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EP1856669A1 - Procede et dispositif pour mesurer des proprietes magnetiques d'un document - Google Patents

Procede et dispositif pour mesurer des proprietes magnetiques d'un document

Info

Publication number
EP1856669A1
EP1856669A1 EP06707245A EP06707245A EP1856669A1 EP 1856669 A1 EP1856669 A1 EP 1856669A1 EP 06707245 A EP06707245 A EP 06707245A EP 06707245 A EP06707245 A EP 06707245A EP 1856669 A1 EP1856669 A1 EP 1856669A1
Authority
EP
European Patent Office
Prior art keywords
measuring
signal
field
measuring element
alternating
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.)
Withdrawn
Application number
EP06707245A
Other languages
German (de)
English (en)
Inventor
Klaus Thierauf
Helmut Pradel
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.)
Giesecke and Devrient GmbH
Original Assignee
Giesecke and Devrient GmbH
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 Giesecke and Devrient GmbH filed Critical Giesecke and Devrient GmbH
Publication of EP1856669A1 publication Critical patent/EP1856669A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G07—CHECKING-DEVICES
    • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
    • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
    • G07D7/04—Testing magnetic properties of the materials thereof, e.g. by detection of magnetic imprint

Definitions

  • the present invention relates to a method and a device for measuring magnetic properties of documents, in particular banknotes, as well as a suitable measuring head for measuring magnetic field changes.
  • DE 40 22 739 A1 describes a device with a magnetic circuit consisting of soft and permanent magnetic material, wherein the static magnetic field generated by the permanent magnetic material passes through the magnetic circuit.
  • the magnetic circuit generates a stray field which undergoes changes when a sample with magnetic particles is moved into the stray field region.
  • These changes are detected by means of a coil by inducing a voltage due to the changes in the coil.
  • DE 39 31 828 A1 describes a method and an apparatus for reading a bar code, which consists of a plurality of juxtaposed strips of ferromagnetic material. Above the bar code, a high-frequency electromagnetic alternating field is generated so that a change of the electromagnetic alternating field is caused by the ferromagnetic strip.
  • sensor coils which induce a changing electrical voltage according to the changes, is an inductive detection of the
  • the measured signal is additionally supplied to a synchronous demodulator and a low-pass filter.
  • the measured signal is multiplied in the synchronous demodulator with a reference signal of the same frequency and possibly the same phase.
  • high-frequency components are filtered out in the low-pass filter in order to obtain a corrected signal which essentially contains only the measured changes.
  • This type of signal processing is sometimes referred to as a lock-in principle.
  • a disadvantage of the aforementioned inductive method is that small changes in the electromagnetic alternating field, for example, when only a very low concentration of ferromagnetic material is provided in the strip or the exciting magnetic field is weak, are very difficult or not recognizable.
  • the reason for this is above all that interference fields are frequently present in the measurement environment, which superimpose the measurement in such a way that an additional slight change in the electromagnetic alternating field due to a document to be measured can no longer be reliably detected by conventional means.
  • the object of the invention is now to provide a solution to be able to classify documents with small amounts of magnetic particles reliably.
  • a document to be tested in which magnetic particles are contained, is introduced into an electromagnetic alternating field, wherein for measuring the change of the alternating field, a measuring element is used, which converts an electrical input signal of the measuring element into an electrical output signal depending on the voltage applied to the measuring element alternating electromagnetic field.
  • the measurement with such a measuring element has the advantage that it is time-independent, since the change in the electrical resistance in a given test document only and directly depends on the strength of the applied magnetic field.
  • purely inductive methods are (also) time-dependent, since a voltage is only induced in the coil when the magnetic flux passing through the coil is subject to a temporal or spatial change. The invention therefore enables a static measurement or a slow document feed, making the measurement more accurate.
  • a measuring element is used in which the electrical resistance of the measuring element changes as a function of the changes in the electromagnetic alternating field.
  • the measuring element can be supplied, for example, with a current, so that an alternating voltage drops across the measuring element. Now changes due to the change of the measuring element
  • the electrical resistance of the measuring element also changes the amplitude of the applied AC voltage. This detected amplitude change can then be further processed accordingly.
  • a magnetoresistive element is used as the measuring element.
  • This is preferably a Giant Magneto Resistance (GMR) element.
  • GMR Giant Magneto Resistance
  • the GMR element is capable of converting magnetically encoded information into an electrical signal by adjusting the amplitude of the Output signal of the GMR element changes depending on the resistance value of the GMR element.
