WO1998038792A1

WO1998038792A1 - Magnetoresistive scanning system

Info

Publication number: WO1998038792A1
Application number: PCT/US1998/003989
Authority: WO
Inventors: J. M. Henson; S. R. Fuelling
Original assignee: University And Community College System Of Nevada
Priority date: 1997-02-28
Filing date: 1998-02-27
Publication date: 1998-09-03
Also published as: AU6343898A

Abstract

A magnetoresistive scanning array (110) and system (118) are provided for scanning magnetic fields on an area of an object (58). The sensor array (110) comprises a plurality of independent magnetoresistive sensors held in a predetermined configuration. Several sensor array configurations are disclosed that are capable of generating two-dimensional data of the magnetic fields on an object. The system further comprises a processor device that is capable of analyzing and manipulating the data and performing other functions related to the system. Applications for the present invention include currency validation, document scanning, and read only memory devices.

Description

MAGNETORESISTIVE SCANNING SYSTEM

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims priority of U.S. provisional patent application serial No.

0/038,547 filed on February 28, 1997.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to an array and system for scanning and analyzing magnetic

fields. More particularly, this invention relates to an array and system that is capable of

scanning magnetic fields in two-dimensional areas, generating two-dimensional data,

generating two dimensional images of the magnetic fields, and analyzing the data.

2. Description of Related Art

Magnetoresistive sensors are well known in the art for measuring or detecting

magnetic fields. These sensors utilize materials in which internal electrical resistance

changes in response to changes in applied magnetic fields. The output signals produced by

magnetoresistive sensors may be proportional to the intensity of the applied magnetic fields.

Magnetoresistive sensors have been adapted for use in a variety of applications. For

example, U.S. patent number 5,378,85,2 to Jones Jr. et al. discloses a device that is intended

for use with currency validation equipment. U.S. currency and other currencies utilize

magnetic ink to produce a distinctive magnetic signature. Figures 1 A and IB illustrate the

operation of a prior art one-dimensional magnetoresistive sensor, such as the sensor disclosed

in Jones Jr. et al., in currency validation. As the sensor moves across a bill 20 on a line 24, it produces an output signal that is proportional to magnetic fields on the bill. The output signal

may be plotted to obtain a magnetic curve 22 in which spikes a-k correspond to magnetic ink

lines a-k on bill 20. Curve 22 may then be compared to a standard curve to determine the

validity of bill 20.

Prior art magnetoresistive devices, however, have failed to provide sensors and

systems that are capable of efficiently scanning two-dimensional areas and producing high

resolution two-dimensional data of magnetic fields. Although a one-dimensional line of data

across an object renders useful information, a much greater amount of information can be

obtained from two-dimensional data. In the field of currency validation, for example, a two-

dimensional "magnetic image" can be generated for verifying the authenticity of a bill.

Figure 2 A is an optical image of a zero on a 1997 U.S. $100 bill taken with a charge coupled

device camera with a magnification system. Figure 2B is a two-dimensional magnetic image

of the zero in Figure 2 A that may be produced by the present invention. Figure 2C is a two-

dimensional magnetic image of a portion of the portrait of a U.S. $100 bill. As can be seen

from Figures 2B and 2C, two-dimensional magnetic images are capable of generating optical

quality images. Although it is difficult for counterfeiters to reproduce a one-dimensional

magnetic curve of a bill (as seen in Figure 1 A), it is much more difficult to reproduce intricate

two-dimensional magnetic patterns. One-dimensional scanning systems are also more

sensitive to variations in printing, migration of magnetic material over time, and the

positioning of bills in the scanning system.

Two-dimensional magnetoresistive scanning systems may also be utilized in other

applications. For example, many computer printers utilize or can be adapted to utilize

magnetic toner. When the toner is deposited on a printed page, the letters and figures on the

page are capable of producing a magnetic image. Two-dimensional magnetoresistive scanning systems may be used to efficiently scan the letters and figures on the page to

generate accurate two-dimensional data. Well known character and pattern recognition

techniques may then be used to analyze and manipulate the data.

