Showing papers on "Relative permittivity published in 1979"

Dielectric properties of brain tissue between 0.01 and 10 GHz.

Abstract: Dielectric permittivity and conductivity are reported for grey and white matter from dog brain tissue between 0.01 and 10 GHz. Between 0.01 and approximately 1 GHz, the permittivity decreases and conductivity increases as a power law of frequency. Above 1 GHz, the conductivity increases quadratically with frequency due to dipolar reorientation of free water molecules in tissue; the apparent rotational relaxation frequency at 37 degrees C is 21--25 GHz, slightly below the 25 GHz characteristic frequency of pure water at that temperature. The microwave data are analysed using the Maxwell mixture theory applicable for a suspension of nonconducting, low permittivity spheres in bulk water. From the increase in conductivity above 1 GHz, and the tissue permittivity at 2--4 GHz, the apparent volume fraction of water is approximately 0.70 and 0.55 for grey and white matter, respectively, about 10--15% lower than respective values from the literature. This discrepancy is apparently due to a small fraction of water which does not contribute to the tissue permittivity above 1 GHz. Empirical equations are given to summarise the dielectric properties of 'average' brain tissue at 37 degrees C for future theoretical studies of microwave absorption in the head.

In vivo dielectric spectrometer

Abstract: An instrument is described for measuring the relative permittivity and dielectric loss of body tissues and organsin vivo, over the frequency range 0·1 Hz to about 100 kHz. A voltage transient is applied by means of suitable electrodes and the resulting waveform is sampled, digitised and Fourier transformed using a microprocessor to give a spectrum in the frequency domain. The results show differences in relative permittivity and dielectric loss between different types of tissue. Much of the preliminary clinical work with this apparatus has been done using measurements on breast tumours.

Calculations on ionic solvation. III. The electrostatic free energy of solvation of ions, using a multilayered continuum model

Abstract: For the calculation of the electrostatic free energy (and also the entropy) of solvation of an ion, a model is set up in which an ion of given crystallographic radius is surrounded by a series of concentric spherical layers, each with a different relative permittivity, immersed in the bulk liquid. A complete general solution is given for any number of such layers, both for the electrostatic free energy of solvation and the corresponding entropy term. The dielectric saturation effect is taken into account through the different relative permittivities of the layers. The first layer, next to the ion, is considered to have a special role and to have a relative permittivity e=n2, independent of the dielectric saturation effect of the ion.

Determination of conductivity profiles by time-domain reflectometry

Abstract: A new numerical method for the reconstitution of the inhomogeneous media conductivity is described. The conducting medium is nonmagnetic, and its relative permittivity equals one. Its frequency-independent conductivity varies normally to its interface. The medium is normally illuminated by a transverse electromagnetic (TEM) plane wave of causal time dependence. The reconstruction process is a direct approach to the inverse problem. It is based on a space time discretization of an exact integral equation. The conductivity profile is determined step-by-step without approximations other than numerical. Some examples are given to illustrate the most interesting properties of the method; special attention is given to the simulation of experimental errors.

Interface characteristics of Inp MOS capacitors

Abstract: A new electrolyte based on a solution of 10 g of ammonium pentoborate in 100 ml of ethylene glycol buffered to a ph of 6.0 has been used to produce a dielectric layer on the surface of InP. The relative permittivity of the anodic oxide is 7.9 and its dielectric breakdown strength is 3×106v/cm. The electrical characteristics of the surface states at the anodic oxide–‐type InP interface have been investigated using MOS capacitors. Capacitance–voltage data at 200 kHz indicate that the InP surface is already depleted at zero bias with a flat band voltage of 0.85 V. An inversion‐type low frequency (1 Hz) response has been observed for the first time on an InP MOS structure using an anodic oxide. Our analysis of the admittance data yields a U‐shaped surface state distribution having a minimum density of 4×1011 cm−2 eV−1 at mid‐band gap. Many other fea ures of our results also resemble those previously obtained with InP/organic insulator structures.

Time-Domain Measurements for Determination of Dielectric Properties of Agricultural Materials

Abstract: A time-domain reflectometer (TDR) system was used to obtain data on the frequency dependence of the dielectric properties of a few agricultural materials. Values for the complex relative permittivity in the frequency range from about 30 MHz to 1 or 2 GHz were obtained from the reflection coefficient, which was calculated from the ratio of the Fourier transforms of the incident and reflected waveforms from the dielectric sample in a coaxial line. With the TDR system, broad dielectric dispersion and absorption regions, similar to those found by frequency-domain measurements, were determined with significant reductions in time and effort.

The Magnetic-Dipole Resonances of Ring Resonators of Very High Permittivity

Abstract: The lowest magnetic-dipole mode with symmetry of revolution is investigated in a coaxial ring resonator of height L, inner radius b, and outer radius a. Theoretical data are given about the Q of the mode, the eigen magnetic dipole at resonance, and the structure of the fields (electric and magnetic) inside and outside the resonator. The variables are the dielectric constant epsilon/sub r/ = N/sup 2/ and the dimensionless ratios b/a and L/2a. The data are valid in the limit of very high epsilon/sub r/. Experiments show them to be already useful at epsilon/sub r/ = 35.

