Showing papers on "Relative permittivity published in 2000"

Mixing Rules with Complex Dielectric Coefficients

Abstract: This article discusses the determination of effective dielectric properties of hetereogeneous materials, in particular media with lossy constituents that have complex permittivity parameters. Several different accepted mixing rules are presented and the effects of the structure and internal geometry of the mixture on the effective permittivity are illustrated. Special attention is paid to phenomena that the mixing process causes in the character of the macroscopic dielectric response of the mixture when the losses of one or several of the components are high or when there is a strong dielectric contrast between the component permittivities.

Complex permittivity, permeability, and X-band microwave absorption of CaCoTi ferrite composites

Abstract: The effect of Co2+Ti4+ substitution on complex permeability, permittivity, and microwave absorption has been studied for [Ca(CoTi)xFe12−2xO19]96.0[La2O3]4.0 ferrite-epoxy composites, wherein x varies from 0 to 1.0 in steps of 0.2, in the frequency range from 8.0 to 12.4 GHz. The ferrites with x>0 exhibit significant dispersion in complex permittivity (e′−je″) with the maximum value of e″ observed for x equal to 0.2. The dispersion in complex permeability (μ′−jμ″) is not significant. The variations of reflection loss and percentage absorption have been studied as a function of frequency, Co2+Ti4+ content, and thickness of the absorber. A maximum reflection loss of 31.0 dB is obtained for composites with x equal to 0.2 and absorber thickness of 2.5 mm. The experimental values of the matching frequency and the matching thickness agree well with the theoretical values obtained from an impedance-matching solution map.

Impacts of the Real and Imaginary Components of Relative Permittivity on Time Domain Reflectometry Measurements in Soils

Abstract: Time domain reflectometry (TDR) is widely used for routine field monitoring of water content and salts in soils. Most estimates of water content assume the TDR-measured apparent relative permittivity, e a , is a good approximation for the real component, e τ ', of the soil's complex relative permittivity with the magnitude of e τ ' being determined primarily by water content. We examine this assumption and show that e a is influenced by both the real and imaginary components of the relative permittivity. Increases in e a resulted from the de conductivity and dielectric loss arising from the presence of ions in solution and clay content. At water contents above 0.15 m 3 m -3 in soils with high clay content and/or salt, specific calibrations are needed for precise determinations of water content from TDR. We use the wave propagation equations to separate the real and imaginary component contributions to e a . The Giese and Tiemann interpretation for de conductivity was again shown to he within 10% of that from a conductance meter and this fact was used to propose a method using only TDR data to separate real and imaginary components of the relative permittivity. It was found that the dielectric losses and conductive losses did not differ according to the source of conductivity, whether from clay content in the soil matrix or electrolyte in the soil solution.

Method for forming film with low dielectric constant on semiconductor substrate

Abstract: In a method for forming in a reactor a film having a low relative dielectric constant on a semiconductor substrate by plasma reaction, the improvement can be achieved by lengthening a residence time, Rt, of a reaction gas in the reactor, wherein 100 msec≦Rt. The film includes insulation films and mask films.

The design of an electrical capacitance tomography sensor for use with media of high dielectric permittivity

Abstract: This paper concerns the application of electrical capacitance tomography (ECT) for media of high dielectric permittivity such as water. The performance of an ECT sensor was analysed numerically for a range of dielectric materials (1≤er≤80) and geometrical parameters. On the basis of numerical simulations an ECT sensor with internal electrodes was built. Experimental results concerned with imaging air voids in distilled water and water-continuous dispersions of oil, using a commercially available PTL tomography system, are presented. Effects arising from the conductivity of water are studied and prospects of using the ECT system in an `electrical resistivity' mode for weakly conductive solutions are outlined.

The Dielectric Properties of Tissues

Abstract: It is generally true to say that the dielectric properties are intrinsic parameters that determine the effects of electric fields on matter. This leads to the statement that dielectric properties (relative permittivity e’ and effective conductivity σ) play a dominant role in the overall consideration of interaction between electromagnetic fields and matter and in related applications in numerous disciplines including electromagnetic dosimetry.

Density, Relative Permittivity, and Viscosity of Propylene Carbonate + Dimethoxyethane Mixtures from 25 °C to 125 °C

Abstract: Density, relative permittivity, and viscosity measurements on propylene carbonate + dimethoxyethane were made over the temperature range 25 °C to 125 °C at all mole fractions, completing the previous data for the temperature range −45 °C to 25 °C. New measuring equipment developed in our laboratory for measurements over the temperature range 20 °C to 180 °C is described.

