Complex Electrical Permittivity Research Articles

Electrical and dielectric properties of glass system NaPO 3–KHSO 4

Glass samples have been prepared in the NaPO 3–KHSO 4 binary system with the classical melting, casting and annealing steps. Electrical and dielectrical properties of glass samples were studied. Measurements of DC and AC conductivity and complex electrical permittivity of xNaPO 3–(100 − x)KHSO 4 glass system were carried out at temperatures ranging from room temperature to temperature located 15 °C below glass transition temperature T g. Results showed that changes of NaPO 3 concentration considerably affect values of observed parameters. DC conductivity of glass increases as NaPO 3 concentration grows until concentration x = 60. However, beyond this value a sharp decrease of DC conductivity was observed. In addition relaxation times showed abrupt changes at concentration x = 60, corresponding to the lowest relaxation times at the temperature 90 °C.

Complex conjugate media: Alternative configurations for miniaturized lasers

We show that complex conjugate materials, in which the ratio of the complex electrical permittivity and the complex conjugate magnetic permeability is real, are characterized by a real refractive index and thus allow non-attenuated propagation of electromagnetic waves. Although complex conjugated media obey the same Snell law as common right-handed non-magnetic materials with the same refractive index, they differ from the latter through the reflection and transmission coefficients of electromagnetic waves. The complex conjugate materials could have important applications in miniaturized optical amplifiers and lasers.

Open ended-coaxial Cable Measurements of Saturated Sandy Soils

The application of electromagnetic methods in the radar and micro-wave frequency band allows the fluid content of soils to be estimated; the heuristic or physically-based models permit to relate the observed electrical permittivity of the soils with the porosity and fluid saturation. The role of the effect of the free water and bound water in the overall electromagnetic behaviour of soils is discussed. The measurements of the complex electrical permittivity of samples with different fluid content were carried out using an open ended coaxial cable in the frequency range between 0.2 and 6 GHz. The data processing permitted to estimate the water content with good accuracy; the slight overestimate of the values with respect to the standard laboratory measures of the fluid content is due to the propagation of the experimental uncertainties and to the effect of the bound water.

Dielectric anomalies of the relaxor-based 0.9Pb(Mg1∕3Nb2∕3)O3-0.1PbTiO3 single crystals

The temperature, frequency, and orientation dependence of complex electrical permittivity in 0.9Pb(Mg1∕3Nb2∕3)O3-0.1PbTiO3 (0.9PMN-0.1PT) unpoled single crystals have been investigated in detail. The spontaneous ferroelectric-to-relaxor (FE-R) phase transition was observed in 0.9PMN-0.1PT crystals at about 280K. Interestingly, the Vogel-Fulcher-type anomaly of the dielectric constant has been obtained, with the fitted temperature Tf being very close to this FE-R phase transition temperature. A small frequency dependence of electric permittivity magnitude appears at and below 280K. The changes of the polar nanoregion subsystem and the peculiarities of the domain structure play an important role in the dielectric anomalies and the appearance of the FE-R crossover region.

Investigation of dielectric anomalies at cryogenic temperatures in (1−x)[Pb(Mg1∕3Nb2∕3)O3]–xPbTiO3 system

Complex electrical permittivity measurements in (1−x)[Pb(Mg1∕3Nb2∕3)O3]–xPbTiO3 ceramics for 0.10⩽x⩽0.40 were performed in the frequency and temperature range from 1to100kHz and from 15to600K, respectively. Unexpected dielectric anomalies, which were frequency dependent, were found at cryogenic temperatures. It was verified that this dielectric behavior is always observed, independent of whether the composition presents a “normal” ferroelectric or a relaxor characteristic. The results were analyzed within the framework of two current models found in the literature. It was concluded that none of the proposed mechanisms uniquely satisfies the experimental results in the composition range investigated here.

The Exact Photonic Band Structure for a Class of Media with Periodic Complex Moduli

An exact formula for the photonic band structure (and hence the dispersion relation) is found for a certain class of periodic media. These media have the special property that the spatially fluctuating part of their complex electrical permittivity and magnetic permeability, when Fourier transformed, vanishes in half of Fourier space. As a result the band structure is proved to be exactly the same as for a lossy homogeneous medium, at least when the frequency is not too high.

