EP0762355B1 - Antenne et dispositif de détection électromagnétique incluant une telle antenne - Google Patents

Antenne et dispositif de détection électromagnétique incluant une telle antenne Download PDF

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Publication number
EP0762355B1
EP0762355B1 EP19960202459 EP96202459A EP0762355B1 EP 0762355 B1 EP0762355 B1 EP 0762355B1 EP 19960202459 EP19960202459 EP 19960202459 EP 96202459 A EP96202459 A EP 96202459A EP 0762355 B1 EP0762355 B1 EP 0762355B1
Authority
EP
European Patent Office
Prior art keywords
antenna
circuit
branch
coil
detection system
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP19960202459
Other languages
German (de)
English (en)
Other versions
EP0762355A1 (fr
Inventor
Paulus Rebers
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nederlandsche Apparatenfabriek NEDAP NV
Original Assignee
Nederlandsche Apparatenfabriek NEDAP NV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nederlandsche Apparatenfabriek NEDAP NV filed Critical Nederlandsche Apparatenfabriek NEDAP NV
Publication of EP0762355A1 publication Critical patent/EP0762355A1/fr
Application granted granted Critical
Publication of EP0762355B1 publication Critical patent/EP0762355B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING SYSTEMS, e.g. PERSONAL 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
    • G08B13/2422—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 acoustic or microwave tags
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING SYSTEMS, e.g. PERSONAL 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
    • G08B13/2477—Antenna or antenna activator circuit

Definitions

  • the invention relates to a circuit for connecting two antenna coils to a source, whereby the coupling of the power available at the source to the energy in the two antenna coils is maximal at a given bandwidth. More particularly, the invention relates to an antenna device for use in an electromagnetic detection system, comprising two loop antenna coils for generating a detection field for detecting responders provided with a loop antenna coil in a detection zone, the loop antenna coils in operation forming part of an antenna circuit connected to an exciting circuit, which antenna circuit comprises a series resonance circuit and a parallel resonance circuit with the same resonance frequency as the series resonance circuit. Further, the invention relates to an electromagnetic detection system.
  • the Q factor of the circuit and hence the bandwidth fo/Q, is equal to the situation with one current-controlled parallel circuit.
  • the available power is therefore utilized twice, in two coils instead of one coil.
  • the object of the present invention is to increase the energy available in the antenna coils.
  • a doubling of the available antenna energy is possible, with otherwise the same properties, that is an increase of the antenna efficiency by 3dB.
  • the invention provides for a circuit as claimed in claim 1.
  • Fig. 1 schematically shows a rotary field network according to EP-A-0 579 332, in which the two antenna coils are designated as L1 en L2 and the associated tuning capacitors as C1 and C2.
  • Fig. 2 shows an equivalent-circuit diagram of two seriesconnected resistors R.
  • Fig. 3 schematically shows the modified rotary field network of Fig. 1 after replacement of the two resistors and the elimination of parallel resistor 2R.
  • Fig 4 schematically shows an example of a net work that emerges after the conversion to an input impedance of R and the shift of the transformer T of Fig. 3 to the coil L1.
  • Fig. 5 schematically shows an example of an application of a rotary field network according to the invention in combination with a directional coupling to distinguish the signal to the receiver RX from the signal of the transmitter TX.
  • the series connection of two resistors is electrically identical to a resistor with the value 2R parallel to an ideal transformer T with a resistor 2R in series, the central branch of the transformer T replacing the nodal point of the series connection (see Fig. 2).
  • the transformer consists of two series-connected windings T1, T2, which are coupled 100%.
  • this network is converted to an input impedance R and the transformer T is moved to the parallel circuit, a network emerges consisting of a parallel circuit with coil L3 and capacitor C3 and a series circuit with coil L4 and capacitor C4 on the central branch of coil L3, as shown in Fig. 4.
  • This network comprises a single shared damping resistor R instead of the two resistors R of Fig. 1.
  • Coil L3 now forms one whole with the transformer T and so consists of two 100% coupled coils with a value of one quarter of the self-inductance L3 in series.
  • this network is also known as a passive second-order allpass-filter.
  • the input voltage is transmitted unchanged to the only resistor R at the output of the filter.
  • a frequency-dependent group running time makes it impossible to utilize the power dissipated in the resistor in the same manner for still more coils in which the current changes with respect to the input voltage according to a second-order transfer function.
  • the circuit according to the invention is useful not only for adjusting coils to a constant impedance or generating a rotary field, but also for increasing the efficiency or the bandwidth of a single antenna coil.
  • one of the antennas, for instance L4 can be replaced by a fixed coil.
  • the signal-to-noise ratio of the transmitter generally constitutes a limitation of the detection sensitivity.
  • the sensitivity is then determined directly by the antenna efficiency and the Q factor of the antenna.
  • the frequency dependence of the antenna impedance constitutes an additional limitation for the permitted Q factor.
  • Fast changes of the impedance as a result of too high a Q factor cannot be distinguished from the labels to be detected.
  • the Q factor does not have any direct influence on the impedance of the antenna system and it can therefore be increased to a value which the desired bandwidth and tuning accuracy still permit. The detection sensitivity can thereby be further improved.
  • the rotary field network according to the invention is eminently suitable for absorption systems because the gain in sensitivity can be greater than the 6 dB already expected.
  • the rotary field network according to the invention provides the possibility in an absorption system to further improve the sensitivity by the use of a directional coupling.
  • a directional coupling can distinguish between the power going one way and the other.
  • An absorption system comprising an antenna system according to the invention and a directional coupling is schematically shown in Fig. 5.
  • a directional coupling consists of a small coil Lk in series in the transmitter line 50, 51 and a series connection of a small capacitor Ck and a resistor Rk parallel to the transmitter line 50, 51.
  • the signal of the transmitter TX does not reach the receiver RX directly, but only via disturbances of the impedance of the antenna network caused by responders.
  • the receiver signal is here attenuated by the slight coupling factor of the directional coupling, determined by (2 ⁇ f) 2 * L* C ⁇ 1, but because the receiver sensitivity is mostly not determined by its own noise, this attenuation is not of importance.
  • the limitation of the receiver sensitivity by noise and other undesired signals derived from the transmitter can be reduced in this manner.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Automation & Control Theory (AREA)
  • Computer Security & Cryptography (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Near-Field Transmission Systems (AREA)
  • Transmitters (AREA)
  • Testing Relating To Insulation (AREA)
  • Measurement Of Resistance Or Impedance (AREA)

