Patent Application
20050237197
1. Field of the Invention
This invention relates to remote detection of articles having substantially rectangular cross-sections; and more particularly to a method and apparatus wherein ferromagnetic metallic glass-coated articles are detected remotely by sensing the harmonic frequencies of an alternating magnetic field that emanates from an article having a substantially rectangular cross-section.
2. Description of the Prior Art
Amorphous and nanocryastalline alloy-cored glass-coated wire and its production have been disclosed in the technical and patent literature: Horia Chirac, “Preparation and Characterization of Glass Covered Magnetic Wires”, Materials Science and Engineering A304-306 (2001) pp. 166-171], U.S. Pat. No. 6,270,591 to Chiriac et al., and U.S. Pat. No. 5,240,066 to Gorynin. Without exception, all disclosures of these kinds of materials refer to articles having round cross-sections. Magnetic methods have been used to detect the presence of both substantially rectangular amorphous alloy articles that do not have a glass coating [U.S. Pat. No. 4,484,184 to Gregor et al.] and of amorphous alloy microwire (circular cross-section) both with [U.S. Pat. No. 6,441,747 to Antonenco] and without [U.S. Pat. No. 5,921,583 to Matsumoto; U.S. Pat. No. 4,660,025 Humphrey] glass coating. Indirect methods for the detection of glass-coated amorphous alloy wire have been disclosed as well [U.S. Pat. No. 6,137,41 to Tyren; U.S. Pat. No. 6,232,879; U.S. Pat. No. 6,225,905].
Greater detection distance for various configurations of ferromagnetic elements has been demonstrated by Tyren using radio frequency-based technology; see, for example: U.S. Pat. No. 6,137,411; U.S. Pat. No. 6,232,879; U.S. Pat. No. 6,225,905. A limitation of these disclosures, again, is that detection is limited to an article comprised of either a single amorphous wire or a plurality thereof. The detection of glass-coated ferromagnetic articles having substantially rectangular cross-sections is not addressed by Tyren.
The use of certain soft magnetic alloys and of glass-coated amorphous metallic alloy microwire or of articles made therefrom in anti-theft system applications, for example, has broadly been based on the sensing of a magnetic output from the article, while being excited with an a.c. magnetic field. Sensing of output is typically achieved by utilizing a magnetic pick-up coil. For example, in U.S. Pat. No. 4,484,184 to Gregor et al. there is disclosed a magnetic excitation system in combination with a magnetic output pick-up means. Just a few years later, a much more thorough analysis of magnetic output in such a system is given in U.S. Pat. No. 4,660,025 to Humphrey, in which details of the magnetic harmonics generated are given. To this day, the measurement of magnetic output is the most widespread method used in anti-theft systems. While effective to a certain extent, prior art technologies are limited in terms of both orientation-dependent sensitivity and also distance over which detection of the article is possible. The orientation-dependence of the article being sensed arises predominantly from both the high geometric aspect ratio of that article and also from the directionality of the magnetic field used to drive said article. The limited sensing distance of prior art technologies stems from the rapid decrease of magnetic field with distance from its source: magnetic field decreases as an inverse exponent of distance. These two factors clearly limit the utility and effectiveness of prior art technologies.
Accordingly, there exists a need in the art for an apparatus that remotely detects the presence of glass-coated ferromagnetic articles having substantially rectangular cross-section. Also needed are detection systems that offer improved performance. Such systems, if present would open possibilities of much greater opportunities and markets than presently exist for articles having a simple wire shape.
The present invention provides a means for detecting the presence of a soft magnetic article within an interrogation zone of an electronic article surveillance system. When compared to conventional systems, the orientation dependence of the article being detected is greatly diminished. In addition, the distance from which an article can be sensed reliably is much greater than that of conventional systems. A “tickler” magnetic field having alternating direction is applied to the article which, in turn, causes the article to become magnetized alternately as well. The directional sensitivity of the article being detected is mitigated either through article configurational considerations or by engineering the manner in which the “tickler” magnetic field is applied to excite the article.
A magnetic field is detected either directly, using a variety of magnetic methods, or indirectly by causing the emanating magnetic field to modify a traveling radio frequency (RF) or other field. Detection of articles is readily accomplished using the articles' substantially rectangular cross-section (binary function), or by reading of multi-bit (encoded) data associated therewith. As a result, the method and means of this invention are especially well suited for detection of glass-coated articles associated with a wide variety of applications, including anti-theft systems; monitoring of tamper-proof packages; tracking, tracing and identification of currency, secure documents, drivers licenses, and passports; tracking of personnel, labels and paper products, merchandising items, and composites; monitoring movement of textiles including clothing and garments and materials used to make said textiles containing the invention; authentication and brand theft protection, credit card verification and protection against fraud; biometrics and other medical applications.
Installation of the instant invention is much simpler and operation much more forgiving than with conventional systems. Accordingly, when compared with conventional systems, the system of the present invention is less expensive to construct, easier to install and use, and more reliable in operation.
