Classifications

• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B13/00—Burglar, theft or intruder alarms
  • G08B13/22—Electrical actuation
  • G08B13/24—Electrical actuation by interference with electromagnetic field distribution
  • G08B13/2402—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
  • G08B13/2405—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting characterised by the tag technology used
  • G08B13/2414—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting characterised by the tag technology used using inductive tags
• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B13/00—Burglar, theft or intruder alarms
  • G08B13/22—Electrical actuation
  • G08B13/24—Electrical actuation by interference with electromagnetic field distribution
  • G08B13/2402—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
  • G08B13/2465—Aspects related to the EAS system, e.g. system components other than tags
  • G08B13/2468—Antenna in system and the related signal processing
  • G08B13/2471—Antenna signal processing by receiver or emitter
• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B13/00—Burglar, theft or intruder alarms
  • G08B13/22—Electrical actuation
  • G08B13/24—Electrical actuation by interference with electromagnetic field distribution
  • G08B13/2402—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
  • G08B13/2465—Aspects related to the EAS system, e.g. system components other than tags
  • G08B13/2488—Timing issues, e.g. synchronising measures to avoid signal collision, with multiple emitters or a single emitter and receiver

Definitions

• the present invention relates to an electronic anti-theft device with a transmitter that generates an electromagnetic field that excites the resonance circuit on a resonance tag, which may be located in the reception area of the transmitter, and a receiver that responds to the signals of the transmitter and one, if applicable, in the reception area addressed resonance tag, evaluates these signals and triggers an alarm signal when a signal of the resonance tag is detected and a method for operating such a device.
• the object of the present invention is now to provide a device of the type defined at the outset, which is able to eliminate the interfering influences without complex and often ineffective filter device.
• the invention makes use of the fact that when the transmitter or transmitters are switched off, on the one hand, the emitted signals (electromagnetic field) and the interferences caused by them are practically immediate, i.e. practically without delay, e.g. disappear after 1/2 ⁇ sec. (within one oscillation period), on the other hand the signal caused by the resonance label decays only relatively slowly, since the vibrational energy stored in the resonance label of the labels acting as transmitter is only slowly reduced (up to 5 ⁇ sec. , or 20-30 oscillation periods of the resonance frequency).
• the transmitter emits an electromagnetic pulse periodically for a short period of time, the spectrum of which (broadband) covers the resonance frequency of the label and which is sufficiently energetic to excite the resonance circuit of the resonance label
• This echo method is particularly effective because the receiver can be set to a very high sensitivity in the transmission pause due to the complete absence of the transmission signal (no "idle signal").
• a pulse with only one frequency can be used instead of a broadband transmission pulse, in which case this frequency is changed in a manner known per se by a small amount for each further pulse compared to the frequency of the previous pulse.
• the transmitter can be swept in steps and the resonance label is also recorded in this case if the frequency steps are sufficiently small and the entirety of the “discrete” transmission frequencies defined in this way covers the resonance frequency of the label.
• the receiver can then also be designed to be very narrow-band, the reception frequency being automatically matched to the transmission frequency and carried with it.
• the narrowband receiver offers the additional advantage of high interference suppression and low noise.
• the narrow-band transmitter arises in such multiple systems if the individual transmitters are swept through with a frequency offset, ie all transmitters transmit at the same time and for the same period of time, but each transmitter on a frequency which is different from the frequency of any other transmitter, however, in such a way that each transmitter also transmits once on each of the defined "discrete" wobble frequencies during a wobble cycle.
• a transmitter jumps, which transmits at the maximum wobble frequency, with the subsequent transmission pulse back to the minimum transmission frequency.
• each transmitter-receiver device Since the superposition principle of the electromagnetic fields applies because of the linear behavior of the label, and since each transmitter transmits at a frequency that is different from the frequency of every other transmitter, and since each receiver only receives at the respective frequency of its assigned transmitter, so see none of the receivers has an effect that comes from a transmitter other than the transmitter assigned to it, ie each individual transmitter-receiver device also functions in the presence of all other installations of the overall system as if it were installed as a single system, ie as if all the others Installations would be switched off. If a transmitter-receiver pair is optimally set in single operation, it remains optimal even during the simultaneous operation of all transmitter-receiver pairs in the entire system.
• the individual transmitter-receiver pairs are synchronized by signals that are transmitted to them wirelessly from a central office or that they transmit directly to one another (e.g. via their transmitters and receivers, which are intended for resonance label detection).
• the transmitter antenna and the receiver antenna are at the same location, e.g. can be accommodated in the same frame. It is also readily possible to use the same (single) antenna for the transmitter and the receiver, since any alarm-triggering signals only have to be received or evaluated during the pauses in transmission. This may simplify essential the installation of monitoring devices.

Landscapes

• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Automation & Control Theory (AREA)
• Computer Security & Cryptography (AREA)
• Electromagnetism (AREA)
• General Physics & Mathematics (AREA)
• Signal Processing (AREA)
• Burglar Alarm Systems (AREA)
• Mobile Radio Communication Systems (AREA)

Applications Claiming Priority (2)

Publications (3)

Family

ID=4201949

Family Applications (1)

Country Status (4)

Citations (6)

• 1989
  • 1989-03-22 CH CH107889A patent/CH681051A5/de not_active IP Right Cessation
• 1990
  • 1990-02-02 EP EP19900102051 patent/EP0388609B1/fr not_active Expired - Lifetime
  • 1990-02-02 DE DE59010785T patent/DE59010785D1/de not_active Expired - Fee Related
  • 1990-03-22 JP JP6992190A patent/JPH02284294A/ja active Pending

Patent Citations (6)

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