Butterfly Wings
Qualcomm
Many butterfly species use light-interacting structures on their wing scales to produce color in a way that suggests a novel model for producing environmentally-benign coloration with unique and valuable properties. The cuticle on the scales of these butterfly species’ wings are composed of nano-sized, transparent, chitin-and-air layered structures that, rather than statically absorb and reflect certain light wavelengths as pigments and dyes do, selectively cancel out certain colors through wavelength interference while reflecting others, depending on the exact structure and interspatial distance between diffracting layers. This system of producing color allows for the dynamic control of light flow and wavelength interaction, which butterflies rely upon for camouflage, thermoregulation, and signaling.
Human-made systems of structurally-produced color are now being designed which do not require the toxic heavy-metals or manufacturing methods common to many pigments and dyes (e.g., for iridescent fabrics and cosmetics), and to create high-performance electronic color displays by actively varying the interspatial distances of light-interacting layers (e.g., for cell phones), which can change colors rapidly, remain vibrant under low-light conditions, and require less energy than other electronic display methods.
Scientists are being inspired by nature to design the next generation of security devices. Arrays of nanoscale holes create beautiful reflected colours that are almost impossible to forge. Soon these nanoscale security devices could replace holograms. They are many times more reflective than holograms, and although the structures are smaller scale, they are lower aspect ratio and therefore easy to manufacture in bulk.
Iridescent Butterfly Wing Properties
Researchers studying the iridescent properties of butterfly wings think that this could help engineers develop temperature sensors that are smaller and faster. This technology could work without the need for cumbersome cooling techniques, something that has always been needed in thermal imaging and medical diagnostics.
Most sensitive thermal imagers necessitate cooling, which are large and based on liquid-helium refrigeration, in order to give accurate readings. Potyrailo and his colleagues at the General Electric Global Research Center at the University of Albany in New York have shown that a material inspired by the wings of a butterfly from the genus Morpho, which are covered in scales that reflect light at some wavelengths and absorb it at others, could help.
The iridescence isn’t yet completely understood, but it’s known that as the wing heats up, the intensity of different wavelengths of visible radiation reflected changes slightly, altering the color of the wing.
The team used this to construct a synthetic temperature sensor to see if it would have a significant advantage over current sensors. The wings of butterflies are made out of chitin, a natural polymer, which can, unlike metals, cool down quickly without heat sinks.
Then, they coated the material with carbon nanotubes, which also have excellent thermal conductivity, to enhance its ability to absorb infrared radiation. This provided them with a molecular heat sink.
Researchers still need to find a way to produce nanostructured chitin synthetically before they can produce a viable sensor.
Biomimicry: Copying our way to conservation
Morpho butterfly wings have tiny scales covered with microscopic ridges, cross ribs, and other structures. These play with light waves to create brilliant blues and speckles. The structure, instead of a chemical, creates the color.
“Brilliant iridescent colouring in male butterflies enables long-range conspecific communication and it has long been accepted that microstructures, rather than pigments, are responsible for this coloration. Few studies, however, explicitly relate the intra-scale microstructures to overall butterfly visibility, both in terms of reflected and transmitted intensities and viewing angles.
“Using a focused-laser technique, we investigated the absolute reflectivity and transmissivity associated with the single-scale microstructures of two species of Morpho butterfly and the mechanisms behind their remarkable wide-angle visibility. Measurements indicate that certain Morpho microstructures reflect up to 75% of the incident blue light over an angle range of greater than 100 degree in one plane and 15 degree in the other.
“We show that incorporation of a second layer of more transparent scales, above a layer of highly iridescent scales, leads to very strong diffraction, and we suggest this effect acts to increase further the angle range over which incident light is reflected.
mirasol™ display technology
“Qualcomm’s mirasol displays bring living color to technology by applying one of nature’s most remarkable innovations-the butterfly’s wings. These highly developed structures reflect light so that specific wavelengths interfere with each other to create nature’s purest, most vivid colors. By studying and mimicking nature’s processes and structures – a field of study called biomimetics – Qualcomm engineers have developed the nature-inspired mirasol display solution. By using this brilliant, time-tested biological development as the launching point for the new IMOD technology, Qualcomm brings nature to light effectively and efficiently in a cutting-edge display that will reshape the industry.” (from company website)
Qualcomm uses a so called IMOD (interferometric modulation) technology to create its color. In plain English, the technique adjusts precisely the color wavelengths that will be cancelled out by interfering with each other. The remaining color is what you will see.
I always point out that this technology is not trying to recreate an epithelium, but that engineers have abstracted the principles of the butterfly color phenomenon and applied achievable methods and materials to produce the same effect. In this case, the manufacturing processes of the silicon wafer industry are used to great advantage.