Intrinsic Dielectric Loss Research Articles

Measurement of Complex Dielectric Constant above Room Temperature and Its Application to Determination of Intrinsic Dielectric Loss

Measurements of the complex permittivity on single crystal dielectric materials with different crystal symmetry have been carried out at high temperatures. The theory of intrinsic dielectric loss proposed by Gurevich et al.. was confirmed for Oh7 and D3d6 symmetries. X-ray topography images showed that crystal disorientation caused a deleterious influence on dielectric loss.

Intrinsic dielectric loss in crystals

Abstract We review the current theory of intrinsic dielectric loss, that is the loss in a perfect crystal due to anharmonic interaction of a.c. electric field with the phonon system of the crystal. Both ordinary dielectrics and displacive ferroelectrics are considered. The theory predicts dependence of the loss on frequency ω and temperature T. This dependence is very sensitive to the symmetry of the crystal. For ordinary dielectrics, the results are presented and tabulated for all 32 symmetry groups, except for non-symmorphic groups. The existing experimental date are analysed and explained on the basis of the theory.

Dielectric losses in ferroelectrics of displacive type as compared to the losses in ordinary dielectrics

The theory of intrinsic (phonon) dielectric losses in ferroelectrics of displacive type is reviewed and compared with the theory of losses in ordinary dielectrics. The authors in 7-12 have calculated the temperature and frequency dependence of losses for a wide range of variation of the parameters. The results are compared with those of the previous papers1-5.

Resonant-frequency temperature coefficient andQ-factor of a dielectric resonator at 6 mm wave-length and 850 °C

The resonant-frequency temperature coefficient andQ-value of a sapphire resonator at 50 GHz has been measured at temperatures ranging from 20 to 850°C. The resonator operates in an open-structure configuration, without any metal part. In this way it is possible to work at high temperatures, theQ-factor being affected only by the intrinsic dielectric losses of the crystal. The results indicate that the sapphire resonator is well suited for applications up to 850°C.

Low−temperature dielectric loss in polyethylene

A calorimetric technique was used to accurately determine the dielectric loss tangent of both additive−free and commerical grades of polyethylene at liquid−helium temperature. We found that the loss tangent of polyethylene often exhibits a broadened dielectric relaxation peak. Although this peak is centered in the kilohertz region, its existence increases the loss tangent at 60 Hz. Thus, the possibility of the elimination or reduction of this peak is important in evaluating the suitability of polyethylene as an insulator for a superconducting ac power transmission line. We have measured the intrinsic dielectric loss tangent of polyethylne and have found it to be ∼5×10−6. In addition, by systematically studying the influence of chemical additives on the dielectric loss, we have found the conditions necessary to obtain polyethylene exhibiting this low loss using present industrial production methods.

Dielectric studies on cellulose fibers

AbstractA method for obtaining the intrinsic dielectric constant and loss factor of dry cellulose fiber along the fiber axis was developed, and the dielectric properties of viscose rayon, Bemberg (cuprammonium rayon), and cotton sliver were measured over the frequency range from 500 cycles/sec. to 3 Mcycles/sec. and the temperature range from −60 to + 20°C. by using the mutual inductance bridge. Only one dispersion could be observed in this temperature and frequency range. Cole‐Cole's circular are law could be satisfactorily applied to the data obtained, and the parameters of the are (ϵ0 – ϵ∞) and β for the three samples could be determined at each temperature. The value of (ϵ0 – ϵ∞), which is proportional to concentration of the dipoles contributing to the orientation, increased with rising temperature and reached a limiting value at about −20°C. The value of β relating to the width of the distribution of relaxation times also increased with rising temperature, showing a little rise in the degree of increase at temperatures above −20°C. On the other hand, the apparent activation energy for dipole orientation, as calculated from the temperature dependence of the dispersion frequency, reached a maximum around −20°C. All these facts suggest that some transition will take place in the neighborhood of −20°C. This temperature is not considered to be likely to be the glass transition temperature for dry cellulose, since −20°C. is too low for a primary transition in stiff molecules such as cellulose, and since the observed value of the apparent activation energy is too small to activate the segmental movement of the main chains. It might be possible to expect some secondary transition, probably of a thermodynamical nature, relating to the movement of local parts such as side chains, especially methylol groups on glucose residue, at about −20°C., though there is no other support for this expectation. Moreover, the effect of the fine structures on the dielectric properties is that the magnitude of (ϵ0 – ϵ∞) at each temperature decreases in the order, viscose rayon > Bemberg > cotton sliver, and this order parallels that of the accessibility of the three samples. This fact suggests that the dipoles in the amorphous region and on the surface of the crystallite provide the chief contribution to this dispersion.