TechKnowledgey 2004
by Jeff Eckert
TechKnowledgey
2004
Events, Advances, and News
From the Electronics World
Advanced
Technologies
Lords of the Flies
The hyperacute directional hearing of
Ormia ochracea results from its unique
ears, which are part of the prothorax
behind its large head, as shown.
Photo by R. Hoy and G. Haldeman/Cornell
University. Copyright Cornell University,
reproduced with permission.
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NUTS & VOLTS
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Recently, some researchers at
Cornell and Binghamton
Universities ( www.cornell.edu and
www.binghamton.edu) have been
spending a lot of time with flies. No,
this is not a reflection of their personal hygiene, but an embodiment of a
grant from the National Institute on
Deafness and Other Communication
Disorders (NIDCD, www.nidcd.
nih.gov) that has underwritten a
study of Ormia ochracea, which is a
peculiar cousin of your common
housefly. Most flies primarily eat
plants and animals that are already
dead or decaying, but Ormia is a par-asitoid; it lives off of living animals.
When a female Ormia hears the
chirp of a male field cricket, she flies
to within a few inches of it, sneaks up
on its back, and deposits larvae that
eventually burrow down into the
cricket. In a few days, the larvae
8
emerge from the unfortunate, dead
cricket and fly away, much as relatives flee from your home after
devouring a huge holiday meal and
finishing off all of the good Scotch.
Perhaps the most remarkable
thing about this process is that, even
though Ormia is endowed with the
standard array of sensory equipment
(compound eyes, antennae, and
ultrasensitive legs), it locates the
cricket by directional hearing in the
same way that humans use stereo
processing to determine which nearby car is blaring the offensive music
at 140 dB. However, the fly’s
eardrums — located beneath its head
— are only 0.5 mm apart, which,
theoretically, is too close to allow
“bilateral interaural intensity differences” to be detected at the cricket’s
chirp frequency of about 5 kHz
(which translates into a wavelength
of approximately 69 mm).
The secret lies in the fact that the
fly’s eardrums are connected by a
small bridge. The official explanation
is that, when a sound is detected in the
right ear, the right eardrum vibrates,
causing the left eardrum to vibrate out
of sync, and vice versa. This back-and-forth vibration of the eardrums creates
a difference in pressure between the
two ears, which the fly’s ganglia and
brain quickly compute. Within 50
nanoseconds (1,000 times faster
than you can do it), Ormia’s brain
sends a signal to its muscles and the
fly turns toward its target. When a
recording of a cricket’s chirp is played
for the subject fly, it responds quickly
and accurately (much more so than a
female cricket, which was what the
male was actually hoping to attract).
By now, you are probably wondering what this has to do with elec-
tronics. The connection is that the
fly’s audio equipment has inspired a
novel design for hearing aids that,
within a few years, could perform
better and cost much less than existing designs. As stated by NIDCD
Director James Battey, Jr., “The biological lessons provided by Ormia’s
abilities in hyperacute time coding
and localization of sound promise to
produce strategies for improved nano-or micro-scale directional microphones in hearing aids. Applications
of these new principles may improve
life for individuals with hearing loss
who depend upon hearing aids.”
Improvement in Magnetic
Refrigeration
The concept of magnetic refrigeration has existed since the
1920s and one scientist (Canadian
William Francis Giauque) even won a
1949 Nobel Prize for related work. A
magnetic refrigerator could potentially offer better energy efficiency,
lower operating costs, the elimination of environmentally hostile
coolants, and nearly silent operation.
Nevertheless, the concept has never
been translated into practical, commercial products and we all still live
with the century-old technology of
vapor-compression cooling systems.
The situation could change, however, as a result of developments at
the National Institute of Standards and
Technology (NIST, www.nist.gov).
An NIST team has discovered that, by
adding a small amount (about 1%) of
iron to a gadolinium-germanium
alloy, its cooling capacity can be
increased by 15 to 30%, resulting in,
“a much-improved magnetic refrigerant for near-room-temperature appli-
SEPTEMBER 2004