  • a particular advantage of such a measuring element is that even small changes in the alternating electromagnetic field can be detected, since GMR elements have the property of changing their electrical resistance comparatively strongly even with small magnetic field changes. As a result, GMR elements have an increased sensitivity compared to other measuring elements or sensors.
  • the device according to the invention can be used variably and affects adjacent systems only slightly, since the GMR sensor can operate due to its high sensitivity even with correspondingly low field strengths.
  • the signal generator generates a high-frequency signal
  • another advantage of the GMR element can be used.
  • the disturbing 1 / f noise of the GMR element occurs in a GMR element only in the low-frequency range and disappears above a certain frequency, leaving only a lower, white noise remains. In this way you achieve a much higher signal to noise ratio.
  • High frequency in this context means a frequency of more than 1 kHz, preferably more than 10 kHz.
  • GMR Device can be detected at a reference frequency of 7 kHz. Due to the properties of the GMR element, an improvement of the measurement results is to be expected with a reference frequency between 10 kHz and 50 kHz.
  • the construction of GMR elements and their Functioning is described in detail, for example, in EP 0 793 808 Bl.
  • the output signal of the measuring element is processed by means of a lock-in amplifier.
  • a GMR element is used as the measuring element, even very small changes in the electromagnetic alternating field can be detected by the GMR element. Since these changes result in comparatively small changes in the output signal of the GMR element, the output signal in the lock-in amplifier can be amplified for further processing.
  • the GMR signal after it has possibly been amplified before multiplied in a synchronous demodulator with a normalized reference signal of the same frequency.
  • the signal generator with which the electrical input signal for the GMR element is generated also serves to generate the reference signal.
  • phase-locked loop PLL
  • the output signal of the synchronous demodulator passes through a low pass.
  • the low pass with a certain cutoff frequency removes the interfering high frequency components.
  • the result is a corrected signal which is proportional to the amplitude of the GMR output signal. Since the electrical output signal of the measuring element is multiplied by a system-immanent reference signal of the same frequency and phase, the reference signal preferably being the input signal for the measuring element, even small changes of the alternating electromagnetic field which can be detected and detected by the measuring element can be performed with high accuracy are processed. Additional evaluation electronics can be used to evaluate the measurements accordingly.
  • the measured signal processed by the lock-in amplifier must be compared and evaluated with a predetermined signal and / or other measured signals. This comparison and the evaluation are then carried out in the transmitter, the transmitter can already include, for example, the lock-in amplifier.
  • the device according to the invention can be used particularly advantageously for measuring or detecting soft magnetic particles in documents.
  • the soft magnetic particles are constantly being magnetized by the alternating electromagnetic field.
  • the particles concentrate the magnetic field lines, thereby amplifying the magnetic field.
  • An advantage of soft magnetic materials is that they are easily magnetizable and therefore can also amplify weak magnetic fields.
  • soft magnetic materials change the alternating electromagnetic field only slightly, thus providing only a weak signal to be measured. Therefore, they are not always reliably detectable with conventional measuring devices.
  • the alternating electromagnetic field is generated by high-frequency bursts of a burst generator.
  • a burst excitation is the intermittent / burst transmission of a signal.
  • the burst excitation allows a particularly high current load of the field-generating coil due to the lower average power dissipation.
  • the average power dissipation is lower in the burst, as there is no power dissipation in the burst breaks.
  • the electrical output variable of the measuring element that is, in the case of a GMR element whose electrical resistance, correspondingly more strongly changed, whereby the measurement of the magnetic properties of the document is more accurate.
  • Hard magnetic materials have a much "wider" hysteresis loop than soft magnetic materials. That is, hard magnetic materials have a higher remanence, which, compared to soft magnetic materials, requires a much higher coercive force to make this remanence disappear. Consequently, hard magnetic materials in the absence of an external magnetic field, ie in the absence of energization of the exciter coil, a higher remanence, which is noticeable in the measurement with the measuring element by a larger change in the electrical resistance of the measuring element. Due to these different properties of the hard and soft magnetic materials can be determined by comparison of different measurements, which type of Material is.
  • the particles may be biased in a biasing path. Then measurements can be taken at times when the coil does not generate an alternating electromagnetic field. Burst excitation is particularly preferably used as the excitation for the excitation coil, since in the pulse pauses between the repeating pulse packets in which the excitation coil carries no current, the materials to be measured are premagnetized and can be measured.
