HK1189087A - Marker for coded electronic article identification system - Google Patents

Description

Coded electronic article surveillance system tag

The application is a divisional application of the Chinese invention patent application CN200680019383.0 with the application date of 2006, 3, 31 and a label entitled "encoding electronic article surveillance system".

Technical Field

The present invention relates to ferromagnetic amorphous alloy ribbon and a tag for electronic article surveillance systems comprising one or more rectangular strips based on amorphous magnetostrictive material that vibrates in an alternating magnetic field at multiple resonance frequencies, whereby the magnetomechanical effect of the tag can be effectively exploited. The invention also relates to an electronic surveillance system using such a tag.

Background

Magnetostriction of a magnetic material is a phenomenon in which the magnitude changes when an external magnetic field is applied to the magnetic material. If the magnetization changes in size, the result is elongation of the materialIf it is long, the material is said to be "positively magnetostrictive". If the material is "negatively magnetostrictive," the material will contract when magnetized. Thus, in either case, the magnetic material vibrates when exposed to an alternating magnetic field. If a static magnetic field is applied in conjunction with an alternating magnetic field, the frequency of the mechanical vibration of the magnetic material will vary with the applied static field through magnetoelastic coupling, which is commonly referred to as the Δ E effect, e.g., "Physics of Magnetism" by S.Chikazumi (John Wiley)&Sons, New York, page 1964,435). Where E (H) represents the Young's modulus, which is a function of the applied field H, the vibration or resonant frequency f of the material_rBy passing

f_r=(1/2l)[E(H)/ρ]^1/2, (1)

Associated with E (H), where l is the length of the material and ρ is the mass density of the material. The magnetoelastic or magnetomechanical effects described above were used in the electronic article surveillance systems first taught in U.S. patents 4,510,489 and 4,510,490 (hereinafter referred to as patents 489 and 490). Such a monitoring system is a very good system, since it provides simultaneously high detection sensitivity, high operational reliability and low operational costs.

The tags in such systems are one or more strips of ferromagnetic material of known length wrapped with a hard-magnetic ferromagnet (a material with a higher coercivity) that provides a static field called the bias field to establish the peak magnetomechanical coupling. Preferably, the ferromagnetic label material is amorphous alloy ribbon because of the high efficiency of the magnetomechanical coupling in the alloy. As shown in the above formula (1), the mechanical resonance frequency f_rMainly determined by the length of the alloy strip and the strength of the bias field. When an interrogation signal tuned to a resonant frequency is encountered in an electronic identification system, the tag material responds with a large signal field that is detected by a receiver in the system.

U.S. Pat. No.4,510,490 proposes several amorphous ferromagnetic materials for use in an encoded identification system based on the aforementioned magnetomechanical resonance, including amorphous Fe-Ni-Mo-B,Fe-Co-B-Si, Fe-B-Si-C, and Fe-B-Si alloys. Among these alloys, the commercially available amorphous Fe-Ni-Mo-B groupAlloys are widely used until triggered by the chance of a magnetomechanical resonance marker of other systems based on magnetic harmonic generation/detection. This is because the magnetomechanical resonance tag used at that time sometimes exhibits a nonlinear BH characteristic, thereby generating higher harmonics of the excitation field frequency. To avoid this problem (sometimes referred to as the system "contamination problem"), a series of new label materials have been invented, such as those disclosed in U.S. Pat. Nos. 5,495,231,5,539,380,5,628,840,5,650,023,6,093,261 and 6,187,112. While the new label materials perform better on average than the materials used in the monitoring systems of the prior patents 489 and 490, it has been found that the label materials disclosed in, for example, U.S. Pat. No.6,299,702 (hereinafter referred to simply as patent 702) have better magneto-mechanical properties. These new label materials require complex heat treatment processes to achieve the desired magneto-mechanical properties, such as disclosed in patent 702. Clearly, new magnetomechanical label materials are required that do not require such a complex post-ribbon (post-ribbon) manufacturing process, and it is an object of the present invention to provide such label materials with good magnetomechanical properties without creating the "contamination problem" described above. The new magnetomechanical label material of the present invention is fully utilized, and the present invention includes labels with encoding and decoding capabilities and electronic identification systems using the same. Us patent 4,510,490 teaches a coded surveillance system with magneto-mechanical tags but limits the number of strips making up the tag due to the limitations of the space available in the tag, thereby limiting the range of encoding and decoding functions using such tags.

Clearly, there is a need for a tag in which the number of tag strips can be increased substantially without sacrificing the performance of a coded tag in an electronic article identification system having coding and decoding functions (hereinafter referred to as "coded electronic article identification system").

Disclosure of Invention

According to the invention, the tag of the magnetomechanical resonance based electronic article surveillance system comprises a soft magnetic material.

A tag material with overall enhanced magnetomechanical resonance properties is fabricated from amorphous alloy ribbon to place multiple tag strips in a coded tag. A ribbon of soft magnetic material having magnetomechanical resonance capability is cast on a rotating substrate as taught in U.S. patent 4,142,571. If the width of the tape thus cast is wider than the predetermined width of the label material, the tape is cut to the predetermined width. The tape thus processed is cut into ductile rectangular amorphous metal strips having different lengths, and a magnetomechanical resonance tag is fabricated using a plurality of said strips, said strips having at least one semi-hard magnetic strip providing a biased static magnetic field.

Coded electronic article surveillance systems use the coded tags of the present invention. The system has an article interrogation zone in which the magnetomechanical tag of the present invention is subjected to an interrogating magnetic field having a varying frequency, and signals responsive to the interrogation field excitation are detected by a receiver having a pair of antenna coils located in the article interrogation zone.

