Cantilever bends repeatedly under light exposure for continuous energy generation

October 5, 2010 By Lisa Zyga, feature
(a) An illustration of the energy-harvesting cantilever device. (b) A photo of the cantilever. (c) An optical micrograph and SEM image of the CNF material. Image credit: Venu Kotipalli, et al. ©2010 American Institute of Physics.

( -- With the goal to enable small electronic devices to harvest their own energy, researchers have designed a device that can convert light and thermal energy into electricity. When exposed to visible light and/or heat (infrared) radiation, the 20-mm-long carbon-nanotube-film-based cantilever bends back and forth repeatedly, as long as the light and/or heat remains on. This is the first time that such cyclic bending behavior, which the scientists call "self-reciprocation," has been observed in this kind of system.

The researchers, led by Professor Long Que and including graduate students Venu Kotipalli, Zhongcheng Gong, and other students from Louisiana Tech University, have published a paper on the device in a recent issue of . In their experiments, they demonstrated that the device could generate 2.1 microwatts of power at a of 0.13 W/cm2, which is sufficient to operate some low-power microsensors and integrated sensors. The researchers predict that the power output could be significantly improved with further optimization.

“The greatest significance of this work is that it offers us a new option capable of continuously harvesting both solar and on a single chip, given the self-reciprocating characteristic of the device upon exposure to light and/or thermal radiation,” Que told

The 20-mm-long energy-harvesting device consists of a layer of film (CNF) placed on top of an electrode and a piezoelectric material called lead zirconate titanate (PZT). Since carbon nanotubes are excellent absorbers of photons, the CNF layer efficiently absorbs the radiation and causes the underlying PZT layer to bend. As a piezoelectric material (known for its ability to convert mechanical into ), the moving PZT layer generates power.

The impressive thing about the new device is that, once the cantilever reaches its maximum displacement under the radiation, the displacement decreases, then increases again, and continues this cycle as long as the radiation remains on. When the radiation is turned off, the displacement decreases to zero. As the scientists explain, the self-reciprocation is due to the cantilever continuously absorbing photons, as well as its high electrical conduction and rapid thermal dissipation into the environment. The self-reciprocation characteristic means that the energy-harvesting device has the ability to continuously generate energy without consuming other additional energy, such as for modulating the radiation.

“To the best of our knowledge, previous reported research mainly exploited and developed for DC displacement,” Que said. “We observed this self-reciprocation phenomenon in my lab by accident for the first time, and thereafter we did a series of systematic experiments and confirmed that this phenomenon always occurs not only in the lab but also in the field under sunlight. In order to better understand this observation and optimize the performance of this technology, further fundamental investigations have been underway in our lab.”

In the future, the scientists plan to investigate the contributions from the light and heat when the device is under illumination, although their observations so far indicate that the thermal portion is the major contributor. The scientists also anticipate that decreasing the device's internal resistance, and perhaps operating an array of devices, could improve the power output. The energy-harvesting device could potentially be used to power a wide variety of systems, from implanted biomedical devices to remotely located and communication nodes.

“I also would like to mention that, given the nature of the cantilever-based device, actually this technology can harvest additional multiple types of energies such as all types of vibrational energies and wind energy as well, which we have already experimentally demonstrated but not reported in this article,” Que said. “This technology is truly a hybrid energy-harvesting technology.”

Additional coauthors of the paper are Pushparaj Pathak, Tianhua Zhang, Yuan He, and Shashi Yadav.

Explore further: IMEC reports 40 microwatt from micromachined piezoelectric energy harvester

More information: Venu Kotipalli, et al. “Light and thermal energy cell based on carbon nanotube films.” Applied Physics Letters 97, 124102 (2010). DOI:10.1063/1.3491843


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5 / 5 (1) Oct 05, 2010
This may not sound like much, but it's a significant breakthrough that could well profoundly impact the design of many products. Specifically I'm thinking the design of very small spacecraft and consumer electronics, but this breakthrough isn't limited to those fields (over the very long term, anyway).
not rated yet Oct 05, 2010
Any efficiency figures ?
1 / 5 (1) Oct 05, 2010

It looks like the cantilever is about .5 x 2 = 1.0 cm2 from the picture, so:

(2.1 x 10^-6) W out / 0.13 W in = 1.6 * 10^-5

or .0016%

not rated yet Oct 05, 2010
What if you put the carbon on both sides of the PZT, stood the thing end-on to the light, and then let the cantilever bend back and forth under the alternating pressure from the two carbon layers? When the light bent the device one way, it could expose the other side to more light, causing it to bend back faster. Faster oscillations presumably means more power.

A single cantilever in this set-up might be less efficient than one laid flat under a light, but you could make a forest of them, and they wouldn't care so much about the direction the light is coming from.

However, they don't specify in the article which way the thing bends. I'd guess it's away from the light, not toward it, which is what would be needed for my idea to work at all. All these little lead-carbon sandwiches, doing their little crunches all day long....
not rated yet Oct 05, 2010
the forest would make a great back massager
not rated yet Oct 06, 2010
@Yogaman. Yes conversion efficiency looks pretty small but efficiency matters more when you've a fuel cost to be figuring in.
not rated yet Oct 07, 2010
Interesting, but why not just put a small solar panel on the device?

Generates Electricity under constant exposure to light.
Also way more efficient at it.
5 / 5 (1) Oct 07, 2010
Could miniaturizing and optimizing the device result in much higher efficiency? Sure. That is not the issue I see.

Did they really subject their toy to sunlight while in a Faraday cage to eliminate radio and microwaves? First, any man made light source they use is going to have a ripple. Simple incandescent lamps at 60 (well 120) cycles, a DC powered LED will probably have variations inherited from the switching power supply. Yes, the jitter will be a very small percentage of the light source, but it will be stronger than the amount of energy they are claiming to catch.

How big a problem is this? Huge. When I needed a stable light source many years ago, I finally ended up with an incandescent bulb hooked to a battery and with inductors on the pass through the Faraday cage, and a big capacitor inside. That finally got the noise below one part per million, and still had to correct for it in my data.
not rated yet Oct 07, 2010
What was I doing? Measuring the noise in two inch diameter photometer cells under low light conditions. Yes, I did get to the point where I could measure the 'noise' from individual photons. But it was tough. Why did I need to? The response curves of the cells was not smooth at very low intensities, and I wanted to be able to measure thousandths of a foot-candle acurately.

The result was a product that could be used inside a camera (well usually with the back open and the lens sticking through a light barrier). Aim at a uniform white field, and you can measure small deviations in light levels. (The best camera lenses tested had about a 4% variation across the field, mostly from square law falloff at the corners.)

Back to the constant light source. I tried bunsen burner and acetylene flames. Both made excellent microphones. In fact, it was amazing how good the microphone quality was. ;-)
not rated yet Oct 09, 2010
I love the fact that this one device can make electricity simultaneously from light, heat, vibration and wind.

With technological knowledge increasing at an exponential rate, perhaps in a couple years we will have the perfect energy chip that can be manufactured on a large scale and be priced well below oil and coal energy production.

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