Claims (7)

  1. Dispositif d'antenne pour une utilisation dans un système de détection électromagnétique, comprenant deux bobines d'antenne-cadre pour engendrer un champ de détection rotatif pour détecter des répondeurs munis d'une bobine d'antenne-cadre dans une zone de détection, les bobines d'antenne-cadre en fonctionnement formant une partie d'un circuit d'antenne relié à un circuit d'excitation, ayant une première borne et une seconde borne, le circuit d'antenne comprenant :
    un circuit de résonance en parallèle, le circuit de résonance en parallèle comprenant un premier condensateur de réglage (C3) et une bobine d'antenne-cadre construite comme un transformateur (T) avec une première et une seconde dérivations et une dérivation centrale, le transformateur comprenant deux enroulements très fortement couplés (T1, T2) reliés entre la première dérivation et la dérivation centrale et entre la dérivation centrale et la seconde dérivation respectivement, la première dérivation étant couplée à la première borne, le premier condensateur de réglage (C3) étant couplé en parallèle aux enroulements (T1, T2) ;
    un circuit de résonance en série comprenant un second condensateur de réglage (C4) et une seconde bobine d'antenne-cadre (L4), le circuit de résonance en série étant relié entre la dérivation centrale et la seconde borne, le circuit de résonance en série étant en résonance en série à la fréquence de résonance du circuit de résonance en parallèle ;
    une résistance d'amortissement unique, couplée entre la seconde dérivation et la seconde borne, la résistance d'amortissement étant l'élément de dissipation sensiblement seul dans le circuit d'antenne.
  2. Dispositif d'antenne selon la revendication 1,
    caractérisé en ce qu'au moins l'une des bobines d'antenne-cadre (L3, L4) du dispositif d'antenne est couplée au reste du circuit d'antenne via un transformateur d'adaptation (Tk1, Tk2).
  3. Dispositif d'antenne selon la revendication 2, dans lequel la bobine, construite comme un transformateur, est munie d'un enroulement additionnel, qui est relié à la bobine d'antenne-cadre correspondante (L3).
  4. Système de détection électromagnétique comprenant un dispositif d'antenne selon l'une quelconque des revendications 1 - 3.
  5. Système de détection électromagnétique selon la revendication 4, comprenant un transmetteur (Tx) et un récepteur (Rx),
    caractérisé en ce que le transmetteur (Tx) et le récepteur (Rx) sont reliés au circuit d'antenne via un couplage directionnel.
  6. Système de détection électromagnétique selon la revendication 5,
    caractérisé en ce que le couplage directionnel comprend une bobine (Lk) agencée dans une ligne de connexion (50) entre le transmetteur (Tx) et le circuit d'antenne, ainsi qu'une connexion en série, reliée en parallèle au circuit d'antenne, d'une résistance (Rk) et d'un condensateur (Ck), le point nodal entre la résistance (Rk) et le condensateur (Ck) étant relié au récepteur (Rx).
  7. Système de détection électromagnétique selon la revendication 4,
    caractérisé en ce que le système de détection est un système du type à absorption.
EP19960202459 1995-09-04 1996-09-04 Antenne et dispositif de détection électromagnétique incluant une telle antenne Expired - Lifetime EP0762355B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NL1001125 1995-09-04
NL1001125A NL1001125C2 (nl) 1995-09-04 1995-09-04 Verbeterd draaiveldnetwerk.

Publications (2)

Publication Number Publication Date
EP0762355A1 EP0762355A1 (fr) 1997-03-12
EP0762355B1 true EP0762355B1 (fr) 2002-03-20

Family

ID=19761530

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19960202459 Expired - Lifetime EP0762355B1 (fr) 1995-09-04 1996-09-04 Antenne et dispositif de détection électromagnétique incluant une telle antenne

Country Status (4)

Country Link
EP (1) EP0762355B1 (fr)
DE (1) DE69619911T2 (fr)
ES (1) ES2176398T3 (fr)
NL (1) NL1001125C2 (fr)

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL9201270A (nl) * 1992-07-15 1994-02-01 Nedap Nv Antiwinkeldiefstal-antenne met draaiveld.

Also Published As

Publication number Publication date
ES2176398T3 (es) 2002-12-01
DE69619911D1 (de) 2002-04-25
EP0762355A1 (fr) 1997-03-12
DE69619911T2 (de) 2002-11-21
NL1001125C2 (nl) 1997-03-05

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