  • the integration of the coil and the GMR element on a printed circuit board is inexpensive and is therefore advantageous over known measuring heads.
  • a suitable for evaluating changes in the magnetic evaluation electronics can be cost-effectively arranged on the circuit board. This evaluation electronics can include the lock-in amplifier.
  • the printed circuit board is preferably arranged between two elements, for example of ferrite material, which concentrate the flux of the magnetic field generated by the at least one exciter coil. Furthermore, the arrangement of the excitation coil on the circuit board is inexpensively designed as a multilayer printed coil.
  • Another advantage of the measuring head according to the invention is the space-saving design. This makes it possible, for example, a plurality of measuring heads in the device according to the invention described above can be arranged next to one another in order to be able to carry out the measurements over the entire width of a document to be examined along a multiplicity of measuring tracks simultaneously.
  • magnetoresistive elements can be used instead of GMR elements so-called “spin-dependent tunneling” (SDT) elements .
  • SDT spin-dependent tunneling
  • FIG. 1 shows a measuring head
  • FIG. 3 shows a preferred embodiment of a measuring head in FIG.
  • FIG. 1 shows a measuring head 1 for use in a device according to the invention.
  • a coil 3 is arranged in each case. If the coils 3 are supplied with power, they generate a magnetic field. In this case, an alternating current is used so that an electromagnetic alternating field is formed on the measuring head 1.
  • the coil cores 2 are interconnected only at one end, so that an air gap 4 is formed between the free ends of the coil cores 2. In the process, a stray magnetic field is formed at the free ends of the coil cores 2.
  • a document 5 with soft magnetic particles for example a banknote whose color of a print image is provided with soft magnetic particles, is moved past the air gap 4 of the device according to the invention such that the stray field of the alternating electromagnetic field acts on the soft magnetic particles.
  • the soft magnetic particles in Document 5 increase the flux density in the stray field region.
  • the measuring element 6 is provided, which detects a corresponding change of the electromagnetic alternating field.
  • the measuring element 6 may be, for example, a GMR element, which changes its electrical properties when a magnetic field is applied.
  • At the GMR element is a signal whose amplitude changes according to the change of the magnetic field.
  • the further processing of the amplitude-modulated GMR output signal is described below with reference to FIG.
  • the GMR element is preferably arranged such that the magnetic field, which is generated for example by burst excitation of the two coils 3, is arranged perpendicular to the sensitive axis of the GMR element. This avoids overriding the GMR element.
  • the GMR element is insensitive to magnetic fields perpendicular to its main axis of sensitivity.
  • a "spin-dependent tunneling" (SDT) element can be used due to the higher measurement sensitivity.
  • the magnetic field must be correspondingly strongly dimensioned because of the large air gap.
  • an exciting burst of high current can be conducted through the coils. But it is also possible to arrange several small measuring heads next to each other.
  • FIG. 2 shows schematically an embodiment of the device according to the invention.
  • a lock-in amplifier 7 with at least some of its elements is shown.
  • the output signal of the GMR element is first pre-amplified in the illustrated embodiment of the lock-in amplifier 7 by means of an amplifier 8. Subsequently, the preamplified signal is fed to a synchronous demodulator 9 whose operation has already been described above.
  • the synchronous demodulator 9 is also supplied with a reference signal which must be equal in frequency to the preamplified signal, so that the lock-in amplifier 7 provides the desired result.
  • This reference signal is generated in a reference generator 10 and also serves in the illustrated embodiment for the electrical supply of the measuring head 1, in particular of the GMR element 6 with an input signal and the two coils 3 with an exciter signal.
  • the reference signal may be an AC signal. Due to the changes of the electromagnetic Alternating elds, which change the electrical resistance of the GMR element 6, the amplitude of the voltage drop across the GMR element 6 changes. This alternating voltage signal with changing amplitude is provided as an output signal of the GMR element to the lock-in amplifier 7. After the preamplified GMR output signal has been multiplied by the same frequency reference signal in the synchronous demodulator 9, a low pass filter 11 filters out high frequency noise components of the signal so that a signal proportional to the signal amplitude of the GMR output signal is obtained.
  • FIG. 3 shows an embodiment of a preferred measuring head 12 in cross-section.
  • a printed circuit board 13 multi-layer printed coils 14 for generating an alternating electromagnetic field and a Giant MagnetoResistance element 6 for measuring changes in the alternating field are arranged.
  • the circuit board 13 itself is between two
  • Elements 15 are arranged, which concentrate the flow of the magnetic field generated by the coils in the plane of the GMR element 6. These two elements 15 consist for example of a ferrite material, which is also suitable for use in conventional coil cores. As shown in FIG. 3, the document is moved transversely to the vertically arranged measuring head 12.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)

