Showing papers on "Relative permittivity published in 1994"
TL;DR: In this paper, it was shown that the coercive field is independent of thickness having a value of 2.4 V/μm and the ratio ebl/dbl is in the range 20−28 nm−1; the voltage across the blocking layer is proportional to the polarization, Vbl=cP, where c=4.1±0.5 Vm2/C; and (iv) the polarization depends on the electric field in the PZT layer.
Abstract: Ferroelectric capacitors having Pt bottom and top electrodes and a ferroelectric film of composition PbZr0.51Ti0.49O3 (PZT) were fabricated and investigated. The PZT films of thicknesses varying from 0.12 to 0.69 μm were prepared by organometallic chemical‐vapor deposition. Annealed capacitors were investigated by capacitance, hysteresis, and pulse switching measurements. It is found that the thickness dependence of the reciprocal capacitance, the coercive voltage, and the polarization measured by pulse switching can all be explained by a blocking layer model, in which a dielectric layer of thickness dbl and relative permittivity ebl is situated between the PZT film and an electrode. It is shown that (i) the coercive field is independent of thickness having a value of 2.4 V/μm; (ii) the ratio ebl/dbl is in the range 20–28 nm−1; (iii) the voltage across the blocking layer is proportional to the polarization, Vbl=cP, where c=4.1±0.5 V m2/C; and (iv) the polarization depends on the electric field in the PZT layer, independent of thickness. Pulse switching endurance measurements showed that in the saturation range the fatigue for these ferroelectric capacitors is determined by the pulse voltage and is independent of the thickness.
337 citations
TL;DR: In this article, the authors studied the quantized field in a one-dimensional electromagnetic resonant cavity and formulated an effective Hamiltonian so that the dynamics of the cavity field can be described in the Schrodinger picture.
Abstract: We study the quantized field in a one-dimensional electromagnetic resonant cavity. The cavity contains a linear and lossless dielectric medium with frequency-independent polarizability. The dielectric permittivity is an externally prescribed function of both the space and the time. We also allow one of the cavity's mirrors to move in a given trajectory. Unlike other previous studies on the same system, we formulate an effective Hamiltonian so that the dynamics of the cavity field can be described in the Schr\"odinger picture. The effective Hamiltonian is quadratic in structure, therefore two-photon generation from the vacuum state can occur. We also discuss the case of resonant behavior of the system.
275 citations
TL;DR: It is shown that the Vogel-Fulcher relationship for the positions of the temperature maximum for the real and imaginary parts of the dielectric permittivity can be obtained as a direct consequence of gradual broadening of the spectrum with decreasing temperature.
Abstract: The low frequency dielectric response of relaxer ferroelectrics is analyzed. Following the conventional approach this response is considered as a sum of those of relaxators having an exponentially wide and smooth spectrum of the relaxation times. It is shown that the Vogel-Fulcher relationship for the positions of the temperature maximum for the real and imaginary parts of the dielectric permittivity can be obtained as a direct consequence of gradual broadening of the spectrum with decreasing temperature. It is shown that such a Vogel-Fulcher-type relationship does not necessarily imply ''freezing'' in the system.
274 citations
TL;DR: In this paper, the effect of fluorine incorporation on dielectric properties has been studied for a series of polyimides in order to distinguish between several contributing mechanisms to the generally observed decrease in the relative permittivity using low-frequency capacitance measurements after exhaustive in situ drying, in conjunction with refractive index measurements.
Abstract: The effect of fluorine incorporation on dielectric properties has been studied for a series of polyimides in order to distinguish between several contributing mechanisms to the generally observed decrease in the relative permittivity Using low-frequency capacitance measurements after exhaustive in situ drying, in conjunction with refractive index measurements, the overall decrease in dielectric constant was semiquantitatively assigned between changes in the three modes of polarization via the use of fluorine/hydrogen and symmetric/unsymmetric analogs
209 citations
TL;DR: In this paper, the S11 scatter function of a coaxial probe in the frequency domain is shown to be an accurate model for predicting waveforms of a seven-wire coaxial probing in the time domain.
