The world's smallest steam engine measures a few micrometers

Dec 11, 2011
A Stirling engine in the microworld: In a normal-sized engine, a gas expands and contracts at different temperature and thus moves a piston in a cylinder. Physicists in Stuttgart have created this work cycle with a tiny plastic bead that they trapped in the focus of a laser field. Credit: Fritz Höffeler / Art For Science

What would be a case for the repair shop for a car engine is completely normal for a micro engine. If it sputters, this is caused by the thermal motions of the smallest particles, which interfere with its running. Researchers at the University of Stuttgart and the Stuttgart-based Max Planck Institute for Intelligent Systems have now observed this with a heat engine on the micrometre scale. They have also determined that the machine does actually perform work, all things considered. Although this cannot be used as yet, the experiment carried out by the researchers in Stuttgart shows that an engine does basically work, even if it is on the microscale. This means that there is nothing, in principle, to prevent the construction of highly efficient, small heat engines.

A technology which works on a large scale can cause unexpected problems on a small one. And these can be of a fundamental nature. This is because different laws prevail in the micro- and the macroworld. Despite the different laws, some are surprisingly similar on both large and small scales. Clemens Bechinger, Professor at the University of Stuttgart and Fellow of the Max Planck Institute for , and his colleague Valentin Blickle have now observed one of these similarities.

"We've developed the world's smallest steam engine, or to be more precise the smallest Stirling engine, and found that the machine really does perform work," says Clemens Bechinger. "This was not necessarily to be expected, because the machine is so small that its motion is hindered by microscopic processes which are of no consequence in the macroworld." The disturbances cause the micromachine to run rough and, in a sense, sputter.

The laws of the microworld dictated that the researchers were not able to construct the tiny engine according to the blueprint of a normal-sized one. In the invented almost 200 years ago by Robert Stirling, a gas-filled cylinder is periodically heated and cooled so that the gas expands and contracts. This makes a piston execute a motion with which it can drive a wheel, for example.

"We successfully decreased the size of the essential parts of a heat engine, such as the working gas and piston, to only a few micrometres and then assembled them to a machine," says Valentin Blickle. The working gas in the Stuttgart-based experiment thus no longer consists of countless molecules, but of only one individual plastic bead measuring a mere three micrometres (one micrometre corresponds to one thousandth of a millimetre) which floats in water. Since the colloid particle is around 10,000 times larger than an atom, researchers can observe its motion directly in a microscope.

The physicists replaced the piston, which moves periodically up and down in a cylinder, by a focused laser beam whose intensity is periodically varied. The optical forces of the laser limit the motion of the plastic particle to a greater and a lesser degree, like the compression and expansion of the gas in the cylinder of a large heat engine. The particle then does work on the optical laser field. In order for the contributions to the work not to cancel each other out during compression and expansion, these must take place at different temperatures. This is done by heating the system from the outside during the expansion process, just like the boiler of a steam engine. The researchers replaced the coal fire of an old-fashioned steam engine with a further laser beam that heats the water suddenly, but also lets it cool down as soon as it is switched off.

The fact that the Stuttgart machine runs rough is down to the water molecules which surround the plastic bead. The water molecules are in constant motion due to their temperature and continually collide with the microparticle. In these random collisions, the plastic particle constantly exchanges energy with its surroundings on the same order of magnitude as the micromachine converts energy into work. "This effect means that the amount of energy gained varies greatly from cycle to cycle, and even brings the machine to a standstill in the extreme case," explains Valentin Blickle. Since macroscopic machines convert around 20 orders of magnitude more energy, the tiny collision energies of the smallest particles in them are not important.

The physicists are all the more astonished that the machine converts as much energy per cycle on average despite the varying power, and even runs with the same efficiency as its macroscopic counterpart under full load. "Our experiments provide us with an initial insight into the energy balance of a heat engine operating in microscopic dimensions. Although our machine does not provide any useful work as yet, there are no thermodynamic obstacles, in principle, which prohibit this in small dimensions," says Clemens Bechinger. This is surely good news for the design of reliable, highly efficient micromachines.

Explore further: Cold Atom Laboratory creates atomic dance

More information: Valentin Blickle and Clemens Bechinger, Realization of a micrometre-sized stochastic heat engine, Nature Physics, 11 December 2011; DOI: 10.1038/NPHYS2163

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User comments : 13

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Isaacsname
5 / 5 (1) Dec 11, 2011
Hey wow, look everybody,.. a ..laser-driven steam engine.
Nanobanano
2 / 5 (4) Dec 11, 2011
Why don't they work on something a bit more practical, like a protonic motor or something?

Who is going to power micro-machines with a laser?

This is still 2 or 3 orders of magnitude too large for use as a component in a medical nano-bot.

it's also too large to use in nano-assembly or self-repair mechanisms.

What's the point?
antialias_physorg
5 / 5 (2) Dec 11, 2011
like a protonic motor or something?

And a protonic motor would be...?

This is an experiment on a scale where many of our macroscopic ideas have been shown to not play out as excpected (e.g. adhesion forces).
Nanobanano
1.2 / 5 (5) Dec 11, 2011
And a protonic motor would be...?


Cellular biology anyone?

Biomachinery or artificial molecular machinery that runs on glucose and oxygen, or some similar reaction?

I mean in controlled "one molecule at a time" reactions, the way our cells doe it in mitochondria. Not this comic books laser device.

That's the real goal of nano-tech anyway.

