HK1193209A - Magnetomechanical sensor element and application thereof in electronic article surveillance and detection system - Google Patents

Description

Magnetomechanical sensor element and its use in electronic article surveillance and detection system

Technical Field

The present invention relates to ferromagnetic amorphous alloy strips (ribbon) and magneto-mechanical sensor elements (also called markers or tags) for use in electronic article surveillance systems and electronic article recognition systems, the sensor elements comprising one or more rectangular strips (strip) based on such amorphous magnetostrictive material that mechanically vibrates in an Alternating (AC) magnetic field at a resonance frequency that varies with an applied electrostatic field, thereby effectively exploiting the magneto-mechanical effect of the markers. The invention also relates to an electronic article surveillance system and an electronic article identification system using such a sensor.

Background

Magnetostriction of a magnetic material is a phenomenon in which a dimensional change occurs when an external magnetic field is applied to the magnetic material. A material is called a "positive magnetostrictive material" if it undergoes a dimensional change in an elongated manner when magnetized. If the material is a "negatively magnetostrictive material," the material contracts when magnetized. In either case, therefore, the magnetic material vibrates when it is in an alternating magnetic field. When a static magnetic field is applied together with an alternating magnetic field, the mechanical vibration frequency of the magnetic material changes with the applied static field through magnetoelastic coupling (magneto-elastic coupling). This is commonly referred to as the Δ E effect, which is illustrated, for example, in Physics of Magnetism, S.Chikazumi (New York: John West International publications, 1964, page 435). Here, e (H) represents young's modulus, which is a function of the applied magnetic field H. Vibration or resonance frequency f of the material_rIs related to E (H) by the following 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.

It was first proposed in us patents 4,510,489 and 4,510,490 (hereinafter, referred to as '489 and' 490 patents) to utilize the aforementioned magnetoelastic or magnetomechanical effects in electronic article surveillance systems. Such monitoring systems are advantageous in that they provide 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 by a hard magnetic ferromagnet (a material with high coercivity) that provides a static field known as a bias field to establish the magnetomechanical coupling. The ferromagnetic marker material is preferably a magnetostrictive amorphous alloy ribbon because the efficiency of the magnetomechanical coupling within these magnetostrictive amorphous alloys is very high. As shown in the above equation (1), the mechanical resonance frequency f is determined substantially by the length of the alloy strip and the bias field strength_r。

When an interrogation signal tuned to a resonant frequency is encountered in an electronic article surveillance system, the marker material responds with a large signal field that is detected by a receiver in the system.

A variety of amorphous ferromagnetic materials are contemplated in the '489 and' 490 patents for use in electronic article surveillance systems 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, commercially available based on amorphous Fe-Ni-Mo-BThe 2826MB alloy is widely used, but other systems based on magnetic harmonic generation/detection result in accidental triggering by a magnetomechanical resonance marker. This is because the magnetomechanical resonance markers used at the time sometimes exhibit a non-linear 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. patents 495231, 5539380, 5628840, 5650023, 6093261 and 6187112. Although the new marker materials are generally superior to the materials used in the monitoring systems of the original patents '489 and' 490, such as in U.S. patent 6299702 (hereinafter referred to as "U.S. patent"), the new marker materials are useful in the monitoring systems of the previous patentsIn the marker material disclosed in the' 702 patent) found somewhat better magnetomechanical properties. These new marker materials require complex heat treatment processes to achieve the desired magnetomechanical properties as disclosed, for example, in the' 702 patent. Clearly, new magnetomechanical marker materials are required that do not require such a complex post-ribbon (post-ribbon) manufacturing process, and the inventions of U.S. patents 7205893 (hereinafter, patent ' 893), 7320433 (hereinafter, patent ' 433) and 7561043 (hereinafter, patent ' 043) provide such marker materials that do not cause the above-mentioned "contamination problem" and have high magnetomechanical properties. The marker strip of the' 702 patent is widely used for markers having two strips, as disclosed in U.S. patent 6359563. Due to the fact that the two strips have the same radius of curvature in the width direction along the strips (since it happens that they are handled in exactly the same way), according to the' 702 patent, the two strips contact each other at a plurality of points on the strip surface, so that the magnetomechanical vibrations on the strips are damped, thus reducing the effectiveness of the marker. This drawback is alleviated using the conditions of the ' 893, ' 433 and ' 043 patents. In maximizing the effect of the magnetomechanical resonance upon which the patents ' 893, ' 433 and ' 043 are based, a new way of controlling this effect has been discovered, which is the basis of the present invention. Thus, the present invention further enhances the magnetomechanical resonance effect utilized in the ' 893, ' 433, and ' 043 patents. There is also a need for an efficient electronic article surveillance system that utilizes such markers.

