Biomedical Engineering Reference
In-Depth Information
photodiodes were tested by rotationally sweep-
ing the field of view of each photodiode over a
small, bright target (the sun). Their responses are
plotted in
Figure 9.14
. The ultraviolet photodi-
ode had a circular field of view (full width at half
maximum) of 100°, compared to approximately
120° for the green photodiode.
From the data in
Figure 9.2
, it is evident that
the sky is bright in all visible wavelengths and
ultraviolet. The ground is relatively bereft of
shorter wavelengths while remaining almost as
bright as the sky in the green and red wave-
lengths. The sun, on the other hand, is very
bright in all wavelengths captured by the scan-
ning device. Our main concern was to limit the
effect of the sun and clouds on horizon
stabilization.
The ultraviolet band showed a ratio of sky
intensity to ground intensity of 15:1 or more,
whereas the green and red bands had an overall
ratio of 1.1:1 or less.
FIGURE 9.13
The device developed to mimic the func-
tion of ocelli consisted of eight photodiodes composed of
four ultraviolet/green pairs. Two pairs were used to emulate
the broad frontal field of view of the median ocellus.
For the sake of simplicity, we did not use
optics to shape the fields of view of the ocelli. We
thus depended on the intrinsic geometrical prop-
erties of the diodes. Fields of view of the each
750
green
UV
700
650
600
550
500
450
400
-100
-50
0
50
100
Yaw angle (deg)
FIGURE 9.14
Responses of the green (dotted line) and ultraviolet (solid line) photodiodes to being rotated over the sun
on a rotary table. The field of regard of the green
photodiode
is slightly larger than that of the ultraviolet photodiodes due to
the shorter
metal can
packaging of the component. We determined that the fields of view were representative enough of the
dragonfly anatomy to form a lateral ocelli, or one-half of a median ocellus.
