Abstract

Question: What do graceful flickering vividly iridescent tropical butterflies have in common with dull grey ponderous battleships?

Answer: Structured materials giving rather special electromagnetic response.

Taking little other than common cuticle, loaded with a small amount of melanin, butterflies have evolved some stunning microstructures (metasurfaces) in their wing scales. These structured surfaces, often only microns thick, act as selective reflectors and polarizers as well as being sometimes very strong scatterers (white) or very strong absorbers (black) of electromagnetic radiation. This use of structure in nature to give striking effects when interacting with visible radiation is of course limited to dielectrics. Synthetic structures may also incorporate metals. Surface structured metals, metasurfaces, can lead to unexpected effects: for example selective absorption, even at long wavelengths where metals are expected to behave as almost perfect mirrors, or even negative refraction. This talk will illustrate the wonderful structural colours of butterflies and will also explore some recent developments in structured metals, metamaterials and metasurfaces which have surprising properties at microwave frequencies.