Fast mixing of digital droplets under uni-direction acoustic field

A micro-mixer for mixing digital droplets fabricated on 128degY cut X LiNbO₃ is reported, which is composed of one interdigital transducers and one reflector for generating unidirectional acoustic field. After a RF signal amplified by a power amplifier was added on an interdigital transducer, surface acoustic wave was excided by the interdigital transducer, and was conversed into longitudinal acoustic wave and to drive a digital droplet to merge with the other droplet quickly by their rapid molecular diffusion when the surface acoustic wave passed through the droplets. Mixing experiments of 3ul NaCl solution-2ul red dye solution and 3ul glycerine-2ul red dye solution show that their mixing velocities can improve 35 folds and 50 folds respectively under unidirectional acoustic fields. The research is valuable for its simplicity in process and easy integration into lab-on-a-chip.