In a message dated 10/3/1999 1:03:24 AM Eastern Daylight Time, Delvieron@aol.com writes:
<<< In a message dated 10/2/1999 10:40:18 PM Eastern Daylight Time,
Chuck Kuecker writes:
<<Speaking as one who actually tried building a wireless stun gun, I have two
comments about the 'UV laser' approach:
First, any laser powerful enough to ionize air is a weapon all in itself.
Even if it was only breifly pulsed, it takes quite a bit of energy to
ionize a column of air.
Second, to maintain the ionized channel long enough to conduct current will
take a large voltage to strike the plasma arc, and a large discharge
current to keep it lit. I doubt it will be possible to send the 'T-wave'
pulses as used in the original Taser product through this channel - it will
be more like a lightning bolt. Also, the fact that a return path is
required would either put the operator at risk in becoming part of the
circuit, or would require two ionized paths, parallel to each other and
fairly close together. What's to keep the current from taking the easy way
out and arcing right at the projector?
Before patent research found that I had been scooped by Jaycor (check out
their webpage for some really DUMB idea), I built and tested a stun gun
using two conductive streams of water. Due to breakup of the streams, the
best range I got was just over three feet - but I was able to light a neon
target reliably at that distance. The obvious problems with this approach
are that a raincoat completely defends against either conductive streams or
any 'UV' approach that does not incinerate its' target.>>
Thank you very much for your post, Chuck. Some hands on experience is
exactly what we need here in our theoretical musings<g>. Your comments are
the kinds of things I thought might be a problem with the wireless tasers
(though they were quite muddled in the back of my head and I didn't have
enough experience in this area to really be certain if there were anything
to
them). I was worried that it would take a lot of energy to successfully
fire
a taser without wires, and hadn't even considered the two pathway issue.
And
of course the fact that it is easy to foil a taser with relatively common
clothes protection is a problem as well. Too bad that the UV laser would
require so much energy (thus increasing its destructive capability).
Glen Finney >>>
Yeah, I'm replying to my own post<g>.
Found some papers on this guy Herr's concept of a UV laser taser, which they are claiming will be able to create an ionized channel of air without doing significant harm to the body (effects on eye seem to be brought up). Check out the patent and some of the articles on the proposed weapon. Sounds like there is still a lot of work to be done, but does the physics add up? Anyone have any hard data on what it takes to sufficiently ionize the air for something like this to work?
Glen Finney
Websites:
<A
HREF="http://164.195.100.11/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&
p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1='5,675,103'.WKU.&OS=PN/5,675,103&R
S=PN/5,675,103">United States Patent: 5,675,103</A>
<A
HREF="http://www.sunday-times.co.uk/news/pages/sti/99/05/09/x-stiinnnws02007.h
tml?999">THE SUNDAY TIMES: INNOVATION : Ray gun freezes victims without
causing injury</A>
Photonics
Technology News January 1999: UV Lasers Stop People in Their Tracks</A>
A third object of this invention is to provide a non-lethal weapon which is capable of temporarily immobilizing a target subject without causing pain, shock, disorientation, or loss of consciousness.
A fourth object of this invention is to provide a non-lethal weapon which is capable of temporarily immobilizing a target subject without his being aware of the cause.
A fifth object is to provide a non-lethal, immobilizing weapon whose range is substantially greater than prior related weapons that use wires or conductive liquid streams.
A sixth object is to provide a non-lethal, immobilizing weapon which can be fired from a remote location without requiring the physical impact of solid or liquid matter upon the target.
A seventh object is to provide a non-lethal, immobilizing weapon which can be directed continuously and swept across an indefinitely large number of target subjects.
An eighth object is to provide a non-lethal, immobilizing weapon which can rapidly be fired toward a specific location on a single target subject, or to a specific target subject among many because of the highly directional nature of its current-conducting means.
These and other objects are achieved by transmitting relatively high frequency electrical impulses to the target by means of one or two electrically conductive channels of ionized air produced within one or two beams of intense ultraviolet radiation aimed at the target, and by placing a high-voltage field of the opposite polarity across the path of each beam.
The present invention functions by immobilizing the target person or animal at a distance. It performs this function by producing skeletal muscle tetanization in the target subject. Tetanization is the stimulation of muscle tissue by a series of electrical impulses of such frequency as to merge individual muscle contractions into a single sustained contraction. The immobilizing tetanization is maintained as long as the weapon continues to produce an electrical current within a major portion of the skeletal musculature of the subject, and for a brief time thereafter due to paralysis caused by the temporary inhibition of neuromuscular impulses. The optimum current and frequency required to create and maintain immobility while avoiding impairment of cardiac or respiratory activity are 25 milliamperes and 100 hertz, respectively. Currents in the range of 20 to 50 milliamperes and 5 to 2500 hertz may also be employed, with the higher frequencies requiring higher currents. A frequency of about 2 hertz may ultimately be used to produce painful spastic contractions. A minimum electrical potential of approximately 600 volts is required to overcome skin resistance without producing burns.