A magnetoresistive scanning system can also be used to store and read data. Data can

be stored on an object by depositing magnetic material on the object in a predetermined

pattern and in predetermined densities. A scanning system can then read the data from the

object by detecting the location and intensities of the magnetic fields of the magnetic

material. Data stored in this way is more secure than other magnetic storage devices. For

example, disk drives and tape cassettes are vulnerable to strong magnetic fields that can erase

data stored on these devices. Since magnetoresistive scanning systems only rely upon the

location and densities of magnetic material, not polarity of magnetic fields, the data is not

vulnerable to strong magnetic fields. Thus, inexpensive media, such as paper or plastic, may

be used as permanent read only memory.

In many applications magnetoresistive scanners offer significant advantages.

Magnetoresistive scanners tend to be highly robust and durable. Unlike optical scanners,

magnetoresistive scanners are not subject to contamination from dust, oils, and other

substances. Magnetoresistive scanners also do not sense extraneous marks or optical

impurities that may be present on an object. Thus, magnetoresistive scanners can produce

more accurate data under many circumstances.

However, prior art magnetoresistive sensors cannot be efficiently used for two-

dimensional applications. For example, the device disclosed in Jones, Jr. et al. utilizes a four

sensor design that is intended to enhance the output signals of the device. However, the

sensors are positioned in line with the direction of motion of the sensors relative to a bill;

thus, they are not capable of scanning a two dimensional area during a single movement relative to a bill.

U.S. patent number 4,98,850 to Masuda et al. discloses a device that is intended for

use with magnetic media readers. The device utilizes a magnetoresistive element array with

discrete and widely separated magnetoresistive elements. Unlike Jones, Jr. et al., the

elements are positioned in a parallel arrangement with respect to the direction of motion of

the magnetic media relative to the array. However, this device is intended to read separate,

discrete rows or lines of data from a magnetic card. The array is not intended to scan an area

and generate two-dimensional data capable of representing the magnetic fields in that area.

The distance between the sensors is at least twice the width of a sensor; therefore, a

continuous area could not be scanned during a single pass over a two-dimensional area.

Other devices have been developed for producing two-dimensional magnetic data.

The devices disclosed in U.S. patent numbers 3,978,450 to Sanner et al. and 4,058,706 to Kao

et al., for example, disclose read heads with a plurality of sensor elements. The elements are

arranged in two or more parallel arrays that are perpendicular to the direction of movement

over an object. The references are silent as to the type of sensor elements used. However, the

most likely reason why the devices use multiple parallel arrays of sensors instead of a simpler

single array is because they utilize inductive sensors. Unlike magnetoresistive sensors,

inductive sensors cannot be placed close to each other because of interference, cross coupling,

and other problems. To overcome these limitations both Sanner et al. and Kao et al. utilize

multiple parallel arrays of inductive sensors. The sensors in each array are widely spaced and

it is necessary to use a complex circuit to combine the signals of the arrays to obtain two-

dimensional data during a single sweep. Neither Sanner et al. nor Kao et al. suggests the use

of magnetoresistive sensors. SUMMARY OF INVENTION

1. Objects of the Invention

It is an object of the present invention to provide a magnetoresistive sensor array

capable of scanning magnetic fields on an object.

It is another object of the present invention to provide a magnetoresistive sensor array

with differential pairs of magnetoresistive elements for reducing noise caused by ambient

magnetic fields.

It is a further object of the present invention to provide a magnetoresistive sensor

array in which the sensors are formed using integrated circuit manufacturing techniques to

provide a high-density array.

It is a further object of the present invention to provide a magnetoresistive scanning

system in which a sensor array provides data to a processor for performing various functions.

system that is capable of authenticating currencies based on the magnetic material in the

currencies.

system that is capable of generating two-dimensional images of magnetic fields on an object.

It is another object of the present invention to provide a nonvolatile read only memory

in which the two dimensional location of magnetic fields on an object is used to convey

information.

system in which the scanning system may read data and programs by scanning magnetic fields on an object.

These and other objects of the present invention may be realized by reference to the

remaining portions of the specification, claims, and abstract.

2. Brief Description of the Invention

The present invention comprises a magnetoresistive sensor array. The sensor array

comprises at least one substrate and a plurality of magnetoresistive sensors. Both the

substrate and sensors are formed by methods that are well known in the art. In the preferred

embodiment, the sensors are very small providing a high linear density with small distances

between the sensors. This provides high resolution which is necessary in many applications,

such as currency validation.

