Transcript Lecture 11: Individual Topics

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Lecture 11: Additional Topics
Instructor:
Dr. Gleb V. Tcheslavski
Contact:
[email protected]
Office Hours:
Room 2030
Class web site:
www.ee.lamar.edu/gle
b/em/Index.htm
Based on open web sources…
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EM weapons
According to the definition (Wikipedia): Electromagnetic weapons are a type of
directed energy weapons which use electromagnetic radiation to deliver heat,
mechanical, or electrical energy to a target to cause pain or permanent damage.
They can be used against humans, electronic equipment, and military targets
generally, depending on the technology.
1. High-energy radio frequency weapons (HERF) or high-power radio frequency
weapons (HPRF) use high intensity radio waves to disrupt electronics.
One of the
most efficient
HERF is a
nuclear
bomb…
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EM weapons
HERF can be used against humans…
Generally considered 'non-lethal weapons', electromagnetic weaponry do however
pose health threats to humans.
Some common bio-effects of electromagnetic or other non-lethal weapons include
effects to the human central nervous system resulting in physical pain, difficulty
breathing, vertigo, nausea, disorientation, or other systemic discomfort, as
weapons not directly considered lethal can indeed cause cumulative damage to the
human body.
One historical example of using HERF against humans is known as “Project
Pandora”…
In 1953 USSR started directing high frequency radio-waves towards the US
embassy in Moscow. Several embassy employees reported blood diseases
evolved into lymphoma that eventually killed them. Those blood diseases were
believed to result from high frequency radiation.
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EM weapons: MEDUSA
One example of HPRF weaponry being used currently is MEDUSA.
MEDUSA (Mob Excess Deterrent Using Silent Audio) is a directional, non-lethal
weapon designed for crowd control. It uses microwave pulses to generate
uncomfortably high noise levels in human skulls, bypassing the ears and ear drums.
MEDUSA is developed by the Sierra Nevada Corporation…
US NAVY have reported their tests of MEDUSA prototype in 2004 listing its potential
applications “as a perimeter protection sensor in deterrence systems for industrial
and national sites, for use in systems to assist communication with hearing impaired
persons, use by law enforcement and military personnel for crowd control and asset
protection. The system will be portable, require low power, have a controllable radius
of coverage, be able to switch from crowd to individual coverage, cause a
temporarily incapacitating effect, have a low probability of fatality or permanent
injury, cause no damage to property, and have a low probability of affecting friendly
personnel.”
In July 2008, the Sierra Nevada Corporation claimed that it was ready to begin
production of MEDUSA…
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EM weapons: MEDUSA
MEDUSA creates the audio effect with short microwave pulses. These pulses
create a shockwave inside the skull that is detected by the ears…, which may
make the target think he is insane… The MEDUSA can also "produce
recognizable sounds" and is aimed primarily at military uses.
These reports rose concerns that, in order to produce hearable sounds, intensity
of radio waves must greatly exceed safe levels and may, therefore, cause
permanent damage to skin, blood vessels, etc…
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EM weapons: ADS
Another example of HPRF weaponry being implemented is the Active Denial System
(ADS).
The Active Denial System (ADS) is a less-lethal, directed-energy weapon developed
by the U.S. military. It is a strong millimeter-wave transmitter primarily used for crowd
control (the "goodbye effect”). Some ADS such as HPEM ADS are also used to
disable vehicles. Informally, the weapon is also called pain ray. Raytheon is currently
marketing a reduced-range version of this technology.
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EM weapons: ADS
The ADS works by directing electromagnetic radiation, specifically, high-frequency
microwave radiation at a frequency of 95 GHz (a wavelength of 3.2 mm), toward the
subjects. The waves excite water molecules in the epidermis to around 130 °F
(55 °C), causing an intensely painful sensation of extreme heat. While not burning
the skin under ordinary use, the burning sensation is similar to that of an
incandescent light bulb being pressed against the skin. The focused beam can be
directed at targets at a range in excess of 700 meters. The device can penetrate
thick clothing, although not walls.
