Dielectric

About: Dielectric is a research topic. Over the lifetime, 169743 publications have been published within this topic receiving 2777840 citations. The topic is also known as: dielectric medium.

A Dielectric Polymer with High Electric Energy Density and Fast Discharge Speed

Abstract: Dielectric polymers with high dipole density have the potential to achieve very high energy density, which is required in many modern electronics and electric systems. We demonstrate that a very high energy density with fast discharge speed and low loss can be obtained in defect-modified poly(vinylidene fluoride) polymers. This is achieved by combining nonpolar and polar molecular structural changes of the polymer with the proper dielectric constants, to avoid the electric displacement saturation at electric fields well below the breakdown field. The results indicate that a very high dielectric constant may not be desirable to reach a very high energy density.

Nonlinear Dielectric Polarization in Optical Media

Abstract: The physical mechanisms which can produce second-order dielectric polarization are discussed on the basis of a simple extension of the theory of dispersion in ionic crystals. Four distinct mechanisms are described, three of which are related to the anharmonicity, second-order moment, and Raman scattering of the lattice. These mechanisms are strongly frequency dependent, since they involve ionic motions with resonant frequencies lower than the light frequency. The other mechanism is related to electronic processes of higher frequency than the light, and, therefore, is essentially flat in the range of the frequencies of optical masers. Since this range lies an order of magnitude higher than the ionic resonances, the fourth mechanism may be the dominant one. On the other hand, a consideration of the linear electro-optic effect shows that the lattice is strongly involved in this effect, and, therefore, may be very much less linear than the electrons. It is shown that the question of the mechanism involved in the second harmonic generation of light from strong laser beams may be settled by experiments which test the symmetry of the effect. The electronic mechanism is subject to further symmetry requirements beyond those for piezoelectric coefficients. In many cases, this would greatly reduce the number of independent constants describing the effect. In particular, for quartz and KDP there would be a single constant.

Automatic measurement of complex dielectric constant and permeability at microwave frequencies

Abstract: With the advent of the computer and automatic test equipment, new techniques for measuring complex dielectric constant (e) and permeability (µ) can be considered. Such a technique is described where a system is employed that automatically measures the complex reflection and transmission coefficients that result when a sample of material is inserted in waveguide or a TEM transmission line. Measurement results of e and µ for two common materials are presented.

Compilation of the Dielectric Properties of Body Tissues at RF and Microwave Frequencies.

Abstract: : Knowledge of the dielectric properties of biological materials is of importance in solving electromagnetic interaction problems. There is, as yet, no consensus on such data among scientists dealing with these issues. This project is geared towards producing a database of dielectric data based on measurements using recently developed techniques. This has been achieved through measurement over a wide frequency range. The new data were evaluated by comparison with corresponding data from the literature where available. To facilitate the incorporation of the dielectric data in numerical solutions, their frequency dependence was modelled to a spectrum characterised by 4 dispersion regions. The conductivity of tissues below 100 Hz was estimated from the recent measurements mitigated by data from the literature and used to estimate the body and of various body parts.

Relation between the ion size and pore size for an electric double-layer capacitor.

Abstract: The research on electrochemical double layer capacitors (EDLC), also known as supercapacitors or ultracapacitors, is quickly expanding because their power delivery performance fills the gap between dielectric capacitors and traditional batteries. However, many fundamental questions, such as the relations between the pore size of carbon electrodes, ion size of the electrolyte, and the capacitance have not yet been fully answered. We show that the pore size leading to the maximum double-layer capacitance of a TiC-derived carbon electrode in a solvent-free ethyl-methylimmidazolium-bis(trifluoro-methane-sulfonyl)imide (EMI-TFSI) ionic liquid is roughly equal to the ion size (∼0.7 nm). The capacitance values of TiC−CDC produced at 500 °C are more than 160 F/g and 85 F/cm3 at 60 °C, while standard activated carbons with larger pores and a broader pore size distribution present capacitance values lower than 100 F/g and 50 F/cm3 in ionic liquids. A significant drop in capacitance has been observed in pores that w...