Fig. 3.

Trapping behavior of MBs observed under an inverted microscope in the static condition. (A) Experimental setup in which the AVT transducer was placed on the top to trap MBs for bottom-view observations. (B) Series of bright-field (Top) and fluorescent (Bottom) images. During the trapping sequence, the MBs were swirled into the AVT center to form a large cluster. (C) The AVT transducer was rotated 90° to record the trapping behavior from a side view. (D) Series of side-view images showing that MBs initially experience the radiation force pushing on the wall and then the trapping force that immediately collects the dispersed clusters into the center of the AVT focal zone. The MB concentration was 10.0 × 10⁸ MBs per milliliter and AVT were applied at an acoustic pressure of 800 kPa and a duty cycle of 30%.