A double-chamber ultrasonic resonance field device was used for the se
paration and retention of animal cells. By controlling operational par
ameters such as flow and power input, the device can retain viable cel
ls more efficiently, allowing for selective removal of nonviable cells
and cell debris. A simple model describing the forces acting on spher
ical particles in a sound field (primary radiation force, Bernoulli fo
rce, secondary radiation force) is presented. Field stability increase
s with decreasing average flow rates and increasing power input. At ve
ry high field stability, as achieved with low flow rates and high powe
r input, the selectivity for viable cells is reduced, due to the effic
ient retention of all types of particles. At high flow rates and resul
ting low field stability, selectivity is also reduced, due to poor sep
aration efficiency, resulting in equally low retention of viable cells
, nonviable cells, and cell debris.