Picture a health-monitoring patch you wear like a tattoo and that doesn’t need a battery.
That’s the idea behind a demonstration by John Rogers, a stretchable electronics pioneer at the University of Illinois at Urbana-Champaign, whose lab created a stretchy skin patch that uses light pulses to monitor heart rate or sun exposure.
But the gadget doesn’t have a battery. Instead, it’s powered by a cell phone or tablet that’s equipped with a near-field communications (NFC) chip, the kind that’s used in apps like Apple Pay or for sharing photos between phones. That is, radio signals from a phone actually power the device and let it transmit information.
Rogers says it means health-monitoring gadgets could be cheaper, smaller, and more lightweight than ever before.
Rogers is a specialist in “epidermal electronics,” and he’s come up with a variety of devices that integrate LEDs, tiny bits of electronics, and sensors onto stretchy materials where they’re wired up with spring-like metal wires.
His latest creation, described today in the journal Science Advances, puts together several of these innovations. For instance, one sensor uses light-sensitive dyes to measure exposure to ultraviolet light—a feature also found in the first product developed by Rogers’s startup, Lexington, Massachusetts-based MC10. The company’s My UV Patch is being marketed by cosmetics giant L’Oreal and also uses dyes to monitor UV exposure.
This new device also measures heart rate and blood oxygenation using four LEDs to shine different colors of light into the skin. Changes to the color of the reflected light is picked up by photodetectors. A person’s heart rate is displayed as a flashing light.
A drawback of this system is that to power the device, the wearer must be within a few centimeters of a cell phone or tablet—or within a meter of a long-range NFC reader. But most of us are never much farther from our devices anyway.
The need for a battery adds a millimeter or two of thickness to one of MC10’s other products, the BioStampRC, a device sold to researchers who want to monitor people’s health signs and biomechanics while they are on the go. Rogers says new battery-free designs could open up new applications in hospitals and sleep monitoring.