Soft bionic actuation explains the functional role of whisking in seal whisker sensing

Seals exhibit exceptional ability to navigate and detect underwater prey with high precision, even in complete darkness using their ultra-sensitive whiskers. These whiskers combine two key adaptations: undulatory morphology, which suppresses self-induced vibrations and rhythmic whisking, which actively probes surrounding water. Most previous studies of whisker-based hydrodynamic sensing focused on static artificial whiskers, leaving the functional role of whisking largely unexplored. We show that undulated harbor seal whiskers exhibit threefold lower vortex-induced vibrations (VIV) and over fiftyfold higher signal-to-noise ratio (SNR) than California sea lion whiskers. To study the functional role of whisking in the sensing performance of the whiskers, an artificial muscle comprised of an electrohydraulic soft actuator was integrated at the base of a natural whisker, allowing precise stiffness control and rhythmic whisking. Finally, we developed a bionic seal muzzle with 30 natural whiskers per side, capable of whisking at variable angles and frequencies, closely mimicking natural dynamics. Our results indicate that undulatory morphology and active whisker protraction are essential for seals to achieve sufficiently high SNR to track prey trails.