Showing papers on "Relative permittivity published in 1983"

Anisotropy in the dielectric properties of skeletal muscle

Abstract: The dielectric permittivity and conductivity of freshly excised dog skeletal muscle were measured at frequencies between 20 Hz and 1 MHz, with the tissue samples oriented either parallel or perpendicular to the applied electric field. At frequencies below 100 kHz a four-electrode technique was employed; at frequencies above 100 kHz a conventional two-electrode technique was used in conjunction with a commercial admittance bridge. All measurements were performed with the tissue sample at body temperature. Over the entire frequency range of the study, the dielectric properties of the muscle were found to be significantly anisotropic. At audio frequencies, the conductivity of the muscle measured in a direction parallel to the fibre orientation was typically found to be ten times higher than that measured perpendicular to the fibre axis; at frequencies approaching 1 MHz the conductivities measured in both directions approached a common value, near 8 ms cm−1. The dielectric permittivity in both orientations is strongly dependent on frequency. These data are analysed using the suspension equation, and comments are made on the mechanisms that are responsible for the observed properties. In an Appendix these results are related to some of the very early work on the subject.

Dielectric Permittivity and Electrical Conductivity of Fluid Saturated Bone

Abstract: The dielectric permittivity and electrical conductivity of freshly excised and formalin fixed samples of rat femoral bone were determined over a frequency range of 10 Hz-100 MHz. Impedance measurements were performed in the frequency domain using a vector impedance meter and an impedance analyzer. The results of these measurements show that the conductivity of fixed and fresh bone is nearly independent of frequency below 100 kHz, with the conductivity of fresh bone being two to three times greater than that of the fixed sample. At higher frequencies, the conductivity increases as a power function of frequency. The permittivity of bone reaches very high values at low frequencies, but decreases rapidly with increasing frequencies and approaches a limiting value of about ten. This high-frequency limit is consistent with the water content of the tissue, and with the permittivity of the anhydrous matrix. It is suggested that the olarizability observed at audio and radiowave frequencies is in part sssociated with the collagen phase, although other interfacial polarization effects can also be present.

Analysis of pressure-wave methods for the nondestructive determination of spatial charge or field distributions in dielectrics

Abstract: A pressure wave propagating through a charged dielectric produces an electric signal at the sample electrodes. This signal reveals information on the spatial charge or field distribution in the sample. In the present study, the mathematical relations between the signal response and the desired distribution are derived from first principles. For the derivation, the pressure dependence of the relative permittivity must be known; therefore this dependence was calculated for nonpolar as well as for polar dielectrics with the use of the Clausius-Mossotti equation. The resulting response equations are applicable to pressure-pulse, pressure-step, and arbitrary pressure-profile experiments on one- and two-sided metallized samples in open-circuit and in short-circuit configuration. The common features and the differences between the present analysis and existing theoretical descriptions are discussed in detail.

Precise Millimeter-Wave Measurements of Complex Refractive Index, Complex Dielectric Permittivity and Loss Tangent of GaAs, Si, SiO/sub 2/, A1/sub 2/O/sub 3/, BeO, Macor, and Glass

Abstract: Highly accurate continuous spectra of the complex refractive index and complex dielectric permittivity are given in the millimeter range for a variety of potentially useful materials. The absorption coefficient is found to increase monotonically with increasing frequencies. Small amounts of glassy inclusions or water were found to increase losses at all frequencies, but impurities and radiation damage (except in semiconductors) have not yet proved to be detrimental to performance. Materials have been found for which the millimeter-wave losses can be tolerated when used as dielectric waveguide, high-power windows, and other applications. Nominal consideration must be given, however, to the conditions of preparation and the nature of contaminants, The measurements were made in a modular, polarizing, dispersive Fourier-transform spectrometer.

Temperature Dependence of the Static Relative Permittivity of Octylcyanobiphenyl (8CB)

Abstract: Measurements of the relative static permittivity e of octylcyanobiphenyl (8CB) in the smectic A, the nematic and the isotropic phases between 22°C and 140°C are reported. The resolution of the measurements was better than 0.01% and the temperature stability was better than 0.01 °C. Detailed measurements have been carried out near the AN and NI transitions. For the AN transition. no discontinuity in e|| or e| was observed, which is consistent with the second-order nature of this transition in 8CB. From the dielectric anisotropy in the N-phase, a critical exponent β ≃ 0.25 was obtained for the temperature dependence of the order parameter. This value of β is in support of the hypothesis of quasi-tricriticality for this transition. In the isotropic phase of 8CB, a pretransitional anomalous maximum in e was observed near T N1- The same effect was also measured for two other materials with cyano-end groups (undecylcyanobiphenyl and pentylcyanophenylcyclohexane). For two compounds without a cyano-end g...

