Microwave is an electrotherapeutic technique that uses radio frequencies at 2.45 GHz or 915 MHz to induce heat deep into the body and is commonly used for muscle relaxation and as an accompaniment to soft-tissue manual therapies.
The use of high-frequency currents became possible through the works of Nikola Tesla and Jacques Arsene d’Arsonval. Tesla ascribed the healing effect of high-frequency currents to the action of heat, while d’Arsonval was convinced that healing properties were due to a specific electrical effect. In 1892 d’Arsonval modified the Tesla circuit and produced an arrangement that came to be widely used for medical purposes. Contributions from other scientists allowed quantitative determination of the heating rate of tissue as a function of frequency and current density.
From these ideas, Karl Franz Nagelschmidt developed the concept of diathermy in 1909. Here heat was generated by high-frequency currents agitating molecular structures within the body. Nagelschmidt also developed the prototype of diathermy apparatus that used condenser discharges to produce high-frequency oscillations. A few years later, he published a textbook (1913) that inaugurated a new era of high-frequency electrotherapy.
Modern microwave energy is generated by an electronic device known as a magnetron. The magnetron was invented in 1938 but did not find civilian application until 1945 when the classified military role in airborne radar became less important.
Description provided by Cesare Alfaro-Redondo of Costa Rica
References:
Ho M, Popp FA and Warnke U. 1994. Bioelectrodynamics and Biocommunication. World Scientific. pp. 10–11.