The frequency of 95 GHz was chosen since, due to the stronger absorption of water
at those frequencies, the wave would penetrate the skin to a depth of less than 1/64
of an inch (0.4 mm), which is where the nerve endings are located.
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EM weapons: ADS
A spokesman for the Air Force Research Laboratory described his experience as a
test subject for the system:
"For the first millisecond, it just felt like the skin was warming up. Then it got
warmer and warmer and you felt like it was on fire.... As soon as you're away from
that beam your skin returns to normal and there is no pain."
While the effects can be unpleasant, ADS has undergone extensive testing since
its inception in mid 90th. Many aspects of the research are classified, making
independent evaluation impossible. The beam is designed only to affect an
individual for a short moment, due to safety presets and features. According to a
public release, there have been over 10,700 "shots" by ADS.
The ADS is currently only a vehicle-mounted weapon, though U.S. Marines and
police are both working on portable versions.
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EM weapons: ADS
Raytheon has developed a smaller version
of the ADS, the Silent Guardian. This
stripped-down model is primarily marketed
for use by law enforcement agencies, the
military and other security providers. The
system is operated and aimed with a
joystick and aiming screen. The device can
be used for targets up to 550 m away.
Michael Hanlon, who volunteered to
experience its effects, described it as "a bit
like touching a red-hot wire, but there is no
heat, only the sensation of heat." Contrary
to Raytheon's claims that the pain ceases
instantly upon removal of the ray, Hanlon
said that the finger he subjected "was
tingling hours later."
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EM weapons: ADS
Closeup of
a "Desk
top"
millimeter
wave
projector.
This
simulates
the feeling
of the ADS
beam in a
small
dime-sized
region.
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EM weapons: guns
2. Electromagnetic projectile devices (EPG) are devices using electromagnetic
means to accelerate solid materials. There are three general types of such devices:
1) Coilgun (Gauss gun)
A coilgun is a type of projectile accelerator that consists of one or more
electromagnetic coils in the configuration of a synchronous linear electric motor.
These are used to accelerate a magnetic projectile to high velocity. The name
Gauss gun is sometimes used for such devices in reference to Carl Friedrich
Gauss, who formulated mathematical descriptions of the electromagnetic effect
used by magnetic accelerators.
Coilguns consist of one or more coils arranged along the barrel that are switched in
sequence so as to ensure that the projectile is accelerated quickly along the barrel
via magnetic forces. The first operational coilgun was developed and patented by
Norwegian physicist Kristian Birkeland.
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EM weapons: guns
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EM weapons: guns
A handheld single
stage coilgun
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EM weapons: guns
Effectively a coilgun is a solenoid: an electromagnetic coil with the function of
drawing a ferromagnetic object through its center. A large current is pulsed through
the coil of wire and a strong magnetic field forms, pulling the projectile to the
center of the coil. When the projectile nears this point the electromagnet is
switched off and the next electromagnet can be switched on, progressively
accelerating the projectile down successive stages. In common coilgun designs
the "barrel" of the gun is made up of a track that the projectile rides on, with the
driver into the electromagnetic coils around the track. Power is supplied to the
electromagnet from some sort of fast discharge storage device, typically a battery
or high-capacity high voltage capacitors designed for fast energy discharge.
There are two main types or setups of a coilgun, single stage and multistage. A
single stage coilgun uses just one electromagnet to propel a ferromagnetic
projectile. A multistage coilgun uses multiple electromagnets in succession to
progressively increase the speed of the projectile.
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Coilgun limitations
Electrical resistance is a major limitation of a typical coil gun; due to the extremely
large currents used, even a well designed coil will waste the majority of the input
energy as heat, dictated by Ohm's Law. Electrical resistance as a design limitation
could be overcome through the use of a superconducting material. However, there
are no known materials that are superconductive at room temperature.
