Capillary wave sieve: Continuous particle separation using millimeter-scale capillary waves

Size-dependent continuous microparticle separation is important for various applications in sensing and drug delivery to particle manufacturing. Several invasive, noninvasive, active, and passive methods have been developed, spanning operation across a wide range of system scales, from bulk-macroscale devices to precise-microscale systems. However, devices in these wide system scales have contradictory benefits. Bulk methods have limitations with the size of particles that can be manipulated, while microscale methods have limitations with processing volumes. Here, we present a method to continuously separate micron- and submicron-sized particles using low-frequency vibrations (of the order of 10 Hz). We generate capillary waves in an open channel with a continuous particle-laden flow perpendicular to the vibration direction. The size-based response of the ensuing flow field aligns particles above a critical size along the center of the channel, while the remaining particles remain in the bulk and undergo downstream separation. A key feature of this mechanism is that the separated particle sizes can be controlled by changing the vibration amplitude. The proposed mechanism and design provides a semibulk method to distinguish submicron-sized particles with robust in situ control using a simple millimeter-scale setup and operation.