Showing papers on "Relative permittivity published in 2002"

The negative index of refraction demystified

Abstract: We study electromagnetic wave propagation in media in which the effective relative permittivity and the effective relative permeability are allowed to take any value in the upper half of the complex plane. A general condition is derived for the phase velocity to be oppositely directed to the power flow. That extends the recently studied case of propagation in media for which the relative permittivity and relative permeability are both simultaneously negative, to include dissipation as well. An illustrative case study demonstrates that in general the spectrum divides into five distinct regions.

Application of a microgenetic algorithm (MGA) to the design of broadband microwave absorbers using multiple frequency selective surface screens buried in dielectrics

Abstract: Over the years, frequency selective surfaces (FSSs) have found frequent use as radomes and spatial filters in both commercial and military applications. In the literature, the problem of synthesizing broadband microwave absorbers using multilayered dielectrics through the application of genetic algorithms (GAs) have been dealt with successfully. Spatial filters employing multiple, freestanding, FSS screens have been successfully designed by utilizing a domain-decomposed GA. We present a procedure for synthesizing broadband microwave absorbers by using multiple FSS screens buried in a dielectric composite. A binary coded microgenetic algorithm (MGA) is applied to optimize various parameters, viz., the thickness and relative permittivity of each dielectric layer; the FSS screen designs and materials; their x- and y-periodicities; and their placement within the dielectric composite. The result is a multilayer composite that provides maximum absorption of both transverse electric (TE) and transverse magnetic (TM) waves simultaneously for a prescribed range of frequencies and incident angles. This technique automatically places an upper bound on the total thickness of the composite. While a single FSS screen is analyzed using the electric field integral equation (EFIE), multiple FSS screens are analyzed using the scattering matrix technique.

Organic field effect transistor with an organic dielectric

Abstract: A process of manufacturing an organic field effect device is provided comprising the steps of (a) depositing from a solution an organic semiconductor layer; and (b) depositing from a solution a layer of low permittivity insulating material forming at least a part of a gate insulator, such that the low permittivity insulating material is in contact with the organic semiconductor layer, wherein the low permittivity insulating material is of relative permittivity from 1.1 to below 3.0. In addition, an organic field effect device manufactured by the process is provided.

Wire media with negative effective permittivity: A quasi‐static model

Abstract: In this Letter artificial media formed by dense arrays of parallel conducting wires are considered. A simple analytical model for the effective permittivity is derived from quasi-static considerations. The result gives a formula for the permittivity in terms of the geometrical parameters and the frequency. The analysis covers lossy and loaded wires as well. The phenomena that lead to negative permittivity values are discussed. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 47–51, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10512

Structural and dielectric studies of BaFe0.5Nb0.5O3

Abstract: Ferroelectric BaFe0.5Nb0.5O3 (BFN) ceramic is synthesized by the solid-state reaction technique for the first time. The x-ray diffraction of the sample at room temperature shows a monoclinic phase. Dielectric studies of the sample show a frequency dependence of the temperatures at which the dielectric permittivity (real and imaginary) peaks. The temperature variations of the real and imaginary components of the dielectric permittivity show broad maxima. There is evidence for Vogel-Fulcher-type relaxational freezing. The analysis of the real and imaginary parts of the dielectric permittivity with frequency has been performed assuming a distribution of relaxation times as confirmed by Cole-Cole plots as well as the scaling behaviour of the dielectric loss. All these observations clearly suggest that BFN is a relaxor ferroelectric. The Mossbauer spectrum of the sample at room temperature shows a symmetric doublet, with the iron being trivalent.

Characterization of liquid crystal polymer for high frequency system-in-a-package applications

Abstract: Liquid crystal polymer (LCP) is a promising substrate for electronics packaging. In this paper, the high frequency characteristics of LCP were investigated using a microstrip ring resonator to verify the possibility of applying the material in RF packaging. The relative dielectric constant and the loss tangent have been measured. The radiation loss of the ring is considered to accurately determine the loss tangent. A GaAs MMIC switch circuit was fabricated using LCP as substrate to demonstrate the application of this material for system-in-a-package. From the high frequency measurements, it is shown that LCP has low dielectric constant and low loss tangent in the frequency range from 1 GHz to 35 GHz. It is also found that LCP can be used in system-in-a-package applications.

