PAPER DESCRIBES NEW SYSTEM FOR DETECTING CONCEALED WEAPONS.NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. scientists are developing a system for detecting concealed weapons (Law) dangerous weapons so carried on the person as to be knowingly or willfully concealed from sight, - a practice forbidden by statute.<- in some states! -> See under Concealed. See also: Concealed Weapon that could be mounted on a vehicle. Driven into a crowd, the system would scan members and identify guns, knives and other dangerous objects hidden under clothing. The approach combines the chief advantages of both active and passive detection systems into one unit. The active part involves the illumination of a subject with a millimeter-wave source and then detecting the radiation reflected from it. Because the NIST system uses bolometers (devices that detect and measure small amounts of radiation), it is a significantly more powerful detection tool than conventional passive imaging systems. On the other hand, the NIST system is relatively broadband so it eliminates the problem of glint often associated with active detection systems. Glint is produced by uncontrolled standing waves generated between the target and its environment. To obtain a large bandwidth, the developers use high power oscillators that operate at 95 GHz in a pulsed mode. These are commercially available at a low-enough price that does not impact the overall system cost. The detection portion of the system is centered on a focal plane The plane, perpendicular to the optical axis of the lens, in which images of points in the object field of the lens are focused. array of uncooled, millimeter-wave bolometers. The array consists of a 75 mm diameter silicon wafer populated pop·u·late tr.v. pop·u·lat·ed, pop·u·lat·ing, pop·u·lates 1. To supply with inhabitants, as by colonization; people. 2. by a 117-element array of thin-film niobium niobium (nīō`bēəm), metallic chemical element; symbol Nb; at. no. 41; at. wt. 92.9064; m.p. about 2,468°C;; b.p. 4,742°C;; sp. gr. 8.57 at 20°C;; valence +2, +3, +4, or +5. bolometers, each of which is coupled to the incident radiation by a planar, lithographically fabricated fab·ri·cate tr.v. fab·ri·cat·ed, fab·ri·cat·ing, fab·ri·cates 1. To make; create. 2. To construct by combining or assembling diverse, typically standardized parts: , millimeter-wave antenna. For a copy of paper no. 12-01 describing this system, contact Sarabeth Harris, NIST, MC104, Boulder, CO 80305-3328; (303) 497-3237; sarabeth@boulder.nist.gov. |
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