The sensor array may be designed in many different configurations. One

configuration provides pairs of magnetoresistive sensors in a differential configuration. The

differential configuration provides for the cancellation of ambient magnetic fields. The

present invention may also include a flux guide for directing magnetic fields to a sensor. The

sensor array may also comprise amplifying and multiplexing circuitry for conditioning the

output signals of each sensor. The amplifying and multiplexing circuit may receive impute

signals from a processor or other associated device.

The present invention also comprises a magnetoresistive scanning system for scanning

data from an object. The scanning system comprises at least one magnetoresistive sensor

array, at least one magnet, and a processor. The magnet is provided for magnetizing

magnetic material on the object before it is scanned by the array. The processor is adapted to

control the scanning system and analyze data obtained from the object. Analysis of the data may include many methods that are well known in the art, such as character and pattern

recognition. The processor may also communicate with other devices for performing various

functions related to the scanning system.

One embodiment of the present invention is to provide a currency validation system

for verifying the authenticity of a currency object. The currency object may be a bill,

banknote, certificate, license, title, checks, or any other document that is capable of holding

magnetic material. The currency object is introduced into the system of the present invention and the sensor array scans data from the object. The processor then analyzes the data,

comparing it to a template or set of acceptable parameters. The system is also capable of

generating a high resolution image of the magnetic fields of the object and presenting this

image to users of the system.

The above description sets forth, rather broadly, the more important features of the present invention so that the detailed description of the preferred embodiment which follows

may be better understood, and contributions of the present invention to the art may be better

appreciated. There are, of course, additional features of the invention that will be described

below and which will form the subject matter of claims. In this respect, before explaining at

least one preferred embodiment of the invention in detail, it is to be understood that the

invention is not limited in its application to the details of the construction and to the

arrangement of the components set forth in the following description or as illustrated in the

drawings. The invention is capable of other embodiments and of being practiced and carried

out in various ways. Also, it is to be understood that the phraseology and terminology

employed herein are for the purpose of description and should not be regarded as limiting.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1A is substantially a schematic representation of a magnetic material bearing

$100 bill with a scanning path of a prior art one-dimensional magnetoresistive sensor

indicated thereon.

Figure IB is substantially a magnetic curve of the bill shown in Figure 1 A of a type

that may be produced by a prior art sensor.

Figure 2A is a magnified optical image of a zero from a 1997 U.S. $100.00 bill.

Figure 2B is substantially a two-dimensional magnetic image of the zero shown in

Figure 2 A that may be produced by the present invention.

Figure 3 is substantially a top schematic view of one embodiment of the sensor array

of the present invention.

Figure 4A is substantially a front schematic view of another embodiment of the sensor

array of the present invention that utilizes differential sensors and a permanent magnet.

Figure 4B is substantially a cross sectional schematic view of the embodiment in

Figure 4 A taken along line I-I.

Figure 4C is substantially an isometric schematic view of a differential sensor

configuration of the embodiment shown in Figure 4A.

Figure 5 is substantially a cross sectional schematic view of an another sensor array of

the present invention that utilizes a flux guide.

Figure 6 is substantially a schematic view of a multiplexing circuit in use with a

sensor array of the present invention.

Figure 7 is substantially a side schematic view of a scanning system of the present

invention.

Figure 8 is substantially a block schematic diagram of a scanning system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As seen in Figure 3, the present invention comprises a magnetoresistive sensor array

generally indicated by reference number 30. Sensor array 30 comprises a plurality of

magnetoresistive sensors 32 attached to a substrate 34. Sensors 32 and substrate 34 are

shown in simple block form for purposes of illustration; many shapes and configurations may

be utilized. Sensor array 30 also comprises conductive input connectors 36 for supplying

electrical current to each sensor 32 and output connectors 38 for transmitting output signals to

processing circuits.

In the preferred embodiment, sensors 32 and substrate 34 are formed using

techniques that are well known in integrated circuit and sensor manufacturing technology.

