Average Permittivity Research Articles

Simplified description of asymmetric right‐handed composite right/left‐handed coupler in microstrip chip technology

AbstractThe coupling frequency range of the asymmetric coupler composed of a conventional microstrip right‐handed (RH) transmission line and a composite right/left‐handed (CRLH) transmission line with lumped‐elements is investigated. It shows theoretically that the coupling frequency range can be explicitly determined by the given formulas. In the coupling frequency range, the effective permittivity and permeability of the CRLH transmission lines are both negative, at the same time the product of the average permittivity and the average permeability is negative, i.e., ϵL < 0, μL < 0, and $\bar{\varepsilon}$ · $\bar{\mu}$ < 0. Two types of RH‐CRLH couplers are designed, simulated, and measured. The coupling frequency range obtained from the simulated and the experimental results confirms the theoretical results. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2063–2068, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22643

Band structure of comb-like photonic crystals containing meta-materials

We study the transmission properties and band structure of comb-like photonic crystals (PC) with backbones constructed of meta-materials (negative-index materials) within the frame of the interface response theory. The result shows the existence of a special band gap at low frequency. This gap differs from the Bragg gaps in that it is insensitive to the geometrical scaling and disorder. In comparison with the zero-average-index gap in one-dimensional PC made of alternating positive- and negative-index materials, the gap is obviously deeper and broader, given the same system parameters. In addition, the behavior of its gap-edges is also different. One gap-edge is decided by the average permittivity whereas the other is only subject to the changing of the permeability of the backbone. Due to this asymmetry of the two gap-edges, the broadening of the gap could be realized with much freedom and facility.

Structural and dielectric properties of PbMg1/3Nb2/3O3-PbZrO3 solid solutions synthesized at high pressures and temperatures

(1 − x)PbMg1/3Nb2/3O3 · xPbZrO3 (1 − x)PMN · xPZ) solid solutions have been synthesized at a pressure of 5 GPa and temperatures from 1300 to 1700 K, and their structural and dielectric properties have been studied. The composition dependences of the average unit-cell parameter and dielectric permittivity for the solid solutions indicate that the PMN-PZ system has a morphotropic phase boundary near x = 0.65. The solid solutions have a cubic structure for x 0.9. The temperature and frequency dependences of dielectric permittivity suggest that the (1 − x)PMN · xPZ samples with x < 0.65 consist of two ferroelectric phases: a relaxor with antipolar dipole order and a normal ferroelectric with a diffuse phase transition. The effect of annealing temperature on the ferroelectric state of the samples with x < 0.65 is examined. In the composition range 0.65 < x < 0.9, the samples have normal ferroelectric properties, independent of annealing temperature.

In-Liquid Sensing of Chemical Compounds by QCM Sensors Coupled With High-Accuracy ACC Oscillator

A novel oscillator circuit with automatic capacitance compensation (ACC) capability has been coupled with quartz-crystal-microbalance (QCM) sensors coated with quinoxaline- and pyrazine-bridged cavitands to detect aromatic and chlorinated compounds in water. With double-side immersed 10-MHz crystals coated with the quinoxaline cavitand, the detection of toluene in deionized water was possible down to concentrations of a few parts per million. The ACC oscillator advantageously provides the simultaneous measurement of the sensor resonant frequency, damping, and value of the compensated parallel capacitance. This enabled observing that the analyte sorption in the cavitand coating not only brings about a mass uptake but also an increase of losses and, apparently, a rise in the coating average permittivity