Abstract: The S11 scatter function of a coaxial probe in the frequency domain is shown to be an accurate model for predicting waveforms of a seven-wire coaxial probe in the time domain. Reproducibility of discrete Fourier analyses carried out on waveforms measured with the Tektronix 1502b cable tester (Tektronix, Incorporated, Beaverton, Oregon) indicated a frequency band width ranging from 20 kHz to approximately 1.5 GHz. The frequency dependent complex dielectric permittivity can be calculated from measured waveforms by inverting the S11 scatter function. Results indicate that a seven-wire coaxial probe, connected to a 1-m RG214 coaxial cable, emulates a coaxial tube for frequencies up to 150 MHz. Application of the frequency domain model to time domain reflectometry waveforms shows that the apparent dielectric permittivity calculated from the travel time in the probe is very dependent on the relaxation frequency of the material in which the probe is embedded. For materials with low relaxation frequencies the apparent dielectric permittivity is much lower than the static permittivity. Inversion of the frequency domain model allows for solving the frequency dependent complex dielectric permittivity of soils from measured waveforms.
206 citations
TL;DR: Low profile rectangular dielectric resonator antennas, fabricated out of a very high permittivity material ( epsilon /sub r/=100), were reported in this paper. But their performance was limited to 3% bandwidth.
Abstract: Low profile rectangular dielectric resonator antennas, fabricated out of a very high permittivity material ( epsilon /sub r/=100) are reported. An antenna having a height of approximately 0.026 lambda /sub 0/ and a bandwidth of 3% is demonstrated.<
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160 citations
TL;DR: In this paper, a four-component complex dielectric mixing model based on the volumetric mixing of the refractive indices of the soil components was proposed to describe the soil electrical conductivity.
Abstract: Although time domain reflectometry (TDR) is becoming accepted as an important tool for the measurement of soil water content and bulk soil electrical conductivity, a major part of the method is based on empirical relationships. An improved understanding of dielectric measurements on soils may give more insight into soil properties other than soil water content and bulk soil electrical conductivity. Frequency domain analysis of TDR waveforms enables the measurement of the frequency dependent complex dielectric permittivity of soils. The frequency dependent complex dielectric permittivity of soils can be described with a four-component complex dielectric mixing model based on the volumetric mixing of the refractive indices of the soil components. The four soil components in the model are air, solids, bound water, and free water. Results indicate that the apparent dielectric permittivity obtained from the travel time of the TDR pulse in the soil is the dielectric permittivity at the highest measurement frequency of the cable tester, probe, and soil system. The model based on the volumetric mixing of real permittivities underestimates the measurements in situations with high values of the imaginary part of the dielectric permittivity. Because the model based on the mixing of the complex dielectric permittivities can describe the data, we conclude that the apparent dielectric permittivity is influenced by the imaginary parts in the dielectric, permittivities of the soil components. Combination of the four-component complex dielectric mixing model with the complex dielectric permittivity obtained from the frequency domain analysis of TDR waveforms gives a tool for modeling the bulk soil electrical conductivity by separating the conductivity of the soil water into a bound water conductivity and a free water conductivity.
130 citations
TL;DR: In this paper, a single crystal of pyridinium tetrafluoroborate was analyzed and two solid-solid phase transitions at 205 and 240 K were revealed, and the real part of the dielectric permittivity was measured between 190 and 290 K.
Abstract: The differential thermal analysis of a single crystal of pyridinium tetrafluoroborate was performed revealing two solid-solid phase transitions at 205 and 240 K. The real part of the dielectric permittivity was measured between 190 and 290 K. The large anomaly at the higher phase transition is interpreted as the Curie point of a new ferroelectric crystal.
115 citations
TL;DR: The model identified as most suitable for the measurement of the dielectric properties of biological materials is used to determine the relative permittivity and conductivity of muscle and skull bone in the frequency range 1 MHz to 20 GHz.
Abstract: Starting from a rigorous formulation for the admittance of an open ended coaxial probe, the authors identify the simplifying assumptions that are introduced to obtain more practical solutions. The predictions of the models are compared to each other and to experimental data obtained on an independently calibrated experimental set-up. The advantages and limitations of a model are determined by the theoretical derivation and the numerical solution. The model identified as most suitable for the measurement of the dielectric properties of biological materials is used to determine the relative permittivity and conductivity of muscle and skull bone in the frequency range 1 MHz to 20 GHz.
