The transparency of Greta oto’s wings results from the combination of several properties: wing material has a low absorption of visible light, there is low scattering of the light that passes through the wings, and there is low reflection of the light impinging on the wing's surface.
The latter occurs for a broad range of incident wavelengths, covering the entire visible spectrum, and all incidence angles.
This broadband and omnidirectional anti-reflection property originates from nanopillars standing on the wing's surface which ensures a gradient of refractive index between the incident medium, air, and the wing's membrane.
These nanopillars, non-periodically arranged on the wing's surface, possess a high aspect ratio (defined as height divided by radius), where the radii are below the wavelengths of the visible light.
Additionally, they feature a random height and width distribution, which is directly responsible for the smooth refractive index gradient and thereby for the broadband and omnidirectional anti-reflection properties.
These properties are further improved by the presence of pedestals at the base of the nanopillars.
Additionally, the structure of the nanopillars allows for the wings to have a low roughness factor because of its tiny hair-like microtrichia features.
This was experimentally tested through water droplet adhesion to the wings.
The transparency of Greta oto’s wings results from the combination of several properties: wing material has a low absorption of visible light, there is low scattering of the light that passes through the wings, and there is low reflection of the light impinging on the wing's surface. The latter occurs for a broad range of incident wavelengths, covering the entire visible spectrum, and all incidence angles. This broadband and omnidirectional anti-reflection property originates from nanopillars standing on the wing's surface which ensures a gradient of refractive index between the incident medium, air, and the wing's membrane. These nanopillars, non-periodically arranged on the wing's surface, possess a high aspect ratio (defined as height divided by radius), where the radii are below the wavelengths of the visible light. Additionally, they feature a random height and width distribution, which is directly responsible for the smooth refractive index gradient and thereby for the broadband and omnidirectional anti-reflection properties. These properties are further improved by the presence of pedestals at the base of the nanopillars. Additionally, the structure of the nanopillars allows for the wings to have a low roughness factor because of its tiny hair-like microtrichia features. This was experimentally tested through water droplet adhesion to the wings.
Greta oto