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(a) Exploded view of the device, showing the droplet, micro-grippers, silicon substrate, and piezoelectric transducer. (b) Image of particles collected within the micro-grippers using an actuation frequency of 1.480 MHz. Images showing (c) the focal plane level with the top of the grippers and (d) the substrate (base of the grippers), which are clearly distinguishable. Snapshots over time showing the dispersion of particles from (e) a stacked arrangement to ((f) and (g)) a dispersed arrangement after actuation is turned off. This occurs in the focal plane, which coincides with the substrate.
(a) and (b) Images of the whole droplets placed on top of the micro-grippers. It can be seen that despite the different shapes of the droplets, particle collection still occurs within the centre of the micro-grippers. The centre of droplet is marked with a black square, the gripper centre with a diamond, and the centroid of the particles with a cross. (c) The comparison of the various centres is shown for multiple experiments. Here, the crosses show the offset of the particle centre and the circles the offset of the droplet centre, both offsets being with respect to the gripper centre. (d) Particle collection at the same frequency within a droplet, which is 5% larger in volume.
Slice plots of the time averaged force potential field from top view are shown for (a) no-offset and (b) 10% (256 μm) offset droplets in the x direction with micro-grippers, and the absence of micro-grippers for (c)no-offset and (d) 10% (256 μm) offset droplets in the x direction. The locations of predicted particle collection are outlined with white ovals. The insets depict the location of the piezoelectric transducer (grey), the micro-grippers (black), and the centralised (filled) and offset (outline) droplets. A side view of is also shown in (a). All the top view slices were taken at 50 μm above the silicon surface (half the micro-gripper height). The piezoelectric transducer was driven at (a) 1.57 MHz, (b) 1.56 MHz, and (c) and (d) 1.59 MHz.
Images of particles collected at driving frequencies of (a) 1.480 MHz, (b) 1.550 MHz, (c) 1.920 MHz, and (d)2.050 MHz.
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