Patent Grant
7561043
1. Field of the Invention
The present invention relates to ferromagnetic amorphous alloy ribbon and to a marker for use in an electronic article surveillance system, the marker consisting of one or a plurality of rectangular strips based on an amorphous magnetostrictive material that vibrates in an alternating magnetic field mechanically at a resonant frequency varying with an applied static magnetic field, whereby the magnetomechanical effect of the marker is effectively utilized. The present invention is also directed to an electronic article surveillance system utilizing such a marker.
2. Background of the Invention
Magnetostriction of a magnetic material is a phenomenon in which a dimensional change takes place upon application of an external magnetic field on the magnetic material. When the dimensional change is such that the material elongates upon its being magnetized, the material is termed “positive-magnetostrictive”. When a material is “negative-magnetostrictive”, the material shrinks upon its magnetization. Thus in either case, a magnetic material vibrates when it is in an alternating magnetic field. When a static magnetic field is applied along with the alternating field, the frequency of the mechanical vibration of the magnetic material varies with the applied static field through magneto-elastic coupling. This is commonly known as ΔE effect, which is described, for example, in “Physics of Magnetism” by S. Chikazumi (John Wiley & Sons, New York, 1964, page 435). Here E(H) stands for Young's modulus, which is a function of applied magnetic field H, and the material's vibrational or resonance frequency fr is related to E(H) through
fr=(½l)[E(H)/ρ]1/2, (1)
where l is the length of the material and ρ is the mass density of the material.
The magneto-elastic or magneto-mechanical effect described above is utilized in electronic article surveillance systems which were first taught in the U.S. Pat. Nos. 4,510,489 and 4,510,490 (hereinafter the '489 and '490 patents). Such surveillance systems are advantageous systems, in that they offer a combination of high detection sensitivity, high operating reliability and low operating costs.
A marker in such systems is a strip, or a plurality of strips, of known length of a ferromagnetic material, packaged with a magnetically harder ferromagnet (material with a higher coercivity) that provides a static field termed as bias field to establish peak magneto-mechanical coupling. In accordance with embodiments of the invention, ferromagnetic marker material is an amorphous alloy ribbon, since the efficiency of magneto-mechanical coupling in the alloys is very high. The mechanical resonance frequency, fr is determined essentially by the length of the alloy ribbon and the bias field strength, as Equation (1) above indicates.
When an interrogating signal tuned to the resonance frequency is encountered in a surveillance system, the marker material responds with a large signal field which is detected by a receiver in the system.
Several amorphous ferromagnetic materials were considered for electronic article surveillance systems based on magnetomechanical resonance described above in the original '489 and '490 patents and included amorphous Fe—Ni—Mo—B, Fe—Co—B—Si, Fe—B—Si—C and Fe—B—Si alloys. Of the alloys, a commercially available amorphous Fe—Ni—Mo—B based METGLAS®2826MB alloy was used extensively until accidental triggering, by a magnetomechanical resonance marker, of other systems based on magnetic harmonic generation/detection. This occurs because a magnetomechanical resonance marker used at that time sometimes exhibited non-linear BH characteristics, resulting in generation of higher harmonics of the exciting field frequency. To avoid this problem, sometimes called a system “pollution problem,” a series of new marker materials were invented, examples of which were disclosed in U.S. Pat. Nos. 5,495,231, 5,539,380, 5,628,840, 5,650,023, 6,093,261 and 6,187,112. Although the new marker materials perform, on average, better than the materials utilized in the surveillance systems of the original '489 and '490 patents, somewhat better magnetomechanical performance was found in the marker materials disclosed, for example, in U.S. Pat. No. 6,299,702 (hereinafter, the '702 patent). The new marker materials require complicated heat-treatment processes to achieve desired magnetomechanical properties as disclosed, for example, in the '702 patent. Clearly, a new magnetomechanical marker material is needed which does not require such complicated post-ribbon fabrication processes, and the present invention provides such a marker material with high magnetomechanical performance without causing the “pollution problem” that is mentioned above. A marker strip in accordance with the '702 patent is widely used for a marker with two strips, as is disclosed in U.S. Pat. No. 6,359,563. Due to the fact that the two strips have the same radius of curvature along the strip width direction since each of them was processed in exactly the same way, in accordance with the '702 patent, the two strips touch each other at many points on the strip surfaces, damping the magnetomechanical vibration on the strips, and hence reducing the effectiveness of the marker. This drawback needs to be ameliorated. Furthermore, there is a need for an effective electronic article surveillance system which utilizes such a marker.
