Health Tech Insider publisher Alfred Poor wrote in 2015 that energy harvesting is key to wearable success. Alfred’s premise was that for wearables to be ultimately successful they had to “disappear into our lives.” If we need to replace batteries or plug in devices to charge them, after a while we’re likely to discontinue using them. When devices draw energy from self-supporting energy-harvesting technology, however, we’re more likely to continue with them. We’ve written about several types of energy-harvesting technology including yarn with embedded nanotubes, harvesting from air, the sun, and even from human knee movement.

Engineers from The Chinese University of Hong Kong (CUHK) working with finger-sized water tubes (WTs) have developed harvesting technology that converts low-frequency mechanical energy into electricity. The CUHK researchers published their research results in Advanced Energy Materials. The device relies on triboelectricity, which is energy generated when an object in contact with another moves or otherwise comes in contact with a different type object or material. As with rubbing a plastic comb with a piece of fur, we used to call this “static electricity.”

The CUHK engineers created tubes containing deionized water with different conductors at each end. When the tube is moved in any direction tiny waves of water move from contact with one conductor to the other. The mechanical water movement creates minute amounts of electrical energy. According to the CUHK engineers, it’s a simple matter to connect multiple water tube triboelectric nanogenerators (WT-TENGs) to form a larger integrated unit to generate more power. In one example of WT-TENG technology the researchers created a wristband with 10 WT-TENG units. When a team member swing her arms the devices created enough electricity to light 150 LED lamps.

It’s early yet to start designing water-tube garments to harvest user movement to power wearable devices, but the CUHK developments suggest interesting new approaches to create disappearing devices.