Fig. 3. Bidirectional rolling of microchains along the acoustic virtual wall.
a Bidirectional rolling motion (the direction is indicated by a yellow arrow) along the x-axial acoustic virtual wall upon flipping the rotational direction of the magnetic field (green curved arrow). The white dotted line denotes the net displacement. b Bidirectional rolling motion along the y-axial acoustic virtual wall. The pink curved arrows denote the magnetic rotational direction. For both panels, the acoustic excitation voltage and frequency were 20 VPP and 1.55 MHz, respectively. The magnetic intensity was 21 mT. The magnetic rotational velocity as depicted in panel (a) and (b) was 24 rpm and 30 rpm, respectively. Scale bar, 100 μm.