In accordance with an embodiment of the invention, a soft magnetic material is utilized for a marker of an electronic article surveillance system based on magnetomechanical resonance.
A marker material with enhanced overall magnetomechanical resonance properties is fabricated from an amorphous alloy ribbon. The magnetic marker material in a ribbon form having magnetomechanical resonance capability is cast on a rotating substrate as taught in the U.S. Pat. No. 4,142,571. When the as-cast ribbon width is wider than the predetermined width for a marker material, said ribbon is slit to said predetermined width. The ribbon thus prepared is cut into ductile, rectangular amorphous metal marker strips having a predetermined length to fabricate a magnetomechanical resonance marker using one or a plurality of said marker strips with at least one semi-hard magnet strip which provides a bias static magnetic field. Said magnetomechanical resonance marker does not trigger other systems based on the principle of magnetic higher harmonics generation/detection.
An electronic article surveillance system utilizes a marker of the present invention. The system has an article interrogation zone in which a magnetomechanical marker of the present invention is subject to an interrogating magnetic field at the resonance frequency of a marker strip, the signal response to the interrogating magnetic field excitation being detected by a receiver having a pair of antenna coils situated in the article interrogation zone. The received magnetomechanical resonance signal is then processed by a signal detection circuit which identifies the marker.
In accordance with an embodiment of the invention, a marker of a magnetomechanical resonant electronic article surveillance system, comprises: at least one ductile magnetostrictive strip cut from an amorphous ferromagnetic alloy ribbon that has a curvature along a ribbon length direction and exhibits magnetomechanical resonance under alternating magnetic field excitation with a static bias field, the at least one marker strip having a magnetic anisotropy direction along a direction perpendicular to a ribbon axis.
Where selected, a radius of curvature of the at least one ductile magnetostrictive marker strip is less than 120 cm.
In accordance with an embodiment of the invention, the amorphous ferromagnetic alloy ribbon has a saturation induction ranging from 0.6 tesla to 1.1 tesla.
In accordance with an embodiment of the invention, the amorphous ferromagnetic alloy ribbon has a saturation magnetostriction ranging from 6 ppm to 18 ppm.
In accordance with an embodiment of the invention, the amorphous ferromagnetic alloy ribbon has a composition based on Fea—Nib—Moc—Bd with 30≦a≦43, 35≦b≦48, 0≦c ≦5, 14≦d≦20 and a+b+c+d=100, up to 3 atom % of Mo being optionally replaced by Co, Cr, Mn and/or Nb and up to 1.5 atom % of B being optionally replaced by Si and/or C.
In accordance with an embodiment of the invention, the amorphous ferromagnetic alloy ribbon is an alloy having a composition of one of Fe41.7Ni39.4Mo3.1B15.8, Fe41.5Ni38.9Mo4.1B15.5, Fe39.8Ni39.2Mo3.1B17.6C0.3, Fe40.2Ni39.0Mo3.6B16.6Si0.6, Fe36.5Ni42.9Mo42.2B16.5, Fe40.6Ni40.1Mo3.7B15.1Si0.5, Fe39.6Ni38.3Mo4.1B18.0, Fe38.0Ni38.8Mo3.9B19.3, Fe36.9Ni41.3Mo4.1B17.8, Fe36.7Ni41.9Mo4.0B16.6Si0.8, Fe35.6Ni42.6Mo4.0B17.9, Fe34.7Ni43.5Mo4.0B17.8, Fe33.3Ni43.8Mo3.9Co0.2Cr0.1B17.7Si1.0, or Fe32.5Ni44.7Mo3.7Co0.1Cr0.2B18.0Si0.8.
In accordance with an embodiment of the invention, the at least one marker strip has a discrete length and exhibits magnetomechanical resonance at a length-related frequency.
Where selected, the at least one marker strip has a length ranging from about 15 to about 65 mm.
Where selected, the at least one marker strip has a marker strip width ranging from about 3 mm to about 15 mm.
In accordance with an embodiment of the invention, the at least one marker strip has a length-to-width ratio exceeding 3.
