Acoustic Tweezers For Sub-Mm Microparticle Manipulation

This paper reports a new design of an acoustic tweezers that can trap microparticles up to 0.5 mm in diameter through a 3-dimensional energy well formed in a bulk of liquid. The acoustic tweezers is built on a 1.02 mm thick lead zirconate titanate (PZT) substrate, with symmetric sectors (pie shaped when viewed from top) of air-cavity Fresnel lens. Each of the sectors is designed to have a different focal length, so that the acoustic waves from different sectors interfere with each other such that they produce a Bessel beam zone (with negative axial radiation force) along the center line perpendicular to the transducer surface. The negative radiation force traps and holds particles. The fabricated acoustic tweezers operating at 2.07 MHz has successfully been shown to trap polyethylene microsphere from 0.3 to 0 5 nun in diameter at 5 mm away from the transducer surface, providing a way to remotely manipulate large-size microparticles without physical contact to any rigid body.