Disclosure of Invention

According to an embodiment of the invention, soft magnetic materials are used for markers or sensor elements of electronic article surveillance and identification systems based on magnetomechanical resonance.

Marker materials with enhanced overall magnetomechanical resonance characteristics are made from amorphous alloy strips. Strip-shaped magnetic marker materials having magnetomechanical resonance capabilities are cast on a rotating substrate as taught in U.S. patent No.4142571 (hereinafter, the' 571 patent). When the width of the as-cast strip is wider than the predetermined width of the marker material, the strip is cut to the predetermined width. The strip thus prepared is cut into ductile rectangular amorphous metal marker strips having a predetermined length to produce a magnetomechanical resonance marker using one or more of the marker strips and at least one semi-hard magnet strip for providing a biased static magnetic field.

Electronic article surveillance systems use markers or sensor elements according to embodiments of the present invention. The system has an article interrogation zone in which the magnetomechanical marker or sensor element of the invention is subjected to an interrogation magnetic field at the resonant frequency of the marker strip, the signal excited in response to the interrogation magnetic field being detected by a receiver having an antenna coil pair located in the article interrogation zone. The received magnetomechanical resonance signal is then processed by a signal detection circuit for identifying the marker.

According to an embodiment of the invention, there is provided a sensor element or marker of a magnetomechanical resonance electronic article surveillance system, comprising: at least one ductile magnetostrictive strip cut from a strip of amorphous ferromagnetic alloy. The strip has a strip length direction, a strip plane and a line-like surface pattern having a surface line direction. The magnetic anisotropy direction of the at least one marker strip is located in the strip plane at an angle between 80 degrees and 90 degrees away from the strip length direction, and the surface line direction coincides with the direction of the magnetic anisotropy, the magnetic anisotropy direction being introduced during strip casting by adjusting the casting conditions. The at least one marker strip exhibits magnetomechanical resonance under excitation by an alternating magnetic field having a static bias field.

According to an embodiment of the invention, the amorphous ferromagnetic alloy ribbon has a saturation induction in the range of 0.8 tesla to 1.0 tesla.

According to an embodiment of the invention, the amorphous ferromagnetic alloy ribbon has a saturation magnetostriction in the range of 9ppm to 14 ppm.

According to an embodiment of the invention, the amorphous ferromagnetic alloy strip has a Fe-based_a-Ni_b-Mo_c-B_dWherein a is more than or equal to 35 and less than or equal to 42, b is more than or equal to 38 and less than or equal to 45, c is more than or equal to 0 and less than or equal to 5, and 11<d ≦ 17 and a + B + C + d =100, up to 3 at% of Mo may optionally be replaced by Co, Cr, Mn and/or Nb, and up to 1.5 at% of B may optionally be replaced by Si and/or C.

According to an embodiment of the invention, the amorphous ferromagnetic alloy strip is an alloy having one of the following compositions: fe_41.3Ni_38.2Mo_3.6B_16.3Si_0.6、Fe_37.6Ni_44.9Mo_4.4B_11.5Si_1.35Co_0.1Cr_0.15、Fe_37.2Ni_41.2Mo_3.6B_16.1Si_0.9C_0.6Co_0.1Cr_0.3、Fe_37.1Ni_42.2Mo_3.7B_16.3Si_0.7、Fe_36.9Ni_42.0Mo_3.9B_16.2Si_0.7Co_0.1Cr_0.2、Fe_36.4Ni_42.6Mo_3.9B_15.9Si_0.9Cr_0.3、Fe_36.0Ni_42.3Mo_3.9B_16.6Si_0.8Co_0.1Cr_0.3And Fe_35.8Ni_43.5Mo_3.5B_16.4Si_0.6Co_0.1Cr_0.1。

According to an embodiment of the invention, the at least one marker strip has a discrete length and exhibits a magnetomechanical resonance at a length-dependent frequency.

