Abstract

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

Answer: Structured materials give somewhat surprising electromagnetic responses.

Taking little other than common cuticle, loaded with a small amount of melanin, butterflies have evolved some stunning microstructures 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 limited to dielectrics. When it comes to synthetic structures we may also use metals. Structured metals can also lead to unexpected effects such as negative index materials, perfect lensing and ‘cloaking’. Even at very long wavelengths (microwaves and beyond) where metals are expected to behave as almost perfect mirrors they can be structured to be almost perfect absorbers. This talk will illustrate briefly the wonderful structural colours of butterflies focusing primarily on some recent developments in the physics of structured metals for use at microwave frequencies.