The transmission
electron microscopy (TEM) image (a) shows a cross section of ribbonfish skin
(scale bar, 5 mm).
Figure (b) illustrates a superlattice of cytoplasm and guanine crystal layers
matching the
dashed red line in (a). Figure (c) illustrate a five-stage Cantor bar.
Changes introduced
into the fractal lead to a pattern that resembles the superlattice in Figure
(b).
Image: Douglas
Werner lab / Penn State
(January 13, 2016) A
nature-inspired method to model the reflection of light from the skin of
silvery fish and other organisms may be possible, according to Penn State
researchers.
Such a technique may be applicable to developing better
broadband reflectors and custom multi-spectral filters for a wide variety of
applications, including advanced optical coatings for glass, laser protection,
infrared imaging systems, optical communication systems and photovoltaics,
according to Douglas Werner, John L. and Genevieve H. McCain Chair Professor in
Electrical Engineering, Penn State.
The proposed model also contributes to the understanding of
the reflective layering in the skin of some organisms. The shiny skins of
certain ribbonfish reflect light across a broad range of wavelengths, giving
them a brilliant metallic appearance. The reflectivity is the result of stacked
layers of crystalline organic compounds embedded in their skin's cytoplasm.
Some organisms with metallic sheens have layers that are stacked in a regular
pattern, while others, including the ribbonfish, have stacking patterns
described as "chaotic" or random. The Penn State team determined that
the stacking is not completely random and developed mathematical algorithms to
replicate those patterns in semiconductor materials.
"We are proposing a model that uses fractal geometry to
describe the layering in the biological structure of silvery fish," says
Jeremy Bossard, postdoctoral researcher in electrical engineering, Penn State.
"While we are not trying to reproduce the structure found in nature, the
same model could guide the design of devices such as broadband mirrors."