EP0608961B1 - Verfahren und System zur Detektierung von Resonanzeffekten eines Etiketts in einem gewobbelten Abfragefeld mittels Einseitenbanddemodulation - Google Patents

Verfahren und System zur Detektierung von Resonanzeffekten eines Etiketts in einem gewobbelten Abfragefeld mittels Einseitenbanddemodulation Download PDF

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Publication number
EP0608961B1
EP0608961B1 EP19940200205 EP94200205A EP0608961B1 EP 0608961 B1 EP0608961 B1 EP 0608961B1 EP 19940200205 EP19940200205 EP 19940200205 EP 94200205 A EP94200205 A EP 94200205A EP 0608961 B1 EP0608961 B1 EP 0608961B1
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EP
European Patent Office
Prior art keywords
frequency
sideband
label
interrogation field
detection system
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EP19940200205
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English (en)
French (fr)
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EP0608961A1 (de
Inventor
Tallienco Wieand Harm Fockens
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Nederlandsche Apparatenfabriek NEDAP NV
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Nederlandsche Apparatenfabriek NEDAP NV
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    • 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
    • G08B13/2414—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 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
    • G08B13/2414—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
    • G08B13/2417—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 having a radio frequency identification chip
    • 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
    • G08B13/2428—Tag details
    • G08B13/2431—Tag circuit details
    • 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
    • G08B13/2471—Antenna signal processing by receiver or emitter

Definitions

  • This invention relates to a detection system for detecting or identifying a label comprising at least one resonant circuit, the system comprising a transmitter unit for generating a frequency-swept electromagnetic interrogation field and a detection unit for detecting resonance effects caused by a label located in the interrogation field.
  • the detection unit comprises a receiver which employs synchronous integration in the form of a dual channel synchronous video integrator to independently process positive and negative pulses of the tag signal in order to differentiate the label signal from extraneous signals and noise. It is an object of the invention to provide the system with another type of receiver unit which is less sensitive to noise and interfering signals.
  • a detection system is characterized in that the detection unit comprises a receiver unit which detects signals coming from just one label frequency sideband of the instantaneous frequency of the interrogation field for detecting resonance effects which occur at least substantially in one frequency sideband of a resonance frequency of the label so that the detection result is based on the response from the label sideband that corresponds with the frequency of the interrogation field just before the present frequency of the swept frequency.
  • the receiver unit for receiving the resonance effects is tuned only to one sideband of the interrogation field, herein referred to as the label frequency sideband, no noise and interfering components coming from the other sideband occur in the further processing of a received signal, since signals from this last sideband are not mixed with signals from the label frequency sideband. This yields a considerable gain in the signal to noise ratio.
  • Dutch patent application NL 8202951 discloses a system comprising a receiver unit where a carrier wave with two sidebands of the interrogation field, together with an output signal of the transmitter unit, are applied to a mixer.
  • An output signal of the mixer comprises the two sideband components transformed to a carrier wave of zero Hertz.
  • a disadvantage of this system is that the signal to noise ratio is often not good enough to be able to detect a resonance effect with certainty. This is partly caused by noise and interfering components present in a sideband.
  • the system according to the Dutch patent application is provided with means for detecting noise and interfering components in a frequency band which does not coincide with the frequency band in which the resonance effects to be expected are detected.
  • This entails the disadvantage that the total radio-frequency bandwidth of the receiver unit must be enlarged to make it possible for both frequency bands to be detected. As a result, the sensitivity of the receiver unit to noise and interfering components is increased, so that the disadvantages referred to are not adequately removed.
  • a frequency sweep will typically be implemented so as to ascend and descend alternately.
  • the position of the label frequency sideband is dependent on this.
  • the system accordingly selects an upper or lower sideband of the interrogation field for the label frequency sideband, depending on the frequency sweep. If a frequency sweep is performed which, for instance, is only ascending (saw tooth), the label frequency sideband may be set at a predetermined sideband.
  • an average frequency of the label frequency sideband at a time of a frequency sweep corresponds with the frequency of the interrogation field at a previous time of the frequency sweep.
  • the label frequency sideband is an upper sideband of the instantaneous frequency of the interrogation field during a period in which the frequency of the interrogation field decreases per unit time and/or the label frequency sideband is a lower sideband of the instantaneous frequency of the interrogation field during a period in which the frequency of the interrogation field increases per unit time.
  • the label frequency sideband may accordingly have been set as such beforehand or selected as such by the system.