Dielectric properties of ocular tissues at 37 degrees C

Abstract: Values of the relative permittivity, dielectric loss and conductivity are given for various rabbit ocular tissues at frequencies in the range 10 MHz-10 GHz. The tissues measured were cornea, retina, choroid, iris, and the cortical and nuclear zones of the lens. The dielectric parameters were determined using the technique of multiple response time domain spectroscopy. For all tissues the water relaxation could be characterised by a Debye dispersion with a relaxation time longer than that of pure water, indicating that its dielectric behaviour was affected by the presence of the biological macromolecules.

Dielectric observations on polystyrene microcapsules and the theoretical analysis with reference to interfacial polarization

Abstract: Dielectric measurements were carried out for polystyrene microcapsules which were prepared by means of an interfacial polymer deposition technique. The microcapsules showed a couple of dielectric relaxations termedP for lower andQ for higher frequencies. The frequency profiles were characteristic of the structure that shelled spheres were dispersed in a continuous medium. Gelatin aqueous solutions, cationic polyelectrolyte solutions and distilled water were loaded in the capsule interior to examine the effect of conductivities of the constituent aqueous phases on the dielectric properties. Relaxation frequencies of the relaxationsP andQ observed were directly proportional to the conductivities of the continuous medium and of the capsule interior, respectively. A dielectric theory was proposed for a suspension of shelled spheres in a continuous phase in order to analyze the relaxation data observed for the microcapsules. Volume fraction of the capsules, relative permittivity and conductivity of the capsule interior and thickness of the capsule wall are evaluated from the dielectric observations by use of the theoretical formulas derived. The dielectric behavior observed for the polystyrene microcapsules are interpreted quantitatively in terms of the dielectric theory proposed.

A molecular theory of the dielectric permittivity of a nematic liquid crystal

Abstract: We present a theory of the dielectric permittivity in which the intermolecular dipole-dipole correlations are treated explicitly. The results for the static permittivity agree with those which have previously been obtained by continuum calculations. The frequency dependence of the permittivity is related to two relaxation times which contain the effects of only short range intermolecular correlations. Approximate relationships are derived between these times and independently measurable properties.

The dielectric properties of normal and tumour mouse tissue between 50 MHz and 10 GHz

Abstract: Microwaves are currently being investigated as a method of inducing hyperthermia. Values of the relative permittivity and conductivity of mouse muscle and tumour tissues over the frequency range 50 MHz to 10 GHz at a temperature of 37°C are reported. The data were obtained by using an on-line computer-based time-domain spectrometer. The tumour tissues were the RIF/1 and KHT fibrosarcomas sited in the hind leg muscle of C3H mice. A significant difference in the relative permittivity between the normal and tumour tissue was shown to exist at frequencies up to 200 MHz.

POLYMER SCIENCE Dielectric observations on polystyrene microcapsules and the theoretical analysis with reference to interfacial polarization

Abstract: Dielectric measurements were carried out for polystyrene microcapsules which were prepared by means of an interracial polymer deposition technique. The microcapsules showed a couple of dielectric relaxations termed P for lower and Q for higher frequencies. The frequency profiles were characteristic of the structure that shelled spheres were dispersed in a continuous medium. Gelatin aqueous solutions, cationic polyelectrolyte solutions and distilled water were loaded in the capsule interior to examine the effect of conductivities of the constituent aqueous phases on the dielectric properties. Relaxation frequencies of the relaxations P and Q observed were directly proportional to the conductivities of the continuous medium and of the capsule interior, respectively. A dielectric theory was proposed for a suspension of shelled spheres in a continuous phase in order to analyze the relaxation data observed for the microcapsules. Volume fraction of the capsules, relative permittivity and conductivity of the capsule interior and thickness of the capsule wall are evaluated from the dielectric observations by use of the theoretical formulas derived. The dielectric behavior observed for the polystyrene microcapsules are interpreted quantitatively in terms of the dielectric theory proposed.