Theory of atomic-scale dielectric permittivity at insulator interfaces

We develop a theory for investigating atomic-scale dielectric permittivity profiles across interfaces between insulators. A local susceptibility $\ensuremath{\chi}(x;\ensuremath{\omega})$ is introduced to describe variations of the dielectric response over length scales of the order of interatomic distances. The nonlocality of the microscopic susceptibility tensor ${\ensuremath{\chi}}_{ij}(\mathbf{r},{\mathbf{r}}^{\ensuremath{'}};\ensuremath{\omega})$ occurs at smaller distances and therefore does not intervene in our formulation. The local permittivity is obtained from the microscopic charge density induced by an applied electric field. We show that the permittivity can conveniently be analyzed in terms of maximally localized Wannier functions. In this way, we can relate variations of the microscopic dielectric response to specific features of the local bonding arrangement. In addition to a continuous description in terms of the local permittivity, we introduce an alternative scheme based on discrete polarizabilities. In the latter case, electronic polarizabilities ${\ensuremath{\alpha}}_{\mathrm{elec}}^{(n)}$ are obtained in terms of the displacements of maximally localized Wannier functions, while ionic polarizabilities ${\ensuremath{\alpha}}_{\text{ion}}^{(I)}$ are determined from the induced ionic displacements and the corresponding dynamical charges. The potential of our scheme is illustrated through applications to two systems of technological interest. First, we consider the permittivity of Si slabs of finite thickness. Our approach indicates that the local permittivity in the slab interior approaches the corresponding value for bulk Si within a few atomic layers from the surface. Therefore, the decrease of the average slab permittivity with thickness originates from the lower permittivity of the outer planes and the increasing surface-to-volume ratio. Second, we address the dielectric permittivity across the $\mathrm{Si}(100)\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{2}$ interface. Using two distinct interface models, we are able to show that the dielectric transition from the silicon to the oxide occurs within a width of only a few \AA{}. The polarizability associated to intermediate oxidation states of Si is found to be enhanced with respect to bulk $\mathrm{Si}{\mathrm{O}}_{2}$, resulting in a larger permittivity of the interfacial suboxide layer with respect to the stoichiometric oxide.

Ferroelectric and dielectric anisotropy in high-quality SrBi2Ta2O9 single crystals

High-quality SrBi2Ta2O9 single crystals were obtained by a self-flux solution method. The crystals were naturally oriented with [001] direction perpendicular to the major face and edges parallel to [110] axes. The dielectric and ferroelectric properties of the crystals were investigated along the c axis and in the ab plane of the orthorhombic unit cell. The ferro–paraelectric phase transition was observed at TC=355°C. The anisotropy of dielectric permittivity, i.e., the ratio between average permittivity in the ab plane and along c axis was about 10 at TC and decreased to ∼2 at room temperature. Saturated hysteresis loops were observed for switching in the ab plane. The spontaneous polarization along ferroelectric a axis was estimated to be ≈20μC∕cm2.

Precise microwave characterization of MgO substrates for HTS circuits with superconductingpost dielectric resonator

Accurate data of complex permittivity of dielectric substrates are needed for efficient designof HTS microwave planar circuits. We have tested MgO substrates from three differentmanufacturing batches using a dielectric resonator with superconducting partsrecently developed for precise microwave characterization of laminar dielectrics atcryogenic temperatures. The measurement fixture has been fabricated using aSrLaAlO3 post dielectricresonator with DyBa2Cu3O7 end plates and silver-plated copper sidewalls to achieve the resolution of loss tangent measurementsof 2 × 10−6. The tested MgO substrates exhibited the average relative permittivity of 9.63 andtanδ from 3.7 × 10−7 to 2 × 10−5 at frequency of 10.5 GHz in the temperature range from 14 to 80 K.

Magnetic induction tomography: phase versus vector-voltmeter measurement techniques

In magnetic induction tomography (MIT) the in-quadrature component, and hence the phase, of the received signal contains information about the conductivity of the tissue. The quality of imaging will depend on the precision with which phase can be measured. Preliminary studies suggest that a precision of 10 m° may be required for a practical biomedical MIT system operating at 10 MHz. This paper describes the results of measurements carried out with a 16-channel, downconverting, 10 MHz, MIT system utilizing two types of data extraction techniques: direct-phase measurement and measurement of the in-phase and in-quadrature components of the signal with a vector voltmeter. The basic precision provided by each technique was 50 m°, with thermal drift representing the major limiting factor. Preliminary measurements of average conductivity and permittivity for a human thigh in vivo are given.

