Abstract: A deactivator for deactivating targets used in electromagnetic article surveillance systems comprises a solid element with a convexly curved outer surface, e.g., a cylinder and a plurality of permanent magnets which form a patter of variously directed magnetic fields is a plane adjacent the surface. The curved surface of the deactivator is rolled over a target to be deactivated. The magnets are also arranged in adjacent layers with the magnets of one layer extending in a different direction from the magnets of the other layer to form a composite magnetic pattern which is discontinuous in all directions.

Abstract: Targets (14) mounted on objects (12) for detection by a magnetic type theft detection system are deactivated in a target deactivator (26,64) which has magnet assembly (40,72) made up of spaced apart magnets with alternately opposed poles extending in a plane and guide walls (36, 38, 68, 70) extending perpendicular to the plane. Targets are reactivated by a reactivator (46, 76) having a magnet (52, 80) mounted thereon and arranged to be slid along the target.

Abstract: A self contained electronic theft detection apparatus comprising a housing (30) from which a rigid tubular transmitter antenna loop (32) extends; and a wire loop receiver antenna (56) extends inside the transmitter antenna loop. The transmitter antenna (32) is provided with a capacitor (C54) with which it resonates at the frequency of responder elements to be detected and the transmitter antenna is supplied with sharp voltage pulses from a pulse forming circuit (66) and a power amplifier (68) which cause the antenna to resonate in a rapidly decaying manner.

Abstract: Items of merchandise (30) are protected from shoplifting or theft by affixing to them, special responder targets (32), which are formed by drawing a material of high magnetic permeability into a thin wire, then heat treating the wire to substantially increase its magnetic permeability and thereafter severing the wire into individual lengths. Several wires (32a, 32b and 32c) may be positioned on a common adhesively coated base strip (42) and covered by a peel strip (46) and wire like deactivation elements (48) of hard magnetic material may be positioned adjacent the wires for deactivating them.

Abstract: In an electronic theft detection apparatus the passage of a resonant circuit wafer 16 through an interrogation zone formed by transmitter and receiving antennas (30, 90) (32, 92) is detected by generating sharp pulses of electromagnetic energy to cause the resonant circuit wafer to resonate for a duration following each pulse. A receiver is provided with a switch (54), signal accumulators or filters (56 and 58) and a comparator (60) to sense the decay of the signal from the resonating wafer and to activate an alarm (36) when that decay occurs at a predetermined value.

Abstract: An electronic article theft detection system accurately senses the presence of a target on a protected article by sensing electromagnetic disturbances at a plurality of frequences, comparing their relative amplitudes and producing a detection signal when the compared relative amplitudes correspond to those produced by the presence of a target.