The Sophisticated Threads behind a Hat That Senses Traffic Lights

By Payal Dhar

A team of electrical engineers and fabrics scientists has invented a hat that tells its wearer when it’s safe to cross the road. The researchers’ proof-of-concept beanie is knitted with germanium fibers that can sense changing traffic lights—and tell pedestrians with visual impairments when they’re clear to walk. This prototype shows how fibers with a semiconductor core can be woven into functional garments that gather, process and store information, and it may one day lead to computers that can be worn like clothes.

Fabricating conductive fibers that are flexible enough to use in clothing is no simple matter. Crystalline forms of the elements silicon and germanium—prized by the wearable electronics industry for their optical and electrical properties—must be encased in a protective cladding and then spun into durable strands. Previous attempts that used a process called thermal drawing could only produce strands that were typically too short (usually no longer than a few tens of centimeters) and left fractures or other disabling flaws in the cores. But now, for the first time, researchers have developed a method that creates long, flexible fibers with intact light-detecting and electronic properties—as the woven beanie proved. The team described these results in a recent study in Nature.

In a typical thermal drawing process, silicon is placed inside a glass tube and heated until both materials are soft enough to stretch into thin fibers. But “because the silicon and the glass outer jacket are totally different, when we heat them up, they will show completely different behaviors” in their ability to stretch, says the new study’s senior…