Table 2.

The differences among bubble propulsion, sharp-edge propulsion, and in-situ microrotor.

Propulsion Type	Principle	Advantages	Disadvantages
Bubble propulsion	Bubbles’ vibration produces a source of net momentum	Fast and strong propulsion	Narrow frequency selection range; Bubbles may burst; Hard operation
Sharp-edge propulsion	Sharp-edge’s vibration generates propulsion	Wide frequency selection range; Simple manufacturing, and operation	Low propulsion
In-situ microrotor	Similar to sharp-edge propulsion, but there is a fixed axis in the center	In-situ propulsion; Low fluid influence	Complex design