How do shape anisotropy and spatial orientation of the constituents affect the permittivity of dielectric heterostructures

Abstract: The study of dielectric heterostructures has been advancing at a rapid pace. Much of the interest in these materials stems from the fact that their physical properties can be systematically tuned by variation of the size and shape of the constituents. Here we report on extensive computer simulations of the effective permittivity of dielectric periodic (deterministic) heterostructures, having monosized hard core inclusions of anisotropic shape (rod, ellipsoid) embedded in an otherwise homogeneous and isotropic matrix. The real and imaginary parts of the permittivity, in the quasistatic limit, are rigorously evaluated with the use of the PHI3D field calculation package and the resolution of boundary integral equations. In this article, we show that the effective permittivity has critical properties near a conduction threshold. The conduction threshold concentration can be significantly modified by the size, shape, and spatial arrangement of the constituents. More specifically, it obeys a square law dependen...

Mixture Behavior and Microwave Dielectric Properties in the Low-fired TiO2–CuO System

Abstract: The mixture behavior and microwave dielectric properties of TiO2 doped with CuO sintered at around 900°C for 2 h were investigated using X-ray powder diffraction and a network analyzer. Low-fired TiO2 with 2% CuO had a quality factor of 14000, relative dielectric constant (er) of 98, and a temperature coefficient of resonant frequency (τf) of 374 ppm/°C. The microwave dielectric properties of low-fired, CuO doped TiO2 could be interpreted by observing the dielectric properties of CuO: high loss tangent (tan δ), low dielectric constant, and a negative temperature coefficient of resonant frequency. The microwave dielectric properties of low-fired, CuO doped TiO2 showed a dependence on the mixture formation of TiO2 and CuO. More importantly, the er of low-fired TiO2 with CuO could be predicted by the logarithmic mixing model. Therefore, the variation of the microwave dielectric properties was attributed to the mixture behavior of TiO2 and CuO.

Quantitative imaging of dielectric permittivity and tunability with a near-field scanning microwave microscope

Abstract: We describe the use of a near-field scanning microwave microscope to image the permittivity and tunability of bulk and thin film dielectric samples on a length scale of about 1 μm. The microscope is sensitive to the linear permittivity, as well as to nonlinear dielectric terms, which can be measured as a function of an applied electric field. We introduce a versatile finite element model for the system, which allows quantitative results to be obtained. We demonstrate use of the microscope at 7.2 GHz with a 370 nm thick Ba0.6Sr0.4TiO3 thin film on a LaAlO3 substrate. This technique is nondestructive and has broadband (0.1–50 GHz) capability. The sensitivity of the microscope to changes in permittivity is Δer=2 at er=500, while the nonlinear dielectric tunability sensitivity is Δe113=10−3 (kV/cm)−1.

Electric and dielectric properties of Bi12TiO20 single crystals

Abstract: The frequency dependence of the electrical properties of the Bi12TiO20 single crystal was investigated by impedance spectroscopy The data were presented in the Nyquist diagram form, from which electrical resistivity was determined Values ranged from 193×105 and 107×103 Ω cm in the temperature range of 400–700 °C The electrical conductivity followed the Arrhenius law, with an activation energy of 099 eV The dielectric behavior was investigated from room temperature to 700 °C Permittivity was calculated based on the relaxation frequency, using an alternative approach based on the variation of the imaginary impedance component as a function of reciprocal angular frequency The permittivity values obtained by means of these two methods showed good agreement up to 600 °C The frequency dependence of real and imaginary permittivities from room temperature to 700 °C was also investigated

Epitaxial growth of non-c-oriented SrBi2Nb2O9 on (111) SrTiO3

Abstract: Epitaxial SrBi2Nb2O9 thin films have been grown with a (103) orientation on (111) SrTiO3 substrates by pulsed-laser deposition Four-circle x-ray diffraction and transmission electron microscopy reveal nearly phase-pure epitaxial films Epitaxial (111) SrRuO3 electrodes enabled the electrical properties of these (103)-oriented SrBi2Nb2O9 films to be measured The low-field relative permittivity was 185, the remanent polarization was 157 μC/cm2, and the dielectric loss was 25% for a 05-μm-thick film

Phase transitions from the isotropic liquid to liquid crystalline mesophases studied by linear and nonlinear static dielectric permittivity

Abstract: Results of studies of static dielectric permittivity (epsilon) and nonlinear dielectric effect (NDE) in the isotropic phase of 4-n-4'-isothiocyanatobiphenyl (nBT) homologous series from n = 2 to n = 10 exhibiting the isotropic-smectic E (I-SmE) transition, are presented. They are compared with results of similar studies in 4-cyano-4-n-alkylbiphenyls (nCB) from n = 4 to n = 12. In this homologous series isotropic-nematic (I-N) and isotropic-smectic-A (I-Sm-A) transitions take place. Despite significant differences between N, Sm-A, and Sm-E phases the same pretransitional behavior of epsilon and NDE in the isotropic phase, described by critical exponents gamma = 1 and alpha = 0.5, was found. It has been shown that when the length of the alkyl chain of a compound increases the discontinuity of the transition drops in nBT and rises in nCB. The influence of pressure on the discontinuity is also discussed.

