Researchers have created a prototype of a robotic insect that mimics a biological digestive system to meet its energy needs, uses the Janus interface to ensure a steady supply of nutrients, and is packed with sensors that move on the surface of the water like a water flea.
In 2017, DARPA proposed a program to develop and deploy thousands of floating sensors that would collect “environmental data such as ocean temperature, sea conditions, and location, as well as activity data on commercial ships, aircraft, and even marine mammals moving across the ocean.”
The project, dubbed the Ocean of Things (OoT), is essentially a smart device equipped with a large number of sensors that collect information from the Internet of Things (IoT). According to the project page, the sensor data will be uploaded to a government-owned cloud storage for analysis, and OoT will be open to research organizations and commercial interests while supporting military missions.
Binghamton University professor Seok-Heum Choi has been working on just such a device for the past decade, with funding from the Office of Naval Research. Now, Choi and his team have developed a tiny underwater robot that can skim across surfaces and is powered by onboard bacteria instead of conventional energy systems like solar, kinetic, or thermal.
“Researchers are actively pursuing a variety of innovative strategies to enable autonomous robots to harvest energy directly from the marine environment,” the team notes in their paper. “These strategies include harnessing solar power, kinetic energy from waves or currents, the osmotic potential of salinity, thermal gradients, and water-driven energy sources.
“Despite the innovative nature of this approach, the variable availability of light and mechanical energy in marine environments, combined with the relatively low energy yields from salinity gradients, thermal differences, and moisture levels, pose significant challenges. These limitations currently hamper the ability to ensure reliable and sustained operation of aquatic robots based solely on energy harvesting technologies.”
Binghamton University
The new system’s power plant is built around a microbial fuel cell that uses spore-forming bacteria. Bacillus subtilis Inspired by the biological digestion process, we developed a mini-generator that converts organic matter into electricity through a catalytic reduction-oxidation reaction.
“If the conditions are favorable for the bacteria, they become plant cells and generate power, but if conditions are not favorable—for example, if it’s too cold or there are not enough nutrients—they revert to spores,” Choi said. “That way, they can extend their operational lifespan.”
The anode of the fuel cell is made of carbon cloth coated with polypyrrole, chosen for its excellent conductivity and ability to support bacterial colonization. The electron-accepting cathode is also carbon cloth, but is decorated with platinum coated with polypyrrole, chosen for its “catalytic properties that accelerate oxygen reduction.” The final piece of the puzzle is the Nafion 117 membrane for selective proton transfer.
The integrated power plant also features adjacent hydrophobic and hydrophilic surfaces, allowing for a “unidirectional flow of organic substrate” from seawater to provide nutrients to the bacterial spores.
A single fuel cell setup managed “maximum power densities of 135 µW cm-2 and open-circuit voltages of 0.54 V,” but when scaled up to a six-unit array, power generation of nearly a milliwatt was observed. That output may seem relatively small in the grand scheme of things, but it’s more than enough for the small DC motors and onboard sensors atop the platform.
“To achieve smooth underwater locomotion, the robot uses the rotational force of the motors to apply a counterforce to the platform, propelling it forward across the water surface without exerting a direct force on the water itself,” the researchers explained. “The hydrophobic properties contribute to the main buoyancy.” The little robot’s legs are also treated with a hydrophobic coating, allowing it to glide across the water’s surface like a splash.
So the idea here is that rather than being tied to one location for its entire operational life, you can deploy small data collection devices wherever they are needed, whenever they are needed.
“While this study successfully demonstrated autonomous locomotion on the surface driven by an integrated MFC array, exploration of practical applications such as localization, sensing, signal processing, and transmission on an underwater robotic platform still requires development,” the team noted. Additional work should also be done on long-term performance and suitability for a variety of environmental conditions. However, the current system serves as a proof-of-concept for the new design.
The research paper was published in a journal. Advanced materials technology.
Source: Binghamton University
