HK1117618B

HK1117618B - Marker for coded electronic article identification system

Info

Publication number: HK1117618B
Application number: HK08108205.6A
Authority: HK
Inventors: Ryusuke Hasegawa
Original assignee: Metglas, Inc.
Priority date: 2005-04-01
Filing date: 2006-03-31
Publication date: 2013-03-15

Description

Marker for coded electronic article identification system

Technical Field

The present invention relates to ferromagnetic amorphous alloy strips (ribbon) and to a marker for electronic article identification systems, comprising a plurality of rectangular strips (strip) based on amorphous magnetostrictive material, which mechanically oscillate at several times the resonance frequency in an alternating magnetic field, whereby the magneto-mechanical (magneto-mechanical) effect of the marker is effectively used for encoding and decoding purposes. The invention also relates to an electronic identification system using such a marker.

Background

Magnetostriction of a magnetic material refers to a phenomenon in which the magnetic material undergoes a dimensional change when an external magnetic field is applied thereto. A material is said to be "positively magnetostrictive" when the dimensional change is such that the material elongates when magnetized. If the material is "negatively magnetostrictive," the material contracts when magnetized. In either case, therefore, the magnetic material oscillates when subjected to an alternating magnetic field. When a static magnetic field is applied together with an alternating field, the frequency of mechanical oscillation of the magnetic material varies with the applied static field through magnetoelastic (magnetoelastic) coupling. This is commonly referred to as the Δ E effect, as described in S.Chikazumi (John Wiley & Sons, New York, 1964, page 435) "Physics of Magnetism". Where E (H) represents Young's modulus as a function of applied field H, and the oscillation or resonant frequency fr of the material is related to E (H) by the equation:

f_r＝(1/2l)[E(H)/ρ]^1/2 (1)

where l is the length of the material and ρ is the mass density of the material. The magnetoelastic or magneto-mechanical effects described above are used in electronic article surveillance systems, which are first taught in U.S. patent nos. 4,510,489 and 4,510,490 (hereinafter the '489 and' 490 patents). An advantage of such a supervision system is that the system provides a combination of high detection sensitivity, high operational reliability and low operational costs.

The marker in such a system is one or more strips of a known length of ferromagnetic material encapsulated with a more magnetically hard ferromagnetic (material with higher coercivity) that provides a static field known as the bias field to establish peak magneto-mechanical coupling. The ferromagnetic marker material is preferably amorphous alloy ribbon because of the very high magneto-mechanical coupling efficiency in these alloys. Mechanical resonance frequency f_rIs determined essentially by the length of the alloy strip and the bias field strength as shown in equation (1) above. When an interrogation signal tuned to the resonant frequency is encountered in an electronic identification system, the signature material responds with a large signal field that is detected by a receiver within the system.

A variety of amorphous ferromagnetic materials are contemplated for use in code recognition systems based on magneto-mechanical resonance as described above in U.S. Pat. No.4,510,490, and include amorphous Fe-Ni-Mo-B, Fe-Co-B-Si, Fe-B-Si-C, and Fe-B-Si alloys. Amorphous Fe-Ni-Mo-B based METGLAS commercially available in these alloys up to the occasional triggering of magneto-mechanical resonant markers of other systems based on magnetic harmonic generation/detectionThe 2826MB alloy is widely used. This is because the magnetomechanical resonant marker used at the time sometimes exhibited a nonlinear BH characteristic, resulting in the generation of higher harmonics of the excitation field frequency. To avoid this problem, sometimes referred to as the "contamination problem" of the system, a series of new marker materials have been invented, examples of which are disclosed in U.S. patent nos. 5,495,231, 5,539,380, 5,628,840, 5,650,023, 6,093,261 and 6,187,112. Although the performance of the new marking materials is superior on average to the materials used in the surveillance systems of the original ' 489 and ' 490 patents, slightly better magneto-mechanical performance has been found in marking materials such as those disclosed in U.S. Pat. No.6,299,702 (hereinafter the ' 702 patent). These new marking materials require complex thermal processing to achieve the same desired magneto-mechanical properties as those disclosed in, for example, the' 702 patent. Clearly, there is a need for a back belt that does not require such complexity(post-ribbon) making process and it is an object of the present invention to provide such a marking material having high magneto-mechanical properties without causing the aforementioned "contamination problems". The present invention includes a marker having encoding and decoding capabilities and an electronic identification system using the marker, all utilizing the novel magneto-mechanical marking material of the present invention. An encoding surveillance system with a magneto-mechanical marker is taught in U.S. patent No.4,510,490, but the number of component marker strips is limited due to the limited space available within the marker, thus limiting the field of encoding and decoding capabilities using such markers.

Clearly, there is a need for a marker in an electronic article identification system having encoding and decoding capabilities, the number of marker strips within which is significantly increased without sacrificing performance as a coded marker, hereinafter referred to as a "coded electronic article identification system".

Disclosure of Invention

According to the invention, the marker of the magnetomechanical resonance based electronic identification system comprises soft magnetic material.

Marker materials having enhanced overall magnetomechanical resonance properties are made from amorphous alloy ribbons such that a plurality of marker strips are contained within a coded marker. Soft magnetic material in ribbon form with magnetomechanical resonance capability is cast on a rotating substrate as taught in U.S. patent No.4,142,571. When an as-cast tape width is wider than a predetermined width for a marking material, the tape is slit into the predetermined width. The strip thus processed is cut into ductile rectangular amorphous metal strips having different lengths to fabricate magnetomechanical resonant markers using a plurality of said rectangular amorphous metal strips having at least one semi-rigid magnetic strip providing a biasing static magnetic field.

