Dielectric loss

About: Dielectric loss is a research topic. Over the lifetime, 20296 publications have been published within this topic receiving 349254 citations.

Non-symmetrical dielectric relaxation behaviour arising from a simple empirical decay function

Abstract: The empirical dielectric decay function γ(t)= exp –(t/τ0)β may be transformed analytically to give the frequency dependent complex dielectric constant if β is chosen to be 0.50. The resulting dielectric constant and dielectric loss curves are non-symmetrical about the logarithm of the frequency of maximum loss, and are intermediate between the Cole-Cole and Davidson-Cole empirical relations. Using a short extrapolation procedure, good agreement is obtained between the empirical representation and the experimental curves for the α relaxation in polyethyl acrylate. It is suggested that the present representation would have a general application to the α relaxations in other polymers. The Hamon approximation, with a small applied correction, is valid for the present function with β= 0.50 in the range log(ωτ0) > –0.5, but cannot be used at lower frequencies.

A Dielectric Resonator Method of Measuring Inductive Capacities in the Millimeter Range

Abstract: A novel technique for the measurement of dielectric and magnetic properties of a homogeneous isotropic medium in the range of approximately 3 to 100 kmc is described. An accuracy of /l.chemc/ 1 per cent is possible in the determination of permittivity or permeability in those cases where the loss tangent is sulliciently small. The measuring structure is a resonator made up of a right circular cyndrical dielectric rod placed between two parallel conducting plates. For measurement of permittivity two or more resonant TE/sub onl/ mode frequencies are determined whereas for the measurement of permeability two or more resonant TM/sub onl/ mode frequencies are determined. The dielectric or magnetic properties are computed from the resonance frequencies, structure dimensions, and unloaded Q. Since the loss tangent is inversely proportional to the unloaded Q of the structure, the precision to which Q is measured determines the accuracy of the loss tangent.

Wave-Number-Dependent Dielectric Function of Semiconductors

Abstract: Expressions for the wave-number-dependent dielectric function are derived for various models of a semiconductor The calculation is carried out for the diagonal part of the dielectric function at zero frequency It is found that calculations based on plane wave models (such as the free electron model) give poor results for small values of the wave number due to neglect of both Bragg reflections and Umklapp processes We use instead an isotropic version of the nearly free electron model in which dielectric function depends on only one parameter ${E}_{g}$ representing an average energy gap that can be determined from optical data It is noted that for small wave numbers Umklapp processes give the major contribution to the dielectricfunction, where-as for large wave numbers normal processes dominate The dielectric function is evaluated numerically for a value of ${E}_{g}$ appropriate to Si

Viscous Liquids and the Glass Transition. II. Secondary Relaxations in Glasses of Rigid Molecules

Abstract: The dielectric loss factor and dielectric permittivity of 8–16 mol% solutions of chlorobenzene, o‐dichlorobenzene, and 1‐chloronaphthalene in cis‐decalin; 50–60 mol% mixtures of pyridine with chlorobenzene, bromobenzene, 1‐chloronaphthalene, and toluene; 50–60 mol% mixtures of tetrahydrofuran with bromobenzene and 1‐chloronaphthalene; the pure liquids cis‐decalin, o‐terphenyl, iso‐propylbenzene, propylene carbonate; and two fused salt systems, 45 mol% Ca(NO3)2–KNO3 mixture and Ca(NO3)2·4H2O have been measured from 50 Hz to 1 × 105 Hz from − 196° in the vitreous state to about 30° above their respective glass transition temperatures. The Tg's of the organic glasses have been measured by DTA. With the exception of propylene carbonate, all glasses show the presence of one secondary relaxation between − 196° and their respective Tg's either as a peak or shoulder in a tanδ–temperature plot at a single frequency, or in the dielectric loss spectrum. Arrhenius plots of the frequency of maximum loss against temper...