Wherein selected, the at least one marker band has a length in the range of about 35mm to about 40 mm.

Wherein selected, the at least one marker strip has a marker strip width in a range of about 5mm to about 8 mm.

Wherein selected ones of said marker bands are stacked as shown in fig. 1 or placed in parallel.

According to an embodiment of the invention, the characteristic time constant of the attenuation of the magnetomechanical resonance signal of the at least one marker strip ranges from 1ms to 2 ms.

According to an embodiment of the present invention, the resonance frequency of the at least one marker strip shifts by more than 19kHz from its minimum resonance frequency to its near highest observable resonance frequency.

Wherein the at least one marker strip is selected to have at least one bias magnet strip positioned along the direction of the at least one marker strip.

According to an embodiment of the invention, said at least one marker strip is accommodated in a cavity separate from said bias magnet strip.

According to another embodiment of the invention, an electronic article surveillance system has the capability to detect resonances of sensor elements or markers and comprises a surveillance system tuned to a predetermined surveillance magnetic field frequency, wherein the surveillance system is capable of detecting magnetomechanical resonances from sensor elements. The sensor element is adapted to resonate mechanically at a preselected frequency and has at least one ductile magnetostrictive marker ribbon cut from a ribbon of amorphous ferromagnetic alloy. The strip has a strip length direction, a strip plane and a line-like surface pattern, and the surface pattern has a surface line direction, the magnetic anisotropy direction of the at least one marker strip deviates from the strip length direction by an angle between 80 degrees and 90 degrees and lies within the strip plane, and the surface line direction coincides with the magnetic anisotropy direction, the magnetic anisotropy direction being introduced during strip casting by adjusting the casting conditions. The at least one marker strip exhibits magnetomechanical resonance under excitation by an alternating magnetic field having a static bias field.

Drawings

The present invention will be more fully understood and further advantages will become apparent by reference to the following detailed description of the preferred embodiments and the accompanying drawings, in which:

FIG. 1 is a perspective view illustrating an electronic article surveillance marker tag or sensor element utilizing two magnetomechanical resonance tape having a surface pattern in accordance with an embodiment of the present invention.

Fig. 2 is a graph illustrating the magnetomechanical resonance characteristics of a single strip marker according to an embodiment of the present invention, wherein the resonance frequency is represented by curve 10, the signal voltage at the termination of resonance excitation is represented by curve 11, and the signal voltage at 1ms after the termination of resonance excitation is represented by curve 12.

Fig. 3 is a laser micrograph image of the surface of the amorphous metal strip of the present invention facing the solidified surface of the liquid metal, where the direction of magnetic anisotropy is represented by line AB (line AB is 88 degrees off the length of the strip) and the line AB is aligned with the surface line (surfaceline).

FIG. 4 is a graph illustrating the magnetomechanical resonance characteristics of a single strip marker (of FIG. 3) illustrating the resonance frequency as a function of bias field, according to an embodiment of the present invention.

Fig. 5 is a laser micrograph image of the surface of the amorphous metal strip facing the solidified surface of the liquid metal outside the scope of the present invention, where line AB (line AB is 78 degrees off the length direction of the strip) is the direction of the magnetic anisotropy and line AB coincides with the surface line direction.

FIG. 6 illustrates the magnetomechanical resonance characteristics of the single strip marker of FIG. 5, illustrating the resonance frequency as a function of the bias field.

FIG. 7 illustrates an example of the magnetomechanical resonance characteristics of a single strip marker of an embodiment of the present invention.

FIG. 8 illustrates an example of the magnetomechanical resonance characteristics of a single strip marker of an embodiment of the present invention.

FIG. 9 is a schematic view of an electronic article surveillance system according to an embodiment of the invention.

