Fig. 9. Summary of the net flow generated by previously reported artificial cilia listed in Table 1. (a) Absolute flow speed as a function of cilia length. The color of the symbols indicates cilia motion with purple, green and blue indicating 3D non-reciprocal motion, 2D non-reciprocal motion and 2D reciprocal motion, respectively. The circle and star symbols indicate whether the associated publication reports the local flow above the cilia tips or the global flow measured far away from the ciliated area, respectively. Solid filled data indicate the existence of a metachronal wave. (b) Normalized flow speed, δ = v/fl, as a function of cilia length (see Table 1 for the corresponding references). The symbols have the same meaning as in panel (a).