Originally posted by: SuperFungus
well i won't claim to understand most of what you said, what with my less than a third of a semester of highschool physics and all, but it seems that if light hits one side of the object and travels around the object to be re-emmited on the other side as if there was no object at all, that light would need to travel at a speed greater than c to travel that greater distance in the same amount of time. In any case i'm sure you're probably correct but it seems that either my understanding that the light is actually bent around the object, or my understanding that these materials work "perfectly" is erroneous, i don't see how i can reconcile the two with speeds at or bellow c. If a laymans explanation of which is erroneous and why is available i'd be very interested.
I think i'll also re-read both articles, perhaps the popular science one is about a different material, or flat out wrong. To give you an idea of why i distrust popular science, consider that they diagram the material with a 3d render of what appears to be an Auston Martin Vanquish, or should i say VANISH? I suspect that they're less concerned with whatever it is that is actually interesting about these materials (or do i dare say accuracy?) and more concerned with a "cool guy" invisible car.
Anyways thanks alot for your explanations, even if they do sometimes blow over my head.
When light strikes and transmits into glass, you can see it refract. The way it refracts is inwards, that is, the angle of transmission is smaller than the angle of incidence. So if you wanted to bend the light inwards, you have to have a curving surface. Hence, a focusing lens is convex. However, these metamaterials are such that light does not bend inward, but outwards. So the bending of light inside these materials is contrary to what normal convention predicts.
For example, whenever we go from a lower index of refraction to a higher one, there is an angle called the critical angle where total internal reflection occurs. That is, at angles greater than the critical angle, all of the light is reflected, or scattered, back off. The analog to our left handed materials is the angle of total refraction, the angle at which all light is transmitted through and none is reflected.
The speed of light never surpasses c. In fact, it will be always less than c because there are non unity permittivity and/or permeabilities.
Take a look at this reference,
Text, this should give you a better idea of how it works. Remember, the wave is going to refract outwards, so you can see that when it strikes the metamaterial cylinder, it is going to be bent away from the radial axis and thus away from the scatterer. Now how do they make the normal incident waves refract, I bet it is from a special layering of various left handed materials to catch the waves that transmit deeper into the material. In fact, the idea of the wave traveling around a cylinder is nothing new. Take a look into whispering gallery modes. These are a well known phenomenon. If you place a point source on the inside edge of a cylinder, the supported wave mode will sometimes follow the inner edge but not project out into the internal body of the cylinder. The name whispering gallery comes from the phenomenon occuring in cylindrical galleries in buildings. One person could be whispering on the opposite wall and you could hear them perfectly due to the whispering gallery mode.
Now how do they come up with the exact layering and geometries of these LH materials? Well, by working through with the physics to do what they want the wave to do. You'd be surprised at the kinds of things that have been developed for EM waves. For example, the Lundeberg lens. The Lundeberg lens takes in any plane wave from any direction and refocuses it into a point source on the opposite side of the spherical lens. And this was developed back in the 50's. Considering that the idea of left handed materials has only been around for probably a decade at the most, it's not that big of a deal for a lot of this to start coming out now.
Oh, and I may have been incorrect before when I stated that there are no naturally occuring metamaterials. Photonic crystals also can exhibit the phenomenon of LH materials and there are naturally occuring photonic crystals. One of the better well knowns are opals. In fact, it is the photonic crystal properties that give opals their coloring. One way to make photonic crystals in the infrared region, which is of interest for the telecomm industry, is to fill the air gaps between the silicon colloids that make up an opal with your refractive material. Then you dissolve the silicon spheres and leave behind a reverse opal. Interesting stuff and I remember back in 2001 one of the labs I worked at was looking into doing photonic crystals and that's how I heard about these reverse opals.
I think the right way to think of this is as a form of complex camoflauge pattern, not "invisibility". It is not magic. For one thing it will only work at certain frequencies.
It will e.g. probably not work at IR frequencies, simply because the amount if IR radiated depends on the temperature of the vehicle and I don't think this material can "bend" IR; the frequency is too low. Same thing with active search methods; it won't help against e.g. radar or microwave beams.
Actually, they are doing this with microwaves. So IR would be at a higher frequency than what they are working at. But you are right, they can only operate these metamaterials at very small bandwidths. Small bandwidths and lossy materials are the main hurdles that need to be over come. But to be able to do this in the visible range is probably impossible with the current methods of fabricating metamaterials. What they do is make a modular design of repeating cells. These cells are usually a LC resonator. They resonate over the effective bandwidth of the metamaterial but this is unpractible with the Terahertz region since this would require extremely small fabrication sizes (though they probably could do so with lithographic techniques) but also the physics starts to cross over into QED and what works in the microwave region may not be efficient or effective at frequencies of visible light. And of course again, for visible light you would need to make a material with a large enough bandwidth, I think the BW is around 65%.
