Showing papers on "Relative permittivity published in 1987"

Dual-frequency stacked annular-ring microstrip antenna

Abstract: Experimental results of a dual-frequency microstrip antenna consisting of two stacked annular rings of outer radii 5 cm and inner radii 2.5 cm are presented. Fabricated on a Duroid substrate with relative permittivity 2.32 and thickness 0.159 cm, the separations of the two resonant frequencies range from 6.30-9.36 percent for the first three modes. The frequency separations can be altered by means of an adjustable air gap between the lower ring and the upper substrate.

Two Methods for the Measurement of Substrate Dielectric Constant

Abstract: Two methods for the accurate and convenient measurement of the dielectric constant of a microwave substrate are proposed. Both methods use the precision measurement capability of the HP-8510 Network Analyzer system and a rigorous theoretical analysis of multilayer transmission lines [6], and hence can also be used for the measurement of the frequency dependence of the relative dielectric constant. Accuracy on the order of 1.0 percent can be obtained by use of these techniques. Measurements were done for various substrates and gave results as predicted.

Precision millimeter-wave measurements of complex refractive index, complex dielectric permittivity, and loss tangent of common polymers

Abstract: Our improved dispersive Fourier transform technique applied to a polarizing two-beam interferometer enables us to provide high-precision continuous spectra of complex refractive index, complex dielectric permittivity, and loss tangent of polyethylene, polypropylene, poly-4 methyl pentene-1 (TPX), polytetrafluorethylene, Plexiglas, acrylic, and nylon over the frequency range 50–300 GHz. The first four are nonpolar polymers and exhibit extremely low-loss characteristics. The last three are typical polar polymers, but they exhibit nearly 20 to 30 times higher loss compared to nonpolar polymers.

Dielectric-relaxation study of alkylcyanobiphenyl liquid crystals using time-domain spectroscopy

Abstract: Time-domain spectroscopy is used to study the complex permittivity of two types of liquid crystals: heptylcyanobiphenyl (7CB) and octylcyanobiphenyl (8CB). The variation of the dominant relaxation frequency values of both 7CB and 8CB as a function of temperature are very similar, showing no influence of the smectic structure in 8CB. The experimental relaxation measurements in the nematic phase agree qualitatively with the existing theory.

The importance of phase measurement in electrical impedance tomography

Abstract: A method is described for reconstructing images of electrical conductivity and relative permittivity in electrical impedance tomography (applied potential tomography). The method relies on measurement of both the amplitude and the phase of the surface electric potential profile. The principle is demonstrated using a computer model to simulate measurements. The reconstructed images, referenced to homogeneous saline, agree qualitatively with the values of conductivity and permittivity used in the computer model. In addition, by displaying the imaginary part of the logarithm of the complex electrical conductivity, certain tissues, e.g. liver and kidney, are emphasised on the image. When the same parameter is displayed for simulated dual-frequency measurements, in which 150 kHz values are referenced against 100 kHz, liver and pancreas are emphasised. These results suggest the possibility of distinguishing between different types of soft tissue more effectively than if only signal amplitudes are measured.

Dispersion Characteristics of Open Microstrip Lines

Abstract: A method based on spectral-domain analysis is derived to compute effectively and automatically the effective relative permittivity of an open microstrip line. Simple but accurate closed-form expressions are used as the basis functions of the longitudinal and transverse current distributions. The numerical results are shown in tables and figures for various cases and compared WMI other available results. The results presented here are seen as having a high degree of accuracy and may be used as reference standards,

Precision millimeter-wave dielectric measurements of birefringent crystalline sapphire and ceramic alumina

Abstract: A quasi-optical technique, namely, dispersive Fourier transform spectrometry, has now been improved to provide high-precision continuous data of complex refractive index, complex dielectric permittivity, and loss tangent of materials at millimeter wavelengths. The use of a polarizing two-beam interferameter is ideally suited for the measurement of birefringent materials. A massive birefringent effect (δ∊′ 2.193) is now observed for crystalline sapphire (Al 2 O 3 ). The bifringent effect for crystalline quartz is much smaller (δ∊′ ⋍ 0.2). New millimeter-wave results of commercially available ceramic alumina (Al 2 O 3 ) are compared with those of crystalline sapphire.

