Showing papers on "Relative permittivity published in 1996"

Microwave permittivity of dry sand

Abstract: The relative dielectric constant, or relative permittivity, /spl epsiv/ of dry snow, is independent of frequency from about 1 MHz up to the microwave range of at least 10 GHz. New measurements of with improved accuracy were made with a specially designed resonator operating near 1 GHz. The coaxial sensor accurately defines the sample volume whose actual mass can be determined to give the density of the snow sample. A special electronic instrument, called a resometer, enabled accurate and rapid measurements under field conditions. Some 90 measurements of different kinds of dry snow (fresh, old, wind-pressed snow, depth hear, and refrozen crusts) were made at test sites in the Swiss and Austrian Alps. The data indicate that /spl epsiv/ is a function of snow density only, given that the standard deviation of 0.006 from the fitted curve is just due to the expected measurement errors. The interpretation of these data in terms of physical mixing theory favors the effective medium formula of Polder and van Santen (1946). The data allow to relate the average axial ratio X as a function of ice volume fraction. Both prolate and oblate spheroids can explain the data. Independent reasoning gives preference to oblate particles. In both cases, the axial ratio increases with increasing fraction up to a critical value of 0.33, followed by a decrease at still higher fractions. The destructive metamorphism of slowly compacting snow explains the increase of X, while the following decrease might be due to sintering. So far, no effect on /spl epsiv/ by a liquid-like surface layer on the ice grains at temperatures between -10/spl deg/C and 0/spl deg/C has been observed.

Influence of Free Volume Change on the Relative Permittivity and Refractive Index in Fluoropolyimides

Abstract: The often observed decrease in relative permittivity (e‘) and refractive index (n) that accompanies fluorine substitution is the result of several effects. Fluorine replacement for hydrogen is known to decrease local electronic polarization and is thought to frequently increase fractional free volume. Both of these effects can independently decrease e‘ and n, and this paper attempts to assign the observed decreases between these mechanisms for a series of hydrogen/fluorine polyimide analogs.

Spatial averaging of water content by time domain reflectometry : Implications for twin rod probes with and without dielectric coatings

Abstract: The averaging of apparent relative dielectric permittivities by time domain reflectometry (TDR) is examined for properties varying along TDR waveguides and in the plane perpendicular to a TDR probe. A square root averaging model with uniform weighting factors describes the measured apparent relative dielectric permittivity for axially varying materials; variations in the transverse plane are described by an inverse averaging model with nonuniform spatial weighting. We define the sensitivity of a TDR probe as the change in the measured travel time for a given change in the average soil water content for rods of a fixed length. For rods with dielectric coatings, this sensitivity increases with the dielectric permittivity of the coating and the rod radius and decreases with the soil dielectric permittivity. Due to the dependence of the sensitivity on the soil water content, coated rods will not measure the actual average water content for conditions of axially variable water contents.

Dielectric behaviour of thin films of β-PVDF/PZT and β-PVDF/BaTiO3 composites

Abstract: Thin films of the composites formed between poly(vinylidene fluoride) (PVDF) and lead zirconium titanate (PZT) and also barium titanate with 0–3 connectivity, have been obtained by dispersion of the ceramic powder in a solution of PVDF in dimethylacetamide DMA Evaporation of the solvent at 65 °C allowed crystallization of PVDF predominantly in the polar β phase, regardless of the amount of PZT or BaTiO3 powder added upto 40 vol % The relative permittivity and loss index values were determined for the pure components and for the composites with different ceramic contents, in the frequency range of 100 Hz to 13 MHz An increase in PZT or BaTiO3 content resulted in an increase in the relative permittivity of the composites, and the experimental results are shown to be in good agreement with those calculated from the theoretical expression of Yamada et al [1] The de electrical conductivity of composites with different compositions was also determined

Material Parameters for Electrostriction.

Abstract: Electrostriction is often described by a phenomenological tensor relating a material’s deformation to an applied electric field. However, this tensor is not a material parameter; for deformable, weakly compressible materials (e.g., elastomers), the field‐induced deformations depend strongly upon boundary conditions. A different approach that relates the deformation to material properties as well as boundary conditions is required. In this article, we describe a linear theory which introduces five material parameters governing electrostriction: the relative dielectric constant, e0, two derivatives of the dielectric constant tensor, a1 and a2, Young’s modulus, Ey and Poisson’s ratio, ν. Knowledge of these parameters and appropriate boundary conditions allow one to predict field‐induced deformations for arbitrary configurations. We demonstrate an experimental procedure for measuring deformations and permittivity changes, from which the parameters a1 and a2 may be extracted (e0, ν, and Ey can be measured by a...

