Relaxation in low-loss dielectrics

The real and imaginary components of the complex susceptibility of the majo rity of non-polar dielectric materials follow a fractional power law depend ence on frequency known as the "universal law". One limiting form of this l aw shows a very low loss and also a nearly frequency-independent, or "flat" amplitudes. Some low-loss materials owe their properties to the presence o f polarising species having intrinsically low losses. In others the polaris ing species have larger inherent losses, but their density is so low that t he overall loss of the material is low. Many low-loss materials have the pr operty that, after removal of any lossy components like dipolar, de or Low- Frequency Dispersion, their flat residual loss has an amplitude falling in a narrow interval of a factor of between 20 and 100 regardless of the natur e of the material. This is not at present understood and some suggestions a re being advanced. (C) 2000 Elsevier Science B.V. All rights reserved.