My gut feeling would be that, since nanoscale devices are much smaller that the wavelength of lots of em radiation, such a scheme might be difficult.

Offtopic, on the macroscopic scale, such a power transmission system has been feasible for about a century – Nocola Tesla worked out how to use VLF EM waves and tuned antennae to broadcast large amounts of power globally. Unfortunately for humanity, the power company sponsoring his research worked out how to keep it quiet and discredit him, so we're still stuck with wires everywhere. People seem to lump Tesla in with the "Free energy" crackpots – but Tesla's scheme was not about "Free" energy, except in the economic sense – the problem the power companies had with his research was that anybody, not just paying customers, could have tapped into the broadcast power. There was no violation of energy conservation laws of physics or anything like that…

See http://www.amasci.com/tesla/nearfld1.h tml for an interesting look at a possible physical mechanism. Please note that I don't necessarily agree with the analysis, but it's a fascinating springboard nonetheless.

One other possiblitiy is to seperate the Rectenna and the nanodevice. Have a millimeter size rectenna that is fixed to the surface and the nanodevice, if its mobile, connected by a nanotube conductor?

Let me point you to an interesting story that appeared in my hometown paper some time ago. If you want to learn more about this research, I would suggest googling the major researchers. The story is here:

http://www.post-gazette.com/healthscience/20000904harvest1.asp

Here's an excerpt from the article that appeared some months ago:

Devices might harvest energy from the air

Monday, September 04, 2000

By Byron Spice, Science Editor, Post-Gazette

We can't see them, we can't feel them, and, except for those of us with CIA-implanted chips in our heads, we can't hear them.

Yet radio waves are all around us, emitted by a growing menagerie of devices, from navigation radars and TV broadcast transmitters to garage-door openers and wireless Internet devices.

But this is more than just a sea of static, say researchers at the University of Pittsburgh. These ambient radio waves could be a source of electricity.

By harvesting the power that is available all around us, Pitt engineers hope to develop electronic sensors, keys, tags and perhaps even simple computers that are not only wireless, but battery-free.

The amount of power that can be skimmed off the radio wave sea might be relatively small, acknowledged Marlin Mickle, a professor of electrical engineering. But as computer chips and other electronic devices have shrunk, so have their power demands. Harvesting just a volt or maybe two out of thin air might be sufficient for many applications.

"It's a very cool technology," said Phil Weilerstein, director of the National Collegiate Inventors and Innovators Alliance, which has funded some of the early Pitt research. It could become a key piece of what's known as the smart environment — small sensors and processors that communicate with each other to autonomously perform tasks.

Philip Shropshire
http://www.threerivertechreview.com
http://www.majic12.com

I suspect the biggest problem you'd have (literally) would be the wavelength. Even "shortwave" radio is >~1mm, which is several orders of magnitude larger than a "nanoscale" device. This isn't to say that it couldn't be done, just that you would have to contend with a large disparity between the aerial and the wave it was riding. My gut feeling is that the amount of power you could extract would drop out of proportion (faster then linear) as the aerial fell below 1/4 the wavelength.

– MarkusQ

Nikola Tesla did some significant work with broadcast power at the turn of the century. I'm afraid I don't know many details, but the basic principles of electrical resonance could possibly be applied to nanomachines. There's a wealth of information about his work available online, and numerous books have been written about him, so it shouldn't be too difficult to get some specifics.

A very interesting idea…

-Ares

But I like the idea of using Neutrinos as a power source (since neutrinos pass through all matter thousands of times per second.) If there were some way to harness the energy of those neutrinos, it would definately be a powerful and infinite source of energy for nanites etc etc.