Active sensing of particles suspended in unsteady flow

Animals can generate highly unsteady flow around their body. We explore how the flow on their mechanical sensors may help in remotely detecting and locating particles suspended in the surrounding fluid. A simple analytical model demonstrates the basic physical principle, which is analogous to active sonar except with flow instead of sound. The model shows that particle-induced fluctuations in pressure or shear on the sensors can be used to reconstruct a hydrodynamic image revealing the size and position of the particle. Our findings suggest that a variety of organisms and devices may actively agitate their surroundings to enhance their sensory range.