Mechanism of microwave heating of matter

If we irradiate an object with microwave and observe its temperature increase, we would recognize the occurrence of “microwave heating.” This article starts with discussing what is heat and what happens in matters during heating. And the interaction between microwave and the matter is learned from an atomistic point of view. Microwave is an electromagnetic wave and has components of alternating electric (E-) and magnetic (H-) field. It is pointed out that microwave E- and H-field interactions are different with materials. The materials are divided into three classes, and the heating mechanisms are discussed by each class of them. Heat is a state of either translational motion of molecules or vibration of lattice consisting of atoms (ions) or elevation of free electron energy in metals. Their moving frequency is much higher than microwave. Nevertheless, these high-frequency motions are excited by microwave of lower frequency. The mechanism of which is not necessarily understood well but is the “state-of-art” in understanding the microwave heating. This article discusses it and provides some clue for this interpretation.