Showing papers on "Relative permittivity published in 1991"

Deposition and characterization of fullerene films

Abstract: Thermal sublimation of pure C60 and C70 has been used for depositing well‐characterized fullerene films on a variety of substrates. Film purity is determined by infrared absorption spectra and the extent of crystallinity of the face‐centered cubic structure by x rays. Thickness‐dependent optical and electrical measurements reveal uniform films over the thickness range 200–1000 A. We obtain optical absorption coefficients having values between those of Si and Ge and a relative permittivity having a value close to that of amorphous SiO2.

Dielectric studies of the soft mode and Goldstone mode in ferroelectric liquid crystals

Abstract: Different contributions to the dielectric permittivity in ferroelectric liquid crystals are discussed, with emphasis on the soft mode and the Goldstone mode and their location in the dielectric spectrum. Experimentally, the complex dielectric permittivity has been studied as a function of temperature and frequency in the range 5 Hz - 13 MHz for three different ferroelectric liquid crystal materials. The main problems encountered in dielectric measurements at low and high frequency are discussed in some detail. The soft mode dielectric behaviour has been studied as a function of temperature, frequency and bias electric field. The applicability of the Curie-Weiss law for the soft mode dielectric contribution in the A* phase was analyzed. In the C* phase the temperature dependence of the dielectric contribution of the Goldstone mode has been measured. By applying a bias electric field, we have been able to study the soft mode dielectric behaviour also deep into the C* phase. In the A* and C* phases ...

Measurement of dielectric constant using a microstrip ring resonator

Abstract: An approach for measuring the permittivity of dielectric materials by means of a microstrip ring resonator is presented. The method is used in conjunction with the variational calculation of the line capacitance of a multilayer microstriplike transmission line to compute the effective permittivity and hence the resonant frequency of the ring. The results are compared with measurements made in X-band waveguide cavity-by-cavity perturbation techniques and tend to confirm that microstrip resonators can be used for dielectric measurements. However, for materials having a large dielectric constant, comparative results seem to diverge rapidly. >

Relative permittivity and dielectric loss tangent of substrate materials for high-Tc superconducting film

Abstract: We measure the relative permittivitye r and dielectric loss tangent tanδ of substrate materials for high-T c superconducting films at 18–300 K and at 5–10 GHz using the cavity-resonator method. The materials measured are single crystals of MgO, LaAlO3, YAlO3, LaSrGaO4, NdGaO3, sapphire, and ZrO2 ceramic. Thee r values are 10–30 and become almost constant below about 50 K. The tanδ values decrease with decreasing temperature and are below 1×10−5 at 77 K except for those of NdGaO3 and ZrO2 ceramic. This suggests that the tanδ values of MgO, LaAlO3, YAlO3, LaSrGaO4, and sapphire do not limit the quality factors of microwave passive components fabricated using high-T c superconducting films. It is also demonstrated that the tanδ of the substrate material is strongly affected by impurities.

Method and apparatus for measuring the permittivity of materials

Abstract: A method and apparatus for determining the permittivity of a sample is disclosed. The method includes applying an AC electrical signal in the microwave frequency range via a coaxial probe having an end position near the sample and measuring the reflection coefficient of the sample. The complex permittivity of the sample is determined from an admittance parameter of the sample/probe combination and a system constant. The system constant is determined by measuring the reflection coefficients of four standards having known complex permittivity. The admittance parameter of the sample/probe combination is determined from the admittance parameters of two standards/probe combinations and the measured reflection coefficients of the sample and the four standards. The admittance parameters of the two standard/probe combinations are determined from the known complex permittivities of the two standards and the system constant. The apparatus includes a coaxial probe having an end positioned near the sample, a microwave frequency generator and a device for measuring a reflection coefficient are connected to the other end of the coaxial probe. A microprocessor determines the complex permittivity of the sample from the measured reflection coefficients of the sample and four standards having known complex permittivities.