According to an embodiment of the present invention, there is provided a coded tag for a magnetomechanical resonance electronic article surveillance system adapted to mechanically resonate at a preselected frequency, comprising: a plurality of ductile magnetostrictive strips of predetermined length cut from a ribbon of amorphous ferromagnetic alloy, the strips having a curvature along the length of the ribbon that produces magnetomechanical resonance when excited by an alternating magnetic field having a static bias field, the strips having a magnetic anisotropy direction perpendicular to the ribbon axis, wherein at least two of the strips are adapted to be magnetically biased to resonate at a single different one of the preselected frequencies.

Alternatively, the radius of curvature of the tag is less than 100 cm.

According to an embodiment of the present invention, an amorphous magnetostrictive alloy ribbon having a magnetic anisotropy direction perpendicular to a ribbon axis is cut to form a rectangular strip having a predetermined length with a length-to-width aspect ratio greater than 3 for encoding.

Alternatively, the strip width of the strip is from about 3mm to about 15 mm.

According to an embodiment of the invention, the slope of the resonance frequency of the bars versus the bias field is from about 4Hz/(A/m) to about 14 Hz/(A/m).

Alternatively, when the strip width is 6mm, the length of the strip is greater than about 18 mm.

According to an embodiment of the invention, the bar has a magnetomechanical resonance frequency of less than about 120000 Hz.

According to an embodiment of the invention, the amorphous ferromagnetic alloy ribbon has a saturation magnetostriction between about 8ppm and about 18ppm and a saturation induction between about 0.7tesla and about 1.1 tesla.

According to an embodiment of the invention, the amorphous ferromagnetic alloy of the amorphous ferromagnetic alloy ribbon has a composition based on Fe_a-Ni_b-Mo_c-B_dWherein 30. ltoreq. a.ltoreq.43, 35. ltoreq. b.ltoreq.48, 0. ltoreq. c.ltoreq.5, 14. ltoreq. d.ltoreq.20 and a + B + C + d =100, up to 3atom% of Mo being optionally replaced by Co, Cr, Mn and/or Nb, up to 1atom% of B being optionally replaced by Si and/or C.

According to an embodiment of the invention, the amorphous ferromagnetic alloy of the amorphous ferromagnetic alloy ribbon has one of the following compositions: fe_40.6Ni_40.1Mo_3.7B_15.1Si_0.5,Fe_41.5Ni_38.9Mo_4.1B_15.5,Fe_41.7Ni_39.4Mo_3.1B_15.8,Fe_40.2Ni_39.0Mo_3.6B_16.6Si_0.6,Fe_39.8Ni_39.2Mo_3.1B_17.6C_0.3,Fe_36.9 Ni_41.3Mo_4.1B_17.8,Fe_35.6Ni_42.6Mo_4.0B_17.9,Fe₄₀Ni₃₈Mo₄B₁₈Or Fe_38.0Ni_38.8Mo_3.9B_19.3。

Alternatively, the coded label comprises at least two strips of labels having different lengths.

Alternatively, the coded label comprises 5 strips of different lengths.

Alternatively, the magnetomechanical resonance frequency of the encoded tag is between about 30000 and about 130000 Hz.

Alternatively, the range of electronic identification of coded labels, including coded labels having two and five tag strips, is up to about 1800 and about 115 million individually identifiable items, respectively.

Alternatively, the electronic identification range of the coded label includes over 115 million individually identifiable articles.

According to an embodiment of the invention, the bar has a magnetomechanical resonance frequency of less than about 120000 Hz.

According to an embodiment of the invention, the electronic article surveillance system has a function of decoding the encoded information of the encoded tag, the system comprising one of: a pair of coils that transmit an AC excitation field to form an interrogation zone; a pair of signal detection coils for receiving encoded information from the encoded tag; an electronic signal processing device having an electronic computer with software to decode the encoded information on the encoded tag; or an electronic device identifying a coded tag, wherein the coded tag is adapted to resonate mechanically at a preselected frequency, the coded tag comprising a plurality of ductile magnetostrictive strips cut from an amorphous ferromagnetic alloy ribbon having a predetermined length, the strips having a curvature along the length of the ribbon that produces magnetomechanical resonance upon excitation with an alternating magnetic field having a static bias field, the strips having a direction of magnetic anisotropy perpendicular to the ribbon axis, wherein at least two of the strips are adapted to be magnetically biased to resonate at a single different one of the preselected frequencies.

Alternatively, the radius of curvature of the tag is between about 20cm and about 100 cm.

Drawings

The present invention and its advantages will be more fully understood from the following detailed description of the preferred embodiments and the accompanying drawings in which:

FIG. 1A is a side view of a strip cut from an amorphous alloy ribbon and having bias magnets in accordance with an embodiment of the present invention; FIG. 1B is a view of a conventional bar with bias magnets;

FIG. 2 is a graph of the magnetomechanical resonance characteristics of a single strip marker according to an embodiment of the present invention and the magnetomechanical resonance characteristics of a conventional single strip marker, showing the resonance frequency as a function of a bias field;

FIG. 3 is a resonance signal of a single bar tag according to an embodiment of the present invention and a resonance signal of a conventional bar tag, giving the resonance signal amplitude as a function of the bias field;

fig. 4 is a BH cycle for a strip of tags taken at 60Hz from an embodiment of the present invention where the strip is about 38mm long by about 6mm thick by about 28 μm.