The individual magnetoresistive sensors 32 may comprise several layers that are deposited

either by vacuum vapor depositions, epitaxy, metalorganic vapor deposition, or sputtering, to

name a few. These films may comprise the actual magnetoresistive film, which may be NiFe

or FeCo, an electrical, nonmagnetic insulating layer, and a magnetically soft alloy, flux guide

layer. A magnetically hard layer may be deposited (which is essential a permanent magnet)

to bias the magnetoresistive film. Bias may be needed to bring the output signal of the

magnetoresistive film into a linear range. Electrical connectors 36 and 38 may be made out

of copper or aluminum. The layers may be deposited on substrate 34, which may comprise

ceramic material, after masks have been consecutively placed on the substrate by

photolithography. Additional shielding layers may be deposited to limit the sensitivity of the magnetoresistive film to a small region.

Many different sensor designs are possible with these manufacturing techniques. For

example, it is possible to produce sensors that utilize the Giant Magnetoresistive Effect and

the ColossafMagnetroresistive Effect.

Once sensors 32 are deposited on substrate 34, the substrate is cut by a stylus and

functional groups are assembled on a second substrate, which could be made of other

material. Once the array is attached to a supporting structure, wire bonds are made that

connect power to individual groups of sensors. The finished assembly can be tested for

proper function and faulty connections may be corrected if necessary. The assembly may

then be inserted into a plastic molded object and embedded with an epoxy. After the epoxy is

cured, the device may undergo a final functionality test.

These and other manufacturing techniques now make it practical to form high-density

magnetoresistive sensor arrays with very small sensors and small sensor separations. Similar

techniques have been used to produce complex optical sensors that may be placed on a single

microchip. Sensors 32 may be placed on substrate 34 in sufficient densities to achieve high

resolution desired in many applications. For example, in bill validation and character

recognition, the linear density of sensors 32 is preferably at least one sensor per millimeter.

Densities of this magnitude are not possible with prior art sensor arrays, such as the one

found in Masuda et al. In order to achieve high resolution it is also desirable to minimize the

distance between sensors. In bill validation and character recognition, the distance between

sensors is preferably less than ten microns. Small sensor separations such as this cannot be

used with prior art inductive sensors because of interference, cross coupling, and other

problems associated with these sensors.

Sensor array 30 may be any length required to meet the needs of a particular application. In bill validation applications, sensor array 30 is substantially the width of a bill.

However, the cost or difficulty of manufacturing long sensor arrays may require the use of

multiple sensor arrays or substrates of shorter lengths. It is recognized that the sensor array

of the present invention may take many different configurations. For example, the array need

not be placed in line or on a single plane. Furthermore, the structure of the individual sensors

need not be the same throughout an array. Smaller sensors may be used in some portions of the array to achieve finer resolution and flux guides may be used in some or all sensors to

direct magnetic fields.

The resolution of array 30 is defined as the ability of the array to distinguish between closely spaced small areas of magnetic ink on an object in both the x and y directions. The resolution in the direction of scan depends on the width of the sensor 32 the width of the flux

guide used to direct the field to the sensing element, and the sampling rate. Decreasing the

width will increase the resolution in this direction. The resolution of the array, Δ y, in the

direction perpendicular to the scan depends on the length of sensor 32 as well as the distance between sensors. Decreasing length and separation enhances resolution.

Figure 4 A and 4B disclose an alternative sensor array configuration 50 in which pairs

of sensors are used in a differential configuration. Upper sensors 52 and lower sensors 54 are

attached to substrate 56 in a substantially parallel arrangement separated by the height of the substrate. A permanent magnet or electromagnet 60 may be provided in close relative

proximity to sensors 52 and 54 for biasing the sensors and for magnetizing the magnetic field bearing substances on object 58. The entire array may be encased in a protective cover 62.

The differential configuration allows for the reduction of noise caused by ambient

magnetic fields. Lower sensors 54 sense magnetic fields from object 58. However, in this

embodiment the additional distance from the object of upper sensors 52 substantially weakens the magnetic fields from the object. As seen in Figure 4C, a differential circuit is used in the

differential configuration to produce an output signal for each sensor pair. A common input

voltage 64 is provided for upper elements 52, a common ground is provided for lower sensors

54, and an output connector 68 is provided for each pair of sensors. As seen in Figure 5, the present invention comprises a sensor array 70 that is adapted

to use a flux guide 72 for directing magnetic flux onto sensors 74 and 76. Magnetic flux guides are well known in the art and many different configurations may be used to achieve

the objects of the present invention. In the preferred embodiment, flux guide 72 and sensors 74 and 76 are integrally formed on substrate 78 using integrated circuit manufacturing

techniques. Sensors 74 and 76 are provided in a differential configuration to provide a

differential output signal.

