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J.J. Hawkes, W.T. Coakley, M. Gröschl, E. Benes, S. Armstrong, P.J. Tasker, H. Nowotny:
"Single half-wavelength ultrasonic particle filter: Predictions of the transfer matrix multi-layer resonator model and experimental filtration results";
Journal of the Acoustical Society of America, 111 (2002), 1259 - 1266.

The quantitative performance of a ``single half-wavelength’’ acoustic resonator operated at
frequencies around 3 MHz as a continuous flow microparticle filter has been investigated. Standing
wave acoustic radiation pressure on suspended particles ~5- mm latex! drives them towards the center
of the half-wavelength separation channel. Clarified suspending phase from the region closest to the
filter wall is drawn away through a downstream outlet. The filtration efficiency of the device was
established from continuous turbidity measurements at the filter outlet. The frequency dependence
of the acoustic energy density in the aqueous particle suspension layer of the filter system was
obtained by application of the transfer matrix model @H. Nowotny and E. Benes, J. Acoust. Soc. Am.
82, 513-521 ~1987!#. Both the measured clearances and the calculated energy density distributions
showed a maximum at the fundamental of the piezoceramic transducer and a second, significantly
larger, maximum at another system’s resonance not coinciding with any of the transducer or empty
chamber resonances. The calculated frequency of this principal energy density maximum was in
excellent agreement with the optimal clearance frequency for the four tested channel widths. The
high-resolution measurements of filter performance provide, for the first time, direct verification of
the matrix model predictions of the frequency dependence of acoustic energy density in the water
layer. © 2002 Acoustical Society of America. @DOI: 10.1121/1.1448341#
PACS numbers: 43.35.Yb, 43.35.Bf, 43.20.Ks, 43.25.Qp @RW#