Detailed Description

Marker materials with enhanced overall magnetomechanical resonance performance are made from amorphous alloy ribbons. As disclosed in the' 571 patent, a strip-shaped magnetic marker material having magnetomechanical resonance capabilities is cast on a rotating substrate. When the as-cast strip is wider than the predetermined width of the marker material, the strip is cut to the predetermined width. The thus prepared ribbon is cut into a ductile rectangular amorphous metal ribbon having a predetermined length to manufacture a magnetomechanical resonance marker using a plurality of such ribbons and at least one semi-hard magnet (semi-hard magnet) ribbon for providing a biased static magnetic field. FIG. 1 illustrates a basic electronic article surveillance marker tag according to an embodiment of the present invention, where 1() () and 101 are outer covers, and 110 and 111 are rectangular amorphous metal strips stacked together as shown and inserted into a cavity region 102. 130 is a line-like surface pattern on the rectangular amorphous metal strip 110. The metal strip 111 has a similar line-like pattern on its surface. 120 are bias magnet strips that are inserted into the cavity region 102 in such a way that the amorphous metal strips 110 and 111 can be mechanically vibrated without physical constraints. In an embodiment of the invention, the amorphous ferromagnetic alloy used to form the marker strip has a Fe-based basis_a-Ni_b-Mo_c-B_dWherein a is more than or equal to 35 and less than or equal to 42, b is more than or equal to 38 and less than or equal to 45, c is more than or equal to 0 and less than or equal to 5, and 11<d ≦ 17 and a + B + C + d =100, up to 3 at% of Mo may optionally be replaced by Co, Cr, Mn and/or Nb, and up to 1.5 at% of B may optionally be replaced by Si and/or C.

In certain embodiments of the present invention, the amorphous ferromagnetic alloy used to form the marker strip has one of the following compositions: fe_41.3Ni_38.2Mo_3.6B_16.3Si_0.6、Fe_37.6Ni_44.9Mo_4.4B_11.5Si_1.35Co_0.1Cr_0.15、Fe_37.2Ni_41.2Mo_3.6B_16.1Si_0.9C_0.6Co_0.1Cr_0.3、Fe_37.1Ni_42.2Mo_3.7B_16.3Si_0.7、Fe_36.9Ni_42.0Mo_3.9B_16.2Si_0.7Co_0.1Cr_0.2、Fe_36.4Ni_42.6Mo_3.9B_15.9Si_0.9Cr_0.3、Fe_36.0Ni_42.3Mo_3.9B_16.6Si_0.8Co_0.1Cr_0.3And Fe_35.8Ni_43.5Mo_3.5B_16.4Si_0.6Co_0.1Cr_0.1. Thus, the casting mold according to the technique and method described in the' 571 patent has the [0025]]An amorphous magnetostrictive alloy of the chemical composition defined in the paragraph. The cast strip has a width of about 100mm and its thickness is about 28 μm. The strip is then cut into narrower strips having different widths. The cut strip is then cut into ductile rectangular strips having a length in the range of about 35mm to about 40 mm. The cut strip was then characterized in the manner described in example 1.

FIG. 2 illustrates the magnetomechanical resonance properties of a typical amorphous alloy ribbon as a candidate for an alloy ribbon of an embodiment of the present invention. Curve 10 shows the magnetomechanical resonance frequency f of the alloy strip_rAs a function of the bias field applied along the length of the strip. Curves 11 and 12 correspond to the signal voltages detected by the method described in example 1 at the start of termination of resonance excitation and at 1msec after termination of resonance excitation, respectively. Points a and B correspond to the maximum signal voltages on the curve 11 and the curve 12, respectively. Point C corresponds to the resonance frequency f being the minimum on curve 10_r. The magnetomechanical resonance characteristic of FIG. 2 is for an embodiment of the invention with Fe_a-Ni_b-Mo_c-B_dMeasured on an alloy of chemical composition, wherein a is more than or equal to 35 and less than or equal to 42, b is more than or equal to 38 and less than or equal to 45, c is more than or equal to 0 and less than or equal to 5, and 11<d ≦ 17 and a + B + C + d =1() (), up to 3 atomic% of Mo is optionally replaced by Co, Cr, Mn and/or Nb and up to 1.5 atomic% of B is optionally replaced by Si and/or C. Table 1 is a list of representative alloys according to the invention and gives the saturation induction B_sValues of (A), these B_sThe value is determined by the method described in example 2. FIG. 2 is the magnetomechanical resonance characteristics obtained for alloy D of Table I.

TABLE I

As shown in table I, the amorphous alloy has a saturation induction in the range of about 0.8 tesla to about 1.0 tesla.

