Showing papers on "Relative permittivity published in 2001"

Uncertainty of complex permittivity measurements by split-post dielectric resonator technique

Abstract: Split-post dielectric resonators operating at frequencies 1.4–5.5 GHz were used to measure complex permittivity of single crystal standard reference dielectric materials with well known dielectric properties previously measured by other techniques. Detailed error analysis of permittivity and dielectric loss tangent measurements has been performed. It was proved both theoretically and experimentally that using split post resonators it is possible to measure permittivity with uncertainty about 0.3% and dielectric loss tangent with resolution 2×10 −5 for well-machined laminar specimens.

Niobate-based microwave dielectrics suitable for third generation mobile phone base stations

Abstract: High unloaded quality factor (Qu), zero temperature coefficient of resonant frequency (τf) and high relative permittivity (er) microwave dielectric ceramics have been fabricated based on BaZn1/3Nb2/3O3. Properties have been optimized for the composition, 0.9Ba([Zn0.60Co0.40]1/3Nb2/3)O3–0.1Ba(Ga0.5Ta0.5)O3 for which Qu=32 000 @ 3.05 GHz, er=35, and τf=0. The new compounds are disordered according to x-ray diffraction (XRD) and may be indexed using a simple perovskite unit cell, a=4.09 A. Small peaks (e.g., d≈3.01 A, relative intensity, 4.5) attributed to a barium niobate second phase are also present in XRD patterns. These ceramics are suitable in terms of cost and performance for base stations supporting third generation architecture.

Effects of very thin strain layers on dielectric properties of epitaxial Ba0.6Sr0.4TiO3 films

Abstract: We have epitaxially grown Ba0.6Sr0.4TiO3 (BST-0.4) thin films on MgO(001) substrates. By inserting a very thin Ba1−xSrxTiO3 (x=0.1–0.7) interlayer between the MgO substrate and the main layer of BST-0.4, we are able to manipulate the degree of the stress in BST-0.4 films. We have controlled the stress states, i.e., the lattice distortion ratio (D=in-plane lattice constant/out-of-plane lattice constant) of the BST-0.4 films by varying the chemical composition of the interlayers. We have found that small variations of D value can result in significantly large changes of dielectric properties. A BST-0.4 film under small tensile stress, which has a D value of 1.0023, shows the largest dielectric permittivity and tunability.

An improved transmission-line model of grounding system

Abstract: This paper presents a time-domain transmission line model of grounding system, which includes the mutual electromagnetic coupling between the parts of the grounding structure and the influence of air-earth interface. The model can be used to simulate the transient behavior of the grounding system under lightning strike. The simulation results are in good agreement with that of the model based on the solution of full Maxwell's equations. The influence of different parameters, such as the soil relative permittivity /spl epsi//sub /spl tau//, the soil resistivity /spl rho/, and the conductivity and diameter of the conductor, on the transient voltage distribution of the grounding system is investigated. It shows that, among the parameters investigated here, the soil resistivity is the most important parameter that affects the transient response of bare buried conductors. The soil permittivity has very little influence on the transient response of the grounding system when the grounding system is buried in the soil with low resistivity, but have moderate influence in the soil with extremely high resistivity. The conductivity of the conductor and skin effect have practically no influence on the peak transient voltage of the grounding system. Increase in conductor diameter tends to decrease the peak transient voltage. The model presented in this paper is simple, but sufficiently accurate and can be used easily in engineering practice. Since the model is in the time domain, it could be easily coupled to the other time-domain models of nonlinear surge-protection components.

Effect of purification of the electrical conductivity and complex permittivity of multiwall carbon nanotubes

Abstract: In this work we report on the complex permittivity spectra and electrical conductivity of both as-fabricated and graphitized multiwall carbon nanotubes (MWNTs). The high-temperature annealing removes the Fe3C catalyst particles present in the as-fabricated material, enabling the intrinsic MWNT properties to be measured. The permittivity spectra of 1 wt % MWNT-polystyrene composite films are measured from 75 to 1875 MHz. Comparison of measurements with an appropriate effective medium model shows that the residual catalyst inclusions in the core of the nanotube increase the average electrical conductivity by approximately a factor of 3.5.