In accordance with an embodiment of the invention, the at least one marker strip has a characteristic time constant for magnetomechanical resonance signal decay ranging from about 0.7 msec to about 3.9 msec.
In accordance with an embodiment of the invention, the at least one marker strip has a characteristic BH loop with a near-zero remanent magnetic induction at zero-applied magnetic field.
In accordance with an embodiment of the invention, the at least one marker strip has a slope of resonance frequency versus bias field ranging from about 4 Hz/(A/m) to about 14 Hz/(A/m).
In accordance with an embodiment of the invention, the marker comprises a plurality of marker strips with different radius of curvatures along the marker strips' length direction.
Where selected, the plurality of marker strips are stacked or placed side-by-side.
In accordance with an embodiment of the invention, the marker comprises two marker strips and has a slope of resonance frequency versus bias field ranging from about 3.5 Hz/(A/m) to about 10 Hz/(A/m).
In accordance with an embodiment of the invention, the marker comprises three marker strips and has a slope of resonance frequency versus bias field ranging from about 4 Hz/(A/m) to about 9 Hz/(A/m).
In accordance with an embodiment of the invention, the marker comprises four or five marker strips and has a slope of resonance frequency versus bias field ranging from about 2 Hz/(A/m) to about 4 Hz/(A/m).
Where selected, at least one bias magnet strip is placed along the at least one marker strip's direction.
In accordance with an embodiment of the invention, the at least one marker strip is housed in a cavity separated from the bias magnet strip.
In accordance with an embodiment of the invention, electronic article surveillance system has a capability of detecting resonance of a marker, and comprises a surveillance system tuned to predetermined surveillance magnetic field frequencies, wherein the surveillance system detects a marker that is adapted to mechanically resonate at a preselected frequency, and has at least one ductile magnetostrictive marker strip cut from an amorphous ferromagnetic alloy ribbon that has a curvature along a ribbon length direction and exhibits magnetomechanical resonance under alternating magnetic field excitation with a static bias field, the at least one marker strip having a magnetic anisotropy direction along a direction perpendicular to a ribbon axis.
Where selected, a radius of curvature of the at least one ductile magnetostrictive marker strip is between about 20 cm and about 100 cm in accordance with embodiments of the invention.
The invention will be more fully understood and further advantages will become apparent when reference is made to the following detailed description of the embodiments and the accompanying drawings in which:
A marker material with enhanced overall magnetomechanical resonance properties is fabricated from an amorphous alloy ribbon. The magnetic marker material in a ribbon form having magnetomechanical resonance capability is cast on a rotating substrate as taught in the U.S. Pat. No. 4,142,571. When the as-cast ribbon width is wider than the predetermined width for a marker material, the ribbon is slit to the predetermined width. The ribbon thus prepared is cut into ductile, rectangular amorphous metal strips having a predetermined length to fabricate a magnetomechanical resonance marker using one or a plurality of the strips with at least one semi-hard magnet strip which provides a bias static magnetic field. The magnetomechanical resonance marker does not trigger other systems based on the principle of magnetic higher harmonics generation/detection.
In one embodiment of the present invention, the amorphous ferromagnetic alloy utilized to form a ribbon for the marker strip has a composition based on Fea—Nib—Moc—Bd with 30≦a≦43, 35≦b≦48, 0≦c≦5, 14≦d≦20 and a+b+c+d=100, up to 3 atom % of Mo being optionally replaced by Co, Cr, Mn and/or Nb and up to 1.5 atom % of B being optionally replaced by Si and/or C.