The magnetomechanical resonance characteristics of the strip material cut from the alloys listed in table I, characterized by the method of example 1, are compiled in table II below. In the table, H_minPhysical quantity f of_rAnd physical quantity H_minCorresponding to the resonance frequency and the bias magnetic field, respectively, at point C in fig. 2. The physical quantity FS is the resonance frequency shift of the bias field from point C to 120A/m. Ho, as shown by point A in FIG. 2_maxCurve 10 is at a maximum value Vo_maxBias field in time. Hl, as shown by point B in FIG. 2_maxIs that the curve 11 is at a maximum value Vl_maxBias field in time. The ratio Vl/Vo represents the efficiency of the magnetomechanical resonance of the strip, this ratio following the following relationship:

V(t)／Vo=exp(-t／τ) (2)

where t is the time measured after termination of the AC field excitation, τ is the characteristic time constant of the resonance signal decay, and Vo is the resonance signal at t = 0. Therefore, the physical quantity Vl defined above is a signal voltage detected at t =1 ms. The last column of table II gives the width of the resonant marker strip. The table also includes resonance characteristics obtained for a commercially available product prepared according to the heat treatment method described in the' 702 patent.

TABLE II

The resonance characteristic described in fig. 2 is important when designing a resonance marker with deactivation capability (deactivation capability). An active surveillance marker tag has a bias magnet as shown in fig. 1 so that the tag is magnetically resonant at a given frequency. During deactivation, the marker is subjected to a bias field change to cause a shift in the resonant frequency. The resonance frequency shift FS as defined above must be unique in order to be effectively deactivated. It is considered that a resonance frequency shift exceeding 1.5kHz is sufficient, but in order to ensure deactivation, the lower limit of the required resonance frequency shift is set to 1.9kHz in the present invention. By observing Table II above, strip material satisfying a frequency shift of 1.9kHz or more exhibits a characteristic resonance decay time τ of greater than 1ms, indicating that these strip materials are effective in maintaining a resonance signal, which is desirable for reliable electronic article surveillance. The strip tapes G-2 and G-3 have chemical compositions within the scope of the embodiments of the present invention, which indicates that the mere chemical composition is insufficient to provide a product according to the embodiments of the present invention. Note that for alloy strips G-2 and G-3, FS is less than 1.9kHz and the signal voltage Vl_maxWell below 50mV, this voltage is too low for efficient signal detection. Further experiments were carried out to complete the present invention as described below.

The casting process of the' 571 patent involves a pool of molten metal that is quenched to rapidly cool into a continuous strip on a molten metal solidification surface, which is essentially a rotating wheel having a high thermal conductivity. Under these conditions, it is inevitable that the molten metal bath is not static but dynamic, usually accompanied by periodic oscillations. This introduces a periodic line-like surface pattern on the surface of the cast strip that is invisible to the naked eye. One such example is illustrated in fig. 3. This type of linear surface pattern (which is invisible to the naked eye but is clear under the laser microscope described in example 3) was observed on the surface of the strip facing the molten metal solidification surface on the rotating cooling wheel. The direction of the surface natural line deviates from the strip length direction by approximately 90 degrees. It is known in the scientific art of magnetic materials that such surface patterns affect the magnetic properties of the strip. According to an embodiment of the invention, this effect is truly reflected in the magnetomechanical resonance characteristics of the strip specified by alloy B in table I. The magnetomechanical properties of the alloy B strip were characterized using the following equations established in "phenometric Model for Magnetization, Magnetization and. DELTA.E Effect in Field-connected Amorphous Ribbens", written by P.T. Squire ("Journal of Magnetic and Magnetic Materials", Vol. 87, p. 299-310, (1990)):