FIG. 5A is a comparison of physical profiles of an embodiment of a magnetomechanical resonance tag according to an embodiment of the present invention, and FIG. 5B is a comparison of a conventional tag using two strips of tags of different lengths;

FIG. 6A is the magnetomechanical resonance characteristic of a tag having two strips of different lengths of an embodiment of the present invention, and FIG. 6B is the magnetomechanical resonance characteristic of a conventional tag having two strips of different lengths;

FIG. 7 is a graph of the resonance signal near the lower resonance frequency of FIG. 6A;

FIG. 8 is a graph of the resonance signal near the higher resonance frequency of FIG. 6A;

FIG. 9 is a label of an embodiment of the present invention in which three strips of different lengths are placed;

FIG. 10 is a magneto-mechanical resonance characteristic of a tag having three bars of different lengths according to an embodiment of the present invention;

FIG. 11 is a graph of the magnetomechanical resonance characteristics of a tag having five strips of different lengths of an embodiment of the present invention.

Detailed Description

Tag materials having overall enhanced magnetomechanical resonance properties are fabricated from amorphous ferromagnetic alloy ribbon for placement of a plurality of tag strips in a coded tag, wherein at least two of the strips are adapted to be magnetically biased to mechanically resonate at a single, different one of a preselected plurality of frequencies. A strip of magnetic material having magnetomechanical resonance capability is cast on a rotating substrate as taught in U.S. patent 4,142,571. If the width of the tape so cast is wider than the predetermined width of the label material, the tape is cut to the predetermined width. The strip thus treated is cut into ductile rectangular amorphous metal strips of different lengths, and a magnetomechanical resonance tag is fabricated using a plurality of strips having at least one semi-hard magnetic strip providing a biased static magnetic field.

In one embodiment of the invention, the amorphous ferromagnetic alloy used to form the ribbon of the tag has a Fe-based composition_a-Ni_b-Mo_c-B_dWherein 30. ltoreq. a.ltoreq.43, 35. ltoreq. b.ltoreq.48, 0. ltoreq. c.ltoreq.5, 14. ltoreq. d.ltoreq.20 and a + B + C + d =100, up to 3atom% of Mo being optionally replaced by Co, Cr, Mn and/or Nb, up to 1atom% of B being optionally replaced by Si and/or C.

In one embodiment of the invention, the amorphous ferromagnetic alloy used to form the ribbon of the tag has a composition of one of: fe_40.6Ni_40.1Mo_3.7B_15.1Si_0.5,Fe_41.5Ni_38.9Mo_4.1B_15.5,Fe_41.7Ni_39.4Mo_3.1B_15.8,Fe_40.2Ni_39.0Mo_3.6B_16.6Si_0.6,Fe_39.8Ni_39.2Mo_3.1B_17.6C_0.3,Fe_36.9Ni_41.3Mo_4.1B_17.8,Fe_35.6Ni_42.6Mo_4.0B_17.9,Fe₄₀Ni₃₈Mo₄B₁₈,or Fe_38.0Ni_38.8Mo_3.9B_19.3。

Thus, the chemical composition is compatible with commercially available amorphous magnetostrictionAmorphous alloy ribbons of similar chemical composition to the ribbons can be cast according to the invention described in U.S. patent 4,142,571. The saturation induction of the as-cast amorphous alloy was about 0.88Tesla and the saturation magnetostriction was about 12 ppm. The width of the strip is about 100mm and about 25mm and the thickness is about 28 μm. The strip is then cut to form narrower strips of different widths. The cut strip was cut into malleable rectangular strips ranging in length from about 15mm to about 65 mm. Each strip has a small curvature which reflects the curvature of the surface of the belt casting wheel. During cutting, the original curvature changes. The curvature of the cut and cut strip can be determined as in example 1. Fig. 1A is the physical appearance of a label strip 10 according to an embodiment of the present invention, and fig. 1B is the physical appearance of a conventional strip 20 manufactured according to the complex heat treatment method disclosed in U.S. patent 6,299,702. The magnetic flux lines 11 in the resonant tag bias strip configuration of the present embodiment are tighter than the magnetic flux lines 21 of the conventional strip of fig. 1B. Thus, better coupling is possible between tag 10 and bias magnet strip 12 of embodiments of the present invention than between conventional strip 20 and bias magnet 22, so that there is less magnetic flux leakage (magnetic flux leakage) across the resonant tag of embodiments of the present invention. The conventional strip and each resonance marker strip of the embodiment of the invention were examined in terms of magnetomechanical resonance performance using the characterizing method of example 2. Fig. 2 compares the resonant frequency of a single bar tag 330 of an embodiment of the present invention as a function of bias field with the resonant frequency of a conventional bar 331. FIG. 2 shows resonance frequency as a function of bias fieldThe change is substantially the same for both cases. The resonance characteristic of fig. 2 is important for designing a resonant tag with deactivation capability because deactivation is accomplished by changing the bias field strength and thus the resonant frequency. During deactivation, the resonant frequency f_rTo bias field H_bOf (2), i.e. df_r/dH_bThe effectiveness of deactivation is determined and is therefore an important factor in effectively resonating the tag. For tags in electronically coded identification systems, where higher sensitivity in the identification system is desired, a larger slope of resonant frequency versus bias field is generally preferred.

