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## Heat Engines Shrunk By Seven Orders of Magnitude168

KentuckyFC writes "The vast majority of motors that power our planes, trains, and automobiles are heat engines. They rely on the rapid expansion of gas as it heats up to generate movement. But attempts to shrink them by any significant amount have mostly ended in failure. Today, the smallest heat engines have a volume of some 10^7 cubic micrometers. Now group of Dutch engineers has built a heat engine that is seven orders of magnitude smaller than this. The engine consists of a piezoelectric bar that expands and contracts in the normal piezoelectric way. However it also heats up and cools at the same time causing a thermal expansion and contraction, which lags the piezoelectric displacement. By carefully choosing the frequency of the driving AC current, the Dutch team found a resonant effect in which the thermal expansion and contraction amplifies the mechanical motion, making it a true heat engine. Operating the thermodynamic cycle in reverse turns the device into a heat pump or refrigerator. The total volume of the device is just 0.5 cubic micrometres."
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## Heat Engines Shrunk By Seven Orders of Magnitude

• #### Re:Usefulness? (Score:5, Interesting)

on Friday January 22, 2010 @10:53AM (#30860090) Homepage
No. You have made a critical error in thinking. You need to think relativity wise. Scale changes how much power we need. As of yet we don't have many small things that need small amounts of power because we have NOT had the engine. Now that we have the small heat engine, it will allow us to develop small devices that use it.

Assuming we had micro engines, we can take full advantege of many things that are better smaller than bigger.

For example, a small device that turns heat into power could power an IMPLANTABLE MEDICAL DEVICE using the bodies own heating/cooling systems? No more changing the battery for the pacemaker every

Then there are small flying devices. I am sure the military would love a flying camera the size of a real fly that uses the solar heat of the sun to power it.

Then there are phones and musical devices. Want one that uses half of its' own waste heat to recharge itself, perhaps doubling battery life?

• #### Re:On Chip cooling? (Score:5, Interesting)

on Friday January 22, 2010 @10:59AM (#30860168)

Already done: see peltier device. They are already made to the correct size and probably better efficiency.
http://www.peltier-info.com/ [peltier-info.com]
http://en.wikipedia.org/wiki/Thermoelectric_cooling [wikipedia.org]

• #### Re:Did someone say pump? (Score:4, Interesting)

on Friday January 22, 2010 @12:19PM (#30861186)

If you've got a thing that small, it's time to give up on it...

• #### Tough call (Score:2, Interesting)

on Friday January 22, 2010 @01:05PM (#30861694)
if this is useful. I've seen micro rotary and piston engine. They suffer from two problems. One is heat loss due to high surface area to volume ratio (heat leaks away before work can be extracted), and the other is charge (fuel/air) leakage. This appears to solve the leakage problem buy not using combustion. Good job!
• #### Read the attached paper... (Score:5, Interesting)

on Friday January 22, 2010 @03:08PM (#30862900)

I read the attached paper on arxiv, and from what I could tell, they passed a DC current through the thing, which caused the small engine beam to expand, causing it to heat up and move the mass. The piezoelectric effect causes the resistance in the small engine beam to change, which causes the beam to cool down and move the mass back with help from the larger spring beam. Rinse, repeat. Effectively a thermoelectric buzzer. The buzzing of this particular device was measured to be about 1.255 MHz at a DC current of 1.045 mA.

Unlike what the Technology Review article says, the paper shows no application of an AC current to get the thing vibrating. In fact, the measured voltage is alternating because the resistance is alternating. The current remains the same. There is no complicated application of a DC current and an AC current. There's just an applied DC current.

Am I understanding the paper correctly?

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