DIELECTRIC PROPERTIES OF GLASSES AT ULTRA‐HIGH FREQUENCIES AND THEIR RELATION TO COMPOSITION *

Abstract

AbstractThe dielectric constants and dielectric losses of 104 glasses of a wide range of compositions have been measured at 10‐cm. and 3‐cm. wave lengths by the resonating cavity method (3000 and 10,000 megacycles, respectively). By correlating the power‐factor data with the compositions of these glasses, the authors propose a qualitative explanation of the mechanisms producing energy absorption and dielectric losses in the microwave range. These mechanisms are determined by the nature of the bonds joining atoms and ions in the randomly oriented atomic networks of glasses.The rigid and continuous networks of SiO2 and B2O3 glasses are relatively transparent to centimeter wave lengths. Energy absorption and dielectric losses are low. Addition of network‐modifying oxides yields glasses of greater energy absorption owing to the oscillation of the interstitial ions thus introduced. Increasing the content of any one of these ions in a glass results in higher losses while the coexistence of a variety of these ions generally results in lower losses.Alkali ions in glasses give rise to high losses, which increase as the number of ions present increases. Glasses containing a combination of alkalis show lower losses than the equivalent compositions with only one alkali. Divalent ions do not contribute as much to losses as alkalis, but high power factors are shown by glasses with high BaO or PbO contents. Using combinations of these oxides instead of only one, slight reductions in power factor are effected. Dissimilar interstitial ions interact in ultra‐high frequency fields with the result that energy absorption is reduced. The losses of high‐lead glasses are thus reduced by alkalis and, on the other hand, the presence of RO lowers the losses of glasses containing R2O. Alumina increases the dielectric losses of glasses in much the same manner as other network modifiers.