Thickness dependent dielectric strength of a low-permittivity dielectric film

Abstract: The dielectric strength of a promising interlevel low relative permittivity dielectric is investigated for various film thicknesses and temperatures by using I-V measurements with metal-insulator-semiconductor (MIS) structures. It is found that the dielectric breakdown mechanism also depends on thickness. For relatively thick films (thickness >500 nm), the dielectric breakdown is electromechanical in origin, i.e. the dielectric strength is proportional to the square root of Young's modulus of the films. By scanning electron microscopy (SEM) observation, a microcrack in thicker films may contribute to a lower value of Young's modulus, which may confirm that the electromechanical breakdown is the dominant mechanism for dielectric breakdown of thicker films. In addition, the thickness dependent dielectric strength can be described by the well-known inverse power-law relation by using different exponents to describe different thickness ranges, However for thinner films, i.e., <500 nm, the experimentally observed relationships among the dielectric strength, Young's modulus, and film thickness cannot be explained by the existing models.

First-principles study of dynamical and dielectric properties of tetragonal zirconia

Abstract: Using the variational density-functional perturbation theory, we investigate the dynamical and dielectric properties of tetragonal zirconia (t-ZrO2). We obtain the phonon frequencies at the center of the Brillouin zone, the Born effective charge tensors, and the dielectric permittivity tensors. For all these quantities, a comparison is made with the related values in the cubic phase. The Born effective charge tensors are found to be quite anisotropic. The calculated phonon frequencies present a better agreement with the infrared and Raman experimental values than previous theoretical calculations. We propose symmetry assignments that solve the contradictions existing in the literature. The electronic and static dielectric permittivity constants are in relatively good agreement with experimental values. We perform a detailed analysis of the contribution of the various infrared-active modes to the static dielectric permittivity and explain its strong anisotropy.

Dielectric characterisation of ceramics from the TiO2–TeO2 system

Abstract: Compositions from TiO 2 –TeO 2 tie line were characterised using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and dilatometry. Results show that the only binary compound existing on the tie line is TiTe 3 O 8 . Single-phase TiTe 3 O 8 was synthesised at 700°C in air and sintered at 720°C to ∼95% of theoretical density. Such ceramics exhibit a relative permittivity of 50, a Q × f -value of 30,600 GHz and a temperature coefficient of resonant frequency ( τ f ) of +133 ppm/°C, measured at ∼5 GHz. The concentration of structural defects in the TiTe 3 O 8 grains is negligible which makes the dielectric properties of TiTe 3 O 8 ceramics insensitive to variations in the heat-treatment conditions. The TiTe 3 O 8 compound is chemically compatible with TeO 2 , which displays a negative temperature coefficient of resonant frequency (a relative permittivity of 19.3, a Q × f -value of 30,000 GHz and a temperature coefficient of resonant frequency of −119 ppm/°C for TeO 2 ceramics with ∼ 20% porosity) and can be used for compensation of the temperature coefficient of resonant frequency of the TiTe 3 O 8 compound. Ceramics from the TiTe 3 O 8 –TeO 2 subsystem can be sintered to >97% of theoretical density at temperatures as low as 670°C, which together with the fact that the ceramics exhibit a highly tunable τ f , relative permittivity around 30 and a Q × f -value of ∼22,000 GHz suggests a potential for use in LTCC technology.

Dielectric and ferroelectric properties of SrBi4Ti4O15 single crystals

Abstract: SrBi4Ti4O15 single crystals were grown, and their dielectric and ferroelectric properties were investigated along the a(b) axis and c axis, separately. The dielectric permittivity at 1 MHz was 1900 along the a(b) axis at the Curie temperature of 520 °C. This value was ten times higher than that along the c axis. With respect to the ferroelectricity, the saturated remanent polarization was 29 μC/cm2 and the saturated coercive field was 26 kV/cm along the a(b) axis under an electric field of 59 kV/cm, and ferroelectricity was not observed along the c axis.