Figure 6 discloses an amplifying and/or multiplexing circuit that may be used with the

sensor arrays of the present invention. Sensor array 90 comprises a plurality of sensors 92.

In the example disclosed in Figure 6, differential sensor pairs are used to produce differential

output signals; however, a non-differential configuration may also be used. Each sensor pair

has an output connection 94 for transmitting output signals to amplifying and multiplexing

circuit 96. The circuit 96 amplifies sensor output signals and multiplexes the signals for

transmission to a processor. Circuit 96 may also receive input signals, such as clock signals,

synchronizing signals, and bias signals, from other devices. Although sensor array 90 and

circuit 96 are shown as separate elements, it is possible to integrate the two elements into a

single integrated device. Furthermore, it is possible to integrate sensor array 90 with a processor or other device.

As seen in Figure 7, the present invention comprises a scanning system generally

indicated by reference number 118. Scanning system 118 comprises sensor arrays 110, processor 112, transport device 114, and magnet 116. Sensor arrays 110 may be any of the

sensor arrays discussed previously that are adapted to meet the needs of the particular application. Although two arrays are shown, any number of arrays may be used depending on

the application. Transport device 114 is provided to produce relative motion between a

magnetic material bearing object 58 and sensor arrays 110. Magnet 116 is provided to magnetize magnetic material on object 58 so that the magnetic material produces detectable

magnetic fields. The shape and orientation of magnet 116 may be altered and still achieve the

objects of the invention. In addition, a greater number of magnets may be used. Sensor

arrays 110 is operatively connected to processor 112. Processor 112 may be adapted to perform a number of functions that are related to the function of system 118. For example,

processor 112 may analyze and store data transmitted from array 110. Tensioning devices 120

may also be provided for placing object 58 in a preferred position relative to sensors 110.

Scanning system 118 allows object 58 to be used as a read only memory device. In this embodiment magnetic material is deposited on object 58 in a predetermined two-

dimensional pattern with predetermined densities. The pattern and densities of the magnetic

material serves as a code that is capable of conveying information to processor 112. Because

it is the pattern of the magnetic material that conveys information and not the polarity of the

material, object 58 is capable of permanently storing data. As object 58 passes between

magnet 116, the polarity of the magnetic material is adjusted to a predetermined orientation. Sensor array 110 is then able to read the two-dimensional pattern of the material.

Scanning system 118 may also comprise any number of other sensors and devices.

For example, system 118 may comprise a photodiode array or charge couple device array

121, a photo transistor 122 with an opposing ultraviolet light source 123, and a photo diode

125 with an opposing infrared or visible light source 124. Any one of these sensors or a combination of these sensors with other sensors may be used by system 118 to read additional

data from object 58. For example, in currency validation photodiodes and a light source may

be used to analyze certain patterns, materials, and structures on the currency.

One of the advantages of the present invention is that data or programs may be conveniently entered into processor 112. Object 58 may be a preprogrammed read only

memory device that is inserted into system 118. As sensor arrays 110 read the data, processor

112 recognizes the data as data or programs to be added to the processor. Processor 112 then

performs the necessary functions to either store the data or reprogram itself. In this way, an

untrained operator may easily and efficiently reprogram or add data to system 118. This may be especially advantageous to currency validators that must be reprogrammed when new currencies are issued.

Another advantage of the present invention is that changes in currency do not require

modifications of scanning system 118. Governments periodically change the properties of

their currencies to hinder counterfeiting. If a system relies upon one-dimensional sensors, it may be necessary to reposition the sensors to obtain appropriate data. Since the present

invention is capable of scanning the entire surface of a currency object, there is no need to

modify the scanning array of the system to accept modified currencies. It is only necessary to

update the standard data of the system. This may be done using object 58 as discussed above.

