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| Number | Title | Issue Date |
| 4646090 | Codeable identifying tag and method of identification thereof A tag is receptive of two radio frequencies (RF signals) for mixing the two frequencies and radiating a signal which is either or both the sum and difference of the two RF frequencies. A uniquely identifiable tag includes, in addition to the mixer one or ... | 02/24/1987 |
| 4644286 | Article surveillance system receiver using synchronous demodulation and signal integration An article surveillance system includes a generator of a first inductive magneticc field having on and off duty cycle portions. The generator derives the first magnetic field at a predetermined AC frequency during the on duty cycle portions. The articles ... | 02/17/1987 |
| 4623877 | Method and apparatus for detection of targets in an interrogation zone Targets (30) of readily saturable mangetic material and mounted on protected articles (14) are detected when taken through an interrogation zone (24) in which an alternating magnetic interrogation field is generated by transmitter antenna coils (42, 44). ... | 11/18/1986 |
| 4622542 | Magnetic article surveillance system, method and coded marker A surveillance system is based upon generation and detection of phase shifted harmonic signals responsive to transmission of a reference signal at a fundamental frequency in a detection zone. Phase shifted harmonic signals may be generated by markers comp... | 11/11/1986 |
| 4595915 | Electronic surveillance system employing the doppler effect A coherent frequency, velocity responsive electronic surveillance system detects the motion of a transponder relative to two receiving antennas on opposite ends of a surveillance zone positioned at the exit of a retail store. Motion in opposite directions... | 06/17/1986 |
| 4565996 | Range limited coherent frequency doppler surveillance system A time limited coherent frequency doppler radar system monitors a precisely bounded merchandise detection zone for motion of a transducer therein. False alarms are reduced without limiting sensitivity by limiting the maximum radar signal propogation times... | 01/21/1986 |
| 4539558 | Antitheft system The present invention provides an antitheft system comprising a pair of spaced coils which are excited to produce an alternating magnetic field within a surveillance zone between the coils. Thus, a magnetic marker having a permeability of less than 150,00... | 09/03/1985 |
| 4535323 | Preamplifying and signal processing method and apparatus for theft detection systems Improvements in theft-detection or surveillance systems of the type in which an alternating electromagnetic field is established across a doorway or other portal and is monitored to detect the presence within the field of a marker or tag member comprising... | 08/13/1985 |
| 4531117 | Variable frequency RF electronic surveillance system An electronic article surveillance system is disclosed, having a transmitter means for producing in an interrogation zone sequences containing a plurality of discrete different radio frequencies thereby causing a circuit present within the zone to resonat... | 07/23/1985 |
| 4527153 | Detectable element and sensor A detectable element is attached to an object for detecting the presence or passage of the object and comprises a capsule and a permanent magnet rotatably and vibratably mounted in the capsule. When the detectable element enters an alternating magnetic fi... | 07/02/1985 |
| 4519066 | Duplexer with sum and difference signal outputs A duplexer is provided in which a transmit input signal is fed in parallel through two autotransformers to a pair of portal loops for establishing an interrogation field. Significantly lower voltage response signals returning via the autotransformers are ... | 05/21/1985 |
| 4476459 | Theft detection method and apparatus in which the decay of a resonant circuit is detected 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 th... | 10/09/1984 |
| 4471345 | Randomized tag to portal communication system Communication between portal units and identification tags is accomplished by continually radiating an interrogation signal consisting of a code pattern from each portal unit followed by a listening interval. Tags within range of such interrogation signal... | 09/11/1984 |
| 4429302 | Electronic security system with noise rejection The system includes a transmitter producing an electromagnetic field at a frequency repetitively swept through a predetermined range at a predetermined sweep frequency. A receiver senses a resonant frequency produced by a resonant tag circuit when the tag... | 01/31/1984 |
| 4356477 | FM/AM Electronic security system An electronic security system utilizing a transmitter and receiver in combination with a resonant tag circuit which is responsive to at least one frequency of electromagnetic radiation. The transmitter provides electromagnetic radiation in a predetermined... | 10/26/1982 |
