| Summary: | Control over particle positioning is of particular importance in microfluidic systems. Acoustic techniques offer a low- power, minimally invasive method of achieving such control. This thesis discusses such control using surface acoustic waves. Mathematical models are first developed to describe the control over particles in liquids using acoustic radiation forces , which highlight the influence of acoustic power and particle size. The formation of both one and two dimensional particle arrays in fluidic channels are t hen demonstrated experimentally in a range of fluidic channels. Particle acceleration during array formation is shown by experiment to be directly proportional to the acoustic power level, indicating both fast and slow regimes of operation for this technique. Additionally, the time taken for particle arrays to form is shown to follow an inverse square relationship with particle size, allowing the possibility of sorting particles according to their size. A method of transporting particle arrays is reported, by sequential increments in the acoustic frequency. This is a cyclic process and the controlled transport of arrays of micron-sized particles by distances greater than 100 11m is demonstrated. A biocompatible microfluidic device is presented, which enables the use of the techniques presented here with biologically relevant samples. A significant biological application is demonstrated by the formation and transportation of arrays of microbubbles. This could allow the characterisation of individual micro bubbles in targeted drug delivery studies, for example.
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