In physics, a surface wave is 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.
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 of travel, like sound waves) and transverse motion. Seismic waves are studied by seismologists and measured by a seismograph or seismometer. Surface waves span a wide frequency range, and the 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 waves are caused when P waves and S waves come to the surface.
The term "surface wave" can describe waves over an ocean, even when they are 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.
Ground waves refer to the propagation of radio waves parallel to and adjacent to the surface of the Earth, following the curvature of the Earth. These surface waves are also known loosely as the Norton surface wave, the Zenneck surface wave, Sommerfeld waves, and gliding waves. They have contemporaneously been referred to as the THz surface plasmon (TSP). See also Dyakonov Surface Waves (DSW) propagating at the interface of transparent materials with different symmetry. 
Lower frequencies, below 3 MHz, travel efficiently as ground waves. This is because they are more strongly diffracted around obstacles due to their long wavelengths, allowing them to follow the Earth's curvature. 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. Ground waves propagate in vertical polarization, with their magnetic field horizontal and electric field (close to) vertical.
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 is not a perfect electrical conductor, ground waves are attenuated as they follow the earth’s surface. The wavefronts initially are vertical, but the Earth's greater refractive index causes the wavefronts to "lean over" at a progressively greater angle in the direction of propagation as they travel, until they are dissipated.
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), including AM broadcast band, travel both as groundwaves and, for longer distances, as skywaves. Ground losses become lower at lower frequencies, so the attenuation of ground waves decreases with frequency. 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, which operates mainly at frequencies between 2 and 20 MHz over the sea, which has a sufficiently high conductivity to convey the surface waves to and from a reasonable distance (up to 100 km or more; over-horizon radar also uses skywave propagation at much greater distances). 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. During daylight hours, the lower "D" layer of the ionosphere forms and absorbs lower frequency energy. This prevents skywave propagation from being very effective on mediumwave frequencies in daylight hours. At night, when the "D" layer dissipates, mediumwave transmissions travel better by skywave. Ground waves do not include ionospheric and tropospheric waves.
Microwave field theory
Within microwave field theory, the interface of a dielectric and conductor supports "surface wave transmission." Surface waves have been studied as part of transmission lines and some may be considered as single-wire transmission lines.
Characteristics and utilizations of the electrical surface wave phenomena include:
- The field components of the wave diminish with distance from the interface.
- Electromagnetic energy is not converted from the surface wave field to another form of energy (except in leaky or lossy surface waves) such that the wave does not transmit power normal to the interface, i.e. it is evanescent along that dimension.
- In optical fiber transmission, evanescent waves are surface waves.
- In coaxial cable in addition to the TEM mode there also exists a transverse-magnetic (TM) mode which propagates as a surface wave in the region around the central conductor. For coax of common impedance this mode is effectively suppressed but in high impedance coax and on a single central conductor without any outer shield, low attenuation and very broadband propagation is supported. Transmission line operation in this mode is called E-Line.
- Seismic waves
- Seismic communication
- Surface Acoustic Wave
- Sky waves, the primary means of HF transmission
- Surface plasmon, a longitudinal charge density wave along the interface of conducting and dielectric mediums
- Surface-wave-sustained mode, a propagation of electromagnetic surface waves.
- Evanescent waves and evanescent wave coupling
- Ocean surface waves, internal waves and crests, dispersion, and freak waves
- Love Wave and Rayleigh-Lamb Wave
- Gravity waves, occurs at certain natural interfaces (e.g. the atmosphere and ocean)
- Stoneley wave
- Scholte wave
- Dyakonov surface wave
- Arnold Sommerfeld – published the mathematical treatise on the zenneck wave
- Jonathan Zenneck – Pupil of Sommerfeld; Wireless pioneer; developed the zenneck wave
- John Stone Stone – Wireless pioneer; produced theories on radio propagation
- Ground constants, the electrical parameters of earth
- Near and far field, the radiated field that is within one quarter of a wavelength of the diffracting edge or the antenna and beyond.
- Skin effect, the tendency of an alternating electric current to distribute itself within a conductor so that the current density near the surface of the conductor is greater than that at its core.
- Green function, a function used to solve inhomogeneous differential equations subject to boundary conditions.
External articles, further readings, and references
- This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188).
- The Physical Reality of Zenneck's Surface Wave. Alcatel-Lucent.
- Tae-In Jeon and D. Grischkowsky.. THz Zenneck surface wave (THz surface plasmon) propagation on a metal sheet. Appl. Phys. Lett. 88, 061113 (2006); http://dx.doi.org/10.1063/1.2171488 (3 pages).