Study on Bandwidth of 2-D Dielectric PBG Material

�H by extending Bloch theorem to the vector field Maxwell equations, the characteristics of 2-D dielectric rod array with square cross-section elements arranged in square lattice is analyzed in detail. From the numerical results, empirical expressions for both the relative bandwidth of frequency band gap and the midgap frequency with respect to the average permittivity, under the optimal filling fraction of dielectric/air in cross-section for wider bandwidth, are formulated by means of data fit.

An investigation into the spectral analysis of dielectric aging in ferroelectrics.

Aging and degradation indicate the time-dependent change of physical and electrical properties. Most studies neglect to report the effects of aging on the electromechanical properties of an electroactive material and subsequent deterioration of performance. Recent work has shown that the strain and polarization response of an electroactive device can be transformed into its harmonic spectrum (transformation from the time domain to the frequency domain) through the implementation of Fourier analysis. The ability to create this harmonic spectrum provides a new way to characterize the effects of aging by revealing subtle changes in the fundamental components that comprise the response. This study shows how Fourier analysis can be applied to an aged PMN-PT-BT composition to characterize and quantify the effects of aging. The average weak-field permittivity is measured as a function of time, temperature, and frequency. A typical "saddle" in the permittivity and dielectric loss is apparent, and the magnitude decays logarithmically with time. Harmonic analysis of the strain response reveals a slight time-dependent amplitude variation and logarithmic dependence of the phase of the 6th order harmonic. Similar analysis of the polarization response, as a function of time, fully characterizes the development of constriction or wasting seen in a typical aged electrostrictive material. Variations in the amplitudes of the 5th and higher order harmonics of polarization, logarithmic in nature, and the phase of the 5th order harmonic combine to define aging on the harmonic level.

BEHAVIOR IN ELECTRIC FIELDS OF SIMPLE BIOLOGICAL MEMBRANES

The latest studies in biophysics and biochemistry have revealed the major role that liquid crystals (LC) and related phenomena play in biological processes. To account for a number of membrane mechanisms in view of the theoretical model developed by S. J. Singer, studies were carried out on mixtures of fatty acids (arachidic, lauric, butyric) and cholesterol in different weight percentages. Such mixtures may help one understand some mechanisms on which the operation of biological membranes relies. To this end, the way these mixtures behave in an electric field was studied. Electric measurements were conducted from which the average time of electric relaxation (τ) and average electric permittivity (ε r ) were determined. Depending on cholesterol percentage, changes by more than one order of magnitude were found to occur in the electric relaxation time. The ratio between the various fatty acid components did not influence the average time τ in any significant manner. By contrast, the relative electric permittivity ε r was seen to decrease by at least one order of magnitude with raising the cholesterol percentage. The electric properties of such systems essentially depend on changing the amount of cholesterol in the system.

A clinical prototype for active microwave imaging of the breast

Despite its recognized value in detecting and characterizing breast disease, X-ray mammography has important limitations that motivate the quest for alternatives to augment the diagnostic tools that are currently available to the radiologist. The rationale for pursuing electromagnetic methods is strong given the data in the literature, which show that the electromagnetic properties of breast malignancy are significantly different than normal in the high megahertz to low gigahertz spectral range, microwave illumination can effectively penetrate the breast at these frequencies, and the breast is a small readily accessible tissue volume, making it an ideal site for deploying advanced near-field imaging concepts that exploit model-based image reconstruction methodology. In this paper a clinical prototype of a microwave imaging system, which actively illuminates the breast with a 16-element transceiving monopole antenna array in the 300-1000 MHz range, is reported. Microwave exams have been delivered to five women through a water-coupled interface to the pendant breast with the participant positioned prone on an examination table. This configuration has been found to be a practical, comfortable approach to microwave breast imaging. Sessions lasted 10-15 min per breast and included full tomographic data acquisition at seven different array heights beginning at the chest wall and moving anteriorly toward the nipple for seven different frequencies at each array position. This clinical experience appears to be the first report of active near-field microwave imaging of the breast and is certainly the first attempt to exploit model-based image reconstructions from in vivo breast data in order to convert the measured microwave signals into spatial maps of electrical permittivity and conductivity. While clearly preliminary, the results are encouraging and have supplied some interesting findings. Specifically, it appears that the average relative permittivity of the breast as a whole correlates with radiologic breast density categorization and may be considerably higher than previously published values, which have been based on ex vivo tissue specimens.

