Low cost material for multi-bit remote sensing

Information

  • Patent Grant
  • 6278368
  • Patent Number
    6,278,368
  • Date Filed
    Thursday, September 30, 1999
    25 years ago
  • Date Issued
    Tuesday, August 21, 2001
    23 years ago
Abstract
Multiple bits of information may be conveyed by passive target material incorporating filaments of magnetizable material having different magnetization functions and, in particular, different coercivities. Detection of the presence or absence of the individual filaments may be done remotely by measuring induced flux B as a function of an externally imposed magnetic field waveform and subjecting the measured induced flux signal to differentiation or Fourier transform techniques.
Description




BACKGROUND OF THE INVENTION




The present invention relates to systems and materials for presence sensing, and in particular, to a low cost material with magnetizable filaments whose presence may be sensed remotely by an industrial control system to communicate multiple bits of information.




In the manufacture of a multi-component product, for example, packaged pharmaceuticals intended for over-the-counter sale, it is important to verify that the package includes a paper insert listing the characteristics of the drug and instructions for safe use. While considerable care is taken in placing the insert into the package, ideally, its presence in the package could be verified after the package is sealed. One way of doing this is by weighing the package to detect the additional weight of the insert. For light inserts or products that vary in weight, such an approach is unreliable.




The parent to the present application describes a method of verifying the presence of a component of a manufactured product by incorporating a small percentage of filamentized magnetic material into that component whose presence may be detectable at a distance. The filaments are of low cost and may be freely dispersed into the material of the component for manufacturing convenience and may be remotely sensed even through packaging or the like.




While the ability to sense an individual component in a manufactured product is valuable, often it may be necessary to sense combinations of components or to distinguish between different component types. It would be desirable to have a method of communicating not simply presence or absence of a component representing a single binary “bit” of information, but to be able to detect combinations of components and to distinguish between different components such as requires the communication of multiple bits of information.




BRIEF SUMMARY OF THE INVENTION




The present inventors have recognized that low cost magnetizable filaments similar to those described above may be used to convey, not merely a “presence” or “absence” signal, but multiple bits of information. In particular by using magnetic materials having different coercivities, distortions in an externally imposed periodic magnetic waveform will be displaced in phase for the different magnetic materials allowing independent detection of each material. The presence or absence of each material provides one bit of information in a multi-bit word. The length of the multi-bit word is determined by how many different materials are used.




Specifically, the present invention provides a marker material suitable for remote sensing of multi-bit information including a non-magnetic matrix and at least a first and second set of magnetic filaments supported and dispersed by the matrix. Each set of magnetizable filaments has a first functional relationship between magnetic induction (B) and magnetic field (H) that differs from the others.




Thus, it is one object of the invention to provide an easily manufactured and low cost material for conveying multiple bits of information to a remote sensor. The filaments are relatively inexpensive and their orientation need not be precisely controlled, therefore they may be easily incorporated into a variety of materials.




The proportion of the filaments of the first and second filament sets may be a predetermined unequal proportion based to their detectability by a remote sensor.




Thus it is another object of the invention to provide flexibility in selecting the magnetic material allowing the use of materials with different coercivity and low permeability while ensuring adequate signal levels.




The present invention also provides for a sensing apparatus for the material containing the multiple sets of magnetizable filaments. Specifically, the sensor includes an electric oscillator producing a waveform having a fundamental frequency and an antenna structure connected to the electric oscillator for transmitting the waveform as an electromagnetic field to envelop the sets of magnetizable filaments. A receiver, connected to the antenna structure, receives the electromagnetic field as modified by the sets of magnetizable filaments and a detector discriminates between their magnetic properties to independently detect the individual sets of magnetizable filaments.




Thus, it is another object of the invention to provide a simple method of remotely detecting the multi-bit information.




The detector may be a differentiator (as is implicit in a coil detector) and a phase sensitive threshold detector detecting peaks in the derivative of the received electromagnetic field as a function of the phase of the waveform of the electric oscillator.




Thus, it is another object of the invention to exploit the effect of the magnetizable filaments in causing distortions of an applied magnetic field such as changes the instantaneous slope with respect to time of the electromagnetic field.




Alternatively or in addition, the remote sensing system may include a Fourier transformer and a threshold detector for detecting magnitudes of Fourier components at predetermined harmonics of the waveform of the electric oscillator.




