Two-dimensional mid-air manipulation of particles using acoustic levitator

Abstract

Acoustic levitation technology is the use of ultrasound to form standing waves. Sound is a form of mechanical waves that carries momentum that acts on particles due to acoustic radiation force. Such standing waves allow small particles to levitate in air when placed at its pressure nodes and the acoustic forces acting on the particles is greater than that of gravity. In conventional studies, small particles not only are capable of levitating in air but also able to be manipulated. Manipulation along one dimensionally was achieved by constructing the levitator to produce ultrasound beams parallel to gravity, and the levitated objects were manipulated by tuning the phase or frequencies of the transducers. In order to achieve extended manipulation whereby levitated particles are moved three dimensionally, the manipulation system would have two features. One provides vertical acoustic forces against gravity to move levitated particles in the vertical axis whereas the other feature provides horizontal acoustic forces to manoeuvre levitated particles in the horizontal axis. With the system set at this configuration, particles are capable of levitating in mid-air and manipulate in three-dimensional axis. In this study, acoustic levitators are designed and fabricated to achieve two-dimensional manipulation of levitated particles using various amounts of transducers. Limiting a small number of transducers to lower costs and minimize the size of the features. Also, testing the capability of the levitator by achieving as many particles levitate and manipulate/ at the same time. In order to achieve the specification, several tests were carried out by studying different separation distances and voltage applied at different orientations.