In certain embodiments of the present invention, the amorphous ferromagnetic alloy utilized to form a ribbon for the marker strip has a composition of one of Fe41.7Ni39.4Mo3.1B15.8, Fe41.5Ni38.9Mo4.1B15.5, Fe39.8Ni39.2Mo3.1B17.6C0.3, Fe40.2Ni39.0Mo3.6B16.6Si0.6, Fe36.5Ni42.9Mo4.2B16.5, Fe40.6Ni40.1Mo3.7B15.1Si0.5, Fe39.6Ni38.3Mo4.1B18.0, Fe38.0Ni38.8Mo3.9B19.3, Fe36.9 Ni41.3Mo4.1B17.8, Fe36.7Ni41.9Mo4.0B16.6Si0.8, Fe35.6Ni42.6Mo4.0B17.9, Fe34.7Ni43.5Mo4.0B17.8, Fe33.3Ni43.8Mo3.9Co0.2Cr0.1B17.7Si1.0, or Fe32.5Ni44.7Mo3.7Co0.1Cr0.2B18.0Si0.8
Thus, an amorphous magnetostrictive alloy having a chemical composition similar to a chemical composition of a commercially available amorphous METGLAS®2826MB ribbon was cast in accordance with the invention described in the U.S. Pat. No. 4,142,571. The amorphous alloy had a saturation induction ranging from 0.6 Tesla to 1.1 Tesla and a saturation magnetostriction ranging from 6 ppm to 18 ppm. The cast ribbon had widths of about 100 mm and about 25 mm, and its thickness was about 28 μm. The ribbon was then slit into narrower ribbons with different widths. The slit ribbon then was cut into ductile, rectangular strips having a length ranging from about 15 mm to about 65 mm. Each strip had a slight curvature reflecting ribbon casting wheel surface curvature. During slitting, the original curvature was modified. The curvature of a slit and cut strip was determined as described in Example 1.
Comparison of the resonance response between the two cases is illustrated in
Table I summarizes a comparison of parameters critical for the performance of a marker strip as a magnetomechanically resonating element between representative conventional marker strips and examples from the marker strips of an embodiment of the present invention. It is noted that the performance of the marker strips of the embodiment of the present invention is close to, or superior to, the performance of conventional marker strips. As far as the performance of a marker strip is concerned, the signal voltage, V1, is a critical factor that determines the marker performance in an electronic article surveillance system. In view of this, all of the marker strips of embodiment of the present invention in Table I are acceptable for use in markers of the embodiment of the present invention with each of the strip's height h, as defined in
In Table I, maximum signal voltage for V0 and V1 measured at bias field strength, Hb0 and Hb1, respectively, and the resonance frequency slope, dfr/dHb, measured at Hb1 for marker strips of the embodiment of the present invention with strip curvature h, as defined in
The length, l of the strips were all about 38 mm, and their widths were about 6 mm. A radius of curvature for each marker strip was calculated from h and l. The resonance frequency of each strip was about 58 kHz.
Table I contains data for a marker strip width of about 6 mm, which is presently widely used. It is one aspect of the present invention to provide marker strips with widths different than about 6 mm. Marker strips with different widths were slit from the same ribbon used in Table I, and their magnetomechanical resonance characteristics were determined. The results are summarized in Table II. The resonance signal voltages, V0 max and V1max decreased with decreasing width, as expected. The decrease in the characteristic field values, Hb0 and Hb1, with decreasing width is due to demagnetizing effects. Thus, a bias field magnet must be selected accordingly. A marker with a smaller width is suited for a smaller article surveillance area, whereas a marker with a larger width is suited for a larger article surveillance area because resonance signals are larger from larger marker strips, as Table II indicates. Since the resonance frequency depends primarily on the strip length, as Equation (1) indicates, the strip width change does not affect the resonance frequency of the article surveillance system used.
Table II shows the magnetomechanical resonance characteristics of marker strips of an embodiment of the present invention with strip height h, as defined in
Another aspect of the present invention is to provide a variety of available markers operated under different conditions. For this purpose, magnetomechanical resonance characteristics were varied by changing the chemical composition of the amorphous magnetic alloy ribbon from which marker strips were produced. The chemical compositions of the alloys examined are listed in Table III, in which values of the saturation induction and magnetostrictions for the alloys are given. The results of the magnetomechanical resonance properties of these alloys are given in Table IV below.
Table III shows examples of magnetostrictive amorphous alloys with their compositions, saturation inductions, Bs, and saturation magnetostrictions, λs, for magnetomechanical resonance markers of an embodiment of the present invention. The values of Bs were determined from DC BH loop measurements of Example 3, and the values of λs were calculated by using an empirical formula λs=k Bs2, with k=15.5 ppm/tesla2, following S. Ito et al., Applied Physics Letters, vol. 37, p. 665 (1980).
Table IV shows the magnetomechanical resonance characteristics of marker strips having different chemical compositions listed in Table III of an embodiment of the present invention with strip height h as defined in
All of the chemistries examined yielded magnetomechanical resonance signal such as V1 close to, or greater than, corresponding values for conventional marker strips listed in Table 1. Thus, depending on the requirement of an electronic article surveillance system, a most appropriate chemical composition may be selected from the above list.
