Showing papers on "Relative permittivity published in 1992"
TL;DR: It appears to be possible to move and rotate cells or particles at will using very-high-frequency fields and media of increased relative permittivity, as shown by experimental data on levitation and rotation.
132 citations
TL;DR: A method of correcting for the RF inhomogeneity in the body by dielectric loading of the coil‐to‐shield space in an RF resonator (coil and shield assembly) is described and a method for adjusting the RF homogeneity by manipulating the axial propagation constant, kz, is proposed.
Abstract: A method of correcting for the RF inhomogeneity in the body by dielectric loading of the coil-to-shield space in an RF resonator (coil and shield assembly) is described. The presence of the RF coil and RF shield have significant effects on RF homogeneity. Based on theoretical calculations, a method for adjusting the RF homogeneity by manipulating the axial propagation constant, kappa z, is proposed. This is accomplished by loading the coil-to-shield space with dielectric material of suitable relative permittivity so as to increase kappa z and decrease the radial propagation constant, kappa rho. In this manner, the radial wavelength (lambda rho = 2 pi/kappa rho) can be increased relative to the body dimensions, and the field amplitude variations in the axial plane minimized. Theoretical calculations indicate that a value of between 30 and 40 for the relative permittivity of the dielectric material in the coil-to-shield space would reduce the RF field inhomogeneity from +/- 15% to about +/- 3% over a central 30-cm-diameter region of a homogeneous 40-cm-diameter body at both 64 and 170 MHz. The theoretical model was verified in laboratory measurements of the [formula; see text] field generated in a test coil at 170 MHz which was scaled to correspond to a body at 64 MHz. However, the improved RF field homogeneity would be accompanied by increased RF power requirements and reduced coil sensitivity.
71 citations
TL;DR: In this article, the authors used the time-domain reflectometry (TDR) technique at various temperatures for dimethyl sulfoxide-water mixtures to determine complex dielectric spectra in the frequency range 10 MHz-10 GHz.
Abstract: Complex dielectric spectra, Iµ*(ω)=Iµ′– iIµ″, in the frequency range 10 MHz–10 GHz have been determined using the time-domain reflectometry (TDR) technique at various temperatures for dimethyl sulfoxide–water mixtures. The dielectric spectra can be described by the Davidson–Cole relaxation model. The thermodynamic properties of the mixture have also been evaluated. The behaviour of the principal relaxation time of the mixture shows a maximum at a value corresponding to a mixture with 30% of water. An attempt has been made to explain the dielectric behaviour of binary mixtures by the hydrogen-bonding model as suggested by Luzar. The static relative permittivity of the mixtures can be explained if one assumes that the dipole moments of water and DMSO in the mixture are 14% and 10% larger than the corresponding values in the gas phase.
68 citations
TL;DR: The measured electrical constitutive parameters (effective relative permittivity and effective conductivity) for Georgia red clay are presented and should be useful in designing and characterizing broadband systems whose performance is dependent upon or affected by the Earth, such as ground-penetrating radars.
Abstract: The measured electrical constitutive parameters (effective relative permittivity and effective conductivity) for Georgia red clay are presented. These results are for the frequency range 50 MHz-1.25 GHz and for six samples with water contents by dry weight ranging from approximately 0-30%. These electrical parameters should be useful in designing and characterizing broadband systems whose performance is dependent upon or affected by the Earth, such as ground-penetrating radars. >
50 citations
TL;DR: In this article, a segmented rigid-rod polyimide was synthesized from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 2,2′-bis(trifluoromethyl)-4, 4′-diaminobiphenyl (PFMB) in order to develop new materials for microelectronic applications.
50 citations
TL;DR: A resonant cavity perturbation technique has been developed which provides a quick, simple and accurate method of measuring the microwave dielectric properties of small, easily prepared samples of tissues, tissue-simulating materials and biological fluids.
Abstract: A resonant cavity perturbation technique has been developed which provides a quick, simple and accurate method of measuring the microwave dielectric properties of small, easily prepared samples of tissues, tissue-simulating materials and biological fluids. The method gives dielectric properties averaged over the sample volume. The measurement accuracy with the apparatus used is +/- 2.2% for relative permittivity and +/- 3.5% for the loss factor for most tissue and biological material samples. With appropriate basic microwave equipment the method can be applied over the 1.5-6 GHz range of frequencies of interest for active and radiometric tissue microwave imaging.