A comparison of the resonance response between these two cases is given in FIG. 3, where V₀Is the amplitude of the response signal, V, when the excitation field is switched off₁Is the signal amplitude at 1msec after termination of the excitation field. Obviously, to get better resonant tag performance, higher V₁/V₀The ratio is preferred. Therefore, both signal amplitudes are used in the industry as part of the quality factor of the magnetomechanical resonance marker. FIG. 3 shows the signal amplitude V for a resonance marker strip in accordance with an embodiment of the invention₀441 and V₁442 are respectively in bias field H_bo=5OO A/m and H_b1Maximum at 400A/m for the conventional resonance marker strip signal V₀443 and V₁444 are respectively in bias field H_bo=460A/m and H_b1Maximum at 400A/m. In addition, FIG. 3 also shows the V of the resonance marker strip at these maximum points for embodiments of the present invention₁/V₀This is a comparison of larger than conventional tags, which demonstrates that the tag of embodiments of the present invention has better signal retention than conventional tags, thus enhancing the effectiveness of current coded electronic identification systems.

Table 1 summarizes a comparison of critical parameters of performance of a tag as a magnetomechanical resonator between a typical conventional tag and an example of a tag of an embodiment of the present invention. Note that the performance of the tag of embodiments of the present invention approaches or exceeds that of conventional tags. All of the strips of labels in table 1 for embodiments of the present invention are acceptable as labels for embodiments of the present invention.

Table 1 tag strips having a strip curvature H as defined in figure 1A for embodiments of the present invention have a bias field strength H_boAnd H_b1V measured separately₀And V₁Maximum signal voltage of and at H_b1Measured resonant frequency slope df_r/dH_bA comparison was made with the corresponding characteristics of 10 randomly selected conventional tags. The lengths l of the strips are all about 38mm and their widths are about 6 mm. The radius of curvature of each tag is calculated using h and l. The resonant frequency of each bar is approximately 58 kHz.

TABLE 1

Magnetic mechanical resonance characteristic

Table 1 includes data for a tag strip of approximately 6mm width which is currently in common use. One aspect of the present invention is to provide a strip of tags having a width different from about 6 mm. Tag strips having different widths were cut from the same tape used in table 1 and their magnetomechanical resonance characteristics were determined. The results are summarized in table II. As expected, the resonance signal voltage V_0maxAnd V_1maxDecreasing with decreasing width. Characteristic field value H due to demagnetization effect_boAnd H_b1Decreasing with decreasing width. The bias field magnets must be chosen accordingly. The smaller width tag is suitable for smaller article identification areas, while the larger width tag is suitable for larger article identification areas because the resonance signal from the larger tag strip is larger, as shown in table II. Since the resonance frequency is mainly dependent on the length of the strip, as shown in equation (1), a change in the width of the strip does not affect the resonance frequency of the article identification system used.

Table II gives the magnetomechanical resonance characteristics of marker strips according to embodiments of the present invention having a strip height h as defined in fig. 1A and different strip widths. V_0max,H_b0,V_1maxAnd df_r/dH_bAre as defined in table I. The length l of the strips is about 38 mm. The radius of curvature of each tag is calculated using h and l. The resonant frequency of each bar is about 58 kHz.

TABLE II

Magnetic mechanical resonance characteristic

It is another aspect of the present invention to provide a variety of tags that can operate under different conditions. To this end, the magnetomechanical resonance characteristics are altered by changing the chemical composition of the amorphous magnetic alloy ribbon used to manufacture the tag. The chemical composition of the alloys examined is set forth in table III, which gives the values of saturation induction and magnetostriction of the alloys. The results of the magnetomechanical resonance properties of these alloys are given in table IV below.

Table III sets forth examples of magnetostrictive amorphous alloys, including their composition, saturation induction B, for use in magnetomechanical resonance markers according to embodiments of the present invention_sAnd saturated magnetostriction lambda_s。B_sCan be determined by the DC BH cycle measurement described in example 3, lambda_sCan be determined by using an empirical formula lambda_s=k B_s ²Where k =15.5ppm/tesla²See S.lto et al, applied Physics Letters, vol.37, p.665 (1980).

TABLE III

Magnetostrictive amorphous alloy

Alloy number	Chemical composition of label (atom% number)	Saturation induction Bs(tesla)	Saturated magnetostriction lambdas(ppm)
				A	Fe40.6Ni40.1Mo3.7B15.1Si0.5	0.88	12

[0062]

B	Fe41.5Ni38.9Mo4.1B15.5	0.98	15
				C	Fe41.7Ni39.4Mo3.1B15.8	1.03	16
D	Fe40.2Ni39.0Mo3.6B16.6Si0.6	0.93	13.5
				E	Fe39.8Ni39.2Mo3.1B17.6C0.3	0.94	14
F	Fe36.9Ni41.3Mo4.1B17.8	0.83	10.5
				G	Fe35.6Ni42.6Mo4.0B17.9	0.81	10
H	Fe39.6Ni38.3Mo4.1B18.0	0.88	12
				I	Fe38.0Ni38.8Mo3.9B19.3	0.84	11

Table IV showsMagnetomechanical resonance characteristics of tag strips of embodiments of the present invention having different chemical compositions as set forth in table III and having a strip height h as defined in fig. 1A. V_0max、H_b0、V_1maxAnd df_r/dH_bAre as defined in table I. The length l of the strips is about 38 mm. The radius of curvature of each tag is calculated using h and l. The resonant frequency of each bar is about 58 kHz.

TABLE IV

Magnetomechanical resonance characteristics of the alloys in Table III

All amorphous alloys with different chemical compositions as listed in table III have excellent magnetomechanical resonance characteristics as shown in table IV and are therefore useful in coded electronic identification systems according to embodiments of the present invention.

