In this study, we proposed a novel mixing method using alternate pulsed flows from three inlet channels using three piezoelectric valveless micropumps. Two solutions are assigned into one micropump and the other two micropumps, respectively. The fabricated microfluidic device consists of a cross-shaped mixing channel with three inlet microchannels and three valveless micropumps. According to the experimental results, it was confirmed that the pulsed mixing using three inlet microchannels increased mixing speed with increasing the switching frequency of the micropump driving up to 200 Hz. The proposed method solved the problem of a bias of concentration ratio near the sidewalls which has happened in the previous pulsed mixing method using T- or Y-shaped microchannel with two inlet microchannels. Furthermore, by controlling a solution flow at the confluent area utilizing a reverse flow of the micropump, the mixing speed dramatically increased and the mixing time of 3.6 ms for 90% mixing ratio was achieved at the micropumps switching of 400 Hz.

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