Showing papers on "Relative permittivity published in 1974"

High dielectric constant microwave probes for sensing soil moisture

Abstract: Implantable soil moisture sensors suitable for long-term monitoring of moisture in highway subgrades and for similar applications are needed. Two candidate designs of microwave sensors (operating range 4 to 6 GHz) have been investigated for such applications. One design uses the fringing field of a low-loss dielectric slab waveguide (relative dielectric constant of 25) to obtain good resolution for finely divided soil such as bentonite clay with moisture ranging from 10 to 50 percent by dry weight for effective sample volumes of 20 to 40 cm2. The response of the dielectric waveguide sensor has been calculated in terms of the effective dielectric constant of the soil-water mixture. A model based on index of refraction yields an effective dielectric constant in reasonable agreement with experiment when effects of ionic conduction are accounted for. Another sensor design, better adapted for coarse materials, such as crushed limestone aggregate, uses waves launched from a tapered dielectric slab. By using either frequency or spatial averaging methods, the launched wave sensor accommodated aggregate particles passed by a 0.63-cm mesh sieve, and was found to have satisfactory resolution for the range of 0- to 10-percent moisture by dry weight.

Elementary properties of surface polaritons

Abstract: The properties of polaritons which exist at the plane boundary between two isotropic dielectric media, one of which has a negative relative permittivity for part of the frequency range, are investigated by classical electromagnetic theory. The energy flow, density and velocity of the surface polariton are derived. The quantum-mechanical vector-potential operators in the two media are expressed in terms of surface-polariton creation and destruction operators. The thermal fluctuations in surface electric fields are determined, and the frequency-dependent relaxation rates of the surface polaritons are derived; the main concern is with polaritons which are mixtures of photons with optic phonons, but the photon-plasmon type of polariton is also discussed as a special case.

Permittivity Measurements at Microwave Frequencies Using Lumped Elements

Abstract: A simple frequency-domain method for measurement of the dielectric properties of materials is described. Theoretical analysis of the frequency dependence of the reflection coefficient of a shunt lumped capacitor located at the end of a transmission line and filled with a very small amount of the dielectric (typically a few microliters) is given. Analysis and calculations of the overall uncertainty in permittivity measurements, as well as experimental results for some normal alcohols, are presented and limitation of the method discussed.

Simple Nondestructive Method for the Measurement of Complex Permittivity

Abstract: A simple nondestructive method is presented for the measurement of the complex permittivity ?r of materials. The reflection coefficient ? of a flanged open-ended rectangular waveguide placed, next to a flat large sample is computed by a variational method as a function of the dielectric constant. Computer-generated charts and an optimization computer program are elaborated. ?r can then be easily determined from the measured amplitude and phase angle of the reflected wave in the waveguide. The method is best suited for materials having high dielectric constants and large losses.

Comparison of Cavity and Open-Resonator Measurements of Permittivity and Loss Angle at 35 GHz

Abstract: A comparison has been made between cavity and open-resonator measurements of permittivity ?' and dielectric loss angle ? at 35 GHz. Two comparisons were made, the first using one set of samples of unsintered polytetrafluoroethylene measured in both systems and the second using two sets of similar samples, one set measured in each system, of a high density polyethylene (Rigidex 2000), cut from the same rod. The measured values of ?' and ? obtained by the two systems agreed within the limits of the experimental errors. The standard deviations obtained for ?' and ? were 0.0021 and 2.1 ?rad, respectively. A discussion of the uncertainties associated with each measured parameter is given.

Non-Destructive Measurement of Complex Permittivity for Dielectric Slabs

Abstract: A method has been developed for a precise non-destructive measurement of the dielectric constant and losses of slab-like samples, such as microstrip substrates for instance. The test setup basically consists of an open-ended rectangular waveguide whose flange is placed in contact with one side of the dielectric material, the other one being backed by a metal plate. The measured amplitude and phase of the reflection coefficient with respect to a short-circuit in the aperture plane are related to the real and imaginary parts of the permittivity by means of computer generated charts.