Ideally, 100% of the magnetic flux generated by the coil would be delivered to and
act on the projectile, but this is often far from the case due to the common aircore-solenoid / projectile construction of most coilguns.
Since an air-cored solenoid is simply an inductor, the majority of the magnetic flux
is not coupled into the projectile, instead being stored in the surrounding air. The
energy that is stored in this field does not simply disappear from the magnetic
circuit once the capacitor finishes discharging; much of it returns to the capacitor
when the circuit's electric current is decreasing. As the coilgun circuit is inherently
analogous to an LC oscillator, it does this in the reverse direction ('ringing'), which
can seriously damage polarized capacitors (such as electrolytics).
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Coilgun limitations
Another significant limitation of the coilgun is the occurrence of ferromagnetic
projectile saturation. When the core is saturated, magnetic flux will only increase
marginally with the current. Since losses are proportional to I2, increasing current
beyond this point eventually decreases efficiency (yet it may further increase the
force). This puts an absolute limit on how much a given projectile can be accelerated
with a single stage at acceptable efficiency.
In addition to saturation, hysteresis and the reaction time of the projectile material
may be other limiting factors. Due to hysteresis, the projectile becomes permanently
magnetized and some energy will be lost to a permanent magnetic field of the
projectile. The projectile reaction time, on the other hand, makes the projectile
reluctant to abrupt changes in magnetic flux - the flux will not rise as fast as desired
while current is applied.
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EM weapons: guns
2) A railgun is an entirely electrical gun that accelerates a conductive projectile
along a pair of metal rails using the same principles as the homopolar motor.
Railguns use two sliding or rolling contacts that permit a large electric current to
pass through the projectile. This current interacts with the strong magnetic fields
generated by the rails and this accelerates the projectile.
The U.S. Navy has tested a railgun that accelerates a 3.2 kg projectile to eight
times the speed of sound.
Coilguns are distinct from railguns, which pass a large current through the
projectile or sabot via sliding contacts. Coilguns and railguns also operate on
different principles.
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EM weapons: guns
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EM weapons: guns
A railgun consists of two parallel metal rails (hence the name) connected to an
electrical power supply. When a conductive projectile is inserted between the rails (at
the end connected to the power supply), it completes the circuit. Electrons flow from
the negative terminal of the power supply up the negative rail, across the projectile,
and down the positive rail, back to the power supply.
This current creates a strong magnetic field in the region of the rails up to the position
of the projectile. According to the right-hand rule, the magnetic field is created around
each conductor. Since the current is in opposite direction along each rail, the net
magnetic field between the rails is directed vertically. In combination with the current
across the projectile, this produces a Lorentz force which accelerates the projectile
along the rails. The projectile slides up the rails away from the power supply.
A large power supply providing, on the order of, one million amperes of current will
create a tremendous force on the projectile, accelerating it to a considerable speed.
20 km/s has been achieved with small projectiles explosively injected into the railgun.
Although these speeds are possible theoretically, the heat generated from the
propulsion of the object is enough to erode the rails rapidly. Such a railgun would
require frequent replacement of the rails, or use a heat resistant material that would
be conductive enough to produce the same effect.
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EM weapons: guns
Materials:
The rails and projectiles must be built from strong conductive materials; the rails
need to survive the violence of an accelerating projectile, and heating due to the
large currents and friction involved. The recoil force exerted on the rails is equal
and opposite to the force propelling the projectile. The rails also repel themselves
via a sideways force caused by the rails being pushed by the magnetic field, just
as the projectile is. The rails need to survive this without bending, and must be
very securely mounted.
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EM weapons: guns
Design considerations
The power supply must be able to deliver large currents, sustained and controlled
over a useful amount of time. The most important gauge of power supply
effectiveness is the energy it can deliver. As of February 2008, the greatest known
energy used to propel a projectile from a railgun was 32 million joules. The most
common forms of power supplies used in railguns are capacitors and compulsators
which are slowly charged from other continuous energy sources or using a Van de
Graaff generator.
