Dielectric trends in 1947

In the year 1947 the trend in the field of dielectrics has been toward the use of higher frequencies, both as to application and theoretical studies of dielectric systems. Many of the constants of dielectric phenomena formerly obtained by extrapolation, have now been experimentally investigated at these microwave frequencies. The designers of measuring equipment have been concerned with making instruments of greater precision and versatility. On the practical side high-power sources have been developed in the centimeter-wave region bringing about a new era in dielectric heating consideration. Dielectric loss measurements of gases at these high frequencies and reduced pressures have led to the flourishing field of microwave spectroscopy. In the field of breakdown studies of solids, the tendency has been toward a more thorough investigation of the temperature dependence of breakdown strength and direction taken by the breakdown paths. The influence of polyatomic molecules on breakdown strength and corona of gases has also been given attention. The ceramic industry has shown continued interest toward the development of electrical insulating materials with lower losses at higher frequencies. Some stimulation in this direction has resulted from the use of ceramics as vacuum tube insulators at the microwave frequencies. Paper insulation research has progressed along such varied lines as lowering of power factor, impregnation with semi-conducting liquids, effects of oxidation, and statistical analysis of conducting particles. Perhaps the most significant trend in the field of synthetic plastics has been concerned with the use of polymeric plasticizers for the vinyl type resins. These plasticizers are much less susceptible to migration and are immune to vaporization loss as compared with conventional plasticizers.