Fig. 3: Characterization of the synchronization effect.

a Heatmap depicting the percentage of one-to-one pairing droplets at various reinjection flow rates. The flow rate of the small droplets ranges from 10 to 30 μL/h at an interval of 5 μL/h, while the large-droplet flow rate ranges from 30 to 130 μL/h. The tested region with a synchronization ratio higher than 90% is outlined by an indigo line. b Graphs showing the matched frequencies that can achieve synchronization ratios of 100, 95, and 90%. The cross dots denote the matched frequencies for our device, while the dashed lines indicate the theoretical working ranges of frequencies for the negative control. c Top and side views showing the shape of the large droplet entering the constriction channel. d Top and side views showing the shape of the small droplet at its critical volume to block the junction