Dielectric relaxor and ferroelectric relaxor: Bi-doped paraelectric SrTiO3

Abstract: In this article, we report the evolution of the dielectric behavior from a dielectric relaxor to a ferroelectric relaxor with variation of Bi concentration in (Sr1−1.5xBix)TiO3 (0⩽x⩽0.2). In the doping range 0.0005⩽x⩽0.002, two dielectric modes A and B are induced. The temperature (Tm) where the permittivity maximum occurs for modes A and B is independent of Bi concentration and of dc electric fields. The complex permittivity of modes A and B follows the empirical Cole–Cole equation. The relaxation time for modes A and B follows the Arrhenius law. The dielectric possessing this type of dielectric behavior is named as a “dielectric relaxor.” At x⩾0.0033, an additional mode C appears, whose Tm increases with increasing Bi concentration. The complex permittivity for mode C does not follow the Cole–Cole equation. The relaxation time of mode C follows the Vogel–Fulcher law, indicating typical relaxor-ferroelectric behavior. In this work, we refer it to a “ferroelectric relaxor” mode. In the range of 0.0033⩽x⩽0...

Nanometer silicon carbide powder synthesis and its dielectric behavior in the GHz range

Abstract: In this paper, the dielectric properties of nano-sized SiC powders have been investigated in the GHz frequency range. The polytypes of SiC have been changed from β type (3C) to α type (12H and 21R) by varying the aluminum contents and the reaction atmospheres. The β-SiC powder has much higher relative permittivity ( e ′ r =30∼50) and loss tangent ( tgδ =∼0.7) than α-SiC powders. Though the doping of Al and N decrease the resistivity of SiC to the order of 10 2 Ω cm, the pivotal factor on the dielectric behaviors is ion jump and dipole relaxation, namely the reorientation of lattice defect pairs (V Si –V C , Si C –C si ). The conductivity of SiC has little effect on the dielectric behaviors.

Effect of sintering aid and repeated sol infiltrations on the dielectric and piezoelectric properties of a PZT composite thick film

Abstract: Thick PZT films have been produced using a combination of spin coating of a composite slurry and subsequent infiltration of PZT producing sol. The effect of adding a Cu2O–PbO sintering aid and repeated sol infiltrations have been studied with the aim of producing dense PZT films. Relative permittivity has been shown to increase with the addition of sintering aid and increased levels of sol infiltration. Measurements of piezoelectric properties indicate that sol infiltrations have no effect on d33 once a critical density has been exceeded. A sample with approximately 10% closed porosity was obtained following the incorporation of sintering aid and four infiltration steps per layer. This resulted in a mean relative permittivity of approximately 700 and a d33 of 62 pC/N (poling conditions: 8 V/μm for 5 min at 200 °C).

Iron oxides as a cause of GPR reflections

Abstract: Iron oxides frequently occur as secondary precipitates in both modern and ancient sediments and may form bands or irregular patterns. We show from time-domain reflectometry (TDR) field studies that goethite iron-oxide precipitates significantly lower the electromagnetic wave velocity of sediments. Measured variations in magnetic permeability do not explain this decrease. The TDR measurements and a dielectric mixing model also show that neither electrical conductivity nor relative permittivity of the solid material are altered significantly by the iron-oxide material. From drying during all of the measurements, the amount of iron oxides appears to correlate with the volumetric water content, which is the result of differences in water retention capacity between goethite and quartz. These variations in water content control relative permittivity and explain the observed variation in electromagnetic wave velocity. Using 2-D synthetic radar sections, we show that the pattern of iron-oxide precipitation may have a profound influence on the GPR reflection configuration and can cause major difficulties in interpretation.

Field dependent permittivity of composite materials Field dependent permittivity of composite materials containing ferromagnetic wires

Abstract: A type of a composite material is proposed, the microwave permittivity of which changes under the effect of a dc magnetic field applied to the whole composite sample. The composite consists of short ferromagnetic wires embedded into a dielectric matrix. A strong field dependence of the permittivity is seen in the vicinity of the antenna resonance, where the dispersion behavior can experience a transformation from a resonant spectrum to a relaxation one under the effect of the field. This permittivity behavior is due to a high sensitivity of the ac surface impedance of a ferromagnetic wire to a magnetic field, known as the magnetoimpedance (MI) effect. If the resonance-like dispersion behavior is realized, the real part of the effective permittivity can be made negative past the resonance for wire inclusion concentrations well below the percolation threshold. Applying a magnetic field, the negative peak continuously decreases as the dispersion tends to become of a relaxation type. The effective permittivit...

