Flexible plastics that turn mechanical vibrations into electrical energy

Apr 09, 2014
Flexible plastics that turn mechanical vibrations into electrical energy
A ‘green’ alternative to batteries that could power electronic devices is one step closer thanks to multilayered polymer cantilevers that can turn mechanical vibrations into electricity. Credit: Eyematrix/iStock/Thinkstock

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 —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 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 , 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, 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

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MR166
not rated yet Apr 09, 2014
"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."

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
5 / 5 (1) Apr 09, 2014
More "free green energy" nonsense from the Ministry of Truth. The energy density of everyday noise is less than miniscule it is "picoscule".

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
not rated yet Apr 09, 2014
Anti a solar cell mounted on the phone would provide 10x more power. There is some application somewhere for a device like this but to classify it as free green energy is hyperbole.
antialias_physorg
5 / 5 (1) Apr 09, 2014
Anti a solar cell mounted on the phone would provide 10x more power.

Unlikely. Unless you are different than most people who carry their phones in some sort of pocket most of the time
MR166
not rated yet Apr 09, 2014
Anti I did think of usage. You also have to consider the power generating parameters of the 2 devices. A device that uses ambient vibrations would generate powers in the nano or micro watt range. A solar cell would generate power in the milliwatt range in use or out of a pocket. In reality neither of these are real solutions for cell phones.
MR166
5 / 5 (2) Apr 09, 2014
Off the top of my head I can think of one good use for personal motion/vibration power sources. When the government implants ID chips in you, a power source could greatly increase their tracking range.
24volts
not rated yet Apr 09, 2014
I know it's silly but the first thing I thought of after reading the article was a playing card clamped on a bike frame with a clothespin vibrating in the spokes like we used to do as kids to pretend we had engines on them. Only now you can have the engine sound and run a headlight at the same time! :)
antialias_physorg
not rated yet Apr 10, 2014
Anti I did think of usage

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
not rated yet Apr 10, 2014
I know it's silly but the first thing I thought of after reading the article was a playing card clamped on a bike frame with a clothespin vibrating in the spokes like we used to do as kids to pretend we had engines on them. Only now you can have the engine sound and run a headlight at the same time! :)

You know we used to have a lot of fun with simple stuff when we were kids.