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By the use of radio-frequency power it is possible to obtain controlled power concentrations which far exceed those obtainable by other means. For example, in the induction heating of steel or other metals, the application of 100 kilowatts to a square inch of area on the work is not difficult. At a frequency of 1 megacycle, 99 per cent of the resulting heat generation is confined to a layer approximately 1/16 inch thick. If very high power concentrations are used for short heating times, the resulting high temperatures may be localized in the regions of heat generation. This technique results in more uniform case-hardening, less distortion, and high heating efficiency, as well as high production rates. The effect of frequency upon power concentration is discussed. It is shown that the optimum frequency varies with the size and shape of the work to be heated. Induction-heating technique is contrasted, and compared, with radio-frequency dielectric heating. In the latter class of work, the heat generation is equally distributed throughout the body of the work. With the use of radio-frequency dielectric heating, power concentrations in the order of 1 kilowatt per cubic inch can be obtained in thick wood sections, as for gluing operations. This is to be contrasted with the application of heat by heated press platens where power concentrations of only about 0.05 watt per cubic inch can be attained. Again, the optimum frequency is determined by the size and shape of the work.