Seal Whisker-Inspired Sensor for Amplifying Wake-Induced Vibrations in Underwater Marine Animal Monitoring

TL;DR

This work tackles the challenge of detecting weak wake-induced vibrations from swimming marine animals by introducing a seal whisker-inspired sensor with a spiral-perforated base that amplifies target-frequency vibrations. Using frequency-response simulations, the authors demonstrate significant amplification (up to $51\times$ RMS displacement) and show how base geometry can be tuned to match the natural frequencies of different whisker morphologies. The main contributions include the spiral-base design, systematic parameter characterization to guide frequency-band targeting, and validation across multiple whisker geometries, highlighting practical potential for non-invasive, energy-efficient underwater monitoring. The results suggest that such bio-inspired, tunable sensors could enable robust long-range detection of animal wakes in challenging underwater environments, with future work focusing on real-world deployment and multi-sensor arrays.

Abstract

Underwater marine animal monitoring is essential for assessing biodiversity, evaluating ecosystem health, and understanding the effects of offshore structures. Traditional approaches such as tagging, sonar, and camera systems are often invasive, energy-intensive, or limited by poor visibility and water turbidity. Inspired by the hydrodynamic sensing of seal whiskers, wavy whisker vibration sensors have been developed for flow velocity and angle-of-attack detection. However, most prior work has focused on sensor characterization and only forward modeling, with limited exploration of the inverse problem of inferring animal movement. Moreover, current sensor sensitivity to vortex street wakes generated by swimming animals remains insufficient for practical monitoring. To address this gap, we develop a whisker-inspired sensor with a spiral-perforated base that amplifies vibrations within frequency ranges relevant to animal-induced wakes. We further characterize the influence of spiral parameters on the sensitive frequency band, enabling adaptation of the design to specific species. We evaluated the amplification effect of the spiral-perforated design using frequency response simulations of the whisker-base structure under harmonic water pressure. Results show up to 51x enhancement in root mean squared displacement at the target sensor location within frequency bands associated with animal-induced wakes compared to the baseline design, confirming the effectiveness of the amplification.

Figures (6)

• Figure 1: (a) Seals track prey using wavy shape whiskers that detect vibrations induced by vortex street wakes generated by swimming animals. (b) Enlarged view of the wavy whisker cross-section, illustrating elliptical geometry with major and minor axes $(a, b, k, l)$ and orientation angles $(\alpha, \beta)$. (c) Seals have an array of whiskers with various natural frequencies, facilitating broadband hydrodynamic sensing across multiple frequency ranges.
• Figure 2: (a) Design of the whisker-inspired sensing unit and spiral perforated base. The whisker is mounted on a spiral perforated base, which amplifies vortex-induced vibrations. (b) Photo of the spiral perforated base. The vibration sensing point is at the middle of the base, where a vibration sensor will be mounted to capture vortex-induced whisker vibrations.
• Figure 3: Mode shapes of the spiral-perforated whisker base showing flexible vibrations along (a) the x-axis, (b) the y-axis, and (c) the z-axis.
• Figure 4: Frequency response of RMS displacement at the sensing location under an applied pressure of 15 Pa. Subplots compare the effects of different whisker base parameters: (a) whisker base thickness, (b) number of spiral turns, (c) spiral growth rate, (d) spiral aspect ratio, (e) spiral slot width, and (f) force direction (x vs. y).
• Figure 5: Resonance coupling between whisker base and whisker modes. (a) Base torsional mode shape about the x-axis for Whisker 1 with the natural frequency of 78.59 Hz. (b) Whisker bending mode shape along the x-axis with natural frequency of 74.18 Hz. (c) Coupled system visualization demonstrating near-resonant interaction between base torsion and whisker bending modes. (d) Modal frequency comparison for three whisker geometries showing base ($f_{base}$) and whisker ($f_{whisker}$) natural frequencies in Hz.