Measurements of Complex Dielectric Constant of Human Sera and Erythrocytes

Abstract: A method for measuring the complex permittivity of biological liquids at microwave frequencies is presented. The calibration needs three reference materials; this method allows measurements to be made very quickly, using only very small amounts of material. Measurements were made on human erythrocytes, obtaining their inner conductivity using Fricke's equation, and on human sera of normal and sick individuals. Using an optimization technique, some parameters related to the water bound to the serum proteins were identified, showing differences possibly related to the presence of certain diseases.

Calculation of the Bandwidth of Microstrip Resonator Antennas

Abstract: In this paper one presents an analysis of the bandwidth of microstrip resonator antennas in function of the antenna parameters. Starting from the general expression for the quality factor of a resonator, it will be proved that the bandwidth of a microstrip resonator antenna is directly proportional to the thickness of the substrate, to the square of the resonant frequency and inversely proportional to the square root of the relative permittivity of the substrate material. Comparing the theoretical results with experimental data one finds a good agreement.

Theory of the dielectric constant of the smectic phases, and comparison with experiments

Abstract: 2014 The relation between the order parameters and the static dielectric constant of the smectic phases is investigated here, in the cases of one or more dipoles per molecule. We predict the temperature dependence of the dielectric constant and compare with experimental results. LE JOURNAL DE PHYSIQUE TOME 40, JUILLET 1979,

Static Dieleciwc Peiwmtmty Measurements on Aligned Smectic-C Phase

Abstract: Dielectric permittivity was measured in nematic, smectic-A and smectic-C phases. Three permittivity components were deternined in the SC phase.

Dynamic permittivity of microstrip ring resonator

Abstract: A simplified method for calculation of the dynamic dielectric constant for a microstrip ring resonator is presented. Attention is also given to the sectors of the annular structure. The new results are compared with earlier work.

An Open Transmission Line UHF CW Phase Technique for Thickness/Dielectric Constant Measurement

Abstract: A description is given of a system which employs open-balanced transmission line structures and UHF CW phase measurement techniques to determine either the thickness or dielectric constant or moisture content of film or slab-like materials in the thickness range of 1 to 400 mil and the relative dielectric constant range of approximately 2 to 20. Both experimental and analytical results are presented.

Miniaturized dielectric radio frequency filter for 850 MHz band mobile radio

Abstract: A newly designed 806 ∼ 947 MHz band RF filter has been developed for the vehicular communication radio. This newly developed filter features a simple structure of miniaturized size and light weight. The new waveguide which makes the basis of the resonator is constructed with a dielectric rod having a thin central conductor, inserted between two parallel plates. The principal modes of the electromagnetic field propagating along the waveguide are the quasi-TEM mode on the lower frequency side and the quasi-TM 01 mode on the higher frequency side of the mode coupling frequency. Two new coupling design methods are employed: spacing control and wire control. In the spacing control method, the required amount of coupling is obtained by slightly changing the spacing between adjacent resonators. The wire control method obtains the expected amount of coupling by changing the number of equi-distantly inserted thin wires and their positions. The lowest spurious spectrum is about 2.3 GHz. The unloaded Q (Qu) of the resonator is about 1600, and of the resonator having loop excitation, Qu is about 1000. The relative permittivity of the dielectric is 20.0 and tan δ is 1.1 × 10-4at 6 GHz.

Complex permittivity and microwave heating of pure water, tap water and salt solution

Abstract: The complex permittivity and temperature rise versus time have been measured for pure water, Maltese tap water and pure water—commercial salt solution at 2.45GHz. The experimental results are related to empirical or theoretical calculations. The complex permittivity of commercial salt concentration in pure water has also been reported.

A Method for Measurement of the Permittivity of Thin Samples

Abstract: A simple method for measurement of the dielectric properties of plant leaves at microwave frequencies is described. Theoretical analysis is given of the frequency dependence of the reflection coefficient of a sample holder with a sample located at the end of the coaxial line which opens into a circular wave guide operating below cut-off. Analysis and calculations of the uncertainty in permittivity measurements, as well as experimental results for rape leaves, are presented and the limitation of the method are discussed.

Microwave dielectric measurements of lunar soil with a coaxial line resonator method

Abstract: A method is given for sensitive dielectric measurements at a series of microwave frequencies using a section of coaxial line. The line is used as a 1-port cavity resonator; it resonates when the electrical length of the center conductor equals 1, 2 . . . , N half-wave lengths. The dielectric properties of an Apollo 17 dried soil sample were measured in vacuum over a temperature range of 173 to 373 K. The relative permittivity and the loss tangent were determined and the frequency dependence was very small. The derivative with respect to temperature, per degree, was 0.00045 for the permittivity and 0.00002 for the loss tangent.

Measurement of the complex permittivity of thin films in the very low frequency range

Abstract: A method and an apparatus for measuring the dispersion characteristics of thin-film metal-insulator-metal structures at frequencies below 1 Hz are described. Application of this apparatus makes it possible to study the complex permittivity of thin films having a loss tangent of the order of 10.

