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304 Biomimetics: Biologically Inspired Technologies

(x ,y )
1
1
2
(x 2 ,y )

d

Figure 11.17 Depth perception through different visual fields.

As humans can triangulate depth from the fields of view of two eyes, a compound eye may prove
to be even more adept at discerning distances and dimensional measurements. This is because the
distances measured are based on calculations using multiple data points, decreasing the error of any
pair of eyes alone. This has applications in robotic navigation systems, surveillance cameras, and
borescopic devices.

11.4 OTHER BIOMIMETIC APPROACHES

This section deals with biomimetic engineering approaches to optics which do not fit easily into the
categories of camera or compound eyes. While the first two examples of brittlestar microlenses and
Melanophila acuminate beetle pit organs may seem simplistic relative to the other eye designs, they
are no less suited for their applications. In addition, it is important that ‘‘simple’’ is not confused
with ‘‘easily replicated’’ or even ‘‘easily understood.’’ Indeed, the idea of image formation by
projection from a lens onto a retina was noted by Johannes Kepler in 1604. But, as described below,
it was not until 2001 that scientists even recognized that the brittlestar had eyes, let alone was
covered with them.

11.4.1 Brittlestar Eyes

By all accounts, the brittlestar is a curious creature (see Figure 11.18). In particular, the species
Ophiocoma wendtii demonstrates marked photosensitivity and the ability to evade predators, all
without readily apparent eyes or a brain. In a letter published in 2001, Aizenberg et al. (2001)
reported that, in fact, the calcite crystals embedded throughout the skeletal structure were the
elements of an enveloping compound eye. The crystals, 40 to 50 mm in diameter, appear to form
doublet lenses with the ability to correct for spherical aberration and birefringence. In addition, the
focal point of the lenses is approximately 4 to 7 mm with a 3-mm spot size. This matches nerve
bundle locations and sizes beneath the calcite crystal array, supplying evidence to the notion that
the array forms a pixelated image of its surroundings.
Bell Laboratories or Lucent Technologies have used this discovery to design process flows for
artificial lenses which also limit birefringence and spherical aberration effects. This may have
applications in optical networking equipment and improved photolithography techniques. By organ-
ically modifying micropatterned templates, researchers are able to direct the growth of single calcite
crystals into sub-10-mm patterns and defined crystallographic orientation (Aizenberg et al., 2003).
Self-assembled monolayers (SAMs) of v-terminated alkanethiols on gold or silver supports are
used as crystallization templates, and organic posts can be added without upsetting single-crystal
growth. These posts allow for removing water and impurities during the transition from an