Biomedical Engineering Reference
In-Depth Information
aircraft to create a class of extremely small,
remotely piloted vehicles with a gross weight on
the order of tens of grams and a dimension on
the order of tens of centimeters. These are
collectively referred to as
micro-aerial vehicles
, or
micro air vehicles
(MAVs).
The concept of using miniaturized, remotely
piloted aerial vehicles for covert surveillance is not
new. In the 1970s, the Central Intelligence Agency
(CIA) developed an insect-sized, mechanical
dragonfly to carry a miniature listening device
[1]
.
The flapping wings of the dragonfly were actuated
by a miniature engine powered by a liquid
propellant. This MAV was designed to be steered
using a laser beam. Due to difficulties in controlling
the dragonfly, the project was not pursued beyond
the fabrication of a flying prototype, which is now
on display in the CIA museum.
In the early 1990s, a research project at Los Ala-
mos National Laboratory theoretically investi-
gated the feasibility of microrobots fabricated
using microlithographic techniques for military
uses
[2]
such as intelligence gathering and sen-
sing or disruption of a variety of environmental
stimuli (electrical, mechanical, and chemical). The
small size of these systems would have made
them difficult to detect, and the intent was to
increase the probability of mission success by
deploying a large number of microrobots. Mass
production, similar to the process used to fabri-
cate integrated circuits, was expected to keep the
costs of each individual robot low. During the
course of this research, the conceptual design of
a rotary-wing vehicle was explored using the
smallest commercially available electromagnetic
motors (
∼
1.5 g in mass), with different rotor
blades, thin-film batteries, and miniaturized video
cameras, acoustic sensors, and communications
chips. Four different flying vehicle configurations
were also investigated: fixed-wing, rotary-wing,
microairship, and a passive, autorotative device
based on a maple seed. The conceptual fixed-wing
vehicle had a total mass of 4 g, with 1 g of sensors
and a cruising speed of 900 cm/s. The conceptual
rotary-wing vehicle had a counter-rotating rotor
configuration with a sensor mass of 1 g, a cruising
speed of 200 cm/s, and an endurance of 5 min.
The conceptual microairship had a total mass of
1.8 g, featured an almost transparent film enve-
lope filled with hydrogen, and had a cruising
speed of 200 cm/s. The conceptual autorotating
device had a total mass of 0.3 g, with a wing area
of 1.5 cm
×
5 cm. These were designed to remain
aloft for the maximum time possible after being
deployed by a stealthy mother vehicle.
In late 1992, the RAND Corporation con-
ducted a workshop for the Advanced Research
Projects Agency (ARPA) on “Future Technology-
Driven Revolutions in Military Operations”
[3]
.
The objective of this workshop was to identify
breakthrough technologies that could revolu-
tionize future military operations. The identified
applications included a “fly on the wall,” or a
miniature fly-sized vehicle carrying sensors,
navigation, processing, and communication
capabilities. The vehicle design featured the
ability to move around by flying, crawling, or
hopping. Another application involved the
addition of a “stinger” on the vehicle that was
intended to disable enemy systems. For concep-
tual design, a vehicle mass on the order of 1 g,
with a size on the order of 1 cm, was selected.
The power required for hovering and for for-
ward flight was estimated, using momentum
theory, to be
∼
30 mW/g and
∼
45 mW/g. In
comparison, the hovering power requirement of
large insects ranges from
∼
9 mW/g to 19 mW/g,
and for hummingbirds,
∼
19 mW/g to 26 mW/g.
Based on using a 530 J thin-film lithium polymer
battery, this was calculated to yield an estimated
hover time of 4.9 h and a flight time of 3.3 h,
covering 80 km.
In the late 1990s, the Defense Advanced
Research Projects Agency (DARPA) released a
solicitation for MAVs that would have a dimen-
sion no larger than 15 cm, a mass of about 100 g
(with a payload of 20 g), and a mission endur-
ance of around 1 h.
These vehicles were intended to be man-
portable robots that could fly to a target and
