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Biologically Inspired Optical Systems 305

Figure 11.18 (a) The brittle star, (b) electron micrographs, (c) ray tracing through a calcite lens.
amorphous calcium carbonate phase to the crystalline phase. The result is a large, microporous
single crystal. Light microscopy images of the crystallization process, as well as infrared spectral
response of the crystals, are shown below (Figure 11.19).

11.4.2 Melanophila acuminate Beetle

Yet another interesting animal, the M. acuminate beetle, has the uncanny ability to find forest fire
areas for breeding purposes. Females of this species lay their eggs in burnt wood, where the natural
defense mechanisms of living trees are absent. This is the only place their larvae can survive. While
M. acuminate is not the only creature with this practice, it is often the first to arrive, sometimes
outpacing other insects by weeks to months (Sowards et al., 2001).
M. acuminate are guided by specialized structures, known as pit organs, which are more
sensitive to the frequency of infrared light emitted by forest fires (Figure 11.20). These organs
(450 mm 200 mm 108 mm deep) house 50 to 100 sensilla (each 15 mm in diameter). Following
infrared light absorption, the expansion of a cuticular apparatus is detected by mechanoreceptors
which direct the beetles to the fire (Sowards et al., 2001).
Equivalent man-made guidance systems, heat-seeking missiles, for example, rely on sensors
that need to be cooled to freezing temperatures at significant cost. Schmitz et al. have been working
on adapting insights gleaned from analyzing the M. acuminate beetle for use in similar applications
(Roach, 2004). Their design uses a disc which expands in response to infrared radiation. The
composition of the disc depends on the infrared source, with examples such as Teflon for heat from
a human hand or polyethelene for fire detection. Currently, the mechanosensors used are able to
detect a source 30 to 40 cm away. The sensitivity is expected to increase greatly with more sensitive
mechanosensors and tailored disc materials.

11.5 CONCLUSION

When it comes to designing optical systems, humans have been unquestionably creative. Still, it has
not been until relatively recently that there has been a major thrust towards biologically inspired
optics. Of the multitude of natural vision systems that exist, only a relative few have been emulated
using man-made materials. And it is probably safe to say that none of these artificial systems have
matched the performance of their biological counterparts.