electromagnetism - Is it possible to "focus" a radio wave to target an area much smaller than its wavelength?

Recently I was reading about a technology that uses radio waves to stimulate neurons to fire. The radio waves have the advantage of being able to pass through the skull (hence being non-invasive) but they are very coarse. Would it be possible to target individual neurons with radio waves (for example by having a bunch of low-powered radio waves converge on a focal point only nanometers large without diffusing to surrounding tissue)?

http://sfari.org/news-and-opinion/toolbox/2012/radio-waves-turn-on-gene-expression

Answer

My original answer is that it is not possible in a laboratory setting, the wavelengths are enormous,

The wavelength is the distance from one peak of the wave's electric field to the next, and is inversely proportional to the frequency of the wave. The distance a radio wave travels in one second, in a vacuum, is 299,792,458 meters (983,571,056 ft) which is the wavelength of a 1 hertz radio signal. A 1 megahertz radio signal has a wavelength of 299.8 meters (984 ft).

In order to focus a wave one should be able to interact with the beam, refract it, in a coherent manner, create a lens. The size of the lens has to be commensurate to the wavelength, nanometers are not in the ball park. Look at the size of the antennas used for radio communications .

Nevertheless, all the above is for conventional materials and lens geometries.

Searching on the internet I found in MIT news :

Researchers at MIT have now fabricated a three-dimensional, lightweight metamaterial lens that focuses radio waves with extreme precision. The concave lens exhibits a property called negative refraction, bending electromagnetic waves — in this case, radio waves — in exactly the opposite sense from which a normal concave lens would work.

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To test the lens, the researchers placed the device between two radio antennae and measured the energy transmitted through it. Ehrenberg found that most of the energy was able to travel through the lens, with very little lost within the metamaterial — a significant improvement in energy efficiency when compared with past negative-refraction designs. The team also found that radio waves converged in front of the lens at a very specific point, creating a tight, focused beam.

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The device, which weighs less than a pound, may be used to focus radio waves precisely on molecules to create high-resolution images — images that are currently produced using bulky, heavy and expensive lenses. Ehrenberg says that such a lightweight device could also be mounted on satellites to image stars and other celestial bodies in space, “where you don’t want to bring up a hefty lens.”

So in principle the answer is yes from now on.