Thus, it is another object of the invention to provide a method for more generally detecting distortion of the applied electromagnetic field.




The present invention may be used in verifying manufacturing operations in the assembly of multi-component products or the like. In this application, a first and second component of the multi-component product are identified and magnetizable filaments having different magnetic properties are attached respectively to the first and second components. The assembled multi-component product is then exposed to an electromagnetic waveform and the distortion of the waveform caused by different magnetic induction in the magnetizable filaments is detected to detect the presence of the first and second components. An output signal is provided indicating proper assembly of the multi-component product.




The output signal may indicate that none or both sets of magnetizable filaments for the first and second components have been detected or that a specific one and only one of the sets of magnetizable filaments have been detected.




Thus, it is another object of the invention to provide a method not only of ensuring proper assembly of multiple component devices requiring both a first and second component or in distinguishing between different versions of a multi-component product having, in the alternative, the first or second components. Numbers may be encoded in binary format according to the presence or absence of the detected sets.




The foregoing and other objects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof and in which there is shown by way of illustration a preferred embodiment of the invention. Such embodiment does not necessary represent the full scope of the invention, however, and reference must be made to the claims herein for interpreting the scope of the invention.











BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS





FIG. 1

is a perspective view of an assembly line in which a product including material of the present invention is enclosed in a package and later remotely sensed by a sensing device of the present invention;





FIG. 2

is a perspective view of example uses of material of the present invention including a package cap, label, and instructional insert;





FIG. 3A

is a plan view showing the instructional insert of

FIG. 2

having magnetic filaments dispersed within a paper matrix;





FIG. 3B

is a plan view showing a magnetic filament of

FIG. 3A

in enlarged detail;





FIG. 4

is a schematic diagram of the sensing device of

FIG. 1

employing synchronous detection of magnetization of the filaments;





FIG. 5

is a figure similar to that of

FIG. 4

showing an alternative embodiment of the sensing device employing frequency domain analysis of the total magnetization to detect saturation of the filaments of

FIG. 3

;





FIG. 6

is a spectrum diagram of the output of the sensing device of

FIG. 5

in the absence of material of the present invention;





FIG. 7

is a figure similar to that of

FIG. 6

showing output of the sensing device of

FIG. 5

in the presence of material of the present invention;





FIG. 8

is a plot of magnetic induction M vs. external magnetic field H showing saturation of the magnetic filaments of the material of the present invention;





FIG. 9

is a plot similar to that of

FIG. 8

showing the definition of magnetic coercivity;





FIG. 10

is a plot similar to that of

FIGS. 8 and 9

showing the effect on the hysteresis curve of the introduction of three different filaments providing three different magnetic coercivities per the present invention;





FIG. 11

is a figure similar to that of

FIG. 4

showing a sensing device for detecting multiple different filaments having different coercivities and using a differentiating circuit;





FIG. 12

is a plot of signal output from the differentiation of

FIG. 11

versus time measuring a derivative of the induction units of the graph of FIG.


10


and showing multiple peaks caused by each of the magnetic filaments of the three sets;





FIG. 13

is a figure similar to that of

FIG. 10

showing a sensing device for detecting multiple different filaments having different coercivities and using a Fourier transform circuit; and





FIG. 14

is a plot of the output of the Fourier transform circuit of

FIG. 13

for different combinations of the three filament types of FIG.


10


.











DETAILED DESCRIPTION OF THE INVENTION




Referring now to

FIG. 1

, an assembly line


10


may include a conveyor belt


12


transporting boxes


14


along a direction


18


. At a first station


20


, the box


14


may be opened and a product


16


is installed therein. With further motion of the conveyor belt


12


in direction


18


, the box


14


is brought to a second station (not shown) where the box is closed and sealed.