112 citations
TL;DR: It is shown that even though horizontally directed methylene-group moments cannot make a direct contribution to the surface potential of a condensed monolayer, they do make a significant indirect contribution via their local field.
Abstract: A quantitative model is presented which enables contributions to the surface potential of a monolayer at the air-water interface to be determined from known values of group dipole moments. Based on the Lennard-Jones and Dent approach, the model shows that the head- and tail-group moments in a condensed, long-chain, n-alkanoic acid monolayer may be assumed to be noninteracting so long as the monolayer-forming molecule is more than about 0.5 nm in length, thus confirming one of the main tenets of the model by Demchak and Fort [J. Colloid Interface Sci. 46, 191 (1974)]. By the same token, it is shown that imaging effects in the subphase are only important for the head group and negligible for the tail group of a molecule more than about 0.5 nm long. The present model shows that the local field acting on dipoles in the monolayer can be described in terms of a relative permittivity for the monolayer. An upper bound of between 1.98 and 2.24 is established for the local relative permittivity of the hydrophobic chain region of alkanoic acids. The major contribution to the local field which leads to these values is from the ``layers'' of methylene groups forming the hydrophobic region of the monolayer. For the case of the distal methyl groups of an alkanoic acid, consideration of only the mutual induced depolarization of in-plane methyl dipoles leads to a local relative permittivity as low as 1.18. Thus, it is shown that even though horizontally directed methylene-group moments cannot make a direct contribution to the surface potential of a condensed monolayer, they do make a significant indirect contribution via their local field.
90 citations
TL;DR: In this article, the interphases formed on Li electrodes in various propylene carbonate solutions were investigated using impedance spectroscopy, and the influences of temperature and solution composition (salt, concentration, additive and contaminants) were studied.
TL;DR: In this article, the electrostatic environment in a lossless composite structure made of three dielectrics and two dividing closed and disjoined surfaces has been determined, using appropriate surface integrals on these interfaces.
Abstract: The electrostatic environment in a lossless composite structure made of three dielectrics and two dividing closed and disjoined surfaces has been determined, using appropriate surface integrals on these interfaces. These integral equations are transformed to approximate matrix equations and then are solved numerically. The electrostatic potential distribution, dipole moment and the effective permittivity of different composite structures are calculated. >
Patent•
18 Mar 1994
TL;DR: In this article, the authors proposed to match the impedance of a radiating element to the free space of the surrounding free space or air by making the permeability of the transmission medium substantially equal to its relative permittivity.
Abstract: Antenna elements and systems and other radio and microwave frequency devices are constructed with a high index of refraction medium having high matched values of relative permeability and relative permittivity, and a low loss tangent. By making the permeability of the transmission medium substantially equal to its relative permittivity, the impedance of the material is matched to that of the surrounding free space or air. By immersing a radiating element in such a material, and/or by using such a material between adjacent radiating elements or between a radiating element and a reflective ground plane, the physical size and/or the spacing of the elements may be substantially reduced without appreciable performance loss, thereby resulting in a more compact device that is particularly desirable for mobile applications. At least one exemplary such material is formed in layers and has electrical properties which are anisotropic and homogeneous and which vary as a function of frequency; the layers of such a material are preferably oriented such that the particular frequencies of radiation propagating through each layer are presented with high matched values of relative permittivity and relative permeability, and low values of dielectric and magnetic loss tangents.
TL;DR: In this article, the ionic dielectric polarizabilities and the ion additivity rule have been used to calculate molecular dielectrics for perovskite substrate materials used for high-temperature superconductors.
Abstract: Dielectric polarizabilities for most of the ions in known perovskites scale with the ionic volume and the valence. These ionic dielectric polarizabilities and the ion additivity rule have been used to calculate molecular dielectric polarizabilities for perovskite substrate materials used for high-temperature superconductors. Using the ion additivity rule to predict possible low permittivity compositions seems to suggest that the constraints of the perovskite structure and stoichiometry, lattice match to high-temperature superconductors, and congruent melting required for bulk growth limit the compositions to ones unlikely to be superior to the currently available materials. The most limiting factor on the relative permittivity of the perovskites is probably the close-packed nature and lack of voids in the structure. However, in nonferroelectric perovskites, the polarizabilities derived from relative permittivity data using the Clausius-Mossotti relation are significantly less than the calculated values, with deviations that correlate with degree of cation compression. Use of cation compression to reduce the polarizability shows some promise for improving dielectric constants.
