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Graphene Thermoacoustic Speakers

09/08/2016 10:47 AM

https://www.theengineer.co.uk/video-of-the-week-graphene-moves-speakers-out-of-the-box/?cmpid=tenews_2612037

I think this will be a breakthrough in many sound (not any unsound) applications.

On the other hand, I wonder has any effect ever been discovered where incident sound energy has been so sharply focused or intense enough to heat an object? Not that I would want an orchestral arrangement playing be used to heat up my pizza in a graphene speaker oven.

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#1

Re: Graphene Thermoacoustic Speakers

09/08/2016 11:43 AM

It's my understanding that the graphene is heated by the electrical current and in turn heats the surrounding air. The graphene film has a very low heat capacity and so heats and cools quickly enough to expand and contract the surrounding air and generate sound.

I wouldn't have thought that was possible.

https://www.chemistryworld.com/news/graphene-speaks-volumes-/5467.article

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#2

Re: Graphene Thermoacoustic Speakers

09/08/2016 12:41 PM

A massless speaker without the ozone, interesting.

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#4
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Re: Graphene Thermoacoustic Speakers

09/08/2016 1:43 PM

Ozone? Your speakers make ozone? Tell me more...

Aerogels have some mass, just not very doggone much mass.

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#6
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Re: Graphene Thermoacoustic Speakers

09/08/2016 2:21 PM

A plasma speaker makes ozone. [Click the image for the DIY article instead of the Wikipedia link.]

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#7
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Re: Graphene Thermoacoustic Speakers

09/08/2016 2:23 PM

Nice.

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#3

Re: Graphene Thermoacoustic Speakers

09/08/2016 1:13 PM

Too bad one of the uses of graphene isn't producing large sheets of graphene....or is it?

https://thefisheriesblog.com/2012/08/05/small-things-can-make-a-big-difference/

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#5
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Re: Graphene Thermoacoustic Speakers

09/08/2016 1:45 PM

Average citizen (Joe or Jane) will not see these speakers any time soon, unless any time soon includes mass production of graphene transfers to aerogel.

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#8

Re: Graphene Thermoacoustic Speakers

09/08/2016 2:57 PM

"... I wonder has any effect ever been discovered where incident sound energy has been so sharply focused or intense enough to heat an object? ..."

Certainly. Ultrasonic welders are used on plastics. You might also be interested in SASERs

.

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#9
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Re: Graphene Thermoacoustic Speakers

09/08/2016 4:19 PM

Thank you for that. I have been interested in phonon effects for a couple years in my spare time, such as phonon cells, electric cells that recharge using a source of heat. The heat is not intense, as 60-120 °C seems to be the limits of what I can do with the common crystals I have been experimenting with. Lowest output impedance of any device I made was 3 Ω for a short time, then it went up gradually. Open circuit voltage for some is less than 1 Volt, but some are near 1.6 V. As you can imagine, there are fabrication issues to overcome in a home, backyard shop as laboratory. At least purity requirements are no where near as strict as in typical semiconductor work.

I do not know how a SASER could help my research, but what if I had access to a tunable SASER to expose the phonon cells to? Suppose resonances were found, where the phonon cell current (short-circuit or nearly so) would increase by an order of magnitude? Very interesting.

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#10
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Re: Graphene Thermoacoustic Speakers

09/08/2016 4:52 PM

That sounds very interesting. So are you describing ferro electric crystals or perhaps pyroelectric crystals?

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#11
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Re: Graphene Thermoacoustic Speakers

09/08/2016 5:05 PM
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#13
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Re: Graphene Thermoacoustic Speakers

09/09/2016 10:16 AM

https://en.wikipedia.org/wiki/Pyroelectric_fusion

https://en.wikipedia.org/wiki/Zinc_oxide

https://en.wikipedia.org/wiki/Pyroelectricity

http://www.chem.uh.edu/people/faculty/Halasyamani/

Very interesting stuff!

Phonon cells do not exhibit such high potentials, do not operate between such low temperatures and slightly above room temperature, as such. I have not tried single crystals (mixed materials) coupled together with dissimilar crystals, but always have done with simple powder mixes. The voltage of the phonon cell is strictly DC, but I have learned that the cells discharge with a time constant that is slower near room temperature under applied load resistor. At higher temperatures, the lower voltage during applied load rapidly assumes a constant value, and represents a much higher load current.

Heat (up to some temperature limit) is sufficient to "recharge" a phonon cell to full open circuit voltage. Pyroelectric materials lose their potential with a decay constant at the upper temperature, as I understand the topic, and the cycle may be repeated by alternate cooling and heating. Very interesting. Suppose this could be incorporated into aerogel, such that the cycle time of heating and cooling could be accelerated? What would be the result? I don't know. It might not match the characteristics of what the crystals need to be effective generators. I did see one part of an article that mentioned electric efficiency greater than 60%, so that is of interest.

pyroelectricity and ferroelectricity are broad subject, and much research will continue to be forthcoming on these, I suspect. Of particular interest to me would be to somehow be able to fabricate a device that utilizes low grade waste heat, but would not have the requirement to be cooled down so low in order to repeat the generating cycle.

