Acoustic levitation is a method for suspending matter in a medium by using
acoustic radiation pressurefrom intense soundwaves in the medium. Acoustic levitation is possible because of the non-lineareffects of intense sound waves. [Cite web |url=http://science.howstuffworks.com/acoustic-levitation2.htm |title=Nonlinear Sound and Acoustic Levitation |accessdate=2008-07-01]
Some methods can levitate objects without creating sound heard by the human ear such as the one demonstrated at Otsuka Lab, [cite web|url=http://otsuka-lab.ee.cit.nihon-u.ac.jp/ken2-e.html|title=Ultrasonic Levitation|accessdate=2006-11-15] while others produce some audible sound. There are many ways of creating this effect, from creating a wave underneath the object and reflecting it back to its source, to using an
acrylic glasstank to create a large acoustic field.
Acoustic levitation is usually used for
containerless processingwhich has become more important of late due to the small size and resistance of microchips and other such things in industry. Containerless processing may also be used for applications requiring very high purity materials or chemical reactions too rigorous to happen in a container. This method is harder to control than other methods of containerless processing such as electromagnetic levitation but has the advantage of being able to levitate nonconducting materials.
There is no known limit to what acoustic levitation can lift given enough vibratory sound, but currently the maximum amount that can be lifted by this force is a few kilograms. [cite web|url=http://www.ia.csic.es/sea/revista/VOLXXXIII34/02.pdf|title=Phenomena, theory and applications of near-field acoustic levitation|accessdate=2006-11-15|format=PDF] Acoustic levitators are used mostly in industry and for researchers of anti-gravity effects such as
NASA; however some are commercially available to the public.
* [http://www.thothweb.com/article2902.html Levitation and Flight in the Ancient World: A Modern Perspective]
* [http://www.accessscience.com/Encyclopedia/0/00/Est_006200_frameset.html?doi McGraw-Hill AccessScience: Acoustic radiation pressure]
* [http://jjap.ipap.jp/link?JJAP/39/2982/ A Multi-Transducer Near Field Acoustic Levitation System for Noncontact Transportation of Large-Sized Planar Objects]
* [http://www.honda-el.co.jp/english/5_05.html Honda Electronics: Ultrasonic levitation]
* [http://www.livescience.com/technology/061129_acoustic_levitation.html Live Science - Scientists Levitate Small Animals]
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