Surface acoustic wave (SAW) induced patterning of micro beads in microfluidic channels

Micro beads were patterned in microfluidic channels by using standing surface acoustic waves (SSAW). The SSAW were formed through two parallel interdigital transducers (IDTs) on a LiNbO₃ substrate. A PDMS microchannel was aligned with the IDTs and bonded with the substrate. A solution of fluorescent polystyrene beads (diameter: 1.9 mum) was injected into the channel through a pressure driven flow. When a 25 dBm AC signal (frequency: 23.9 MHz) was applied to the IDTs, the beads were patterned into two straight lines (~5 mum in width) along the pressure nodes inside the channel.