TE waves in a symmetric dielectric slab waveguide with a Kerr-like nonlinear permittivity

Abstract: The propagation characteristics of TE waves guided by a film with a Kerr-like nonlinear permittivity are investigated theoretically. The dispersion equations for positive and negative nonlinear coefficients are derived by introducing the maximum field amplitude as a parameter for the nonlinearity. Typical numerical results for dispersion characteristics are shown. For a hollow waveguide with positive nonlinear coefficient, the threshold power flow is determined numericlly from the viewpoint of applications to optical power clipping. It is found that the threshold power flow is proportional to the square root of the unperturbed permittivity difference between the film, and cladding.

Hybrid multilayer wiring board

Abstract: A multilayer wiring board structure includes a plurality of conductor layers and insulation layers interleaved between each ones of the conductor layers. The conductor layers includes power (or ground) line layers and signal line layers, and one type of insulation layer having lower relative permittivity and another type of insulation layer having higher relative permittivity is used between power (ground) line layers interposed by signal line layer(s).

Microwave Processing and Diagnosis of Chemically Reacting Materials in a Single-Mode Cavity Applicator

Abstract: On-line chemically reacting microwave processing and dielectric diagnosis of materials (epoxy/amine) have been successfully performed using a TM/sub 012/-mode cylindrical cavity at a frequency of 2.45 GHz in conjunction with fluoroptic temperature measurement. Complex permittivity measurements by this single-frequency technique are repeatable and consistent with those obtained by conventional swept frequency methods. 'The accuracy of complex permittivity measurements for both methods is within +-5 percent for permittivity (epsilon') and +-15 percent for loss (epsilon"). Both techniques are based on material-cavity perturbation theory. Perturbation equations for cylindrical shapes of the cavity and loaded material have been derived to account for volume variation of the sample due to thermal expansion. Complex permittivity of epoxy/amine as a function of the extent of cure and temperature was determined in order to monitor the chemical reaction progress during microwave processing.

Analysis of the Parallel-Disk Sample Holder for Dielectric Permittivity Measurement

Abstract: The parallel-disk sample holder used to measure the conductivity and the dielectric permittivity of dissipative materials is analyzed in terms of quasistatic electromagnetic theory. It is shown that the commonly used static solution is not accurate enough to interpret data at high frequencies. Interpretation of the data is improved when higher order correction terms are added to the zeroth-order static solution.

Precision waveguide cells for the measurement of complex permittivity of lossy liquids and biological tissue at 35 GHz

Abstract: A waveguide system is described which enables the complex permittivity of high loss, high permittivity liquids and solid tissues to be measured accurately at 35 GHz. The design and constructional details of an experimental cell are given. Some test data are presented and the experimental errors are considered.

The determination of dielectric anisotropy in ferroelectric smectic C

Abstract: The method of determination of the three main components of the electric permittivity tensor, e, in chiral smectics C was proposed. To illustrate the method we measured the electric permittivity for the ferroelectric smectic DOBAMBC in the SmC and SmA phases and calculated the components of ∊-tensor as a function of temperature.

Reflecting characteristics of anisotropic rubber sheets and measurement of complex permittivity tensor

Abstract: It is well known that rubber sheets mixed with carbon particles or carbon fiber usually exhibit large surface anisotropy due to the rolling process employed in fabrication. The use of such materials for special microwave applications requires measurement of the complex permittivity tensors. However, no reliable method for this purpose in such lossy anisotropic materials has been established. In this paper the reflection loss of anisotropic sheet materials is measured and a method for obtaining complex permittivity tensors from the experimental results is given. That is, the frequency characteristics of the reflection loss are measured for various polarization directions of incident waves at the sheet materials and each element of the tensors including nondiagonal ones can be estimated by the least squares method using these data. As a result of study of the principal direction of the sheet using measured values of this tensor, it is found that the real and imaginary parts differ largely in the principal direction for some of the rubber sheets with carbon used for this measurement.