I would even settle for one where the lower temperature was above room temperature somewhat, and the upper temperature could be called downright hot.

Is there a way to combine phonon cell effects with pyroelectric crystals to get a completely unique power supply? I do not know. I suspect there would be issues getting that work all in one device. Sure easy to make one of this and one of that, and use them somehow in tandem, but I suspect the pyroelectric cells would way outperform the phonon ones....

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#14
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Re: Graphene Thermoacoustic Speakers

09/09/2016 10:33 AM

Not directly. What I am referring to is a mixture of crystalline materials (as powders) pressed between two dissimilar metal plates or wires or cylinders, such that the more active metal becomes the anode. Phonons in the crystals result in charge carrier transfers between the valence band of one crystal type and the conduction band of another, so potential develops similar to the galvanic potential of the two metals, and current is from energy band transfers. At room temperature of 0-25 °C, the open circuit voltage will be ~1.5 for the "good" combinations, but the current will be probably less than 1 mA at short circuit. At temperatures around 70-90 °C, current at short circuit can be over 100 mA for a short time, then it might drop off.

A lot more research on phonon cells needs to take place. I am certain that crystal combinations will be found where the Fermi energies are much more favorable, and the electrodes will be more "reversible", and still produce higher open circuit values, without having to protect the anode from oxidation by air.

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#16
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Re: Graphene Thermoacoustic Speakers

09/09/2016 10:43 PM

Interesting. Am I understanding correctly that this is distinguished from thermoelectric effect in that the change in temperature does not require a gradient specific to the dissimilar metals, i.e. this isn't about keeping one end hotter than the other, right?

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#17
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Re: Graphene Thermoacoustic Speakers

09/12/2016 9:32 AM

I am not too sure. So far, phonon cell research could be said to be in infancy, and I seem to be drifting quickly toward second childhood.

Alum is one of the mainstays used in this line of study. I suppose Alum crystals are lacking a center of symmetry. I have always studied these systems with a mixture of inorganic salts and oxides. There can certainly be better choices, and much better ways of laying down the matrix between the metals.

I do find this area of study somewhat fascinating.

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#12

Re: Graphene Thermoacoustic Speakers

09/09/2016 8:22 AM

Gives credence to some old adages. That's a hot band. Cool music man.

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#15
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Re: Graphene Thermoacoustic Speakers

09/09/2016 10:34 AM

LOL.

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#18

Re: Graphene Thermoacoustic Speakers

09/13/2016 3:52 PM

I still don't understand how graphene can be "shown" to be such a miracle material. It is invisible, only 1 atom thick, made by vapor deposition. How do they know it is only 1 atom thick, and not 2, 5, 17, or 43 atoms thick? How do they know it adheres to a substrate, if they can't see it? How do they know it will not vaporize into carbon dioxide at some future time/event/condition?

Heat is a problem today with electromechanical loudspeakers. If these graphene aerogel speakers produce sound by heating air......what happens when heat builds up in the air molecules around the graphene, and is not removed? What happens to the 1 atom thick layer of graphene when it heats up?

Back in 1978, I visited a company in Philadelphia that used ultrasonic transducers to weld aluminum plates together, for the aviation industry. They were trying, at that time, to make commercially viable a system for fusing together aluminum panels/ribs in aircraft, to eliminate rivets. I saw with my own eyes that it worked......don't know where the technology went as far as mass production.

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#19
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Re: Graphene Thermoacoustic Speakers

09/14/2016 9:26 AM

The idea is to heat up the graphene within its tolerable limits, and allow it to cool by gas contact, which sets up the acoustic vibrations (waves). No magic, just physics.

The aerogel backing is there to prevent heat loss to whatever is behind it that makes up the support structure for the speaker (core).

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#20
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Re: Graphene Thermoacoustic Speakers

09/14/2016 9:43 AM

The rapid heating and cooling cycles move the acoustic material (air?) without moving an object with mass (piston, diaphragm, cone) to produce sound. I don't think this approach will make a room filling sub-woofer. This might make for some exceptional ear bud headphones.

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#21
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Re: Graphene Thermoacoustic Speakers

09/14/2016 10:07 AM

"An array of these aerogels was then aligned in a 4×4 configuration to form a 40W speaker."

I think if they can do 40W, they can go much higher.

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#22
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Re: Graphene Thermoacoustic Speakers

09/14/2016 11:12 AM

Saint Saëns organ symphony will be either a little wimpy or melt the aerogel.

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#23
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Re: Graphene Thermoacoustic Speakers

09/14/2016 11:26 AM

Can't they still use the pipes for that one?

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