43 citations
TL;DR: In this paper, the dielectric behavior and structure of the BaxSr1-x(Zn1/3Nb2/3)O3 (BSZN) solid solution have been investigated with the intention of understanding an anomaly which exists in the temperature coefficient (τϵ) at x ≈ 0.5.
Abstract: The dielectric behaviour and structure of the BaxSr1–x(Zn1/3Nb2/3)O3 (BSZN) solid solution have been investigated with the intention of understanding an anomaly which exists in the temperature coefficient of the dielectric constant (τϵ) at x ≈ 0.5. A correlation between τe and the occurrence of O-octahedra tilts has been established.
39 citations
TL;DR: In this article, the authors extended the analysis for the interaction impedance of the helix supported by a number of dielectric bars/rods of rectangular or circular cross section, the whole enclosed in a metal envelope.
Abstract: The helical slow-wave structure of a traveling-wave tube is usually supported by wedge-shaped bars or rods or circular or rectangular cross section. Such supports present an inhomogeneous loading of the helix caused by the variation of the effective permittivity of the helix surrounding with the radial coordinate. In one of the approaches to the analysis of such structures for dispersion characteristics, the discrete supports are azimuthally smoothed out into continuous dielectric-tube regions, the number of such tubes being increased for converging results. This method is extended for the interaction impedance of the helix supported by a number of dielectric bars/rods of rectangular or circular cross section, the whole enclosed in a metal envelope. The method gives more accurate results than that given by a single tube, particularly for situations in which the relative permittivity and radial thickness of the dielectric supports and the frequency of operation are high. The analysis developed is rather general. >
30 citations
TL;DR: In this article, three derivatives of a hexadec-1-ene-maleic anhydride alternating polymer and two poly-(vinyl pyridine) derivatives have been deposited as alternate-layer films using a two-compartment trough.
Abstract: In an attempt to produce polymeric pyroelectric Langmuir-Blodgett films, three derivatives of a hexadec-1-ene-maleic anhydride alternating polymer and two poly-(vinyl pyridine) derivatives have been deposited as alternate-layer films using a two-compartment trough. 1-Docosylamine and 22-tricosenoic acid were also alternated with some of the above polymers. Pyroelectric coefficients measured by the quasi-static technique were found to have a maximum value of 0.8 mu C m-2 K-1, comparable to that of other Langmuir-Blodgett structures. Relative permittivity and dielectric loss values of pyroelectric films (in the range 10 Hz-100 kHz) were typically 4 and 0.06 respectively. Finally, these parameters are compared with those of commonly used pyroelectric organic materials.
29 citations
TL;DR: The relationship between the lowfrequency electric properties in the axial, tangential, and radial directions along the diaphysis of a femoral bovine bone is presented in this paper.
Abstract: The relationship between the low-frequency electric properties in the axial, tangential, and radial directions along the diaphysis of a femoral bovine bone is presented It is shown that below 1 MHz the relative permittivity of the diaphysis exhibits a significant positive correlation with respect to the low-frequency conductivity, as measured in any direction, and therefore it could be related to the amount of fluid contained in the channels that provide low-frequency electrical connectivity in the measurement direction There is no significant correlation between permittivity, in either of the three measurement directions, and the total fluid volumetric fraction in the bone >
29 citations
TL;DR: In this article, the authors present a mathematical approach for studying electromagnetic wave scattering from a finite cylinder with radially layered permittivity, based on the approximation that the internal fields are the same as those induced within an infinitely-long cylinder having the same dielectric configuration.
Abstract: This paper presents a mathematical approach for studying electromagnetic wave scattering from a finite cylinder with radially layered permittivity. An estimation of finite-sized cylinder's scattering cross section is based on the approximation that the internal fields are the same as those induced within an infinitely-long cylinder having the same dielectric configuration. Numerical examples and convergence, and consistency with physical principles are tested, and agreement with literature is demonstrated. The study indicates that permittivity arrangements within the confines of the cylinder, its size, and angular distribution have significant effects on backscattering energies. Depending on the permittivity arrangements, trunks' representation by a single-layer dielectric cylinder in image synthesis could compromise the accuracy of their backscattered energy returns. Although the solution has been presented in terms of dielectric cylinders, it could be extended to cases of conducting and ferrite material...
