Principles of Microwave Radiation

Abstract

Microwaves, such as those used in cooking and processing food, are part of the broad spectrum of electromagnetic radiation which includes radio waves. microwaves. infrared radiation, visible light. ultraviolet radiation. x-rays and Gamma rays. Electromagnetic radiation has a dual nature, it is both wave-like and particle-like. An understanding of this dual nature of electromagnetic radiation is necessary for an understanding of the processes of emission. transmission and absorption of microwaves. which is in turn necessary for understanding the processes and phenomena which are important in the use of microwave radiation as a source of energy for heating and food processing. The properties of electromagnetic waves and the processes of emission. transmission and absorption are described and some effects in microwave-heating applications are discussed. Establishment of electric and magnetic fields in empty space requires the expenditure of energy, much the same as stretching a spring requires an expenditure of energy. When the spring is stretched we say that the work done in stretching it is stored as elastic energy in the stretched spring. We can get the energy back by letting the spring relax to its original condition. Similarly, we say that the energy expended in establishing electric and magnetic fields is stored in those fields and we can get the energy back by letting the fields relax to nothing. Of course, if we want to use the stored energy for some purpose we may have to be quite ingenious as to how we couple the electric and magnetic fields to the material on which we want to do work. In a long spring, if we stretch some local region and release it, the strained region of the spring will travel in both directions from its original position. We can think of the energy stored in the stretched part of the spring as traveling along the spring. When the stretched region reaches the end of the spring, it can deposite its energy in the mounting at the end, if the mounting is what we call a "lossy" one. Similarly, energy deposited by a pebble striking the surface of a pond travels outward and is carried in waves to the shore where it is deposited. When energy is put into a region by establishment of an electric field, the field will start to decrease at the original location if the cause of the field is removed. This will cause a magnetic field to be formed, the change of which gives rise to generation of new electric fields in the surrounding space and a wave of the electric field will travel outward and carry energy with it.