The Active Denial System (ADS) is a non-lethal, directed-energy weapon developed by the U.S. military.[1] It is a strong millimeter-wave transmitter used for crowd control (the "goodbye effect"[2]). Informally, the weapon is also called pain ray.[3] Raytheon is currently marketing a reduced-range version of this technology.[4] The ADS is currently being considered for deployment in the Iraq War.

The ADS works by directing electromagnetic radiation, specifically, high-frequency microwave radiation at a frequency of 95 GHz[5] (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 actually burning the skin, the burning sensation is similar to that of a light bulb being pressed against the skin.[5] The focused beam can be directed at targets at a range of just under half a kilometer, or about 550 yards.[6] The device can penetrate thick clothing, although not walls.[6]

At 95 GHz, the frequency is much higher than the 2.45 GHz of a microwave oven. This frequency was chosen because, due to the stronger absorption of water at those frequencies, they penetrate the skin to a depth of less than 1/64 of an inch (0.4 mm),[7] which is where the nerve endings are located.

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."


http://en.wikipedia.org/wiki/Active_Denial_System