The invention will be more fully understood and further advantages will become apparent when reference is had to the following detailed description and the accompanying drawings, in which:
As used herein, the term “amorphous metallic alloy” means a metallic alloy that substantially lacks any long-range order and is characterized by x-ray diffraction intensity maxima that are qualitatively similar to those observed for liquids or oxide glasses. By way of contrast, the term “nanocrystalline metallic alloy” pertains to those metallic alloys having constituent grain sizes on the order of nanometers.
The term “glass”, as used throughout the specification and claims, refers to an inorganic product of fusion that has cooled to the solid state without crystallizing, or to glassy materials formed by chemical means such as a sol-gel process, or by “soot” processes, both of which are used to form glass preforms that are used in fiber optic processing. These materials are not fused; but rather are consolidated at high temperatures, generally below the fusion temperatures of the constituents in question.
The term “microwire”, as used herein, means an article that is present as a single element or as multiple elements, and comprises at least one metallic material.
The term “article”, as used herein, refers to a long geometric body having any number of cross-sectional shapes, including circular (wire, rod, ribbon, fiber, etc.).
The term “substantially rectangular”, as used throughout the specification and claims, refers to an article having thickness-to-width ratio ranging from nearly 1 to over 100.
The term “tickler magnetic field”, as used herein, refers to the ac magnetic field that is used to exite the article to be detected.
The term “harmonic”, as used herein, refers to an integer multiple of some fundamental frequency, usually that of the tickler magnetic field.
The enabler for the remote detection of ferromagnetic articles having substantially rectangular cross-section centers upon the generation of magnetic harmonic signal output by said article, while being excited by a tickler magnetic field. These induced magnetic harmonics are broadcast from either end of the article. The value of this is that any harmonic (multiple of tickler frequency) can be selected either in unison or in combination with other harmonics to provide a unique signal identity. Detection of an article of the instant invention is, in fact, detection of the magnetic harmonics that are caused to emanate from said article.
Given totally magnetic systems, such as those described above, there is limited detectability resulting from the very rapid drop-off in amplitude of the harmonics-containing magnetic field emanating from the ends of the glass-coated article having substantially rectangular cross-section during its tickling by the drive field. The limits governing use of such totally magnetic approaches to detection are about 4 feet and at best 8 feet if using tandem detection coil gates working in concert.
Other means by which detection could be achieved include the use of an RF field in conjunction with the magnetic field emanating from the ends of a glass-coated article having substantially rectangular cross-section. For example, the excited article is situated in the path of a propagating radio wave and causes therein a perturbance that is now carried along with radio wave. The perturbance, in fact, results in replication and mixing of the signal emanating from the excited article with the radio wave. It is the compound RF-magnetic effect that enables extended detection distances of glass-coated articles having substantially rectangular cross-sections.
The invention also serves to overcome a limitation common to both the magnetic and the compound article detection systems, and also systems of the Prior Art. That is, a high degree of orientational sensitivity variation occurs when working with the soft magnetic properties of long slender articles. Properties improve as the long axis of the article is aligned with the direction of the magnetic drive field. Approaches by which this problem can be remedied include the use of long slender articles as an ensemble, with them in mutually orthogonal directions. Using this approach, part of at least one of the constituent long slender articles is aligned with the direction of the magnetic drive field. This approach may not be acceptable in some applications because of the ensemble's conspicuous size. An alternative approach is to have a tickler magnetization field that is made to change direction either continuously or incrementally over time. In this way, some part of the single article is in-line with the tickler magnetic field. One way in which to create a tickler field that controllably changes direction with time is to have three separately wound pairs of tickler coils, each set creating a magnetic field that is orthogonal to the tickler field created by the other two sets of coils.
Another approach to achieving direction-independent detection of an article having high dimensional aspect ratio is to mount at least three articles or groups of articles mutually orthogonally so that a significant fraction of these articles would be in-line with a unidirectional magnetic field at any time.
The teaching of the present invention can be used in conjunction with metallic alloys having various compositions, whether such alloys are amorphous, nanocrystalline, or otherwise. The present invention can also be with various kinds of glasses of which the preforms are made.
The following examples are presented to provide a more complete understanding of the invention. The specific techniques, conditions, materials, proportions and reported data set forth to illustrate the principles and practice of the invention are exemplary and should not be construed as limiting the scope of the invention.