TL;DR: The experimental results show that the complex permittivity increases linearly with concentration of doped acid, when the concentration of acid is expressed by molarity, and this linear relation is independent of the sort of acid.
Abstract: The relative complex dielectric permittivity of acid-doped ice was measured at 9.7 GHz with the standing wave method. The objective of this measurement is to clarify the basic physical properties of ice necessary for the microwave remote sensing of the cryosphere. The acid-doped ice was investigated because acid is one of the major impurities found in snow and ice in the cryosphere. The experimental results show that the complex permittivity increases linearly with concentration of doped acid. Moreover, when the concentration of acid is expressed by molarity, this linear relation is independent of the sort of acid. The complex permittivity of acid-doped ice can be expressed as a function of concentration of acid and temperature definitely. A possible mechanism for enhancing the complex permittivity of acid-doped ice is formation of liquid phase in ice. >
18 May 1992
TL;DR: In this article, the fabrication and application of high-permittivity ceramic materials for use in power electronic circuits is investigated. And the ability to manufacture materials with a wide range of epsilon /sub r/ values and the influence of dielectric permittivity on the circuit behavior of a converter employing planar connections are studied.
Abstract: The fabrication and application of high-permittivity ceramic materials for use in power electronic circuits are investigated. The ability to manufacture materials with a wide range of epsilon /sub r/ values and the influence of dielectric permittivity on the circuit behaviour of a converter employing planar connections are studied. It is shown conclusively that the circuit behavior of a power electronic circuit can be modified by only varying the properties of the materials used for supporting the connections. This mechanism can be used to improve the power transmission characteristics of the connections. Methods are described whereby the dielectric properties of BaTiO/sub 3/-based materials can be varied over a very wide range of 4 >
TL;DR: In this paper, the influence of Mn dopant on light absorption, electric conductivity, dielectric permittivity was observed in PbTiO3:Mn and the defect centers of Mn24, Mn4+, Vo, Fe3+-Vo were determined with EPR test.
Abstract: The crystals PbTiO3:Mn have been obtained. The influence of Mn dopant on light absorption, electric conductivity, dielectric permittivity was observed. The defect centers of Mn24, Mn4+, Vo, Fe3+-Vo were determined with EPR test.
TL;DR: In this article, the relative permittivity, έ, and dielectric loss factor, tan δ, were measured in the frequency range 50-105 Hz for the solid state track detector CR-39 irradiated with γ-rays (5-100 kGy).
Abstract: The relative permittivity, έ, and dielectric loss factor, tan δ, were measured in the frequency range 50–105 Hz for the solid state track detector CR-39 irradiated with γ-rays (5–100 kGy). The variation of έ and tan δ with γ-dose have been interpreted in terms of structural changes as emphasized from infrared spectra. A mathematical model has been introduced describing the use of CR-39 as a dielectric dosimeter.
TL;DR: In this paper, the relative permittivity of gaseous 1,1,1-trichlorotrifluoroethane, 1,2-difluoromethoxy-1, 1 1-trifluorosethane at temperatures between 293 and 378 K has been obtained from capacitance measurements using a parallel plate capacitor.
Abstract: The relative permittivity (dielectric constant) in gaseous 1,1,1-trichlorotrifluoroethane, 1,2-difluoroethane, 1,1,2-trichlorotrifluoroethane, and 2-(difluoromethoxy)-1,1,1-trifluoroethane at temperatures between 293 and 378 K has been obtained from capacitance measurements using a parallel plate capacitor. Molecular polarizabilities have been determined from the results
TL;DR: In this paper, a millimeter-wave twist reflector design procedure is described and an effective dielectric constant for capacitive susceptance correction for a unidirectional planar grating at the interface of free space and dielectoric material in the twist reflectors environment is introduced.
Abstract: A millimeter-wave twist reflector design procedure is described. An effective dielectric constant for capacitive susceptance correction for a unidirectional planar grating at the interface of free space and dielectric material in the twist reflector environment is introduced. The loss factor of the dielectric material is taken into account for the prediction of twist reflector performance. With the introduction of these corrections experimental results are found to be in close agreement with the theory. Normalized curves for the design of twist reflectors in terms of grating parameters, dielectric substrate relative permittivity, and dielectric material thickness are presented. Experimental results are given. >
TL;DR: In this article, a charge simulation method was used to predict the electric potential distribution produced by charges implanted within the surface layer of a solid dielectric, and the potential distribution was matched with the experimental distribution using the scanning electron microscope (SEM) mirror technique.
