Military Ray Gun

Vehicle-Mounted Active Denial System (V-MADS)

"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. It is expected to save countless lives by providing a way to stop individuals without causing injury, before a deadly confrontation develops.

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.

Countermeasures against the weapon could be quite straightforward — for example covering up the body with thick clothes or carrying a metallic sheet — or even a trash can lid — as a shield or reflector. Also unclear is how the active-denial technology would work in rainy, foggy or sea-spray conditions where the beam's energy could be absorbed by water in the atmosphere."

In media reports its been stated:

"The millimeter waves cannot go through walls or glass, but they can penetrate most clothing, officials said."

So there seems to be a fair amount of defense techniques that could make this weapon less effective than one might imagine, a suicide car bomber just needs to make sure he has a windshield and that his windows are rolled up. In addition what is meant by "most" clothing, it wouldn't take much to determine what materials and thickness would minimize the beam's effect.