Abstract: A short but large apertured coil of the sloped-helix type allows deep heating of a part of the human body by RF waves, for example with a three-turn coil having a central part wherein parts of a pair of turns are parallel. The length of the coil equals two wavelengths of the RF wave. Each loop or turn is widened with for instance a conducting ribbon, having specific twists to provide corresponding vertical and horizontal parts if the coil is considered to have its axis aligned vertically.

Abstract: A deep-heating diathermy apparatus consisting of a hollow tube adapted to receive a part of the body, or other dielectric material to be treated. An rf coil coaxially surrounds the tube and is driven by an rf generator. The total wire length of the coil is approximately 0.7 to 1.3 (depending on specific electrical properties and volume of the treated material) times the wavelength of a basic driving frequency provided by the generator. The output of the generator is supplied to the coil via a 50-ohm coaxial cable and a matching impedance. The coil may be driven by frequencies corresponding to integral multiples of one-half the basic wavelength, to enable shifting the heat focus volume along the coil axis from the normal centered location on the axis produced by full-wave excitation.