Phase transitions and microwave dielectric properties in the perovskite-like Ca(Al0.5Nb0.5)O3−CaTiO3 system

Abstract: Phase transitions and microwave dielectric properties in the (1−x)Ca(Al0.5Nb0.5)O3–xCaTiO3 system were analyzed using x-ray and neutron powder diffraction, transmission electron microscopy, Raman spectroscopy, and dielectric measurements at microwave frequencies (2–8 GHz). Rietveld structural refinements demonstrated that both end compounds exhibit similar octahedral tilted frameworks, while in Ca(Al0.5Nb0.5)O3, tilting is superimposed onto NaCl-type ordering of Al and Nb on the B sites. Accordingly, the room-temperature structures of CaTiO3 and Ca(Al0.5Nb0.5)O3 are described by orthorhombic Pbnm and monoclinic P21/n symmetries, respectively, with similar lattice parameters, √2ac×√2ac×2ac (where ac is the lattice parameter of cubic perovskite). The (1−x)Ca(Al0.5Nb0.5)O3–xCaTiO3 system features both cation ordering and octahedral tilting phase transitions. The Ca(Al0.5Nb0.5)O3 structure remains ordered at least up to 1625 °C. However, the temperature of the order/disorder transition decreases rapidly with increasing Ti content, which correlates with a progressive increase of cation disorder in the specimens. A disordered structure is attained at x=0.5. For the “solid solutions,” the nonlinear dependence of both permittivity e and the temperature coefficient of the resonant frequency τf on Ti content corresponds to a linear dependence of the macroscopic polarizability on composition; that is, the oxide additivity rule was closely obeyed. Therefore, this rule can be used to predict e and τf for any intermediate composition from the permittivities and temperature coefficients of permittivity of the end compounds. A zero temperature coefficient of the resonant frequency occurs at the composition x≈0.5 with a relative permittivity of 50 and a Qf value of approximately 30 000 GHz (@4 GHz).

Structural and DC electrical investigations of ZnO thin films prepared by spray pyrolysis technique

Abstract: Thin films of ZnO onto glass substrate at different substrate temperatures Ts, ranging from 180°C to 450°C, have been prepared using a spray pyrolysis process. X-ray diffraction showed that the films prepared at Ts greater than 300°C exhibit the hexagonal wurtzite structure with a preferential orientation along (0 0 2) direction. All electrical properties have been investigated for films at Ts=400°C. A relative permittivity of 9.8 is calculated from the capacitance measurements. Thermally generated electron concentration, n0=(2.8–6.7)×1010 m−1, and trapping factor, θ=(8.02–18.22)×10−12 have been evaluated from the analysis of current–voltage characteristics at room temperature assuming a plausible value of carrier mobility, 1.8 m2 V−1 s−1. The obtained values n0 and θ are correlated with the crystallite size.

Electromagnetic materials enter the negative age

Abstract: Electrical permittivity and magnetic permeability are concepts that are deeply embedded in electromagnetism. The electrical permittivity of a material determines its response to an applied electric field, while the permeability summarizes how it reacts to an applied magnetic field. Together the permittivity and permeability determine how the material responds to electromagnetic radiation of all wavelengths. Indeed, the speed of light in vacuum can be defined as c = 1/√0μ0, where 0 is the permittivity of free space and μ0 is the permeability.

Complex permittivity measurements at Ka-Band using rectangular dielectric waveguide

Abstract: The rectangular dielectric waveguide (RDWG) technique has been developed for the determination of the dielectric constant of materials from effective refractive index measurements in the Q and W bands. This paper describes the use of an optimization method in conjunction with the RDWG technique for the determination of both the dielectric constant and loss tangent of materials at Ka-Band. The effect of the uncertainty in the measured sample thickness is presented.

A simple method for measuring the relative permittivity of printed circuit board materials

Abstract: This paper presents a simple method to measure the relative permittivity of glass-epoxy printed circuit boards (PCBs). In this method, the relative permittivity as a function of frequency is measured using an actual PCB. In order to estimate the relative permittivity, the reflection coefficient is measured with a network analyzer. The relative permittivity is calculated by observing the frequencies of the resonant cavity modes. We show that the relative permittivity of an FR-4 sample decreases from 4.3 to 4.2 at frequencies from 300 MHz to 2 GHz.