Dielectric induction logging system for obtaining water and residual oil saturation of earth formations

Abstract: DIELECTRIC INDUCTION LOGGING SYSTEMFOR OBTAINING WATER AND RESIDUAL OIL SATURATION OF EARTH FORMATIONS (D#73,809-F) Abstract of the Disclosure Radio frequency electromagnetic fields are used to excite earth formations in the vicinity of a well borehole. The total field amplitude at a single coil receiver and at a dual coil receiver are detected and signals representative thereof are combined according to a predetermined relationship to obtain the relative permittivity and resistivity of the earth formations. By combining the measured permittivity with porosity measurements from another source according to predetermined relationships, the water saturation Sw and residual oil saturation ROS may be determined and logged as a function of borehole depth. -I-

Dielectric relaxation in non-aqueous solutions. Part 5.—Propylene carbonate (4-methyl-1,3-dioxolan-2-one)

Abstract: The permittivity (Iµ′) and loss (Iµ″) of propylene carbonate (4-methyl-1,3-dioxolan-2-one) have been measured at several temperatures between 0° and 50°C in the frequency range 05 to 35 GHz The overall frequency response of the complex permittivity is unsymmetrical but can be satisfactorily represented by the equation Iµ′(ω)– iIµ″(ω)=Iµ∞+(Iµs–Iµ∞)/(1 + iωτ0)ξThe temperature dependence of the relative static permittivity (Iµs) is accurately described by the empirical relation, Iµs=A exp(–LT), with A= 1956 and L= 3681 × 10–3 K–1, although the dielectric relaxation times (τ0) do not fit the usual Arrhenius expression The distribution parameter (ξ) and high frequency limiting permittivity (Iµ∞) both vary in an irregular manner with increasing temperature Propylene carbonate also absorbs in the far infra-red between 20 and 170 cm–1 with a maximum absorption at about 70 cm–1Values of the Kirkwood correlation parameter (g) calculated from Iµs indicate that short range order is not significant in liquid propylene carbonate The unsymmetrical frequency response of (Iµ′– iIµ″) has been discussed in terms of current molecular theories

The permittivity of suspensions and two-phase mixtures

Abstract: Equations analogous to those derived for the elastic moduli and conductivity of composite materials are proposed for calculating the permittivity (dielectric constant) of two-phase systems, including metals dispersed in dielectric media. The equations not only take into account the permittivity of the pure components and their concentration but also the shape of the dispersed particles and the manner in which they pack. Agreement between experiment and theory generally appears to be very good.

The resonant linear antenna as a probe for measuring the in situ electrical properties of geological media

Abstract: A method is presented that uses the resonant linear antenna as a probe to measure the electrical properties of dissipative media. Parametric equations are derived for the length and driving point resistance of the antenna in terms of the relative permittivity and loss tangent of the ambient medium. Graphs constructed from these equations permit a simple determination of the electrical properties of the medium from the length and resistance at resonance. The application of the method to the measurement of the relative permittivity and loss tangent of in situ geological media is described. Calculations for different geological materials indicate that the method is particularly useful for making measurements with antennas of convenient length at frequencies in or near the VHF band. The method was tested experimentally by measuring the electrical properties of freshwater, saltwater solutions, and moist sand. The results of these measurements are discussed.

The transient response of a dielectric layer

Abstract: The transient response of an atmospheric surface duct will be studied when the distance between receiving and transmitting end is arbitrarily chosen. The duct model used is that of Kahan and Eckart, consisting of a layer of relative permittivity e1 overlying an infinitely conducting plane earth. At heighth, this permittivity decreases discontinuously to the value e2. The source of the electromagnetic field is assumed to be a vertical magnetic dipole at the height ξ (ξ

Dielectric relaxation in water in the neighborhood of 4°C

Abstract: The complex permittivity of water has been measured at seven temperatures between 3 and 5°C over a frequency range of 0.4–4 GHz. The data are analyzed first in terms of a small but significant distribution of relaxation times of magnitude larger than that observed previously and then as two separate Debye process having relaxation times separated by a factor of ∼2. It is shown that one possible interpretation of these observations is that a bond breaking process takes place in which the rate of formation of one bonded molecules from two bonded molecules depends upon whether the latter are bonded symmetrically or unsymmetrically. The value of the high frequency permittivity (e∞) calculated from this model is shown to agree well with experiment. There is no evidence of any abrupt changes (``kinks'') greater than random experimental error in the temperature variation of the dielectric parameters of water between 3–5°C.