At a third station


22


, the box and the product


16


contained therein pass between coils


24


coaxially opposed across the conveyor belt


12


perpendicular to the direction


18


. As will be described below, the coils


24


are connected together as a Helmholtz coil pair for the generation and detection of electromagnetic signals in the volume between the coils


24


. It will be understood that the coils


24


may be connected in series or in parallel to provide the Helmholtz configuration or may use separate properly phased amplifiers. Other well known types of sensing and excitation coils may be used. A pair of sensing coils


28


may also be positioned coaxial with the coils


24


, but closer to the path of the box


14


on the conveyor belt


12


. Alternatively as shown, four detection coils


28




a-




28




d


may be used to substantially reduce the detection of the fundamental signal from the coils


24


. The pair


28




b


and


28




c


are arranged so that the induced voltages add. The second pair


28




a


or


28




d


are added so that one of the coils


28




a


is to the left of left coil


24


and the other coil


28




d


is to the right of right coil


24


. They are further away from the magnetic filaments so that they do not detect them but substantially only the fundamental from coils


24


. The signals from coils


28




a


and


28




d


subtract from the signals from coils


28




b


and


28




c


reducing the first harmonic substantially to zero allowing a higher dynamic image in the detection of the filament signals. Alternatively, as will be understood in the art, the sensing coils may be replaced or supplemented with a Hall effect device, a giant- or anomalous magneto resistance sensor, a flux-gate device or any other magnetometer. These detectors may also be combined with fundamental canceling detectors analogous to coils


28




a


and


28




d


described above.




Conventional proximity sensing elements


30


such as photoelectric sensors may also be positioned along the conveyor belt


12


to detect the presence of the box


14


in third station


22


so as to activate the sensing of the box's contents, as will be described below.




Referring now also to

FIG. 2

, the product


16


within the box


14


may include, for example, a bottle


32


containing a pharmaceutical material. The bottle may have a resealable cap


34


, a label


36


affixed to the bottle's surface, and may be packaged with a paper insert


38


providing information about the pharmaceutical material.




At different stages of the product's manufacture, it may be desirable to determine the presence of any one or all of the cap


34


, label


36


and paper insert


38


. Accordingly, any one or all of the materials of these elements may be treated by the incorporation of a plurality of magnetic filaments


40


into the material of the element. In the case of a cap


34


, the filaments may be mixed with the thermoplastic from which the cap is molded in the manner of fiberglass and other reinforcement materials according to techniques well known in the art in which the filaments are dispersed in the liquefied plastic.




For the label


36


, which for the purpose of example, may be printed directly on the bottle


32


, the filaments


40


may be mixed with the printing inks. It will be understood that alternatively, the filaments could be in the label paper or adhesive. The paper insert


38


may have filaments


40


that were introduced during the papermaking process to blend and disperse with the cellulose fibers of the paper pulp. The paper may then be processed and printed by conventional means. The filaments may also be encompassed into woven, knitted or nonwoven fabrics, cardboard, ceramic and composite wood products.




Referring now to

FIG. 3

, in the present example of

FIG. 1

, it may be desired to confirm that the paper insert


38


is within the box


14


after the box has been sealed. Accordingly, in this case, only the paper insert


38


includes the filaments


40


. The filaments


40


are randomly dispersed within the paper constrained only by the thickness of the paper (causing the filaments to lie within the plane of the paper) and a degree of alignment caused by papermaking process which align the fibers of the paper in a “grain” generally determined by the water flow over the Fourdrinier screens. In the present example, however, within the plane of the paper, it is desired that the filaments


40


obtain the greatest random dispersion both in location and orientation to ensure a signal regardless of orientation of the paper insert


38


after it has been folded and placed in the box


14


.




Each of the filaments


40


in the preferred embodiment is constructed of an easily magnetizable material or “soft” magnetic material of coercivity of less than 2400 amperes/meter (30 Oersted) and preferably less than 1200 amperes/meter (15 Oersted). Coercivity is the magnetic field that must be applied opposite to the magnetization direction of a magnetically saturated material that is required to reduce the magnetization to zero. Suitable materials include Permalloy, Nickel iron alloy, Supermalloy, and Feralloy, Magnetic Stainless Steel, low carbon steel, however, other similar materials may be used. The more easily the material is magnetized and the greater its saturation, the greater the signal that may be produced by the filaments


40


and the further away the filaments


40


may be detected as will be described. The material of the filaments


40


may preferably have a saturation induction from about 0.5 to 2 tesla (5000 to 20,000 gauss) to allow them to be more readily detected. A permeability of larger than 100 is preferred. A limit on the permeability or the number of filaments, however, may be established so that the filaments


40


do not trigger anti-shoplifting devices which may use a similar principle of detecting saturation of larger foils of magnetic materials within a magnetic field.




Desirably the filaments


40


have a very high aspect ratio, the aspect ratio being a ratio between the filament's length


42


and diameter


44


(shown much exaggerated in FIG.


