We've covered plenty of so-called human-powered devices on TreeHugger and they've all fallen into two categories: friction-powered (triboelectric) devices that harness the energy created from two materials rubbing together and piezoelectric devices that feature crystals that generate energy from being compressed or bent.
These devices have been used to generate electricity for charging gadgets, capturing energy from doors and sidewalks for powering lighting in stores and buildings and more, but MIT researchers say these devices have limits and aren't suitable for capturing energy from smaller scale human movements like walking or exercising, so they developed something new.
“When you put in an impulse” to traditional piezoelectric materials, “they respond very well, in microseconds. But this doesn’t match the timescale of most human activities,” said MIT professor Ju Li. “Also, these devices have high electrical impedance and bending rigidity and can be quite expensive,” he says.This new energy harvesting device uses an electrochemical process similar to that in lithium ion batteries to produce electricity instead of a physical process like the other piezoelectric materials, which will likely make it inexpensive to manufacture. It features two thin sheets of lithium alloys which act as electrodes sandwiched around a layer of porous polymer soaked in a liquid electrolyte. The device takes in mechanical energy and puts out electricity.
MIT says, "When bent even a slight amount, the layered composite produces a pressure difference that squeezes lithium ions through the polymer (like the reverse osmosis process used in water desalination). It also produces a counteracting voltage and an electrical current in the external circuit between the two electrodes, which can be then used directly to power other devices."
This ability to generate electricity from such small movements means this device could be embedded in wearable electronics that would be powered from everyday motions like walking and swinging your arm. It could also be used in biomedical applications and used to power stress sensors in roads, bridges and other structures.