Dielectric properties of wood from 2 to 3 GHz.

Abstract: Many applications of microwave energy to wooden materials have been developed in the last few decades, both for treatment and for diagnostic purposes. All these applications require a reliable estimation of the permittivity of the wood species of interest, which is the physical parameter of crucial importance in the absorption of electromagnetic energy. This paper presents results obtained in the dielectric characterization of five wood species in the frequency range from 2 to 3 GHz, including the ISM frequency of 2.45 GHz. Permittivity was measured by an open-ended coaxial-line probe of new design on wood samples conditioned at several moisture levels. The influence of the natural variability of wood characteristics on the measured permittivity was also investigated by a suitable experimental setup consisting of a poplar table including both sapwood and heartwood regions. Finally, a theoretical discussion on the meaning of a scalar measurement on anisotropic dielectrics is conducted in terms of an isotropic-equivalent permittivity, which is related to the permittivity tensor of the dielectric material.

Accurate microwave resonant method for complex permittivity measurements of liquids [biological]

Abstract: A method available for accurate measurements of lossy liquids is presented, tested on standard materials, and compared with the perturbation technique commonly adopted in cavity measurements. The method is based on numerically solving a complex characteristic equation. Realization of the method was done using an E/sub 010/ cylindrical cavity. Results show that measurement errors may be decreased with application of the method presented. The method excludes uncertainties in complex permittivity determination when material has losses and high permittivity.

Quantitative imaging of dielectric permittivity and tunability

Abstract: A near-field scanning microwave microscope images the permittivity and dielectric tunability of bulk and thin film dielectric samples on a length scale of about 1 micron or less. The microscope is sensitive to the linear permittivity, as well as to non-linear dielectric terms, which can be measured as a function of an applied electric field. A versatile finite element model is used for the system, which allows quantitive results to e obtained. The technique is non-destructive and has broadband (0.1-50 GHz) capability.

Quasicritical behavior of dielectric permittivity in the isotropic phase of smectogenic n-cyanobiphenyls

Abstract: Results are presented of temperature and pressure studies of static dielectric permittivity (epsilon) and the nonlinear dielectric effect (NDE) in the isotropic phase of smectogenic n-cyanobiphenyls: 9CB, 10CB, and 12CB (4-cyano-4'-n-alkylbiphenyl, n = 9, 10, and 12). For the mentioned properties, pretransitional effects can be well portrayed by applying the relations used for the isotropic phase of nematogens, where evidence of the quasicritical, fluidlike behavior with exponents alpha approximately 0.5 and gamma = 1 exists. This kind of behavior one can also observe on approaching the isotropic-smectic A transition. NDE studies in 10CB and 12CB made it possible to determine the pressure evolution of the discontinuity (delta T) of the I-SmA transition. It was found that pressure first decreases the discontinuity of the transition, and that next a gradual rise appears. This behavior is unlike the one observed for the isotropic-nematic transition, where only an increase of delta T with rising pressure was observed.

Dielectric properties of materials using whispering gallery dielectric resonators: Experiments and perspectives of ultra-wideband characterization

Abstract: Measurements for the determination of the complex permittivity of liquid and solid materials based on the use of whispering gallery (WG) dielectric resonators are presented. The procedure implies the measurement of the electromagnetic parameters of the involved resonator interacting with the material under study. The field distribution in the different WG resonant modes was obtained by an analytical calculation under the mode matching method approximation. The results of this calculation, combined with the experimental data, well account for the values of the complex permittivity of materials of interest. Due to the peculiar properties of WG resonators, the method shares the advantages of the wideband systems with the sensitivity and accuracy of the resonator systems in dielectric measurements. Dielectric permittivity of alumina (Al2O3) and of cyclohexane is measured in the frequency range 18–26 GHz. The overall accuracy of the measurements is discussed and the different sources of errors analyzed. Specif...