E／E_s=1／{1+(9λ_s ²E_s／8K)F(h；θ，γ)} (3)

and isWherein E is the Young's modulus in the above equation (1) and E_sIs the saturation modulus (K) and the magnetic anisotropy energy, h is equal to (applied field)/(2K/M)_s) (wherein, M_sIs saturation magnetization), γ =3 λ_sσ/4K (σ: internal strain), θ is the angle of the magnetic anisotropy direction with respect to the strip length direction,is the saturation magnetization M_sAnd the magnetic anisotropy K. The magnetomechanical resonance data obtained for strip alloy B cut strip listed in table II as alloy strip B-1 was fitted to equation (3) above, as shown in fig. 4, curve 41 being the measured curve and curve 42 being the calculated curve using equation (3). From this curve fit, the result is θ =88 degrees, which is represented by line AB in fig. 3. Thus, the surface line direction of the surface pattern in fig. 3 coincides with the direction of the magnetic anisotropy in the strip. Similar curve fitting was performed on strips cut from strip alloy G in table I listed in table II as alloy strip G-2, which strips exhibited the line-like surface pattern of fig. 5. The results of the curve fitting are given in fig. 6, where curve 61 is the measured curve and curve 62 is the calculated curve using equation (3), which shows that the surface line direction coincides with the direction of the magnetic anisotropy in the strip, i.e. is deviated from the strip length direction by 78 degrees as shown by line AB in fig. 5. A similar curve fit was performed on the strip G-1 of table II, the results of which are shown in fig. 7, wherein curve 71 is the measured curve and curve 72 is calculated using equation (3). In this case, the angle θ of the magnetic anisotropy deviates from the strip length direction by 88 degrees. Another curve fit was performed on the strip a-2 of table II, the results of which are shown in fig. 8, where curve 81 is the measured curve and curve 82 is calculated using equation (3), indicating θ =82 degrees. The surface pattern introduced during strip casting ensures a high level of magnetomechanical resonance properties of the cast strip. Furthermore, the surface pattern on the strip provides a number of technical advantages, for example, making the quality control process faster and easier, which considerably improves the yield of strip products. For example, in contrast, the products according to the ' 433, ' 893 and ' 043 patents require lengthy quality control resulting from the following steps: the method includes the steps of cutting the strip into a given width, cutting the strip into a predetermined length, and measuring the magnetomechanical resonance characteristics to determine whether the strip meets specifications. The products of the ' 433, ' 893 and ' 043 patents can be eliminated by using a tape having a surface pattern according to an embodiment of the present inventionAll or part of these additional steps in the quality control of the product.

A magnetomechanical resonance curve fit was performed on a representative strip having the chemical composition determined in natural paragraph [0025 ]. The results of curve fitting for the representative alloys listed in table I are given in table III.

TABLE III

Table III shows that: magnetic anisotropy at 250J/m³To 700J/m³Of (d); saturated magnetostriction lambda_sIn the range of 9.5ppm to 14.5 ppm; and the magnetic anisotropy direction is in a range of 78 degrees to 90 degrees with respect to the stripe length direction. Physical quantity E_sClose to 1.5 × 10¹¹N／m². By comparing the data in tables II and III, the inventors of the present invention have obtained a preferred range of directions of magnetic anisotropy in the strip: is offset from the strip length direction by an angle between 80 degrees and 90 degrees. Therefore, the strip tapes G-2 and G3 in tables II and III are not suitable as magnetomechanical resonance elements according to embodiments of the present invention, since they show Vl at 37 and 34, respectively_maxValue despite their chemical composition in the natural paragraph [0025]Within the preferred compositional ranges given in (1).

In one aspect of a magnetomechanical resonance element according to an embodiment of the invention, the signal voltage emanating from the magnetic element is proportional to the volume of the element. For example, as shown in Table II, Vo for a strip having a width of 7mm_maxIn the range between 240mv and 320mv, and Vo for a strip of 6mm width_maxIn the range between 150mV and 214 mV. Therefore, if a larger detection signal is required, the width of the magnetomechanical element is preferably 7 mm.

In practical electronic article surveillance systems currently in use in the industry, either a single strip or a two strip configuration is employed. Thus, the performance test of example 1 was used to evaluate the magnetomechanical properties of two strip markers, and the results are listed in table IV. The first letter, such as a, corresponds to the alloy listed in table I.

TABLE IV

Since the signal Vl is a tracking signal in commercially available electronic article surveillance systems, a high voltage amplitude of V1 is preferred. In a commercially available product, the maximum value Vl of V1 in the signal detection circuit of example 1_maxIs in the range of 160 to 190 mv. As shown in Table IV, the strip made from alloys A, B, C, D, E, F and H in Table I exhibited a Vl in excess of 160mv_max. All of these strip tapes had FS over 1.9kHz and a characteristic time constant τ over 1.8ms, indicating that these tapes are suitable for use in two-tape markers in commercially available electronic article surveillance systems. The two-strip tape marker G-4 having the strip surface pattern of FIG. 5 exhibited a Vl of 39mv_maxThe Vl_maxToo low to be used in electronic article surveillance markers in commercially available systems.