3


). In the preferred embodiment, a length of 3 mm and a diameter of 8 microns has been found to be achievable, however, generally aspect ratios of greater than 3 will realize some improvement in signal strength and aspect ratios of greater than 200 may be desired. The high aspect ratio decreases demagnetization effects in which the material of the filaments


40


fight the external magnetic field applied to the filaments


40


. Thus generally higher aspect ratios are preferred.




The size of the filaments


40


in length and diameter may be adjusted so as to improve their miscibility with the matrix material


41


of paper, plastic or paint. Generally in these cases, it is desired that the filaments


40


remain suspended and not settle from the matrix during the processing. The optimum size of the filaments


40


may be determined empirically. The small size in diameter of the filaments


40


render them invisible or nearly invisible when incorporated into paper or other materials. Filaments


40


may be clad with a noncorrosive material so as to prevent rusting in place in the matrix.




The matrix material


41


may be selected from a variety of non-magnetic low permeability materials. Together the filaments


40


as dispersed in the matrix material


41


produce a target material


39


whose presence may be remotely sensed.




Referring to

FIG. 4

, detection of the target material


39


may be performed in a number of different manners. In a first system, the Helmholtz coils


24


are connected to electrical amplifier/oscillator


48


driving the coils with a sine wave signal preferably having a value between 500 Hz and 3000 kHz so as to make use of high powered audio frequency amplifier components. It will be understood that the exact frequency may be chosen for convenience. High frequencies increase the sensitivity of the pick-up coil and decrease the interference from 60 cycle harmonics from power lines and the like. The amplifier/oscillator


48


, so connected, creates an oscillating external magnetic field


50


(H) aligned with the axis of the coils


24


. The target material


39


when stimulated by the H-field


50


causes a magnetic induction field


52


(B), being the result of a magnetization M of the filaments


40


(and in particular those filaments aligned with the H-field


50


).




The B-field


52


may be received by sensing coils


28


which measure the derivative with respect to time of the B-field


52


and detected by means of phase detector


54


whose output may be provided to a magnitude or threshold detector


56


to produce a signal at I/O block


58


such as may be connected to an industrial control system or the like to provide an output signal and effect a predetermined control action. The phase detector


54


detects the B-field


52


only so far as it is at the proper phase with the H-field


50


so as to reduce the effects of environmental noise on the detection process. It will be understood that the coils


28


may be another form of magnetization detection such as a Hall effect device or the like.




Referring now to

FIG. 5

, in an alternative embodiment of the detection system, the coils


24


are again attached to amplifier/oscillator


48


in parallel so as to generate an oscillating H-field


50


along their axis. The sensing coil


28


may be used to detect the B-field


52


from the target material


39


or alternatively the coils


24


may serve double duty both as transmitting and receiving antennas. In either case, a B-field signal may be provided to a band pass filter


60


having a pass band admitting only a frequency significantly above the fundamental frequency f


o


of the amplifier/oscillator


48


. In this way, together or as an alternative to the signal subtraction described above, distortion of the waveform may be detected such as results in the introduction of higher ordered harmonics to a sine wave. It will be recognized that other waveform distortion detection systems may be used.




Referring now to

FIG. 8

, the distortion of the B-field


52


with respect to the H-field waveform results from phenomenon of magnetic saturation of the filaments


40


. The filaments


40


under the presence of the external field H


50


and as a function of their permeability and softness, will become magnetized in conformity with the H-field


50


producing a greater magnetization M with increasing field H up to saturation limits


62


whereafter no further increase in magnitude of the magnetization may be had because all magnetic domains are aligned. At this point the M field is truncated as indicated by plateaus


63


with the effect that the B-field


52


experiences a distortion introducing the higher ordered harmonics that are detected.




Referring to

FIG. 6

, if the H-field is essentially a pure sine wave, in the absence of any saturated material, the detected B-field


52


will exhibit a fundamental frequency


64


at the frequency of the sine wave and possibly a low order harmonic


66


resulting from imperfections in the sine wave generation but essentially no harmonic content above the third harmonic.




Referring to

FIG. 7

, with the introduction of the target material


39


however and its saturation, harmonic components


68


will be introduced starting at the third harmonic and extending to the fortieth and beyond harmonic as shown in

FIG. 7

in amount depending on the strength of the M component, the magnitude of the applied field


50


, and the sharpness of the saturation plateaus


63


. These harmonic components, isolated through the band pass filter


60


of

FIG. 5

are provided to the threshold detector


56


to provide the output I/O block


58


to an industrial control system or other output device as has been described. The control system may provide an output indicating proper assembly of a multi-component product having a critical component incorporating the target material


39


.