  • the receiver unit comprises means for detecting spectral components of noise and interfering signals in an interfering frequency sideband of the frequency of the interrogation field, whilst the label frequency and interfering frequency sidebands are located on opposite sides of the instantaneous frequency of the interrogation field, and signals coming from these sidebands are detected separately from each other.
  • the resonance effects only occur in one sideband, herein referred to as the label frequency sideband.
  • interference sideband In the complementary sideband associated with this sideband, hereinafter referred to as interference sideband, these resonance effects do not occur, so that only the noise and interfering components, if any, are present in this sideband.
  • interfering components are accordingly detected separately from any resonance effect and may further be used for determining and setting, for instance, noise threshold levels in the receiver unit.
  • the radio-frequency bandwidth of the receiver unit need not be enlarged, in contrast with the system according to Dutch patent application 8202951.
  • the sensitivity of the system according to the invention is not reduced when the noise and interfering signals referred to are detected.
  • label is understood to include the broader term responder.
  • the resonance effects of a label can be caused by, for instance, coils in combination with a capacitor.
  • the coils can be wound air-core coils or etched coils, such as for instance the coils used in adhesive labels, or coils wound onto a ferrite core.
  • label as used herein is understood to include labels resonating in a different manner, for instance labels based on mechanical resonance, in combination with the magnetostriction effect, or labels based on ferroresonance.
  • the present invention further relates to a method for detecting or identifying a label comprising at least one resonant circuit, in which method a frequency-swept electromagnetic interrogation field is generated and resonance effects caused by a label located in the interrogation field are detected.
  • the method is characterized in that said detection is carried out within just one label frequency sideband of the instantaneous frequency of the interrogation field.
  • a transmittive circuit 1 controls a transmitting coil circuit 2.
  • This circuit comprises an antenna coil L 1 and a tuning capacitor C 1 .
  • the electric losses in the antenna coil are represented by the resistor R 1 .
  • the label, whose circuit is indicated by 3 comprises in this example an air-core coil L 2 and a capacitor C 2 .
  • the resistor R 2 represents the electric circuit losses.
  • the current I 1 (t) through the coil L 1 generates a primary magnetic alternating field H 1 (t), also referred to as the interrogation field.
  • the voltage V 2 (t) causes a current I 2 (t) to flow in the series circuit L 2 , C 2 , R 2 .
  • the magnitude and the phase of the current I 2 (t) with regard to the voltage V 2 (t) depends on the (instantaneous) frequency f c of the interrogation signal - in this example defined as the primary alternating field H 1 (t) or the current I 1 (t) - and on the resonance frequency f o of the circuit 3.
  • v is also referred to as the normalized frequency
  • Q as the quality factor of the circuit 3.
  • I 2 and V 2 are the known rotary vector notations of I 2 (t) and V 2 (t), respectively.
  • the absolute magnitude of the current I 2 can be defined as:
  • Relation (5) gives the known resonance curve, as shown in Fig. 2a.
  • Fig. 2b shows the phase relation between I 2 and V 2 .
  • the phase difference lies between 0 and 90 degrees, so that the current I 2 leads the voltage V 2 in phase.
  • f c > f o i.e. for v > 0, the phase difference lies between 0 and -90 degrees, so that the current I 2 lags behind the voltage V 2 in phase.
  • the current V 2 already lags 90 degrees behind the alternating field H 1 , so that the phase difference between the current I 2 and the alternating field H 1 lies between 0° and -180°.
  • the scale for the phase difference between the current I 2 and the alternating field H 1 is shown on the right-hand side of Fig. 2b.
  • Fig. 3 shows a vector diagram of vectors H 1 ,V 2 and I 2 .
  • the direction of H 1 , V 2 and I 2 corresponds, respectively, with the phase of the alternating field H 1 (t), the voltage V 2 (t) and the current I 2 (t).
  • the magnitude of H 1 , V 2 and I 2 corresponds with the amplitude of the alternating field H 1 (t), the voltage V 2 (t) and the current I 2 (t).
  • the direction of vector V 2 is fixed (relative to vector H 1 ), but the direction of I 2 is dependent on the frequency.
  • the direction of I 2 coincides with that of V 2 if the frequency of the interrogating signal is equal to the resonance frequency of the circuit 3.
  • Fig. 3 further shows a circle 6.
  • This circle 6 is the geometrical position of all possible vectors I 2 as a function of the normalized frequency v.
  • Arrow 7 indicates the direction in which the circle 6 is traversed if the normalized frequency v is varied from low to high.