A coded electronic article identification system uses the coded marker of the present invention. The system has an article interrogation zone wherein the magneto-mechanical marker of the present invention is subjected to an interrogation magnetic field having a varying frequency, the signal response to the interrogation field excitation being detected by a receiver having a pair of antenna coils disposed within the article interrogation zone.

In accordance with an embodiment of the present invention, there is provided a coded marker of a magnetomechanical resonant electronic article identification system for mechanically resonating at a preselected frequency, the coded marker comprising: a plurality of ductile magnetostrictive strips cut to a predetermined length from an amorphous ferromagnetic alloy ribbon having a curvature along the length of the ribbon and exhibiting magnetomechanical resonance with a static bias field under excitation by an alternating magnetic field, the magnetostrictive strips having a direction of magnetic anisotropy perpendicular to the ribbon axis, wherein at least two of the magnetostrictive strips are adapted to be magnetically biased to resonate at a single different frequency of the preselected frequency.

In the optional case, the curvature radius of the marking strip is less than 100 cm.

According to an embodiment of the present invention, encoding is performed by cutting an amorphous magnetostrictive alloy ribbon whose magnetic anisotropy direction is perpendicular to a ribbon axis into rectangular strips having a length/width ratio greater than 3 with a predetermined length.

Where selected, the strip has a strip width ranging from about 3mm to about 15 mm.

According to an embodiment of the invention, the strip has a slope of the resonance frequency with respect to the bias field in the range of about 4Hz/(A/m) to about 14 Hz/(A/m).

Optionally, when the strip width is 6mm, the strip has a length greater than about 18 mm.

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

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

According to an embodiment of the present invention, theAmorphous ferromagnetic alloys for shaping ferromagnetic alloy ribbon having 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.ltoreq.100, up to 3 at.% of Mo being optionally substituted by Co, Cr, Mn and/or Nb, and up to 1 at.% of B being optionally substituted by Si and/or C.

According to an embodiment of the invention, the amorphous ferromagnetic alloy of the amorphous ferromagnetic alloy ribbon comprises 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_36.9Ni_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。

Optionally, the coded marker includes at least two marker strips having different lengths.

In the optional case, the coded marker comprises five marker-strips having different lengths.

Optionally, the coded marker has a magnetomechanical resonance frequency between about 30000 and about 130000 Hz.

The coded marker optionally has up to about 1800 and about 1.15 x 10 for coded markers having two and five marker strips, respectively⁸Respectively, can identify an electronic identification universe (univorse) of the item.

Optionally, the coded marker has a mark size of more than 1.15 × 10⁸Respectively, to identify an electronic identification universe of the item.

In accordance with an embodiment of the present invention, the magnetostrictive strip has a magnetomechanical resonance frequency less than about 120000 Hz.

In accordance with an embodiment of the present invention, an electronic article identification system has the capability of decoding the encoded information of a coded marker. The system includes one of: a pair of coils emitting an AC excitation field aimed at the coded marker to form an interrogation zone; a pair of signal detection coils receiving encoded information from the encoded marker; an electronic signal processing device having an electronic computer with software to decode the information on the coded marker; or an electronic device identifying the coded marker, wherein the coded marker is configured to resonate mechanically at a preselected frequency, wherein the coded marker comprises a plurality of ductile magnetostrictive strips cut to a predetermined length from an amorphous ferromagnetic alloy ribbon having curvature along the ribbon length and exhibiting magnetomechanical resonance with a static bias field under excitation by an alternating magnetic field, the magnetostrictive strips having a direction of magnetic anisotropy perpendicular to the ribbon axis, wherein at least two of the magnetostrictive strips are configured to be magnetically biased to resonate at a single different one of the preselected frequencies.

Optionally, the marker strip has a radius of curvature of between about 20cm and about 100 cm.

Drawings

The present invention will be more fully understood and further advantages thereof will become apparent, with reference to the following detailed description of the preferred embodiments and the accompanying drawings.

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

FIG. 2 illustrates magnetomechanical resonance characteristics of a single strip marker in accordance with an embodiment of the present invention and magnetomechanical resonance characteristics of a conventional single strip marker, with resonance frequency shown as a function of bias field;

FIG. 3 illustrates a resonance signal of a single bar marker and a resonance signal of a conventional bar marker, showing the resonance signal amplitude as a function of bias field, in accordance with an embodiment of the present invention;

FIG. 4 illustrates a BH loop acquired at 60Hz on a marker strip of an embodiment of the present invention having a length of about 38mm, a width of about 6mm, and a thickness of about 28 μm;

FIG. 5A illustrates a comparison of physical profiles of embodiments of magnetomechanical resonant markers in accordance with embodiments of the present invention, and FIG. 5B illustrates a comparison of conventional markers, in both cases utilizing two marker strips having different lengths;

FIG. 6A illustrates magnetomechanical resonance characteristics of a marker having two strips of different lengths of an embodiment of the present invention, and FIG. 6B illustrates magnetomechanical resonance characteristics of a conventional marker having two strips of different lengths;

FIG. 7 illustrates the resonant signal profile near the low resonant frequency region of FIG. 6A;

FIG. 8 illustrates the resonant signal profile near the high resonant frequency region of FIG. 6A;

FIGS. 9-1 and 9-2 illustrate a marker of an embodiment of the present invention in which three strips having different lengths are accommodated;

FIG. 10 illustrates magnetomechanical resonance characteristics of a marker having three strips of different lengths in accordance with an embodiment of the present invention;

FIG. 11 illustrates magnetomechanical resonance characteristics of a marker having five strips of different lengths in accordance with an embodiment of the present invention; and

FIG. 12 illustrates a coded electronic article identification system of an embodiment of the present invention.

