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From BBC News | Science & Environment | UK Edition:
Engineers have doubled the efficiency of piezoelectric devices that harvest energy from movement and vibration.
The trick lies purely in the size of the devices: a narrow range of thicknesses around 5,000 times thinner than a human hair.
The result means that "self-powered" devices, such as phones that charge when you speak into them, are one step closer to reality.
The research was reported in the journal Physical Review B.
The piezoelectric effect occurs in some crystalline and ceramic materials. Stretching or compressing them causes a separation of electric charge across their width, and that sets up a voltage that can be put to use.
Such piezoelectric materials have been in use for years in devices such as electronic lighters and microphones, where pressure from a thumb or even a sound wave is harvested.
More recently, plans to engineer piezoelectrics that collect energy from footsteps or the motion of clothing have made it to the drawing board. Several clubs even incorporate piezoelectrics into their dance floors, recycling a small part of the energy imparted by clubgoers.
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