Field behaviour at a triple junction in composite dielectric arrangements

Abstract: The author examines the field behaviour at and near various points of contact between a solid dielectric and a conductor. The topics discussed include analytical expressions and numerically calculated results of field strength as well as their potential practical applications. The effect of conductivity is explained in some cases. There are principally three contact conditions depending on the contact angle; 90, 0 to 90, and 0 degrees . The contact angle between 0 and 90 degrees results in a field concentration of K*l/sup m/ near a contact point where l is the distance from the point. In the case of zero contact angle, where a solid dielectric and a conductor are both rounded or planar, a simple mathematical function expresses the effect of relative permittivity on the field concentration at the contact. >

Dielectric permittivity and loss of an aluminum-filled epoxy resin

Abstract: Dielectric behaviour of an epoxy resin filled with 0–30 wt% aluminum powder is reported. Permittivity, loss index and dissipation factor are characterized as a function of temperature in the range 20–150°C and frequency in the range 20 Hz–20 kHz. The filled resin shows a higher permittivity and higher dielectric loss. An interfacial or Maxwell-Wagner-Sillars polarization effect is clearly evident and glass transition temperature is unaffected by the filler.

Analysis of microstrip antennas on circular-cylindrical substrates with a dielectric overlay

Abstract: The use of dyadic Green's functions and the moment method is explored for the solution of microstrip antenna problems on circular cylindrical substrates. The dyadic Green's functions of the electric type are obtained for a medium consisting of three cylindrical dielectric layers concentric with a perfectly conducting cylinder, and integral equations are developed for the evaluation of the electromagnetic fields. The effect of a dielectric overlay on the resonant frequency of a cylindrical-rectangular microstrip antenna is analyzed. The patch is directly fed by means of a microstripline printed along the cylinder axial direction. The results show that the effect of the dielectric overlay is substantial when its relative permittivity and thickness are increased, such that this effect has to be very carefully considered in the design of microstrip antennas. >

Detection and imaging of electric conductivity and permittivity at low frequency

Abstract: The authors discuss low-frequency electrical impedance imaging, the process of constructing images of the electrical impedance of a body's interior based on measurements of voltage and current made at the body's surface. The electrical impedance accounts for both resistivity and permittivity. It is shown how permittivity can be exploited to improve the performance of an electrical impedance imaging system. It is shown that explicit use of the independent information in the data due to the permittivity will enhance a system's ability to distinguish objects in the interior of a body. In addition. the results of experiments performed using the Rensselaer ACT 2 system on a saline bath containing various objects are reported. These objects include both living tissue and metal conductors with oxide layers. The system's ability to distinguish these objects is demonstrated. and gray scale images of both their resistivity and permittivity distributions are given. >

Ethane-1,2-diol–2-methoxyethanol solvent system. Dependence of the relative permittivity and refractive index on the temperature and composition of the binary mixture

Abstract: The extrathermodynamic parameters, relative permittivity (Iµr) and refractive index (n), have been measured for ethane-1,2-diol–2-methoxyethanol binary mixtures over the entire composition range, at various temperatures ranging between –10 and 80 °C. For this system, as far as for many solvent–cosolvent systems which are useful for analytical and electrochemical applications, the properties cited above are continuous but not linear functions of the binary composition.Various equations have been applied in order to establish the best regression models for the relationship y=f(X), where X is the composition of the mixture. On the whole, minima occurred in the excess function (IµE), showing the existence of various solvent–cosolvent complexes of different stoichiometric ratios (2 : 1, 1 : 1 or 1 : 2) and of different thermostabilities, which may be interpreted in terms of moderate interactions such as dipolarity, polarizability and hydrogen bonding between the mixed solvents. Among the above complexes, the ethane-1,2-diol–2-methoxyethanol 1 : 2 adduct is suggested to be the true ‘limiting mixture’, on the borderline between the types of behaviour typical of the two pure solvents. Furthermore, empirical patterns in the refractive index were used to scrutinize the most important mixing rules in order to determine the properties of the mixture on the basis of those of its pure components.

