Realizing the potential of nano magnets

It is always of interest when researchers suggest an alternative power supply that while not breaking any laws of thermodynamics seems to offer an interminable source of power with apparently no ongoing demands. Working, not on the wind farm or solar-array scale, Josef Polácek and Petr Alexa of the Institute of Physics and Institute of Clean Technologies, at the VŠB – Technical University Ostrava, in the Czech Republic, have turned to nanoscopic magnets and Brownian motion to demonstrate proof of principle.

To recap, Brownian motion is the random movement of particles due to thermal fluctuations discovered by botanist Robert Brown around 1827 who noticed the unexpected motion of pollen grains suspended in water. Einstein later characterized the constant buffeting of such pollen grains by the water molecules themselves to explain the phenomenon and this laid the foundations for the work of Jean Perrin to provide evidence of atoms and molecules to be built.

The advent of microelectromechanical systems (MEMS), lab-on-a-chip devices and the micro and nanotechnology has led to the recognition that Brownian motion can be a problem as well as a provider. It can interfere with the movement of fluids in small-scale structures but might also enable a "Brownian motor" that could propel those fluids. Much work is being done in solving the problem of Brownian motion as well as investigating how it might be efficiently exploited. Now, Polácek and Alexa have suggested that Brownian motion might be used in electrical power generation at this scale.

They considered a low-density gas, containing magnetic nanoparticles. The tiny Brownian movements of these magnets might induce random voltages in nearby microscopic electric coil and the energy tapped by a rectifying diode array. Of course, on such a scale, the amplitude of the voltage pulse is, they estimate, going to be around 30 billionths of a volt, a coil with at least a million turns would be required – perhaps based on self-coiling or bio-templated nanowires – to allow a current to reach the rectifier and be put to use. Nevertheless, the team is enthusiastic that such a system, driven only by thermal agitation, would produce an adequate output to drive microscopic devices. One might imagine arrays of such nano-generators powering long-term remote sensors in deep, hot caves or perhaps devices onboard spacecraft heading for the stars.

Such blue-skies thinking is critical to scientific and technological progress. However, significant advances are needed in nanotechnology before requisite million-turn coils and microscopic rectifiers might be constructed. The production of uniform magnetic nanoparticles en masse will be required. This will have to be sufficiently small and not too strong magnetically that they the constant Brownian buffeting of the gas molecules breaks apart any aggregates that form otherwise, the particles will simply precipitate out of the gas. But, smaller, weaker particles would mean a smaller induction effect.

I asked Alexa about the potential of the system. "We are well aware that the practical application is a question for the future", he told me. "In our paper we tried to test whether the Brownian motion of magnetic nanoparticles could be theoretically exploited to generate electric current. For this purpose we constructed a ‘toy model’. This model provides an estimate of basic conditions that have to be fulfilled to reach the rectifying region and to enable the system to work," he adds.

Conventional rotating generators can achieve 95% efficiency, losses arise mainly from the recovery and transmission processes, leading to 40% end-to-end efficiency. Solar are expensive and achieve anything from 2 to 30% efficiency, while Peltier effect thermoelectric generators manage just 5. All of these are likely to outperform a Brownian generator, but admittedly they operate on an entirely different scale.

Alexa adds that, of course, "thermodynamically there is no free lunch." He points out that the efficiency of microscopic mechanical systems has been discussed and calculated before and there are perhaps inherent limitations to nano machines. Regardless, it is a fascinating idea at the cutting edge of nanoscience. I just wonder whether a magnetic Brownian motion generator idea will stick.

References

Polácek, J. and Alexa, P.  (2013) ‘Brownian motion of magnetic nanoparticles as a source of energy?’,  Int. J. Nanotechnol., Vol. 10, No. 12, pp.1109-1114.

David Bradley blogs at http://ift.tt/1dXIL6e and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".

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