In an alternative embodiment not shown, the axis between the coils


24


may differ from the axis of the coil


28


so as to obtain off axis signal B-field


52


. Techniques to reduce the detection of the external field H and to enhance the detection of the local field B may include a subtraction of the signal from the amplifier/oscillator


48


in phase with the detected signal or the use of sensing coils


28


wound in opposition so as to provide a cancellation effect for the H-field


50


positioned asymmetrically with respect to the target material


39


so as not to cancel the detected magnetization, or the coil-based subtraction technique described above, as is generally understood in the art.




Multi-Bit Detection




Referring again to

FIGS. 2 and 3

it may be desirable to detect all three of the cap


34


, label


36


and paper insert


38


. Alternatively, it may be desirable to detect among alternative versions of the paper insert


38


. For these purposes, several different sets of magnetic filaments


40


having different magnetic properties may be used.




Different ones of the sets of filament


40


may be incorporated into each of the cap


34


, label


36


and paper insert


38


so as to individually detect the presence or absence of each of these components. The number of simultaneously detectable components will be equal to the number of different sets of filaments


40


.




Alternatively, different ones or combinations of the set of filaments


40


may be incorporated into the label


38


, the presence or absence of each such filament forming a single binary bit of a multi-bit word. The number of different variations in a single detected component will be equal to 2


N


where N is the number of different types of filaments


40


.




Referring to

FIG. 9

, the different sets of filaments


40


suitable for this purpose have different magnetic properties as defined by the set material's magnetization curve


71


. The magnetization curve


71


shows the functional relationship between an applied external magnetic field H and induced magnetic field B. As is understood in the art, the function relating B and H is dependent upon the direction of change of the H-field producing a hysteresis whose magnitude measured at B=0 is the material's coercivity H


c


. Generally, in the preferred embodiment, the materials of each different set of filaments


40


will have different coercivities.




Referring now to

FIG. 10

, a magnetization curve


71


′ for a mixture of multiple sets of filament


40


is the superposition of the magnetization curves for each different material of the different sets of filaments


40


. As will be noted from inspection of the magnetization curve


71


′ , each material provides an identifying region


75


of increased slope.




Referring now to

FIG. 11

, these regions


75


, and hence the materials causing them, may be detected by differentiating the signal from the B-field


52


as occurs naturally from sensing coil


28


and as is indicated by differentiator block


70


to provide a derivative signal


73


shown in FIG.


12


. The derivative signal


73


plotted as a function of time or of phase of the H-field


50


exhibits peaks


77


corresponding to regions


75


. The presence of each of the different sets of filament


40


may be thus detected by a phase sensitive threshold detector


72


measuring the derivative signal


73


at predetermined times that correspond to the different phases in the cycle of the H-field


50


corresponding to the times of occurrences of the peaks


77


and comparing the derivative signal


73


at those times to predetermined empirically derived thresholds. The sets of filaments


40


providing less distinctive peaks


77


may have their relative proportions with respect to other sets of filaments


40


increased.




Referring now to

FIG. 13

, an alternative detector obtains the signal of the B-field


52


from sensing coil


28


and takes the Fourier transform of that signal or its derivative through Fourier transform circuit


74


to produce the Fourier transform signal


78


shown in FIG.


12


. The Fourier transform circuit


74


may be realized using a digital signal processor (DSP) or the like. The Fourier transform signal may be obtained with an H-field


52


having a frequency of one kilohertz although other frequencies are possible, too.




The asymmetry in the B-field


52


induced by hysteresis causes odd harmonics in the Fourier transform to be of particular value in distinguishing the presence or absence of particular sets of filaments


40


. The Fourier transform signal


78


is provided to a frequency dependent threshold detector


76


which may detect the values of Fourier coefficients of the Fourier transform signal


78


or preferably compare Fourier coefficients against each other to detect individual or combinations of sets of filaments


40


according to empirically derived values. Combinations of different sets of filaments produce destructive reinforcement which is most easily detected with the Fourier transform. Another advantage of the Fourier transform is that the range of the H-field can be kept constant and different harmonics selected to determine the presence or absence of different components.