Detailed Description

Marker materials having enhanced overall magnetomechanical resonance performance are made from amorphous ferromagnetic alloy ribbon such that a plurality of marker strips are housed within a coded marker, wherein at least two of the marker strips are adapted to be magnetically biased to resonate mechanically at a single, different one of a plurality of preselected frequencies. A strip of magnetic material having magnetomechanical resonance capability is cast on a rotating substrate as taught in U.S. patent No.4,142,571. When the as-cast strip of marking material is wider than the predetermined width, the strip is slit to the predetermined width. The strip thus processed is cut into ductile rectangular amorphous metal strips having different lengths to fabricate magnetomechanical resonant markers using a plurality of said rectangular amorphous metal strips having at least one semi-rigid magnetic strip providing a biasing static magnetic field.

In one embodiment of the invention, the amorphous ferromagnetic alloy used to form the bands of the marker strip has a Fe-based basis_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.ltoreq.100, up to 3 at.% of Mo being optionally substituted by Co, Cr, Mn and/or Nb, and up to 1 at.% of B being optionally substituted by Si and/or C.

In one embodiment of the invention, the amorphous ferromagnetic alloy used to form the strip of the marker strip comprises one of the following compositions: fe_40.6Ni_40.iMo_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。

Thus, according to the invention described in U.S. Pat. No.4,142,571, a casting mold having a shape similar to commercially available amorphous magnetostrictive METGLAS2826MB of amorphous alloy ribbon of similar chemical composition. The as-cast amorphous alloy had a saturation induction of about 0.88 tesla and a saturation magnetostriction of about 12 ppm. The tape has a width of about 100mm and about 25mm and a thickness of about 28 μm. The strip is then cut into narrow strips having different widths. The cut strip is then cut into ductile rectangular strips having a length in the range of about 15mm to about 65 mm. Each strip has a slight curvature that reflects the curvature of the belt casting wheel surface. The initial curvature is adjusted during slitting. The curvature of the cut, slit strips was determined as shown in example 1. Fig. 1A shows the physical appearance of a marker strip 10 of an embodiment of the present invention, and fig. 1B shows the physical appearance of a conventional strip 20 produced according to the complex heat treatment method disclosed in U.S. patent No.6,299,702. As shown, the magnetic field lines 11 in the resonant marker-bias strip configuration of the present embodiment are more closed than the magnetic field lines 21 of the conventional strip shown in FIG. 1B. This allows the coupling between the marker strip 10 and the bias magnet 12 of embodiments of the present invention to be superior to the coupling between the conventional strip 20 and the bias magnet 22, which results in less magnetic flux leakage across the resonant marker strip of embodiments of the present invention. The resonant marker strip and the conventional strip of an embodiment of the present invention were examined by magnetomechanical resonance performance using the characterization method of example 2, respectively. FIG. 2 compares the resonant frequency of a single strip marker 830 as a function of bias field for an embodiment of the present invention with the resonant frequency of a conventional strip 831 as a function of bias field. Fig. 2 shows that the change in resonance frequency as a function of the bias field is about the same in both cases. The resonance characteristic described in fig. 2 is important when designing a resonance marker with deactivation (deactivation) capability, since deactivation is achieved by changing the resonance frequency by changing the bias field strength. At deactivation, the resonant frequency f_rWith respect to the bias field H_bSlope of (i) df_r/dH_bThe effectiveness of the deactivation is determined and is therefore an important factor for an effective resonant marker strip. For markers within an electronically coded identification system, a greater slope between the resonant frequency and the bias field is generally used when greater sensitivity is desired in the identification systemIs preferred.

A comparison of the resonant response between the two cases is shown in FIG. 3, where V₀Is the amplitude of the response signal when the excitation field is off, and V₁The signal amplitude 1msec after termination of the excitation field. Obviously, higher V₁/V₀Is preferred for better performance of the resonant marker. Both signal amplitudes are therefore in the industry as part of the quality factor of magnetomechanical resonant markers. FIG. 3 shows signal amplitude V for a resonant marker strip of an embodiment of the present invention₀441 and V₁442 are respectively at H_b0500A/m and H_b1Maximum at a bias field of 400A/m; for conventional resonant marker strips, V₀443 and V₁444 are respectively at H_b0460A/m and H_b1The maximum is 400A/m bias field. Furthermore, FIG. 3 shows the ratio V of the resonant marker strips at these maximum points for an embodiment of the present invention₁/V₀Higher than conventional marker strips, indicating that the signal of the marker strip of the present embodiment remains superior to conventional marker strips, thus enhancing the effectiveness of the coded electronic identification system of the present invention.

