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edited by: RON DELORENZO
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and analogiw Wave Interaction Applications and Analogies: Killer Waves, Anti-Sound Machines, Camera Lenses, and Invisible Airplanes Ronald DeLorenzo Middle Georgia College Cochran, GA 31014
The superimposition, interference, and reinforcementof waves plays an important role in the study of both quantum mechanics and the solid state. Recently, several periodicals have published articles containing interesting applications andlor analogies to wave phenomina to which an instructor can allude. These include articles on (1)Killer Waves, (2) Anti-Sound Machines, (3) Camera Lens Coatings, and (4) Invisible War Planes. 1. Killer Waves
Killer ocean waves of 100 feet or more have been reported by seaman for centuries. However, such reports were considered tall tales until the latter part of this century when agiant wave damaged the superstructure of the 44,000 ton Italian liner Michelangelo some 80 feet above its waterline. Such reinforced waves, called e~isodicwaves, are formed when trains of smaller waves t.onie 1rm1diii(.rm dirvc.~i,,nsmrel i l l .!(.I) !:.I. .. ~ h t ,h.~vc s the wnr wave I ~ I I ~ I K . w i t h t.rv.~aan(l tn ucii; that coincide),' 2. Anti-Sound Machines S ~ ~l.;cmn(ll S E can h? d1111eri1ttd with , ~ I I I : - - < N ~ Cin,m an anti-iuuml m . hinc. ~ Such n 1 1 1 : ~hilie has l w n d e \ ~ I t , p r ~11)'l
Middle Georgia College Cochran, Georgia 31014
electrical engineers in England. The machine produces sound waves that are one-half of a wavelength out of phase with those of a noise that is to be eliminated. Each crest of "anti-sound" is matched with a trough of the noise. A microprocessor is used to calculate the needed amplitude and wavelength of antisound. The microprocesser then produces an electric current that is amplified and fed to a loudspeaker. Such a device has already been used on ships to eliminate the low-frequency noise from ship engines because such noise causes fatigue and impairs efficiency and alertness of the crew.2 3. Camera Lens Coatings
High quality camera lenses use an anti-reflection coating that keeps light from bouncing around inside the lens. The coating thickness is adjusted so that light bouncing off the hack surface of the coating is perfectly out of phase with the light bouncing off of the front surface. The two reflected waves cancel each other o u t 3 4. Invisible War Planes
The United States has been developing a plane called the Stealth Bomber which has the advantage of being invisible to radar. It is easy to visualize how invisibility can be achieved: a duplicate radar wave that is out of phase with the reflected radar beam is produced by the plane.
' Science News, March 8. 1979, pp. 18-20. Discover, June 1981, p. 66. Sciquest, February 1982, p. 4.
Volume GO
Number 5
May 1983
381