  • the current I 2 through the coil L 2 of the circuit 3 causes a secondary magnetic alternating field H 2 which is in phase with the current I 2 .
  • This secondary alternating field H 2 in turn induces an induction voltage V 3 (see Fig. 1) in a receiver coil L 3 of an antenna circuit 4.
  • the antenna circuit 4 is coupled to a receiver circuit 5.
  • the primary field H 1 also induces an induction voltage V 4 in the receiver coil L 3 .
  • These two induction voltages V 3 and V 4 each lag 90 degrees in phase relative to their respective generatory magnetic fields H 2 and H 1 , so that the phase difference between the voltages V 3 and V 4 is equal to the phase difference between the secondary alternating field H 2 and the primary alternating field H 1 .
  • the phase difference between the voltages V 3 and V 4 will also be between 0 and -180 degrees.
  • a vector diagram can also be constructed for V 3 and V 4 (see Fig. 4).
  • the frequency f c of the interrogating signal is uniformly varied from low (f min ) to high (f max ).
  • f min low
  • f max high
  • the phase angle between V 3 and V 4 will be almost equal to zero. If the frequency f c passes the resonance frequency f o , the phase angle between V 3 and V 4 will shift from approx. 0° to approx. -180°.
  • this negative phase shift means that its frequency, while passing the resonance frequency f o , is temporarily lowered somewhat, since the frequency is the first derivative of the phase of an alternating voltage, as is known from the signal theory.
  • Fig. 6 gives the phase and frequency variation for this situation.
  • the fact is the phase of the voltage V 3 must increase by 180 degrees during the passage of the resonance frequency, which has as a consequence that the instantaneous frequency of V 3 must be temporarily higher than the driving frequency f c of the alternating field signal H 1 (overtaking effect).
  • the current I 2 (t), and hence the voltage V 3 (t), can also be regarded as the result of a double modulation process, in which the amplitude of the current I 2 (t) arises through amplitude modulation of the voltage V 2 (t) in accordance with the amplitude resonance curve according to relation (5), and the phase of I 2 (t) through phase modulation of the voltage V 2 (t) in accordance with the phase resonance curve according to relation (6).
  • I 2 (t) A(t) * cos(2 ⁇ f c .t + ⁇ (t))
  • A(t) 1 R 2 * 1 ⁇ (1 + Q 2 v(t) 2 )
  • ⁇ (t) -arctg(Qv(t))
  • v(t) f c .(t)/f o - f o /f c .(t).
  • f c .(t) represents the varying frequency of the interrogating signal, in this case the alternating field H 1 or the current I 1 .
  • Relation (7) is known per se from the general theory of amplitude-modulated signals. It represents a so-called single sideband signal (SSB).
  • SSB single sideband signal
  • a single sideband signal is an amplitude-modulated signal in which either of the two frequency sidebands, as well as the carrier wave, has been suppressed.
  • Fig. 7a shows the frequency spectrum of an amplitude-modulated signal consisting of a carrier wave component f c and the usual two sidebands: lower sideband and upper sideband (abbreviated as LSB (Lower Side Band) and USB (Upper Side Band)).
  • LSB Lower Side Band
  • USB User Side Band
  • Fig. 7b shows the spectrum of a single sideband signal, with the carrier wave and the upper sideband having been suppressed.
  • relation (7) could indeed represent a single sideband modulated signal.
  • the extent to which the other sideband has dropped away can either be determined by means of a quantitative analysis or must appear from an empirical investigation.
  • Such an empirical investigation has demonstrated that the label signal I 2 (t) is indeed strictly a single sideband signal, in which the other sideband does not occur. Accordingly, the signal energy of the label signal is located entirely in the sideband that lags behind with regard to the frequency sweep.
  • the label signal occurs alternately in the lower sideband during the ascending sweep and in the upper sideband during the descending sweep.
  • the sideband in which the label signal occurs is also referred to as the label sideband, whilst the other sideband is referred to as the interference sideband.
  • the present invention is based on the above-described physical phenomenon.
  • FIG. 9 shows an exemplary embodiment of a schematic diagram of a detection and/or identification system according to the invention.
  • a transmitter circuit 1 feeds a radio-frequency signal I 1 (t) sweeping in frequency f c to a transmitter coil L 1 .
  • the transmitter coil L 1 generates a magnetic alternating field H 1 (t) which is directly proportional to the signal I 1 (t).