Pulse sharpening in a uniform LC ladder network containing nonlinear ferroelectric capacitors

Abstract: A new method of pulse sharpening is described in which the risetime of a high-voltage pulse is progressively reduced as it propagates along a uniform lumped-element delay line containing nonlinear ferroelectric capacitors. The capacitors are made from a barium-titanate-based ceramic dielectric whose relative permittivity reduces with applied voltage stress. The resultant drop in capacitance causes the phase velocity of an electrical pulse propagating on the delay line to increase with increasing pulse amplitude. Therefore, the time delay of each section of the line is also amplitude dependent, causing the crest of the pulse to catch up with the low-amplitude portion of its leading edge. In the experiment described, the risetime of the leading edge of a 28-kV voltage pulse was reduced from 280 to 50 ns as it propagated along a 15-section ladder network. It is found that the impedance of the ladder is amplitude dependent, and the problem of matching the line with a nonreactive linear load resistance is discussed. Techniques are described for characterizing the nonlinearity of the capacitors and also for measuring their loss. >

Broad-band simultaneous measurement of the complex permittivity tensor for uniaxial materials using a coaxial discontinuity

Abstract: A technique is presented for simultaneously measuring the complex values of the permittivity tensor of uniaxial materials. A gap in a coaxial line is filled with the material under test. Complex elements of the permittivity tensor are computed from measurements of the S-parameters (S/sub 11/ and S/sub 21/) made on the gap taking into account higher order modes excited at the discontinuity. The authors demonstrate that this problem is reduced to two systems, each containing three equations with three unknowns. Computer time is therefore reasonable without affecting accuracy. Measured complex permittivity data from 45 MHz to 18 GHz are presented. Good agreement between calculated and generally accepted values is obtained. >

Humidity sensing properties and electrical permittivity of new photosensitive polyimides

Abstract: We present experimental and theoreitcal results for the electrical permittivity of new photosensitive as well as humidity-sensitive polyimides, of potential use in capacitive humidity microsensors. Our designs for the latter are based on interdigitated comb-like microelectrodes for which we have developed a fully three-dimensional simulation program to calculate the capacitance. We solve the Laplace equation, subject to appropriate boundary conditions, for the electric potential and field distributions outside the electrodes using the isoparametric finite-element method. The behaviour of the permittivity of these materials, as a function of relative humidity (RH), is studied at different temperatures, frequencies and thicknesses. Their response to humidity is linear for a wide range of RH. The permittivity changes are modelled using an effective-medium theory (ODEEM). Our modelling work is relevant for gas sensors in general, since gases are known to affect the permittivity of polymeric materials.

Piezoelectric and dielectric properties of some la, mn modified pbtio3 ceramics

Abstract: The piezoelectric and dielectric properties of (Pb1-xLax)(Ti1-yMny)O3 [x = 0.025; 0.15 and y = 0; 0.01] ceramics were investigated. The poling field dependence was determined for the relative dielectric constant, the dielectric loss factor, the piezoelectric coupling factors and the piezoelectric anisotropy.

Ceramic dielectrics and compositions therefor

Abstract: A composition for producing ceramic dielectrics which comprises: a mixture of barium titanate which has average particle size of 0.1-1.5 μm is amounts of 98-60 mole % and a perovskite type barium titanate solid solution which has average particle size of 0.1-1.5 μm and a Curie temperature of 50°-115° C. in amounts of 2-40 mole %; and (A) at least one of niobium oxides and tantalum oxides in amounts of 0.3-2 moles % in relation to 100 mole % of the mixture; and (B) at least one of cobalt oxides, nickel oxides, magnesium oxides, manganese oxides, copper oxides and oxides of a rare earth metal in amounts of 0.1-2 moles % in relation to 100 mole % of the mixture. The composition provides a ceramic dielectric which has a large relative permittivity and still has a small temperature dependence of relative permittivity within ±15% over a temperature range between -55° C. and +125° C. taking a relative permittivity at 20° C. as a standard.