Measurements of the complex permittivity of microwave circuit board substrates using split dielectric resonator and reentrant cavity techniques

Abstract: The split dielectric resonator technique makes it possible to measure the real part of permittivity of isotropic materials for a very broad permittivity range and dielectric loss tangents in the range from 10⁻⁴ to 10⁻¹ with high accuracy. For uniaxially anisotropic materials, the split resonator method permits measurement of the permittivity and and the dielectric loss tangent in the plane parallel to the the sample bottoms. Additional measurements using re-entrant cavity enable determination of permittivity and the dielectric loss tangent perpendicular to this plane.

Effect of temperature on dielectric properties of ice in the range 5-39 GHz

Abstract: The relative complex dielectric permittivity, e*=e′−ie″, of ice has been measured in the frequency range 5–39 GHz and in the temperature range 190–265 K. The cavity resonator method at 5 and 10 GHz and the open resonator method at 33 and 39 GHz were used to determine the low dielectric loss of ice. The real part of permittivity e′ was independent of the frequency. The temperature dependence of e′ was observed and is discussed in terms of contributions from anharmonic effects to infrared polarizability. The e″ obtained bridges the gap of previous results between 200 and 258 K. We discuss the frequency and temperature dependence of the effect of the infrared absorption band on e″. The e″ variation with frequency increased as the temperature decreased at 5–39 GHz. It is possible that absorption takes place at frequencies below the infrared region.

Processing and characterization of Pb(Zr, Ti)O3 films, up to 10 μm thick, produced from a diol sol-gel route

Abstract: A recently developed diol sol-gel route has been modified in order to produce multilayer PbZr 0.53 Ti 0.47 O 3 films on platinized sapphire substrates. Up to 20 depositions of a 1.1 M sol were carried out leading to a final film thickness of 10 μm. A similar thickness could be achieved from 12 coatings of a more concentrated 1.6 M sol. Decomposition and crystallization of the multilayer coatings were performed using a two-stage prefiring sequence, at 350 °C and 600 °C, followed by a final firing step at 700 °C. Ferroelectric remanant polarization increased with increasing film thickness to a value of 40 μC cm −2 for a 10 μm film, with a corresponding coercive field of 30 kV cm −1 ; the relative permittivity of this film was ∼1000 and the dissipation factor 0.04. The thickness dependence of relative permittivity could be modeled on a simple series capacitor circuit representing the ferroelectric Pb(Zr, Ti)O 3 (PZT) film and low-permittivity interface layers; but other possible contributory factors are also discussed.

The resonant frequency of rectangular microstrip antenna elements with various substrate thicknesses

Abstract: Formulas based on transmission-line, cavity, and magnetic-wall models to determine the resonant frequencies of a rectangular microstrip antenna element have been studied and their validity assessed. Their variations were experimentally verified by analyzing a set of newly designed antenna elements with substrates satisfying the criteria h ≤ 0.0815λ0 for 2.22 ≤ ϵr ≤ 10.2, where λ0 is the free-space wavelength, h the thickness, and ϵr the relative permittivity of the dielectric substrate. © 1996 John Wiley & Sons, Inc.

Permittivity measurement of thin liquid layers using open-ended coaxial probes

Abstract: The composition of a thin emulsion layer backed by air can be determined from permittivity measurements with an open-ended coaxial probe. In this work, techniques for probe design and determination of liquid permittivity are studied. Measurements on thin liquid layers backed by a low-permittivity material show that the measured apparent permittivity varies exponentially with the layer thickness, with a probe constant that is independent of measurement frequency and liquid permittivity. It is found that an electrostatic model is applicable for design of probes with regard to the probe's sensitivity depth. Models of different complexity for determination of permittivity are compared and it is shown that a bilinear model in combination with an empirical exponential model estimates the permittivity of thin liquid layers with high sensitivity provided that the thickness of the layer is known. The bilinear model uses calibration measurements on three samples with known permittivities. A somewhat lower precision is obtained with a full-wave model of the probe, but this model has the advantage that no calibration except a simple reference plane rotation is needed. However, the computation time of the full-wave model is high.

Wheat Permittivity Measurements in Free Space

Abstract: Requirements for a free space microwave transmission measurernent system for determining the permittivity of grain are analyzed. Experimental verification of these requirements is providedfor two cultivars ofhard red winter wheat of various densities, moisture contents and temperatures in the frequency range from 10 to 18 GHz. Uncertainties in the dielectric constant determination are less than ±1%, and those for the loss factor are less than ,±.3%.