  • the interrogating signal H 1 (t) has a frequency which is equal to the resonance frequency f o or is equal to one of the resonance frequencies of label 3
  • this label 3 will produce a label signal H 2 (t), which signal induces a voltage V 3 (t) in receiver coil L 3 .
  • the receiver circuit 8, 9 comprises a synchronous demodulation circuit 8, which may for instance comprise one or more multiplication circuits to enable a received signal to be multiplied by a reference signal Ref, produced by the transmitter circuit 1 via line 14, for demodulating the received signal according to the principle of direct conversion so as to obtain a demodulated signal D(t).
  • the reference signal Ref is for instance directly proportional to the signal I 1 (t) and comprises the frequency f c .
  • the demodulated signal D(t) is then provided to a circuit 9, in which the demodulated signal D(t) is split into a signal LSB(t) coming from the lower sideband LSB and a signal USB(t) coming from the upper sideband USB.
  • Both signals are applied to a bipolar switch 10, which is controlled by a control signal 15 from the transmitter circuit 1, in such a manner that during the ascending frequency sweep the signal LSB(t), in which the label signal H 2 (t) is possibly present, is transmitted to a label signal processor 11 and the signal USB(t), in which no label signal H 2 (t) can be present but which may contain noise and interference signals, is transmitted to an interference processor 12.
  • the switch 10 is controlled by the control signal 15, in such a manner that the signal LSB(t) is supplied to the interference processor 12 and the signal USB(t) is supplied to the label signal processor 11.
  • the switch 10 The consequence of the switching operation by means of the switch 10 is that a signal potentially comprising the label signal H 2 (t) is supplied in each case to the label signal processor (11), and that a signal which, except for noise and interfering signals, cannot comprise a label signal H 2 (t) is supplied in each case to the interference processor (12).
  • the receiver circuit 8-13 has been split into two channels, which makes it possible to measure the level of noise and interfering signals independently of the presence of a label signal.
  • Applicant's Dutch patent 8202951 discloses a system in which likewise a received signal is split for the purpose of obtaining a label signal channel and an interference channel.
  • the splitting operation is carried out in an entirely different manner, viz. by splitting the received signal into two different frequency bands.
  • the received signal is split into a label band (l.f. part) 3-15 kHz, and an interference band (h.f. part) 20-50 kHz.
  • the label signal only comprises frequency components in the range of 3-15 kHz (originally also in the 0-3 kHz range, but that part is filtered out in the receiver to enable the sweep frequency itself with its harmonics to be sufficiently suppressed as well).
  • Noise and interference signals - in particular interference signals resulting from interference with radio signals occurring in the radio-frequency band used and signals coming from other shoplifting detection systems - comprise frequency components that occur both in the frequency range of 3-15 kHz and in the range of 20-50 kHz.
  • the interference band of 20-50 kHz referred to above is replaced with an interference channel having at least substantially the same frequency range as the label band, for instance 3-15 kHz.
  • the label signal is separated from the received signal on the basis of a sideband separation.
  • the output signals of the label signal processor 11 and the interference processor 12 are applied to a resonance detector 13.
  • the label signal processor, together with the resonance detector 13, forms a first signal processing channel, and the interference processor 12, together with the resonance detector, forms a second signal processing channel.
  • the label signal processor processes the label signal in a manner known per se.
  • the label signal processor may for instance comprise a matched filter adapted to a resonance circuit of a label.
  • the interference processor 12 is likewise of a known type and determines, for instance, the amplitude of spectral components of the detected noise and interfering signals. On the basis of this amplitude, a detection threshold level is determined which is supplied to the resonance detector 13. The resonance detector 13 produces an output signal, for instance only when the amplitude of the signal generated by the label signal processor exceeds the detection threshold level. The output signal of the resonance detector 13 may then be a predetermined signal ('alarm') or, for instance, the signal generated by the label signal processor 11.
  • the radio communications technique For separating the two sidebands, a number of methods are known from the radio communications technique, such as for instance the filter method, the phase or quadrature method and the third or Weaver method.
  • the filter method is useful only in combination with a superheterodyne receiver, which, however, is not preferred for practical reasons.
  • the phase method is used, which is moreover entirely in line with the direct conversion technique already in use.
  • Fig. 10 shows the block diagram of a first preferred embodiment of a receiver/demodulator 8, 9 according to the phase method.
  • the label signal is received by antenna coil L 3 and passed to mixers 16 and 17.
  • Both mixers 16, 17 also receive the reference signal Ref, comprising the frequency of the carrier wave, from the transmitter circuit 1.
