Methods for generating particulate clusters and nodal trapping lines having desired widths are disclosed. The devices include an acoustic chamber having an inlet and an outlet. An ultrasonic transducer and reflector create a multi-dimensional acoustic standing wave that generates particulate clusters separated by a channel of fluid running therebetween and creates nodal trapping lines. The frequency of the multi-dimensional acoustic standing wave can be selectively tuned so as to selectively control at least one of (a) a width of each particulate cluster, or (b) a width of each channel of fluid. The frequency of the multi-dimensional acoustic standing wave can also be selectively tuned so as to selectively control the width of each nodal trapping line. Also disclosed are particulate clusters separated by a channel of fluid, wherein a ratio of the widths of the particulate clusters and the channel of fluid can be varied as desired.