  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.
