Surface acoustic wave (SAW) devices based on the piezoelectric principle have been used
extensively in telecommunication applications over the last 20 years, but have recently
shown promise in the area of biomedical applications due to their efficient micro-fluidic
functions and highly sensitive and label-free detection of pathogens, bacteria, cells, DNA
and proteins. There are two types of surface acoustic wave modes: i.e., Rayleigh SAW
(R-SAW) and shear horizontal SAW (SH-SAW). R-SAW is widely used for
microfluidics and sensing in dry conditions, whereas SH-SAW is mainly used for sensing
in liquid conditions. This thesis firstly reviewed the current theoretical and research
progress related to these devices and application within the biomedical fields to date, and
then the SH-SAW was applied into a novel lab-on-chip combining both bio-sensing and
micro-fluidic functions.
Simulations of the SH-SAW propagation on 36o Y-cut LiTaO3 were undertaken. Results
showed a weak vertical wave component, and at a 90° rotation cut, the crystal was able to
support a vertical Rayleigh component showing mixed sensing and streaming possibilities
on a single crystal. Experimental investigation of the SH-SAW identified the ability for
the shear wave to support mixing, pumping, heating, nebulisation and ejection of sessile
droplets on the surface of the crystal with a theoretical explanation for the behaviour
presented. A comparison with a standard R-SAW devices made of 128o Y-cut LiNbO3
and sputtered ZnO films was performed. This novel behaviour of digital microfludics,
i.e., using sessile droplet with the SH-SAW, demonstrated by this work offers the
possibility to manufacture a fully integrated micro-fluidic bio-sensing platform using a
single crystal to realise a range of micro-fluidic functions
