Physics of the Electromagnetic Spectrum

Electromagnetic (EM) waves, spanning about 15 orders of magnitude of wavelength (or frequency or energy) from radio waves via microwaves, infrared radiation, visible light, ultraviolet radiation, and X-rays to the highly energetic γ-rays, are utilized in food processing. In order to explain all uses of these waves in the food industry, the chapter begins with a general discussion of properties of waves and their description with wavelength frequency, speed of propagation, and also energy transport. Using visible light as starting point, electromagnetic waves in other wavelength regimes are discussed. The interaction of EM radiation with matter reveals that the wave description alone is insufficient to explain all observed phenomena. Understanding the attenuation of EM radiation in matter requires knowledge of the particle properties of electromagnetic waves, most easily summarized by the concept of photons which carry energy as well as momentum. This wave–particle duality does apply not only to EM waves, i.e. photons, but also to the particles which build up matter, in particular electrons, which also need to be described as waves. This leads to respective quantum mechanical explanations of the microscopic structure of matter in the form of atoms, molecules, and nuclei. Knowledge of their structure is a prerequisite to understand, first, the generation of EM radiation and, second, also its interaction with matter. As a result, it will become obvious that there are mostly three different usages of EM radiation in the food industry: preserving, characterizing, and heating.