A magnetic detection system comprised essentially of two concentric wound wire solenoids was constructed, as schematically represented in
Using this equipment, the magnetic tickler field coil was energized with 0.14 A electrical current at 1 kHz frequency to result in approximately 50 A/m a.c. tickler field. The sample tested was three 84 mm long glass-coated microwire lengths spaced less than 1 mm apart and affixed to a piece of paper with double sided adhesive tape. The microwire of this sample had a Pyrex coating of about 6 μm thickness and a 25 μm diameter amorphous alloy core of nominal chemistry Fe77.5B15Si7.5. Harmonics having frequencies of multiples of the 1 kHz magnetic tickler field were observed using a lock-in amplifier. This demonstrates the principle of magnetically detecting the presence of glass-coated microwire that is magnetically tickled. Similar performance is expected with substantially rectangular glass-coated articles having amorphous alloy compositions in the 75≦Fe≦82 at. %, 0≦Co≦10 at. %, 10≦B≦20 at. %, 0≦Si≦10 at. %, and 0≦C≦4 at. %.
Following the same procedures and using the same equipment as in Example 1, a glass-coated microwire with an amorphous alloy core having nominal chemistry CO68.18Fe4.32B15Si12.5 was tested using the magnetic detection system. No harmonics were observed when subjected to the same test protocol as before. It is believed that this difference in performance between the two glass-coated amorphous alloy microwire samples tested is related to the magnetic domain structure of these two kinds of microwire. In the case of the Fe77.5B15Si7.5 glass-coated microwire, the magnetic domain structure is comprised of a single domain aligned along the center of the microwire, surrounded by a torus of small, radial domains of alternating polarity. In contrast, the CO68.18Fe4.32B15Si12.5 glass-coated microwire is comprised of a magnetic center that is not aligned along the center of the microwire. An important distinction between these two kinds of domain structures is that the Fe77.5B15Si7.5 sample has a significant material volume of magnetization that is oriented along the test (magnetic tickler field) direction. Thus, even without the benefit of having the axially oriented domains in the torus surrounding the central domain participate in the magnetization process, there is sufficient volume of favorably oriented magnetic domain in the central part of the microwire. In contrast, neither the central nor the torus domains of the CO68.18Fe4.32B15Si12.5 glass-coated amorphous alloy microwire are favorably oriented (axially) with respect to testing direction of the microwire.
Glass-coated amorphous alloy microwire samples were prepared by affixing four 7.5 cm lengths spaced about 1 mm apart onto a paper substrate using double-sided adhesive tape. This sample was then taken to the Flanders, N.J. Blockbuster store, in which Sensormatic electronic article surveillance gates are installed. I was given permission to do some testing with this magnetic detection system. The sample prepared was found to sound the alarm whenever the microwires therein were held simultaneously horizontally and perpendicular to the direction of walking through the Blockbuster detection gate. It was found, however, that that alarm was not sounded when the sample deviated by more than about 30 degrees from the orientation just described. An important result of this example is that a commercial magnetic detection system, even though not optimized for the detection of glass-coated amorphous microwire, was successful in detecting the presence of a sample made up of microwire lengths. Furthermore, the observation of detection capability dependence on angular disposition of the sample is similar to that observed when using commercial anti-theft tags.
A sample identical to that used in Example 3 was prepared, except that the inner of the glass-coated amorphous alloy had a nominal chemistry of CO68.18Fe4.32B15Si12.5. As with concentric solenoid system for magnetic detection used in Examples 1 and 2, the present sample never set off the Blockbuster alarm, no matter its orientation or proximity to the antennae that generate the magnetic field of the anti-theft system.
A compound detection system consists essentially of two basic components: a magnetic tickler field generating device, and a radio frequency (RF) transmitter/receiver pair, as schematically shown in
Following the same procedures and using the same equipment as in Example 5, a paper clip, scissors, and other common metallic objects were subjected to testing, but no harmonics were observed. The data plots resulting from these tests were identical to that shown in
Following the same procedures and using the same equipment as in Example 5, a single 7.5 cm length of glass-coated amorphous microwire having a core with nominal composition CO68.18Fe4.32B15Si12.5 is positioned parallel to the magnetic tickler field pancake coil. While the results looked similar to those shown in
A portal having a 2 meter×2 meter opening was constructed with three independent sets of tickler magnetic field coils, as shown schematically in
In one mode of operation, each of the three coil sets is repeatedly energized in sequence for a very brief time. In another mode of operation, all tickler magnetic coils are energized simultaneously and continuously, with coil 1 being energized at one frequency of electrical current, coils 2a and 2b at another frequency of electrical current, and coils 3a and 3b at yet another frequency of electrical current. Then, suitable electronic equipment can be used to both recorded and to deconvolute the complex magnetic tickler field contributions oriented in different directions.
It is envisioned that the portal system disclosed here would be useful in both magnetic as well as in compound anti-theft systems.
Using the portal system described in Example 8 in conjunction with a compound detection system, a 7 cm long article of glass-coated amorphous alloy with nominal composition CO68.18Fe4.32B15Si12.5 was tested for signal output. It was found that no matter what the inclination or position within the portal, a presence of strong harmonics was consistently detected.
Having thus described the invention in rather full detail, it will be understood that such detail need not be strictly adhered to but that various changes and modifications may suggest themselves to one skilled in the art, all falling within the scope of the present invention as defined by the subjoined claims.