A marker having a rectangular amorphous magnetostrictive alloy ribbon or a plurality of rectangular amorphous magnetostrictive alloy ribbons (such as illustrated in fig. 1) made according to an embodiment of the invention is used in an electronic article surveillance system shown in fig. 9. As shown, an item 902 having a marker 901 according to an embodiment of the invention is placed in an interrogation zone 903 equipped with an AC field excitation coil pair 912 driven by electronics 910 including a signal generator 913 and an AC amplifier 914. The electronics 910 are programmed to energize the marker strip of an embodiment of the present invention for a predetermined period of time, whereupon the energizing is terminated. After termination of the excitation in the coil 912, the signal detected in the signal receiving coil 911 is fed to a signal detection circuit box 916, wherein the signal detection circuit box 916 is adjusted to the resonance frequency of the marker in the interrogation zone 903. The circuit box 915 controls the termination of the excitation field and the start of signal detection. The signal detector 916 is connected to the identifier 917, and the identifier 917 transmits the inquiry result to the interrogator. When an item 902 having an electronically monitored marker 901 according to an embodiment of the present invention leaves interrogation zone 903, the marker is deactivated by a demagnetizing field, if necessary.

Example 1

The magnetomechanical properties were determined in an apparatus in which a coil pair was used to provide a static bias field and the voltage compensated by a compensation coil (bucking coil) in the presence of the signal detection coil was measured by an oscilloscope and voltmeter. Thus, the measured voltage is correlated to the detection coil and is used to represent the relative signal amplitude. The excitation AC field is provided by a commercially available function generator. The function generator is programmed to excite the marker strip or strips of the present invention for 3msec, after which the excitation is terminated and the measurement signal decays over time. The data thus obtained were processed and analyzed using commercially available computer software.

Example 2

The magnetic induction B as a function of the applied magnetic field H was measured using a commercially available DC BH hysteresis loop measuring device. The magnetic induction B does not change as the applied field approaches 4000A/m, indicating that the material is already magnetically saturated. The magnetic induction at 4000A/m is then identified as the saturation induction B_s。

Example 3

Conventional optical microscopes cannot generate sufficient contrast in images of strip surface patterns that are invisibly visible to the naked eye. However, commercially available laser microscopes improve the stripe surface image. Examples are shown in fig. 3 and 5.

According to an embodiment of the invention, the at least one marker strip has a discrete length and exhibits a magnetomechanical resonance at a frequency related to the length.

According to an embodiment of the invention, an electronic article surveillance system has the capability of detecting the resonance of a sensor element or marker and comprises a surveillance system tuned to a predetermined surveillance magnetic field frequency, wherein the surveillance system detects a marker adapted to mechanically resonate at a preselected frequency and has at least one ductile magnetostrictive marker strip cut from an amorphous ferromagnetic alloy strip having a direction of magnetic anisotropy at an angle between 80 degrees and 90 degrees out of the strip length direction and in the strip plane, the direction of magnetic anisotropy being introduced by adjusting the casting conditions during strip casting, and the amorphous ferromagnetic alloy strip exhibiting magnetomechanical resonance under alternating magnetic field excitation and under static bias fields.

According to an embodiment of the invention, the amorphous ferromagnetic alloy has a Fe-based_a-Ni_b-Mo_c-B_dWherein 35 ≦ a ≦ 42, 38 ≦ B ≦ 45, 0 ≦ C ≦ 5, 11 ≦ d ≦ 17 and a + B + C + d =100, up to 3 atomic% of Mo is optionally replaced by Co, Cr, Mn and/or Nb, and up to 1.5 atomic% of B is optionally replaced by Si and/or C.

