Carmichael’s Concise Review
Mie scattering of similar strength occurs in both circular and triangular hairs; in the latter the total internal refl ection from the bottom fl at surfaces of individual hairs substantially enhances refl ectivity.
An equally important function of the hair array in the thermoregulation of the ants is that it enhances emission of heat radiation from the ant’s body. Shi et al. showed this in a series of thermodynamic experiments where the effi ciencies in dissipating heat as thermal radiation are compared between ants with intact hair covers and with bald surfaces. Furthermore, the hairless bottom surface of the ant was shown to reduce the radiative energy transfer between the hot sand and the cooler ant body so that the animals can reduce the absorption of blackbody radiation from desert fl oor. T is occurs in the mid-infrared range. T e most exciting aspect of these studies is the demon- stration that properties of a structured surface, specifi cally the shape and surface characteristics of hair-like projections, can provide eff ective passive cooling of objects. T is biological solution for a thermoregulatory problem could lead to the development of biomimetic coatings that would be very benefi cial!
References [1] N Shi et al ., Science 349 ( 2015 ) 298 – 301 . [2] T e author gratefully acknowledges Dr. Nanfang Yu for reviewing this article.
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10
2015 November
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