Microstrip patch sensor for measurement of the permittivity of homogeneous dielectric materials

Abstract: An application of a small air-spaced coaxially fed rectangular microstrip patch antenna as a sensor for permittivity measurement is presented. The models used for the calculation of the permittivity from the shift in the resonant frequency for solid and liquid materials are described. The models are experimentally verified by measurements for several liquid and solid samples. The results are compared with those obtained using standard techniques, namely, coaxial probe and waveguide cell measurements. An error correction technique for the elimination of the systematic error of the measurement is also included.

Semiconductor device and manufacture thereof

Abstract: When a semiconductor device using fluorine-containing carbon films (CF films) 21, 22, 23 as inter-layer dielectric films is fabricated using boron nitride films (BN films) as hard masks 31, 32, 33, total inter-wiring capacitance of the semiconductor device can be made low. After a first CF film 21 as an inter-layer dielectric film is stacked, a hard mask 31 composed of a BN film is stacked on the CF film 21, and thereafter selectively removed by etching to form a predetermined groove pattern. The CF film 21 is next etched by using the hard mask 31 as a mask to form grooves for forming wiring layers 51. Then, Cu is buried into the grooves to complete the semiconductor device. Since this semiconductor device uses the CF film and the BN film having low relative dielectric constants, the relative dielectric constant of the entire semiconductor device can be made low. As a result, its total inter-wiring capacitance can be made low as well.

Scaling of the ac permittivity in ion-conducting glasses

Abstract: An approach for scaling the ac conductivity in ion-conducting glasses was recently demonstrated. Here we demonstrate that this proposed scaling can be applied to the corresponding ac permittivity and thus leads to a complete description of the scaling of both the real and imaginary components of the dielectric response associated with ionic relaxation. The origin of this particular scaling is traced to the Kramers-Kronig transforms that relate these two components. (c) 2000 The American Physical Society.

Non-destructive permittivity measurement of solid materials

Abstract: An open-coaxial probe suitable for measuring the permittivity of solid materials has been designed and tested. The peculiar structure of the probe allows an easy and firm contact with the surface of the material under measurement, resulting in highly reliable and reproducible dielectric measurements. The permittivity measurement is absolute, as the calibration procedure - based on a genetic algorithm - does not require the use of dielectric standards. The measurement system - including the probe, a network analyser, and the numerical code to determine the permittivity from reflection measurements - have been tested on solid materials of known properties, and used for determining the dielectric characteristics of several types of wood.

Split post dielectric resonator technique for precise measurements of laminar dielectric specimens-measurement uncertainties

Abstract: A split-post dielectric resonator was used to measure solid laminar dielectric specimens which had been previously measured by a number of other techniques. Detailed error analysis of permittivity and dielectric loss tangent measurements has been performed. It was proved that, by using a 4 GHz split post resonator, it is possible to measure permittivity with uncertainties down to 0.3% and dielectric loss tangent with resolution 2/spl times/10/sup -5/ for well machined laminar specimens.

Parallel Plates Compared with Conventional Rods as TDR Waveguides for Sensing Soil Moisture

Abstract: Dielectric methods of estimating the water content of soils, especially TDR, have become accepted as routine measurement techniques. Basic to the TDR technique is the waveguide, which is inserted into the soil for obtaining measurements of the effective soil permittivity, from which water content is estimated. In this study we compare the use of flat stainless steel plates with cylindrical stainless steel rods. We suggest that the use of plates gives a more even distribution of electromagnetic energy within the soil volume sampled and reduces the so called ``skin effect'' where the electromagnetic energy is concentrated close to the surface of the electrodes. Plates will not be suitable for all measurement purposes but wherever they can be applied they should result in more representative measurements from the medium under investigation. Calculations of electrical field intensity are presented to compare the relative energy density between the electrodes. Field and laboratory studies were alsoconducted considering some of the practicalities of using the alternative waveguides.

Impedance spectroscopy analysis of high-temperature phase transitions in sodium lithium niobate ceramics

Abstract: An investigation was made of the sodium lithium niobate Na0.85Li0.15NbO3 ceramics using permittivity properties. Permittivity measurements were carried out by impedance spectroscopy in a frequency range of 5 to 1.3?107?Hz and at temperatures ranging from 25 to 750??C. The thermal stability of the dielectric behaviour was evaluated as a function of several thermal cycles. The permittivity response was found to depend on both the partial thermal cycle (heating or cooling cycle) and the number of cycles. Three phase transitions are proposed based on a maximum of permittivity response as a function of temperature. The dielectric behaviour and its relationship with the phase transition phenomenon are discussed.