NCJ Number
74483
Journal
Assets Protection Volume: 5 Issue: 6 Dated: (November/December 1980) Pages: 35-37
Date Published
1980
Length
3 pages
Annotation
This article describes current weapon detector technology for screening individuals for concealed metallic weapons.
Abstract
Practical detectors must be reasonably priced, simple to operate, safe to health, have an automatic yes/no decisionmaking capability, and possess a low false alarm rate in the presence of strong relative interference and a background of innocuous normally carried metal. The most satisfactory technology presently employs magnetic fields and electronic processing to make an automatic yes/no decision on the possible presence of a weapon when a person walks through a specially constructed portal. A metallic object exposed to a low frequency sinusoidal magnetic field produces a secondary magnetic field with in-phase and quadrature components. For a conductive, permeable object, the in-phase component is positive in a low frequency range: target objects produce a higher frequency which is negative because conductivity is high and permeability is low. A performance chart is included on a pulsed-field system detector which is similar in transmitter/receiver timing sequence to a range-gated pulsed radar. With the receiver off, a magnetic field excitation is applied for a specific interval and extinguished. After a fixed delay, the receiver window is turned on and the integrated signal is accumulated in a low pass filter. This equipment makes measurements over a wide band of frequencies. The parameters of transmitter pulse width, delay time, and receiver pulse width have been chosen to optimize the detection of handguns while minimizing the false alarm rate on innocuous metal. One figure and six references are included. For related articles, see NCJ 74479.