Tetragonal Tungsten Bronze Niobate, K0.2Sr0.4NbO3: A New Material for Capacitors with Flat Dielectric Curves

Abstract: A new ceramic for capacitors, which exhibits flat dielectric curves with relative permittivity values (ɛ) as high as 3000 (Y7R or X7R class), has been synthesized. Use of a niobate, K0.2Sr0.4NbO3 (KSN), with a tetragonal tungsten bronze structure (TTB), as a major phase for the fabrication of such ceramics is shown for the first time. Nevertheless, the addition of perovskites as minor agents—PbMg1/3Nb2/3O3 (PMN)—is necessary to obtain stable temperature. Moreover, the use of lithium salts as sintering agents has been shown to be important for the fabrication of these ceramics.

A low frequency relative permittivity meter for electrically conducting liquids

Abstract: A technique is described for measuring relative permittivity of conducting liquids (of phase angles 10-6 to 0.3 rad) in the frequency domain below 50 kHz. The low frequency limit of the method, extending down from 20 Hz, is lower, the smaller the conductivity of the solutions, and is determined by the values of the phase angles to be measured and the magnitude of electrode and other parasitic effects that cannot be controlled effectively at very low frequencies. the technique is based on the four-terminal cell principle, but differs from other existing methods in two ways: the amplified potential between the two probes and the voltage converted current through the cell are clipped at practically equal heights before being subtracted and fed into a phase sensitive detector; measurement of the unknown phase angle of the solution investigated is made relative to the known phase angle of a reference solution of the same conductivity.

Calculation of anomalous permeability and permittivity spectra

Abstract: An extended model for calculating the permeability and permittivity spectra of granular materials, which is able to predict resonances, relaxations, and complex spectra that have been explained previously either by a combination of multiple sources or simply labeled as anomalous, is presented. Using the Clausius-Mossotti relation complex spectra are predicted by taking into account the relative size of the internal wavelength and by assigning the individual grains frequency-dependent electromagnetic properties. Scattered multipolar fields about a single sphere are related to the polarizability of a cubic array of such spheres. Using the Clausius-Mossotti relation the effective permeability and permittivity spectra of a polycrystalline (or amorphous) material for arbitrary permittivity and permeability of the individual spheres, packing density, and sphere size, are determined. Although the product of the external wave vector and sphere radius is kept small, typically less than one-tenth, the product of the internal wave vector and sphere radius is unconstrained and seen to have a large effect on predicted spectra. >

Dielectric properties of solutions of tetra-iso-pentylammonium nitrate in dioxane-water mixtures

Abstract: Dielectric properties of solutions of tetra-iso-pentylammonium nitrate, i-Pen 4 NNO 3 . in various dioxane-water mixtures have been studied using dielectric time domain spectroscopy (TDS). The static permittivity of the solutions ɛs increases for low concentrations of solute but levels off to asymptotic values at higher concentrations. The limiting slopedɛsdc, and the asymptotic value depend on the static permittivity of the solvent mixture. The relaxation time due to the solute varies with solute concentration and depends on the solvent mixture. In the solvent mixtures of lowest permittivity the plots of relaxation time vs. concentration go through a maximum, while in the mixtures of highest permittivity the relaxation time initially decreases and then levels off to an asymptotic value. The concentration dependence of the dielectric parameters is discussed in relation to ion association.