ASSESSING SOIL WATER CONTENT USING COMPLEX PERMITTIVITY

For most temperate zone food and fiber plants that require medium amounts of water (mesophytes), it iscrucial for plant health and growth to know the volumetric water content in the growing media. Understanding the basicsof the complex electrical permittivity of wet agronomic soil can lead to the development of a real-time, relatively low-cost,reasonably accurate, dielectric soil-moisture probe. Theoretical and practical concepts are presented concerning thenature of the complex permittivity and dielectric constant within an operating frequency range that can make developmentof a low-cost probe feasible. The real component of the complex permittivity contains water content information while theimaginary component contains soil electrical conductivity information. A commercial soil-moisture probe operating at50 MHz was used to provide the temperature-corrected real component of the complex permittivity in custom-made, 85/15(85% graded sand and 15% pulverized peat moss) golf course greens-mixture soil (soil especially formulated for use ongolf course greens). Gravimetric water-content and real dielectric constant measurements were made simultaneously inthe greens-mixture soil for developing an empirical equation with desired absolute error of less than 0.015 cm 3 /cm 3between the permanent wilting point and field capacity values, and error less than 0.03 cm 3 /cm 3 between zero watercontent and the saturation value. When compared with the results using a time domain reflectometry (TDR) calibrationequation, it is possible that a simple electrical capacitance/dielectric probe may perform as well as the more expensiveTDR equipment. The probe was able to estimate the volumetric water content with reasonable accuracy in the presence ofa 1:1 electrolyte (KCl) at concentrations from zero to 0.01 M.

Complex electrical permittivity of 0–3 superconducting ceramic/polymer composites

The dielectric behaviour of a new high Tc superconducting composite material has been investigated. The composites consist of YBa 2Cu 3O 7−x superconductor powder embedded in a thermoplastic matrix. The complex electrical permittivity has been determined at frequencies between 1kHz and 1MHz and temperatures between 50 and 290K for composites with volume percentage of superconductor from 0 to 70%.

Dielectric permittivity of Y 1Ba 2Cu 3O 7−δ in the microwave region

Complex electrical permittivity of Y 1Ba 2Cu 3O 7−δ superconductor ( T c ≈90 K) has been measured at 9.2 GHz using a perturbation resonance technique. The dielectric constant and microwave absorption exhibit a sharp fall in the vicinity of 90 K, both parameters rise again below the transition temperature.

Dielectric properties of liposome vesicles at the phase transition

The complex electrical permittivity of liposome vesicles was measured at frequencies from 10 kHz to 100 MHz and in a range of temperatures from 25 degrees C to 45 degrees C which includes the phase-transition temperature of 40 degrees C. Liposome vesicles of an average diameter of 200 nm were DPPG and DPPC (1:4 mole ratio) suspended in low-conductivity water. At all frequencies real and imaginary parts of the permittivity changed abruptly near the phase-transition temperature. Data analysis indicated at least two relaxation processes in the frequency range investigated. For both processes the relaxation parameters undergo a rapid change in their dependence on temperature slightly below the theoretical phase-transition temperature. The low-frequency relaxation exhibits an anomalous behaviour above the transition temperature.

Refractive indices of soot particles deduced from in-situ laser light scattering measurements

Classical and dynamic laser light scattering data are obtained for a fuel-rich premixed methane/oxygen flat flame. Particle size distribution is determined directly from the dynamic light scattering measurements. Particle number density and complex refractive index are then inferred from classical scattering and extinction data by introducing a relation between the real and imaginary parts of the complex electrical permittivity.

Bounds on the Electromagnetic, Elastic, and Other Properties of Two-Component Composites

A simple relation between three-point correlation functions is derived for two-component materials. This relation enables one to find concise expressions for the Beran, Molyneux, and McCoy bounds on transport and elastic coefficients in terms of the volume fraction, ${f}_{1}$, and two fundamental geometric parameters, ${\ensuremath{\zeta}}_{1}$ and ${\ensuremath{\eta}}_{1}$. The parameter ${\ensuremath{\zeta}}_{1}$ also determines bounds on the complex electrical permittivity. No simple interpretation of ${\ensuremath{\zeta}}_{1}$ and ${\ensuremath{\eta}}_{1}$ has been found.