  • the reference signal Ref which is supplied to the mixer 17 has been phase-shifted 90° by means of a phase shifter 18.
  • the output signal of either of the mixers, for instance mixer 17 in Fig. 10 is also phase-shifted 90° by means of a phase shifter 19.
  • the sideband selecting operation will be evident from the following simple derivation.
  • an input signal S generated by the coil L 3 and supplied to the mixers 16, 17 comprises two frequency components, viz. a first component in the upper sideband, having frequency f usb , and a second component in the lower sideband, having frequency f lsb .
  • phase shifter 19 This circuit must meet the requirement that it can provide very accurately a phase shift of a magnitude of 90 degrees over a relatively wide frequency range of, for instance, 3-15 kHz. This requires a circuit which must meet very high quality requirements with regard to accuracy.
  • a sideband splitting method derived from the phase method involves the use of 'Polyphase Networks' (PN), as disclosed in "Single Sideband Modulation using Sequence Asymmetric Polyphase Networks" by M.J. Gingell, Electrical Communication, vol. 48, nos. 1 and 2, 1973, pp. 21 - 25, and in British patent specifications 1,174,709 and 1,174,710.
  • PN Polyphase Networks'
  • Fig. 11 shows a block diagram of a second preferred embodiment of the receiver/demodulator 8, 9, comprising two PNs 22, 23.
  • the mixers 16 and 17 are symmetrically coupled to the PNs 22, 23. Since the signals from the mixers 16, 17 are shifted 90 degrees relative to each other, the combined four outputs of the mixers will form a ring to which the phases 0°, 90°, 180° and 270° can be assigned.
  • Fig. 12 this is shown symbolically in a vector diagram.
  • the reference numerals 24, 25, 26 and 27 indicate the input terminals of the PNs 22, 23, which are connected with the outputs of the mixers 16, 17, as shown in Fig. 11.
  • a signal received by the coil L 3 gives a displacement vector 28 as shown in the vector diagram according to Fig. 12.
  • the rotary direction of the vector 28 depends on the order in which the mixers 16, 17 are connected and on the frequency of the received signal. If the frequency of the received signal is greater than the carrier wave frequency f c , i.e. a signal in the upper sideband, then the frequency of the output signal of the mixers is called positive (see also f usb in the relations 9 and 10).
  • Fig. 13 shows an example of a Sequence Asymmetric Polyphase Network.
  • the characteristic property of a PN is that a presented four-phase signal which, for instance, is presented in such an order that the vector 28 rotates counterclockwise, for instance, does propagate from the left to the outputs on the right through the circuit and that this signal does not as such propagate when it is presented in the reverse phase sequence, i.e. when the vector 28 rotates clockwise.
  • PN 22, 23 discriminates between a positive frequency and a negative frequency.
  • PN 22 will only transmit signals having positive frequencies, i.e. signals resulting from the detection with mixers 16, 17 of upper sideband signals with the carrier wave.
  • PN 23 on the other hand, as a consequence of the reversal of the connections 25 and 27 of mixer 17, will only transmit signals having negative frequencies, i.e. signals resulting from the detection of signals in the lower sideband.
  • USB(t) the demodulation product of the upper sideband signal appears
  • LSB(t) the demodulation product of the lower sideband
  • the circuit of Fig. 11 is therefore equivalent to that of Fig. 10.
  • the advantage of the circuit of Fig. 11 is that the tolerances of components 22, 23 in the PN need to meet considerably less strict requirements than the tolerances of components in the phase shift network 19 of Fig. 10.
  • DSP Digital Signal Processor
  • Fig. 14 shows a particular embodiment of the invention in which a DSP is used.
  • the circuit of Fig. 14 replaces the switch 10, label signal processor 11, interference processor 12 and resonance detector 13 according to Fig. 9.
  • the lower sideband signal LSB(t) and the upper sideband signal USB(t) are applied, respectively, to an analog/digital converter ADC1 and ADC2.
  • Switch 10, label signal processor 11, interference processor 12 and resonance detector 13 are integrated into an algorithm of the DSP.
  • the synchronization signal Ref 5 of the transmitter circuit 1 is supplied to the DSP.
  • the adder and subtracter circuits 20 and 21, respectively, of Fig. 10 can for instance be integrated into the algorithm of the DSP.
  • the broadband 90° phase shifter 19 of Fig. 10 can be of digital design. This phase shift is called a Hilbert transformation in the signal theory, and DSP algorithms for this purpose are known per se.
