Scientists Make Item Invisible to Microwaves

Vicissidude writes "A team of American and British researchers has made a cloak of invisibility. In their experiment the scientists used microwaves to try and detect a copper cylinder. Like light and radar waves, microwaves bounce off objects making them visible and creating a shadow, though it has to be detected with instruments. If you can hide something from microwaves, you can hide it from radar and visible light. In effect the device, made of metamaterials — engineered mixtures of metal and circuit board materials, which could include ceramic, Teflon or fiber composite materials — channels the microwaves around the object being hidden. When water flows around a rock, co-author David R. Smith explained, the water recombines after it passes the rock and people looking at the water downstream would never know it had passed a rock. The first working cloak was in only two dimensions and did cast a small shadow, Smith acknowledged. The next step is to go for three dimensions and to eliminate any shadow."

Comments

meta-materials

[lgw]

If you can hide something from microwaves, you can hide it from radar and visible light.

I don't think this follows, at least when we're talking about metamaterials. So far no one has invented metamaterials for optical wavelengths, as metamaterials rely on complex structure that's somewhat wavelength specific. It's easier to play "fool the photon" with microwaves (because of the longer wavelength) or X-rays (because of the higher energy) than it is with visible light. (Xiang Zhang's experiments in extending near-field effects of visible light are a very different mechanism, and are lumpedin with metamaterials simply for lack of a better term.)

Re:Why should Harry Potter have all the fun?

[thermopile]

I was on a selection committee for DARPA to look into this stuff a few years ago.

Negative Index of refraction Materials (NIMs), metamaterials, or whatever you want to call them, are relatively easy to make in the microwave region, since the wavelengths are on the order of centimeters. Thus, using a special arrangement of rings, loops, and wires, you can craft a lattice-like material that exhibits negative refraction. Technically, it has a negative magnetic permeability (mu) and negative permittivity (epsilon).

This has all kinds of weird implications. The group velocity is still in the forward direction, but the phase velocity goes in reverse. Evanescent waves propogate, not die off. Perfect lenses can be made. Measurements LESS than the wavelength of light can be taken. There was a list of implications in the August issue of Scientific American, I believe.

Anyhow, this works great at the ~cm scale. Visible light is hard as hell: the scale there is on the order of nanometers. And the copper or silver or tungsten wires used to make the metamaterials have MISERABLE magnetic losses at these small scales, so mu is no longer negative. The energy no longer propagates in the medium. As of three years ago, there were no promising candidates for solving this problem. There was an outside hack at using carbon nanotubes -- which may or may not maintain their permeability down to small scales -- but it was a long shot at best. Arranging the little guys would have been devilishly difficult.

Glad to see that Pendry, who's been in this field almost as long as Veselago, is still making good strides. Even if they can't get to the visible wavelength, NIM's have spectacular applications for microwave antennae.