As seen in Figure 8, system 118 may comprise a processor 130 that is operatively connected to transport mechanism 114, sensor array 110, other sensor 148, memory 140, and

analog to digital converter (ADC) or comparator 138. Processor 130 is capable of controlling the scanning process as well as performing other tasks associated with the scanning

application. Processor 130 controls transport mechanism 114 so that object 58 and sensor

array 110 move relative to each other at a predetermined rate. Transport mechanism 114 may also be made to reject object 58. Processor 130 may communicate with sensor array 110,

sensor 148, and ADC 138 to provide synchronization signals and other data.

As the sensor array scans data from object 134, it multiplexes the data and transmits

the data to ADC 138. ADC 138 may convert the multiplexed data to serial eight bit data and

transmits the data to memory device memory device 140, processor 130, or both. Process

130 and memory device 140 may be any of a large number of devices that are well known in

the art. Alternate sensor 148 may be provided for scanning object 58 for a type of data not

provided by sensor array 110. After scanning the data, the data may be transmitted to ADC 138 for conversion to serial eight bit data.

Analysis software and data 144 may be provided to processor 130 by erasable

programmable read only memory (EPROM) 142. This allows analysis software 144 to be changed by switching EPROM 142 with another programmed EPROM. Many other methods

and devices may also be used for introducing new software and data into system 118. For

example, a communication network may be provided for loading software remotely or object

58 may be used as a read only memory as discussed above.

Analysis software may comprise a large number of methods that have been devised in

the art for recognizing patterns and comparing features. For example, analysis software may

comprise a very fast two-dimensional template-patching algorithm. This algorithm takes into

account printing/plate tolerances and known irregularities. Templates may be based on known

binary (black and white) patterns, such as the one shown in Figure 2B. Additionally, full

eight bit gray level image information (not shown) may be used during the analysis

procedure. System 118 may be used to analyze the entire surface of object 58 or, because it is

capable of high resolution, small individual features of the object may be analyzed. Once the

analysis is complete, system 118 may perform other appropriate tasks and functions. Processor 146 may also be adapted to communicate with device 146. Device 146 may

be any device that is relevant to the operation of system 118. For example, device 146 may

be a display device, such as a monitor or printer, for displaying magnetic images. In the field

of currency validation, it may be very useful to display a magnetic image of object 58. This may be particularly useful to closely examine known counterfeit currency.

It is recognized that some or all of the components and elements shown in Figure 8 may be integrated into a single embedded device. This may facilitate efficient manufacturing

and maintenance.

SUMMARY

It may now be seen from the above specification that the present invention comprises

a novel magnetoresistive sensor array and scanning system. The present invention comprises:

1. A magnetoresistive sensor array that is capable of efficiently scanning

magnetic fields on at least a two-dimensional area of an object during a single

movement by the object; 2. A system for collecting magnetic field data on a two-dimensional area of an

object;

3. A system for analyzing magnetic field data on a two-dimensional area of an

object;

4. A system that may be reprogrammed by scanning the pattern and intensities of magnetic fields on an object; and

5. A system for recognizing and validating currency objects.

While the above description contains numerous specificities, these should not be

construed as limitations on the scope of the invention but rather as exemplifications of some of the presently preferred embodiments thereof. For example: 1. The number and type of magnetoresistive sensors comprising an array may be

varied;

2. The shapes, sizes, and arrangements of the magnetoresistive sensors may be

varied singly or in combination;

3. The number, shapes, sizes, and arrangements of the magnets can be varied

singly or in combination; and

4. The shape, number, and configuration of the magnetic flux guides may be

varied; and

5. The sampling rate of each sensor may be varied independently or in unison

with other sensors in a scanning movement.

Thus, the scope of the invention should be determined by the appended claims and

their legal equivalents rather than by the examples given.

Claims

CLAIMSWhat is claimed is:

1. A sensor array for scanning magnetic fields on an object and producing output signals

for generating two-dimensional data, comprising:

(A) at least one substrate;

(B) a plurality of adjacent magnetoresistive sensors attached to said substrate in

close relative proximity, said sensors being adapted to produce variable output

signals responsive to magnetic fields applied to said sensors, the signals being

adapted to produce two-dimensional data of the magnetic fields on the object,

wherein the sensor array is adapted to scan a two-dimensional area on the object in a

single motion by the object.

2. The sensor array of claim 1 wherein said sensors are arranged in a substantially linear

configuration on said substrate.

