Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
  • G01V15/00—Tags attached to, or associated with, an object, in order to enable detection of the object
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
  • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
  • G01V3/02—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with propagation of electric current
  • G01V3/06—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with propagation of electric current using ac

Definitions

• TITLE AN ARTICLE IDENTIFICATION TAG, AND A
• the present invention relates to article identification tags and the detection thereof . More particularly, the invention relates to article identification tags having a plurality of electrically conductive members. The invention also relates to a method of detecting such an article identification tag.
• a simple electronic article surveillance system which is arranged to provide an alarm signal, once a protected article is carried into a detection zone.
• a tag having one single sensor element in the form of a thin metal strip or wire with magnetic properties.
• the sensor element may be detected magnetically by means of arc-shaped magnetic generators/detectors, which expose the sensor element to an alternating magnetic field, that affects a physical property of the sensor element.
• each tag comprises a wire-shaped element of amorphous or nano- crystalline metal alloy.
• An important feature of the amorphous or nano-crystalline metal alloy is that the permeability thereof may be controlled by an alternating magnetic modulating field.
• the amplitude of an electromagnetic reply signal from the tag is modulated by the magnetic modulating field, when the tag is excited by an electromagnetic interrogation signal.
• the modulation in amplitude of the reply signal is detected and used for determining the presence of the tag in the detection zone.
• 098/36393 A similar application is shown in 098/36393, where very thin amorphous or nano-crystalline wires are used as sensor elements. These wires (also known as microwires) have a diameter of less than 30 ⁇ m, preferably 5-15 ⁇ m.
• Optical article identification systems have a distinct drawback, however, in that the operating distance thereof is quite restricted; the barcode tag will have to pass in close proximity with the optical reader for allowing a successful reading of the barcode. Furthermore, since the barcode is read by optical means, the tag must be attached to a visible surface portion of the article in question.
• a non-optical system with longer operating range is disclosed in WO88/01427, wherein the tag or marker is provided with a number of sensor elements in the form of magnetostrictive strips or ribbons made of an amorphous ferromagnetic material and arranged in predetermined angular relationships or at predetermined distances from each other.
• the identity of such a tag is represented by the predetermined relationships as well as the respective type of individual sensor elements.
• the sensor elements are excitable to mechanical resonance by magnetic energy.
• the magnetic signals generated by the resonating sensor elements may be detected magnetically or inductively.
• the tag of O88/01427 provides a significantly more limited codespan.
• prior art tags for remote non-optical detection of objects are either of a single-element type, allowing only the presence of each tag to be detected, or of a multi-element type, allowing also an identity of each tag to be detected.
• Single-element tags are easier to design and produce and therefore have a lower unit cost.
• multi -element tags require a supporting carrier (particularly for mechanically resonating sensor elements) and/or capacitive and inductive components (for the electric resonant circuit versions) . Naturally, this implies a higher cost per unit.
• the codespan (number of different code values) of the multi-element tags described above is clearly inferior in comparison with optical barcode tags.
• the multielement tags mainly operate by magnetic or inductive link, the operating distance of the detection system is quite narrow (although better than for optical barcode systems) .
• an object of the present invention is to provide an article identification tag at a considerably lower cost than previously known tags. More specifically, the invention aims at providing a tag, which combines the good characteristics of optical barcode tags (large code span) and non-optical multi-element tags (long operating distance) at a very low price per tag.
• FIG 1 illustrates an article identification system, in which the method and the tag according to the present invention may be applied
• FIGs 2 and 3 are diagrams illustrating the physical basis behind the method according to the present invention.
• FIGs 4-7 are schematic illustrations of different exemplifying embodiments of a tag according to the invention.
• FIG 1 illustrates an article identification system for detecting a tag 30 attached to an object 20, and for determining an identity thereof .
• a system similar to the one illustrated in FIG 1 is thoroughly disclosed in WO 97/29463, WO 97/29464 and WO 98/36393, all of which are fully incorporated herein by reference.
• a transmitter antenna 11 and a receiver antenna 12 are arranged in a detection zone 10.
• the transmitter antenna 11 is operatively connected to an output stage 13, which in turn is connected to a controller 14.
• the output stage comprises various commercially available driving and amplifying circuits and means for generating an alternating electric current of high frequency f HF , said current flowing back and forth through the transmitter antenna 11 when supplied thereto, wherein a high-frequency electromagnetic field is generated around the transmitter antenna.
• This electromagnetic field is used, as will be described in more detail below, for exciting the tag 30 within the detection zone 10, so that the tag will transmit, at the reception of a first electromagnetic signal 50 from the transmitter antenna 11, a second electromagnetic signal 60, which is received by the receiver antenna 12 and transformed into a corresponding electric signal 70.
• the receiver antenna 12 is operatively connected to an input stage 15, which comprises conventional means with amplifying and signal processing functions, such as bandpass filtering and amplifying circuits.
• the input stage 15 also comprises means for demodulating the received signal 70 and supplying it, as a reply signal 80, to the controller 14.
• the transmitter antenna 11 as well as the receiver antenna 12 thus have the purpose of converting, in a known way, between an electrical signal of high frequency and an electromagnetic signal.
• the antennas are helically formed antennas with rotating polarization (for optimal coverage in all directions) , or alternatively conventional end-fed or center-fed halfwave whip antennas, but other known antenna types are equally possible.
• the detection zone 10 may optionally be provided with means 16, such as a coil, for generating a magnetic modulating field H mod .
• the means 16 is connected to the controller 14 via a driving stage 17.
• the driving stage 17 comprises means for generating a modulating current, which is supplied to the means 16, wherein the magnetic modulating field H mod is generated in essential portions of the detection zone 10.