Submillimeter-wave measurements on liquid dielectrics

Abstract: Recent advances in submillimeter-wave complex relative permittivity measurements on liquids are described. The developments include direct measurements of both real and imaginary parts of the complex relative permittivity both at spot frequencies using submillimeter-wave laser spectrometry and in the broad band using dispersive Fourier transform spectrometry.

Dielectric behavior of n (p‐octyloxybenzylidene) p‐toluidine (OBT) in nematic mesophase at radio frequencies

Abstract: Dielectric permittivity and loss have been measured in the frequency range 0.5–3.5 MHz in nematic and isotropic phases of OBT. Measurements in the nematic region with a magnetic field greater than saturation value acting parallel to the rf electric field exhibit a Debye type dispersion of e∥ with relaxation frequency 5.3 MHz at 71° C and activation energy of 27.0 kcal/mole. The results can be explained on the basis of the molecular rotation about a transverse axis occurring under hindering nematic potential. Measurements also indicate that OBT behaves as a positive dielectric material at low frequencies and a negative dielectric material at higher frequencies.

Complex Permittivity of Rubber-Carbon Mixtures

Abstract: This communication describes the complex permittivity of various mixtures of synthetic rubber and carbon (acetylene black, furnace black and channel black) in the microwave region. The effects of temperature on the complex permittivities are also noted for different concentrations of carbon.

Spread in effective permittivity of alumina substrates

Abstract: Measured data on the spread in effective permittivity of alumina substrates in the range 1–18 GHz are presented. The data show both the spread from sample to sample and over the area of a single substrate. Effective permittivities were calculated from the resonant frequencies of open-ended straight-line resonators.

Antiferroelectricity of CsD2PO4 under hydrostatic pressure

Abstract: The observation of P-E double hysteresis loops under hydrostatic pressure in CsD2PO4 suggests that the high-pressure phase is antiferroelectric. The dielectric properties such as the relative permittivity and the polarisation in the pressure-induced antiferroelectric phase were measured. The effect of pressure on the dielectric properties was found to be striking.

A Variational Approach to Compute the Equivalent Capacitance of Coaxial Line Discontinuities

Abstract: A variational approach is presented which enables both to compute the discontinuity capacitance in coaxial structures and to state its frequency behaviour. The results compare favorably with the ones previously given in literature. Moreover, the method enables to consider structures having different dielectric permittivities at the sides of the discontinuity.

The microwave dielectric properties of chalcogenide glasses

Abstract: The microwave dielectric properties of the chalcogenide glass ASggTeggGe^g (by atomic percent) were determined, utilizing the trans­ mission method. The relative permittivity was found to be 15.9 + 0.9 for the 8.0 to 12.4 GHz frequency band. The loss tangent was found to be less than or equal to 0.3 throughout the same frequency band. The error in the relative permittivity measurements was determined to be less than 5%. Samples were prepared from 99.99%.pure arsenic, tellurium, and germa­ nium. Quartz ampules containing the As^gTe^^Ge^Q were heated to 1000 degrees centigrade for 24 hours and then quenched in liquid nitrogensoaked sand. Test samples were produced by placing the quenched ASg^Teg^Ge^Q in chrome-plated molds, reheating to 600 degrees centigrade, and requenching, using dry ice. The transmission method yielded excellent results for low, medium, or high relative permittivity samples, regardless of sample thickness. The method is based on the comparison of the dominant Transverse Electric fields in a rectangular waveguide with and without a sample being present. The resulting transcendental equation with two unknowns was solved by generating tables based on the substitution of various values of complex relative permittivity, and comparing the corresponding phase shift and amplitude change with the measured values. A unique solution was found by comparing results of samples of different thicknesses.

Dispersion of the dielectric permittivity in mixtures of nematic liquid crystals

Abstract: The spectrum of relaxation time for the low-frequency dispersion has been found to become wider in mixtures of nematic liquid crystals, which can be interpreted as a superposition of two Debye relaxation mechanisms.

Comparative Microwave Measurements of Complex Dielectric Constant of High Permittivity Thin Films

Abstract: In the proposed work, complex dielectric constants of high permittivity thin films of BaTiO/sub 3/ and PbNb0/sub 3/ are measured at microwave frequencies. Working equations are presented for epsilon' and tgdelta by means of a new method of measurement, earlier reported by the author, with corrections for supporting substrate reactance in the present work. Verification of experimental results are done by means of multilayered dielectric slab loaded waveguide method and modified Drude's method. The working equations for latter two methods are also presented. Experimental results of BaTi0/sub 3/ and PbNb0/sub 3/ thin films as measured by these three methods are given.

Microwave Dielectric Relaxation of Lithium Salts in Media of Low Permittivity at t=25°C

Abstract: This paper reviews data (taken in our laboratory) of complex permittivities of solutions of lithium salts at U.H.F. and microwave frequencies. The solvents used were tetrahydrofuran, dimethyl- and diethylcar-bonate.