International Comparison of Complex Permittivity Measurement at 9 GHz

Abstract: Dielectric constant and loss measurements made by three government laboratories (of the USSR, Canada, and the U. S. A.) are compared. The two materials measured were glasses. The measurements utilized cavity resonators in the H01n mode. The errors in dielectric constant reported by the laboratories were usually ± 0.3 percent; actual differences between laboratories of the average corrected results were only ± 0.05 percent. The loss tangent results disagreed when multimoding occurred; however, the errors may be as low as ± 0.00002 or ± 3 percent, whichever is the larger, if multimoding is avoided.

Dielectric Properties of Zinc Oxide-Eugenol Type Cements

Abstract: Relative permittivity and resistivity of zinc oxide-eugenol cements was measured during setting. During setting the relative permittivity goes through a very pronounced maximum; simultaneously, resistivity suddenly increases by a few orders of magnitude. Such behavior is explicable in the initial function of water, which subsequently becomes bound.

Measurement of complex permittivity of liquids. II

Abstract: Improvements on the method of Lovell and Cole (1959) for the measurement of complex permittivity of liquids by means of the Boonton R-X Meter are presented. A new approach to the calibration of the cell and connecting line, considering ohmic losses, is described. Results obtained for the aliphatic alcohols compare closely with the values of complex permittivity measured by means of coaxial line techniques. The relative error in the real and imaginary components of permittivity are 1.2% and 2.5% respectively.

Measurement of the permittivity of films at microwave frequencies

Abstract: A method is proposed for the measurement of phase shift and attenuation using a slotted line. These measurements enable the complex permittivity of isotropic films to be found by mounting the specimen longitudinally at the centre of a rectangular waveguide, the electric field being in the plane of the film. Experiments have been performed on films of Mylar and Teflon for a range of thicknesses from 75 to 250 mu m. The experimental results agree well with the accepted values (within approximately 2%).

Modified Perturbation Method for Permittivity Measurements at Microwave Frequencies

Abstract: A method of permittivity measurement by a cavity perturbation technique is described. The cavity resonates in two modes at two different frequencies. Continuous measurement of the dielectric constant of a test sample can be performed using a low frequency digital counter (up to 500 MHz) while the loss factor can be determined from the difference in the transmission coefficients at the two resonant frequencies. Experimental results for rectangular and circular cylindrical geometries of cavities used for permittivity monitoring at 2450 MHz are also reported.

New Microwave System to Determine the Complex Permittivity of Small Dielectric and Semiconducting Samples

Abstract: This paper describes the new microwave bridge system with dielectric antennas of very small transverse dimensions (smaller than 10 mm) convenient for measurements of the complex permittivity of slab materials. This system enables (i) to measure by nondestructive way the complex permittivity of dielectric and semiconducting samples the dimensions of which are comparable or smaller than the wavelength of probing microwaves, (ii) to detect the material inhomogeneities. This system was verified at the frequency 37,5 GHz. Measurements of the specific resistivity of the Si samples are given. Obtained results are in good agreement with the theory.

A microwave barrel resonator for permittivity measurements on dielectric rods

Abstract: The theory of the barrel resonator with a central rod of dielectric material is developed. The equations for resonance are derived and it is shown how this configuration can be used for the measurement of permittivity.

Dielectric properties of RbH2AsO4

Abstract: Measurements of the dielectric, pyroelectric properties of RbH2AsO4 single crystals in their ferroelectric phase are reported. As a result of the experiments (a relatively small value of the dielectric constant e at the Curie point Tc, the jump of the reverse dielectric permittivity on the 1/e (T) curve, the difference between the Curie and the Curie-Weiss temperatures, the jump of the spontaneous polarization at Tc, and the negative sign of the thermodynamic coefficient β) concluded that a phase transition of the first order takes place.

Permittivity increments in non-dipolar solvents due to high electric fields

Abstract: Measurements of the change in relative permittivity (ΔIµ) have been made as a function of applied electric field (E) at 22°C for the non-dipolar liquids n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, cyclohexane, benzene, carbon tetrachloride and carbon disulphide. The measurements were made at fields of up to 2 × 107 V m–1, the ΔIµ being detected via the change in frequency of an oscillator as measured using a computing counter. The range of ΔIµ/E2 values obtained were from about 10 to 30 × 10–20m2V–2. The values were generally larger than could be attributed to the anisotropy of polarizability, particularly for the nearly spherical carbon tetrachloride molecule and much larger than the expected contributions due to electrostriction and the electrocaloric effect. The measured values are undoubtedly made up from a number of effects, including the Kielich local fluctuating intermolecular effects.