- Dyakonov, M. I. (Published 1988-04). "New type of electromagnetic wave propagating at an interface". Soviet Physics JETP 67 (4): 714.
- "Naval Electrical Engineering Training Series", Chapter 2 Radio Wave Propagation, Ground Waves. Integrated publishing.
- Antennas and Radio Propagation, TM 11-666, Dept. of the Army, Feb. 1953, pp. 17-23.
- Eric W. Weisstein, et al., "Surface Wave", Eric Weisstein's World of Physics, 2006.
- "Surface waves". Integrated Publishing (tpub.com).
- David Reiss, "Electromagnetic surface waves". The Net Advance of Physics: Special Reports, No. 1
- Gary L. Peterson, "Rediscovering the Zenneck wave". Feed Line No. 4. (ed. reproduction available online at 21st Century Books)
- 3D Waves by Jesse Nochella based on a program by Stephen Wolfram, Wolfram Demonstrations Project.
- U.S. Patent 2,685,068, "Surface wave transmission line". George J. E. Goubau
- U.S. Patent 2,921,277, "Launching and receiving of surface waves". George J. E. Goubau.
- U.S. Patent 7,567,154, "Surface wave transmission system over a single conductor having E-fields terminating along the conductor ". Glenn E. Elmore.
Standards and doctrines
- "Surface wave". Telecom Glossary 2000, ATIS Committee T1A1, Performance and Signal Processing, T1.523-2001.
- "Surface wave", Federal Standard 1037C.
- "Surface wave", MIL-STD-188
- "Multi-service tactics, techniques, and procedures for the High-Frequency Automatic Link Establishment (HF-ALE): FM 6-02.74; MCRP 3-40.3E; NTTP 6-02.6; AFTTP(I) 3-2.48; COMDTINST M2000.7" Sept., 2003.
- Collin, R. E., "Field Theory of Guided Waves". New York: Wiley-IEEE Press, 1990.
- Waldron, Richard Arthur, "Theory of guided electromagnetic waves". London, New York, Van Nostrand Reinhold, 1970. ISBN 0-442-09167-2 LCCN 69019848 //r86
- Weiner, Melvin M., "Monopole antennas" New York, Marcel Dekker, 2003. ISBN 0-8247-0496-7
- Wait, J. R., "The Waves in Stratified Media". New York: Pergamon, 1962.
- Wait, J. R., "Electromagnetic Wave Theory", New York, Harper and Row, 1985.
- Budden, K. G., " The propagation of radio waves : the theory of radio waves of low power in the ionosphere and magnetosphere". Cambridge (Cambridgeshire); New York : Cambridge University Press, 1985. ISBN 0-521-25461-2 LCCN 84028498
- Budden, K. G., "Radio waves in the ionosphere; the mathematical theory of the reflection of radio waves from stratified ionised layers". Cambridge, Eng., University Press, 1961. LCCN 61016040 /L/r85
- Budden, K. G., "The wave-guide mode theory of wave propagation". London, Logos Press; Englewood Cliffs, N.J., Prentice-Hall, c1961. LCCN 62002870 /L
- Barlow, H.M., and Brown, J., "Radio Surface Waves", Oxford University Press 1962.
- Sommerfeld, A., "Partial Differential Equations in Physics" (English version), Academic Press Inc., New York 1949, chapter 6 - "Problems of Radio".
- Rawer, K.,"Wave Propagation in the Ionosphere", Dordrecht, Kluwer Acad.Publ. 1993.
Journals and papers
- Zenneck, Sommerfeld, and Norton
- J. Zenneck, (translators: P. Blanchin, G. Guérard, É. Picot), "Précis de télégraphie sans fil : complément de l'ouvrage : Les oscillations électromagnétiques et la télégraphie sans fil", Paris : Gauthier-Villars, 1911. viii, 385 p. : ill. ; 26 cm. (Tr. Precisions of wireless telegraphy: complement of the work: Electromagnetic oscillations and wireless telegraphy)
- J. Zenneck, "Über die Fortpflanzung ebener elektromagnetischer Wellen längs einer ebenen Leiterfläche und ihre Beziehung zur drahtlosen Telegraphie", Ann. der Physik, vol. 23, pp. 846–866, Sept. 1907. (Tr. "About the propagation of electromagnetic plane waves along a conductor plane and their relationship to wireless telegraphy" )
- J. Zenneck, "Elektromagnetische Schwingungen und drahtlose Telegraphie", gart, F. Enke, 1905. xxvii, 1019 p. : ill. ; 24 cm. (Tr. "Electromagnetic oscillations and wireless telegraphy.")
