Nowadays, with the generation of electricity, large amounts of heat are released into the surrounding space. It’s tempting to use these losses to your advantage, but modern technology offers solutions with very low efficiency – just a few percent. Scientists in the US created Metamaterial that promises a significant increase in the efficiency of such a transformation.
The thermoelectric effect – the appearance of a potential difference at the ends of two dissimilar conductors connected in series if there is a difference in temperature between the two – was discovered two hundred years ago by the physicist Thomas Seebeck. Effect called by his name. For efficient conversion of heat into electricity, a material must be a good conductor of electrons and a poor conductor of heat. Then there is a large temperature difference at its ends and thus a high level of efficiency. Unfortunately, such materials do not occur in nature. If a material conducts electricity well, it also conducts heat and vice versa.
Researchers at the National Institute of Standards and Technology (NIST) have created a metamaterial that is a good conductor of electrons but a poor conductor of heat. It should be said that in bodies with a fixed crystal lattice, heat is transferred by quasiparticles phonons. And although they are not real particles, they are still subject to the corpuscular wave theory – they are particles and waves at the same time. The new metamaterial uses the wave properties of phonons to affect how fast they propagate through the material.
Structurally, the new metamaterial is a silicon layer on which gallium nitride nanocrystals grow. The silicon substrate is then thinned to the required thickness. It turns out the following. When heat is transferred from one edge of the sheet to the other, the transfer is also via nanopillars. Standing waves appear in the pillars with a period whose value is determined by their shape – a narrow pillar. These waves are much, much shorter than the phonon wave that propagates freely in silicon. It turned out that standing waves in nanopillars resonate with phonon waves in silicon, forcing the phonons in silicon to match their wavelength to the ‘locked’ one.
As a result of the experiment, the told In the magazine advanced materialsthe scientists were able to reduce the thermal conductivity of silicon by 21% without affecting its electrical conductivity. Physicists hope to soon present a solution with a high heat-to-electricity conversion rate, paving the way for new thermoelectric devices or enabling more efficient heat sinks for electronics.