O6 (ZN) powder, which was synthesized using a microwave heating method, was used to prepare ZN ceramics via conventional and microwave sintering methods. The results show that all samples were single phase with no second phases present. The maximum densities obtained for microwave and conventionally sintered samples were 94.6% and 93.8%, respectively, of the theoretical value at 1250°C. SEM analysis showed that for all sintering temperatures, microwave sintered samples exhibit lower grain size values than those sintered via the conventional method. The variations in relative permittivity (er) for samples sintered at different temperatures via both methods followed those of density values. The highest values for er for conventionally and microwave sintered samples, which were observed at 1250°C, were 22.9 and 23.1, respectively. The variation of quality factor (Q × f) with sintering temperature for samples prepared through the microwave method also followed the density data. Q × f values of samples sintered via the conventional method were higher than those for samples sintered in a microwave oven because higher grain sizes were observed for these ceramics. The highest Q × f values for conventionally and microwave sintered samples were 26,197 GHz and 16,200 GHz, respectively.

Multilayer Functional Tapes Cofired at 450 °C: Beyond HTCC and LTCC Technologies.

This paper reports the first ultralow sintering temperature (450 °C) cofired multifunctional ceramic substrate based on a commercial lead zirconium titanate (PZ29)-glass composite, which is fabricated by tape casting, isostatic lamination, and sintering. This substrate was prepared from a novel tape casting slurry composition suitable for cofiring at low temperatures with commercial Ag electrodes at 450 °C. The green cast tape and sintered substrate showed a surface roughness of 146 and 355 nm, respectively, suitable for device-level fabrication by postprocessing. Additionally, the ferroelectric and piezoelectric studies disclosed low remnant polarization due to the dielectric glass matrix with average values of piezoelectric coefficient (+ d33) and voltage coefficient (+ g33) of 17 pC/N and 30 mV/N, respectively. The dielectric permittivity and loss value of the sintered substrates were 57.8 and 0.05 respectively, at 2.4 GHz. The variation of relative permittivity on temperature dependence in the range of -40 to 80 °C was about 23%, while the average linear coefficient of thermal expansion was 6.9 ppm/°C in the measured temperature range of 100-300 °C. Moreover, the shelf life of the tape over 28 months was studied through measurement of the stability of the dielectric properties over time. The obtained results open up a new strategy for the fabrication of next-generation low-cost functional ceramic devices prepared at an ultralow temperature in comparison to the high-temperature cofired ceramic and low-temperature cofired ceramic technologies.

Four Dielectric Substrate Analysis for Millimeter Wave Application

Substrate Integrated Waveguide technology is most promising technology to develop millimeter microwave components. The selection of substrate is very important in millimeter microwave design. By selecting a good substrate to design any microwave components which gives good results. In this paper various substrates materials like RT duriod 5880, Rogers 4350, FR4 and Glass are considered to design a hybrid coupler at 60 GHz which is suitable for millimeter wave applications. The results are discussed with respect to reflection coefficient, VSWR, insertion loss, relative permittivity variation with frequency, surface current variation, loss tangent variation and losses. A good substrate gives good mechanical support at higher frequency operation. RT duriod 5880 substrate is most suitable for millimeter wave applications like RADAR and 5G. All the design parameter values meeting required standards.

Ultra‐low temperature sintering microwave dielectric ceramics based on Ag2O–MoO3 binary system

AbstractThe Ag2Mo2O7 and Ag6Mo10O33 ceramics for ultra‐low temperature co‐fired ceramic application were prepared by the solid‐state reaction route. The optimized densification temperatures of Ag2Mo2O7 and Ag6Mo10O33 are 460°C and 500°C, respectively. The phase structures and microstructures of these ceramics were systematically studied. The Ag2Mo2O7 ceramic sintered at 460°C/4 h exhibits excellent microwave dielectric properties with εr=13.3, Q×f=25 300 GHz and τf=−142 ppm/°C at 9.25 GHz. The Ag6Mo10O33 ceramic sintered at 500°C/4 h shows the microwave dielectric properties with εr=14.0, Q×f=8500 GHz and τf=−50 ppm/°C at 9.00 GHz. Moreover, when Ag2Mo2O7 samples are sintered at ultra‐low sintering temperatures of 420°C‐490°C, the Q×f values of them are all above 20 000 GHz. Besides, the Ag2Mo2O7 ceramic does not react with silver powder or aluminum powder. The variation of relative permittivity, resonant frequency, and Q×f values as a function of operating temperature has been also studied. All the results indicate that the Ag2Mo2O7 ceramic is a good candidate for ultra‐low temperature co‐fired microwave devices.

Incipient ferroelectric to a possible ferroelectric transition in Te4+ doped calcium copper titanate (CaCu3Ti4O12) ceramics at low temperature as evidenced by Raman and dielectric spectroscopy

Partial replacement of Ti4+ by Te4+ ions in calcium copper titanate lattice improved its dielectric behaviour mostly due to cubic-to-tetragonal structural transformation and associated distortion in TiO6 octahedra. The relative permittivity values (23–30 x 103) of Te4+ doped ceramics is more than thrice that of un-doped ceramics (8 x 103) at 1 kHz. A decreasing trend in relative permittivity with increasing temperature (50–300 K) is observed for all the samples. Barrett’s formula, as a signature of incipient ferroelectricity, is invoked to rationalize the relative permittivity variation as a function of temperature. A systematic investigation supported by temperature dependent Raman studies reveal a possible ferroelectric transition in Te4+ doped ceramic samples below 120 K. The possible ferroelectric transition is attributed to the interactions between quasi-local vibrations associated with the micro-clusters comprising TiO6 and TeO6 structural units and indirect dipole-dipole interactions of off-center B–cations (Ti4+ and Te4+) in double perovskite lattice.

