How many times have you been out when your phone dies at the wrong moment? The physical energy you use just by walking from A to B can be harvested and turned into electricity, and it could have applications well beyond keeping your phone charged. A new kind of wearable tech promises to power all sorts of devices worn on the body—like prosthetic limbs and maybe even, one day, an artificial exoskeleton.
Enter the triboelectric nanogenerator, or TENG. These devices, which have been around for a few years, use friction from movement to generate an electrical charge, a big step up from the usual bulky battery pack. The problem is that TENGs tend to be rigid, and unsuitable to wear with flexible electronics that are appearing on the market.
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On Friday, a research group in China and the US published a study in Science Advances showing the development of a “shape-adaptive” TENG that promises to move with all the twists and turns of a human body in motion. Its flexibility comes thanks to the use of a conductive liquid electrode and a flexible rubber casing.
These twisty TENGs are only in the prototype stage, but the results are already impressive. Wearing one on the foot enabled a user to light up a panel of LEDs with a simple rhythmic tap. The same can be said of a TENG worn around the wrist—when the wearer gives the bracelet a shake, enough juice is generated to power 80 of the bulbs.
Harvesting mechanical energy based on household plumbing, using flowing water as the electrode. Credit: Yi et al. Sci. Adv. 2016. GIF: Navi Lamba
“That’s the goal of our work for the last 10 years,” said ZL Wang, a professor at the Georgia Institute of Technology, whose lab led the research, to Motherboard in an interview. “We may not power the world, but we can power small things.” And “small things” can go a long way to improving a person’s life: one of the most obvious, and promising, applications of technology like this is in prosthetics. These devices increasingly employ electronics to sense and react to changes in environmental conditions. Some prosthetic legs with embedded electronics, for example, can sense and react to a change in the user’s gait.
“The idea is that during walking, we are giving off mechanical energy which can be captured,” Jan Andrysek, a professor at the Institute of Biomaterials and Biomedical Engineering at the University of Toronto, told me. Although he was not involved in this new paper, he led the development of a prosthetic leg that captures energy from knee movements. “We focused on capturing [energy] at the knee joint. But [TENG] could be more flexible, like capturing energy from the foot coming down.
“With the miniaturization of controllers, artificial limbs are now computer-controlled to monitor what the prosthesis is doing and modify it based on the requirements of a task. The benefit [of TENGs] would be that you don’t need to charge your prosthesis. If [users] don’t do that, they could become quite stranded.”
Further down the pipe is the holy grail of wearable devices: the robotic exoskeleton. DARPA, the US Army’s research arm, recently tested a “soft”, battery-powered exoskeletal device that connects bulky batteries to the suit via cables, lessening the load of heavy packs while soldiers are on the move. What if the weight of such an exoskeleton could be dramatically slashed with the use of lightweight, wearable power sources like TENGs?
Andrysek, who’s worked on exoskeletal devices, is hopeful, but cautious. Building your own Iron Man suit requires quite a bit more power than the moving body alone can provide. “[TENGs] might have a limited application,” said Andrysek. But we don’t know until we try.
The next step for Wang’s group is to address this issue by increasing the power output of flexible TENGs. One way to accomplish this might be to string a bunch of the devices together, which could “increase the power output,” he said.
Given that TENGs are so cheap to make—the ones used in Wang’s paper cost about 50 cents each—there’s reason to hope their effectiveness can be stepped up dramatically. A fully-powered exosuit might be on the market sooner than you think.
