Acoustic Manipulation-Eng
Non-Contact Micromanipulation Using Ultrasound
For further information:
E-mail kozuka@nirin.go.jp
T. Kozuka, Material Structure Designing Laboratory
National Industrial Research Institute of Nagoya, AIST
When propagation of ultrasound in a fluid is interrupted by an object, there appears force to push the object in the direction of sound propagation; this is called acoustic radiation pressure. Although this force is very small, it is converged easily up to the order of acoustic wavelength using focused ultrasound and may be applied to manipulate micro objects without contact.
When a reflector is set in front of the transducer, the incident wave and the reflected wave generate a standing wave field. If an object, which is much smaller than the wavelength, is placed in the field, the acoustic radiation pressure pushes it toward stable point. The micro particles in suspension move from antinodes of sound pressure to nodes, and they agglomerate every half wavelength (Fig.1).
Fig.1 Trapped particles in a standing wave field.
f=1.75MHz, ƒ=0.86mm, alumina:16ƒm
Use of plural standing wave fields realize micro manipulation. Figure 2 shows details of agglomeration at a crossing point of two sets of standing wave fields settled orthogonally. The agglomeration changes its shape depending on the ratio of field strength.
Fig.2 Changes in the shape of agglomeration at the crossing point of orthogonal standing waves.
Combination of a standing wave field and a focused traveling wave field realize selective transportation of micro particles. Figure 3 shows the action of focused force of traveling ultrasound on particles trapped by the vertical standing wave field. A limited part of trapped particles are transported using focused ultrasound.
Fig.3 Transportation of trapped particles using focused ultrasound.
Last Modified: 1996/02/08
