The Power of Touch
Battery-free, on-skin user interfaces can be developed using a system called Skinergy that is inexpensive and adaptable to many use cases.
On-skin user interfaces, often taking the form of smart tattoos or temporary electronic patches, have garnered significant attention due to their potential for transforming the way we interact with technology. By utilizing conductive ink or other miniature electronic components, these interfaces enable seamless communication between the human body and external devices, opening up a whole new realm of possibilities for a number of applications.
One of the primary benefits offered by on-skin user interfaces is their ability to provide convenient and discreet access to digital information and control mechanisms. By placing interactive elements directly on the skin, users can easily monitor their health metrics, such as heart rate, blood pressure, or even receive notifications from their smartphones. Moreover, these interfaces can be personalized to cater to individual preferences and styles, allowing for a unique and personalized user experience.
However, despite their promising capabilities, the practical adoption of on-skin user interfaces faces significant challenges. The reliance on batteries for power adds to their bulk, and the frequent need for recharging limits their usability, making them cumbersome and impractical for widespread use. As a result, while the concept of on-skin user interfaces holds immense potential, significant advancements in present technologies are required to address the current limitations and make them more feasible for everyday use.
A group of researchers at the Hybrid Body Lab of Cornell University have recently put forth an idea that may help to address this problem. They have developed an on-skin sensing system that they call Skinergy. These input devices are machine-embroidered silicone-textile composites that produce their own electricity by harvesting it from mechanical energy. This eliminates the need for a battery, however, it is important to note that Skinergy is an input device only — capturing and processing that data will require additional hardware, and likely batteries, but this work is still a step in the right direction.
The team’s primary innovation centers around their clever use of a triboelectric nanogenerator (TENG) embedded in the skin patch to convert mechanical energy to electricity. When it comes to energy harvesters, questions always arise about how reliably they will be able to produce enough power for a device’s operation. In this case, that is of little concern because the energy is harvested from interactions with the skin patch itself. For example, the act of pressing a button supplies sufficient energy to register that it was pressed. Aside from eliminating worries about generating sufficient power, this approach also eliminates the need for a battery that can store energy for later use — energy is always produced exactly when it is needed.
The Skinergy prototypes were made from inexpensive and readily-available materials via a process that is easy to customize for different use cases. Producing TENGs typically requires expensive equipment and materials, but the researchers proved that they could achieve sufficient performance for their purposes using such materials as conductive thread, silicone rubber, and interactions with human skin.
A custom sensing board, with a Seeed Studio XIAO nRF52840 microcontroller unit at its heart, was produced to process data from Skinergy patches (yes, this board required a battery for operation). A Skinergy patch, with a grid of touch sensors, was wired to the sensing board for interpretation. A number of demonstrations were then carried out showing how the device could be used to detect simple touches, multi-touches, and even more complex gestures as a finger interacted with the patch. After defining a set of eleven gestures, it was found that they could be correctly identified in 92.8% of cases.
Looking ahead, the researchers intend to investigate the possibility of harvesting energy from other sources and storing it, perhaps with a supercapacitor, to provide power from the sensing board and make the entire system battery-free. They also plan to try to reduce the manufacturing time for each device with the hope that this will allow for the wider adoption of on-skin devices.