Figure 8.

(a) A schematic drawing of acoustic streaming inside a liquid droplet, (b) a snapshot of acoustic streaming induced by the flexible SAW device, showing a double vortex streaming pattern. (c) Streaming velocity as a function of RF signal voltage with droplet size as a parameter, showing a linear increase in streaming velocity with signal voltage. (d) A schematic drawing to show circulating streaming and particle concentration induced by SAW off the central wave path. Particles are uniformly distributed in liquid (e) and partial concentration in the droplet after applying a RF signal for 25 sec (f) and 70 sec (g) with a signal voltage of 25 V. The SAW device used for these experiments has 50 pairs of IDT fingers, and a wavelength of 12 μm. Only the Rayleigh Wave was used for microfluidic experiments. The red curved arrows are indicative of the streaming direction, and the green circle shows the area with the highly concentrated nanoparticles.