Dielectric properties of microwave ceramics investigated by infrared and submillimetre spectroscopy

Abstract: Results of our 10 years study of more than 80 microwave ceramics varying in composition and processing with the aid of infrared reflectivity and submillimetre transmission spectroscopy are reviewed. These techniques are unavoidable for understanding the origin of microwave permittivity and losses. Extrapolation from submillimetre to microwave range is discussed as well as the observed steep overall increase in losses on increasing permittivity. The most important structural parameter for dielectric properties is the packing degree. Ideally packed structures show the lowest permittivity and losses. On lowering the packing degree, permittivity and losses increase and the lattice becomes more anharmonic. Extrinsic part of losses due to defects is discussed on the basis of their temperature and frequency dependences, but no clear quantitative conclusions can be drawn in most cases.

Offset dual-disk dielectric resonator antenna of very high permittivity

Abstract: An aperture-coupled offset dual-disk dielectric resonator antenna of very high permittivity is investigated experimentally. It is found that the new configuration offers an impedance bandwidth 4.6 times wider than that of the single element. The voltage standing wave ratio, radiation patterns, and antenna gain of the configuration are studied.

Structural study of aqueous solutions of tetrahydrofuran and acetone mixtures using dielectric relaxation technique

Abstract: The complex permittivity, static dielectric constant and relaxation time for tetrahydrofuran-water and acetone-water mixtures have been determined at 0°, 10°, 25° and 35°C using time domain reflectometry technique (TDR). The behaviour of relaxation time of the mixture shows a maxima for the mixture with 30% of water by volume. This suggests that the tendency to form cluster between water and solute molecule is maximum for this mixture. The excess permittivity for both tetrahydrofuran-water mixture and acetone-water mixtures, are found to be negative. The Kirkwood correlation factor has been determined at various concentrations of water. Static dielectric constant for the mixtures have been fitted well with the modified Bruggeman model. The values of the Bruggeman parametera for tetrahydrofuran is found to be more than the corresponding value for acetone.

Measurement of complex permittivity and permeability and thickness of multi-layered medium by an open-ended waveguide method

Abstract: A circular waveguide radiating into a layered medium is used for the determination of permittivity and permeability of materials. Better accuracies are obtained by modeling an air gap between the hanged waveguide and material. Simultaneous determination of complex permittivity and thickness of the material is also possible. Theoretical results have been compared with those obtained by the Finite Element Method. Many measurement have been made on a few materials with various dielectric and magnetic losses and the results have been comparable to those obtained using the well known free space method of Gaussian focused beams.

Formulas for the computation of the physical properties of rectangular microstrip antenna elements with various substrate thicknesses

Abstract: Formulas available in the literature for the design of the physical properties of rectangular microstrip antenna elements are discussed, and their validity is assessed. Their variations have been experimentally examined by analyzing a set of newly designed antenna elements with substrates satisfying the criterion h ≤ 0.0815λ0 for 2.22 ≤ ϵr ≤ 10.2, where λ0 is the free-space wavelength, h is the thickness, and ϵr is the relative permittivity of the dielectric substrate. New formulas that can determine the antenna physical properties and the effective dielectric constant are empirically determined. ©1996 John Wiley & Sons, Inc.

Polar fluctuations in proteins: molecular-dynamic studies of cytochrome c in aqueous solution

Abstract: The equilibrium fluctuations (the polar fluctuations), of yeast cytochrome c are studied using nanosecond molecular-dynamic simulations in a spherical droplet of water, with a particular emphasis on the fluctuations of the total dipole moment, which determine the average relative permittivity. These fluctuations follow a simple probability distribution, predicted by continuum electrostatics, and already observed in simulations of several polar liquids. An important component consists of diffusive, mutually independent, motions of the charged side chains at the protein surface. A quasiharmonic normal mode analysis of the trajectory shows that while motions covering a large range of frequencies contribute to the polar fluctuations, the four lowest frequency modes account for 50% of the overall static relative permittivity of ca. 25. The fluctuations of the protein bulk, i.e. parts other than the charged side chains, are distributed over a larger number of modes. Modes up to at least 60 cm-1 contribute to the average relative permittivity of the protein interior of ca. 4. The water surrounding the protein, despite the structural perturbation represented by the protein, has fluctuations similar to pure water, consistent with the idea of a linear solvent response to the protein charges. The relationship between the microscopic fluctuations seen in the simulations and simple continuum models is discussed.

Complex permittivity measurement method based on asymmetry of reciprocal two-ports

Abstract: The authors describe a simple method for complex permittivity measurement using network analysers. The essential feature is the exploitation of the asymmetry of a reciprocal two-port. Calibrated results are obtained using a coaxial line or waveguide section, from whose centre a sample is installed only once. The theory is validated by numerical simulation.

Phenomenological three-layer model for surface second-harmonic generation at the interface between two centrosymmetric media

Abstract: A three-layer model is presented to account within a single framework for the different contributions to the surface second-harmonic response at the interface between two centrosymmetric media. It is shown that the optical relative permittivity for the intermediate layer can be incorporated in the geometrical factors of the second harmonic response. The problem of the bulk non-local contribution is then discussed within the same formalism and the associated response incorporated into the effective susceptibility tensor. Three particular cases are given as application of the model to experimental procedure.