Preparation of BaTiO3Films by RF Sputtering and Their Crystallographic, Dielectric and Optical Properties

Abstract: BaTiO3 films having a perovskite structure were fabricated onto a platinum and a fused-quartz substrates by RF planar-magnetron sputtering at a substrate temperature above 500°C. However, to obtain a ferroelectric film, it is necessary to anneal at about 1000°C in an atmosphere of oxygen. One of ferroelectric films obtained had a relative dielectric constant of 1680, a remanent polarization of 0.8 µC/cm2 and a coercive field of 3 kV/cm at room temperature.

Dielectric and pyroelectric properties of polymer-ceramic composite

Abstract: The dielectric and the pyroelectric behaviour and the nature of absorption and steady state of currents have been studied for a ceramic and a polymer-ceramic composite over wide ranges of frequency and poling field and a limited range of temperature. The relative permittivity and the pyroelectric coefficient of the composite are observed to be significantly higher than those of the polymer. The dielectric loss processes of the composite are observed to be dominated by those of the polymer whereas the ceramic phase contributes significantly to the steady state electrical conduction which is observed to be of ionic nature.

Dielectric spectroscopy on aqueous solutions of pyridine and its derivatives

Abstract: The complex (dielectric) permittivity has been measured as a function of frequency between 1 MHz and 40 GHz for aqueous solutions of pyridine, 2- and 3-methylpyridine, as well as 2,4- and 2,6-dimethylpyridine at various temperatures and solute concentrations. Different relaxation spectral functions are used to analytically represent the data, in particular the Cole-Cole function. The solute contribution to the extrapolated static permittivity has been calculated to show that, in correspondence with other aqueous solutions of organic molecules and ions, the permittivity of the solvent seems to be enhanced with respect to the pure water value. Also in accordance with other aqueous systems it is found that the principal dielectric relaxation time for equimolar solutions of stereo isomers at the same temperature may significantly differ from one another. A further result is the finding of an unusually strong temperature dependence in the relaxation time of the 1 molar solution of 2,6-dimethylpyridine.

Oxide thin film having high permittivity and formation thereof

Abstract: PURPOSE:To make the title thin film low in leakage current and high in dielectric strength without remarkable decrease in relative permittivity and restriction on a substrate, by containing silicon as an additive. CONSTITUTION:An oxide thin film is formed on a substrate by a CVD method. At this time, silicon is mixed in the oxide thin film. As the amount of the silicon, which is mixed in the film, about 0.01-20atmic% is desirable. When the amount is less than this value, the effect of decrease in defects based on the mixing of the silicon is less. Meanwhile, when this range is exceeded, the decrease in specific inductive capacity of the oxide thin film is striking. When optical oxygen annealing is performed for the formed oxide thin film, the silicon included in the film is further diffused. Leaking currents can be further decreased by suitable position arrangement. Thus, the oxide thin film having high permittivity can be formed by a CVD method at low leaking currents without striking decrease in relative permittivity and without restriction on the substrate.

Temperature and Permittivity Measurements using a Cylindrical Microwave Imaging System

Abstract: The capabilities of a cylindrical imaging system used in remote thermal sensing and dielectric constant measurements are investigated. The paper presents simulations of absolute and differential reconstructions of bodies within the Born approximation and of stronger diffracting objects. In addition a preliminary experiment is presented.

