Air temperature drives the evolution of mid-infrared optical properties of butterfly wings

This study uncovers a correlation between the mid-infrared emissivity of butterfly wings and the average air temperature of their habitats across the world. Butterflies from cooler climates have a lower mid-infrared emissivity, which limits heat losses to surroundings, and butterflies from warmer climates have a higher mid-infrared emissivity, which enhances radiative cooling. The mid-infrared emissivity showed no correlation with other investigated climatic factors. Phylogenetic independent contrasts analysis indicates the microstructures of butterfly wings may have evolved in part to regulate mid-infrared emissivity as an adaptation to climate, rather than as phylogenetic inertia. Our findings offer new insights into the role of microstructures in thermoregulation and suggest both evolutionary and physical constraints to butterflies’ abilities to adapt to climate change.

A thin and optically transparent infrared-radar compatible stealth structure with low emissivity and broadband absorption

In this paper, an optically transparent structure that combines broadband absorption and low infrared emissivity for dual-band stealth is proposed. The whole structure includes two functional layers. The periodic resistive film of the upper functional layer acts on infrared stealth. Its emissivity in the infrared band of 8-14μm is lower than 0.3. Another functional layer achieves greater than 90% wide absorption from 6 to 18.5 GHz. The whole optically transparent composite structure has a low profile of 0.141λ0, where λ0 is the wavelength of free space at the center frequency. It has an absorptivity that greater than 90% in the region of 5.7-16.5 GHz and has wide angular stability. Measured result is consistent with the simulation which verify the performance of the proposal. The infrared-radar compatible stealth structure proposed in this paper has potential application in the field of multi-spectrum compatible stealth.