Also, strips of about 6mm width cut according to example 1 were cut into strips of different lengths, and their magnetomechanical resonance properties were examined. In addition to the properties of tables I, Il and IV above, additional tests were performed to determine the effectiveness of the magnetomechanical resonance strip using the following equations

V(t)=Vo exp(-t/τ), (2)

Where t is the time measured after termination of the AC field excitation and τ is the characteristic time constant of the resonance signal decay. V in tables I, Il and IV_1maxIs determined from the data at t =1 msec. The results are given in table V, in which other parameters characterizing the resonance properties of the different strip lengths are summarized. Note that f_rThe relation (1) given above is well followed. Note also that τ increases with increasing strip length. If delayed signal detection is preferred, a larger value of the time constant τ is preferred. However, in the coded electronic article identification system, when the interrogation AC field is scanned, V in Table I₀Value ratio V of₁Of importance isMuch more.

In table V, the magnetomechanical resonance characteristics of tag strips having different lengths l of embodiments of the present invention are determined. The width and thickness of each strip was about 6mm and about 28 μm, respectively. The formulas (1) and (2) define the resonance frequency f_rAnd a time constant τ. V_0max、H_b0、V_1max、H_b1And df_r/dH_bAre as defined in table I. The label height h is defined in fig. 1 and the radius of curvature of each bar is calculated using h and l.

TABLE V

In addition to the basic magnetic properties required to produce magnetomechanical resonance in the tag of embodiments of the present invention, such as saturation induction and magnetostriction listed in table III, the direction of magnetic anisotropy must be substantially perpendicular to the length direction of the tag, the direction of magnetic anisotropy being the direction of easy magnetization in the tag. This is true and FIG. 4 shows the BH cycle at 60Hz for an approximately 38mm long strip taken from Table V above using the measurement method of example 3. The BH loop of fig. 4 indicates that the residual induction, i.e., B (H =0), is close to zero at H =0, and the permeability defined by B/H around H =0 is linear. The shape of the BH loop in fig. 4 represents the BH behavior of a magnetic stripe in which the average direction of magnetic anisotropy is perpendicular to the direction of the stripe length. The result of the magnetisation behaviour of the tag in the embodiment of the invention in figure 4 is that no higher harmonics are generated in the tag when the tag is placed in an AC magnetic field. Thus, the "contamination problem" of the system mentioned in the background of the invention is minimized. To further verify this, the higher harmonic signals of the tag of fig. 4 were compared to tags of an electronic article surveillance system based on generation/detection of magnetic harmonics. The results of the comparison are given in table Vl below.

As shown in Table Vl, a tag in an embodiment of the present inventionCo-based monitoring system for electronic article surveillance system based on magnetic harmonic generation/detection systemThe magnetic higher harmonic signals are compared between tags of the alloys. The strips were the same size in both cases, approximately 38mm long and approximately 6mm wide. The fundamental excitation frequency was 2.4kHz and the harmonic signal detection method of example 4 was used to compare the 25 th harmonic signal.

Table Vl

Type of label	25thHarmonic signal (mV)
		The invention	4
Harmonic tag	40

As shown in Table Vl, the negligible small harmonic signals of the tags of embodiments of the present invention do not trigger an electronic article surveillance system based on the generation/detection of magnetic harmonics.

Two tags of embodiments of the present invention having different lengths are randomly selected from a number of tags characterized in tables I, II, IV and V, mounted on top of each other, and the tags produced are shown in bar 110 and bar 111 of fig. 5A. Two tag strips having different lengths are placed in the hollow portion between the non-magnetic housings 100 and 101. A bias magnet 120 is attached to the outer surface of the housing 101. By way of comparison, strip 210 and strip 211 in fig. 5B present a label configuration of two conventional label strips, wherein the available planar area of the two strips is the same as that of the two strips of fig. 5A. The labels 200, 201, and 220 in fig. 5B correspond to 100, 101, and 120, respectively, in fig. 5A.

The magnetomechanical resonance behavior of a tag corresponding to the two strips of the embodiment of the present invention of FIG. 5A is given in FIG. 6A, the tag comprising the approximately 20mm strip and the approximately 57mm strip of Table V, and the magnetomechanical resonance behavior of a tag corresponding to the conventional two strips prepared according to the' 490 patent of FIG. 5B, the two strips used having a length of approximately 20mm and approximately 57mm, is given in FIG. 6B. It is clear from fig. 6A-6B that the overall signal magnitude of both tags of the embodiment of the present invention is much greater than that of both conventional tags. For the tag of the embodiment of the invention of FIG. 5A, the signal amplitude V of the longer bars of the embodiment of the invention₀(FIG. 6A) the corresponding value V for a longer conventional tag than that of FIG. 5B₀(FIG. 6B) is about 280% higher. For shorter bars, the signal amplitude V generated by the bars of embodiments of the present invention₁(FIG. 6A) signal amplitude V vs. corresponding conventional tag₁(FIG. 6B) 370% higher. In FIG. 6 f_rThe amplified co-amplitude value plot around the lower resonance frequency of =38,610Hz is given in fig. 7, which gives the width of the magnetomechanical resonance, defined as the width of the frequency at 1/2 with amplitude of the peak amplitude, which is about 420 Hz. At f_rIn the upper resonance frequency interval around =109,070Hz, the signal amplitude has a frequency width of approximately 660Hz, as shown in fig. 8. This width of frequencies, hereinafter referred to as the resonance linewidth, is used to determine the minimum resonance frequency separation between two adjacent resonance frequencies of two tag strips of slightly different lengths.