Table I summarizes a comparison of parameters critical to the performance of a marker strip as a magneto-mechanical resonator between representative conventional marker strips and an example marker strip of an embodiment of the present invention. Note that the performance of the marker strip of the embodiments of the present invention is close to or better than that of the conventional marker strip. All of the marker strips of the embodiments of the present invention in table I can accept markers for use in embodiments of the present invention.

In Table I, are each at H_b0And H_b1V of bias field strength measurement₀And V₁And the marker strip of the embodiment of the invention having the strip curvature H defined in fig. 1A is at H_b1Measured resonant frequency slope df_r/dH_bRespectively, compared with the corresponding characteristics of ten randomly selected conventional marker strips. The strips each have a length l of about 38mm and a width of about 6 mm. The radius of curvature of each marker strip is calculated from h and l. The resonant frequency of each bar is about 58 kHz.

TABLE I magneto-mechanical resonance characteristics

Marking device	V_0max(mV)	H_b0(A/m)	V_1max(mV)	H_b1(A/m)	df_r/dH_b[Hz/(A/m)]	h(mm)	Radius of curvature (cm)
								General of	140～180	440～500	60～102	360～420	5.60～11.5	-	-
No.1 of the present invention	167	490	97	400	12.0	0.18	100
								No.2	156	470	86	410	9.50	0.18	100
No3	159	490	84	410	12.5	0.20	90
								No.4	167	490	94	400	11.8	0.20	90
No.5	183	458	110	390	11.8	0.23	78
								No.6	165	488	94	370	12.5	0.23	78
No.7	178	471	106	391	12.3	0.28	65
								No.8	160	460	92	379	10.8	0.28	65
No.9	157	461	87	351	9.10	0.36	50
								No.10	147	420	76	391	10.3	0.64	28

Table I contains data for marker strip widths of about 6mm that are currently in widespread use. One aspect of the present invention provides a marker strip having a width different from about 6 mm. The marker strips with different widths used in table I were cut from the same strip and their magnetomechanical resonance characteristics were determined. The results are summarized in table II. Resonance signal voltage V_0maxAnd V_1maxAs expected, decreases with decreasing width. Characteristic field value H_b0And H_b1The decrease with decreasing width is due to demagnetization effects. Therefore, the bias field magnets must be chosen accordingly. A tag with a smaller width is suitable for a smaller item identification area, while a tag with a larger width is suitable for a larger item identification area because the resonance signal from the larger tag strip is larger, as shown in table II. Since the resonant frequency is primarily dependent on the strip length, as shown in equation (1), strip width variations do not affect the resonant frequency of the article identification system used.

Table II shows the magnetomechanical resonance characteristics of marker strips of embodiments of the present invention having a strip height h as defined in fig. 1A and having 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 38mm each. The radius of curvature of each marker strip is calculated from h and l. The resonant frequency of each bar is about 58 kHz.

TABLE II magneto-mechanical resonance characteristics

Mark Width (mm)	V_0max(mV)	H_b0(A/m)	V_1max(mV)	H_b1(A/m)	df_r/dH_b[Hz/(A/m)]	h(mm)	Radius of curvature (cm)
								4	107	310	56	330	4.69	0.61	30
5	153	300	76	300	6.05	0.41	44
								9	194	500	101	440	4.84	0.81	22
14	321	590	174	511	4.86	0.84	21

Another aspect of the present invention provides a variety of available markers 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 make the marker strip. The chemical composition of the alloys examined is shown 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 shown in Table IV below.

Table III shows the composition, saturation induction B, of an example magnetostrictive amorphous alloy for a magnetomechanical resonant marker of an embodiment of the present invention_sAnd saturated magnetostriction lambda_s。B_sThe value is determined by the DC BH loop measurement described in equation 3, λ_sThe value is obtained by using an empirical formula lambda_s＝kB_s ²According to S.Ito et al Applied Physics Letters, vol.37, p.665(1982) using k-15.5 ppm/Tesla²To calculate.

TABLE III magnetostriction amorphous alloys

Alloy number	Chemical composition of marking (atomic%)	Saturation induction B_s(Tesla)	Saturated magnetostriction lambda_s(ppm)
				A	Fe_40.6 Ni_40.1 Mo_3.7 B_16.1 Si_0.5	0.88	12
B	Fe_41.6 Ni_38.9 Mo_4.1 B_15.5	0.98	15
				C	Fe_41.7 Ni_39.4 Mo_3.1 B_15.8	1.03	16
D	Fe_40.2 Ni_39.0 Mo_3.6 B_16.6 Si_0.6	0.93	13.5
				E	Fe_39.8 Ni_39.2 Mo_3.1 B_17.6 C_0.3	0.94	14
F	Fe_36.9 Ni_41.3 Mo_4.1 B_11.8	0.83	10.5
				G	Fe_35.6 Ni_42.6 Mo_4.0 B_17.9	0.81	10
H	Fe_39.6 Ni_38.3 Mo_4.1 B_16.0	0.88	12
				I	Fe_38.0 Ni_38.8 Mo_3.9 B_19.3	0.84	11

Table IV shows the magnetomechanical resonance characteristics of marker strips of different chemical composition listed in Table III of embodiments of the present invention 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 38mm each. The radius of curvature of each marker strip is calculated from h and l. The resonant frequency of each bar is about 58 kHz.