Why not actually work on that, instead of a silly laser motor that's nothing more than a novelty anyway?
antialias_physorg
5 / 5 (2) Dec 11, 2011
Ah. You probably mean a protein motor - not a protonic motor.

Cellular biology anyone?

You are aware that MEMS and cellular biology are a wee bit different.
You're asking a mechanic to bake you a cake. That's a little bit odd. This is a physics group*

That's the real goal of nano-tech anyway.

There are many goals of nanotech.
This article isn't about nanotech, and the group in question aren't a nanotech group.

*Though the institute they are from does have biotech and nanotech groups
http://www.is.mpg.de/2178/en

Why are you're complaining about physicists not manipulating proteins? I don't get it.
Nanobanano
1.3 / 5 (4) Dec 11, 2011
I usd the term "protonic" because at the molecular level, biology works based on hydrogen ion transports.

Ok, let's put it another way.

What can they possible do with this that's practical?

They didn't even suggest a practical use...

At least Ralph merkle's group has ideas for nano machine's uses...
Ober
3.3 / 5 (4) Dec 11, 2011
Nano is actually right when he talks about a PROTONic motor. So NO it's NOT a PROTEIN motor. Go and look at how a flagellum (whip like tail on bacteria) is powered. It has a PROTEIN HOUSED MOTOR, which is powered by the passage of Hydrogen ions from the interior of the cell to the exterior. The motor is simply an exhaust where internal high pressure H ions can escape which causes the motor to turn on a frictionless bearing, which inturn rotates the flagellum. The cell itself has proton pumps on its surface. Its uses ATP to drive the pumps, which pulls hydrogen from the environment, and builds up the internal pressure of the cell. Again the H ions escape (to maintain equilibrium) through the flagellum "exhaust" motor.
Nano's point is that tiny machines driven by LARGE EXTERNAL power sources is not good enough!!! Life can do it at the size of cells and virii. We need to focus on building our machines using the tech of life.
Though this experiment was to TEST a mechanical idea!!!!
pratiksaptarshi
4 / 5 (1) Dec 11, 2011
The fact that a "micro-scale something" like this is working or rather capable of doing PHYSICAL WORK creates lot of possibilities. The issue of surrounding water molecules hampering the WORKING PARTICLE because of their brownian motion is the next challenge to over-come now. In simple words, we need to isolate this WORK producing system. And after that comes the matter of conveying/propagating the work-done.

(This might sound a bit like science fiction)

We're already aware of and use piezoelectric materials (natural and synthetic) that we use for multiple things. Such materials generally have a multiple laminas/layers made up of molecules that change their shape/vibrate upon passage of electric current/electrical field variation/analog signalling.

Now, applying the same use to this case, if we could put could arrange such microscale engines in lamina and then overlap them one over other (i.e. 2D and 3D arrangement); we could create vibrating surfaces too.
pratiksaptarshi
3 / 5 (1) Dec 11, 2011
I believe the challenges are isolation of this WORKING SYSTEM from surrounding (brownian motion of) particles and then work propagation for use.

I was thinking, that if the size of the surrounding particles is very less as compared to the plastic bead then the effect of impinging of surrounding particles might be solved. Liquefied H2 could be used but then it is at a freezing temperature. Liquified H2 would surely destroy the elasticity and piezoelectric property of the bead and quite possibly make it hard.
kevinrtrs
1.1 / 5 (10) Dec 12, 2011
This was not necessarily to be expected, because the machine is so small that its motion is hindered by microscopic processes which are of no consequence in the macroworld. The disturbances cause the micromachine to run rough and, in a sense, sputter

This should be a wake-up call to anyone who still believes that life came about through some random physical process. It takes some really special tools and techniques to construct any of the cell's specialized enzymes and motors, to name but a few complex items inside the cell. There's just no way to overcome the chemical and physical requirements thru sheer random motion.
Take for instance the simple pin-needle. A small piece of steel topped with a simple head. To date there is no record of this piece of simple utensil being created by any random process whatsoever. Here I'm referring to both the specified mechanical construction as well as the metallurgical make-up. So to think that far more complex things can arise by chance...
antialias_physorg
5 / 5 (2) Dec 12, 2011
What can they possible do with this that's practical?

They didn't even suggest a practical use...


They have demonstrated that his type of process works the same (i.e. can be handled with the same formulae) as on a macroscopic scale. This is an important finding. Up to now everybody just assumed that it did, but no one actually checked it out. In the past there have been many surprises when people just scaled stuff down and assumed that things keep on working the same way (conductors turning into isolators, adhesion forces becoming a real problem, tunel effects, brownian motion affecting temperature transport, etc., etc. )
While this may look like applied mechanics it is simply a validation of theoretical physics. No one (not even the authors) are claiming that we'll run microrobots on steam. Why would you make such an assumption?
roboferret
5 / 5 (3) Dec 12, 2011
Take for instance the simple pin-needle. A small piece of steel topped with a simple head. To date there is no record of this piece of simple utensil being created by any random process whatsoever. Here I'm referring to both the specified mechanical construction as well as the metallurgical make-up. So to think that far more complex things can arise by chance...


You've completely lost the plot on this one. Features evolve to survive in a niche. No niche exists where survival and reproduction would be enhanced by frikkin' PINS! What a bizarre strawman. Although the evolution of snake's venom injectors might be of interest to you (not that you'll even bother checking).
MarkyMark
5 / 5 (1) Dec 13, 2011
^^^ Well said ^^^

sometimes when confronted by his sheer stupidaty i sometimes wonder if he has some form of mental retardation, afterall he believes the voice in his head is from God.