New asymptotic method for nonuniform grating investigation

A new method for the analytical investigation of nonuniform gratings (NG) is presented. For this type of grating, the average permittivity, local period, and depth of modulation are arbitrary and slowly varied along the grating. The method enables one to obtain analytical formulas for the characteristics of arbitrary NG. A special case of linearly chirped grating (LCG) is investigated in detail, and closed-form expressions for the reflective function in all frequency intervals are obtained for the first time. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 20: 436–440, 1999.

Membrane dielectric responses of human T-lymphocytes following mitogenic stimulation

Human peripheral blood T-lymphocytes, normally resting at the G 0 phase, were stimulated with phytohemagglutinin (PHA) and interleukin-2 (IL-2) to induce the cell division cycle. The cells were examined at 24-h intervals for up to 96 h by flow cytometry to determine cell cycle distributions and by electrorotation to determine dielectric properties. The average membrane specific capacitance was found to vary from 12 (±1.5) mF/m 2 prior to stimulation to 10 (±1.5) and 16 (±3.5) mF/m 2 at 24 and 48 h after stimulation, respectively, and to remain unchanged up to 96 h after stimulation. Scanning electron microscopy studies of the cells revealed an increased complexity in cell membrane morphology following stimulation, suggesting that the observed change in the membrane capacitance was dominated by the alteration of cell surface structures. The average electrical conductivity of the cell interior decreased from ∼1.1 S/m prior to stimulation to ∼0.8 S/m at 24 h after stimulation and showed little change thereafter. The average dielectric permittivity of the cell interior remained almost unchanged throughout the course of the cell stimulation. The percentage of T-lymphocytes in the S and G 2/M phases increased from ∼4% prior to stimulation to ∼11 and ∼34% at 24 and 48 h after stimulation, respectively. The large change in membrane specific capacitance between the 24 and 48 h time period coincided with the large alteration in the cell cycle distribution where the S and G 2/M populations increased by ∼23%. These data, together with an analysis of the variation of the membrane capacitance during the cell cycle based on the cell cycle-dependent membrane lipid accumulation, show that there is a correlation between membrane capacitance and cell cycle phases that reflects alterations in the cell plasma membrane.

Leaky wave radiation of millimetre waves by photoinduced plasma grating in a semiconductor slab

The paper reports investigations on leaky wave radiation of millimetre waves from a periodically photoinduced semiconductor slab waveguide. The photoinduced plasma grating structure is modelled as a permittivity modulated layer by considering the average permittivity as of a uniform plasma occupied thin layer and is systematically analysed using a singular perturbation procedure based on multiple space scales up to second order. The radiation efficiency of a leaky wave is derived and the results are outlined as a function of optically induced plasma density. Experiments have been carried out at 40 GHz by illuminating the grounded silicon slab using the slide of a periodic slit pattern through a xenon arc lamp. The dependence of periodicity on the radiation pattern is also reported.

The results of computerized simulation of the influence of dislocations on the degree of phase transition diffusion in BaTiO 3

The results of the computerized simulation of the influence of the edge dislocations on the diffusion of the phase transition in model ferroelectric material — BaTiO 3 are presented in this paper. Positions of dislocations have been chosen randomly in some considered area. The tensors of the strains have been summed up. As a result it was possible to calculate local Curie-Weiss temperatures and to calculate the average dielectric permittivity in effective medium approximation, i.e. it was possible to calculate how dislocations influence the dielectric properties.

