Mechanisms to Generate Heat

Microwaves are electromagnetic radiations lying between radio wave frequencies and infrared frequencies (between 0.3 and 300 GHz). These are produced by a magnetron, which consists of a thermionic diode having an anode and a directly heated cathode. Microwaves contain an electric and a magnetic field component. It is the interaction between the electric field component and the matter that generates the heat through two mechanisms.  

The frequencies that allow microwave dielectric heating to take place are 918 MHz and 2.45 GHz, the latter being the most used. This mechanism depends on the ability of the dipole to reorientate under the applied electric field. The capability of a substance to convert the electromagnetic energy into heat is given by the dielectric loss tan 8 that is equal to the ratio of the dielectric loss e to the relative permittivity e. The relative permittivity represents the measure of the ability of a molecule to be polarized, while the dielectric loss is the ability of a medium to convert dielectric energy into heat. 

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Heat dissipation can also be achieved by increased production of sweat, because evaporation of sweat on the skin surface consumes heat (evaporative heat loss). Shivering is a mechanism to generate heat. Autonomic neural regulation of cutaneous blood flow and sweat production permit homeostatic control of body temperature (A). 

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