Fig. 9 shows labels of an embodiment of the present invention having three labelling strips 311, 312 and 313 of different lengths randomly selected from tables I, II and IV above. Cavity 302 between the two housings 300 and 301 is used to house label strips 311, 312 and 313 of embodiments of the present invention, reference numeral 330 representing a bias magnet attached to the outer surface of housing 301. FIG. 10 shows the magnetomechanical resonance characteristics of a tag having three strips with lengths of about 25mm, about 38mm and about 52mm, respectively, and a width of about 6 mm. Note that the mechanical resonance observed in fig. 6A and 7 is very sharp, with a resonance linewidth around a lower resonance frequency interval of about 40,000Hz of about 400Hz, and a resonance linewidth around a higher resonance frequency interval of about 110,000Hz of about 700Hz, as shown in fig. 6A and 8, indicating that the magneto-mechanical interference between different lengths of tag strips in the tag of embodiments of the present invention is negligible, allowing more than three tag strips to be stacked. There is no strip-to-strip magneto-mechanical interference evident in fig. 9, as the three marker strips of different lengths touch each other along a line near the centre of the strip in the width direction. From tables I, II, IV and V, five similar strips were selected having a length of about 30mm, about 38mm, about 42mm, about 47mm and about 52mm and a width of about 6mm to produce labels. The resonance characteristics of these five tags are given in fig. 11. The resonance characteristics of tags using different lengths of tag strip in accordance with embodiments of the present invention are summarized in table VII.

As shown in Table VII, the resonance signal V according to the coded signature of the present invention_0maxAnd V_1maxAt respective resonance frequencies f_r。

TABLE VII

Label sample

V0max(mV)

V1max(mV)

Length of strip (mm)

[0085]

No.1 (bias =461A/m)
				fr1=51,300	92	43	42
fr2=61,250	104	48	35
				No.2 (bias field =301A/m)
fr1=38,070	133	90	57
				fr1=109,070	55	10	20
No.3 (bias =360A/m)
				fr1=37,880	100	57	57
fr2=57,260	69	24	38
				fr3=108,440	45	3	20
No.4 (bias =420A/m)
				fr1=46,100	65	28	47
fr2=57,100	53	24	38
				fr3=72,720	61	14	30
No.5 (bias =399A/m)
				fr1=41,590	92	47	52
fr2=57,070	75	3	38
				fr3=87,060	59	12	25
No.6 (bias =490A/m)
				fr1=37,640	61	20	57
fr2=45,740	55	12	47
				fr3=56,680	68	21	38
fr4=86,280	48	4	25
				No.7 (bias =550A/m)
fr1=41,440	51	12	52
				fr2=45,930	42	5	47
fr3=51,510	45	6	42
				fr4=56,770	42	5	38
fr5=72,080	50	4	30

In Table VII, the label strip width and thickness are about 6mm and about 28 μm, respectively.

According to an embodiment of the invention, the resonance signal V is given in Table VII_0maxAnd V_1maxSufficiently large to be detected in an electronic article identification system. The data in Table V show the data at the resonant frequency f_rAnd the relationship between the length of the strip

f_r=2.1906x10⁶/l(Hz),

Where l is the length of the strip in mm. Using this relationship in accordance with equation (1), the variation in resonant frequency caused by the tolerance when the tape is cut to a predetermined length can be determined as follows. From above f_rThe relation between l and f can be found_r/Δl=-2.906x10⁶/2l²Where Δ f_rIs the change in resonant frequency due to the change in the strip length Δ l. The cutting tolerance of the tag using a commercially available tape cutter can be determined by comparing the nominal or target length of the tag with the actual length given in table V. For example, a target bar length of 18.01mm long bars in Table V is 18mm, giving a cut tolerance of 0.01 mm. Using the cutting machine tolerances thus obtained, the frequency Δ f due to the variation in the length of the strip can be calculated_rFrom about 3Hz for short strips to about 400Hz for long strips. The resonance linewidth of the long bars is about 400Hz and the resonance linewidth of the short bars is about 700Hz, so that the minimum discernable frequency spacing in an electronic article identification system according to embodiments of the present invention is about 800 Hz. Thus, to ensure that there are no false identifications, a resonant frequency interval of 2kHz (more than twice the minimum discernible resonant frequency interval) is selected to determine the number of identifiable items in the selected range. The tag strips listed in Table V cover resonant frequencies from about 34,000Hz to about 120,000Hz, covering a span of resonant frequencies of about 86,000 Hz. According to an embodiment of the present invention, using a 2kHz resonant frequency spacing without misidentification as determined above, electrical is used when the tag has only one barThe number of sub-identifiable items is 43, and the number of identifiable items increases to approximately 1800, 74000, 2.96 million and 115.5 million at a given range when tags having tag strips of different lengths, respectively, are used in the coded electronic article identification system. Adding more tag strips and/or changing the magnitude of the bias field in the tag may also increase the number of identifiable or coded articles.