Mapping of the resistivity, susceptibility, and permittivity of the earth using a helicopter-borne electromagnetic system

Abstract: Interpretation of helicopter-borne electromagnetic (EM) data is commonly based on the mapping of resistivity (or conductivity) under the assumption that the magnetic permeability is that of free space and dielectric permittivity can be ignored. However, the data obtained from a multifrequency EM system may contain information about the magnetic permeability and dielectric permittivity as well as the conductivity. Our previous work has shown how helicopter EM data may be transformed to yield the resistivity and magnetic permeability or, alternatively, the resistivity and dielectric permittivity. A method has now been developed to recover the resistivity, magnetic permeability, and dielectric permittivity together from the transformation of helicopter EM data based on a half-space model. A field example is presented from an area which exhibits both permeable and dielectric properties. This example shows that the mapping of resistivity, magnetic permeability, and dielectric permittivity together yields more credible results than if the permeability or permittivity is ignored.

Quasi-static effective permittivity of periodic composites containing complex shaped dielectric particles

Abstract: A methodology is described for computing the quasi-static effective permittivity of a two-dimensional (2-D) or three-dimensional (3-D) lattice of dielectric particles. The particles in this composite material may have complicated shapes. This methodology uses a moment method based technique to determine the electric dipole moments of the particles immersed in a uniform electric field. The effective permittivity is then obtained using an appropriate macroscopic model. With this methodology, the mutual interaction between particles can be accounted for accurately. The computed effective permittivity for round cylinders and spheres suspended in a host are compared with our previous T-matrix method results as well as the Maxwell Garnett (MG) formula predictions. Three additional examples involving square (2-D), rounded square (2-D), and spherical (3-D) dielectric inclusions are also given, illustrating the shape effects on the computation of the quasi-static effective permittivity. While the square- and cubic-shaped particles can possess great mutual interaction, surprisingly their effective permittivity is well predicted for all volume fractions by the simple MG formula in both 2-D and 3-D problems.

Electrical parameters of soils in the frequency range from 1 kHz to 1 GHz, using lumped‐circuit methods

Abstract: For studying electrical properties of soil samples with various compositions and water contents, we applied a lumped-circuit approach. The extension of this method up to 1GHz was made possible by using a coaxial sample holder. The complex electrical parameters of soils, such as the relative permittivity , conductivity , and resistivity , were obtained by measuring the magnitude Z and phase ϕ of the sample impedance . The experimental setup is described in our previous paper [Levitskaya and Sternberg, 2000]. The relative real permittivity e′ and imaginary permittivity (dielectric losses) e″ for high-loss soils from Arizona decrease with frequency and increase with water content. Regression equations, derived for the relative permittivity e′ versus water content at a given frequency, can be used to determine the water content in soil from e′ data. The third-degree polynomial equations, which relate the relative permittivity to the volumetric soil moisture content, are different for various frequencies. The complex electrical resistivity components ρ′ and ρ″ reveal a time-dependent polarization process at frequencies above 1 MHz, which shifts to higher frequencies with increasing water content. The propagation parameters, such as attenuation constant α, phase velocity Vp, and penetration depth P, which we calculated from the electrical parameters, also depend on soil wetness. Our comparison of the electrical and propagation parameters for different soils shows that the high-loss soil samples from Avra Valley, Arizona, have higher values e′ and e″, higher attenuation constant α, and lower penetration depth P than the low-loss soils from Brookhaven, New York. For example, at 500 MHz, a high-loss soil (Avra Valley) with volumetric moisture content of ∼10%, exhibits an attenuation of 43 dB/m, whereas for a low-loss soil (Brookhaven) with the same wetness the attenuation constant is only 4 dB/m. We also note that very dry, clean sand in a sheltered “sand box,” which is a favorite medium for testing ground-penetrating radar (GPR), is usually not representative of natural conditions. Therefore, GPR data from such “sand box” experiments must be used with considerable caution because they yield unrealistically large penetration depths and unnatural target responses.

Estimation of conductivity and permittivity of water trees in PE from space charge distribution measurements

Abstract: Using an improved pulsed electroacoustic system which is capable of measuring space charge distribution at minimum intervals of 25 /spl mu/s, the charge distribution inside water-treed polyethylene (PE) was examined. From the results, the frequency dependencies of conductivity and permittivity were examined for water trees grown in PE. The conductivity of the water-treed region is found to be >10/sup 10//spl times/ higher than that of non-treed regions, while the permittivity increase is only slight.