TABLE IV

Magnetomechanical resonance characteristics of the alloys in Table III

Alloy No.	V_0max(mV)	H_b0(A/m)	V_1max(mV)	H_b1(A/m)	df_r/dH_b[Hz/(A/m)]	Radius of curvature (cm)
							A	184	370	94	330	8.10	71
B	174	490	89	348	10.4	36
							C	188	471	70	368	13.0	33
D	158	580	83	580	4.85	33
							E	160	320	72	300	8.80	25
F	160	341	84	329	7.06	34
							G	154	420	94	389	8.51	36
H	171	472	85	351	9.73	27
							I	146	352	60	250	13.4	30

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

Further, the tape cut to a width of about 6mm according to example 1 was cut into strips having different lengths, and the magneto-mechanical resonance performance thereof was examined. In addition to the properties covered by tables I, II and IV above, additional tests were performed to determine the effectiveness of the magnetomechanical resonance strip using the following equation:

V(t)＝V₀exp(-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, II and IV_1maxThe value of (d) is determined from the data of t ═ 1 msec. The results are shown in table V, which summarizes other parameters characterizing the resonance behavior for different strip lengths. Note that f_rIn good agreement with the relation given above for equation (1). Note also that τ increases with increasing strip length. A larger value of the time constant τ is preferred if delayed signal detection is preferred. However, in coded electronic article identification systems where the interrogation AC field sweeps, V in Table I₀Value ratio V of₁The value of (c) is more critical.

As shown in Table V, the magnetomechanical resonance characteristics of marker strips of embodiments of the present invention having different lengths l were determined. The width and thickness of each strip was about 6mm and about 28 μm, respectively. Resonant frequency f_rAnd the time constant τ are defined in equations (1) and (2), respectively. V_0max、H_b0、V_1max、H_b1And df_r/dH_bAre as defined in table I. The height h of the bars is defined in fig. 1, and the radius of curvature of each bar is calculated from h and l.

TABLE V

Strip Length/(mm)	f_r(Hz)	V_0max(mV)	H_b0(A/m)	Time constant T (msec)	V_1max(mV)	H_b1(A/m)	df_r/dH_b[Hz/(A/m)]	Radius of curvature (cm)
									18.01	120,772	73	610	0.85	23	520	6.65	26
20.16	108,536	68	550	0.92	25	370	8.07	22
									24.99	87,406	94	460	1.16	42	338	6.55	22
30.02	72,284	135	461	1.35	69	342	9.44	36
									35.03	61,818	143	387	1.74	79	322	8.73	29
37.95	56,782	160	389	1.86	91	337	7.89	31
									41.90	51,336	184	389	2.03	109	350	6.67	43
46.95	45,992	178	330	2.49	116	320	5.21	45
									52.12	41,438	197	331	2.69	132	312	5.28	35
56.99	37,900	187	292	3.30	135	291	5.93	37
									62.07	34,864	197	293	3.56	148	279	4.94	34

In addition to the basic magnetic properties listed in Table III, such as saturation induction and magnetostriction, required to produce magnetomechanical resonance in marker strips of embodiments of the present invention, the direction of magnetic anisotropy, which is the direction of easy magnetization, in marker strips must be substantially perpendicular to the length direction of the strip. This is the case, as shown in FIG. 4, which depicts a BH loop taken at 60Hz using the measurement method of example 3 for a strip of Table V above about 38mm long. The BH loop of fig. 4 indicates that the residual induction at H ═ 0, i.e., B (H ═ 0), is close to zero, and the permeability defined by B/H is linear near H ═ 0. The shape of the BH loop shown in fig. 4 is typical of BH behavior of a magnetic stripe in which the average direction of magnetic anisotropy is perpendicular to the length direction of the stripe. The result of the magnetization behavior of the marker strip of the embodiment of the invention shown in fig. 4 is that higher order harmonics are not generated when the strip is placed in an AC magnetic field. Thus, the "contamination problem" of the system mentioned in the "background" section is minimized. To further check this, the higher order harmonic signals from the marker strip of fig. 4 were compared with the higher order harmonic signals of the marker strips of the electronic article surveillance system based on magnetic harmonic generation/detection. The results of this comparison are shown in table VI below.

As shown in FIG. VI, the marker strip and Co-based METGLAS of the present invention are examplesThe magnetic higher order harmonic signals of marker strips of alloy 2714A were compared, the latter being widely used in electronic article surveillance systems based on magnetic harmonic generation/detection systems. The strip dimensions were the same for both cases, about 38mm long and about 6mm wide. The fundamental excitation frequency was 2.4kHz and the 25 th harmonic signal was compared using the harmonic signal detection method of example 4.

TABLE VI

Marker type	Harmonic signal of order 25 (mV)
		The invention	4
Harmonic marker	40

As shown in table VI, the negligible small harmonic signals from the markers of the embodiments of the present invention do not trigger electronic article surveillance systems based on magnetic harmonic generation/detection.

Two marker strips of embodiments of the invention having different lengths are randomly selected from a plurality of strips as characterized in tables I, II, IV and V, mounted on top of each other and form a marker as shown by strip 110 and strip 111 in fig. 5A. The two marker strips having different lengths are accommodated in the hollow region between the non-magnetic outer cases 100 and 101. The bias magnet 120 is attached to the outer surface of the housing 101. For comparison, the marking configuration of two conventional marking strips is shown in fig. 5B by strips 210 and 211, wherein the available planar area for the two strips is the same as for the two strips of fig. 5A. Numerals 200, 201, and 220 in fig. 5B correspond to items 100, 101, and 120 in fig. 5A, respectively.