  • the entire signal processing after the mixers 16, 17 can be carried out in a DSP, as schematically shown in Fig. 15.
  • the invention relates to shoplifting dectection systems of the so-called radio-frequency type.
  • labels are used with an air-core coil, both in a design with a coil wound from wire and in a design with a coil etched on a support material.
  • a different type of shoplifting detection system utilizes the mechanical resonance of a plate of magnetic material, the magnetostriction effect being used for coupling to the magnetic interrogation field H 1 (t). This mechanism is described, for instance, in European patent 0096182 to Identitech Co.
  • the invention can also be used for detection or identification of labels in which resonance effects according to the principle of magnetic ferroresonance are utilized, whereby the resonance is the result of the precession effect of the electron or nuclear spin. This identification technique is disclosed in applicant's Dutch patent application 9101941.
  • the invention can moreover be used in adsorption as well in transmission detection systems.
  • a code number can be assigned to a label by detecting both the number of resonances and the precise frequencies of these resonances. This renders such a label useful for identification applications such as, for instance, person admission control, livestock management systems and for the identification of goods.
  • the invention is applicable and can give rise to greater recognition distances and improved recognition reliability. Nor is the invention limited to the type of frequency sweep shown in Fig. 8.
  • the invention is applicable wherever one or more resonance effects are to be detected or measured by means of a frequency-swept interrogating signal ans all of these applications are understood to fall within the concept of the invention.

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  • Automation & Control Theory (AREA)
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Claims (25)

  1. Erkennungssystem zum Erkennen oder Identifizieren einer Markierung (3) mit wenigstens einer Resonanzschaltung (L2C2), wobei das System eine Sendereinheit (1) zum Erzeugen eines frequenzgewobbelten elektromagnetischen Abfragefeldes und eine Erkennungseinheit (8-13) zum Erkennen von Resonanzeffekten aufweist, die durch eine in dem Abfragefeld (H1(t)) befindliche Markierung (3) ausgelöst wird, dadurch gekennzeichnet, daß die Erkennungseinheit (8-13) eine Empfängereinheit (8, 9) aufweist, die Signale erkennt, die von nur einem Markierungsfrequenzseitenband der momentanen Frequenz des Abfragefeldes kommen, um Resonanzeffekte zu erkennen, die wenigstens im wesentlichen in einem Seitenband einer Resonanzfrequenz der Markierung (3) auftreten, so daß das Erkennungsergebnis auf der Reaktion ds Markierungsseitenbandes basiert, das der unmittelbar vor der gegenwärtigen Frequenz der Wobbelung erzeugten Frequenz (fc) des Abfragefeldes (H1(t)) entspricht.
  2. Erkennungssystem nach Anspruch 1, dadurch gekennzeichnet, daß das System, je nach Wobbelung, ein oberes (USB) oder ein unteres Seitenband (LSB) des Abfragefeldes als das Markierungsfrequenzseitenband auswählt.
  3. Erkennungssystem nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die - mittlere Frequenz des Markierungsfrequenzseitenbandes zum Zeitpunkt eines Frequenzhubs der Frequenz des Abfragefeldes zu einem vorherigen Zeitpunkt des Frequenzhubs entspricht.
  4. Erkennungssystem nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß das Markierungsfrequenzseitenband ein oberes Seitenband (USB) der momentanen Frequenz (fc) des Abfragefelds (H1(t)) in einem Zeitraum ist, in dem die Frequenz des Abfragefelds (H1(t)) pro Zeiteinheit abnimmt.
  5. Erkennungssystem nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß das Markierungsfrequenzseitenband ein unteres Seitenband (LSB) der momentanen Frequenz (fc) des Abfragefelds (H1(t)) in einem Zeitraum ist, in dem die Frequenz des Abfragefelds (H1(t)) pro Zeiteinheit zunimmt.
  6. Erkennungssystem nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß das Markierungsfrequenzseitenband auf einer Seite der momentanen Frequenz (fc) des Abfragefelds (H1(t)) angeordnet ist, die der Seite der momentanen Frequenz des Abfragefeldes entspricht, auf der sich die Frequenz befindet, bei der die Markierung (3) wenigstens im wesentlichen zu dem Zeitpunkt resonant ist, zu dem die Frequenz des Abfragefeldes eine Resonanzfrequenz der Markierung passiert.
