Physical Mechanisms for Irradiation Effects of Sound and Ultrasound

Abstract

Of the many known ways in which high-amplitude sound can produce changes in material processes and systems, there are only a few for which the basic physics is understood. In this paper a report will be made on research directed toward some aspects of the general problem. Since typical sonic irradiation conditions seem forbiddingly complex, an attempt has been made to define “elementary” situations for study, which are nevertheless close enough to practical ones to permit carryover of results. Particular attention is being given to fields in liquids in the neighborhood of (1) a single vibrating bubble resting on a wall and (2) a vibrating tip brought near a wall. In the former case there is interest in the heat produced by the bubble; also, in heat transfer through the wall, as affected by bubble-associated acoustic streaming. In the second case, acoustic streaming motions are seen near the vibrating tip which, e.g., exert steady viscous forces on the neighboring wall, capable of removing surface films. Observations are also made of steady circulation and related events induced in plant cells when a leaf is contacted with a vibrating tip. The present frequency range is mainly from 10 to 100 kc. Important features of the acoustic streaming patterns can be explained on the basis of an approximate theory for boundary layer. [This work is supported by the National Institute of Health (Bio-physics Section) and by the U. S. Air Force, contract AF18(603)-54. W. L. Nyborg is on leave as U.S.P.H. Research Fellow at the School of Advanced Study (Biology), Massachusetts Institute of Technology, Cambridge, Massachusetts. F. S. Brunschwig is now at the University of Illinois, Bio-acoustics Laboratory, Urbana, Illinois.]