As shown in fig. 12, the coded label 501 as described above can be effectively used in an electronic article identification system according to an embodiment of the present invention. An item 502 to be identified having a coded tag 501 of an embodiment of the invention is placed in an interrogation zone 510 of fig. 12 flanked by a pair of interrogation coils 511. The coil 511 emits, in alignment with the article 502 to be identified, an AC magnetic field fed by an electronic device 512, the electronic device 512 being constituted by a signal generator 513 and an AC amplifier 514 with variable frequency, the switching operation of which is controlled by a circuit box 515. When the item 502 is placed in the area 510, the circuitry box 515 is turned on to interrogate the AC field frequency, sweeping from the lowest frequency to the highest frequency, the range depending on the predetermined frequency range of the tag. In such a frequency sweep, the resonance signal of the coded tag 501 of an embodiment of the present invention is detected in a pair of signal receiving coils 516, thereby producing the resonance signal pattern shown in FIG. 11. The resulting signal pattern from signal detector 517 is then stored in computer 518, and computer 518 is programmed to recognize the sequence of resonant frequencies encoded in encoded tag 501 of embodiments of the present invention. When this identification is complete, the computer 518 sends a signal reporting the identification to the identifier 519 and circuit box 515 to reset the system. If desired, the bias magnet in the tag may be demagnetized after the item 502 is located in the interrogation zone 510, thereby deactivating a coded tag according to embodiments of the present invention.

The coded electronic article identification system given above may be used to identify articles by scanning an AC excitation field having a varying frequency. In some cases, identification of the need for delay may be accomplished by tracking V in FIG. 3, FIG. 5(a), FIG. 10, and FIG. 11₁And (5) realizing. This is done by programming computer 517 in FIG. 12 to process as the scan frequencyV of a function of₁To be implemented electronically.

Example 1

The cut strip was cut into ductile, rectangular strips using a conventional metal strip cutter. The curvature of each strip is determined by measuring the height h of the curved surface over the strip length l as defined in fig. 1A.

Example 2

The magnetomechanical properties were determined in an apparatus in which an internal pair of coils provided a static bias field, and the voltage in the signal detection coil compensated by the compensation coil was measured using a voltmeter and oscilloscope. The measured voltage is therefore related to the detection coil and indicates the relative signal amplitude. The excitation AC field is provided by a commercially available functional generator and AC amplifier. The signal from the voltmeter was voltage tabulated and the data collected was analyzed and processed using commercially available computer software.

Example 3

The magnetic induction B as a function of the applied field H was measured using a commercially available DC BH loop measurement device. For the AC BH loop measurement, an excitation coil detection coil assembly similar to example 4 was used, and the output signal of the detection coil was fed to an electronic integrator. The integrated signal is calibrated to give the value of the magnetic induction B of the sample. The resulting B is plotted against the applied field H, resulting in an AC BH cycle. For both AC and DC, the applied field and the direction of measurement are along the length of the tag.

Example 4

A tag prepared according to example 1 was placed in an exciting AC field of a predetermined fundamental frequency and its higher harmonic response was detected using a coil containing the tag. The excitation coil and the signal detection coil are wound around a bobbin having a diameter of about 50 mm. The number of windings of the excitation coil and the signal detection coil is about 180 and about 250, respectively. The fundamental frequency of 2.4kHz was chosen and the voltage of the excitation coil was approximately 80 mV. The 25 th harmonic voltage from the signal detection coil is measured.

Thus, in embodiments of the invention, the radius of curvature of the tag may be less than about 100cm or between about 20cm and about 100 cm.

Alternatively, the amorphous magnetostrictive alloy ribbon whose magnetic anisotropy direction is perpendicular to the ribbon axis is cut to form a rectangular strip having a predetermined length with a length-to-width aspect ratio of more than 3 for encoding.

Alternatively, the strip width of the strip is from about 3mm to about 15 mm.

In one embodiment of the invention, the slope of the resonant frequency of the bars versus the bias field is from about 4Hz/(A/m) to about 14 Hz/(A/m).

Alternatively, when the strip width is 6mm, the length of the strip is greater than about 18 mm.

Alternatively, the bar has a magnetomechanical resonance frequency of less than about 120000 Hz.

In one embodiment of the invention, the amorphous ferromagnetic alloy ribbon has a saturation magnetostriction between about 8ppm and about 18ppm and a saturation induction between about 0.7Tesla and about 1.1 Tesla.

In one embodiment of the invention, the coded label comprises at least two strips of different lengths, and optionally the coded label comprises 5 strips of different lengths.

In one embodiment of the invention, the magnetomechanical resonance frequency of the encoded tag is between about 30000 and about 130000 Hz.

In one embodiment of the invention, the electronic identification range of coded tags includes about 1800 and about 115 million individually identifiable items of coded tags having two and five tag strips, respectively.

In one embodiment of the invention, the electronic identification range of the coded label includes over 115 million individually identifiable articles.

Accordingly, in an embodiment of the present invention, a coded tag for a magnetomechanical resonance electronic article identification system adapted to resonate mechanically at a preselected frequency comprises a plurality of ductile magnetostrictive strips cut from an amorphous ferromagnetic alloy ribbon having a predetermined length, the strips having a curvature along the ribbon length direction that produces magnetomechanical resonance when excited by an alternating magnetic field having a static bias field, the strips having a magnetic anisotropy direction perpendicular to the ribbon axis, wherein at least two of the strips are adapted to be magnetically biased to resonate at a single different one of the preselected frequencies.

In addition, in an alternative embodiment of the present invention, the electronic article identification system has a function of decoding the encoded information of the encoded tag. The encoded tag is adapted to resonate mechanically at a preselected frequency, the encoded tag comprising a plurality of ductile magnetostrictive strips cut from a ribbon of amorphous ferromagnetic alloy having a predetermined length, the strips having a curvature along the length of the ribbon, the strips being magnetomechanical resonant when excited by an alternating magnetic field having a static bias field, the strips having a direction of magnetic anisotropy perpendicular to the ribbon axis, wherein at least two of the strips are magnetically biased to resonate at a single different one of the preselected frequencies. The electronic article identification system comprises at least one of: a pair of coils that transmit an AC excitation field to form an interrogation zone; a pair of signal detection coils for receiving encoded information from the encoded tag; an electronic signal processing device having a computer with software to decode the encoded information on the encoded tag; or an electronic device that identifies the coded tag. And providing identification of the coded tag, the electronic article identification system may identify an article having the coded tag attached thereto.

Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.

Claims (25)

1. A coded tag for a magnetic mechanical resonance electronic article surveillance system that mechanically resonates at a preselected frequency, comprising:

cutting a predetermined length of a first marker strip having magnetostriction from an amorphous ferromagnetic alloy ribbon, said first marker strip having a curvature along the length of the ribbon and generating magnetomechanical resonance under excitation by an alternating magnetic field having a static bias field,

the first tag has a direction of magnetic anisotropy perpendicular to the tape axis.

2. The coded tag of claim 1, wherein the radius of curvature of the first marker strip is less than 100 cm.

3. The coded tag of claim 1, wherein the aspect ratio of the first tag strip is greater than 3.

4. The coded tag of claim 1, wherein the first strip of tags has a width of from 3mm to 15 mm.

5. The coded tag of claim 3, wherein the slope of the resonant frequency of the first tag strip versus the bias field is from 4Hz/(A/m) to 14 Hz/(A/m).

6. A coded label according to claim 1, wherein the predetermined length of the first strip is from 15mm to 65 mm.

7. The coded tag of claim 6, wherein the first marker strip has a magnetomechanical resonance frequency of less than 120000 Hz.

8. The coded tag of claim 1, wherein the saturation induction of the amorphous ferromagnetic alloy ribbon is between 0.7tesla and 1.1 tesla.

9. The coded tag of claim 8, wherein the amorphous ferromagnetic alloy ribbon has an Fe-based basis_a-Ni_b-Mo_c-B_dWherein 30 is<a<43，35<b<48，0<c<5，14<d<20, and a + b + c + d = 100.

10. The coded tag of claim 9, wherein up to 3 at% of Mo is replaced by Co, Cr, Mn and/or Nb and up to 1 at% of B is replaced by Si and/or C.

11. The coded tag of claim 8, wherein the amorphous ferromagnetic alloy ribbon is an alloy having one of the following: fe_40.6Ni_40.1Mo_3.7B_15.1Si_0.5,Fe_41.5Ni_38.9Mo_4.1B_15.5,Fe_41.7Ni_39.4Mo_3.1B_15.8,Fe_40.2Ni_39.0Mo_3.6B_16.6Si_0.6,Fe_39.8Ni_39.2Mo_3.1B_17.6C_0.3,Fe_36.9Ni_41.3Mo_4.1B_17.8,Fe_35.6Ni_42.6Mo_4.0B_17.9,Fe₄₀Ni₃₈Mo₄B₁₈Or Fe_38.0Ni_38.8Mo_3.9B_19.3。

12. The coded tag of claim 1, further comprising a second strip of tags having a different radius of curvature along the length of the tape than the first strip of tags and a predetermined length different than the first strip of tags.

13. The coded tag of claim 12, wherein the first strip of tags and the second strip of tags are stacked.

14. The coded tag of claim 13, wherein the magnetomechanical resonance frequency of the first tag and the second tag is between 30000Hz and 130000 Hz.

15. The coded tag of claim 14, wherein the coded tag has an electronic identification range including up to 1800 individually identifiable items.

16. The coded tag of claim 14, further comprising a third tag, a fourth tag, and a fifth tag, wherein the coded tag has an electronic identification range that includes more than 1 billion 1 thousand 5 million individually identifiable items.

17. The coded tag of claim 1, wherein the radius of curvature of the first marker strip is between 20cm and 100 cm.

18. The coded tag of claim 2, wherein the first tag strip has a predetermined length and produces magnetomechanical resonance at a frequency that is related to the length.

19. The coded tag of claim 18, wherein the amorphous ferromagnetic alloy ribbon has a saturation magnetostriction ranging from 8ppm to 18 ppm.

20. The coded tag of claim 18, wherein the amorphous ferromagnetic alloy ribbon has an Fe-based basis_a-Ni_b-Mo_c-B_dWherein 30 is<a<43，35<b<48，0<c<5，14<d<20 and a + b + c + d = 100.

21. The coded tag of claim 20, wherein up to 3 at% of Mo is replaced by Co, Cr, Mn and/or Nb and up to 1 at% of B is replaced by Si and/or C.

22. The coded tag of claim 1, further comprising a magnetically biased strip positioned along the length of the first strip of tags.

23. A coded tag for a magnetic mechanical resonance electronic article surveillance system that mechanically resonates at a preselected frequency, comprising:

cutting a predetermined length of a first marker strip having magnetostriction from an amorphous ferromagnetic alloy ribbon, said first marker strip having a curvature along the length of the ribbon and generating magnetomechanical resonance under excitation by an alternating magnetic field having a static bias field, said first marker strip having a magnetic anisotropy direction perpendicular to the ribbon axis

Wherein the amorphous ferromagnetic alloy is based on Fe_a-Ni_b-Mo_c-B_dWherein 30 is<a<43，35<b<48，0<c<5，14<d<20 and a + b + c + d = 100.

24. The coded tag of claim 23, wherein up to 3 at% of Mo is replaced by Co, Cr, Mn and/or Nb and up to 1 at% of B is replaced by Si and/or C.

25. An electronic article surveillance system comprising the coded tag of claim 1.