  7. Erkennungssystem nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die Empfängereinheit (8, 9) eine Einrichtung zum Erkennen spektraler Komponenten von Rausch- und Interferenzsignalen in einem störenden Frequenzseitenband der Frequenz des Abfragefeldes aufweist, wobei das Markierungsfrequenzseitenband und das störende Frequenzseitenband auf entgegengesetzten Seiten der momentanen Frequenz des Abfragefeldes angeordnet sind und Signale von diesen Seitenbändern getrennt voneinander erkannt werden.
  8. Erkennungssystem nach Anspruch 7, dadurch gekennzeichnet, daß das Markierungsfrequenz- und das störende Frequenzseitenband in bezug zur momentanen Frequenz des Abfragefeldes spiegelsymmetrisch angeordnet sind.
  9. Erkennungssystem nach einem der vorhergehenden Ansprüche 6-8, dadurch gekennzeichnet, daß die Erkennungseinheit (8-13) ferner einen Interferenzprozessor (12) aufweist, an den die in dem störenden Frequenzseitenband erkannten Signale zum Bestimmen der Amplitude der spektralen Komponenten und zum Bestimmen eines Erkennungsschwellenwerts auf der Basis dieser Amplituden angelegt werden, mit dessen Hilfe für in dem Markierungsfrequenzseitenband erkannte Signale festgestellt werden kann, ob in diesen Signalen ein Resonanzeffekt vorliegt oder nicht.
  10. Erkennungssystem nach Anspruch 9, dadurch gekennzeichnet, daß die in dem Markierungsfrequenzseitenband erkannten Signale an einen Resonanzdetektor (13) angelegt werden, der auf den Erkennungsschwellenwert eingestellt ist, wobei der Resonanzdetektor (13) diese Signale zuläßt und/oder ein anderes vorbestimmtes Signal erzeugt, wenn die Amplitude dieser Signale den Schwellenpegel übersteigt.
  11. Erkennungssystem nach einem der Ansprüche 7-10, dadurch gekennzeichnet, daß die Empfängereinheit (8, 9) zwei Einzel-Seitenbanddemodulatoren (16-23) aufweist, durch die gleichzeitig Signale des Markierungsfrequenzseitenbandes und, separat von diesen, Signale des störenden Frequenzseitenbandes empfangen werden können.
  12. Erkennungssystem nach Anspruch 11, dadurch gekennzeichnet, daß die Sendereinheit (1) nacheinander ein Abfragefeld (H1(t)) mit ansteigender Frequenz und ein Abfragefeld (H1(t)) mit abfallender Frequenz erzeugt, und daß die Erkennungseinheit (8-13) ferner einen ersten Verarbeitungskanal (11) zum Verarbeiten von Signalen des Markierungsfrequenzseitenbandes, einen zweiten Verarbeitungskanal (12) zum Verarbeiten von Signalen des störenden Frequenzseitenbandes und eine Schalteinheit (10) aufweist, über die die Ausgangssignale der beiden Einzel-Seitenbanddemodulatoren (16-23) an den ersten und den zweiten Verarbeitungskanal (11, 12) angelegt werden, wobei die Schalteinheit (10) im Falle eines in der Frequenz ansteigenden Abfragefeldes eine erste Position einnimmt, so daß über einen ersten Einzel-Seitenbanddemodulator (16, 18, 21, 22) aus dem Markierungsfrequenzseitenband erhaltene Signale an den ersten Verarbeitungskanal (11) angelegt werden und über einen zweiten Einzel-Seitenbanddemodulator (17, 18, 20, 23) aus dem störenden Frequenzseitenband erhaltene Signale an den zweiten Verarbeitungskanal (12) angelegt werden, und die Schalteinheit (10) im Falle eines in der Frequenz abfallenden Abfragefeldes eine zweite Position einnimmt, so daß über einen zweiten Einzel-Seitenbanddemodulator (17, 18, 20, 23) erhaltene Signale an den ersten Verarbeitungskanal (11) angelegt werden und über einen ersten Einzel-Seitenbanddemodulator (16, 18, 21, 22) erhaltene Signale an den zweiten Verarbeitungskanal (12) angelegt werden.
  13. Erkennungssystem nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die Empfängereinheit einen Einzel-Seitenbanddemodulator vom Phasentyp (16-21) oder einen ein Mehrphasen-Netzwerk verwendenden Einzel-Seitenbanddemodulator (22, 23) aufweist.
  14. Erkennungssystem nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die Erkennungseinheit (8-13) einen digitalen Signalprozessor (DSP) aufweist.
