This is a 2D periodic photonic crystal-- metal which is ordinarily reflective across the entire IR and visible can be made to have selective reflectance, and hence selective emissivity. The key is to tailor the hole dimensions so that the rate of radiation and the rate of absorption are equal. This is called Q-matching. This is critical for efficiently converting thermal energy into electricity.

Thermophotovoltaics is the phenomena whereby radiant heat energy can be converted into electricity. The key components are fuel, a very hot emitter (our 2D photonic crystal), and a low-bandgap PV cell (InGaAs).

Textiles are usually invisible to electromagnetic radiation below 0.1 to 1 THz. However by weaving metal threads we can make the textile strongly interact with radio waves and create LC-circuit like resonances.

Making a fiber with non-circular cross-sections is very difficult with melt extrusion. However by utilizing 3D printing to make preforms and then thermal drawing the preforms, retroreflective fibers can be produced.