• the magnetic modulating field H mod may have a frequency of about 500-800 Hz, and the electromagnetic excitation and reply signals may have a frequency within the GHz band, such as 1.3 GHz or 2.45 GHz. Frequencies outside these ranges are however also possible.
• the object 20 which has been schematically illustrated in FIG 1 in the form of a box- shaped package, is provided with the tag 30 according to the invention, comprising a number of electrically conductive members 31-3n (FIG 4) , which provide an identity of the tag 30, or of the object 20 to which the tag is attached, as will be described in more detail below.
• the members 31-3n are electromagnetically detectable.
• the members 31-3n may comprise a magnetic material, the permeability of which is controllable by a magnetic field and the high- frequency impedance of which depends on said permeability, according to an effect commonly known as Gigant Magneto- Impedance. This effect causes a modulation in amplitude of the second electromagnetic signal 60 transmitted from the tag 30 and received by the receiver antenna 12 as the signal 70.
• the amplitude is modulated by the magnetic modulating field H mod .
• the detection method according to the present invention will now be described with reference to FIGs 2 and 3.
• the method according to the invention is based on novel use of a skin-depth phenomenon known per se, which occurs for high-frequency electrical signals in electrical conductors.
• Skin-depth is a common name for the fact that the conduction of electrical current will only take place in an outer layer or skin layer of the conductor at high frequencies.
• the penetration depth is related to the signal frequency as well as the electrical resistivity and magnetic permeability of the conductor.
• the effective conductor impedance R eff will vary with the signal frequency, provided that the signal frequency is not reduced to an extent, where the skin-depth d reaches and equals the radius R of the electrically conductive member 1.
• FIG 3 illustrates the effective impedance R eff of the electrically conductive member 1 when exposed to an electromagnetic high-frequency (HF) signal, such as the excitation signal 50 submitted by the transmitter 11 of FIG 1.
• HF electromagnetic high-frequency
• an alternating electric current is caused to flow through the member 1, for instance by exciting the member 1 by means of a high-frequency electromagnetic field, such as the excitation signal 50 of the system shown in FIG 1.
• the frequency of the alternating electric current is varied, and a corresponding variation in impedance is monitored for the member 1.
• This correspondingly varying impedance may for instance be monitored via the reply signal 60 received by the receiver antenna 12 in FIG 1. Then, a discontinuity is detected in the varying impedance, and the frequency at which this discontinuity appears is detected.
• this frequency (at which the discontinuity appears) will also be predetermined and may be used for providing the member 1 with an identity, since the skin- depth thereof depends on all these parameters .
• FIG 4 illustrates a first embodiment of a tag 30 according to the invention.
• the tag 30 comprises n electrically conductive members 31, 32, 33...3n, having respective predetermined diameters ⁇ i- ⁇ n , respective predetermined electrical resistivities Pi-p n or respective predetermined magnetic permeabilities ⁇ rl - ⁇ rn . Combinations of these parameters are also possible.
• each electrically conductive member 31-3n of the tag 30 will have one of the above predetermined properties, and consequently the frequency at which the discontinuity appears in the reply signal from the tag 30 will also be well-defined.
• the tag 30 of FIG 4 is particularly well adapted for use in an electromagnetic article surveillance system, such as the one illustrated in FIG 1.
• FIG 5 illustrates a second embodiment of a tag 34, having a plurality of interconnected sections with different respective diameters ⁇ - L , ⁇ 2 , ⁇ 3 and ⁇ 4 .
• FIGs 6 and 7 illustrate further embodiments of a tag 35, 36, respectively, according to the invention.
• the tag 35 comprises five interconnected members having different respective predetermined diameters, electrical resistivities and/or magnetic permeabilities.
• the tag 36 comprises nine different interconnected electrically conductive members.
• a simpler tag comprising only one electrically conductive member, may also be used according to the invention.
• a tag may be used consisting of e.g. a copper wire wound in a single-turn loop.
• an FM-modulating inductive excitation signal having a frequency deviation, which sweeps past the tag discontinuity frequency
• an AM- modulated tag signal will be received in the pick-up coils of the pedestals. This AM modulation results from the change in impedance of the copper wire loop, as its skin- depth changes with the excitation frequency. Starting at the maximum frequency, the AM signal will increase in amplitude, as the frequency decreases and the skin-depth increases.
• the loop impedance will abruptly cease to decrease, and a plateau (or flat region) will appear in the received AM signal.
• a plateau or flat region
• the clipping region represents the frequency interval, during which the skin- depth exceeds the radius of the conductor.
• Different electronic or digital signal processing techniques may be utilized to precisely determine the frequency of the amplitude modulation (voltage drop) discontinuity related to the frequency modulation of the applied alternating signal.
• One such technique involves an amplitude demodulation of the alternating voltage drop signal, followed by subtraction of the FM reference signal in order to detect the discontinuity point.
• the conductor radius detection criterion represents a discontinuity in the measuring signal, which may be easily distinguished from continuously varying features in the measuring signal, resulting from e.g. frequency-related changes in inductance, reflections, capacitive couplings, etc .
• tubular conductors may be used for article identification tags.
• the thickness of the tube wall will define the discontinuity point.
• One advantage of a tubular conductor over a solid conductor is that the total volume of conductive material will be larger for the same skin-depth saturation point, thereby providing larger tag signal levels.
• the multi-member tag embodiments shown in FIGs 4-7 will assist in reducing the risk of false alarms, since the multi-member tag will be provided with an identity thanks to the predetermined respective diameters, resistivities and/or permeabilities.
• Yet another possibility to reduce the risk of false alarms and to add a further information coding parameter is to use non-circular cross-sections e.g. rectangular cross- sections. In such a case, the minimum dimension may be measured by the discontinuity point. For e.g. a rectangular cross-section, the thickness would be measured through the discontinuity point .
• the width may then be measured by using a secondary effect of the skin-depth, namely that for a certain change in skin-depth (related to a certain change in frequency) , the corresponding change in effective impedance will depend on the width.
• the electrically member (s) described for the different embodiments above may be given many different shapes, e.g. in the form of wires, strips or ribbons, and may comprise various different materials, such as non- magnetic metals (e.g. copper or aluminium), magnetic metals (e.g. iron), metal alloys (e.g. steel), or alternatively amorphous metal alloys.

