Acoustically controlled rotations of a disk in free field
Por:
Santillán A.O., Volke-Sepúlveda K., Boullosa R.R.
Publicada:
1 ene 2007
Resumen:
In general, forces are caused on objects when sound waves interact with their surfaces. Based on this phenomenon, acoustical lévitation is a technique in which stationary sound fields are used to trap small samples, liquid or solid, compensating the action of gravity. Rotations of suspended objects in acoustic lévitation devices are common, which are due mainly to asymmetries of the samples and sometimes to instabilities of the system. This fact turns out to be disadvantageous for applications where a precise control of the sample position is desired. The general objective of this work has been to study the extent to which it is possible to transfer angular momentum from a sound field to matter, and to control the rotations of an object. An original contribution of the work is that the acoustic fields have been produced in free space, i.e., without the need of a cavity, which gives the advantage of free access to the sample. We present an analysis of the properties of acoustic fields analogous to optical vortices; by using these kinds of sound fields, we show experimentally the generation of rotations in a solid disk produced by acoustic waves. In addition, by generating acoustic vortices of the first and second orders, we demonstrate that the direction of rotation is consistent with the corresponding helicity; we also analyse the differences of the angular momentum transfer between both cases. On this basis, we conclude that this mechanism can be used to achieve rotational control of acoustically levitated objects.