Dielectric relaxation in ferroelectric PZT–PVDF nanocomposites

Abstract: Composites of electroactive ceramics and ferroelectric polymers are important for applications since they combine the most important features of the both phases and their properties can be easily tailored to various requirements. As the dielectric permittivity is involved in figures of merit of the quantities important for applications we studied dielectric response of Pb(Zr 0.5 Ti 0.5 )O 3 –polyvinylidene fluoride nanocomposites over a wide frequency and temperature range. It was found that though the permittivity value of the composites is high due to the high permittivity of the ceramics, the glass transition of the polymer and dielectric relaxation related to the wide-angle oscillation of polar groups attached to the main polymer chain determine the dielectric behaviour of the composites.

Zero permittivity materials: Band gaps at the visible

Abstract: We theoretically discuss the possibility of having materials with zero effective permittivity that would create band gaps in a wide range of frequencies up to the visible. The physical realization of these materials is also discussed in terms of embedding metallic nanoparticles and nanowires in a dielectric medium. In the limit of long wavelengths, these composites will behave like a homogeneous medium with zero permittivity that will completely reflect electromagnetic waves. We present transmittivity calculations by using finite-difference time domain for periodic structures that proves the concept and shows the validity of the long wavelength approximation. The striking result is that the cutoff frequency ωc is determined by the lattice parameter of the composite. By properly choosing the lattice constant of the composite and permittivity of metal and dielectric constituents, we can have full band gaps at any frequency range but especially in the visible.

Dielectric properties of blood: an investigation of temperature dependence.

Abstract: We have investigated the temperature dependence of the electrical parameters (permittivity and conductivity) of blood. The measuring system, composed of an impedancemeter (HP 4291 A), an open-ended coaxial line and a temperature controlling set, was designed for dielectric measurement in the frequency range of 1 MHz to 1 GHz. Measurements were performed on ex vivo blood of humans and animals (cow and sheep). The results obtained show the weak sensibility and a change of sign of the temperature coefficient of the relative permittivity (about 0.3% degrees C(-1) at 1 MHz and -0.3% degrees C(-1) at 1 GHz). The conductivity presents a more significant variation (of the order of 1% degrees C(-1) over the whole operating frequency range.

Grain-Boundary Effect on the Curie-Weiss Law of Ferroelectric Ceramics and Polycrystalline Thin Films: Calculation by the Method of Effective Medium

Abstract: The influence of grain boundaries on the dielectric properties of ferroelectric ceramics and polycrystalline thin films is described theoretically by the method of effective medium. Grain boundaries are modeled by low-permittivity (“dead”) layers, which do not exhibit ferroelectric instability. The effective permittivity of a polycrystalline material is calculated in the paraelectric regime above the transition temperature. The calculations are based on the solution of electrostatic problem for a spherical dielectric inclusion separated from the surrounding dissimilar matrix by a low-permittivity interface layer. For isotropic bulk ceramics, an analytic expression is derived for the effective permittivity as a function of the grain size, dead-layer thickness, and its permittivity. Temperature dependence of the aggregate dielectric response is calculated for BaTiO3 (BT) ceramics of different grain sizes and found to be in good agreement with measurements. It is shown that grain boundaries not only renormalize the Curie-Weiss temperature and constant, but may also cause deviations from the Curie-Weiss law. For BT polycrystalline thin films grown on dissimilar substrates, numerical calculations of the effective dielectric constants are performed, taking into account both the grain-boundary and substrate effects on the film anisotropic dielectric response. Theoretical predictions are compared with the grain size dependence of the permittivity of BT films grown on Pt-coated Si.