Internal configuration and electric potential in planar negatively charged lipid head group region in contact with ionic solution

The lipid bilayer composed of negatively charged lipid 1-palmitoyl-3-oleoyl-sn-glycero-3-phosphatidylserine (POPS) in contact with an aqueous solution of monovalent salt ions was studied theoretically by using the mean-field modified Langevin–Poisson–Boltzmann (MLPB) model. The MLPB results were tested by using molecular dynamic (MD) simulations. In the MLPB model the charge distribution of POPS head groups is theoretically described by the negatively charged surface which accounts for negatively charged phosphate groups, while the positively charged amino groups and negatively charged carboxylate groups are assumed to be fixed on the rod-like structures with rotational degree of freedom.The spatial variation of relative permittivity, which is not considered in the well-known Gouy–Chapman (GC) model or in MD simulations, is thoroughly derived within a strict statistical mechanical approach. Therefore, the spatial dependence and magnitude of electric potential within the lipid head group region and its close vicinity are considerably different in the MLPB model from the GC model.The influence of the bulk salt concentration and temperature on the number density profiles of counter-ions and co-ions in the lipid head group region and aqueous solution along with the probability density function for the lipid head group orientation angle was compared and found to be in qualitative agreement in the MLPB and MD models.

Investigation on the effect of sintering under oxygen atmosphere on microstructure and microwave dielectric properties of ZnNb 2 O 6 ceramics

The effect of sintering in air and oxygen atmospheres on microstructure and microwave dielectric properties of ZnNb2O6 ceramics has been investigated and compared. For most cases samples sintered in oxygen atmosphere exhibited higher density than those sintered in air atmosphere. The highest densities obtained for samples sintered in air and oxygen atmospheres were 93.6 and 95.2% of the theoretical value, respectively. The variation of relative permittivity (e r) values with temperature for samples sintered in air and oxygen atmospheres followed the variation in the density values. The highest values of e r for samples sintered in air and oxygen atmospheres were 22.6 and 23.5, respectively. A considerable improvement in Q × f (Q and f are quality factor and resonant frequency, respectively) was obtained for most sintering temperatures when sintering was performed in oxygen atmosphere. The highest Q × f obtained for samples sintered in air and oxygen atmospheres were 82,688 and 81,204 GHz, respectively. Temperature coefficient of resonant frequency (τ f) values closer to the ideal value (0 ppm/°C) was exhibited by samples sintered in oxygen atmosphere. The best values of τ f for air and oxygen sintering atmospheres are −59.4 and −48.6 ppm/°C, respectively.

The Effect of Niobium Doping on the Electrical Properties of 0.4(Bi0.5K0.5)TiO₃-0.6BiFeO₃ Lead-Free Piezoelectric Ceramics.

Ceramics in the system (Bi0.5K0.5)TiO3-BiFeO3 have good electromechanical properties and temperature stability. However, the high conductivity inherent in BiFeO3-based ceramics complicates measurement of the ferroelectric properties. In the present work, doping with niobium (Nb) is carried out to reduce the conductivity of (Bi0.5K0.5)TiO3-BiFeO3. Powders of composition 0.4(K0.5Bi0.5)Ti1−xNbxO3-0.6BiFe1−xNbxO3 (x = 0, 0.01 and 0.03) are prepared by the mixed oxide method and sintered at 1050 °C for 1 h. The effect of Nb doping on the structure is examined by X-ray diffraction. The microstructure is examined by scanning electron microscopy. The variation in relative permittivity with temperature is measured using an impedance analyzer. Ferroelectric properties are measured at room temperature using a Sawyer Tower circuit. Piezoelectric properties are measured using a d33 meter and a contact type displacement sensor. All the samples have high density, a rhombohedral unit cell and equiaxed, micron-sized grains. All the samples show relaxor-like behavior. Nb doping causes a reduction in conductivity by one to two orders of magnitude at 200 °C. The samples have narrow P-E loops reminiscent of a linear dielectric. The samples all possess bipolar butterfly S-E loops characteristic of a classic ferroelectric material. Nb doping causes a decrease in d33 and Smax/Emax.

Ray Tracing Theory in a Radially Uniaxial Sphere

Ray tracing theory for a radially uniaxial dielectric sphere is presented in this communication. Reflection and transmission of the plane waves obliquely incident on the spherical interface between air and uniaxial are briefly examined and the general formulations for phase velocities as well as the refractive indices of the ordinary and extraordinary waves propagating in a radially uniaxial medium are investigated. The ray tracing method is implemented for both ordinary and extraordinary rays and the results are applied to evaluate the propagation paths and arrival times of the shortcut wave returns appearing in the transient backscattering response of a uniaxial dielectric sphere. The effect of the variation in relative permittivity on the arrival times of shortcut waves is studied. The results of the ray tracing method are compared with those computed using the Mie and Debye series solutions with good agreement.