The magnetomechanical resonance performance of the two bar marker of the embodiment of the present invention corresponding to FIG. 5A is shown in FIG. 6A, which is a marker for a bar from Table V containing about 20mm and about 57 mm; and the magnetomechanical resonance performance of a conventional two strip marker made according to the' 490 patent, corresponding to figure 5B, is shown in figure 6B, using two strips having a length of about 20mm and about 57 mm. As is apparent from fig. 6A-6B, the overall signal amplitude from two marker strips of an embodiment of the present invention is significantly higher than the overall signal amplitude from two conventional marker strips. For the case of the mark of the embodiment of the invention shown in FIG. 5A, the signal amplitude V from the longer dimension bars of the embodiment of the invention₀(shown in FIG. 6A) the value V of a conventional marker strip of longer dimension than its corresponding FIG. 5B₀(shown in fig. 6B) is about 280% higher. For shorter size bars, the signal amplitude V generated by the bars of embodiments of the present invention₁(shown in FIG. 6A) is greater than the signal amplitude V of its corresponding conventional marker strip₁(shown in fig. 6B) 370% higher. Low resonant frequency f shown in FIG. 6A_rThe amplified harmonic amplitude profile around 38610Hz is shown in FIG. 7, which showsThe width of the magnetomechanical resonance is approximately 420Hz, where the width of the magnetomechanical resonance is defined as the width of the frequency at the point where the amplitude becomes the peak amplitude 1/2. For f_rThe signal amplitude has a frequency width of about 660Hz, shown in fig. 8, at a high resonance frequency region around 109070 Hz. This frequency width, hereinafter referred to as the resonance line width, is used to determine the minimum resonance frequency separation (frequency separation) between two adjacent resonance frequencies of two marker strips having slightly different lengths.

Fig. 9-1 shows a marker of an embodiment of the present invention comprising three marker strips 311, 312 and 313 of different lengths randomly selected from the above tables I, II and IV. The cavity space 302 between the two outer housings 300 and 301 contains marker strips 311, 312 and 313 of an embodiment of the present invention, and numeral 330 represents a bias magnet attached to the outer surface of housing 301. The magnetomechanical resonance characteristics of a marker having three bars with lengths of about 25mm, about 38mm and about 52mm and a width of about 6mm are shown in FIG. 10. Note that the observed mechanical resonance is evident in fig. 6A and 7, with a resonant line width of about 400Hz near the low resonant frequency region of about 40000Hz and a resonant line width of about 700Hz near the high resonant frequency region of about 110000Hz, as shown in fig. 6A and 8, indicating that magnetomechanical interference between marker strips having different lengths in the marker of an embodiment of the present invention is not significant, which in turn allows more than three marker strips to be stacked. No magneto-mechanical interference between the stripes is apparent in fig. 9-2 because three marker stripes having different lengths contact each other along a line near the center of the stripe width direction. Similarly, five strips having different lengths of about 30mm, about 38mm, about 42mm, about 47mm and about 52mm and a width of about 6mm were selected from the strips of tables I, II, IV and V and marked. The resonance characteristics of the five-bar tag are shown in fig. 11. A summary of the resonant characteristics of the marker of embodiments of the present invention utilizing marker strips of different lengths is provided in Table VII.

As shown in Table VII, the resonance signal V_0maxAnd V_1maxAt the corresponding resonance frequency f from the coded marker of the invention_r。

TABLE VII

Marking a sample	V_0max(mV)	V_1max(mV)	Strip Length (mm)
				No.1 (offset 461A/m)
fr1＝51,300	92	43	42
				fr2＝61,250	104	48	35
No.2 (offset 301A/m)
				fr1＝38,070	133	90	57
fr1＝109,070	55	10	20
				No.3 (offset 360A/m)
fr1＝37,880	100	57	57
				fr2＝57,260	69	24	38
fr3＝108,440	45	3	20
				No.4 (offset 420A/m)
fr1＝46,100	65	28	47
				fr2＝57,100	53	24	38
fr3＝72,720	61	14	30
				No.5 (offset 399A/m)
fr1＝41,590	92	47	52
				fr2＝57,070	75	3	38

fr3＝87,060	59	12	25
				No.6 (offset 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 (offset 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 marker strip width and thickness are about 6mm and about 28 μm, respectively.

Resonance signal V given in Table VII_0maxAnd V_1maxClearly sufficient to be detected within the electronic article identification system of an embodiment of the present invention. The data in Table V yields the resonant frequency f_rAnd the length of the strip, the relationship being:

f_r＝2.1906×10⁶//(Hz)

