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Sound Harvesting

Has anyone heard of sound harvesting?
I think you’ll be hearing a lot about this in the future

Nanotechnologist Tahir Cagin, a professor at of Chemical Engineering at Texas A&M University published an article with his colleagues this fall in “Physical Review B,” the scientific journal of the American Physical Society. It deals with a breakthrough he made that could lead to cell phones with no conventional batteries; powering themselves using energy harvested from sound. No more plugging in your phone to charge it overnight, it gets charged by using it. Could this be a real possibility or is it just a ploy to make us go over our cell minutes?

I can see it now…”Hello Jay, How’s it hanging?….No, nothing’s new, I’m just calling cause my phone needs charging…”

As far as I can tell, this does seem plausible (the breakthrough, not the ploy)

Cagin’s breakthrough involves a very cool class of materials called piezoelectrics. Piezoelectrics (usually crystals and ceramics) generate an electric potential when they experience mechanical stress like stretching, bending or twisting. This happens because the stress in the material separates the charge across the material’s width which sets up a voltage that can be put to use. I’m not sure how this occurs at an atomic level. If anyone knows, please let me know. Conversely, piezoelectrics also change their physical properties in the presence of an electric field.

This phenomenon isn’t new, it was discovered in the 1880s by French scientists. They were used first in sonar during World War 1. Today you can find them in quartz watches, microphones, and car cigarette lighters. Do they even make those anymore?

There’s even a night club in Europe that has piezoelectrics under the dance floor that are used for power generation from people walking and dancing.

One problem with these materials is that they’ve been impractical. They produce a nice amount of voltage or pure electric charge, but not much current which is the directed charge that powered devices depend on.

What Cagin discovered is a specific performance sweet spot for a piezoelectric ceramic.
As Cagin says: “We have demonstrated that when you go to a particular length scale – between 20 and 23 nanometers – you actually improve the energy-harvesting capacity by 100 percent.”
A nanometer is a billionth of a meter
To give some perspective…The basketball player Shaquille O’Neal, is 2,160,000,000 nanometers tall.
I hope that helps

Presumably, the idea would then be that you’d have thousands of these tiny buggers in your cell phone, harvesting energy from sound you make or perhaps even ambient sound. This energy would then be transferred to the cell-phone’s battery to run the device.

Other applications could include harvesting the energy of tiny pressure changes or miniscule body movements to power laptops or even drug delivery devices and sensors that are in our bodies.

One of the take homes from this that I feel strongly about is that this is a great example of how little we really know about the nano-scale. We’ve learned much in the last few decades but it is still primarily an undiscovered country. We’re not at the point where we could have predicted that at 21 nanometers this material would double its efficiency. That’s why basic science research is so important. Basic research in nanotechnology is especially important because the nano realm is so unknown and offers so much potential (so to speak :-) ).

8 comments to Sound Harvesting

  • RevWubby

    I’ve seen various other ideas like this that attempt to capture some energy from daily life and use it for electrical power. The dance floor, or people in a subway for lights, or cars on the road for traffic lights.

    One flaw in all of these is that the energy isn’t free. It never is. The surface used to “capture” the mechanical energy is different than it would normally be constructed. That captured energy is taken from the dancers bounce, the walkers stride or the cars momentum. They must then use a little more energy to recover that. Dancers and walkers would have to use more calories, and the car would use more gas.

    Does the net difference really mean less energy used, OR does it simply shift the burden of that energy cost?

    The battery-less phone would need to capture some of that sound energy, which means it couldn’t be used as sound anymore. Sure, maybe only a little is subtracted, but how does that effect the service? Will that lost sound need to be accounted for and the voice amplified somewhere else, and therefore require an addition of energy use?

    Conservation of Energy: It’s the Law!

  • That is cool, but…

    Wouldn’t you get orders of magnitude more energy by using a similar mechanism to the one in self-winding watches? How much energy is contained in your voice versus the kinetic energy the average cell phone is subjected to while being carried around on your Utility Belt?

  • People will be holding up their cell phones at concerts for a new reason.

  • IPVlazy

    This is very interesting. I do believe that nanotechnology has a large part to play in the future of technology as things get smaller and smaller.

  • This sounds fishy to me. Transducers (i.e. speakers/microphones) are extremely inefficient unless built into a horn or some other impedance matching resonator. For example, a 3 inch, direct radiator loudspeaker can fill a room with an extremely loud sound, using only 1 watt of electrical power.

    Assuming this speaker is 5% efficient (not a terrible guess for a pretty efficient speaker), that means loud acoustical levels are on the order of 1 W * 0.05 = 50 mW.

    Now, just reverse the situation. Say a person is talking REALLY LOUDLY, filling the room with the equivalent sound of 1 W going into a 3″ loudspeaker. That’s a sum total of about 50mW that could be harvested, if the device captured 100% of the sound that emanated from your lips! Of course, when you take into account the efficiency of the piezo collector (say 5% of impinging energy, or 10% with the new nano piezo), and an average of 15% of sound actually impinging the sensor (you are holding this thing some distance from your mouth, right?), the energy to be captured becomes pretty small. 50mW * .1 * .15 = .75 mW.

    A CR2032 button cell will deliver .75 mW for 40 days. A single AA Ni-MH battery will deliver 0.75mW for 4.4 months.

    A GSM cell phone transmits at either 1 or 2 watts at maximum power.

    The backlight on your phone requires about 60mW.

    I think I’ve been pretty generous in estimating 0.75 mW — I suspect reality is an order of magnitude less. The 100% efficiency improvement seems kind of useless at that point.

    Maybe this would be useful for some devices that need to sit for years. in a noisy environment. Perhaps very-short-range spy microphones to listen on your incredibly loud mother-in-law.

  • Just a slight edit to the previous post: A 100% efficiency boost is great if what you need to do is *almost* possible already with typical piezo transducers. Cell phones are nowhere near that limit.

  • fredeliot2

    During WWII the military had voice powered telephones using moving magnets in a coil. I wonder what could be done using today’s technology. Although you might not get as small you probably would be more efficient. It could be another application for nano-technology. I doubt that a sound harvesting cell phone will be practical but a watch might be.

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