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Shell Game: Mollusc inspires research into new generation of augmented reality screens


via flickr © goat_girl_photos (CC BY-SA 2.0)

Lurking in the in rock crevices in the cold water kelp beds around the UK, Norway and Iceland are little molluscs about the size of a finger nail. There are a lot of them but, being almost entirely translucent they are almost impossible to see.

However, when sunlight refracted through the water hits the creatures at certain angles it impinges on a series of dotted lines that radiate across the shell. These stripes then reflect back a brilliant bright blue/green fluorescent flash indicating where the blue-ray limpet (patella pellucida) is living it's quietly contemplative vegetarian life.

This natural phenomena has led intrigued scientists to wonder if a limpet's natural light-show could somehow be co-opted and adopted to provide advanced augmented reality screen technologies of the sort that would permit car drivers to overlay navigation and other data on a vehicle windscreen without it in any way interfering with the view of the road.

Head-up displays are fairly commonplace but this is different. The hope is that if it is possible to mimic the blue-ray limpet's ability to change its appearance under different lighting conditions new augmented reality screens might be built that display information even as users look straight through them.

Researchers working in teams at both Harvard University and MIT in Massachusetts in the US are examining crystalline mineral formations in the limpet's shell and have learned that the various calcium carbonate strata therein are laid down in different depths in such a way that they divert wavelengths of light to reflect only in blue.

Thus, the scientists are working on re-arranging the thickness and spacings of material used in augmented displays so that a user would be able to access different data simply by tilting the head rather than touching a screen or toggling a key.

Mathias Kolle, a professor of mechanical engineering at MIT, and his team examined the molluscs though a scanning electron microscope, a spectroscope and a diffraction microscope.

Then, applying  2D and 3D structural analysis they ascertained that at a depth of 30 microns beneath the surface of the limpet shell, the three-dimensional calcium carbonate architecturec changes into a multilayered photonic pattern that sits atop a layer of randomly spaced spherical particles. The topmost zigzag pattern reflects only blue (and some  green) lightwaves while the  the layer of disordered particles beneath absorbs the other wavelengths making the stripes appear to be blue.

The research is covered in considerable in the academic journal "Nature Communications" and is well worth a read,

Professor Kolle and his team have considerable previous form in the area of adapting some of the tricks of nature, such as animal and insect camouflage, to industrial use. For example, in 2014, the researchers demonstrated how the patterning on butterfly wings could be co-opted and be printed on bank notes that are then practically impossible to counterfeit.

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