The rails need to withstand enormous repulsive forces during shooting, and these
forces will tend to push them apart and away from the projectile. As rail/projectile
clearances increase, arcing develops, which causes rapid vaporization and
extensive damage to the rail surfaces and the insulator surfaces. This limited some
early research railguns to one shot per service interval.
The inductance and resistance of the rails and power supply limit the efficiency of a
railgun design. Currently different rail shapes and railgun configurations are being
tested, most notably by the United States Navy, The Institute for Advanced
Technology, and BAE Systems.
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EM weapons: guns
Heat dissipation
Massive amounts of heat are created by the electricity flowing through the rails, as
well as by the friction of the projectile leaving the device. The heat created by this
friction itself can cause thermal expansion of the rails and projectile, further
increasing the frictional heat. This causes three main problems: melting of
equipment, decreased safety of personnel, and detection by enemy forces. As
briefly discussed above, the stresses involved in firing this sort of device require
an extremely heat-resistant material. Otherwise the rails, barrel, and all equipment
attached would melt or be irreparably damaged.
In practice the rails are, with most designs of railgun, subject to erosion due to
each launch; and projectiles can be subject to some degree of ablation also, and
this can limit railgun life, in some cases severely.
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EM weapons: guns
Railguns are being researched as weapons with projectiles that do not contain
explosives, but are given extremely high velocities: 3,500 m/s (11,500 ft/s,
approximately Mach 10 at sea level) or more (for comparison, the M16 rifle has a
muzzle speed of 930 m/s, or 3,050 ft/s), which would make their kinetic energy equal
or superior to the energy yield of an explosive-filled shell of greater mass. This would
allow more ammunition to be carried and eliminate the hazards of carrying
explosives in a tank or naval weapons platform. Also, by firing at greater velocities,
railguns have greater range, less bullet drop and less wind drift, bypassing the
inherent cost and physical limitations of conventional firearms: the limits of gas
expansion prohibit launching a projectile to velocities greater than about 1.5 km/s
and ranges of more than 50 miles [80 km] from a practical conventional gun system."
If it were possible to apply the technology as a rapid-fire automatic weapon, a railgun
would have further advantages of increased rate of fire. The feed mechanisms of a
conventional firearm must move to accommodate the propellant charge as well as
the ammunition round, while a railgun would only need to accommodate the
projectile. Furthermore, a railgun would not have to extract a spent cartridge case
from the breech, meaning that a fresh round could be cycled almost immediately
after the previous round has been shot.
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EM weapons: guns Reality
The United States Naval Surface Warfare Center Dahlgren Division demonstrated an
8 MJ rail gun firing 3.2 kg projectiles in October 2006 as a prototype of a 64 MJ
weapon to be deployed aboard Navy warships. The main problem the Navy has had
with implementing a railgun cannon system is that the guns wear out due to the
immense heat produced by firing. Such weapons are expected to be powerful
enough to do a little more damage than a BGM-109 Tomahawk missile at a fraction
of the projectile cost. Since then, BAE Systems has delivered a 32 MJ prototype to
the Navy.
On January 31, 2008 the US Navy tested a railgun that fired a shell at 10.64 MJ with
a muzzle velocity of 2,520 m/s. Its expected performance is a muzzle velocity over
5,800 m/s, accurate enough to hit a 5 meter target over 200 nautical miles (463 km)
away while firing at 10 shots per minute. The power was provided by a new 9megajoule (MJ) prototype capacitor bank using solid-state switches and highenergy-density capacitors delivered in 2007 and an older 32-MJ pulse power system
from the US Army’s Green Farm Electric Gun Research and Development Facility
developed in the late 1980’s that was previously refurbished by General Atomics
Electromagnetic Systems (EMS) Division. It is expected to be ready between 2020
to 2025.
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EM weapons: guns
Naval Surface
Warfare Center
test firing in
January 2008,
leaving a plume
of plasma behind
the projectile.
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