Scientists Pave Way For Nano-Scale 'Self-Powered' Devices
Posted on: Thursday, 4 December 2008, 16:05 CST
Scientists at Texas A&M University have successfully doubled the efficiency of piezoelectric devices that gather energy from movement and vibrations.The work could mean that devices such as "self-powered" phones that charge when you speak into them are one step closer to reality.
The piezoelectric effect occurs in some ceramic and crystalline and materials. Stretching or compressing the materials causes a separation of electric charge across their width, which establishes a voltage.
The increased efficiency discovered by the Texas A&M engineers was made possible through altering the size of the device, using a narrow range of thicknesses around 5,000 times thinner than a human hair.
Piezoelectric materials have long been used in devices such as electronic lighters and microphones, where pressure from a thumb or a sound wave is harvested. Engineers even looked at using piezoelectrics to gather energy from footsteps or the motion of clothing. And many nightclubs even incorporate piezoelectrics into their dance floors, recycling a portion of the energy given by dancer.
However, the behavior of materials in comparatively large devices can dramatically change when reduced to the nanometer (billionth of a meter) scale.
Tahir Cagin and his colleagues at Texas A&M University found that when piezoelectric materials are constructed in a narrow size range around 20 nanometers a new “flexoelectric effect” is observed . This phenomenon produces a voltage from twisting and bending, instead of the uniform compression or stretching as in traditional piezoelectricity.
The researchers demonstrated that the effect can be maximized in nano-scale cantilevers, beams like tiny diving boards that generate a voltage, by customizing the cantilevers' shape.
The theoretical study showed that the effect could increase the amount of available energy, gram for gram, of piezoelectric materials by up to 300 percent.
Piezoelectric materials have been used for years in microphones and acoustic instruments. In these devices the pressure wave of sound or simple vibrations create a corresponding electric signal. The latest research may mean that such sounds and vibrations could now be used to produce substantially higher amounts of energy.
"Even the disturbances in the form of sound waves ... may be harvested for powering nano- and micro-devices of the future if these materials are processed and manufactured appropriately for this purpose," Professor Cagin told BBC News.
In other words, instead of the tiny electric signal produced in a microphone, piezoelectrics customized at the nano-scale could directly power small devices or even charge a battery.
The research was reported in the journal Physical Review B.
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Source: redOrbit staff
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