Faraday waves observed in water in aPetri dish, vibrated at a frequency of about 50 hertz.Faraday waves in a singing bowl
Faraday waves, also known asFaraday ripples, named afterMichael Faraday (1791–1867), arenonlinearstanding waves that appear on liquids enclosed by a vibrating receptacle. When the vibration frequency exceeds a critical value, the flat hydrostatic surface becomes unstable. This is known as the Faradayinstability. Faraday first described them in an appendix to an article in thePhilosophical Transactions of theRoyal Society of London in 1831.[1][2]
If a layer of liquid is placed on top of a vertically oscillating piston, a pattern ofstanding waves appears which oscillates at half the driving frequency, given certain criteria ofinstability.[3] This relates to the problem ofparametric resonance. The waves can take the form of stripes, close-packedhexagons, or evensquares orquasiperiodic patterns. Faraday waves are commonly observed as fine stripes on the surface of wine in awine glass that is ringing like a bell. Faraday waves also explain the 'fountain' phenomenon on asinging bowl.
Faraday waves are used as a liquid-based template for directed assembly of microscale materials includingsoft matter,rigid bodies, biological entities (e.g., individual cells, cell spheroids and cell-seededmicrocarrier beads).[5] Unlike solid-based template, this liquid-based template can be dynamically changed by tuning vibrational frequency and acceleration and generate diverse sets of symmetrical and periodic patterns.
This phenomenon is also used by alligators to call mates. They vibrate their lungs at low frequencies slightly below the surface, causing their spikes to move and induce surface waves. These surface waves are basically Faraday waves and one can observe the splashing effect characteristic of certain resonances.[6][7]
This effect can also be used for mixing two liquids acoustically. Faraday waves form on the interface between the two liquids, which increases the surface area between the two, rapidly and thoroughly mixing the liquids.[8]
^Faraday, M. (1831) "On a peculiar class of acoustical figures; and on certain forms assumed by a group of particles upon vibrating elastic surfaces",Philosophical Transactions of the Royal Society (London), vol. 121, pp. 299–318. "Faraday waves" are discussed in an appendix to the article,"On the forms and states assumed by fluids in contact with vibrating elastic surfaces". This entire article is also available on-line (albeit without illustrations) at"Electronic Library".
^Moriarty, Peter; Holt, R. Glynn (2011). "Faraday waves produced by periodic substrates: Mimicking the alligator water dance".The Journal of the Acoustical Society of America.129 (4): 2411.Bibcode:2011ASAJ..129.2411M.doi:10.1121/1.3587858.
