IEEE Spectrum May, 2010 - 33

The idea of building a high-tech

defense against disease-carrying pests had come up in
discussions that Myhrvold and Wood had been having
with Bill Gates, who was Myhrvold's boss when he
was chief technology officer at Microsoft in the 1990s.
Through the Bill and Melinda Gates Foundation, Gates
has been trying to improve living conditions in some of
the world's poorest countries and in particular to come
up with ways to eradicate malaria, a mosquito-borne
disease that sickens about a quarter billion people a year
and kills nearly a million annually, including roughly 2000
children a day (see Web-only sidebar, "New Techniques
Against a Tenacious Disease").
Wood, a veteran of advanced weapons development
at Lawrence Livermore National Laboratory, in California,
and one of the scientists behind the Strategic Defense
Initiative (otherwise known as "Star Wars"), had
suggested trying a similarly high-tech approach against
malarial mosquitoes-to take advantage of inexpensive,
low-power sensors and computers to somehow track
individual mosquitoes and shoot them out of the air. If it
could be done cheaply enough, this might offer the first
really new way in many years to combat malaria, as well
as other diseases transmitted by flying insects, such as
West Nile virus and dengue fever.
Hyde and I had worked with Wood at Livermore. Hyde
now manages Intellectual Ventures' stable of staff and
consulting inventors, and he assigned me the challenge
of making the idea work-or showing why it couldn't.
Three years later, my colleagues and I at Intellectual
Ventures have now worked out many of the trickiest
aspects of the photonic fence and have constructed
prototypes that can indeed identify mosquitoes from
many meters away, track the bugs in flight, and hit
them with debilitating blasts of laser fire. And we
did it without a multimillion-dollar grant from some
national Department of Entomological Defense. Nearly
everything we used can be purchased from standard
electronics retailers or online auction sites.
In fact, for a few thousand dollars, a reasonably
skilled engineer (such as a typical IEEE Spectrum reader)
could probably assemble a version of our fence to shield
backyard barbecue parties from voracious mosquitoes. We
therefore present the following how-to guide to building a
photonic bug killer, in five parts: selecting an appropriate
weapon, spotting the bugs, distinguishing friends from foes,
getting a pest in your sights, and finally shooting to kill.
32

NA * iEEE SpEctrum * mAy 2010

Why build a fence? You could
try to lure bugs to one spot
and kill them, but more will
just keep arriving. For all
practical intents, the supply of
mosquitoes is infinite.
You could build a system that
scans your entire yard for bugs.
But as any infantryman knows,
the first step in defense is to
establish a perimeter; it's much
more effective (and safer) to
concentrate your firepower
in a narrow zone. Mosquitoes
generally don't spend their
whole lives in your backyard,
unless you live in a swamp.
They fly back and forth from
their breeding grounds, so to
get to you they have to cross
your laser-guarded perimeter. A
few may fly over the fence, but
not many. The average flying
altitude varies among mosquito
species but is usually only about
2 meters. They will fly over
obstacles when necessary-even
into an upper-story window-
but if your virtual fence is 3 to 5
meters high, it can catch almost
all mosquitoes that fly by.
Of course, there are any number of ways to build a fencelike
barrier. You could detect mosquitoes acoustically, with radar, or
with ultrasonic sonar. You could
shoot them down with tiny bullets, break them apart with sonic
pulses, or cook them with microwaves. We considered these and
many other possibilities, but it's
hard to beat the range, precision,
and literally lightning-fast
response of optics. Good digital
cameras and powerful diode
lasers are relatively affordable
and easy to find. So for us, photonic technology is the way to go.

geTTing a
bug in The
Crosshairs

To detect mosquitoes, you'll
need several video cameras-
four per fence post for a full-

coverage fence (two at the top
and two at the bottom facing
the two adjacent fence posts-
see "Spot the Skeeter"). The
cameras don't have to be sharp
enough to take a good photo of
a mosquito many meters away,
but they should have a resolution high enough so that a distant insect will at least fill up
most of one pixel. If the bug
occupies several pixels in the
frame, that's even better, as this
will allow you to find its center.

LIGhTS, cAMERA... Here's
some of the equipment needed
to image a tiny bloodsucker flying
at up to 1 meter per second.

A 1.3-megapixel (1280- by 1024pixel) camera turned sideways
can cover a 4-meter-high fence
post with pixels 3 millimeters on
a side. If you're economizing, you
could even try VGA-resolution
(640- by 480-pixel) cameras.
The speed of your cameras
matters as much as the
resolution. It's no good if the bug
is already through the fence by
the time your system registers its
presence. Mosquitoes fly up to a
meter per second, so if the active
zone is 10 centimeters wide, the
frame rate must be more than
10 frames per second. Standard
video cameras supply 30 frames
per second, but the frames are
interlaced-odd and even rows
of pixels are delivered separately,
1
/60 second apart-which will
make it hard to follow a small
moving object. So you'll want
to use noninterlaced cameras,
or at least units on which you
can disable the interlacing.
You're interested only in a
narrow vertical strip of image, less
than 100 pixels wide, so you can
drastically cut down the amount
of data your cameras produce if
you capture only that strip. Many
digital video cameras allow you to
spectrum.ieee.org

Ryan Smith/intellectual VentuReS

Choose
Your Weapon

http://spectrum.ieee.org

Table of Contents for the Digital Edition of IEEE Spectrum May, 2010