Engineers from the University of Glasgow have developed an electronic skin which could help create a new generation of smart robots.

By using a new type of processing system based on synaptic transistors that mimic the brain’s neural pathways, the e-skin can learn by reacting to external stimuli.

Previous methods to develop e-skin with human-like sensitivity have focused on using pressure sensors to inform it when it touches an object. A computer then interprets the information, a time-consuming process that reduces reaction time, making the skin unsuitable for real-world tasks.

To eliminate this latency, the Glasgow team’s e-skin draws inspiration from how the human peripheral nervous system interprets signals from skin.

The human peripheral nervous system begins processing information from our skin at the point of contact. This filters out irrelevant data, sending only vital signals to the brain. Reducing sensory data makes more efficient use of communication channels, which then responds almost immediately.

To build this e-skin, Glasgow researchers printed a grid of 168 synaptic transistors made from zinc-oxide nanowires directly onto the surface of a flexible plastic surface. Then, they connected the synaptic transistor with the skin sensor present over the palm of a fully articulated, human-shaped robot hand.

When the sensor is touched, it registers a change in its electrical resistance – a small change corresponds to a light touch, and harder touch creates a larger change in resistance.

By adding a circuit to the actual skin, the input is simplified to a spike of voltage whose frequency varies according to the level of pressure applied to the skin, speeding up the reaction process.

In addition, the team used the varying output of that voltage spike to teach the skin appropriate responses to simulated pain, which would trigger the robot hand to react. By setting a threshold of input voltage to cause a reaction, the team could make the robot hand recoil from a sharp jab in the centre of its palm.

In other words, it learned to move away from a source of simulated discomfort through a process of onboard information processing that mimics how the human nervous system works.

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Professor Ravinder Dahiya from the University of Glasgow’s Bendable Electronics and Sensing Technologies (BEST) Group, who led the project, said: “We all learn early on in our lives to respond appropriately to unexpected stimuli like pain in order to prevent us from hurting ourselves again.

“Of course, the development of this new form of electronic skin didn’t really involve inflicting pain as we know it – it’s simply a shorthand way to explain the process of learning from external stimulus.

“What we’ve been able to create through this process is an electronic skin capable of distributed learning at the hardware level, which doesn’t need to send messages back and forth to a central processor before taking action. Instead, it greatly accelerates the process of responding to touch by cutting down the amount of computation required.”

In addition to creating more reactive robots, the e-skin research field could help enable avatar technology. This would allow a human to control a robot in remote locations and receive information as if they were physically there.

However, this would require low latencies and the ability to interpret a vast variety of stimuli, such as pressure, temperature, and texture.

Fengyuan Liu, a member of the BEST group and a co-author of the paper, added: “In the future, this research could be the basis for a more advanced electronic skin which enables robots capable of exploring and interacting with the world in new ways, or building prosthetic limbs which are capable of near-human levels of touch sensitivity.”

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