A Fabric That Delivers the Juice You Need

Concern and speculation about battery life had been building for months before yesterday’s launch of the Apple Watch. Up to a few days ago, when information started leaking in advance of the device’s release, rumors were flying that it wouldn’t last through a day’s normal usage before needing to be recharged.

The good news for Apple enthusiasts is that the company seems to have pushed energy efficiency to the point where the watch won’t bow out before the sun goes down. But what if this wearable tech, or the myriad others coming down the pipe, didn’t ever need to be plugged in to get its electron tanks topped off? What if the device could get what it needed by harvesting the energy in a user’s movements?

We’ve reported on a number of projects whose goal is to make generators that take advantage of the triboelectric effect, an electrical phenomenon where two different types of materials create a charge when they rub together. Imagine capturing the hundreds of volts generated when you walk across a carpeted floor in sneakers and throwing it into your phone battery for later use.

Now researchers in South Korea and Australia say they have built an energy-generating cloth that uses the triboelectric effect to generate power for wearable electronics.

Starting with a silver-coated, weaved textile, they were able to grow zinc oxide nanorods on the cloth, which they then coated with a common type of silicone. This process left a flexible, foldable cloth that could also generate steady current when rubbed together. In lab tests their so-called wearable triboelectric nanogenerator (WTNG) delivered 120 volts at 65 microamps.

(a] schematic of WTNG. b] fabrication process. c] Electron microscopy images of the WTNG textile. d] The flexible, foldable WTNG. Image courtesy of Seung et al./ACS Nano.)

When the textile was stacked into four layers, it output 170 volts at 120 microamps when compressed under normal force and rubbed together. This was enough to power six LEDs, a small liquid crystal display and a remote control used for keyless vehicle entry. They also put the WTNGs through wear testing and found no significant differences in output over the course of 12,000 cycles.

“We successfully demonstrated the self-powered operation of LEDs, the LCD and the keyless vehicle entry system only with the output power of our WTNG without any help from external power sources, which proves potential applications of WTNGs in self-powered smart clothes, healthcare monitoring and self-powered wearable devices, and even personal electronics,” the authors of the paper published recently in the journal ACS Nano wrote.

Top Image: Self-powering of commercially available LEDs, an LCD, and a remote control keyless vehicle entry system in a self-powered smart suit using the WTNG. Courtesy of Seung et al./ACS Nano.