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Active Denial Technology
Dr. Kirk E. Hackett of the Air Force Research Laboratory's Directed Energy Directorate and
Lt Col Charles W. Beason of the Human Effectiveness Directorate wrote this article.

Do you wonder how hardened our electronics are to such new weapons?

Active Denial Technology is a breakthrough non-lethal technology that uses millimeter-wave electromagnetic energy to stop, deter, and turn back an advancing adversary from relatively long range.

AFRL's Directed Energy Directorate, High Power Microwave Division, Applications Branch, Kirtland AFB NM

AFRL scientists and sponsors from the Joint Non-Lethal Weapons Directorate (JNLWD) announced the existence of a revolutionary non-lethal directed energy technology called Active Denial Technology (ADT) at a Pentagon press conference in March 2001. The Marine Times said that ADT was potentially the biggest breakthrough in weapons technology since the atom bomb.

ADT enables a new class of weaponry using directed energy. This technology uses a beam of millimeter waves to heat an adversary's skin, causing intense pain without damage. This makes the adversary flee.

AFRL began research into non-lethal weapons in the mid-1980s. This research resulted in the building and testing of a low power repel demonstrator funded by the Air Force. Congress directed the Department of Defense (DoD) to create a joint organization to develop non-lethal technology and capabilities in 1996. The Marine Corps is the executive agent for the DoD. The JNLW program funded AFRL to produce two vehicle-mounted repel demonstrators based on previous research.

ADT exploits intolerance of thermally induced pain. Pain intolerance depends on pain intensity and duration. The intensity of pain depends on skin temperature, starting at a threshold of 45C and increasing rapidly until pain intensity is maximized at a skin temperature of 55C. ADT uses a beam of energy to heat the skin. The frequency has favorable scaling in several respects. A powerful and efficient millimeter-wave source technology exists. As frequency increases, the ability of an antenna to concentrate energy increases with the square of the frequency. The depth of energy deposition in tissue is 0.3 mm, the same depth as pain-sensing nerves.

ADT does not burn and does not cause prolonged or unnecessary suffering, permanent damage, or long-term effects. A large safety margin exists between causing intolerable pain and burning in the operational range of ADT. This margin allows exploitation of pain intolerance while avoiding damage. Researchers explored the possibility of eye damage and skin cancer and have eliminated these as a concern. The eye has many pain receptors on the cornea and an aversion response protects the eyes. Experiments also demonstrated that millimeter-wave energy does not promote cancer. Scientists continue performing extensive volunteer human testing in strict accord with approved laws and regulations requiring informed consent. An institutional review board and the Air Force Surgeon General's Research Oversight Council approve human and animal research protocols.

An ADT system consists of an electrical power source, a device producing a beam of millimeter-wave energy, an antenna directing energy towards a target, and a beam transport connecting the source and antenna. Raytheon constructed a full-power, full-range demonstration system for vehicle-mounted technology integrating these elements (see Figure 1). Users can assess the potential operational utility of ADT, demonstrate key technologies in a field environment, and perform large spot effects testsusing the demonstration system.

Figure 1. ADT field demonstration system

Communications and Power Industries of Palo Alto, California, designed and built the gyrotron millimeter-wave source. In the gyrotron, a superconducting magnet with a cryocooler generates a rotating electron beam in a strong magnetic field (~3.4 Tesla). The electrons interact resonantly with electromagnetic waves in a cavity. This interaction bunches the electron beam and electron energy converts into millimeter waves. The millimeter-wave energy is extracted from the cavity and mode-converted to a quasi-gaussian beam. The beam, shaped by mirrors, passes through a window made of polycrystalline diamond, which has low loss, high thermal conductivity, and high mechanical strength.

The antenna is similar in configuration to satellite television receivers. The shape of the secondary mirror optimally illuminates the two-meter primary reflector. This gives high-aperture efficiency and increases power density on target. Malibu Research designed and built a flat parabolic surface (FLAPS) as the primary aperture. The FLAPS surface is a Fresnel mirror constructed from an array of dipoles that achieves high gain with reduced mechanical tolerances.

The antenna is mounted on an azimuth-elevation turret. Spatial stabilization allows antenna operation in buffeting winds. A boresighted low-light video camera and thermal imager are mounted on the antenna. The operator maneuvers the antenna with a joystick and depresses a trigger to fire the beam. Since the operator sees the target and surrounding area, he knows exactly what the beam will hit when he fires it. The atmosphere slightly absorbs the millimeter-wave beam and heavy rain can degrade performance. These effects are not considered important, however, since the operator must see the target to engage it.

 


Figure 2. Infrared image of silhouette targets

Testing of the ADT demonstration system took place at Kirtland AFB, New Mexico. Figure 2 is a thermal image of a high-power beam of millimeter waves hitting two silhouette targets consisting of a microwave-absorbing material. The beam does not affect the nearby silhouette target. This test was the final phase of a Force Protection Battlelab demonstration. The exit criteria from the Battlelab demonstration that were met or exceeded included a characterization of peak power density on target at range, dwell time, and beam width. Earlier phases of the demonstration used modeling and simulation, and live force-on-force exercises to study the operational benefits of ADT. The Battlelab demonstration showed that ADT has significant operational potential.

Figure 3. Vehicle-mounted ADT concept

Use of the demonstration system in a series of experiments will aid researchers in studying the repel effect on animals and people. The program will then transition to the Electronic Systems Center at Hanscom AFB, Massachusetts for development of a vehicle-mounted version of ADT (see Figure 3). The demonstrator will be used as a test bed and for additional effects studies.

In the final analysis, ADT is meant to save lives. Active denial is a revolutionary force protection technology that will help fill the US non-lethal capability gap. ADT systems will provide field commanders with a non-lethal force option in situations where the use of lethal force is authorized, but not preferred.

One of the attractive features of ADT is that the probability of hit is 100% since ballistics effects are irrelevant. The energy beam travels at the speed of light. As long as electricity is available, a continuous or pulsed beam of energy can be projected. Operators can direct this beam toward individual targets, sweep it across many targets, dwell it to suppress snipers, or create an energy barrier. The range of ADT considerably exceeds the range of conventional non-lethal technologies and is meant to outrange small arms fire. Possible applications of ADT are airborne, maritime, fixed site, or man-portable. Researchers are studying all applications for their operational benefits and technical feasibility.



Dr. Kirk E. Hackett of the Air Force Research Laboratory's Directed Energy Directorate and Lt Col Charles W. Beason of the Human Effectiveness Directorate wrote this article. For more information contact TECH CONNECT at (800) 203-6451 or place a request at http://www.afrl.af.mil/techconn/index.htm.

 

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