Abstract: Computational analysis based on the charge simulation method (CSM) is used to predict the electric potential distribution produced by charges implanted within the surface layer of a solid dielectric. The potential distribution thus obtained is used to match the experimental distribution using the scanning electron microscope (SEM) mirror technique. Using an optimization iteration process, a comparison is obtained for quartz, alumina, and yttria. The computational analysis assumes a surface layer with a permittivity higher than that of the bulk. The justification for this assumption is discussed. The electric potential distribution produced by a surface with increased surface defects, as determined by the SEM mirror technique, indicates a surface with a higher permittivity. It is also shown that the ability of such a surface to store charges is decreased. The results are consistent with physical models based on band structure (or trapping energy) considerations. >
Patent•
23 Dec 1992TL;DR: In this article, the capacitance of the capacitor is not reduced in which the electrodes and the oxide dielectric material having a high permittivity are connected to each other.
Abstract: A semiconductor integrated circuit apparatus according to the present invention has a capacitor formed in such a manner that a ferroelectric thin film is formed after a MOS transistor has been formed on a substrate thereof, a ferroelectric thin film made of, for example, PbZrTiO3 or SrTiO3 or the like is formed into a columnar shape to form electrodes positioned in direct contact with the side wall portions of said columnar ferroelectric thin film, and the top portion is removed As a result, a fact that an oxide of each electrode, which deteriorates the relative permittivity, is formed on the interface between the electrode and the ferroelectric material is prevented, and a large capacity can be realized with respect to the area of the substrate because the ferroelectric thin film is formed into the columnar and elongated shape, resulting in that the capacitance of the capacitor is not reduced in which the electrodes and the oxide dielectric material having a high permittivity are, in series, connected to each other The capacitor is formed into a DRAM or an FRAM memory cell so as to realize a semiconductor memory revealing a high degree of integration and a high processing speed
22 Jun 1992
TL;DR: In this paper, an experimental approach involving the study of the electrical properties of single trees extracted from field-aged cables has been applied, where the authors present first results on the measurement of the permittivity parallel and perpendicular to the tree growth direction, i.e. to the field direction in the cable.
Abstract: An experimental approach involving the study of the electrical properties of single trees extracted from field-aged cables has been applied. The authors present first results on the measurement of the permittivity parallel and perpendicular to the tree growth direction, i.e. to the field direction in the cable. Capacitance measurements on single water trees, extracted from field-aged cables, show a large permittivity enhancement compared to untreed material. The parallel and perpendicular measurements show an asymmetry of at least 1.3. With the help of a simple model, the water content and length of the substructure in a water tree are estimated. It is shown that during longer measurements the above difference disappears. These findings suggest that: (a) the morphology of a water tree consists of elongated structures, filled at least partially with water, and (b) the permittivity enhancement disappears either due to the collapse of the microstructure or simply due to the outdiffusion of water. >
22 Jun 1992
TL;DR: In this paper, a breakdown mechanism based on a local enhancement of the electric field due to the dielectric nature of the water tree was investigated using a laboratory model made of a water needle and a facing metallic needle simulating a defect.
Abstract: A breakdown mechanism based on a local enhancement of the electric field due to the dielectric nature of the water tree was investigated. Using a laboratory model made of a water needle and a facing metallic needle simulating a defect, it was shown that: (i) the presence of a water tree at the water electrode clearly lowers the dielectric strength; (ii) the dielectric strength decreases when the water tree length increases; and (iii) for a fixed water tree length, the dielectric strength decreases when the absorption of the light in the water tree increases. This last result is explained by increasing field enhancement on the metallic needle due to the change in water tree permittivity induced by the increasing water content. >
TL;DR: In this paper, the measurement error of complex permittivity in the dielectric rod resonator method has been investigated, and it was shown that the measurement accuracy of 0.05% (standard deviation) is permissible for the applications of resonators.
