24 July 2017
An ultrathin energy harvesting system developed at Vanderbilt University in the US is said to have the potential to power cell phones, fitness trackers and other electronic devices from movement, such as walking, waving and even sitting.
Based on battery technology and made from layers of black phosphorus, the device generates small amounts of electricity when it is bent or pressed.
“Compared to the other approaches designed to harvest energy from human motion, our method has two advantages,” said assistant professor Cary Pint.
“The materials are small enough to be impregnated into textiles without affecting the fabric’s look or feel and it can extract energy from movements that are slower than 10Hz over the whole low frequency window of movements corresponding to human motion.”
According to the researchers, extracting usable energy from such low frequency motion has proven to be extremely challenging. A number of research groups are developing energy harvesters based on piezoelectric materials that convert mechanical strain into electricity.
However, these materials often work best at frequencies of more than 100Hz. This means that they achieve limited efficiencies of less than 5 to 10% even under optimal conditions.
“Our harvester is calculated to operate at over 25% efficiency in an ideal device configuration, and most importantly harvest energy through the whole duration of even slow human motions,” Pint said.
The engineers found that bending their prototype devices produces as much as 40µW/ft2 and can sustain current generation over the full duration of movements as slow as 0.01Hz.
Applications include powering clothes impregnated with LCDs that allow wearers to change colours and patterns with a swipe on their smartphone.
Pint also believes there are potential applications for their device beyond power systems. “When incorporated into clothing, our device can translate human motion into an electrical signal with high sensitivity that could provide a historical record of our movements. Or clothes that track our motions in 3D could be integrated with virtual reality technology.”
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