Fiber Bragg Grating Whiskers For Bioinspired Hydrodynamic Perception On Underwater Robots

Underwater robots often operate where vision and acoustic sensing are degraded by turbidity, darkness, or ecological constraints. Harbor seals navigate these conditions using facial whiskers that detect hydrodynamic trails left by swimming prey, enabled by an undulating, tapered morphology that suppresses self-induced vibrations during forward motion. Inspired by this capability, this report presents the design, fabrication, and robotic deployment of Fiber Bragg Grating (FBG)-based whisker sensors for passive hydrodynamic perception on autonomous underwater vehicles. The whisker shaft combines a superelastic nitinol core with a urethane elastomer overmold, fabricated through a two-stage compliant molding process that replicates the seal’s elliptical, undulating geometry. The FBG sensing module was characterized and refined through beam-spring and discretized elastic modeling, with experimental characterization across five bridge geometries validating model predictions and achieving sub-millinewton force detection with two-axis moment resolution. Controlled pool experiments quantified flow-speed response from 0.1 to 0.6 m/s, angle-of-attack dependence, and wake detection from a pitching foil at biologically relevant Strouhal numbers (St ≈ 0.25–0.35). A single whisker mounted on a small remotely operated vehicle distinguished between straight and turning trajectories in delayed foil-generated wakes, selecting the correct branch in 17 of 20 trials (85% success rate). Field deployment in coastal ocean water confirmed sensor robustness, detecting vortices shed by a human diver’s fins at approximately 600 mm standoff distance. These results establish FBG whiskers as a viable technology for bio-inspired hydrodynamic sensing, demonstrating for the first time that optical whisker sensors can support autonomous navigation decisions from delayed wake cues.