Ultrasonic waves have been shown to provide a means of liquid/solid separation. When a standing wave is set up in a liquid, forces act on particles acting towards nodal planes within the liquid. The effect has been used in the past for cell separation in biology. The motivation for this proposal is for a flow-through separation technique (acoustic filter). Existing work at Southampton has demonstrated the feasibility of such an approach based on the concept of having a single flow inlet one side of an acoustically-driven rectangular cell and several outlets on the opposite face. The system holds its resonance condition via closed loop electronic control using an embedded microcontroller. The proposed programme of work will aim to produce a microfluidic version of the device capable of filtering solid particles (in the range 1-100 microns) from liquids with relatively low flow-rates. The fabrication will exploit the latest results of our research into combining thick-film processing with silicon micromachining methods. Finite element techniques will be used to model the system.