Low-power acoustic harvesting of aerosols

Abstract

A new acoustic device for levitation and/or concentration of aerosols and small liquid/solid samples (up to several millimeters in diameter) in air has been developed. The device is inexpensive, low-power, and, in its simplest embodiment, does not require accurate alignment of a resonant cavity. It is constructed from a cylindrical PZT tube of outside diameter D=19.0 mm and thickness-to-radius ratio h/a /spl sim/0.03. The lowest-order breathing mode of the tube is tuned to match a resonant mode of the interior air-filled cylindrical cavity. A high Q cavity results that can be driven efficiently. An acoustic standing wave is created in the interior cavity of the cylindrical shell where particle concentration takes place at the nodal planes of the field. It is shown that drops of water in excess of 1 mm in diameter may be levitated against the force of gravity for approximately 100 mW of input electrical power. The main objective of the research is to implement this low-power device to concentrate and harvest aerosols in a flowing system. Several different cavity geometries are presented for efficient collection of the concentrated aerosols. Concentration factors greater than 40 are demonstrated for particles of size 0.7 /spl mu/ in a flow volume of 50 L/minute.