Active Denial Technology uses a transmitter to send a narrow beam of 95-GHz millimeter waves towards an identified subject. Traveling at the speed of light, the energy reaches the subject and penetrates less than 1/64 of an inch into the skin, quickly heating up the skin's surface. The 95-GHz energy penetrates 1/64 inch into the skin and produces an intense burning sensation that stops when the transmitter is switched off or when the individual moves out of the beam. Within seconds, an individual feels an intense heating sensation that stops when the transmitter is shut off or when the individual moves out of the beam. According to reports, a 2-second burst from the system can heat the skin to a temperature of 130° F. At 50 °C, the pain reflex makes people pull away automatically in less than a second. Someone would have to stay in the beam for 250 seconds before it burnt the skin,
Despite the sensation, the technology does not cause injury because of the low energy levels used. It exploits a natural defense mechanism that helps to protect the human body from damage. The heat-induced sensation caused by this technology, is nearly identical to the sensation experienced by briefly touching an ordinary light bulb that has been left on for a while. Unlike a light bulb, however, active denial technology will not cause rapid burning, because of the shallow penetration of the beam and the low levels of energy used. The transmitter needs only to be on for a few seconds to cause the sensation.
Air Force scientists helped set the present skin safety threshold of 10 milliwatts per square centimetre in the early 1990s, when little data was available. That limit covers exposure to steady fields for several minutes to an hour - but heating a layer of skin 0.3 mm thick to 50 °C in just one second requires much higher power and may pose risks to the cornea, which is more sensitive than skin. A study published last year in the journal Health Physics showed that exposure to 2 watts per square centimeter for three seconds