Dielectric ceramic, process for producing the same and multilayer ceramic capacitor

Abstract: A dielectric ceramic obtained by providing a reaction product comprised of barium titanate double oxide represented by the formula (Ba1-h-i-mCahSriGdm)k(Ti1-y-j-nZryHfjMgn)O3 in which 0.995≤k≤1.015, 0≤h≤0.03, 0≤i≤0.03, 0.015≤m≤0.035, 0≤y<0.05, 0≤j<0.05, 0≤(y+j)<0.05 and 0.015≤n≤0.035; mixing less than 1.5 mol of Ma (Ba, etc.), less than 1.0 mol of Mb (Mn, etc.) and 0.5 to 2.0 mol of Mc (Si, etc.) with 100 mol of the reaction product; and firing the mixture. The obtained dielectric ceramic excels in moisture resistance; satisfies F characteristics of JIS and Y5V characteristics of EIA standards; has a relative permittivity of 9000 or higher; and excels in reliability at high temperature.

Test of universal scaling of ac conductivity in ionic conductors

Abstract: Electrical relaxation data of crystalline yttria-stabilized zirconia are used to analyze the permittivity change observed in the spectra of the real part of the permittivity in ionic conducting materials. It is found that this permittivity change is independent of both temperature and mobile-ion concentration, and it is determined solely by the degree of interaction among ions in the relaxation process. This finding is at odds with an expression for the permittivity change in the framework of a proposed universal ac conductivity scaling law for glassy ionic conductors. On the other hand, not only the total permitivity change, but also the particular frequency dependence of the permittivity spectra is found to be consistent with the analysis of electrical relaxation in terms of the electric modulus. The results of this work give further support to the use of the electric modulus in describing electrical relaxation in ionic conductors.

Model for the charge trapping in high permittivity gate dielectric stacks

Abstract: The generation of traps in SiOx/ZrO2 and SiOx/TiO2 gate dielectric stacks during gate voltage stress of metal-oxide-semiconductor capacitors is investigated. The voltage and temperature dependence of the trap generation rate is extracted from the analysis of the gate current increase observed during the electrical stress. These data can be explained by a model based on a two-stage degradation process, i.e., (1) H+ proton generation in the high permittivity gate dielectric layer by the injected electrons and (2) transport of the H+ protons in the high permittivity material, resulting in bond breaking and trap generation. The threshold electron energy for H+ generation and the activation energy for H+ transport and bond breaking are extracted from fits to the experimental results.

Modified 2 gradient method and modified Born method for solving a two-dimensional inverse scattering problem

Abstract: This paper concerns the reconstruction of the complex relative permittivity of an inhomogeneous object from the measured scattered field. The parameter of interest is retrieved using iterative techniques. Four methods are considered, in which the permittivity is updated along the standard Polak–Ribiere conjugate gradient directions of a cost functional. The difference lies in the update direction for the field, and the determination of the expansion coefficients. In the modified gradient method, the search direction is the conjugate gradient direction for the field, and the expansion coefficients for field and profile are determined simultaneously. In the Born method (BM) the field is considered as the fixed solution of the forward problem with the available estimate of the unknown permittivity, and only the profile coefficients are determined from the cost function. In the modified Born method, we use the same field direction as in the BM, but determine the coefficients for field and profile simultaneously. In the modified2 gradient method, we use both field directions, and again update all coefficients simultaneously. Examples of the reconstruction of either metal or dielectric cylinders from experimental data are presented and the methods are compared for a range of frequencies.

Reduction-resistant dielectric ceramic compact and laminated ceramic capacitor

Abstract: A dielectric ceramic compact is provided which can decrease loss and heat generation under high frequency and high voltage or large current conditions, which exhibits a stable insulating resistance by AC or DC loading, and which can form a laminated ceramic capacitor using nickel or the like as an internal electrode material. The reduction-resistant dielectric ceramic compact is formed of an auxiliary sintering agent and a solid solution containing barium titanate as a primary component represented by the formula ABO3+aR+bM, where R is a compound containing an element such as La, and M is a compound containing an element such as Mn. In addition, 1.000

Tailoring the temperature coefficient of capacitance in ferroelectric varactors

Abstract: Two BaxSr1-xO3, films with different contents of Ba (Ba0.25Sr0.75O3 and Ba0.75Sr0.5O3), separated by a MgO film, are used to fabricate planar varactors with low temperature coefficient of capacitance (TCC), high tunability and low losses. The TCC of the varactors are small in the temperature interval between the dielectric permittivity peaks of the Ba0.25Sr0.75O3 and Ba0.75Sr0.5O3 films

