In recent years considerable amount of research focussed on development of the socalled lab-on-a-chip (LoC) devices that feature complex laboratory sample preparation
functions (such as sample washing, sorting, detection or drug delivery) on the
microscale. These devices offer lower manufacturing costs, reagent use and the
required sample size can be as small as a few microlitres. In this thesis, particle
and cell separation is investigated utilising the primary acoustic radiation force
in a surface acoustic wave device. After providing review of similar techniques,
various phase and frequency modulation methods are proposed for achieving target
separation based on size, density or compressibility difference. A special form of
primary acoustic radiation force is presented for surface wave devices and is used
to obtain particle trajectories in modulated fields for fast analytical comparison
of the proposed methods. Experiments for size-based particle separation reveal
95% efficiency and >85% purity for particle size ratio as small as 1.45. Physical
property-based separation of iron-oxide and polystyrene microparticles shows even
higher figures of merit: >95% efficiency and >90% purity illustrating the versatility
of the method. Biological cell separation is performed on human red blood cells and
white blood cells, displaying 94% efficiency and >84% purity. Bandpass sorting of
particles and cells is also proposed and validated by experiments. Various numerical
models are developed for flow and acoustic field simulation, including investigation
of secondary acoustic radiation force, and finally a Monte-Carlo study is carried out
to verify the superiority of modulated acoustic sorting methods compared to static
acoustic field separation techniques