TL;DR: In this article, a broad class of tunable microwave devices using high-temperature oxide superconductor and voltage-tunable oxide ferroelectric thin-film multilayer structures were described.
Abstract: We describe materials deposition and characterization for a broad class of tunable microwave devices using high-temperature oxide superconductor and voltage-tunable oxide ferroelectric thin-film multilayer structures. Tl-Ba-Ca-Cu-O thin films deposited by sputtering ore-beam evaporation were patterned into microwave resonators, each consisting of two colinear microstrip line sections separated by a 5–20μm gap. A Ba0.1Sr0.9TiO3 (BST) layer was then over-coated to fill the gap. The relative dielectric constant of the BST films deposited by physical vapor or chemical techniques was measured at 77 K in the 1–10 MHz range and found to vary by up to a factor of 2 or more with voltage bias in test capacitor structures using Pt electrodes. In the BST (variable capacitor)-HTSC microwave resonator structures, the change of the relative dielectric constant of the BST under voltage bias has allowed variation of the fundamental frequency of up to 80 MHz in the 5–10 GHz range at 4 K. Film deposition by various techniques and associated structural, morphological, and electronic properties, as well as materials compatibility issues, are discussed.
TL;DR: In this article, low frequency measurements of lineer and nonlinear components of complex dielectric permittivity were carried out on leed magnoniobate (PMN) single crystals in the wide temperature region.
Abstract: The low frequency measurements of lineer and nonlinear components of complex dielectric permittivity (e) were carried out on leed magnoniobate (PMN) single crystals in the wide temperature region (...
TL;DR: Three blocks of snow approximately 33 cm on each side were harvested from the Greenland ice sheet and it was found that the permittivity of the two deeper firn blocks was anisotropic by 4-7% and agreed well with other measurements on terrestrial snow.
Abstract: Three blocks of snow approximately 33 cm on each side were harvested from the Greenland ice sheet at depths ranging from 0.3 to 2.7 m below the surface and brought back to the lab. A step frequency radar operated from 26.5 to 40.0 GHz was used to measure the wave velocity through the snow in three orthogonal directions. From these measurements, the relative permittivity was calculated; it varied with density from 1.69 to 1.91 and agreed well with other measurements on terrestrial snow. It was also found that the permittivity of the two deeper firn blocks was anisotropic by 4-7%. This anisotropy is explained by the elongation of the snow grains in the vertical direction. Extinction losses of about 5 dB/m were estimated by measuring the change in amplitude of signals propagating through the blocks. Although the estimated losses were highly variable, a minimum penetration depth of 87 cm into the firn was computed. >
Patent•
28 Jan 1994
TL;DR: In this paper, the phase velocity of the odd-mode is significantly affected by the electric field in the gap region (S) between the conducting strips, and the phase shift of an RF signal propagating through the strip transmission medium can be controlled.
Abstract: A length of strip transmission line uses two symmetrically spaced center conductors (22,24) between two groundplanes (28,30). These conductive strips produce an even-mode electric field between the two groundplanes (28,30) when excited in-phase and an odd-mode electric field when excited in anti-phase relationship. For the latter case, the phase velocity of the odd-mode is significantly affected by the electric field in the gap region (S) between the conducting strips. By varying the relative dielectric constant of a material (26) located in the gap region (S), e.g., by means of a voltage-controllable dielectric (26) such as barium-titanate compositions, the phase velocity and, hence, the phase shift of an RF signal propagating through the strip transmission medium can be controlled.
TL;DR: In this paper, the multilayer structures of the charge transfer complex (N-octadecylpyridinium)-Ni(dmit)2 have been deposited by the Langmuir-Blodgett technique onto substrates of gold-coated glass and silicon with a thermally grown overlayer of silicon dioxide.
TL;DR: The scanning potential microscope (SPM) as discussed by the authors is a new form of scanning microscope which maps distributions of spatial potential by direct measurement, which can be used to study the electrical properties of samples through the potential distribution created near the sample in response to an applied electric field.
