While wearable health sensors are becoming more common, current iterations are uncomfortable to use. For example, devices attached to the face can attract unwanted attention, increase self-consciousness, and affect the very signals that users are trying to measure. However, recent research may have found a solution to these problems by introducing ultra-thin sensors that are not visible to observers or felt by the user.
In an article recently published in Advances in Scienceresearchers from the Institute of Industrial Science, the University of Tokyo and partner institutions have reported the development of thin, elastic skin electrodes that are virtually invisible when worn on the face. The new technology can measure biological signals while remaining undetectable to the eye and touch, allowing monitoring to take place under more natural conditions.
Biosignals such as eye movements, facial muscle activity, and brain activity provide valuable information for healthcare monitoring and human-machine interaction. However, conventional facial electrodes can change a person’s appearance and affect social interactions, creating what are called appearance artifacts—changes in behavior or psychological state caused simply by wearing a device that can be seen by the person and others.
To truly integrate wearables into everyday life, they need to fade into the background. People should be able to wear sensors without feeling watched, judged or uncomfortable.”
Naoji Matsuhisa, senior author
The new electrodes achieve this by combining several design features, including an ultra-thin elastic film about 200 nanometers thick and transparent conductive nanowires. The resulting device closely matches the look and texture of natural skin, reducing reflections and eliminating the glossy appearance that often plagues wearable electronics.
“In our experiments, neither users nor external observers could reliably detect the electrodes by sight or touch,” says lead author Yijun Liu. “The devices remain comfortable and breathable during use and work on a wide range of skin tones and features.”
It is important that the electrodes still perform their intended function. The team successfully recorded electroophthalmography signals from eye movements, electromyography signals from facial muscles, and electroencephalography signals from brain activity using these electrodes. For several signal types, the signal quality was measurably better than that obtained using conventional gel electrodes, due to the lower skin resistance.
“By making wearable electronics that are both fully functional and effectively invisible, we move one step closer to a future in which health monitoring and human-machine interaction are seamlessly integrated into everyday life,” observes Matsuhisa.
The team believes that future applications of their sensor could include fine-grained monitoring of emotional state and cognitive function, as well as new ways of controlling virtual reality devices or systems using eye movements and facial expressions. More broadly, invisible sensors like these could help create a future in which technology seamlessly adapts to people, rather than the other way around.
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