Small‐Scale Robots in Fluidic Media

One of the most promising uses of miniature robots (MRs) in the biomedical field is performing local in situ diagnosis and therapy. Researchers have proposed numerous swimming methods utilizing various actuation principles. Herein, the different propulsion methods of MRs are evaluated by analyzing their scalability. Comparing various actuators, how their performance changes with size reduction is evaluated. The swimming of natural flagellar swimmers such as spermatozoa and nematodes is analyzed. It is found that although the fluidic regime and the geometry of these organisms change considerably, there are nondimensional features that remain almost constant; most importantly, the variation of the swimming velocity is much smaller than the variation of the Reynolds number in natural swimmers. Then, several methods of propulsion and actuation principles are compared, and it is found that among the swimming methods examined, the downscaling of a piezoelectrically driven vibrating elastic beam is the most favorable. Similar to natural swimmers, the swimming velocity of a piezoelectric active swimming tail does not depend on the geometry given that its power requirements can be met. This comparative approach tool aids in the development of future actuation methods for MRs and other active microsystems.