“It was in the oceans that life first evolved and where complex animals have thrived for over 600 million years. Marine animals survive in environments as diverse as tropical coral reefs, polar ice-capped oceans, and the lightless abyssal depths,” says Frank E. Fish from West Chester University and Donna M. Kocak from HARRIS CapRock Communications.
“To deal with the rigors of the marine environment, animals have developed specialized sensory systems (e.g., echolocation, electroreception), mechanisms to deal with pressure (e.g., buoyancy control), strategies to economize on energy (e.g., fusiform body design, schooling, burst-and-glide swimming), armor (e.g., bony scales, mollusk shells), stability mechanisms (e.g., paired and median fins), maneuverability (e.g., flexible bodies, vectored thrust), speed (e.g., high-aspect-ratio oscillatory propulsors, jet propulsion), stealth (e.g., camouflage, low acoustic signature), and use of compliant materials (e.g., collagen, protein rubbers, mucous),” they further write.
Artificial whisker reveals source of harbor seal’s uncanny prey-sensing ability
Harbor seals have an amazingly fine-tuned sense for detecting prey, as marine biologists have noted for years. Even when blindfolded, trained seals are able to chase the precise path of an object that swam by 30 seconds earlier. Scientists have suspected that the seal’s laser-like tracking ability is due in part to its antennae-like whiskers.
Now engineers at MIT have fabricated and tested a large-scale model of a harbor seal’s whisker, and identified a mechanism that may explain how seals sense their environment and track their prey. The team found that a seal’s whiskers serve two main functions in sensing the environment: first remaining still in response to a seal’s own movements through the water, and then oscillating in a “slaloming” motion in response to the turbulence left by a moving object.
In their experiments, the researchers observed that once the fabricated whisker enters the wake left by a passing object, it starts vibrating at the same frequency as the wake’s passing vortices. Careful visualizations show that the whisker “slaloms” among the vortices, like a skier zigzagging between flags.
The research shows that this slaloming allows the whisker to extract energy from the wake, causing it to vibrate at the precise frequency of the wake — a mechanism that may give seals a clue to an object’s path, its size, and even its shape.
Michael Triantafyllou, the William I. Koch Professor in MIT’s Department of Mechanical Engineering, says that biologically inspired sensors, modeled after the harbor seal’s whiskers, may aid underwater vehicles in tracking schools of fish, as well as sources of pollution — a goal that he is currently working toward. He and former graduate student Heather Beem, whose PhD thesis formed the basis of the work, have published their results in the Journal of Fluid Mechanics.
Bio-inspired underwater sensing, control and communications
Weakly electric fishes (Gymnotid and Mormyrid) use an electric field to communicate efficiently (termed electrocommunication) in the turbid waters of confined spaces where other communication modalities fail. Inspired by this biological phenomenon, we design an artificial electrocommunication system for small underwater robots and explore the capabilities of such an underwater robotic communication system.
Researchers Wei Wang and others have derived an analytical model for electrocommunication to predict the effect of the key parameters such as electrode distance and emitter current of the system on the communication performance. According to this model, a low-dissipation, and small-sized electrocommunication system is proposed and integrated into a small robotic fish.
They characterized the communication performance of the robot in still water, flowing water, water with obstacles and natural water conditions. The results show that underwater robots are able to communicate electrically at a speed of around 1 k baud within about 3 m with a low power consumption (less than 1 W). In addition, they demonstrated that two leader-follower robots successfully achieve motion synchronization through electrocommunication in the three-dimensional underwater space, indicating that this bio-inspired electrocommunication system is a promising setup for the interaction of small underwater robots.
Biomimetic MEMS pressure/flow sensor arrays for passive fish-like underwater sensing applications
Certain fish have a superior ability to navigate blindly in a complex underwater environment. They perform this unique feat by relying on their lateral-line, consisting of arrays of biological sensors (neuromast) that interact with surrounding flow. An artificial man-made analogue similar to the lateral-line could greatly benefit current unmanned underwater vehicles (UUVs) that operate in similarly difficult environments.
Researchers from MIT have developed flexible arrays of microelectromechanical systems (MEMS) pressure and flow sensors that are easy to fabricate, highly sensitive, low-cost, low-powered, surface-mountable, and are capable of withstanding harsh seawater environments.
“In a quest for reliability and high sensitivity, we developed lithographically fabricated micro sensors out of novel soft polymer materials like polydimethylsiloxane (PDMS) and liquid crystal polymer (LCP) with conductive piezoresistive sensing elements over conventionally used silicon material,” writ the researchers.
ONR grant for bio-inspired underwater sensing and control
Associate Professor Derek Paley (link is external) (AE/ISR) is the principal investigator for a three-year, $700K Office of Naval Research grant, “Bio-inspired Underwater Sensing and Control with Mechanosensitive Hairs.”
The researchers are developing an underwater robotic perception and control system based on the lateral line and vestibular systems in fish that will support a closed-loop control system using bio-inspired, multi-modal sensing. Emerging tools such as functional imaging (a technique used in parallel with optogenetics) will be used to help resolve the role of multi-modal sensing in behavior. Tools from comparative physiology, material science, and dynamical control systems will be applied to solve the problem of closed-loop sensing and robotic control with artificial lateral line and vestibular organs.
Better Robots By Studying The Subtle Movements Of Fish
The constant movement of fish that seems random is actually precisely deployed to provide them at any moment with the best sensory feedback they need to navigate the world, Johns Hopkins University researchers have found. The finding, published in the journal Current Biology, enhances our understanding of active sensing behaviors performed by all animals, including humans, such as whisking, touching, and sniffing. It also demonstrates how robots built with better sensors could interact with their environment more effectively.
Cowan and his colleagues studied fish that generate a weak electric field around their bodies to help them with communication and navigation. The team created an augmented reality for the fish so they could observe how fish movements changed as feedback from the environment changed.
Inside the tank, the weakly electric fish hovered within a tube where they wiggled back and forth constantly to maintain a steady level of sensory input about their surroundings. The researchers first changed the environment by moving the tube in a way that was synchronized with the fish’s movement, making it harder for the fish to extract the same amount of information they had been receiving. Next, the researchers made the tube move in the direction opposite the fish’s movement, making it easier for the fish. In each case, the fish immediately increased or decreased their swimming to make sure they were getting the same amount of information. They swam farther when the tube’s movement gave them less sensory feedback, and they swam less when they could get could get more feedback with less effort. The findings were even more pronounced in the dark, when the fish had to lean even more on their electrosense.
“Their actions to perceive their world is under constant regulation,” said Eric Fortune from the New Jersey Institute of Technology, a co-author on the study. “We think that’s also true for humans.” Because Cowan is a roboticist and most of the authors on this team are engineers, they hope to use the biological insight to build robots with smarter sensors. Sensors are rarely a key part of robot design now, but these findings made Cowan realize they perhaps should be. “Surprisingly, engineers don’t typically design systems to operate this way,” says Debojyoti Biswas, a graduate student at Johns Hopkins and the lead author of the study. “Knowing more about how these tiny movements work might offer new design strategies for our smart devices to sense the world.”