  15. Erkennungssystem nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß das Erkennungssystem als Ladendiebstahlerkennungssystem ausgebildet ist.
  16. Erkennungssystem nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß eine Markierung (3) mehrere separate, kombinierte oder harmonische Resonanzfrequenzen aufweist, die von dem Erkennungssystem erkannt werden können und in Kombination einen Kode bilden, auf dessen Basis eine Markierung oder eine Gruppe von Markierungen identifiziert werden kann.
  17. Erkennungssystem nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß eine elektromagnetische Resonanzschaltung einer Markierung wenigstens eine LC-Schaltung (L2C2) aufweist.
  18. Erkennungssystem nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß eine elektromagnetische Resonanzschaltung einer Markierung eine Einrichtung zum Erzeugen mechanischer Resonanz aufweist, wodurch eine mechanische Bewegung über den Magnetostriktionseffekt mit dem Abfragefeld gekoppelt wird.
  19. Erkennungssystem nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß eine elektromagnetische Resonanzschaltung einer Markierung eine Einrichtung zum Erzeugen einer Elektronenspin-Resonanz aufweist.
  20. Erkennungssystem nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß das Erkennungssystem als Absorptions- oder Transmissionserkennungssystem ausgebildet ist.
  21. Verfahren zum Erkennen oder Identifizieren einer Markierung (3) mit wenigstens einer Resonanzschaltung (L2C2), wobei nach dem Verfahren ein frequenzgewobbeltes Abfragefeld (H1(t)) erzeugt wird und bei dem durch eine in dem Abfragefeld (H1(t)) befindliche Markierung (3) erzeugte Resonanzen erkannt werden, dadurch gekennzeichnet, daß die Erkennung innerhalb nur eines Markierungsfrequenzseitenbandes der momentanen Frequenz des Abfragefeldes durchgeführt wird, so daß das Erkennungsergebnis auf der Reaktion des Markierungsseitenbandes basiert, das der Frequenz (fc) des Abfragefeldes (H1(t)) unmittelbar vor der aktuellen Frequenz des Frequenzhubs entspricht.
  22. Verfahren nach Anspruch 21, dadurch gekennzeichnet, daß, je nach Frequenzhub, ein oberes (USB) oder ein unteres Seitenband (LSB) des Abfragefeldes (H1(t)) als das Markierungsfrequenzseitenband ausgewählt wird.
  23. Verfahren nach Anspruch 21 oder 22, dadurch gekennzeichnet, daß eine mittlere Frequenz des Markierungsfrequenzseitenbandes zum Zeitpunkt eines Frequenzhubs derart gewählt wird, daß sie der Frequenz des Abfragefeldes zu einem vorherigen Zeitpunkt des Frequenzhubs entspricht.
  24. Verfahren nach einem der vorhergehenden Ansprüche 21-23, dadurch gekennzeichnet, daß die Erkennung in einem oberen Seitenband (USB) der momentanen Frequenz (fc) des Abfragefelds (H1(t)) in einem Zeitraum durchgeführt wird, in dem die Frequenz (fc) des Abfragefelds (H1(t)) pro Zeiteinheit abnimmt, und/oder daß die Erkennung in einem unteren Seitenband (LSB) der momentanen Frequenz (fc) des Abfragefelds (H1(t)) in einem Zeitraum erfolgt, in dem die Frequenz des Abfragefelds (H1(t)) pro Zeiteinheit zunimmt.
  25. Verfahren nach einem der vorhergehenden Ansprüche 21-24, dadurch gekennzeichnet, daß Komponenten von Rausch- und Interferenzsignalen in einem störenden Frequenzseitenband der Frequenz des Abfragefeldes (H1(t)) erkannt werden, wobei das Markierungsfrequenzseitenband und das störende Frequenzseitenband auf entgegengesetzten Seiten der momentanen Frequenz (fc) des Abfragefelds (H1(t)) gewählt werden und Signale von diesen Seitenbändern getrennt voneinander erkannt werden.
EP19940200205 1993-01-28 1994-01-28 Verfahren und System zur Detektierung von Resonanzeffekten eines Etiketts in einem gewobbelten Abfragefeld mittels Einseitenbanddemodulation Expired - Lifetime EP0608961B1 (de)

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NL9300180 1993-01-28
NL9300180A NL9300180A (nl) 1993-01-28 1993-01-28 Detectie van resonantie door middel van enkelzijbanddemodulatie.

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NL9300180A (nl) 1994-08-16
DE69412872T2 (de) 1999-05-12

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