Heat emission is a widely used energy source, but it's not used effectively. Even now it is possible to convert it into electricity using thermophotovoltaic cells, but such cells recover only radiation of particular wavelength.
According to thermodynamics, the emissivity of a heated body depends on its absorbability. Thus, the ideal source of heat emission would be an ideal black body that absorbs any and all light rays. This happens due to its specific porous structure: upon getting into the pores, the light reflects and re-reflects in them thus never leaving them and converting into other types of energy, including heat.
When heated, the black body serves as a heat source itself. According to Planck's law, it emits light with all possible wavelengths, but their relative intensity depends on the temperature: at different temperatures, the intensity of some waves will be higher and others — lower. At set temperatures, the radiation in one spectral range will reach a particular maximum value that is defined by Planck's law.
For instance, Sun is an ideal black body with a surface temperature of about 6,000 degree Kalvin. The greater part of Sun's heat emission is within the visible light band that can be seen.
For getting maximum amount of waves on the solid-state detector of the thermophotovoltaic cell, a metamaterial can be used as an intermediate heat emission source. It will absorb heat from the heated body and conduct the heat emission with maximum power in the preset wavelength band. What's more, if such emitter is placed really close to the thermophotovoltaic cell, the conducted power can be even higher than the one predicted using Planck's law — this way, the energy is transfered via surface waves that are close to the emitter, whereas Planck's law works only at lengths greater than the length of the wave.
Still, the efficiency of such devices is still limited, as the metamaterials used as their elements can only absorb the rays that fall on their surface. Can this limitation be overcome as well? Stanislav Maslovski works on this very problem.
«I've created a formula for the object that can be called a „heat black hole based on metamaterial“. At particular wavelengths, this object absorbs (and, consequently, emits) more, than an ideal black body of the same size, which means that it can absorb even those rays that pass it by. One can say that this hole works as a gravitating object that sucks up all passing radiation of particular wavelength», — shared Mr. Maslovski.
At what distances can it absorb radiation? Theoretically — at any. This sounds like something of sci-fi for a physicist. But in practice, the distance will depend on the tangent of the angle of dielectric losses — in other words, on the ability of the dielectric to absorb energy in an electric field. When this value tends to zero and the modulus of electric permittivity in the center of the object tends to infinity, the effective absorption area of this «metamaterial black hole» tends to infinity.
«Is there really any limit to the capacity of heat emission of a finite size body in the farther area on a particular wavelength? My research shows that there is none!», — claims Stanislav Maslovski.
Still, creating a universal emitter or absorber for all wavelengths won't be possible: for each wavelength has to be its own «black hole». At that, the more power is absorbed or emitted using such metamaterial, the narrower the wavelength wand is. Thus, there must be a balance.
Also one has to note that even if the limit on capacity according to Planck's law can't be exceeded. In other words, the bigger the size of the «black hole» in comparison with the wavelength of radiation, the harder it is to exceed the radiation limit of the black body.
Microscopic «black holes» can be applied in medicine and chemical industry. For instance, metal-dielectric nanoparticles that are close to «black holes» in their properties can be used in fluorescent microscopy.
«Also, this effect can be used for cooling nanolasers. These objects are microscopic, so they have really small surface. Furthermore, sometimes nanolasers are used in vacuum and can't be cooled otherwise than vis heat emission. If you add a radiator for cooling, it will become too big. On the other hand, if the laser is coated with my material, then the effective surface for heat dissipation will become times bigger without a significant increase in size», — explained the scientist.
In addition, «heat black holes» can be used for constructing microwave band antennas that will effectively receive microwaves from a larger area than the size of the antenna itself. Using these antennas, we'll be able to create devices that can be effectively charged without using batteries.