Electromagnetic logging technique based on borehole radar

Abstract: An electromagnetic logging technique based on borehole radar is introduced in this paper. The tool consists of one transmitter and two receivers, which can be used to cancel the effect of the antenna characteristics by taking the ratio of two receiver signals. Since receiver signals measured in the time domain can be converted into the frequency domain by Fourier transformation, the amplitude ratio and the phase difference between two receiver signals in a wide-frequency band are obtainable. The response of the tool to different formations is investigated, and the algorithm that converts the amplitude and the phase information to the conductivity and the relative permittivity of the surrounding medium is given by a three-dimensional finite-difference time domain. The effect of the borehole on measurement and the response of the tool to a formation interface are simulated and analyzed numerically. The validity of this technique is confirmed by experiment. This technique can be applied to detect physical properties, including the conductivity and the relative permittivity, of the surrounding medium and the locations of the fractures intersecting the borehole.

Microwave electromagnetic characteristics of a microcoiled carbon fibers/paraffin wax composite in Ku band

Abstract: The complex relative permittivity ∈γ and permeability μγ of microcoiled carbon fibers (MCCFs) imbedded in paraffin wax were measured at Ku band frequencies (12.4–18 GHz). Both the real and imaginary parts of the complex relative permittivity of the MCCFs/paraffin wax composite decreased with increase of the frequency. The real part of the complex relative permeability of the composite increases with increase of the frequency, and the imaginary part is nonzero and nearly constant over the measured frequency range. The dielectric loss tangent (tan δ∈), the magnetic loss tangent (tan δm), and amplitude attenuation factor (α) were determined as well. On the basis of the experimental results, the MCCFs/paraffin wax composite is mainly a kind of dielectric lossy material with small magnetic loss and diamagnetism in the Ku band.

Phase transition at low temperature in NaNbO3 ceramic

Abstract: The electric permittivity of the sodium niobate ceramic was investigated in the temperature range from 15 up to 900 K, at frequencies from 100 Hz to 1 MHz. Three anomalies were found in the permittivity curve. A phase transition for NaNbO3 was assigned to anomaly at around 280 K, while other two ones have previously been reported. In addition, the dielectric permittivity dependence with the temperature and frequency, at temperatures lower than 400 K, showed two regions with typical characteristics of a relaxor ferroelectric materials.

Dielectric properties of BaTiO3-BaZrO3 ceramics under a high electric field

Abstract: Multilayered ceramic capacitors (MLCCs) with BaTiO3–BaZrO3 (BTZ) dielectric layers were fabricated, and the dielectric permittivity of the BTZ layers with different thicknesses in MLCCs was measured The dielectric permittivity of the BTZ ceramic disk was also measured under various ac electric fields The variation in the dielectric behaviors with the thickness of BTZ layers in MLCCs was explained by the ac-field dependence of dielectric permittivity observed in the BTZ ceramic disk The ac-field dependence of dielectric permittivity of BTZ was markedly observed below the temperature of a broad maximum in the dielectric permittivity versus temperature (є versus T) curve It was found that the temperature of the broad maximum shifted to the low-temperature side and the peak shape became asymmetric with increasing ac field These changes in the dielectric properties under high ac fields were explained by a model of relaxors with the concept of the formation of polar microregions (PMRs) and the freezing of fluctuating ipoles in PMRs

The influence of permittivity models on phantom images obtained from electrical capacitance tomography

Abstract: Four different phantoms have been placed within the sensor field of an electrical capacitance tomography (ECT) system mounted on a bench-scale fluidized bed The phantoms were created with fluid catalytic cracking catalyst particles having a packed-bed relative permittivity of 24 Linear back-projection (LBP) image reconstruction has been compared with iterative LBP for three permittivity models: parallel, series, and Maxwell model The parallel permittivity model provides the best representation of the phantoms Tubes of solids placed in an empty bed could only be reconstructed near the ECT wall, while voids created by immersion of an empty tube in a packed bed of solids could be imaged equally well at the centre or wall After 500 iterations, the size of the phantom in the reconstructed image is in very good agreement with the actual size of the phantom

Structural properties and electrical characteristics of electron-beam gun evaporated erbium oxide films

Abstract: We report properties of Er2O3 films deposited on silicon using electron-beam gun evaporation. We describe the evolution with thickness and annealing temperature of the morphology, structure, and electrical characteristics. An effective relative dielectric constant in the range of 6–14, a minimum leakage current density of 1–2×10−8 A/cm2 at an electric field of 106 V/cm and breakdown electric field of 0.8–1.7×107 V/cm are demonstrated. Breakdown electric field and leakage current densities are correlated with the surface morphology. The obtained characteristics make the Er2O3 films a promising substitute for SiO2 as an ultrathin gate dielectric.