Mutiple angle of incidence measurement technique for the permittivity and permeability of lossy materials at millimeter wavelengths

Abstract: : A technique of measuring the permittivity and permeability of lossy, homogeneous, linear, isotropic materials at millimeter wavelengths was developed. The technique was tested by measurement of representative materials at a frequency of 94 GHz. For the type of materials under consideration, the permittivity and permeability are complex and general. Thus there are four unknowns to be determined and a minimum of four measurements are required. The approach taken was to measure the magnitude of the transmission coefficient of a planar material sample in free space at multiple angles of incidence. The system of equations obtained from any four of the angles is solved numerically for the permittivity and permeability of the sample. The equipment consisted primarily of a Gunn phase-locked millimeter-wave oscillator, a pair of conical horn/lens antennae, a sample holder/positioner, and a microwave receiver. Harmonic mixing was employed to convert the test waveform to the operating range of the receiver.

A new technique for free-space permittivity measurements of lossy dielectrics

Abstract: A new technique for permittivity measurements of lossy dielectrics is proposed. It is based on attenuation measurements for both polarizations of backscattered field from a dihedral corner coated by the material under test with respect to that backscattered from an identical perfectly conducting one. Such a technique has the appealing feature of employing an uncritical target without the need of phase measurement, thus overcoming the two main drawbacks of the other available free-space measurement techniques. Numerical simulations assessing the effectiveness of such a technique are also reported and discussed.

The temperature and frequency dependencies of permittivity and dielectric loss in reaction bonded silicon nitride

Abstract: The temperature dependencies of the permittivity and dielectric loss of reaction bonded silicon nitride (RBSN) have been measured between 20 and 900° C at frequencies covering the range from 3 Hz to 300 kHz. Above about 300° C both parameters have a large effect. Analysis of the permittivity data in terms of the theory discussed by Jonscher and by Dissado and Hill predicts loss peaks at 48 Hz and 8 Hz at temperatures of 900 and 800° C, respectively. These values are in close agreement with those found independently from direct observation of the temperature and frequency variations of dielectric loss. On the assumption that a thermal activation process is responsible for the temperature dependence of the loss peak frequency, the associate activation energy is found to be about 1.94 eV.

Measuring system for dielectric spectroscopy.

Abstract: To determine electrical parameters such as relative permittivity, relative permeability and loss factor of materials, a measuring system is proposed which consists of a thermostatic device (1) with regulator and specimen holder, a measuring device (4) for the electrical impedance and for the relative permittivity, relative permeability and the loss factor derived therefrom and which furthermore incorporates a control, regulation and computer unit (3) and an output unit (2). Such a measuring system makes it possible to record and process measured data and also to control the entire measuring device simultaneously.

Divergence of imaginary part of dielectric permittivity at the melting point in KC1

Abstract: The solid–liquid phase transition is a very common phenomenon, whose mechanism, although much studied, is not yet understood. A study of the properties of a solid having simple structure and simple bonding near the melting and the freezing point may be useful. We report the behaviour of the dielectric permittivity in KCl, a typical ionic crystal, in the microwave region in the vicinities of the melting and the freezing point. The imaginary part of the dielectric permittivity, e", diverges at the melting and the freezing point; the real part, e′, varies discontinuonsly. This supports a recent theory of melting, where the density fluctuations are emphasized as the precursors of melting or freezing.

Temperature dependence of ferrobielectric properties of lithium caesium sulphate

Abstract: Ferrobielectric properties of LiCsSO4 crystals have been studied and discussed in terms of reorientation of representation ellipsoid for the low frequency dielectric permittivity tensor. It has been shown that under uniaxial stress the dielectric permittivity changes considerably as the crystal is being shifted from one orientation state to the other. Both, the direction and the amplitude of this change have been found to be temperature dependent.

Partial Discharge Characteristics in Barium Titanate Multi-Layered Structures: Effect of Material and Structural Parameters

Abstract: The partial discharge characteristics of barium titanate multi-layer ceramic capacitors were investigated under 60 Hz voltage excitation. For capacitor specimens which were specifically fabricated for this study, the partial discharge characteristics were found to depend strongly on such para, meters as dielectric film thickness, relative permittivity, porosity and void size distribution.