Thermal imaging & vision systems
Infrared imaging of butterflies from the family Lycaenidae. The intensity of the picture is proportional to thermal emissivity - the capability of dissipating heat via thermal radiation. The image shows that living parts of the wings have elevated thermal emissivity. Image credit: Nanfang Yu and Cheng-Chia Tsai
temperature from their measurements. In addition to mapping out the thermal distribution of butterfly wings, the researchers also conducted behavioural studies that they observed in thermal. Using a small light as a heat source, they demonstrated that butterflies use their wings to sense the direction and intensity of sunlight. At the “trigger” temperature of approximately 40°C, all the species they studied turned within a few seconds to avoid the light and keep their wings from overheating. This is not Yu’s first time using a thermal camera to study insects. “When I was joining Columbia in 2013, the FLIR camera was one of the first pieces of equipment I bought while I was setting up my lab,” Yu says. Though his research is mainly focused on nanophotonics, Yu is particularly interested in the intersection between biology, photonics, and physics. His research friends in the field of biology “often they probe me with questions regarding the life history of animals they are studying... I’m quite interested in helping them solve these mysteries from a physics and photonics point of view.” In an earlier collaboration with a nanobiologist colleague, Yu studied Saharan silver ants, which forage during the heat of the day in one of the
hottest terrestrial environments on earth. In this study, published in Science in 2015, the researchers also used a FLIR scientific camera to monitor the body temperatures of the ants. They wondered how such small insects could survive such harsh conditions. “The interesting thing here is understanding how small and light insects - tiny ants or the thin wings of butterflies - manage thermodynamically, because they are, by default, very bad at it,” Yu explains. Due to their small thermal capacity, small animals like insects can heat up to extreme temperatures within a few seconds. The silver ants deal with extreme heat using the very fine hairs that cover their bodies. These hairs serve two functions: backscattering light in the visible and infrared wavelength to reduce the amount of absorption from solar energy, and enhancing thermal emissivity, so when the body of the ant is heated it can better distribute the heat in the form of thermal radiation. “We wanted to find out how small animals
were hardwired to survive extreme heat,” Yu says. His latest study continues exploring the question of how small insects manage to keep cool. Butterfly wings are covered with mechanical sensors to detect overheating, and their wing
scales contain nanostructures that help facilitate radiative cooling. Besides the biological interest of these findings, Yu thinks they could serve as inspiration for the design of heat-resistant nanostructures and heat-sensing aircraft. Yu and his colleague Naomi E. Pierce, Hessel Professor of Biology, plan to continue their research on butterfly wings. Pierce is the Curator of Lepidoptera at the Museum of Comparative Zoology at Harvard, and has access to a large collection of butterflies and moths. They are currently conducting an extensive scan of the collection using a thermal camera, and hope to gain an understanding of the factors that contribute to the design of a butterfly wing. Yu compares the work to “deciphering a complex book” because of the many diverse elements that have played a part in the evolution of the butterfly wing. Clearly, this is one book that is worth reading closely to see what other discoveries we might uncover.
Teledyne FLIR
www.teledyneflir.com
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November 2022 Instrumentation Monthly
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