3.6.a "But how could you detect plastic guns?"
Description
This article is from the talk.politics.guns Official Pro-Gun FAQ, by Ken Barnes (kebarnes@cc.memphis.edu) with numerous contributions by others.
3.6.a "But how could you detect plastic guns?"
Harris, David A., "Superman's X-Ray Vision and the Fourth Amendment:
The New Gun Detection Technology,""Temple University Law Review,"
v.69 n.1 pp.1-60.
"Contraband Detection System," U.S Patent #5,227,800
issued Jul. 13, 1993 to Millitech, Inc.
Society of Photo-Optical Instrumentation Engineers (SPIE) website
at http://www.spie.org/
In summary: Ever-advancing computer processing power and the
conversion of Cold War defense industries to other purposes have
produced new technologies which improve upon the ability of x-ray
machines and magnetometers to detect weapons. The most intriguing
of these technologies is called millimeter-wave imaging (MMWI),
which could give law enforcement officers the ability to see
through walls and clothing to detect the location of concealed
objects, including weapons. MMWI uses a device similar to an
infrared camera to produce images of objects by detecting invisible
radiation given off in the region of the electromagnetic spectrum
between infrared and microwaves. This radiation, called millimeter
waves due to its wavelength, includes the frequencies of 30 to
300 GHz, and can pass through many common materials. A millimeter-
wave imager contains an array of microscopic antennas formed onto
a chip called an MMIC (for monolithic microwave integrated circuit).
Acting like film in a camera, or the CCD chip in an ordinary
camcorder, millimeter waves are focused onto the MMIC through
lenses, and the image produced by the detector can then be
displayed on a video screen. Originally developed to enable
soldiers (and their computerized weapons systems) to see through
the dust and smoke of battle, and used by astronomers to see
through the clouds of galactic dust between the stars, similar
detectors are beginning to be used in collision avoidance radars
to enable truck drivers and other motorists to see through fog,
rain, and gloom of night.
There are two types of millimeter-wave "radars" being proposed
as additions to the crime-fighting arsenal. The "passive" version
simply images the natural millimeter-wave radiation produced by
warm objects like the human body, and uses the difference between
the millimeter-wave emissions of the body and the lower emissions
transmitted by contraband or weapons, detecting the "darker" objects
that "eclipse" the radiation coming from the body. Due to the
effects of the atmosphere, passive MMWI is limited to a range of
3 meters (about 10 feet). "Active" millimeter-wave imaging combines
a source of millimeter-wave energy with the detector, and works much
like radar, "illuminating" the area to be searched with millimeter
waves, and then imaging the reflected waves. The active version
has a range of 30 meters (90 feet) or more, and could be used to
covertly "frisk" a crowd of people. Though MMWI can see through
clothing, or other materials which transmit millimeter waves but
look opaque to visible light, the resolution is presently not high
enough to reveal intimate anatomical details. Understandably, this
technology has raised Constitutional questions about the Fourth
Amendment right to be free from unreasonable search and seizure.
Manufacturers of MMWI devices argue that they can be configured
to only display an image if suspicious objects are detected,
thus meeting the criteria for "reasonableness," much as the
sensitive nose of a police dog can be used as pretext for a
physical search. However, police dogs don't have the ability to
search a crowd of people from 90 feet away.
Objects which have a high moisture content are difficult for
the MMWI to see through, since water absorbs microwave energy at
frequencies close to those used in MMWI. (Indeed an ordinary
microwave oven works by heating up the water molecules in food
using frequencies about 12 times lower.) MMWI "stealthy" materials
having similar dielectric constants to the body (such as a holster
containing circulating layers of warm water) might be able to
conceal weapons from a passive MMWI scan, or even an active scan
at long range, if resolution is poor. But other technologies could
detect even such MMWI "shielded" weapons, so long as the weapons
have a certain amount of metallic content. (Certain items of
contraband, such as illegal drugs, since they lack metallic content
entirely, will be able to slip by undetected if properly shielded.)
Other weapon detection schemes are on the horizon which, while
they will not be able to detect non-metallic weapons like MMWI can,
will enhance existing abilities to detect metallic weapons. One
system being developed uses an electromagnetic pulse, called a
Heaviside pulse, which induces metal objects to emit characteristic
radio "signatures," and can (theoretically) be used from a distance.
Another system is designed to detect the deviations in the Earth's
magnetic field caused by the presence of metallic objects, and
works like a walk-through metal detector, but can localize and
to some extent "count" the number of possible weapons being carried
on a person.
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