Abstract: A far infrared generator comprising a microwave generating unit and an energy converter for converting microwave energy from the output portion of the microwave generating unit into far infrared rays. The energy converter consists essentially of a magnesium oxide or other dielectric material, and it converts irradiated microwaves into far infrared rays therein, in turn radiating far infrared rays. Although the wave length of this far infrared ray varies with the type and temperature of the dielectric, it covers the range of near infrared to far infrared ray wave lengths; therefore, the far infrared generator can be used as a heat source for cooking appliances and other articles. For this purpose, the energy converter may be provided with a controlling unit for controlling its temperature to regulate the wave length of the far infrared rays.

Abstract: A disposable body warmer comprises a heat generating material and a structure for retaining the material. The retaining structure may be provided on its one side with a reflecting material. The heat generating material consists essentially of at least one oxide of alkaline earth metals such as magnesium oxide with a plate crystal structure and, if necessary, contains an additive such as a salt selected from the group consisting of chlorides and sulphides of alkali metals and alkaline earth metals.