Surface wave Totally Explained

Everything about Groundwave totally explained

In physics, surface wave can refer to a mechanical wave that propagates along the interface between differing media, usually two fluids with different densities. A surface wave can also be an electromagnetic wave guided by a refractive index gradient. In radio transmission, a ground wave is a surface wave that propagates close to the surface of the Earth.

Mechanical waves

In seismology, several types of surface waves are encountered. Surface waves, in this mechanical sense, are commonly known as either Love waves (L waves) or Rayleigh waves. A seismic wave is a wave that travels through the Earth, often as the result of an earthquake or explosion. Love waves have transverse motion (movement is perpendicular to the direction of travel, like light waves), whereas Rayleigh waves have both longitudinal (movement parallel to the direction period of waves that are most damaging is usually 10 seconds or longer. Surface waves can travel around the globe many times from the largest earthquakes.
Surface wave can describe waves over an ocean, even when they're approximated by Airy functions and are more properly called creeping waves. Examples are the waves at the surface of water and air (ocean surface waves), or ripples in the sand at the interface with water or air. Another example is internal waves, which can be transmitted along the interface of two water masses of different densities.

Electromagnetic waves

Ground waves refer to the propagation of radio waves close to or at the surface of the Earth. These surface waves are also known as Norton surface waves, Zenneck waves, Sommerfeld waves, or gliding waves.

Radio propagation

Lower frequencies, especially AM broadcasts in the mediumwave (sometimes called "medium frequency") and longwave bands (and other types of radio frequencies below that), travel efficiently as a surface wave. This is because they're more efficiently diffracted by the figure of the Earth due to their low frequencies. Ionospheric reflection is taken into consideration as well. The ionosphere reflects frequencies in a certain band, which often changes due to solar conditions. The Earth has one refractive index and the atmosphere has another, thus constituting an interface that supports the surface wave transmission.
   A longitudinal mode of a resonant cavity is a particular standing wave pattern formed by waves confined in the cavity. The longitudinal waves corresponding to the wavelengths permitted by the cavity are reinforced by constructive interference after many reflections from the cavity's reflecting surfaces.
   Conductivity of the surface affects the propagation of ground waves, with more conductive surfaces such as water providing better propagation. Increasing the conductivity in a surface results in less dissipation. The refractive indices are subject to spatial and temporal changes. Since the ground isn't a perfect electrical conductor, ground waves are attenuated as they follow the earth’s surface.
   Most long-distance LF "longwave" radio communication (between 30 kHz and 300 kHz) is a result of groundwave propagation. Mediumwave radio transmissions (frequencies between 300 kHz and 3000 kHz) have the property of following the curvature of the earth (the groundwave) in the majority of occurrences. At low frequencies, ground losses are low and become lower at lower frequencies. The VLF and LF frequencies are mostly used for military communications, especially with ships and submarines.
   Surface waves have been used in over-the-horizon radar. In the development of radio, surface waves were used extensively. Early commercial and professional radio services relied exclusively on long wave, low frequencies and ground-wave propagation. To prevent interference with these services, amateur and experimental transmitters were restricted to the higher (HF) frequencies, felt to be useless since their ground-wave range was limited. Upon discovery of the other propagation modes possible at medium wave and short wave frequencies, the advantages of HF for commercial and military purposes became apparent. Amateur experimentation was then confined only to authorized frequencies in the range.
   Mediumwave, and shortwave reflect off the ionosphere at night, which is known as skywave. Because the solar wind "blows" the ionosphere toward the Earth on the day side, and away from it on the night side, this natural radio "mirror" is much closer to the surface during the day. This prevents the high frequency's propagation from being very effective in daylight hours. At night, mediumwave and shortwave transmissions travel better by skywave. Ground waves do not include ionospheric and tropospheric waves.

Microwave field theory

Within microwave field theory, the refractive index of many cavities constitute an interface that supports "surface wave transmission". Surface waves have been studied as part of transmission lines and some may be considered as single-wire transmission line.
Characteristics and utilizations of the electrical surface wave phenomena include:

The field components of the wave diminish with distance from the interface.
Optical energy isn't converted from the surface wave field to another form of energy and the wave doesn't have a component directed normal to the interface surface.
In optical fiber transmission, evanescent waves are surface waves.

Further Information

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