Computation of Dielectric Properties from Short-Circuited Waveguide Measurements on High- or Low-Loss Materials (Computer Program Descriptions)

Abstract: Computation of the relative complex permittivity components /spl epsilon//sub r/' and /spl epsilon//sub r/'' loss tangent, and conductivity from measurements data on materials in coaxial, rectangular, or cylindrical waveguides.

A system for the investigation of nonlinear dielectric effects using digital techniques

Abstract: A novel method for the study of nonlinear dielectric effects has been developed, which allows, for the first time, measurements to be carried out on conductive media such as water. The sample is contained in a dielectric cell which is part of the tank circuit of an oscillator. A rectangular electric field pulse of up to 15 MV m-1 is applied to the sample, and the resulting frequency change of the oscillator due to the nonlinear dielectric effect is measured using a computing frequency counter. This frequency change is simply related to the change in relative permittivity Delta epsilon . By sampling the frequency of the oscillator at different points throughout the duration of the electric field pulse, a very faithful reproduction of the profile of the nonlinear effect can be built up. Details are given of the instrumentation along with illustrative results for diethyl ether.

The anodization of si in an rf plasma

Abstract: The anodization of Si in a 1 MHz oxygen plasma is described. In‐situ film thickness measurements were made using a single angle "s" light reflectance technique and this data, coupled with information on the variation of sample voltage with thickness, was used to determine the dependence of ionic current on oxide field strength. The data for a given oxide thickness could be described by an equation of the form given by the theory of ionic conduction by a thermally activated, field‐assisted process. However, the ionic current and, in paticular, the oxide field strength were dependent on oxide thickness. MOS C‐V measurements on oxides of different thickness indicated a change in flatband voltage that could be attributed to a progressive build‐up of positive charge within the oxide. This space charge could be reduced by a low temperature annealing treatment. The oxides were found to be slightly absorbing optically, to have a relative permittivity in the range 3.5–3.9, and to possess good insulation properties as long as the oxide thickness did not exceed about 2500â.

Influence of a strong electric field on the dielectric permittivity of solutions of alcohols in neutral solvents. I

Abstract: From theoretical considerations. an expression is derived for the change in dielectric permittivity of solutions of alcohols under the influence of a strong applied electric field. Two processes underlying this change are taken into consideration: reorientation of the molecules, and proton tunnelling in hydrogen bridges. Molecular reorientation is dealt with by the domain model of an associated liquid; proton tunnelling in the hydrogen bridge, by a one-dimensional treatment. To within experimental error and approximations made in the course of the calculations. the expression derived yields values in agreement with experiment, for the following solutions: n-butanol-1 in n-hexane; n-butanol-1 in cyclo- hexane; and n-butanol-2 in cyclohexane.

Microwave Permittivity Measurement Using a Multipoint Technique (Short Papers)

Abstract: A multipoint technique for complex permittivity measurements is described. This method is based on experimental determination and fitting of the field pattern existing in the sample placed inside a short-circuited slotted waveguide and verified with experimental results.

The Precise Determination of the Dielectric Properties of Alumina

Abstract: There are three methods for the determination of the dielectric properties of material in sheet form: the Hartshorn-Ward 'resonance-substitution' technique (BS 2067), the Lynch method using a transformer bridge (BS 4542) and the two fluid immersion method. These methods may be used at frequencies up to 1 MHz, and, in this range, it is shown that the two fluid immersion method offers advantages for permittivity measurement but is not suitable for determination of tan ?. A modified form of Q meter is then described for use in the frequency range 1-100 MHz where application of the resonance substitution method permits dielectric loss measurements to be made with a precision of better than five microradians. Measurements at microwave frequencies are made by resonant cavity techniques and comparison is made between the value of permittivity determined at 1 MHz by a cross checkable two fluid method, and those calculated from the high frequency values of permittivity and dielectric loss.