title: Varying the agglomeration position of particles in a micro-channel using Acoustic Radiation Force beyond the resonance condition.
abstract: It is well-known that particles can be focused at mid-height of a micro-channel using Acoustic Radiation Force (ARF) tuned at the resonance frequency (h=λ/2). The resonance condition is a strong limitation to the use of acoustophoresis (particles manipulation using acoustic force) in many applications. In this study we show that it is possible to focus the particles anywhere along the height of a micro-channel just by varying the acoustic frequency, in contradiction with the resonance condition. This result has been thoroughly checked experimentally. The different physical properties as well as wall materials have been changed. The wall materials is finally the only critical parameters. One of the specificity of the micro-channel is the thickness of the carrier and reflector layer. A preliminary analysis of the experimental results suggests that the acoustic focusing beyond the classic resonance condition can be explained in the framework of the multilayered resonator proposed by Hill [1]. Nevertheless, further numerical studies are needed in order to confirm and fully understand how the acoustic pressure node can be moved over the entire height of the micro channel by varying the acoustic frequency. Despite some uncertainties about the origin of the phenomenon, it is robust and can be used for improved acoustic sorting or manipulation of particles or biological cells in confined set-ups.
authors.affiliation: Laboratoire PMMH, CNRS UMR7636/ESPCI/UPMC/UPD, École Supérieure de Physique et de Chimie Industrielles (ESPCI), 10 rue Vauquelin, 75005 Paris, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Dron
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Aider
mesh_terms: D000162:Acoustics; D004867:Equipment Design; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation*; D010316:Particle Size; D019904:Polymethyl Methacrylate; D011312:Pressure
chemical_list: D019904:Polymethyl Methacrylate