The term millimeter wave can be used interchangeably with the term microwaves. Microwaves are a form of electromagnetic energy, or radiation. In frequency (rate of vibration) and wavelength, microwaves fall in the electromagnetic spectrum between infrared rays and radio waves. The term millimeter wave is descriptive of the wavelength of a microwave (one millimeter).

There are two kinds of electromagnetic radiation: ionizing and nonionizing. Ionizing radiation includes, at one end of the spectrum, X rays and gamma rays. Nonionizing radiation, which makes up the rest of the spectrum, includes ultraviolet light, visible light, infrared rays and radio waves. (And it is between the latter two that we find “microwaves.”) The terms ionizing and nonionizing denote an important difference. Ionizing radiation is capable of dislodging electrons from atoms, creating electrically charged, highly unstable, and chemically reactive atoms called ions. In other words, ionizing radiation invariably damages cells of living tissue and can cause genetic mutations. Any exposure to this kind of radiation, however slight, involves some degree of risk.

Microwaves, on the other hand, are nonionizing energy. They are much less powerful in effect and do not have sufficient energy to dislodge electrons from atoms, which is why man has felt relatively free to utilize this form of energy for its beneficial advantages. The military, by far the largest users of microwave devices in today’s world of electronic warfare, employ microwaves for such things as tracking and scanning radar, guidance systems for nuclear missiles and antimissile missiles, range finders for tanks, and for eavesdropping. We are perhaps most familiar with the in-home use of microwaves to power ovens in the kitchen.

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