Create metamaterials that emit 'black' radiation

A team of researchers led by physicist Willie Padilla, who works at Boston College in the US, has discovered that metamaterials can emit " black " radiation with performance that is beyond the limits. Naturally imposed by the temperature of the material.

The results of the study were published in Physical Review Letters .

Metamaterials can emit " black " radiation that represents an ideal theory: a kind of metamaterial absorbs all the radiation that radiates it and at the same time the material also emits amount from its own temperature source. That is, the absorbed energy is equal to the energy emitted in the equilibrium state.

Willie Padilla Physicist

A breakthrough in research by Padilla and colleagues from Duke University, USA and SensorMetrix, Inc., could lead to the introduction of advanced technologies used to generate electricity, from waste heat. in industrial manufacturing processes. Moreover, artificial metamaterials also provide the ability to control emissions, helping to improve energy conversion efficiency.

Padilla said: " This is the first time, metamaterials can emit detected" black "radiation and promise many applications to exploit potential energy. Naturally, it depends only on the temperature of this natural surface, so you don't have much choice, meanwhile, metamaterials allow you to adjust the radiation at will, so you can Control the amount of energy emitted . "

For a long time, researchers have sought to find metamaterials that can emit " black " radiation used in solar or thermal power systems. In the past, finding such heat-emitting metamaterials was not feasible, because some rare earth oxides had limited and expensive supplies, and were unable to control the amount of energy emitted. Photonic crystals have been shown to be ineffective with poor emissions.

Constructed from artificial synthetic materials, metamaterials are designed to provide new features that exceed the physical performance limits of common components that make them and allow this metamaterial to transmit output corresponding " black " radiation . Metamaterial also acts as a negative refractive index. Based on this, the researcher combined metamaterials with artificial optical devices to create " Invisibility cloaks" (basically this is the process of controlling light around a space and hiding the its existence.)

Three years ago, researchers developed a " perfect " metamaterial capable of absorbing all the light that shines on it thanks to its nanoscale geometric surface feature. This is one of the studies that seeks to exploit Kirchoffs' law (about heat radiation), which suggests that the viability of a radiation-emitting material is equivalent to its ability to absorb radiation.

Working in the average infrared range, the heat source provides 98% emission in the test. Dual-band heat source provides peak emission of 85% and 89%. The results confirm the efficiency achieved in accordance with Kirchoff's law, according to the researchers.

" We also found, by implementing both emission and emission absorption measurements, that the emission and absorption processes take place very well, " says Padilla. "Although the experimental results are based on Kirchoff's prediction, this is the first time Kirchoff's law has been proven by metaphysics. "

The researchers said that changing the components of metamaterials could yield a single super-metamaterial, dual-band and broadband metamaterials that allow better control of emitted photons to improve performance. power conversion rate.

Potential applications in the field of energy exploitation such as using this metamaterial as selective sources of heat radiation for thermophotovoltaic cells (TPV), according to Padilla. "Since the discovery of metamaterials has the ability to emit heat radiation to release photons, combined with semiconductor free holes, part of TPV cells, making conversion efficiency. The energy is greatly enhanced.

Author of Willie Padilla Padilla Physicist; Other co-authors of the study include: Liu Xianliang Fellows, Boston College, USA; Nan Marie Jokerst and Talmage Tyler, Duke University, USA and researchers Tatiana Starr and Anthony F. Starr, from SensorMetrix, Inc.