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The prefix “micro-” in “microwave” does not mean a wavelength in the micrometer range. It indicates that microwaves are ”small” compared to waves used in typical radio broadcasting, in that they have shorter wavelengths. The boundaries between far infrared (IR) light, terahertz radiation, microwaves, and ultra-high-frequency (UHF) radio waves are fairly arbitrary and are used variously between different fields of study. Infrared (IR) light is an electromagnetic radiation with a wavelength longer than of visible light, measured from the normal edge of visible red light at 0.74 micrometers (µm), and extending conventionally to 300 µm. In physics, terahertz radiation refers to electromagnetic waves propagating at frequencies at frequencies in the terahertz range. Lastly, UHF designates the ITU Radio frequency range of electromagnetic waves between 300 MHz and 3 GHz (3,000 MHz), also known as the decimetre band or decimetre wave as the wavelengths range from one to ten decimetres (10 cm to 1 metre). Electromagnetic waves longer (lower frequency) than microwaves are called “radio waves.” Electromagnetic radiation with shorter wavelengths may be called “millimeter waves,” terahertz radiation or even T-rays. Definition differ for millimeter wave band, which the IEEE defines as 110 GHz to 300 GHz. Above 300 GHz, the absorption of electromagnetic radiation (in physics, a process in which energetic particles or energetic waves travel through a medium or space) by Earth’s atmosphere is so great that it is in effect opaque, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges. Optical window, usually at least mechanically flat, sometimes optically flat, depending on resolution requirements, is a piece of transparent optical material that allows light into an optical instrument for a wavelength range of interest, not necessarily for visible light. The effects of the following are usually associated with visible light: reflection, the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated; polarization, a property of certain types of waves that describes the orientation of their oscillations; scattering, a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass; diffraction, where various phenomena occur when a wave encounters an obstacle; and atmospheric absorption, which in physics, is the way by which the energy of a photon is taken up by matter, usually the electrons of an atom. All of it is a practical significance in the study of microwave propagation, or the behavior of radio waves when they are transmitted, or propagated from one point on Earth to another, or into some parts of the atmosphere. The same equations of electromagnetic theory apply at all frequencies. Maxwell’s equations are a set of partial differential equations that, together with the Lorentz force law, form the foundation of classical electrodynamics, classical optics, and electric circuits.
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microwave, lights, electromagnetic, ka band,
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