The following is Dan2's Motion Detector text (with minor changes by me).
The [Motion Detector] is a portable device designed to track mass motion in immediate vicinity.
This device contains several modules: an emitter module generating square pulse electromagnetic radiation ranging from radio wavelengths up to microwave radiation, a detector module design to analyze both the intensity of the reflected radiation as well as its polarization angle, and a computer module that processes the information coming from the detector and then subtracts the newly acquired data from images obtained from previous pulses, thus detecting only movement. Unfortunately, the processing power of the miniaturized portable computer is still challenged by the huge amount of data being processed, making it impractical to obtain full spectrum images. When the computer detects movement, it directs the emitter module to send a powerful terahertz radiation beam in the vicinity of movement to obtain more precise readings. Detecting heartbeats or circulating blood is still beyond the sensitivity of the detector, but large body movements are observed accurately on the on-board screen as bright dots in order to allow simple readings and to eliminate confusion.
Terahertz radiation, popularly called "T-Rays", can travel through electrically isolator materials like concrete in the same way light travel through glass, without too much absorption, so information such as angle, shape, mass and velocity can be extrapolated with much higher precision than when using just microwave radiation. T-rays offer better penetration than infrared radiation through walls since paints and other organic materials used in wall and floor construction readily absorb the infrared wavelengths.
T-Rays can be produced by passing an electrical current through a semi-conductive material that injects electrons into a conductive material, like copper. When a conductive material is placed within a strong magnetic field, its randomly oriented electron spins realign, resulting in the release of T-rays. When the T-ray emitter is placed between two mirrors, one highly reflective and one semitransparent, the initial terahertz radiation induces subsequent radiation to be produced having the same wavelength and direction with the original radiation. This cascade phenomenon of T-ray amplification is similar to that of lasers, only the radiation is in the invisible terahertz domain.
*Optional* Unfortunately, this device cannot be used effectively on Alien ships where the floors and/or the walls are made of Alien Composites, which is impenetrable to low energy electromagnetic radiation. (Paraphrase of Dan2: In reality, T-rays cannot penetrate metallic materials; one would have to use gamma rays, which are dangerous and can incidentally cause sterility;))
Edited by Astyanax, 22 February 2005 - 04:32 PM.