EXAMPLE 1




Samples of different sets of filaments


40


were prepared as mixtures of approximately 10-20 milligrams of each of one, two and three magnetic materials comprising Hi-Mu 80 (also known as Supermalloy), Iron-Chromium-Yttrium (Feralloy) and stressed Stainless Steel 304. To precisely control the coercive field produced by the filaments


40


, specific treatments were provided. The Hi-Mu 80 filaments were annealed at 650° Centigrade to obtain smaller hysteresis and to maximize sensitivity. It is noted that heating in the range of 675° to 800° Centigrade results in a smaller increase in permeability than annealing between 625° and 675° Centigrade while heating at temperatures above 800° Centigrade can result in sintering of the filaments. After annealing, the Hi-Mu 80 filaments can be cut without significant decrease in the permeability, suggesting that for production, annealing can be done at the end of the filament drawing process prior to cutting the filaments.




The Fecralloy filaments were used as stressed materials in an unannealed state. It is believed that two or more different distinct magnetic functions may be obtained with Fecralloy depending on the type of annealing process so that the Fecralloy filaments may produce two different functional relationships that may be distinguished.




As shown in

FIG. 10

, the Hi-Mu 80 filaments


40


had lowest coercivity providing for a quick upward rise in the magnetization curve


71


′ with increasing H-field


50


followed by the effect of the Fecralloy alloy and then by the Stainless Steel 304 filaments. Thus in

FIG. 12

the first peak is produced by the Hi-Mu 80 filaments, second by the Fecralloy filaments and the third by the Stainless Steel 304 filaments.




In

FIG. 14

, a combination of the three filament types are shown by a Fourier transform signal


78


plotted using triangular data points. The Fourier transform signal


78


produced by a combination of the Stainless Steel 304 and the Hi-Mu 80 filaments


40


is plotted using rectangular data points. A Fourier transform signal


78


produced by only Stainless Steel 304 filaments is plotted using circular data points.




Measurements of the Fourier transform signals


78


shown in

FIG. 14

, at nine and nineteen kilohertz will accurately define the mixture.




The above description has been that of a preferred embodiment of the present invention. It will occur to those that practice the art that many modifications may be made without departing from the spirit and scope of the invention. For example, because the filaments respond primarily in one direction, three orthogonal coils could be used for detection and/or excitation of the filaments. The coils would be electrically isolated because of their orientation but could also be sequentially activated or distributed along a conveyor belt or the like so as to further minimize interference. In order to apprise the public of the various embodiments that may fall within the scope of the invention, the following claims are made.