Abstract

L'invention concerne un procédé et un dispositif permettant de mesurer les propriétés magnétiques d'un document (5), ainsi qu'une tête de mesure (12) destinée à mesurer les modifications du champ magnétique. Le dispositif comprend un ensemble (2, 3) destiné à produire un champ alternatif électromagnétique, un élément de mesure (6) et un amplificateur (7) enclenché. L'élément de mesure (6) est conçu de façon à ce qu'un signal d'entrée électrique de l'élément de mesure (6) se transforme en un signal de sortie électrique, en fonction des modifications dans le champ électrique, lorsque le document (5) apporte des propriétés magnétiques dans le champ magnétique. De préférence, un élément GMR ou SDT est utilisé en tant qu'élément de mesure (6), lequel modifie fortement, de préférence, sa résistance électrique, lors de transformations faibles du champ alternatif électromagnétique. La tête de mesure (12) utilisée dans le dispositif comprend une plaque conductrice (13) dotée de bobines (14) et d'un élément (6) GDT ou SDT.
EP06707245A 2005-02-28 2006-02-24 Procede et dispositif pour mesurer des proprietes magnetiques d'un document Withdrawn EP1856669A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102005008967A DE102005008967A1 (de) 2005-02-28 2005-02-28 Verfahren und Vorrichtung zum Messen magnetischer Eigenschaften von Dokumenten
PCT/EP2006/001702 WO2006092240A1 (fr) 2005-02-28 2006-02-24 Procede et dispositif pour mesurer des proprietes magnetiques d'un document

Publications (1)

Publication Number Publication Date
EP1856669A1 true EP1856669A1 (fr) 2007-11-21

Family

ID=36227508

Family Applications (1)

Application Number Title Priority Date Filing Date
EP06707245A Withdrawn EP1856669A1 (fr) 2005-02-28 2006-02-24 Procede et dispositif pour mesurer des proprietes magnetiques d'un document

Country Status (4)

Country Link
US (1) US20080143328A1 (fr)
EP (1) EP1856669A1 (fr)
DE (1) DE102005008967A1 (fr)
WO (1) WO2006092240A1 (fr)

