Abstract: Method and apparatus for making electrically conductive concrete articles ed for electromagnetic shielding, the invention also includes the articles of manufacture formed according to the method. Concrete articles formed according to the method of the invention are reinforced with magnetized metallic fibers, preferably steel fibers, a substantial portion of the fibers contacting nearby fibers to provide electrical continuity through the article. Contact between fibers is enhanced according to the invention by vibration of the concrete/fiber mix during forming of the electrically conductive concrete article.

Abstract: A shielding connecting structure is disclosed for permitting the opening closing of the electromagnetic seal of screening material as applied across a door and a door jamb wherein the screening material is attached to the jamb and applied along the door. A pair of compressible parallel oriented rubber hoses are mounted between the jamb and the material attached thereto and a single compressible rubber hose is mounted between the door frame and the material applied thereto. The hose on the door is arranged to be positioned between the two parallel hoses when the door is closed upon the jamb during which the hoses become compressed to produce a wiping contacting action between the associated portions of the material.

Abstract: An EMI/RFI shield for seams and cracks in surfaces of shielded structures disclosed. At least one conductive screen is applied in electrical contact with the surfaces and a conductive coating is applied over the screen to physically bond the screen to the surfaces and to maintain electrical conduction.

Abstract: A method for determining the electromagnetic RF shielding effectiveness of a shielding enclosure including sequentially driving the four diagonally opposite corner pairs of the enclosure with a RF signal, measuring the RF energy leakage for each corner pair, and averaging the four measured RF leakage levels to obtain an average RF energy leakage level. This average RF energy leakage level may then be compared with prior (preferably immediately after manufacture) measured average RF energy leakage levels to obtain an indication of the RF energy shielding effectiveness lost, if any, during the time from the prior test to the current test.

Abstract: A fire detection system using optical fibers to transmit flame signals from a plurality of remote monitoring stations to a central detection and analysis station, the invention comprises a network of optical fibers which connect the monitoring stations to the central detection station for the purpose of transmitting incident analog optical, infrared and ultraviolet spectra to the central station for detection of fire conditions. The central detection and analysis station preferably includes a rotary scanner which scans each of the optical fibers, light from the fibers being dispersed by a prism associated with the scanner to allow detection of the various spectral components of the dispersed light by light sensitive semiconductors. The detected spectral components are then compared to known fire signal signatures which include flicker rate and spectral content information.

Abstract: An improved intrusion detection apparatus for detecting when a fence is cut r has been climbed over, as well as the location of the intrusion. A cable comprising at least one optical fiber having an electrical transmission line running therealong is strung along the fence to be protected. If an intruder either cuts the cable or stresses the fence so that the cable breaks, an optical signal running along the optical fiber or fibers is lost, thus providing an alarm indication at a central station. The loss of the optical signal automatically triggers an electrical pulse generator means which feeds pulses down the transmission line running along the optical fiber. Part of the pulse energy is reflected at the transmission line break, and the time elapsed between transmission and receipt of the pulses is determined by time domain reflectometry techniques (TDR).

Abstract: A modulated light beam from a radiation source on a structure whose posit is to be measured is split into a first beam which propagates through the atmosphere to a first detector and a second beam which travels through an optical fiber to a second detector. The first and second detectors recover the modulation on the first and second beams, the phases of which are compared to determine the distance. In a preferred embodiment, the light source is a sine-wave modulated laser.

Abstract: A gasket structure for the door frame of an electromagnetically shielded enclosure having a flexible inflatable tube with a sleeve or coating of conducting material which upon inflation with the door closed provides intimate electrical contact between the door and the door frame.

Abstract: A method and apparatus for detecting flaws in conduits or the like which prises positioning an annular array of Hall-effect devices transversely around the conduit, applying an electric current to the conduit to flow longitudinally therethrough so as to create a magnetic field around the conduit, sequentially scanning the Hall-effect devices to produce a series of output signals corresponding to the portions of the magnetic field sensed respectively by them, and comparing the output signals for nonuniformities among them, the nonuniformities being indicative of the existence and location of flaws.