Biomedical Engineering Reference
In-Depth Information
beyond the low fidelity of small sensors. For
example, the vibration of flapping wings and
propellors can degrade inertial attitude sensing,
and flight close to the ground results in distorted
measurements of the Earth's magnetic field.
Insects have overcome these problems using a
highly integrated visuomotor system. In addition
to compound eyes, insects typically have three
simple eyes (a retina behind a single lens), called
the
ocelli
. The ocelli in dragonflies and locusts
provide a highly evolved optical stabilization
function by using the horizon as a visual reference.
Polarization sensitivity in the dorsal rim area of
the eyes of many insects provides a measure of
heading with respect to the sun. The small size of
insect sensors makes biomimetic solutions based
on insect eyes desirable. Many of these reflexes
will only function robustly as part of an ensemble
of reflexes, analogous to the biologically inspired
subsumption architecture proposed by Brooks
[4]
.
The characterization of systems deep within
the nervous system of insects is difficult due to
the complex multimodel nature of insect
sensorimotor neurons
[5, 6]
. Direct measurement
of the responses of neurons requires glass tubes
with a tip diameter of <1
μ
m filled with electro-
lyte to be placed and held either inside (intracel-
lular) or outside (extracellular) the cell wall of the
neuron. Ideally, many thousands of neuronal
responses would be measured simultaneously
while the insect is in flight in a natural environ-
ment. Such an experiment is beyond the state of
the art in neurophysiology and quite impractical.
In the absence of direct measurement, another
approach is to implement artificial versions of
the sensors involved, in an attempt to learn what
problems an integrated system must solve. The
remainder of this chapter demonstrates four
biomimetic optical technologies that have been
implemented and flight tested on UAVs. The
resulting systems reveal many challenges faced
by the insect brain and provide cues as to what
neurophysiology experiments should be done to
fully understand the system.
The head of a dragonfly (
Hemianax papuensis
)
is shown in
Figure 9.1
. The dorsal rim area of
FIGURE 9.1
Detail of the head of a dragonfly,
Hemianax papuensis
. The dorsal rim area along the seam between the left
and right eyes of many insects is polarization sensitive. The median ocellus and lateral ocelli receive light from the forward
direction and sideways, respectively.