The most effective current waveform in producing tetanization is that which most closely duplicates the physiologically produced neural impulse. As Offner points out, this waveform is an exponentially rising pulse. The second most effective waveform is a square wave, whereas the least effective is a sine wave. Due to their rapid risetimes, square waves allow the greatest penetration through the clothing and skin of the target subject.
Further, the differences in the effectiveness of various waveforms constitute an inherent safety factor in the operation of the instant weapon. This safety factor is a result of the rapid absorption by biological tissue of the harmonic frequencies within complex waveforms such as square waves. A 20 to 50 milliampere current is thus able to stimulate only the target subject's skeletal muscles, and cannot penetrate to the autonomically-controlled internal muscles such as the heart.
A lethal variation of the present weapon could be implemented by increasing the current above approximately 250 milliamperes. A sine wave current having a density of about 5 milliamperes per square centimeter that flows through cardiac muscle for more than about two seconds may initiate ventricular fibrillation. The duration of the current needed to cause ventricular fibrillation is inversely proportional to the current density within the cardiac muscle.
The current carried by the ionized air channel is limited by the number of free electrons within the ultraviolet beam. A minimum 20 milliampere current required to induce skeletal muscular tetanization can be carried by a gaseous channel with a concentration of 10.sup.8 ions per cubic centimeter. This concentration is most efficiently achieved in air by ionizing molecular oxygen with coherent or columnated incoherent ultraviolet radiation having a wavelength of 193 nanometers. Shorter wavelengths may be employed as optical technology progresses.
At its normal operating intensity and a wavelength of 193 nanometers, the ultraviolet beam is safe to the skin because it cannot produce more than mild erythema akin to a sunburn unless it is directed at the same location for many minutes. Moreover, it is safe to the eyes because wavelengths near 193 nanometers cannot penetrate the cornea to reach internal ocular structures such as the lens and retina.
At this wavelength, molecular oxygen has a two-photon ionization cross section of 1.times.10.sup.-34 cm.sup.4 /watt. Because of its low ionization threshold, the number of photons required for ionization, and its large proportion in the atmosphere, it is easily able to create sufficient electron density.
The most efficient source of 193-nanometer radiation presently available is the argon fluoride discharge-pumped excimer laser. A reasonable power density, pulse duration, and pulse repetition rate for this laser is 5 megawatts per square centimeter, 10 nanoseconds, and 200 pulses per second, respectively.
An argon fluoride laser with an aperture of 1 square centimeter has a power density (energy output) of 10 millijoules per pulse or 1 megawatt per square centimeter. Each pulse liberates 6.3.times.10.sup.6 electrons, or 6.3.times.10.sup.14 electrons per second in the air immediately outside the aperture. A power density of 50 millijoules per pulse or 5 megawatts per square centimeter liberates 1.6.times.10.sup.8 electrons during each pulse, which is equivalent to 1.6.times.10.sup.16 electrons per second.
A narrow beam of ultraviolet radiation may also be generated from the collimated emission of an ultraviolet lamp.
The electron density in the channel of ionized air is a function of the ratio between the electron production and loss rates. In both the two-body and three-body electron attachment processes, the delay time between the end of the laser pulse and the beginning of the high-voltage tetanizing pulse determines the number of available electrons. When the electron energy is only 0.1 electron volt, for example, the three-body attachment is rapid, and the steady-state electron density for a 193 nanometer, 5 megawatt per square centimeter beam falls to 8.times.10.sup.7 per cubic centimeter.
The range of the present weapon is determined by the rate at which the laser beam is absorbed by the atmosphere. A 193-nanometer wavelength beam is attenuated in dry air at about 1.times.10.sup.-4 per centimeter. It will thus propagate approximately 100 meters before its intensity is decreased to 1/e of its initial value. As a consequence, the 1.6.times.10.sup.8 electron density at the aperture of an argon fluoride laser with a power density of 5 megawatts per square centimeter falls to 2.2.times.10.sup.7 after 100 meters. Because the minimum electron density required to transmit a current is between 10.sup.6 and 10.sup.8 per cubic centimeter, the above ionized channel should conduct the tetanizing current at least 100 meters. The range of this weapon could be increased, however, by the use of a more efficient ultraviolet source.
Various techniques, including those suggested in U.S. Pat. No. 4,017,767 Ball and U.S. Pat. No. 5,175,664, Diels et al. which are incorporated herein by reference, may be used in order to enhance the multi-photon and collisional ionization along the laser beams. These techniques are well known to persons skilled in the electrical arts.>>