Diathermy treatment of elbow, 1945. Diathermy is the application of high frequency electric current to create deep heating in body tissues. An electronic oscillator "(rear)" produces a radio frequency current that passes through the wire wrapped around the patient's elbow. The current produces an oscillating magnetic field by electromagnetic induction that heats the tissue. "Long wave" diathermy using frequencies of 0.5-2 MHz was replaced by "short wave" diathermy at frequencies of 10-100 MHz around the 1930s.