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2006
■ BY JEFF ECKERT
ADVANCED TECHNOLOGY
INTERMITTENT SHORT
DETECTOR USES PULSE
TECHNOLOGY
■ Mike Dinallo (right) and Larry
Schneider (left) prepare to employ the
PASD diagnostic on a wiring bundle
in the cockpit of a retired Boeing 737.
Photo by Randy Montoya.
It may not sound all that complicated, but the folks at Sandia National
Laboratories ( www.sandia.gov) have
spent decades developing the
concept of pulsed power, and in
particular the version generated by its
Z machine, which sends short bursts
of trillions of watts down conduits
with diameters the size of your average horse. But a recent adaptation,
known as the Pulsed Arrested Spark
Discharge (PASD) operates on a much
smaller and more mundane level
and, in fact, will soon be available
from a commercial licensee, Astronics
Advanced Electronic Systems
( www.astronicsaes.com). The basic
concept is to introduce a high-voltage,
low-power pulse into an aircraft wiring
harness (up to 40 wires at a time) for
just a nanosecond to detect intermittent shorts that can result in expensive
downtime and even crashes. Because
the voltage is higher than that normally used in airplanes, the electrical
pulse will jump from the smallest
wiring insulation fault (which to
ordinary instrumentation seems
undamaged) to either the bulkhead or
another nearby damaged wire. That
spark, much like an electrostatic
discharge event, in effect lights up the
invisibly damaged spot. The amount
of time it takes for the current to
return to its source is analyzed by the
automated test set to measure, within
inches, how far the break is from the
test entry point. These breaks can be
difficult to locate visually, because the
wiring may have tiny insulation breaks
the size of a pinhole or a cut from a
razor blade, and traditional wire-test
systems have great difficulty finding
these faults, as well.
To enhance the tester’s
fault-locating ability, Astronics has
developed a method to superimpose
the PASD pulse on a DC current.
The DC current provides support for
the high-voltage pulse, which then
can detect breaches as far as 100
feet from its starting point — even
those occurring on branched wire
harnesses. The distance to a fault is
computable, regardless of changes
in impedance produced by the
wiring as it reacts to the PASD pulse
at various voltage levels. Other
possible uses envisioned for PASD
are to perform inexpensive tests on
the wiring of passenger cars and
new homes. Military tanks and the
hard-to-reach wiring behind the steel
bulkheads of submarines are also
possible candidates.
NEW X-RAY DELIVERY
METHOD FOR RADIATION
THERAPY
Researchers at the US Department
of Energy’s Brookhaven National
Laboratory have announced that,
following many years of investigation,
improvements in a heretofore experimental form of radiation therapy
appear to make the technique more
effective and eventually may allow its
use in hospitals. Results on the
improved method, which was tested
on rats, was published online by
the Proceedings of the National
Academy of Sciences and, at least
as of this writing, is viewable at
www.pnas.org/cgi/doi/10.1073/
pnas.0603567103. The technique,
developed in cooperation with
Stony Brook University, the IRCCS
NEUROMED Medical Center in Italy,
and Georgetown University, is known
as microbeam radiation therapy
(MRT). Originally, it simply used a
high-intensity synchrotron x-ray
source to produce parallel arrays of
very thin ( 25 to 90 m) planar x-ray
beams rather than the solid, broad
beams used in conventional radiation
treatment. Studies have shown that
MRT can control malignant tumors in
animals with high radiation doses
while subjecting adjacent normal
tissue to little collateral damage.
A drawback, however, is that only
certain synchrotrons can generate
these very thin beams at adequate
intensity, and such facilities are
available at only a few research
centers around the world. However,
the paper discusses how thicker
microbeams — which can be generated by more common x-ray tubes of
very high current and voltage — may
work, as well. Plus, the authors
describe a way to interlace the beams
to increase their killing potential
while retaining the technique’s
hallmark feature of sparing healthy
tissue outside the target.
In an experiment, they first
exposed the spinal cords and brains
of healthy rats to thicker (0.27 to 0.68
mm) microbeams at high doses of
radiation and monitored the animals
for signs of tissue damage. After
seven months, animals exposed to
beams as thick as 0.68 mm showed
no or little damage to the nervous
8
September 2006