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• Life Sciences & Earth Sciences (AREA)
• Physics & Mathematics (AREA)
• Geophysics (AREA)
• General Physics & Mathematics (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geology (AREA)
• Remote Sensing (AREA)
• Environmental & Geological Engineering (AREA)
• Engineering & Computer Science (AREA)
• Burglar Alarm Systems (AREA)
• Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
• Geophysics And Detection Of Objects (AREA)
• Measurement Of Resistance Or Impedance (AREA)
• Credit Cards Or The Like (AREA)
• Near-Field Transmission Systems (AREA)

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• 1999
  • 1999-01-18 SE SE9900119A patent/SE9900119L/ not_active Application Discontinuation
• 2000
  • 2000-01-18 BR BR0007572-8A patent/BR0007572A/pt not_active IP Right Cessation
  • 2000-01-18 AU AU23380/00A patent/AU2338000A/en not_active Abandoned
  • 2000-01-18 EP EP00902252A patent/EP1149313A1/en not_active Withdrawn
  • 2000-01-18 JP JP2000593969A patent/JP2002535856A/ja active Pending
  • 2000-01-18 CN CN00802899.0A patent/CN1337007A/zh active Pending
  • 2000-01-18 WO PCT/SE2000/000089 patent/WO2000042450A1/en not_active Application Discontinuation

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