To mimic the mechanical response of passive biological cilia in complex fluids, we study the bending dynamics of an anchored elastic fiber submitted to a dilute granular suspension under shear. We show that the bending fluctuations of the fiber accurately encode minute variations of the granular suspension concentration. Indeed, besides the stationary bending induced by the continuous phase flow, the passage of each single particle induces an additional deflection. We demonstrate that the dominant particle/fiber interaction arises from direct contacts of the particles with the fiber and we propose a simple elastohydrodynamics model to predict their amplitude. Our results shed light on the extreme mechanical sensitivity of biological cilia to detect the presence of solid particles in their vicinity and bring a physical framework to describe their dynamics in particulate flows.
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