where l is the length of the strip in mm. Using this relationship consistent with equation (1), the variability (variabilty) of the resonant frequency caused by the tolerance of cutting the tape to a predetermined length is determined as follows. f. of_rThe above relationship between and l yields Δ f_r/Δl＝-2.906×10⁶/2l²Wherein Δ f^rIs the change in resonant frequency due to the change in bar length deltal. The mark strip cut tolerance achievable using a commercially available tape cutter is determined by comparing the nominal or target strip length to the actual length given in table V. For example, a bar of 18.01mm in length in Table V has a target bar length of 18mm, resulting in a cut tolerance of 0.01 mm. Using the cutting machine tolerances thus obtained, the frequency variability Δ f due to the strip length variability is calculated^rThe frequency change rate Δ f^rIs in the range of about 3Hz for shorter strips to about 400Hz for longer strips. Since the resonance linewidth of the longer strip is about 400Hz, as shown in fig. 7, and about 700Hz for the shorter strip, as shown in fig. 8, the minimum frequency separation recognizable in the electronic article identification system of an embodiment of the present invention is determined to be about 800 Hz. Thus, to ensure that no false identifications occur, a resonant frequency separation of 2kHz is selected to determine the number of identifiable items in the selected universe, wherein the resonant frequency separation is greater than twice the minimum identifiable resonant frequency separation. The marker bars listed in Table V cover a resonant frequency range of about 34000Hz to about 120000Hz, covering a resonant frequency band of about 86000 Hz. Using 2kHz resonant frequency separation for error-free identification, as determined above, the number of electronically identifiable items when the tag has only one stripe becomes 43, when the tag of embodiments of the present invention has tags with 2, 3, 4, and 5 tag stripes of different lengthsWhen used in the coded electronic article identification system of the present invention, the number of electronically identifiable articles is increased to approximately 1800, 7400, 2.96 x 10, respectively, in a particular universe⁶And 1.155X 10⁸. The number of identifiable or encoded items may be further increased by adding more marker strips and/or changing the level of the bias field within the marker.

The coded marker 501 described above is effectively used in an electronic article identification system of an embodiment of the present invention, as shown in fig. 12. In fig. 12, an item 502 to be identified bearing a coded marker 501 of an embodiment of the present invention is placed within an interrogation zone 510, the interrogation zone 510 flanked by a pair of interrogation coils 511. The coil 511 emits an AC magnetic field with a varying frequency fed by an electronic device 512 towards the item to be identified 502, the electronic device 512 comprising a signal generator 513 and an AC amplifier 514, the electronic device 512 being controlled in its open-close operation by an electronic circuit box 515. When the item 502 is placed within the area 510, the electronic circuitry box 515 turns on the interrogating AC field frequency sweeping from the lowest frequency to the highest frequency, the range of which depends on the predetermined frequency range of the marker. In such a frequency sweep, the resonant signal from the coded marker 501 of an embodiment of the present invention is detected within a pair of signal receiving coils 516, resulting in a resonant signal profile as exemplarily shown in FIG. 11. The signal profile obtained by the signal detector 517 is stored in the computer 518, and the computer 518 is programmed to identify the sequence of resonant frequencies encoded in the coded marker 501 of an embodiment of the present invention. When the identification is complete, the computer 518 sends a signal reporting result of the identification to the identifier 519 and the electronic circuit box 515 to reset the system. If so desired, the coded marker of embodiments of the present invention may be deactivated by demagnetizing the bias magnet within the marker after the item 502 leaves the interrogation zone 510.

The coded electronic article identification system provided above is used for identifying an article by scanning an AC excitation field having a varying frequency. In certain cases, delayed identification is required, which can be achieved by tracking V as shown in FIGS. 3, 5(a), 10 and 11₁To be implemented. Electrically this is by programming the patternComputer 517 in 12 to process V as a function of scan frequency₁To be realized.

Example 1

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

Example 2

Magneto-mechanical performance was determined in a configuration arranged with a pair of coils supplying a static bias field, and the voltage appearing in the coil was detected by measuring a signal compensated by a compensating coil (bucking coil) by a voltmeter and oscilloscope. The measured voltage is thus associated with the detection coil and represents the relative signal amplitude. The excitation AC field is supplied by a commercially available function generator and Alternating Current (AC) amplifier. The signal voltages from the voltmeter were tabulated and commercially available computer software was used to analyze and process the collected data.

Example 3

Commercially available DC BH loop measurement equipment was used to measure magnetic induction B as a function of applied field H. For AC BH loop measurements, an excitation coil-detection coil assembly similar to example 4 was used, and the output signal from the detection coil was fed to an electronic integrator. The integrated signal is then 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 loop. For both AC and DC cases, the applied field and the direction of measurement are along the length of the marker strip.

Example 4

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

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

In the case of selection, encoding is performed by cutting an amorphous magnetostrictive alloy ribbon whose magnetic anisotropy direction is perpendicular to the ribbon axis into rectangular strips having a predetermined length and a length/width ratio of more than 3.

Further, where optional, the rectangular strips have a strip width of from about 3mm to about 15 mm.

In an embodiment of the invention, the rectangular bar has a slope of the resonant frequency versus the bias field from about 4Hz (A/m) to about 14Hz (A/m).

Where selected, the rectangular strip has a length greater than about 18mm when the strip has a width of 6 mm.

Further, the rectangular bar optionally has a magnetomechanical resonance frequency of less than about 120000 Hz.

In 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 0.7 tesla and about 1.1 tesla.

In an embodiment of the invention, the coded marker comprises at least two marker-strips having different lengths. In the optional case, the coded marker comprises five marker-strips having different lengths.

In an embodiment of the present invention, the coded marker has a magnetomechanical resonance frequency between about 30000 and about 130000 Hz.

In embodiments of the present invention, for a coded marker having two and five marker-strips, respectively, the coded marker has a marker band comprising up to about 1800 and about 1.15 x 10⁸An electronically identifiable universe of separately identifiable items.

In the inventionIn an embodiment, the coded marker has a code pattern comprising more than 1.15 × 10⁸An electronically identifiable universe of separately identifiable items.