High-frequency, complex dielectric permittivity of saline solution at elevated temperatures

Abstract: The complex dielectric permittivity of saline solutions at elevated temperatures of up to 80 degrees C has been measured at 1.1 GHz. The salinity of the solution was varied from 1000 to 5000 parts per million. The measurements were first made in a rectangular waveguide. The phase velocity and attenuation of the electromagnetic wave propagating in the waveguide were measured, and from those the real and imaginary parts of the dielectric permittivity were calculated. The complex permittivity of the heated saline solution was also measured in a parallel-plate radial waveguide. Details of the measurement techniques, together with measured data, are presented. It is found that the high-frequency conductivity and dielectric constant predicted by an empirical formula agree with the measured data in the temperature range of 20 degrees to 40 degrees C. However, for temperatures higher than 40 degrees C, the measured conductivities and dielectric constant are both higher than the empirical data. >

High dielectric permittivity in sol‐gel derived SiO2‐As2O3 glasses

Abstract: Glasses in the system x As2O3(1−x) SiO2 with 0.05

Transistor characteristics in a three‐terminal structure having YBa2Cu3O7−x electrodes on an insulating SrTiO3 substrate

Abstract: Transistor characteristics in which both voltage and current gains exceeded one, were observed at 4.2 K in a three‐terminal superconducting structure. A high critical‐temperature superconducting YBa2Cu3O7−x emitter and collector were fabricated on a high‐permittivity insulating SrTiO3 dielectric with a back‐contact base electrode. The three‐terminal structures were constructed on 500‐μm‐thick (100) single‐crystal SrTiO3 substrates with a relative permittivity of 2×104 at 4.2 K. YBa2Cu3O7−x films were deposited on chemically cleaned substrates by laser ablation and base leads were constructed of silver paste.

Microwave dielectric constant of a low temperature co-fired ceramic

Abstract: Evaluation of low-temperature, cofired ceramic multilayer packaging material at microwave frequencies has revealed a lower dielectric constant than the standard measurement at 1 MHz Examination of resonance comparisons in both the authors' and in previously published work suggests similar conclusions Measurements using various resonators produced results in agreement with the derivations from other indirect methods Time-domain network measurements on microstrip structures designed with the 1-MHz dielectric constant and on revised structures using the dielectric constant are in agreement with the measured values A functional three-dimensional test structure is described >

A Slot Line Microwave Dielectric Permittivity Sensor for Measure and Control of Laminated Materials

Abstract: Measuring dielectric permittivity is a common technique to characterize materials which, sometimes, allows also a nondestructive detection of interesting physical properties of objects and systems.A dielectric permittivity sensor for microwave frequency range is proposed, based on a slot line resonator loaded by the material under test which appears particularly suitedfor characterization of laminated type dielectric materials.The experimentally measured sensitivity resulted about 160 MlIzt unit of er. Some results on the use of the sensor to detect air gaps inside dielectric materials are also reported.

Microstructure and physical properties of transparent thoria-yttria ceramics

Abstract: The investigation of microstructure, some electrical and optical parameters of transparent ThO2-15 mol % yo1.5 ceramics has shown: (a) a very low porosity, close to zero; (b) a higher electrical conductivity than is usual for ThO2 ceramics of the same composition, with the activation energy 1.12 eV; (c) a relative permittivity ɛr ∼ 33 under the given conditions; (d) confirmation of a single-phase fluorite-type cubic structure by means of Raman and infrared spectra.

Improved technique for measuring permittivity of thin dielectrics with a cylindrical resonant cavity

Abstract: A technique for measuring the relative permittivity of thin, low-loss dielectric materials in a cylindrical resonant cavity has been developed. A thin dielectric sample, of unknown characteristics, is placed upon a thicker dielectric sample whose permittivity is well characterized. Both samples are then placed on the end plate in the cylindrical resonant cavity. In this way, the thin sample is placed in a region of the cavity where interaction with the electromagnetic fields is greater. From knowledge of the cavity's resonant frequency, dimensions of the cavity and both dielectric samples, and from the permittivity of the thicker sample, the authors are able to use iterative techniques to accurately determine the permittivity of the thin dielectric sample. A derivation and discussion of the theory used in this layered-dielectric permittivity measurement technique are provided. Measurement results at frequencies between 9 and 10 GHz confirm the accuracy of the technique. Preliminary error estimates are also given to show the worst-case uncertainties associated with this new method. >