Hill, Martyn, Townsend, Rosemary J. and Harris, Nicholas R.
Modelling for the robust design of layered resonators for ultrasonic particle manipulation.
Ultrasonics, 48, (6-7), . (doi:10.1016/j.ultras.2008.06.007).
Several approaches have been described for the manipulation of particles within an
ultrasonic field. Of those based on standing waves, devices in which the critical dimension of
the resonant chamber is less than a wavelength are particularly well suited to microfluidic, or
“lab on a chip” applications. These might include pre-processing or fractionation of samples
prior to analysis, formation of monolayers for cell interaction studies, or the enhancement of
biosensor detection capability.
The small size of microfluidic resonators typically places tight tolerances on the positioning
of the acoustic node, and such systems are required to have high transduction efficiencies, for
reasons of power availability and temperature stability. Further, the expense of many
microfabrication methods precludes an iterative experimental approach to their development.
Hence, the ability to design sub-wavelength resonators that are efficient, robust and have the
appropriate acoustic energy distribution is extremely important.
This paper discusses one-dimensional modelling used in the design of ultrasonic resonators
for particle manipulation and gives example of their uses to predict and explain resonator
behaviour. Particular difficulties in designing quarter wave systems are highlighted, and
modelling is used to explain observed trends and predict performance of such resonators,
including their performance with different coupling layer materials.
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