Dielectric exchange force: a convenient technique for measuring the interfacial water relative permittivity profile

Abstract: Water relative permittivity profiles perpendicular to mica surfaces have been measured by atomic force microscopy using the force acting on uncharged tips when immersed in the mica double-layer. This force is modelled by the gradient of the electrostatic energy variation (dielectric exchange force) involved in the immersion of the tip with a relative permittivity eTip in the double layer region with eDL. The measured variable permittivity profile starting at e≈4 at the interface and increasing to e≈80 about 10 nm from the surface suggests a reorientation of water molecule dipoles in the presence of mica interfacial charges. Changes in water polarization are therefore responsible for the hydration or structural forces acting on the tips immersed in the inner double layer. Corroboration for the proposed model (dielectric exchange force) is given by the observation of an attractive force when metal-coated tips (eTip≈∞) are immersed in the mica double layer. Support for the change in the water relative permittivity at the interface is given by measurements of only a repulsive force component when silicon nitride and silicon tips are immersed in solvent where there is no interaction between the mica surface and the solvent and, consequently, no solvent structuring at the interface.

Dielectric properties of GaN nanoparticles

Abstract: Three kinds of GaN samples (hexagonal coarse-grain powders, hexagonal nanoparticles and cubic nanoparticles) were synthesized by different methods. The room-temperature frequency spectra of the relative dielectric constant and that of the dielectric loss were measured in the frequency range of 100 Hz to 10 MHz. Analysis of these spectra indicates that the grain size of samples has great influence on the dielectric behavior of samples whereas the crystallography symmetry almost has no impact on the relative dielectric constant.

Permittivity measurement of thermoplastic composites at elevated temperature

Abstract: The material properties of greatest importance in microwave processing of a dielectric are the complex relative permittivity e = e’-je”, and the loss tangent, tan 8= This paper describes two convenient laboratory based methods to obtain e’, e” and hence tan 3 of fibre-reinforced thermoplastic (FRTP) composites. One method employs a microwave network analyzer in conjunction with a waveguide transmission technique, chosen because it provides the widest possible frequency range with high accuracy. The values of the dielectric constant and dielectric loss of glass fibre reinforced (33%) low density polyethylene, LDPE/GF (33%), polystyrene, PS/GE (33%), and Nylon 66/GE (33%), were obtained. Results are compared with those obtained by another method using a high-temperature dielectric probe.

Pretransitional behavior of dielectric permittivity on approaching a clearing point in a mixture of nematogens with antagonistic configurations of dipoles.

Abstract: The results of studies of static dielectric permittivity epsilon(T) in the isotropic phase of 4-cyano-4-pentylalkylbiphenyl and n-p-methoxybenzylidene-p'-butylaniline (5CB-MBBA) mixtures are presented. 5CB and MBBA are nematogens with antagonistic permanent dipole moments configurations. An increase in MBBA concentration strongly decreases the pretransitional effect. However, a derivative analysis detected the existence of a pretransitional anomaly even if its weakness made a straightforward epsilon(T) fit impossible. The obtained anomalies can be well portrayed by fluidlike equations, isomorphic to that applied in critical binary mixtures. Every time the same value of the specific heat critical exponent alpha approximately 0.5 was obtained. A preliminary discussion of the influence of the permanent dipole configuration on the pretransitional behavior of dielectric permittivity was also possible.

Dielectric properties of mashed potatoes

Abstract: The dielectric properties of mashed potatoes are measured as a function of sample temperature and preparation procedure. The temperature range for the first sample is between 10 and 80°C, the second sample is characterised in the temperature range from −17.7 to 20.7°C. The results show, that the impact of temperature on the dielectric properties at 2.45 GHz is small in the range above the freezing temperature. In the temperature range, where melting occurs, there is a sharp increase of the relative dielectric constant e′ and the loss factor e′′. The measured, inter- and extrapolated values of the dielectric properties are used to calculate the penetration depth δ p . This parameter can serve as an input parameter for the mathematical modelling of temperature profiles in microwave heating of food of cylindrical and slab-shaped geometry.