To obtain a selected range for the radius of curvature of a marker strip in accordance with embodiments of the invention, signal voltage V0 max is plotted in
Furthermore, ribbons slit to about a 6 mm wide width, in accordance with Example 1, were cut into strips with different lengths, and their magnetomechanical resonance properties were examined. In addition to the properties covered in Tables I, II and IV above, a complementary test to determine the effectiveness of a magnetomechanical resonance strip was performed using the following formula:
V(t)=Vo exp(−t/τ), (2)
wherein t is the time measured after termination of an AC field excitation and τ is a characteristic time constant for the resonance signal decay. The values of V1 max in Tables I, II and IV were determined from the data for t=1 msec. The results are given in Table V, in which other parameters characterizing the resonance properties of differing strip lengths are summarized. It is noted that fr follows the relationship of Equation (1) quite well, giving a relationship of fr=2.1906×106/l Hz, where l is the length of a marker strip in mm. Also noted is the increase of τ with increasing strip length, as shown in
As shown in Table V, magnetomechanical resonance characteristics of marker strips of an embodiment of the present invention with different lengths, l, were measured by using Alloy K in Table III. The width and thickness of each strip were about 6 mm and about 28 μm, respectively. The definitions of V0 max, Hb0, V1max, Hb1 and dfr/dHb were the same as in Table I. The time constant was defined in Equation (2). Marker height h was defined in
In addition to the basic magnetic properties, such as saturation magnetic induction and magnetostriction, listed in Table III, that are required to generate magnetomechanical resonance in a marker strip of an embodiment of the present invention, the direction of magnetic anisotropy, which is the direction of easy magnetization in a marker strip, must be essentially perpendicular to the strip's length direction. This is indeed the case, as indicated in
As shown in Table VI, a magnetic higher harmonics signal comparison was made between a marker strip of an embodiment of the present invention and a marker strip based on Co-based METGLAS®2714A alloy, which is widely used in an electronic article surveillance system based on a magnetic harmonic generation/detection system. The strip size was the same for both cases and was approximately 38 mm long and approximately 6 mm wide. The fundamental excitation frequency was 2.4 kHz and the 25th harmonic signals were compared by using a harmonic signal detection method of Example 4.
As Table VI indicates, a negligibly small harmonic signal from a marker of an embodiment of the present invention does not trigger an electronic article surveillance system based on magnetic harmonic generation/detection.
Two marker-strips for embodiments of the present invention were selected randomly from a number of strips characterized in Table I, II, and V with the same dimension, but with slightly different curvatures or two strips having the same chemical composition with the same dimension and with slightly different curvatures are mounted on top of each other, and a marker was made as in
The magnetomechanical resonance behavior, using V0771 and V1772, of this two-strip marker of an embodiment of the present invention is compared in
As shown in Table VII, resonance characteristics were measured of two-strip markers of an embodiment of the present invention with a length of about 38 mm, a width of about 6 mm and a thickness of about 28 μm. The values for conventional markers with five samples had ranges as shown. The resonance frequency of each marker was about 58 kHz. The definitions of V0 max, Hb0, V1 max, Hb1 and dfr/dHb were the same as in Table 1.
As shown in Table VIII, effects of marker strip shape on the magnetomechanical performance of a two-strip marker in accordance with an embodiment of the present invention and that of conventional two-strip marker were examined. The resonance frequency of each marker was about 58 kHz.
The aspect of reduced mechanical damping in a two-strip marker of an embodiment of the present invention was examined and is demonstrated in
As shown in Table IX, time constants τ are listed for resonance signal decay for two-strip markers, samples No. 25 through No. 30, of an embodiment of the present invention and for conventional samples A through E, which are the same as those found in Table VIII. The signal decay data were fitted to Equation (2) above with the parameters V0 max and τ given below. The resonance frequency of each marker was about 58 kHz. The longer time constants for the two-marker strips of the present invention indicate that signal decay over time is considerably smaller than that of a conventional two-strip marker. Thus, a marker based on two strips from an embodiment of the present invention is superior to that from a prior art material.
The advantages of having multiple marker-strips are further provided by an example of a three-strip marker. For this purpose, three randomly selected strips with the same length and width of an embodiment of the present invention were mounted on top of each other, and a three-strip marker was formed and tested.
