
The shrinking dimensions and decreased power consumption of modern electronic gadgets have created opportunities for energy harvesting processes that tap into free, green energy from the environment. Vibration harvesters, for example, produce small amounts of electricity from everyday mechanical disturbances such as wind currents, traffic noise or footsteps.
Now, Kui Yao and co-workers from the A*STAR Institute of Materials Research and Engineering in Singapore have discovered a way to give lightweight polymer vibration harvesters a hundredfold boost in energy output—a finding that may help to eliminate manual battery recharging in microsensors and mobile devices.
Many vibration harvesters contain piezoelectric substances that create an electric voltage when mechanically bent. By fabricating piezoelectric materials into cantilevers that resemble a diving board, these devices can oscillate from ambient vibrations and generate electricity. Researchers often use piezoelectric ceramics because they impart large amounts of electrical charges; however, the brittleness of ceramics makes them unsuitable for prolonged and large vibrational movements.
Yao and co-workers investigated a plastic-based piezoelectric material, polyvinylidene fluoride (PVDF), which is low cost and readily undergoes mechanical strain. To make efficient vibration harvesters from PVDF, researchers must stack the polymer in multiple layers, improving the output current and reducing the electrical impedance that is inherent to piezoelectric materials. But when too many thin piezoelectric layers are stacked, the cantilever can become too stiff for bending-mode vibrational harvesting.
To optimize piezoelectric harvesting with plastic films, the team deployed an analytical approach. Developing a mathematical model of a multilayered polymer cantilever coated with metal electrodes, the researchers systematically calculated how different material parameters affected the energy output.
Their simulations revealed some often-ignored factors "such as the thinness of electrode coatings and the material's electrical parameters," says Yao. "These can have a dramatic effect on the electricity generated by bending multilayer polymers."
One key parameter identified was the need to match the electrical impedance with an optimum load resistance. The researchers' analysis showed that the energy output of a 22-layered piezoelectric structure could be from 5 to 400 times higher than a single-layer piezoelectric polymer of similar dimensions.
The team then tested the feasibility of their analytical results by fabricating a PVDF-based vibrational harvester on a flexible aluminum substrate. They used scalable dip-coating procedures to build up polymer multilayers and ensured thin metal electrode coatings with physical vapor deposition techniques.
"Our experimental results are promising and show that, for many practical applications, piezoelectric polymer multilayers may enable harvested energy to replace batteries," notes Yao.
Explore further:
Vibration energy the secret to self-powered electronics
More information:
Zhang, L., Oh, S. R., Wong, T. C., Tan, C. Y. & Yao, K. "Piezoelectric polymer multilayer on flexible substrate for energy harvesting." IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control 60, 2013–2020 (2013). dx.doi.org/10.1109/TUFFC.2013.2786
MR166
More "free green energy" nonsense from the Ministry of Truth. The energy density of everyday noise is less than miniscule it is "picoscule".
antialias_physorg
You have two curves here:
Increasing efficiency of electronics (read: decreasing power consumption)
vs
Increasing efficiency of energy harvesting devices.
Yes, the power is very low from such devices, but if your power needs are also low (and getting lower) then the two curves will eventually intersect.
You're not going to heat your home with harvesters any time soon, but it may well be possible to power your phone.
MR166
antialias_physorg
Unlikely. Unless you are different than most people who carry their phones in some sort of pocket most of the time
MR166
MR166
24volts
antialias_physorg
Where are you going to put a solar cell? The side that is up is the screen. Unless you want to reduce screen size and make these bricks even bigger than they already are 8and you wouldn't want to use them in full sunlight in any case..the glare would make it hard to see anything)
MR166
You know we used to have a lot of fun with simple stuff when we were kids.