3. The sensor array of claim 1 wherein separation between said sensors is substantially

ten microns or less.

4. The sensor array of claim 1 wherein linear density of said sensors is substantially at

least one sensor per millimeter.

5. The sensor array of claim 1 further comprising a multiplexing circuit operatively

connected to said sensors.

6. The sensor array of claim 1 wherein each said sensor comprises a first and second

magnetoresistive element, said first element being adapted to receive a stronger

magnetic field form the object than said second sensor, said first and second elements

being operatively connected to provide a differential output signal.

7. The sensor array of claim 1 further comprising at least one magnetic flux guide.

8. The sensor array of claim 1 further comprising a processor operatively connected to

said sensor array.

9. A sensor array for scanning magnetic fields on an object and producing output signals

for generating two-dimensional data, the sensor array being adapted to scan an area of

the object during a single pass by the object, the sensor array comprising:

(A) a plurality of sensor means for scanning a two-dimensional area of an object

and producing variable output signals responsive to magnetic fields on the

object; and

(B) means for holding said plurality of sensor means in a predetermined

configuration relative to the object.

10. The sensor array of claim 9 further comprising means for multiplexing the output

signals.

11. The sensor array of claim 10 further comprising means for guiding magnetic flux to

said sensor means.

12. The sensor array of claim 9 further comprising means for processing the output

signals produced by said sensor means.

13. The sensor array of claim 9 further comprising means for producing a differential

output signal.

14. A system for scanning magnetic fields on an object and producing two-dimensional

magnetic field data, comprising:

(A) at least one magnetoresistive sensor array, said sensor array being adapted to

scan a two dimensional area of the object during a single motion past the

object and generate variable output signals responsive to the magnetic fields

on the object;

(B) at least one processor operatively connected to said sensor array, said

processor being adapted to processes the output signals and generate two-

dimensional magnetic field data.

15. The system of claim 14 further comprising a transport device for producing relative

motion between said sensor array and the object.

16. The system of claim 15 wherein said processor is adapted to control said transport

device.

17. The system of claim 14 wherein said processor is adapted to analyze the data.

18. The system of claim 14 further comprising at least one non-magnetoresistive sensor

operatively connected to said processor, said electromagnetic sensor being adapted to

scan the object and produce output signals.

19. The system of claim 14 wherein said processor is adapted to generate a two- dimensional image of magnetic fields on the object.

20. The system of claim 14 further comprising a display device operatively connected to

said processor.

21. The system of claim 14 further comprising a memory device.

22. The system of claim 14 wherein said system is adapted to read data or programs from

the object, the data or programs being for the operation of the system.

23. A system for scanning magnetic fields on an object and producing two-dimensional

magnetic field data, comprising:

(A) ^_ at least one sensor array means for scanning a two dimensional area of the

object during a single motion past the object and generating variable output

signals responsive to the magnetic fields on the object; and

(B) at least one processor means operatively connected to said sensor array for

processing the output signals and generating two-dimensional magnetic field

data.

24. The system of claim 23 further comprising means for storing the high-resolution data.

25. The system of claim 23 further comprising means for producing relative motion

between said sensor array means and the object.

26. The system of claim 23 further comprising means for scanning non-magnetic data.

27. The system of claim 23 further comprising means for reading data or programs from

the object, the data or programs being for operation of the system.

28. The system of claim 23 further comprising means for displaying a magnetic image.

29. A system for determining the authenticity of a currency object, the system

comprising:

scan a two-dimensional area of the currency object in substantially a single

motion past the object and generate variable output signals responsive to

magnetic fields on the currency object;

(B) at least one memory device, said memory device being adapted to store two-

dimensional magnetic data of a standard currency object; and

(C) at least one processor operatively connected to said sensor array and said

memory data, said computer processor being adapted to compare the output

signals with the magnetic data.

30. The system of claim 29 further comprising a transport device for producing relative

motion between the currency object and said sensor array.

31. The system of claim 30 wherein said processor is adapted to control said transport

device.

32. The system of claim 29 further comprising at least one non-magnetoresistive sensor

operatively connected to said processor.

33. The system of claim 29 wherein the system is adapted to read data and programs from

a programming object, wherein the data and programs are used in the operation of the system.