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 (14)

1. A sensor element of a magnetomechanical resonance electronic article surveillance system, the sensor element comprising:

at least one ductile magnetostrictive marker ribbon cut from a strip of amorphous ferromagnetic alloy,

wherein the strip has a strip length direction, a strip plane and a line-like surface pattern, the surface pattern having a surface line direction,

the direction of magnetic anisotropy of the at least one marker strip deviates from the strip length direction by an angle between 80 and 90 degrees and lies in the strip plane,

the surface line direction coincides with the magnetic anisotropy direction,

the magnetic anisotropy direction is introduced during strip casting by adjusting the casting conditions, and

the at least one marker strip exhibits magnetomechanical resonance under excitation by an alternating magnetic field having a static bias field.

2. The sensor element of claim 1, wherein the amorphous ferromagnetic alloy ribbon has a saturation induction in a range of 0.8 tesla to 1.0 tesla.

3. The sensor element of claim 2, wherein the amorphous ferromagnetic alloy ribbon has a saturation magnetostriction in a range of 9ppm to 14 ppm.

4. The sensor element of claim 2, wherein the amorphous ferromagnetic alloy strip has a Fe-based basis_a-Ni_b-Mo_c-B_dWherein 35 ≦ a ≦ 42, 38 ≦ B ≦ 45, 0 ≦ C ≦ 5, 11 ≦ d ≦ 17 and a + B + C + d =100, up to 3 atomic% of Mo is optionally replaced by Co, Cr, Mn and/or Nb, and up to 1.5 atomic% of B is optionally replaced by Si and/or C.

5. The sensor element of claim 4, wherein the amorphous ferromagnetic alloy strip is an alloy having one of the following compositions: fe_41.3Ni_38.2Mo_3.6B_16.3Si_0.6、Fe_37.6Ni_44.9Mo_4.4B_11.5Si_1.35Co_0.1Cr_0.15、Fe_37.2Ni_41.2Mo_3.6B_16.1Si_0.9C_0.6Co_0.1Cr_0.3、Fe_37.1Ni_42.2Mo_3.7B_16.3Si_0.7、Fe_36.9Ni_42.0Mo_3.9B_16.2Si_0.7Co_0.1Cr_0.2、Fe_36.4Ni_42.6Mo_3.9B_15.9Si_0.9Cr_0.3、Fe_36.0Ni_42.3Mo_3.9B_16.6Si_0.8Co_0.1Cr_0.3And Fe_35.8Ni_43.5Mo_3.5B_16.4Si_0.6Co_0.1Cr_0.1。

6. The sensor element of claim 1, wherein the at least one marker strip has a discrete length and exhibits magnetomechanical resonance at a frequency related to the length.

7. The sensor element of claim 6, wherein the at least one marker strip has a length ranging from about 35mm to about 40 mm.

8. The sensor element of claim 7, wherein the at least one marker strip has a marker strip width in a range of about 5mm to about 8 mm.

9. The sensor element of claim 8, wherein a characteristic time constant of the attenuation of the magnetomechanical resonance signal of the at least one marker strip is in a range of about 1msec to about 2 msec.

10. The sensor element of claim 9, wherein the resonant frequency of the at least one marker strip shifts by more than 1.9kHz from its minimum resonant frequency to its near-maximum observable resonant frequency.

11. The sensor element of claim 1, wherein two marker strips are stacked or placed in parallel.

12. The sensor element of claim 1, further comprising at least one strip of bias magnets positioned in a direction along the at least one marker strip.

13. The sensor element of claim 12, wherein the at least one marker strip is housed in a cavity separate from the bias magnet strip.

14. An electronic article surveillance system, comprising:

a monitoring system tuned to a predetermined monitoring magnetic field frequency,

wherein the monitoring system is capable of detecting magnetomechanical resonance from a sensor element,

the sensor element is adapted to resonate mechanically at a preselected frequency and has at least one ductile magnetostrictive marker ribbon cut from a strip of amorphous ferromagnetic alloy,

the strip having a strip length direction, a strip plane and a line-like surface pattern, the surface pattern having a surface line direction,

the direction of magnetic anisotropy of the at least one marker strip deviates from the strip length direction by an angle between 80 and 90 degrees and lies in the strip plane,

the surface line direction coincides with the magnetic anisotropy direction,

the magnetic anisotropy direction is introduced during strip casting by adjusting the casting conditions, and

the at least one marker strip exhibits magnetomechanical resonance under excitation by an alternating magnetic field having a static bias field.