Editing Microbotics (section)

=== Swimming locomotion ===
Swimming microrobots are designed to operate in 3D through fluid environments, like biological fluids or water. To achieve effective movements, locomotion strategies are adopted from small aquatic animals or microorganisms, such as flagellar propulsion, pulling, chemical propulsion, jet propulsion, and tail undulation. Swimming microrobots, in order to move forward, must drive water backward.<ref name=":1" />

Microrobots move in the low Reynolds number regime due to their small sizes and low operating speeds, as well as high viscosity of the fluids they navigate. At this level, viscous forces dominate over inertial forces. This requires a different approach in the design compared to swimming at the macroscale in order to achieve effective movements. The low Reynolds number also allows for accurate movements, which makes it good application in medicine, micro-manipulation tasks, and environmental monitoring.<ref name=":0" /><ref name=":1" />

Dominating viscous ([[Stokes' law|Stokes]]) drag forces T<sub>drag</sub> on the robot balances the propulsive force F<sub>p</sub> generated by a swimming mechanism.

 <math>T=T_(drag)=\frac{bv}{m}</math>

Where b is the viscous drag coefficient, v is motion speed, and m is the body mass.<ref name=":1" />

One of the examples of a swimming microrobot is a helical magnetic microrobot consisting of a spiral tail and a magnetic head body. This design is inspired by the flagellar motion of bacteria. By applying a magnetic torque to a helical microrobot within a low-intensity rotating magnetic field, the rotation can be transformed into linear motion. This conversion is highly effective in low Reynolds number environments due to the unique helical structure of the microrobot. By altering the external magnetic field, the direction of the spiral microrobot's motion can be easily reversed.<ref>{{Cite journal |last1=Liu |first1=Huibin |last2=Guo |first2=Qinghao |last3=Wang |first3=Wenhao |last4=Yu |first4=Tao |last5=Yuan |first5=Zheng |last6=Ge |first6=Zhixing |last7=Yang |first7=Wenguang |date=2023-01-01 |title=A review of magnetically driven swimming microrobots: Material selection, structure design, control method, and applications |journal=Reviews on Advanced Materials Science |language=en |volume=62 |issue=1 |page=119 |doi=10.1515/rams-2023-0119 |bibcode=2023RvAMS..62..119L |issn=1605-8127|doi-access=free }}</ref>