Permittivity Measurements of Lossy Liquids at Millimeter-Wave Frequencies

Abstract: A measurement system is described which allows the determination of the complex permittivity of high-loss liquids at millimeter waves. Basically, the setup consists of a waveguide interferometer whose unknown arm embodies a liquid holder irradiated by an open-ended rectangular waveguide. The sample thickness is varied by means of a piston driven by a micrometer screw. The bridge output then is read as a function of the liquid thickness. Best fitting between experimental and computed data through a suitable model of the system enables the permittivity to be determined. The system can operate, with high sensitivity, over the whole frequency range of the dominant mode propagating in the waveguide setup employed. System performance is described through a set of experimental results obtained on ethanol, methanol, and pure water at 20° C and 70 GHz.

Microwave permittivity at 35 GHz and phase transitions in ((CH3)4N)2CoCl4 and ((CH3)4N)2ZnCl4

Abstract: Phase transitions and complex permittivity were determined at 35 GHz for the organic compounds: ((CH3)4N)2CoCl4 and ((CH3)4N)2ZnCl4. A differential thermal analysis confirmed the observed microwave transition in the first compound.

Evaluation of dielectric permittivity by dc transient current

Abstract: Inverse Laplace transformation of the Havriliak–Negami (HN) equation of complex dielectric permittivity has been obtained analytically both in short time and long time regions. A convenient procedure for determining the relaxation parameters in the HN equation from the dc transient current has been presented. Even if the current measurement is not carried out over the whole time range but only in a restricted time range, this procedure gives satisfactory values to the relaxation parameters.

Dielectric permittivity measurements in the ultralow frequency region

Abstract: A new dc transient method is described for fast measurements of dielectric permittivity in the μHz frequency region. A square‐wave voltage pulse is applied to the dielectric instead of the usual step voltage pulse. The whole transient current is measured two times faster than in the conventional method using the step voltage.

Dielectric Properties of Ceramics in the Ba(Zn1/3Nb2/3)O3- Sr(Zn1/3Nb2/3)O3Solid Solutions

Abstract: Solid solution ceramics in the Ba(Zn1/3Nb2/3)O3-Sr(Zn1/3Nb2/3)O3 system have been studied in view of finding materials for use as dielectric resonators at microwave frequency. The relative dielectric constant of Ba(Zn1/3Nb2/3)O3 and Sr(Zn1/3Nb2/3)O3 ceramics is 41 and 40, and the unloaded Q is 7500 and 4000 at 9 GHz respectively. A nearly zero temperature coefficient of resonant frequency is obtained for a solid solution ceramic with 0.35 BZN-0.65 SZN. The temperature dependence of dielectric constant is discussed in terms of the Clausius-Mossotti relation.

An equation of state based on measurements of relative dielectric permittivity

Abstract: Measured values of density and dielectric permittivity have been fitted to polynomial expressions in pressure and temperature. These are shown to reproduce measured values of density to within 0.25%. The polynomials are readily manipulated to give analytical expressions for thermodynamic constants, including the velocity of sound. Such constants are compared with values in the literature.

Ceramic dielectric basis on bismuth-containing BaTiO3

Abstract: Ceramic dielectric based on bismuth-containing BaTiO3 in the form of a monophase mixed crystal-ceramic in which 0.02 to 0.12 mol of the layer perovskite PbBi4 Ti4 O15 or SrBi4 Ti4 O15 per mol of BaTiO3 are provided. On account of its comparatively low sintering temperature and in particular on account of the very small change of the value of the relative dielectric constant with applied direct voltage fields, the ceramic is particularly suitable for the manufacture of multilayer capacitors.

Dielectric Properties of Underwater Polystyrene Films Related to Microcapsules

Abstract: Dielectric measurements were carried out on polystyrene films immersed in various kinds of electrolyte aqueous solutions The observed dielectric relaxations were of the Debye type which was characteristic of the series combination of the polystyrene film and the ambient aqueous solution Approximate formulas were derived of the dielectric theory of interfacial polarization for the bilamellar structure under the condition that the capacitance is much larger for the film than for the aqueous solution Capacitance and conductance of the underwater film were evaluated from the dielectric observations by use of these approximate formulas The film capacitance remained unchanged irrespective of the tonic species and the concentration of electrolyte solutions used, being inversely proportional to the thickness of the films The relative permittivity of the polystyrene films was estimated to be 265 The ratio of the film conductivity to the solution conductivity for the same film was unaffected by the change in the concentration of electrolyte solutions, being in the order of 10-4 These features of the film capacitance and the conductivity ratio suggest that micropores in the film filled with the ambient electrolyte solutions are responsible for the electric conduction of the present underwater films

Study of the relaxation of the permittivity in doped and gamma-irradiated TGS single crystals

Abstract: The change of the permittivity in gamma-irradiated and chromium and vanadgl doped TGS single crystals is investigated after switching of an applied d.c. electric field. Two types of the time dependence of the permittivity are observed. This behaviour may be correlated to real domain structure.

