Deconstructed beetles: green composite materials with potential for passive cooling due to high near-infrared reflectivity - Data and Code
This data allowed us to describe the optical properties and underlying structures that produce very high near-infrared reflectance in three species of green scarab beetles Xylonichus eucalypti, Anoplognathus prasinus and Paraschizognathus olivaceus. Although the chiral structures in scarabs have been well described in previous literature, we have limited knowledge of the natural mechanisms to manipulate near-infrared light (NIR; 700 – 1700 nm). In addition, previous studies in light manipulation by the beetle elytra have been focused mainly on the cuticle. Thus, our aim was to explore if other elements in the elytra can contribute to their characteristic visible and NIR reflectance. This dataset contains different types of data including reflectance and transmittance spectra, morphological data of the shape and dimension of the nanostructures that reflect light in the beetle elytron, and results of computational models simulating different scenarios to understand how these structures interact with light. Thus, we are attaching a readme file inside the folder "Data" explaining the data collection and usage for each file. Our Highlights: - The studied beetle species have similar high NIR reflectance and green appearance. - The elytra of these species contains bilayered composite materials, where a structural component reflects light and an overlaying thin layer filters only the reflectance in the visible spectrum. We showed that the transmittance of the outermost component of the composite materials is similar in the three species. - We characterized the shape of the nanostructures that produce broadband reflectance in Xylonichus eucalypti. - We compared different simulated scenarios where the nanostructures varied in separation and size and were illuminated with different polarizations and angle of incidence.
Steps to reproduce
1_HemisphericalReflectance.csv: Data was obtained with a dual spectrometer coupled to an integrating sphere to capture the reflectance from 400 to 1700 nm. 2_Transmittance.csv: Data was obtained with a dual spectrometer with the sample placed in between two fibre optics to capture the transmittance. Although the spectrometer allows a measurement from 300nm, we then limited the wavelength range from 400 to 1700 nm to match the reflectance data. 3_TransmittanceMicroScale.csv: We carefully removed the white underlay and measured the cuticle’s transmittance with the scatterometry set up (see supplementary materials for more information) 4_XylonichusCylinderDiameters.csv: We processed the TEM images from the white underlay of X. eucalypti with the plug-in ‘Analyze particles’ in Fiji, ImageJ. This plugin allowed us to fit ellipses to the transversal section of the air cylinders and extract basic statistics to describe their shape. 5_XylonichusCentroidDistance.csv: Based on the previous file. Using the x and y coordinates provided by the plugin, we were able to calculate the euclidean distance between the centre of two adjacent ellipses. We did this only for a subset of the particles. 6_PrumModelResults.csv:We ran numerical simulations of the structure using a custom MATLAB script adapted from the algorithm previously used to study quasi-coherent scattering from similar structures with two distinctive refractive indices producing diffuse blue scattering in birds. The original version of this algorithm was provided by professor Richard O. Prum. 7_PhotonicCrystalModelResults.csv: We created a 2D photonic crystal model assuming the structure to be a chitin matrix with air cylinders aligned along the longitudinal axis of the elytron (here equivalent to the z plane) (Fig. S4.). We analysed its interaction with light of different wavelengths and polarizations using the Finite Element Method (FEM) as implemented in COMSOL Multiphysics (5.6). This file includes only examples of the models with data around the mean measurements from TEM. 8_PhotonicCrystalScenarios.csv: We created a 2D photonic crystal model assuming the structure to be a chitin matrix with air cylinders aligned along the longitudinal axis of the elytron (here equivalent to the z plane) (Fig. S4.). We analysed its interaction with light of different wavelengths and polarizations using the Finite Element Method (FEM) as implemented in COMSOL Multiphysics (5.6). For this file, we simulated different scenarios based on the main percentiles on the TEM morphological characterization