- J. Zenneck, (translator: A.E. Seelig) "Wireless telegraphy,", New York [etc.] McGraw-Hill Book Company, inc., 1st ed. 1915. xx, 443 p. illus., diagrs. 24 cm. LCCN 15024534 (ed. "Bibliography and notes on theory" p. 408-428.)
- A. Sommerfeld, "Über die Fortpflanzung elektrodynamischer Wellen an längs eines Drahtes", Ann. der Physik und Chemie, vol. 67, pp. 233–290, Dec 1899. (Tr. Propagation of electro-dynamic waves along a cylindric conductor)
- A. Sommerfeld, "Über die Ausbreitlung der Wellen in der drahtlosen Telegraphie", Annalen der Physik, Vol. 28, March, 1909, pp. 665-736. (Tr. About the Propagation of waves in wireless telegraphy)
- A. Sommerfeld, "Propagation of waves in wireless telegraphy", Ann. Phys., vol. 81, pp. 1367–1153, 1926.
- K. A. Norton, "The propagation of radio waves over the surface of the earth and in the upper atmosphere", Proc. IRE, vol. 24, pp. 1367–1387, 1936.
- K. A. Norton, "The calculations of ground wave field intensity over a finitely conducting spherical earth", Proc. IRE, vol. 29, pp. 623–639, 1941.
- Wait, J. R., "Lateral Waves and the Pioneering Research of the Late Kenneth A Norton".
- Wait, J. R., and D. A. Hill, "Excitation of the HF surface wave by vertical and horizontal apertures". Radio Science, 14, 1979, pp 767-780.
- Wait, J. R., and D. A. Hill, "Excitation of the Zenneck surface by a vertical aperture", Radio Science, 13, 1978, pp. 967-977.
- Wait, J. R., "A note on surface waves and ground waves", IEEE Transactions on Antennas and Propagation, Nov 1965. Vol. 13, Issue 6, pg 996- 997 ISSN 0096-1973
- Wait, J. R., "The ancient and modern history of EM ground-wave propagation". IEEE Antennas Propagat. Mag., vol. 40, pp. 7–24, Oct. 1998.
- Wait, J. R., "Appendix C: On the theory of ground wave propagation over a slightly roughned curved earth", Electromagnetic Probing in Geophysics. Boulder, CO., Golem, 1971, pp. 37–381.
- Wait, J. R., "Electromagnetic surface waves", Advances in Radio Research, 1, New York, Academic Press, 1964, pp. 157-219.
- R. E. Collin, "Hertzian Dipole Radiating Over a Lossy Earth or Sea: Some Early and Late 20th-Century Controversies", Antennas and Propagation Magazine, 46, 2004, pp. 64-79.
- F. J. Zucker, "Surface wave antennas and surface wave excited arrays", Antenna Engineering Handbook, 2nd ed., R. C. Johnson and H. Jasik, Eds. New York: McGraw-Hill, 1984.
- Hill, D. and J.R Wait, "Excitation of the Zenneck Surface Wave by a Vertical Aperture", Radio Science, Vol. 13, No. 6, November–December, 1978, pp. 969-977.
- Yu. V. Kistovich, "Possibility of Observing Zenneck Surface Waves in Radiation from a Source with a Small Vertical Aperture", Soviet Physics Technical Physics, Vol. 34, No.4, April, 1989, pp. 391-394.
- V. I. Baĭbakov, V. N. Datsko, Yu. V. Kistovich, "Experimental discovery of Zenneck's surface electromagnetic waves", Sov Phys Uspekhi, 1989, 32 (4), 378-379.
- Corum, K. L. and J. F. Corum, "The Zenneck Surface Wave", Nikola Tesla, Lightning Observations, and Stationary Waves, Appendix II. 1994.
- M. J. King and J. C. Wiltse, "Surface-Wave Propagation on Coated or Uncoated Metal Wires at Millimeter Wavelengths". J. Appl. Phys., vol. 21, pp. 1119–1128; November,
- Georg Goubau, "Surface waves and their application to transmission lines", J. Appl. Phys., vol. 21, pp. 1119–1128; November,1950.
- M. J. King and J. C. Wiltse, "Surface-Wave Propagation on a Dielectric Rod of Electric Cross-Section." Electronic Communications, Inc., Tirnonium: kld. Sci. Rept.'No. 1, AFCKL Contract No. AF 19(601)-5475; August, 1960.
- T. Kahan and G. Eckart, "On the Electromagnetic Surface Wave of Sommerfeld", Phys. Rev. 76, 406–410 (1949).
- L.A. Ostrovsky (ed.), "Laboratory modeling and theoretical studies of surface wave modulation by a moving sphere", m, Oceanic and Atmospheric Research Laboratories, 2002. OCLC 50325097
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