As shown in
As shown in Table X, resonance characteristics of a three-strip marker of an embodiment of the present invention were examined. The definitions of the basic quantities are the same as in Table I. The resonance frequency of each three-strip maker was about 58 kHz.
A further aspect of the present invention is to provide an electronic article surveillance marker with enhanced detection capability. Thus markers with four and five marker strips were examined, and the results are summarized in Table XI.
As shown in Table XI, magnetomechanical resonance characteristics of markers with four and five marker strips of embodiments of the present invention were determined. The definitions of V0max, Hb0, V1max, Hb1 and dfr/dHb were the same as in Table I. The resonance frequency of each marker was about 58 kHz.
The values of V0 max1001 and V1 max1002 from Tables I, IV, VII, X and XI are plotted against a number of marker strips in
A marker with one rectangular amorphous magnetostrictive alloy strip or a plurality of rectangular amorphous magnetostrictive alloy strips prepared in accordance with the present invention, such as the one exemplified in
A slit ribbon was cut into ductile and rectangular strips with a conventional metal ribbon cutter. The curvature of each strip was determined optically by measuring the height, h, of the curved surface over the strip length, l, as defined in
The magnetomechanical performance was determined in a set-up in which a pair of coils supplying a static bias field and the voltage appearing in a signal detecting coil compensated by a bucking coil was measured by an oscilloscope and a voltmeter. The measured voltage therefore is detecting-coil dependent and indicates a relative signal amplitude. The exciting AC field was supplied by a commercially available function generator. The function generator was programmed to excite a marker strip or strips of the present invention for 3 msec, after which period the excitation was terminated, and the signal decay was measured with time. The data thus taken were processed and analyzed with a commercially available computer software.
A commercially available DC BH loop measurement equipment was utilized to measure magnetic induction B as a function of applied field H. For an AC BH loop measurement, an exciting coil-detecting coil assembly similar to that of Example 4 was used, and output signal from the detecting coil was fed into an electronic integrator. The integrated signal was then calibrated to give the value of the magnetic induction B of a sample. The resultant B was plotted against applied field H, resulting in an AC BH loop. In both AC and DC cases, the direction of the applied field and the measurement was along marker strips' length direction.
A marker strip prepared in accordance with Example 1 was placed in an exciting AC field at a predetermined fundamental frequency, and its higher harmonics response was detected by a coil containing the strip. The exciting coil and signal detecting coil were wound on a bobbin with a diameter of about 50 mm. The number of the windings in the exciting coil and the signal detecting coil was about 180 and about 250, respectively. The fundamental frequency was chosen at 2.4 kHz and its voltage at the exciting coil was about 80 mV. The 25th harmonic voltages from the signal detecting coil were measured.
In accordance with an embodiment of the invention, a marker of a magnetomechanical resonant electronic article surveillance system, comprises: at least one ductile magnetostrictive marker strip cut from an amorphous ferromagnetic alloy ribbon that has a curvature along a ribbon length direction and exhibits magnetomechanical resonance under alternating magnetic field excitation with a static bias field, the said at least one marker strip having a magnetic anisotropy direction along a direction perpendicular to a ribbon axis.
Where selected, a radius of curvature of the at least one ductile magnetostrictive marker strip is less than 120 cm. A selected range for the radius of curvature of a marker strip is between about 20 cm and about 100 cm for embodiments of the invention.
In accordance with an embodiment of the invention, the amorphous ferromagnetic alloy ribbon has a saturation induction ranging from about 0.6 tesla to about 1.1 tesla.
In accordance with an embodiment of the invention, the amorphous ferromagnetic alloy ribbon has a saturation magnetostriction ranging from about 6 ppm to about 18 ppm.
In accordance with an embodiment of the invention, the amorphous ferromagnetic alloy ribbon has a composition based on Fea—Nib—Moc—Bd with 30≦a≦43, 35≦b≦48, 0≦c≦5, 14≦d≦20 and a+b+c+d=100, up to 3 atom % of Mo being optionally replaced by Co, Cr, Mn and/or Nb and up to 1.5 atom % of B being optionally replaced by Si and/or C.