| 4333072 | Identification device A closed coupled identification system for verifying the identity of an animal, object or other thing, has a probe including a circuit adapted to be connected to a source of alternating current and a separate, preferably miniature, circuit adapted to be i... | 06/01/1982 |
| 4321586 | Article theft detection 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 ... | 03/23/1982 |
| 4309697 | Magnetic surveillance system with odd-even harmonic and phase discrimination Apparatus for detecting the presence within a surveillance zone of a body of high permeability material creates a surveillance field varying sinusoidally at a fundamental frequency. Parallel filter channels select the second and third harmonic components ... | 01/05/1982 |
| 4303910 | Detection system A system for monitoring the position of a receptor reradiator in a surveillance zone having a first means for transmitting a first signal through the zone, and a receptor reradiator operable in response to reception of said signal to radiate at least one ... | 12/01/1981 |
| 4274090 | Detection of articles in adjacent passageways An article theft detection system for identifying which of two adjacent passageways a protected article passes. Each passageway is provided with spaced apart interrogation and receiver antennas, but a single receiver antenna services both passageways. Mul... | 06/16/1981 |
| 4260983 | Presence sensing detector and system for detecting a receiver/transmitter device affixed to an article A presence sensing system comprises a detector having a transmitter for transmitting an interrogation signal to an area to be kept under surveillance and a receiver for receiving a presence indicating signal. A receiver/transmitter device the presence of ... | 04/07/1981 |
| 4249167 | Apparatus and method for theft detection system having different frequencies Two different frequencies are generated within an interrogation zone. The receiver portion of the system determines the presence of a predetermined marker tag within the interrogation zone by the sensing and processing of a ratio of sideband signals gener... | 02/03/1981 |
| 4242663 | Electronic identification system An electronic identification system includes common transceiver and signal processing apparatus, and relative small electronic circuitry, referred to as a "tag", secured to each item of a population to be identified. Each tag is assigned a multi-bit digit... | 12/30/1980 |
| 4229735 | Rip detector signal detection circuit A detection circuit accurately monitors an AC signal, which is pulse modulated by information characteristic or indicative of the integrity of a conveyor belt or the like, to provide a distinguishable output representative of such integrity. Such distingu... | 10/21/1980 |
| 4215342 | Merchandise tagging technique A merchandise tagging technique includes a transmitter and receiver module, called hereinafter the interrogator, located at the merchandise inspection point. When a piece of merchandise containing an activated tag passes in the vicinity of the interrogato... | 07/29/1980 |
| 4212002 | Method and apparatus for selective electronic surveillance A high frequency (HF) generator projects an electronic wave into a surveillance area to establish a first field. At least one control zone is set up within the surveillance area by two frequency modulated (FM) generators. The first FM generator establishe... | 07/08/1980 |
| 4206453 | Method and apparatus for electronic surveillance A high frequency generator projects an electronic wave into a surveillance area to establish a first field. At least one control zone is set up within the surveillance area by two low frequency (LF) generators. The first LF generator establishes a second ... | 06/03/1980 |
| 4168496 | Quasi-stationary noise cancellation system An electronic security system detects a resonant tag circuit even in the presence of a substantially identical spurious resonance. The spurious resonance is fixed or quasi-stationary in time, in relation to the time that a resonant tag circuit is present ... | 09/18/1979 |
| 4141078 | Library circulation control system An automated library circulation control system includes a plurality of remote book processing terminals and a computer controlling the terminals and processing data between the terminals and the computer to maintain a current inventory of the circulation... | 02/20/1979 |
| 4063230 | Balanced field theft detection system Apparatus and method for identifying the presence in a pre-established location of an object having preselected electrical or magnetic properties. By applying two periodically varying electro-magnetic fields of the same frequency to the pre-established lo... | 12/13/1977 |
| 3938125 | Antipilferage system and marker therefor An antipilferage system utilizing markers comprising a sheet having both ferromagnetic and electrically conductive characteristics, which markers are detected upon passage through an interrogation zone within which are sequentially generated magnetic fiel... | 02/10/1976 |