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2577621A1 (fr) * 2010-06-03 2013-04-10 Spectra Systems Corporation Détection de condition et d'usure de devise à l'aide de détection infrarouge modulée en température
US9678175B2 (en) * 2010-07-26 2017-06-13 Radiation Monitoring Devices, Inc. Eddy current detection
DE102011110138A1 (de) * 2011-08-15 2013-02-21 Meas Deutschland Gmbh Messvorrichtung zum Messen magnetischer Eigenschaften der Umgebung der Messvorrichtung
JP6548868B2 (ja) 2014-03-13 2019-07-24 株式会社東芝 磁気検査装置、および紙葉類処理装置
PL2930651T3 (pl) * 2014-04-11 2017-02-28 Magcam Nv Sposób i urządzenie do mierzenia rozkładu pola magnetycznego magnesu wzdłuż głównej powierzchni wspomnianego magnesu
DE102016015559A1 (de) * 2016-12-27 2018-06-28 Giesecke+Devrient Currency Technology Gmbh Verfahren und Vorrichtung zum Detektieren eines Sicherheitsfadens in einem Wertdokument
US20230210425A1 (en) * 2022-01-05 2023-07-06 Tdk Corporation Methods and Devices for Electromagnetic Measurements from Ear Cavity

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998038792A1 (fr) * 1997-02-28 1998-09-03 University And Community College System Of Nevada Systeme magnetoresistif a balayage

Family Cites Families (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3931828A1 (de) * 1989-09-23 1991-04-04 Krieg Gunther Streifencode sowie verfahren und vorrichtung zum lesen eines solchen
AT398497B (de) * 1990-01-23 1994-12-27 Groessinger R Dr Codiersystem und codeträger
DE4022739A1 (de) * 1990-07-17 1992-01-23 Gao Ges Automation Org Vorrichtung zur pruefung von mit magnetischen eigenschaften ausgestatteten messobjekten
US5545885A (en) * 1992-06-01 1996-08-13 Eastman Kodak Company Method and apparatus for detecting and identifying coded magnetic patterns on genuine articles such as bank notes
US5418458A (en) * 1993-08-31 1995-05-23 Eastman Kodak Company Apparatus and method for authentication of documents printed with magnetic ink
DE4339417A1 (de) * 1993-11-18 1995-05-24 Optima Buerotechnik Gmbh Banknoten - Prüfgerät
DE19501245A1 (de) * 1995-01-17 1996-07-18 Giesecke & Devrient Gmbh Vorrichtung zur Prüfung magnetischer Eigenschaften von Blattgut, wie z. B. Banknoten oder Wertpapiere
US6363164B1 (en) * 1996-05-13 2002-03-26 Cummins-Allison Corp. Automated document processing system using full image scanning
US6822443B1 (en) * 2000-09-11 2004-11-23 Albany Instruments, Inc. Sensors and probes for mapping electromagnetic fields
US6150809A (en) * 1996-09-20 2000-11-21 Tpl, Inc. Giant magnetorestive sensors and sensor arrays for detection and imaging of anomalies in conductive materials
EP0951702B1 (fr) * 1996-12-12 2008-06-11 N.V. Bekaert S.A. Reconnaissance et verification d'un article
WO1999008263A1 (fr) * 1997-08-12 1999-02-18 Itron, Inc. Appareil et procede de traitement de flux magnetique
WO2001036904A1 (fr) * 1999-11-18 2001-05-25 Fujitsu Limited Pachymetre
DE10145657C1 (de) * 2001-03-10 2002-10-10 Automation Hans Nix Gmbh & Co Verfahren zur Eliminierung von Fehlereinflüssen bei dem Einsatz von Magnetfeld-Sensoren zur Schichtdickenmessung
US6911826B2 (en) * 2001-06-12 2005-06-28 General Electric Company Pulsed eddy current sensor probes and inspection methods
US7034523B2 (en) * 2001-09-27 2006-04-25 Marquardt Gmbh Device for measuring paths and/or positions
WO2003054825A2 (fr) * 2001-12-10 2003-07-03 Innovision Research & Technology Plc Composants detectables et appareil de detection concu pour detecter de tels composants

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998038792A1 (fr) * 1997-02-28 1998-09-03 University And Community College System Of Nevada Systeme magnetoresistif a balayage

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of WO2006092240A1 *

Also Published As

Publication number Publication date
US20080143328A1 (en) 2008-06-19
WO2006092240A1 (fr) 2006-09-08
DE102005008967A1 (de) 2006-08-31

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