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by jjohnson » Thu Oct 15, 2009 8:04 am
The idea of concentric shells to focus X-ray 'light' is the basis of Chandra and similar observatories, only they use shaped, polished surfaces rather than the 'cloaking' configuration on the surfaces to bring the desired range of EM wavelengths to the focus. A Fresnel lens is a similar cousin, condensing the curved surfaces of a conventional thick lens form into a thin set of concentric rings. The point of any focusing system is to get the 'light' to go precisely where you want it (whether that is to form an image or to hide an image)
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The problem is that any system which is bandwidth limited (i.e., all real systems) cannot focus all frequencies the same, and in fact likely will not 'see' (respond to) a large range of frequencies, usually those below the low cutoff frequency of the device. Hence, you do not get perfect focusing, and thereby lose or waste some of the incident radiation's energy. Second, the absorption part, only theoretical constructs (viz. blackbodies and black holes) can absorb all and not re-emit any of the incident radiant energy. This is why physicists devised the gray body concept, whereby the emissivity of a body is greater than zero - it is a multiplier or index which ranges from 0 to 1, whereby the blackbody's temperature spectrum calculation can be modified to account for radiant losses.
Real absorbers can be made to be very efficient, especially those which use resonant frequency absorption (see articles on how plants' chlorophyll systems trap incoming energy at preferred wavelengths, and use it almost immediately supply energy to their needed chemical reactions). But at some point something which absorbs particularly well in one region will not be so efficient at others. A large antenna farm with spindly, spiky antennas "tuned" to the frequency of incoming microwave radiation can absorb almost all that energy and channel it into waveguides or cables for subsequent processing and use, while you could stand anywhere under those same antennas and be brightly lit by the accompanying optical portion of the incident EM spectrum. If you are going to absorb incoming radio energy for conversion to heat or electricity, the receiver needs to be scaled relative to the wavelength of that radiation. Why do you think Arecibo and Jodrell Bank and the VLA and VLBA are so large compared to say, Hubble's optical/IR mirror or even the Keck telescopes? It's all about wavelength and collection efficiency in this business. Size matters, but knowing what you're doing with it matters more. Ask anyone.
The experimental device is clever, but it is neither a blackbody nor a black hole, which are 'black' for different but still theoretical reasons. If it can convert a broader or more energetic part of the solar spectrum into energy usable by us down here on the ground under a largely opaque atmosphere, i.e., collect with less loss and greater conversion efficiency, then it is of great interest. If it can't, and is only usable in a narrowband spectrum, it is only a toy and a curiosity. The technology surrounding optical applications and control through meta-materials is certainly interesting and growing, however. Whether it can improve solar collection efficiency and reduce collector losses remains to be demonstrated.
Wow, it does replicate the cosmological black hole to the T! I guess by heat they mean infrared?