Abstract: The measurement accuracy of complex permittivity in the dielectric rod resonator method has been investigated. The measurement error of relative permittivity is 0.05% (standard deviation), which is permissible for the applications of resonators. The dielectric loss was measured by setting conducting plates at both ends of the dielectric resonator. The frequency dependence of the conductivity due to the surface roughness of the plates was investigated using three kinds of standard rod resonators. It is concluded that the measurement error of tan 6 can be reduced to 1.5×10 −6 (standard deviation) for a dielectric specimen with e r =30.2 at 10 GHz by using the high-Q standard dielectric rod resonators which are placed between conducting plates with surface roughness less than the skin depth at the measurement frequency
01 Sep 1992
TL;DR: In this article, an experimental open ended coaxial line coupled to a 50 ohm source and terminated by a sliding short circuit was used to obtain the complex permittivity of liquids from measurements of short circuit length and return loss.
Abstract: An experimental open ended coaxial line coupled to a 50 ohm source and terminated by a sliding short circuit is used to obtain the complex permittivity of liquids from measurements of short circuit length and return loss. For standard liquids, where the permittivity values are well known, the results obtained at 500 MHz are within a few per cent of the reference values, and demonstrate the potential accuracy of the method.
TL;DR: In this paper, the height of the potential barrier has been calculated as a function of temperature on the basis of the Heywang model, using the measured resistivity versus temperature and relative permittivity vs temperature above the Curie temperature.
Abstract: Semiconducting n-type barium titanate with a positive temperature coefficient of resistance (PTCR) has been made by doping BaTiO3 with 0.4 mol% Ho2O3. The d.c. resistivity, a.c. resistivity (1.2 kHz) and relative permittivity (1.2 kHz) at different temperatures between room temperature and 523 K have been measured. The high relative permittivity and the PTCR effect are attributed to the existence of potential barriers at the grain boundaries as proposed by Heywang. The height of the potential barrier has been calculated as a function of temperature on the basis of the Heywang model, using the measured resistivity versus temperature and relative permittivity versus temperature above the Curie temperature. Several different kinds of electrode have been used to study the effect of the contact on measurements of resistivity and relative permittivity.
TL;DR: In this article, the effect of very thin overlays on microstrip resonating structures is studied theoretically and compared with reported experimental results using screen printed dielectric pastes, where the reported data are found to agree with the theoretical predictions for all regions.
Abstract: The effect of very thin overlays on microstrip resonating structures is studied theoretically and compared with reported experimental results using screen printed dielectric pastes. A graph of resonance frequency against log10 (overlay thickness) shows three distinct regions corresponding to different overlay thickness values. Furthermore, using the theoretical curves the relative dielectric constant of the paste material at microwave frequencies is estimated, by curve fitting. The reported data are found to agree with the theoretical predictions for all regions.
TL;DR: This paper presents an equation for calculating the effective complex permittivity of a two-component mixture made with particles of medium 2, dispersed in host medium 1, by assuming that the dielectric response of the mixture follows the universal dielectrics response.
Abstract: This paper presents an equation for calculating the effective complex permittivity of a two-component mixture made with particles of medium 2, dispersed in host medium 1. The geometrical density function which describes the mixture is deduced from the distribution function of relaxation times for the case of medium 2 consisting of metallic particles, by assuming that the dielectric response of the mixture follows the universal dielectric response.
TL;DR: In this article, thin films of potassium tantalum niobate (KTN) formed by metalorganic deposition were subjected to one and two-step sinterings in air and potassium atmosphere, and the maximum relative permittivity, its corresponding rate of change with temperature and film grain size were measured as a function of sintering temperature and time.
Abstract: Thin films of potassium tantalum niobate (KTN) formed by metalorganic deposition were subjected to one- and two-step sinterings in air and potassium atmosphere. These polycrystalline films were found to be mechanically robust and display electrical properties similar to single-crystal KTN. This report shows that film grain size increased with sintering temperature and time. Scanning electron micrographs revealed grain sizes ranging from submicrometer to 5 μm in diameter. The maximum relative permittivity, its corresponding rate of change with temperature, and film grain size were measured as a function of sintering temperature and time.
01 Jun 1992
TL;DR: In this paper, a cavity perturbation method was used to measure the temperature dependence of the complex dielectric permittivity of small samples (volume of the order of 1 mm3).
Abstract: The author describes a versatile frequency-stabilized X-band microwave bridge which uses the cavity perturbation method to measure the temperature dependence of the complex dielectric permittivity of small samples (volume of the order of 1 mm3). Low temperature as well as high temperature experiments can easily be carried out using the same set-up. First results of the temperature-dependent permittivity of PVDP (polyvinylidenefluoride) thin foils are presented.