3D Printed Sensor Mimics Seal Whiskers to Detect Underwater Vortices

The word pinniped refers to semi-aquatic fin- or flipper-footed mammals, including to seals, sea lions and walruses. These creatures also have whiskers, which are part of what makes them so adorable and referred to by some as the puppies of the sea, but these whiskers serve an important purpose – they help the pinnipeds track their prey underwater by sensing the vortices left behind by the movement of said prey. A group of researchers in the Department of Mechatronics Engineering at Jeju National University in South Korea believe that a sensor based on the pinnipeds’ method of hunting could be valuable for soft robotics and underwater exploration, so they set out to create one using 3D printing.

The research was described in a paper entitled “Fully 3D Printed Multi-Material Soft Bio-Inspired Whisker Sensor for Underwater-Induced Vortex Detection,” which you can read here. The artificial whisker was 3D printed with polyurethane as well as graphene, which was printed in four patterns using a multi-head 3D printer.

“The four graphene patterns (90° apart) on the polyurethane cylinder enable the flow detection in all directions (0–360°). The length and diameter of the polyurethane cylinder and graphene patterns are 160 × 8 mm and 60 × 0.3 mm, respectively,” the researchers explain. “The conductivity of the printed graphene pattern is 0.6 Ω-cm. With a maximum deformation distance of 5 mm in any direction (0–360°), a substantial change in resistance is observed (from 5.09 × 10³ to 6.03 × 10⁸ Ω). The change in resistance in four directions (up, down, left, and right) is studied in an underwater environment.”

The clockwise and counter-clockwise vortices were generated by using an artificial fish fin, also 3D printed. The highly sensitive whisker sensor is the first to be 3D printed out of polyurethane and graphene. The dual-extruder 3D printer was used to print the sensor itself, using the first head, out of polyurethane purchased from Fotopolymer, while the second head printed the graphene patterns from filament bought from Black Magic 3D. After printing was complete, the base and the patterns were connected using copper tape. Copper tape was also used to solder signal wires, and a final 1mm water protection polyurethane layer was dip coated and cured with UV light.

The researchers then tested the sensors, using them to detect the vortices by digitizing the analog signals that indicate resistance changes and sending them to a microcontroller. They concluded that the design and fabrication of the whisker sensor is simple, quick, low cost, and easily deployable in commercial applications, as well as delivering good sensitivity and mechanical reliability. Some further development is needed; however, the study was overall a successful one.

“This paper is a wonderful example of bioinspired soft robotics,” said Barry A. Trimmer, PhD, Editor-in-Chief of Mary Ann Liebert, Inc., which published the study. “The authors have used observations of a natural system to build a materials-based sensor that can be used on underwater robots for better positional control, navigation, and object detection.”

Authors of the paper include Jahan Zeb Gul, Kim Young Su, and Kyung Hyun Choi.

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[Images: Mary Ann Liebert, Inc.]