It is well known that a symmetric microstreaming flow field will present in the vicinity of an acoustically actuated bubble. In this study, we demonstrate that oscillating microbubbles confined in teardrop-shaped cavities can result in a break in the symmetry of a microstreaming flow field. The teardrop cavity controls the size and shape of the bubble, regulating the volume and therefore its resonance frequency. If actuated in an acoustic field, the induced flow field can then be turned on and off by changing the acoustic actuation frequency. By harnessing the flow field directing capabilities of symmetry breaks and the switching properties of selective excitation of microbubbles, we generate and characterize a microfiuidic switch for directing flow direction. We also show that a chain of multiple teardrop-shaped cavities can be used as a transport mechanism for directing particles spatially at high flow speeds. Our results demonstrate that teardrop cavities have great potential in future lab-on-a-chip devices by providing simple solutions to complex flow circuits for temporal and spatial flow control.
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