Limiting losses in dielectrics

Examination of a wide range of experimental data relating to 'low-loss' dielectric materials reveals the little acknowledged fact that their loss at high frequencies (kHz to GHz) and low temperatures (typically 100 to 200 K) is weakly or very weakly dependent on frequency, what we call 'flat loss', and is likewise weakly dependent on temperature. Moreover, the absolute value of the loss tangent tan /spl delta/, for a wide range of materials, falls in the relatively narrow range 0.001 to 0.1, although some cases of lower loss /spl sim/10/sup -5/ to 10/sup -4/ are known. Examples of such behavior are given. An explanation of this hitherto apparently not recognized behavior, which is not understood in terms of any accepted mechanism, is proposed in terms of screening of dipoles by other dipoles or by point charges. The principal feature is a constant loss per reversal of polarization, independent of the frequency of reversals, arising from the delayed screening process. The magnitude of the resulting flat loss depends on the dipolar species density, while the power-law index of the frequency dependence depends on the ratio of energy lost per reversal to energy stored in the polarization. The theory of this phenomenon explains the observed behavior and provides a basis for understanding of the residual losses.