Abstract: The scanning potential microscope (SPM) is a new form of scanning microscope, which maps distributions of spatial potential by direct measurement. The SPM may be used to study, non-invasively, the electrical properties of samples through the potential distribution created near the sample in response to an applied electric field. Spatial resolution and sample to SPM spacing are both close to 1 mu m at the present stage of development of the instrument. We present an SPM study of a test sample comprising three dielectric layers with differing relative permittivities: a 35 mu m film of cellulose acetate (CA, epsilon r approximately=5); a 25 mu m film of polyvinylidenefluoride (PVDF, epsilon r approximately=8.4); and a 50 mu m film of polytetrafluoroethylene (PTFE, epsilon r approximately=2-2.1). In the experimental set-up a small, audio-frequency electric displacement was applied through the sample. SPM mapping of the resultant potential distribution close to the sample yielded values of relative permittivity that were within 2% of the material specifications.
01 Oct 1994
TL;DR: In this paper, the effective dielectric constant of a microstrip is given as a function of the strip geometry and its orientation on the surface of the substrate, which can be used in commercial microwave software for simulation of r-cut sapphire substrate based micrstrip devices.
Abstract: The effective dielectric constant of a microstrip is given as a function of the strip geometry and its orientation on the surface of the substrate. An "isotropized" dielectric constant is inroduced which can be used in commercial microwave software for simulation of r-cut sapphire substrate based micrstrip devices. Experimental velification of the analysis is also given.
TL;DR: The evidence for the mechanisms proposed for aromatic nucleophilic substitution reactions by primary and secondary amines in aprotic solvents of low relative permittivity is reviewed in this paper.
01 Apr 1994
TL;DR: In this paper, a variational technique for the analysis of microstrip with dielectric overlay/cover in the Fourier transform domain is investigated with special reference to the strip thickness dependence.
Abstract: A variational technique for the analysis of microstrip with dielectric overlay/cover in the Fourier transform domain is investigated with special reference to the strip thickness dependence. The effective permittivity calculated for different overlay thicknesses and permittivities indicates a mode change from quasi-TEM to TEM as the effect of strip width disappears in agreement with full wave spectral domain analysis. Experimental data on multilayer microstrip effective permittivity and numerical results are found to agree for various microwave bulk materials. Based on this software, with the advantage of easier implementation and faster computation a method has been suggested to determine the microwave permittivity of the bulk and thick film materials with minimum fabrication complexity.
TL;DR: In this paper, a set-up used to accurately measure the resonant frequencies and Q-factors of isolated dielectric resonators is described, and the measured values are compared with those of rigorous numerical methods available in the literature.
Abstract: In this paper, a set-up used to accurately measure the resonant frequencies and Q-factors of isolated dielectric resonators is described. The measured resonant frequencies and Q-factors of first five lowest order modes of two cylindrical dielectric resonators of relative permittivity 38.0 and 79.7 respectively are reported. The measured values are compared with those of rigorous numerical methods available in the literature. >
TL;DR: In this paper, an attempt is made to incorporate the scattering losses in the effective permittivity of the medium consisting of the discrete scatterers immersed in a host material, where the inclusions are assumed to be spherical.
Abstract: Several dielectric models have been previously proposed to explain the permittivity of mixtures from the known dielectric constant and volume fractions of the constituents. The materials may be lossy and this leads to a complex effective permittivity for the mixture where the imaginary part stands for the absorption losses of the mixture. However, the scattering losses are not incorporated in the effective permittivity. The result is therefore confined to a low-frequency limit. In this paper an attempt is made to incorporate the scattering losses in the effective permittivity of the medium consisting of the discrete scatterers immersed in a host material. The inclusions are assumed to be spherical. The results are applicable to general multiphase mixtures, and the scattering spheres of the different phases may have size distribution. The results are applied to calculating the complex effective permittivity of wet snow. The prediction of the model seems to agree with the experimental data if the scattering...
TL;DR: In this paper, the problem of reconstructing both the shape and the relative permittivity of a homogeneous dielectric cylinder from the measurement of scattered field is numerically simulated.