Claims
  • 1. A substance suitable for remote sensing of multi-bit information comprising:a non-magnetic matrix; a first set of magnetizable filaments supported and dispersed by the matrix, the material of the first set of magnetizable filaments having first magnetic properties defining a first functional relationship between magnetic induction (B) and magnetic field (H); and a second set of magnetizable filaments supported and dispersed by the matrix, the material of the second set of magnetizable filaments having second magnetic properties defining a second functional relationship between magnetic induction (B) and magnetic field (H) different from the first magnetic properties; and wherein the first and second sets of filaments overlap within the matrix.
  • 2. The substance of claim 1 wherein the material of the first set of magnetizable filaments has a greater coercivity than the material of the second set of magnetizable filaments.
  • 3. The substance of claim 1 including in addition no less than one additional set of magnetizable filaments supported and dispersed by the matrix, the material of each of the sets of magnetizable filaments having magnetic properties different from the magnetic properties of all other sets of magnetizable filaments.
  • 4. The substance of claim 1 wherein the first and second sets of magnetizable filaments are randomly dispersed in the matrix.
  • 5. The substance of claim 1 wherein the filaments of the first and second filament sets are dispersed in the matrix in predetermined unequal proportion based on their detectability by a remote magnetic sensor system.
  • 6. The substance of claim 1 wherein the materials of the sets of filaments are selected from the group consisting of: Supermalloy, Nickel iron alloys, low carbon steel, Fecralloy and stressed Stainless Steel.
  • 7. The substance of claim 1 wherein the filaments have an aspect ratio of length to thickness of greater than 3.
  • 8. The substance of claim 1 wherein the matrix is selected from the group consisting of: paint; paper, woven textiles, knitted textiles, non-woven textiles, compost wood products, ceramic, and solid polymer.
  • 9. The substance of claim 1 wherein the filaments have a length greater than 1 millimeter.
  • 10. A remote sensor for sensing a target formed of a non-magnetic matrix material supporting a plurality of sets of magnetizable filaments each of the sets of magnetizable filaments having a magnetic property defined as a functional relationship between magnetic induction (B) and magnetic field (H) different from the magnetic properties of all other sets of magnetizable filaments, the remote sensor comprising:(1) an electric oscillator producing a waveform having a fundamental frequency; (2) an antenna structure connected to the electric oscillator for transmitting the waveform as an electromagnetic field to envelop the sensing target within a sensing zone; (3) a receiver connected to the antenna structure for receiving an electromagnetic field as modified by the sensing target; and (4) a detector discriminating between the magnetic properties of the sets of magnetizable filaments to independently detect individual at least two sets of magnetizable filaments, wherein at least a portion of the at least two sets of magnetizable filaments are simultaneously disposed within the sensing zone.
  • 11. The remote sensor of claim 10 wherein the detector includes a differentiator and a phase sensitive threshold detector detecting peaks in the derivative of the received magnetic field as a function of the phase of the waveform of the electric oscillator.
  • 12. The remote sensing system of claim 10 wherein the detector includes a Fourier transformer and a threshold detector for detecting magnitudes of Fourier components at predetermined harmonics of the waveform of the electric oscillator.
  • 13. A remote sensing system comprising:a sensing target formed of a non-magnetic matrix material supporting a plurality of sets of magnetizable filaments each of the sets of magnetizable filaments having a magnetic property defined as a functional relationship between magnetic induction (B) and magnetic field (H) different from the magnetic properties of all other sets of magnetizable filaments; a remote sensor including (1) an electric oscillator producing a waveform having a fundamental frequency; (2) an antenna structure connected to the electric oscillator for transmitting the waveform as an electromagnetic field to simultaneously envelop at least two of the sets of magnetizable filaments within the sensing target; (3) a receiver connected to the antenna structure for receiving an electromagnetic field as modified by the sensing target; and (4) a detector discriminating between magnetic properties of the sets of magnetizable filaments to independently detect individual sets of magnetizable filaments.
  • 14. The remote sensing system of claim 13 wherein the detector includes a differentiator and a phase sensitive threshold detector detecting peaks in the derivative of the received magnetic field as a function of the phase of the waveform.
  • 15. The remote sensing system of claim 13 wherein the detector includes a Fourier transformer and a threshold detector for detecting magnitudes of Fourier components at predetermined harmonics of the waveform.
  • 16. A method of verifying manufacturing operations in the assembly of multi-component products comprising the steps of:(a) identifying at least a first and second component of the multi-component product; (b) attaching to the first component a plurality of magnetizable filaments having a first magnetic property defined as a functional relationship between magnetic induction (B) and magnetic field (H); (c) attaching to the second component a plurality of magnetizable filaments having a second magnetic property defined as a functional relationship between magnetic induction (B) and magnetic field (H) and different from the first magnetic property; (d) simultaneously exposing at least a portion of the first and second components of the assembled multi-component product to a magnetic waveform; (e) detecting a distortion of the waveform caused by magnetic induction in the magnetizable filaments to detect the presence of the first and second components; and (f) providing an output signal indicating proper assembly of the multi-component product.
  • 17. The method of claim 16 wherein the step (f) provide an output signal indicating proper assembly of the multi-component product if both magnetizable filaments of both the first and second components have been detected.
  • 18. The method of claim 16 wherein the step (f) provide an output signal indicating proper assembly of the multi-component product if a predetermined one and only one of the magnetizable filaments of both the first and second components have been detected.
  • 19. The method of claim 16 wherein the volume ratio of filaments to supporting material of either of the first and second component is less than 1%.
  • 20. The substance of claim 16 wherein the volume ratio of filaments to supporting material of either of the first and second component is less than 0.1%.
CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No. 09/290,454 filed Apr. 12, 1999.

US Referenced Citations (7)
Number Name Date Kind
4215342 Horowitz Jul 1980
4915728 Schell Apr 1990
5576693 Tyren et al. Nov 1996
5664582 Szymaitis Sep 1997
5834748 Litman Nov 1998
5988500 Litman Nov 1999
6053406 Litman Apr 2000
Continuation in Parts (1)
Number Date Country
Parent 09/290454 Apr 1999 US
Child 09/409331 US