New ultrathin device powered by everyday motion

Researchers in the US have created a new ultrathin energy harvesting system that can be powered by human motion.

The devices, based on battery technology, are made from layers of black phosphorous a few atoms thick. Potential uses for this technology could be electrified clothing, with applications including everyday use or virtual reality technology.

Harnessing low frequency motion

Professor Cary Pint, who led the research at Vanderbilt University, in the US, said: “Compared to the other approaches designed to harvest energy from human motion, our method has two fundamental advantages. The materials are atomically thin and small enough to be impregnated into textiles without affecting the fabric’s look or feel. It can also extract energy from movements slower than 10 Hertz (Hz) over the whole low-frequency window of movements corresponding to human motion.”

Extracting usable energy from such low frequency motion is extremely challenging. Currently scientists are developing energy harvesters based on piezoelectric materials; however these materials work best at frequencies of more than 100 Hz – meaning efficiency rates lower than 10% in ideal conditions.

The new devices created at Vanderbilt University, are calculated to operate at an efficiency of more than 25% in ideal conditions and are able to harvest energy though actions such as sitting or standing. When placed under tension, the voltage rises and under compression, it drops. The battery is constructed with both negative and positive electrodes made from the same material, so it is unable to store energy. However, it can take advantage of voltage changes caused from bending and twisting, producing significant amounts of electrical current.

Professor Pint said: “In the future, I expect that we will all become charging depots for our personal devices by pulling energy directly from our motions and the environment.” The devices, 1/5000^th the thickness of a human hair, can produce as much as 40 microwatts per sq ft and can create current through movements as slow as 0.01Hz. The research was published in ACS Energy Letters.