Physics of the Microwave Oven

From the stars we see in the night to the cells in our body, physics exists in every field of life. In details, even the simplest one is actually very complicated in fact. Physics helps us understand the basics of how life works. Microwave ovens are often used for food reheating, TV dinners and cooking of frozen foods, and food heating rapidly, but rarely they are perceived and understood by people using them. People usually do not know how microwave ovens work, how they are configured, or how the food is actually being heated.

The actual picture of the microwave oven represents a typical microwave oven (there are many details). Microwaves are generated in the magnetron and the magnetron enters the cooking chamber through the waveguide. This rectangular parallelepiped has a metal wall so it can be used as a Faraday crate. Glass front doors and bulb cavities are covered with metal mesh. Since the holes in the grid are small compared to the wavelength of the microwave, the grid is like a metal plate. The microwave incident on the metal wall of the oven behaves like a visible light hitting a silver mirror, for example. Microwaves are absorbed very efficiently because the electric field of the waves interacts very strongly with the metal's almost free electrons. In a simple model, the electronic behavior is described as damped forced oscillation. These accelerating electrons re-radiate electromagnetic waves at the same frequency

Abstract This is the first of two articles on microwave physics. This article describes the problem of generating microwaves in an oven, including the operation of standing waves in magnetrons, waveguides, and resonant cavities. Next, we consider chemical changes that can occur during food microwave absorption, water dielectric relaxation, penetration depth of electromagnetic waves in materials, microwave heating, multiphoton ionization or dissociation.