Rigorous Coupled Wave Theory Solution of Phi-Periodic Circular Cylindrical Dielectric Systems

A state variable electromagnetic (EM) analysis technique called rigorous wave coupled theory (RCWT) (used for the EM and optical analysis of planar diffraction gratings) is applied to determine the radiation and scattering that arises from phi-periodic circular cylindrical dielectric systems which have arbitrary radial and azimuthal, inhomogeneous, permittivity variation. The RCWT state matrix equations and the associated boundary matrix equations (derived from a multi-layer cylindrical ladder analysis) are presented and solved for the cases: (1) when a plane wave (TM polarization, electric field parallel to the cylinder axis) is incident on the phi-periodic dielectric cylinder and (2) when an electric line current source excites EM radiation inside the phi-periodic dielectric cylinder. Numerical examples of plane wave scattering and line source radiation from phi-periodic dielectric cylinder systems are presented. Comparisons for the first time of scattering and radiation from inhomogeneous step profile dielectric cylinder systems are made with scattering and radiation from uniform dielectric cylinder systems (assuming that both systems have an equal bulk or average dielectric permittivity value).

Thin electromagnetic wave absorber for quasi-microwave band containing aligned thin magnetic metal particles

Soft magnetic material has been produced in which flaky thin amorphous metal particles, about 2 /spl mu/m thick, are aligned in polymer in the direction perpendicular to electromagnetic wave propagation. This material yields a permeability two to three times higher than the spinel-type ferrite system in the quasi-microwave band. We have designed a thin wave absorber composed of the present material by introducing a low-permittivity area such as a free space into the present metal-containing material. This decreases the average permittivity, striking a balance between complex permeability and permittivity values, and thus reducing the reflection coefficient of the absorber. A thin (about 3-mm thick) wave absorber with a reflection loss of over 30 dB in the quasi-microwave band was successfully obtained when the free space region was 5% of the total volume.

Polar fluctuations in proteins: molecular-dynamic studies of cytochrome c in aqueous solution.

The equilibrium fluctuations (the polar fluctuations), of yeast cytochrome c are studied using nanosecond molecular-dynamic simulations in a spherical droplet of water, with a particular emphasis on the fluctuations of the total dipole moment, which determine the average relative permittivity. These fluctuations follow a simple probability distribution, predicted by continuum electrostatics, and already observed in simulations of several polar liquids. An important component consists of diffusive, mutually independent, motions of the charged side chains at the protein surface. A quasiharmonic normal mode analysis of the trajectory shows that while motions covering a large range of frequencies contribute to the polar fluctuations, the four lowest frequency modes account for 50% of the overall static relative permittivity of ca. 25. The fluctuations of the protein bulk, i.e. parts other than the charged side chains, are distributed over a larger number of modes. Modes up to at least 60 cm-1 contribute to the average relative permittivity of the protein interior of ca. 4. The water surrounding the protein, despite the structural perturbation represented by the protein, has fluctuations similar to pure water, consistent with the idea of a linear solvent response to the protein charges. The relationship between the microscopic fluctuations seen in the simulations and simple continuum models is discussed.

A microcellular communications propagation model based on the uniform theory of diffraction and multiple image theory

Presents a comprehensive uniform theory of diffraction (UTD) propagation model for a city street grid, using the multiple image concept and the generalized Fermat's principle to describe the multiple reflections and diffractions. The model is a quasi 3D one in the sense that the building walls are assumed to be much higher than the transmitter height so that the diffractions from the rooftops can be neglected. The model includes all possible specular wall and ground reflections and corner diffractions in the main street, side streets, and parallel streets of a microcell. This enables the signal propagation through all the possible paths to be tracked to the receiver at various line-of-sight (LOS) or out-of-sight (OOS) positions. Previous papers on such propagation models have included only a limited number of specular reflections and diffractions or they are restricted to a rectilinear grid where all the building walls on each side of the street are coplanar. Our model includes contributions to the received signal from all possible propagation paths, including ground and wall reflections from diffracted and specularly reflected signals both in the LOS and OOS regions. Within the scope of the UTD model, the accuracy of our model is limited mainly by the assumptions of characterizing the building walls as smoothed-out flat surfaces with average relative permittivity /spl epsiv//sub r/ and conductivity /spl sigma/. Our theoretical results of the signal path loss along the streets are compared with measurements which have been reported for city streets in Tokyo and New York City.