Dielectric permittivity and resistivity mapping using high-frequency, helicopter-borne EM data

Abstract: The interpretation of helicopter‐borne electromagnetic (EM) data is commonly based on the transformation of the data to the apparent resistivity under the assumption that the dielectric permittivity is that of free space and so displacement currents may be ignored. While this is an acceptable approach for many applications, it may not yield a reliable value for the apparent resistivity in resistive areas at the high frequencies now available commercially for some helicopter EM systems.We analyze the feasibility of mapping spatial variations in the dielectric permittivity and resistivity using a high‐frequency helicopter‐borne EM system. The effect of the dielectric permittivity on the EM data is to decrease the in‐phase component and increase the quadrature component. This results in an unwarranted increase in the apparent resistivity (when permittivity is neglected) for the pseudolayer half‐space model, or a decrease in the apparent resistivity for the homogeneous half‐space model. To avoid this problem,...

Pre-scaled two-parameter Gauss–Newton image reconstruction to reduce property recovery imbalance

Abstract: Gauss–Newton image reconstruction in microwave imaging can be formulated in terms of a single complex quantity, the wave number squared (k2), with the understanding that the relative permittivity and conductivity images can be extracted afterwards through a simple constitutive relationship. However, this approach ignores the fact that the magnitude of the average real and imaginary components can be considerably out of balance depending on the operating frequency and tissue characteristics which can inadvertently imbalance the process in favour of one parameter over the other. In an effort to achieve property recovery which is balanced, we introduce a pre-scaling procedure at the property update stage of the reconstruction. Utilization of this concept in conjunction with our two-step regularization process for both simulation and phantom experiments demonstrates that the penalty term weighting parameters for the optimal mean-squared property errors for the two recovered distributions (relative permittivity and conductivity) together with that yielding the lowest least-squared electric field error coincide only when the scaling is applied. The scheme provides a means for simultaneous optimization of the two permittivity and conductivity images.

The effective permittivity of dense packings of glass beads, quartz sand and their mixtures immersed in different dielectric backgrounds

Abstract: Dielectric methods, which measure the effective dielectric permittivity of granular materials, e.g., rocks, sediments and soils are often applied to estimate water or oil content. To test physically based models requires that the permittivity values of all phases are known. Measurements of the solid permittivity of glass spheres, quartz sand grains and their mixtures are made using an immersion method. The results obtained are tested against several classical models including the Maxwell Garnett, the symmetric effective medium approximation (SEMA) and the non-SEMA. The results demonstrate inadequate predictions between these models and the measured data. However, the Maxwell Garnett model comes close to predicting the effective permittivity of the media. Divergence between this model and the measurements is known to be due to interaction effects between grains that is not accounted for by a model based simply on the mixing of volumetric fractions of the components. With water as the background (contrast of 10 for glass) the Maxwell Garnett model overestimates the effective permittivity ∼5% as the contrast reduces this error decreases. For contrasts <4 the error for the permittivity estimate using the Maxwell Garnett formula was <3%. The modeling is simply used to demonstrate that the permittivity of the inclusions, for practical purposes, can be considered a linear function of the volumetric fraction times its respective permittivity.

Anisotropic permittivity and attenuation extraction from propagation constant measurements using an anisotropic full-wave Green's function solver for coplanar ferroelectric thin-film devices

Abstract: In this paper, a full-wave spectral-domain integral-equation technique is used to study double substrate layer coplanar devices with the ferroelectric thin film adjacent to the conductor guiding interfacial surface. The Green's function is used in the anisotropic situation for anisotropic permittivities. In examining specific laboratory data, going from an unbiased static electric field to the biased case, the permittivity tensor is allowed to go from a unity tensor to a uniaxial one. Consistent with this permittivity tensor behavior, the attenuation trend with frequency and its amplitude is also found.