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

Further, in selected embodiments of the present invention, the electronic article identification system has the ability to decode the encoded information of the encoded marker. The coded marker is adapted to resonate mechanically at a preselected frequency and comprises a plurality of ductile magnetostrictive strips cut to a predetermined length from an amorphous ferromagnetic alloy ribbon having a curvature along the ribbon length and exhibiting magnetomechanical resonance with a static bias field under excitation by an alternating magnetic field, the magnetostrictive strips having a direction of magnetic anisotropy perpendicular to the ribbon axis, wherein at least two of the magnetostrictive strips are adapted to be magnetically biased to resonate at a single different one of the preselected frequencies. The electronic article identification system includes one of: a pair of coils emitting an AC excitation field aimed at the coded marker to form an interrogation zone; a pair of signal detection coils receiving encoded information from the encoded marker; an electronic signal processing device having an electronic computer with software to decode the information encoded on the coded marker; or an electronic device that identifies the coded marker. Thus, in addition to providing identification of the coded marker, the electronic article identification system may identify an article to which the coded marker is attached.

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

1. A coded marker of a magnetomechanical resonant electronic article identification system, for mechanically resonating at a preselected frequency, said coded marker comprising: a plurality of ductile magnetostrictive strips cut to predetermined lengths from an amorphous magnetostrictive ferromagnetic alloy ribbon having a curvature along the length of the ribbon and exhibiting magnetomechanical resonance with a static bias field under excitation by an alternating magnetic field, said magnetostrictive strips having a direction of magnetic anisotropy perpendicular to the ribbon axis, wherein at least two of said magnetostrictive strips each serve for magnetic biasing and resonate at a different preselected frequency.

2. A coded marker according to claim 1, wherein the radius of curvature of the ductile magnetostrictive strip is less than 100 cm.

3. A coded marker according to claim 1, wherein the encoding is performed by cutting an amorphous magnetostrictive ferromagnetic alloy ribbon with a direction of magnetic anisotropy perpendicular to the ribbon axis into rectangular strips having a predetermined length and a length to width ratio greater than 3.

4. A coded marker according to claim 3, wherein the magnetostrictive strip has a strip width in the range from 3mm to 15 mm.

5. The coded marker of claim 4, wherein the magnetostrictive strip has a slope of resonant frequency versus bias field ranging from 4Hz/(A/m) to 14 Hz/(A/m).

6. A coded marker according to claim 4, wherein the magnetostrictive strip has a length greater than 18mm when the strip width is 6 mm.

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

8. The coded marker of claim 1, wherein the amorphous magnetostrictive ferromagnetic alloy ribbon has a saturated magnetostriction between 8ppm and 18ppm and a saturated induction between 0.7 tesla and 1.1 tesla.

9. The coded marker of claim 8, wherein the amorphous ferromagnetic alloy of the amorphous magnetostrictive ferromagnetic alloy ribbon has a Fe-based basis_a-Ni_b-Mo_c-B_dWherein a, B, C and d are numbers in atomic%, 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 3 atomic% of Mo can be substituted by at least one of Co, Cr, Mn and Nb, and up to 1 atomic% of B can be substituted by at least one of Si and C.

10. The coded marker of claim 8, wherein the amorphous ferromagnetic alloy of the amorphous magnetostrictive ferromagnetic alloy ribbon comprises 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_36.9Ni_41.3Mo_4.1B_17.8、Fe_35.56Ni_42.56Mo_4.00B_17.88、Fe₄₀Ni₃₈Mo₄B₁₈Or Fe_38.0Ni_38.8Mo_3.9B_19.3。

11. The coded marker of claim 1, wherein the coded marker comprises at least two magnetostrictive strips having different lengths.

12. The coded marker of claim 11, wherein the coded marker comprises five magnetostrictive strips having different lengths.

13. The coded marker of claim 12, wherein the coded marker has a magnetomechanical resonance frequency between 30000 and 130000 Hz.

14. The coded marker of claim 11, which isThe coded marker has an electronically identifiable universe of respectively identifiable items of up to 1800 for a coded marker having two magnetostrictive strips; for a coded marker having five magnetostrictive strips, there are up to 1.15 × 10⁸Respectively identifiable objects of (a).

15. The coded marker of claim 13, wherein the coded marker has a mark size of more than 1.15 x 10⁸Respectively identifiable objects of (a).

16. A coded marker according to claim 1, wherein the magnetostrictive strip has a radius of curvature between 20cm and 100 cm.

17. An electronic article identification system having the capability of decoding encoded information of an encoded marker, wherein said encoded marker comprises a plurality of ductile magnetostrictive strips cut to a predetermined length from an amorphous magnetostrictive ferromagnetic alloy ribbon having curvature along the ribbon length direction and exhibiting magnetomechanical resonance with a static bias field under excitation by an alternating magnetic field, the magnetostrictive strips having a direction of magnetic anisotropy perpendicular to the ribbon axis, and wherein each of at least two of said magnetostrictive strips is adapted to be magnetically biased and resonate at a different preselected frequency, said system comprising:

a pair of coils emitting an AC excitation field of varying frequency aimed at the coded marker to form an interrogation zone;

a pair of signal detection coils receiving encoded information from the encoded marker; and

an electronic signal processing device having an electronic computer with software to decode the information encoded on the coded marker.