Dielectric Permittivity on Commensurate and Incommensurate Smectic Phases

Abstract: Dielectric permittivity and calorimetric data are presented on mixtures at the nematic-smectic A phase transitions. The permittivity change was found to be linearly dependent on the McMllan temperature ratio T NA /T NI. The experimental data obtained on the induced SA1 and the incommensurate SA2 phases have shown a similar behaviour.

Ferromagnetic resonance in weakly electrically conducting ferromagnets

Abstract: For low electrically conducting anisotropic ferromagnetic metals an analytical FMR theory was deduced, which considers the influence of dielectric permittivity (the displacement current in Maxwell equations); it is applicable especially at frequencies in the mm or far infrared region. The dispersion relations of the AR effect were shown as valid also in this FMR case (forΩ2L2 ≫e r 2 ). The surface impedance (of a small asymmetry due to the dielectric permittivity), the FMR point shift (to the higher values of static magnetic fields), and the expressions for the ellipticity factors and hf components of magnetization and magnetic fields were derived; only the electromagnetic wave was shown as predominantly excited in the FMR of low conductive materials.

Dielectric dispersion and dynamics near the transition temperature in crystalline ammonium hydrogen bischloroacetate

Abstract: Dielectric permittivity and losses measurements were carried out on crystalline ammonium hydrogen bis-chloroacetate in the frequency range 100-2000 MHz near the transition temperature. The observed dielectric relaxation process was nearly monodispersive. From the analysis of the various experimental results it is suggested that the most probable model of the transition observed in this crystal is the so-called pseudo-spin lattice coupled model given by Nath and co-workers (1979).

Light-induced electric permittivity change in the presence of a dc electric field

Abstract: Observation of the full theoretically predicted range of electric permittivity changes induced in nitrobenzene by the simultaneous action of dc and strong optical fields is reported. The influence of the dc field‐induced oscillation of the light polarization ellipse on this effect is shown. It is proved that the components of the fourth rank susceptibility tensor of an isotropic medium composed of anisotropic molecules fulfill the permutation symmetry relations.

Evaluation of Dielectric Permittivity by DC Transient Current Method

Abstract: Inverse Laplace transformation of the Havriliak–Negami (HN) equation of complex dielectric permittivity has been obtained analytically both in short time and long time regions. A convenient procedure for determining the relaxation parameters in the HN equation from the dc transient current has been presented. Even if the current measurement is not carried out over the whole time range but only in a restricted time range, this procedure gives satisfactory values to the relaxation parameters.

Investigation of changes in the permittivity of liquids in a strong optical field

Abstract: An investigation was made of changes in the permittivity e of liquid insulators (benzene and nitrobenzene) in strong optical field. The change in the permittivity Δe was deduced from a change in the capacitance C of a capacitor filled with the investigated liquid and subjected to illumination with laser radiation of 100–250 kW/cm2 power density. The corresponding electric field intensity of laser radiation was 10 kV/cm and the change produced by this field Δe was positive and amounted to about 10−5. The influence of various effects contributing to the permittivity change was analyzed.

Noncontact Measurements of Permittivity of a Smooth Convex Target with bistatic Radar

Abstract: This paper describes noncontact measurements of the permittivity of a smooth convex target. Two methods are presented. The first one is developed by modifying Erteza and Doran's method[l]. The second one is measuring the reflection coefficient of the target and then evaluating the desired permittivity. Both methods are implemented in the open with a S-band bistatic radar. The experimental results are in good agreement with those obtained by the perturbation method.

Correction Due to Finite Permittivity for a Dielectric Resonator

Abstract: To determine the resonant fields of a dielectric resonator with high permittivity ?r the asymptotic theory with 1/??r as a small parameter, is extended with a correction term to yield accurate results even for relatively low values of ?r. Data are shown for the lowest ?-independent, "non-confined" mode of a ring resonator, which radiates as a magnetic dipole.