Stanford’s stretchy wireless “BodyNet” isn’t just flexible in order to survive being worn on the shifting surface of the body; that flexing is where its data comes from.
The sensor is made of metallic ink laid on top of a flexible material like that in an adhesive bandage. But unlike phones and smartwatches, which use tiny accelerometers or optical tricks to track the body, this system relies on how it is itself stretched and compressed. These movements cause tiny changes in how electricity passes through the ink, changes that are relayed to a processor nearby.
Naturally if one is placed on a joint, as some of these electronic stickers were, it can report back whether and how much that joint has been flexed. But the system is sensitive enough that it can also detect the slight changes the skin experiences during each heartbeat, or the broader changes that accompany breathing.
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the skin sensor is powered by harvesting RFID signals, a technique that renders very little in the way of voltage.