In accordance with an embodiment of the invention, the amorphous ferromagnetic alloy ribbon is an alloy having a composition of one of Fe41.7Ni39.4Mo3.1B15.8, Fe41.5Ni38.9Mo4.1B15.5, Fe39.8Ni39.2Mo3.1B17.6C0.3, Fe40.2Ni39.0Mo3.6B16.6Si0.6, Fe36.5Ni42.9Mo4.2B16.5, Fe40.6Ni41.9Mo3.7B15.1Si0.5, Fe39.6Ni38.3Mo4.1B18.0, Fe38.0Ni38.8Mo3.9B19.3, Fe36.9Ni41.3Mo4.1B17.8, Fe36.7Ni41.9Mo4.0B16.6Si0.8, Fe35.6Ni42.6Mo4.0B17.9, Fe34.7Ni43.5Mo4.0B17.8, Fe33.3Ni43.8Mo3.9Co0.2Cr0.1B17.7Si1.0, or Fe32.5Ni44.7Mo3.7Co0.1Cr0.2B18.0Si0.8 In accordance with an embodiment of the invention, the at least one marker strip has a discrete length and exhibits magnetomechanical resonance at a length-related frequency.
Where selected, the at least one marker strip has a length ranging from about 15 to about 65 mm.
Where selected, the at least one marker strip has a marker strip width ranging from about 3 mm to about 15 mm.
In accordance with an embodiment of the invention, the at least one marker strip has a length-to-width ratio exceeding 3.
In accordance with an embodiment of the invention, the at least one marker strip has a characteristic time constant for magnetomechanical resonance signal decay ranging from about 0.7 msec to about 3.9 msec.
In accordance with an embodiment of the invention, the at least one marker strip has a characteristic BH loop with a near-zero remanent magnetic induction at zero-applied magnetic field.
In accordance with an embodiment of the invention, the at least one marker strip has a slope of resonance frequency versus bias field ranging from about 4 Hz/(A/m) to about 14 Hz/(A/m).
In accordance with an embodiment of the invention, the marker comprises a plurality of marker strips with different radius of curvatures along the marker strips' length direction and with the same length.
Where selected, the plurality of marker strips are stacked or placed side-by-side.
In accordance with an embodiment of the invention, the marker comprises two marker strips and has a slope of resonance frequency versus bias field ranging from about 3.5 Hz/(A/m) to about 10 Hz/(A/m).
In accordance with an embodiment of the invention, the marker comprises three marker strips and has a slope of resonance frequency versus bias field ranging from about 4 Hz/(A/m) to about 9 Hz/(A/m).
In accordance with an embodiment of the invention, the marker comprises four or five marker strips and has a slope of resonance frequency versus bias field ranging from about 2 Hz/(A/m) to about 4 Hz/(A/m).
Where selected, at least one bias magnet strip is placed along the at least one marker strip's direction.
In accordance with an embodiment of the invention, the at least one marker strip is housed in a cavity separated from the bias magnet strip.
In accordance with an embodiment of the invention, electronic article surveillance system has a capability of detecting resonance of a marker, and comprises a surveillance system tuned to predetermined surveillance magnetic field frequencies, wherein the surveillance system detects a marker that is adapted to mechanically resonate at a preselected frequency, and has at least one ductile magnetostrictive marker strip cut from an amorphous ferromagnetic alloy ribbon that has a curvature along a ribbon length direction and exhibits magnetomechanical resonance under alternating magnetic field excitation with a static bias field, the at least one marker strip having a magnetic anisotropy direction along a direction perpendicular to a ribbon axis.
Where selected, a radius of curvature of the at least one ductile magnetostrictive marker strip is between about 20 cm and about 100 cm for embodiments of the invention.
In accordance with an embodiment of the invention, the amorphous ferromagnetic alloy has a composition based on Fea—Nib—Moc—Bd with 30≦a≦43, 35≦b≦48, 0≦c≦5, 14≦d≦20 and a+b+c+d=100, up to 3 atom % of Mo being optionally replaced by Co, Cr, Mn and/or Nb and up to 1.5 atom % of B being 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.
This application is a continuation-in-part of U.S. Ser. No. 11/095,611, filed Apr. 1, 2005 now U.S. Pat. No. 7,205,893, the disclosure of which is incorporated herein by reference.
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| Number | Date | Country | |
|---|---|---|---|
| 20070080808 A1 | Apr 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11095611 | Apr 2005 | US |
| Child | 11607997 | US |
