Ultrasonic microfluidic transportation based on a twisted bundle of thin metal wires

We report a method by which tiny quantity of liquid can be transported in microchannels by ultrasound induced capillary action. The microchannels with a width of 12 μm are constructed by a twisted bundle of thin metal wires, whose vibration is excited by a sandwich type ultrasonic transducer. After confirming the capillary flow in the channels by experimental observation, a physical model is proposed to explain the ultrasound induced capillary action, and the performances of liquid transportation are measured and analyzed. The capillary flow speed is affected by the driving conditions of the transducer and the viscosity of the liquid, and reaches a maximum near the resonance point. The maximum capillary flow speed observed in our experiments is 15 mm/s. The performance of liquid transportation are also tested for two twisted bundles of metal wires in parallel, and for a twisted bundle of metal wires with two branches. The results show the possibility to apply the method in branched multi-channel microfluidic systems. Water droplets may form on the surface of the metal wire bundle, which gives a method to extract the tiny amount of liquid transported in the microchannels.