Fluid electrical measurement apparatus and method

Abstract: Measurement apparatus for electrical measurement of fluid such as oil, or brake fluid for use in an engine, vehicle or hydraulic machine is provided in which a circuit includes a sensor sensing variables dependent on complex relative permittivity of the fluid in the sensor. The circuit provides a first value dependent upon the imaginary part, and a second value dependent on the real part of the complex relative permittivity. A number of capacitive sensing arrangements for use in the apparatus are disclosed. The apparatus may be used for continuous or periodic monitoring of the fluid, and may provide an audible signal, the frequency or volume of which is indicative of the permittivity of the fluid.

Dispersion characteristics of cylindrical coplanar waveguides

Abstract: A full-wave analysis of the coplanar waveguide (CPW) printed on a cylindrical substrate is presented, and the dispersion characteristics of the cylindrical CPW are studied. Numerical results of the effective relative permittivity are calculated using a Galerkin's moment-method calculation. Experiment is also conducted, and the measured data are in good agreement with the theory.

Determining the relative permittivity and thickness of a lossless dielectric overlayer on a metal film using optically excited surface plasmon polaritons

Abstract: Numerical simulations based on the exact Fresnel equations are used to show that it is possible to determine uniquely the relative permittivity and thickness of a thin lossless dielectric film adsorbed on a gold or silver layer. The calculations, which include the effects of up to 1% random noise on the experimental data, show clearly that there is no degeneracy in the solutions of the Fresnel equations even for films as thin as 2 nm. It is shown that gold is preferable to silver as a substrate when the overlayer properties need to be determined accurately. It is further shown that, if the overlayer is bounded by water rather than air, then the experimental constraints would preclude the use of silver as a substrate but measurements would still be possible with gold.

Three theorems on zero backscattering

Abstract: A body of revolution (BOR) which is axially symmetric in terms of both geometric and material properties is considered. It consists of simply or multiply connected impenetrable portions characterized by an impedance boundary condition with a relative surface impedance /spl eta/=/spl plusmn/1, and by penetrable (and possibly inhomogeneous) portions characterized either by scalar permittivity, scalar permeability and chiral admittance, or by uniaxial permittivity and permeability tensors. For an axially incident plane wave, two theorems are stated in which sufficient conditions are imposed on the constitutive parameters to ensure a zero backscattered field. A third theorem is concerned with the superposition of two structures, each of which individually yields zero backscattering.

Image reconstruction of a complex cylinder illuminated by TE waves

Abstract: The electromagnetic inverse scattering of a complex cylinder illuminated by transverse electric (TE) waves is investigated. The complex cylinder is a conductor coated by dielectric materials, A group of various unrelated TE waves is incident upon the object and the scattered fields are measured outside. With prior knowledge of the conductor's shape, the complex permittivity distribution of the dielectric materials can be reconstructed. The algorithm is based on the moment method and the unrelated illumination method. Some numerical examples are given to demonstrate the capability of the algorithm. Numerical results show that the dielectric constant and the conductivity distribution of the materials can be reconstructed even when the scattered fields are contaminated by random Gaussian noise.

Effect of fillers on the dielectric properties of polymers

Abstract: The effect on the permittivity of two different base polymer materials was investigated with two types of fillers. Several theories were investigated to determine which most closely predicted the permittivity of the composites. The fillers utilized were a low permittivity material (alumina) and a high permittivity compound (barium titanate). The base materials investigated were epoxy and silicon rubber. It was found that the permittivity of the alumina filled composite was most closely predicted by the formulae which considered the permittivity of the filler in the calculation, i.e. the log law, Rayleigh's formula, and effective medium theory. The permittivity of the barium titanate filled materials were most closely predicted by the percolative theories, i.e. Bruggeman's formula and the effective medium theory, as these materials demonstrated percolative tendencies. The effect of the base material selection on the loss tangent of the filled material was also investigated. It was found that the epoxy samples exhibited little change in the loss tangent over the range of filler levels tested, whereas the silicon rubber samples showed increasing loss tangent with increasing filler level for both the alumina and barium titanate filled samples.

A resonant cavity for high-accuracy measurement of microwave dielectric properties

Abstract: This paper demonstrates that, along with the change in resonant frequency, the coupling coefficient between a resonant cavity and a transmission line will be altered once a dielectric sample is inserted into the cavity. These changes affect the measurements of the Q factors, and thus cause uncertainties in the permittivity measurements of dielectric samples. An X-band TE112 mode cavity is designed to overcome the uncertainties in the permittivity measurements, with which the Q values can be measured at the same resonant frequency and the same coupling conditions before and after the introduction of a dielectric sample.