ABSTRACT
A symmetric antenna driven from its center (dipole) radiates most effectively when its overall length equals half a wavelength at the driving frequency. Simply speaking, microwave heating is a result of rotational motion of molecules in an oscillating electric field. When a polar molecule, such as water, experiences an electric field, its positive pole rotates in the direction of the field and its negative pole moves oppositely. Thus, it attempts to align itself with the field vector. Since the field is varying sinusoidally with time, the molecule will also rotate sinusoidally. The molecule may not rotate with great amplitude if the frequency is high, since it may not have time to respond before the electric field reverses. However, any motion is opposed by frictional forces and conversion from rotational energy into heat energy takes place. Hyperthermia can also be produced by other physical mechanisms, such as a purely conductive system.
