Researchers at the National University of Singapore (NUS) have developed a sensing electronic skin that functions underwater, detects nearby objects, senses physical contact, recognizes when it has been punctured or cut, and repairs itself after damage.
The technology, called a self-healing magnetoelectric sensory system (SMES), is an elastomeric, stretchable “skin” that combines touch and proximity sensing with built-in damage detection and autonomous self-repair, working both on land and underwater. The researchers demonstrated potential applications of the SMES via two prototypes: a smart diving glove divers can use to communicate wirelessly through hand gestures and an underwater robotic arm that can grasp objects.
Outside of space, one of the harshest conditions for sensitive electronics is beneath the waves. It's mostly frigid; water can seep through tiny gaps and short conductive paths; salt accelerates corrosion; and hydrostatic pressure increases with depth. That’s not all. Contact sensors face plenty of physical abuse as well, as they must scrape against rocks, shells, inhabitants of the sea, and submerged infrastructure. When something gets damaged or develops a fault, repairs typically require retrieval to the surface.
The SMES skin, detailed in the Advanced Materials journal, attempts to tackle every one of these problems, borrowing a thing or two from the OG, biological skin. Human skin detects touch, but can also alert us when it has been damaged and can repair itself afterward, albeit slowly.
The electronic version divides these jobs between stacked layers. At the top is a damage-sensing layer, the system's alarm system, if you like. It sits above a separate magnetoelectric layer responsible for touch and proximity sensing. Both are made using a soft, stretchable, self-healing elastomer containing patterned liquid-metal conductors. The liquid metal provides an electrical pathway that can deform with the surrounding rubber-like material instead of snapping when the skin bends or stretches.
The system works layer by layer, starting with its damage-sensing abilities. When the material (upper layer) is punctured, the damage interrupts the conductive pathway and causes its electrical resistance to spike. That spike serves as an electronic equivalent of a pain signal, informing the system that an injury, as opposed to an ordinary touch, has occurred. Keeping this layer physically separate from the ordinary sensing layer helps the device distinguish routine contact from an actual injury.
“In our bodies, pain is a protective alarm. It tells us when something is wrong so we can respond before more damage is done,” said project leader Assistant Professor Tan Yu Jun. “Our work gives underwater electronics that same capability, enabling devices to sense injury and begin healing autonomously.”
Once damage occurs, the elastomer begins putting itself back together. The repair mechanism lies in the elastomer’s chemistry. Its molecular network contains reversible interactions that can break when the material is damaged and reconnect when the torn surfaces are brought back together. During tests, small punctures restored their original electrical performance within seconds without external intervention, while larger cuts required the damaged faces to be pressed together briefly to start the repair, after which the material continued healing over a longer period.
The elastomer achieved up to 92% elastic recovery. With mild heating, it reached approximately 82% healing efficiency in air after seven days and almost 100% underwater after 10 days. Interestingly, it healed more completely underwater, an environment in which many adhesives and self-healing materials struggle because water interferes with bonding between exposed surfaces.
Beneath the damage layer lies the system responsible for actually feeling its surroundings. Inside the lower layer, a small magnet sits beside a coil made from liquid-metal wiring. Pressure on the surface, or movement near the sensor, shifts the magnet relative to the coil. The changing magnetic field induces a voltage in the conductor, the same basic electromagnetic induction principle used in electrical generators.
In tactile mode, contact pressure displaces the magnet. For proximity sensing, relative movement between the magnet and coil produces a signal before physical contact occurs. The latter could be particularly useful for soft robotic grippers. Rather than blindly closing until they collide with an object, they could detect its approach and adjust their movement before making contact.
In tests, the sensor responded in about 41 milliseconds and continued producing stable signals after 10,000 operating cycles. Its proximity-sensing performance also remained consistent after 10 days of immersion, including tests in simulated seawater. These results establish durability in a laboratory setting, although they do not yet demonstrate indefinite service in the harsh conditions of the deep. Recall that both the damage-detection layer and the sensing layer are made from the same self-repairing material.
Now, because motion itself produces the signal, the sensing element does not need an external power supply to register touch or proximity, hence the “self-powered sensing” designation. However, other electronic components of the system still need power. The self-powered sensing eliminates the need to energize the touch sensor itself continuously.
To show what the technology could do outside a material test rig, the researchers incorporated the skin into a smart diving glove. Sensors fitted to the fingertips produced different voltage patterns as the wearer formed different gestures. The glove’s electronics then transmitted the corresponding message over Bluetooth to a smartphone.
The team programmed five gestures representing “Normal,” “Going up,” “Going down,” “Holding,” and “Help.” This could give divers a simple way to communicate status information without speaking, writing, or frantic underwater charades. Red LEDs on the glove also illuminated when the damage layer detected a serious injury.
The second prototype was a robotic hand designed for underwater grasping and delivery tasks. Its SMES covering allowed it to pick up and transport objects while monitoring punctures caused by sharp shells. Three LEDs acted like a traffic-light health display: green indicated normal operation, yellow identified minor damage eligible for rapid self-repair, and red warned of severe structural damage requiring intervention.
With further development, the material could give underwater robots a far more resilient sense of touch. Beyond gloves and robotic grippers, the researchers envision the technology being incorporated into soft robots, prosthetics, wearable devices and other human-machine interfaces. An underwater inspection robot, for example, could feel its way along a pipeline, detect nearby obstacles, recognize when its outer surface had been pierced and potentially restore the damaged sensor without being hauled immediately back to the surface.
For now, the technology is still at the prototype stage. The tests demonstrate the underlying sensing and healing mechanisms, not a finished skin ready to spend years clinging to a deep-sea robot. Major cuts still require the surfaces to be pushed together, and full healing can take days. Real-world systems would also need all their supporting electronics to survive the same environment.
Source: NUS
