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ELEN 3371 Electromagnetics Fall 2008 1 Lecture 11: Additional Topics Instructor: Dr. Gleb V. Tcheslavski Contact: Office.

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Presentation on theme: "ELEN 3371 Electromagnetics Fall 2008 1 Lecture 11: Additional Topics Instructor: Dr. Gleb V. Tcheslavski Contact: Office."— Presentation transcript:

1 ELEN 3371 Electromagnetics Fall Lecture 11: Additional Topics Instructor: Dr. Gleb V. Tcheslavski Contact: Office Hours: Room 2030 Class web site: b/em/Index.htm b/em/Index.htm Based on open web sources…

2 ELEN 3371 Electromagnetics Fall

3 ELEN 3371 Electromagnetics Fall 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…

4 ELEN 3371 Electromagnetics Fall 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.

5 ELEN 3371 Electromagnetics Fall 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…

6 ELEN 3371 Electromagnetics Fall 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…

7 ELEN 3371 Electromagnetics Fall 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.

8 ELEN 3371 Electromagnetics Fall 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.

9 ELEN 3371 Electromagnetics Fall 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 90 th. 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.

10 ELEN 3371 Electromagnetics Fall 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."

11 ELEN 3371 Electromagnetics Fall 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.

12 ELEN 3371 Electromagnetics Fall 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.

13 ELEN 3371 Electromagnetics Fall EM weapons: guns

14 ELEN 3371 Electromagnetics Fall EM weapons: guns A handheld single stage coilgun

15 ELEN 3371 Electromagnetics Fall 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.

16 ELEN 3371 Electromagnetics Fall 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 air- core-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).

17 ELEN 3371 Electromagnetics Fall 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 I 2, 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.

18 ELEN 3371 Electromagnetics Fall 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.

19 ELEN 3371 Electromagnetics Fall EM weapons: guns

20 ELEN 3371 Electromagnetics Fall 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.

21 ELEN 3371 Electromagnetics Fall 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.

22 ELEN 3371 Electromagnetics Fall 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.

23 ELEN 3371 Electromagnetics Fall 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.

24 ELEN 3371 Electromagnetics Fall 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.

25 ELEN 3371 Electromagnetics Fall 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 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 9- megajoule (MJ) prototype capacitor bank using solid-state switches and high- energy-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.

26 ELEN 3371 Electromagnetics Fall EM weapons: guns Naval Surface Warfare Center test firing in January 2008, leaving a plume of plasma behind the projectile.


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