Abstract: The problem of reconstructing both the shape and the relative permittivity of a homogeneous dielectric cylinder from the measurement of scattered field is numerically simulated. The Newton-Kantorovitch algorithm and the moment method are used to solve a set of nonlinear integral equations. Numerical results show that, with multiple incident directions, good reconstruction is obtained. This algorithm can be applied at a single frequency without limitation on the value of dielectric constant. The effect of random noise on imaging reconstruction is also investigated. >
05 Jun 1994
TL;DR: In this article, the authors compared the properties of polyimide and aromatic polyamide (Aramid) films and concluded that the Aramid film is more hydrophilic than the polyimides and there is no free water detected in both.
Abstract: Specimens of an aromatic polyamide(Aramid) film as well as a polyimide film, which were subjected to various degrees of moisture adsorption as well as water immersion, were investigated both dielectrically and thermoanalytically in order to compare how much the adsorbed moisture and the stored water affect each dielectric and thermoanalytical behavior. It became clear that the polyimide film is more hydrophilic than the Aramid film and there is apparently no free water detected in both films. It followed from the thermogravimetry (TG) measurements that the polyimide film appears extraordinary in such a manner that its weight loss occurs dominantly at room temperature and then does not occur almost above 200/spl deg/C reaching totally about half of the water content value measured by the weight increase. It means that there is a large discrepancy existing between the weight loss and weight increase of the polyimide film, being demonstrated by the calculation of dissipated moisture from the polyimide film during the DSC measurements, too. The results for the dielectric measurements at room temperature show that in the whole frequency range both relative permittivity and dielectric dissipation factor values increase along with their water contents and that in the low frequency region there are large increases in both values particularly for their soaked specimens. Comparing the relationships between their relative permittivity/dielectric dissipation factor values and water contents, both values of the Aramid film were more dependent on the water contents than those of the polyimide film particularly in the low frequency region. Finally, it was concluded that, while in the Aramid film the moisture can be assumed to exist mainly in a state of bound water in the same way as that in humid Aramid papers, in the polyimide film the moisture can be assumed to exist in a state of surface attaching at room temperature up to about 80/spl deg/C and then the biggest part of the residual moisture is thought to be transformed to a strongly bound state with the imide linkages over 200/spl deg/C. >
01 Dec 1994
TL;DR: In this paper, the effect of substrate permittivity on coplanar waveguide probe-tip scattering parameter calibrations is modeled as a capacitance at the probe tip, which can be compensated using generic off-wafer standards.
Abstract: We demonstrate a method of compensation for the effect of substrate permittivity on coplanar waveguide probe-tip scattering parameter calibrations, modeling the effect as a capacitance at the probe tip. Comparison to on-wafer multiline TRL calibration verifies its accuracy. The method allows calibration to the probe tip using generic off-wafer standards with accuracy comparable to that of on-wafer calibration.
TL;DR: In this paper, the dielectric properties of inhomogeneous media constituted by a glassy semicrystalline polymer (polypropylene) impregnated by an aromatic fluid (monodibenzyltoluene) are studied.
Abstract: The dielectric properties of inhomogeneous media constituted by a glassy semicrystalline polymer (polypropylene) impregnated by an aromatic fluid (monodibenzyltoluene) are studied. The measured permittivity is compared to various forms of mixture equations. The closest agreement is obtained with the Lichteneker’s logarithmic mixing expression. The frequency dependence of ionic conductivity in these swollen materials has also been investigated at low electric fields. An attempt is made to interpret these measurements in terms of Niklasson’s [J. Appl. Phys. 62, R1 (1987)] fractal model taking into account the inner topology of the structure of the medium.
TL;DR: In this article, a new approach of measuring the quality factor of the reflection type microwave cavity resonator for calculating the complex dielectric permittivity of solid and liquid samples in the cavity perturbation technique is proposed.
Abstract: A new approach of measuring the quality factor of the reflection type microwave cavity resonator for calculating the complex dielectric permittivity of solid and liquid samples in the cavity perturbation technique is proposed. This approach, based on the measurement of reflected power from the cavity at resonance, effectively reduces the measurement procedure and increases the accuracy. As the quality factor can be measured very fast using this approach, this approach can be extended to monitor the conductivity decay of the semiconductor samples.