CA1074445A - Electromagnetic sensor and memory device - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

ELECTROMAGNETIC SENSOR AND MEMORY DEVICE

An electromagnetic sensor and memory device for employment with a reader for magnetically encoded cards has a plurality of bit indicators that detect magnetized data bits in such cards. Each bit indicator is formed from a ferromagnetic core magnetizable to either of two opposite stable magnetized states that switch from one stable state to the other upon application of an appropriate magnetizing field. A control element disposed through the core serves to provide the magnetizing field for switching the stable state of the core and also serves as a sensing means for detecting each switch between stable states.
In a modified embodiment, bias magnetizing field sources are employed with the bit indicators to provide a variety of bit sensing operations.

Description

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EIECTROMAG~TIC SENSOR AND MEMORY DEVICE

The present invention relates in general to electr~-magnetic reading of magnetically encoded cards, and more specifically to a sensor for detectin~ magnetlzed bits in regions in such cardsO

Various readers and sensing devices for detecting magnetized bits in regions in magnetically encoded cards are known in the art7 Although the prior sensors appear to provide satis-factory senslng of bits .125 lnch (3 mm) or larger in diameter, , there is an increasing need for sensors that will detect bits ,-of much small diameters in order that considerably more infor-mation may be encoded ln a credit card or the like. Further- .
more, as more and more information is encoded in a card the ,' importance of rellabllity of operation and simplicity of construction o~ a,sensor for reading e~coded cards is likewise increased.

- The present invention prov~des an in.proved,electro-magnetic sensor ~or detecting magnetized data bits in an ad;acent magnetically encoded card, and includes a plurality ~20 ;of bit indicators that are each formed of a ferromagnetic core ~ ' ' magnetizable to at least two equal and opposite magnetically ¦ -stable states, and~a control means disposed through said core Forming the control means are a drive means that provides a . magnetic field ~or switching the magnetizatlon of each core ~ :
from one stable state tc the other and a sense means ln which an electrical signal is lnduced during each s~able state t~ransition.
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~7~5 In a preferred embodiment, the indicator cores are substantially toroidal in shape and the control means is formed of a pair of electrical conductors, one of which serves as the drive means and the other serves as the sense mear.s.
When an electrical pulse is applied to the drlve means o~ the indicators, a ~irst stable remanent magnetized state is induced in the indicator cores. The squareness ratio of the cores is high and such magnetized state remains virtually unchanged until a second electrical pulse opposite to the first pulse is applied to the drive means for producing a transition of the magnetization in the cores from the first state to a second remanent state.
The transition between stable remanent states occurs abruptl~ and ir.duces a sharp electrical sigrlal pulse in the sense means, which slgnal can be readily detected by common electronic circuitryO However, when a magnetized bit of a magnetically encoded card is wlthin close prox~mity of the cores, the bit magnetic fields of the card induce the lndicator cores into a nonremanent magnetized state that pre-~vents the colls from switching between stable states. Thus, if electrical pulses ~or sw~tching the magnetization of the cores ~rom one stable state to the other stable s~tate are applied to the drive means of the indlcators, a transition t of the magnetization of the cores does not occur. As a result, drive pulses onIy produce sensing pulses in the sense means when a core is not in the magnetic influence of a magnetlzed bito Accordingly, the sensor of the present invention provides a readily discernible indicat1on o~ the presence or absence of magnetized bitso In a modifled embodiment the sensor include3 a '. :' .
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plurality of magnetic ~ield sources, one such source near each bit indicator core to normally influence the cores with a magnetic ~ield similar to that induced by the bit o~ a mag-netically encoded card. The field sources, there~ore, also pre~ent the indicator cores from switching between magnetized stable states. Thus, core stable state transitions do not occur unless the cores are near a magnetized bit that provides a magnetic field opposite in polarity and substantially equal to the field o~ the bias field sources so that there is a cancellation of the two ~ields. Upon such cancellation, drive pulses therea~ter cause the stable state of the cores to switch and result in sensing indications in the sense means~
Accordingly, this modified embodiment only provides readily detectable pulses when the cores of the sensor are in the magn~tic influence of a specific type of encoded card bit, and such embodiment can be employed with a wide variety of magnetically encoded cards.

A preferred embodiment ls described below in connec-tion with the following drawings wherein:

Fig. 1 is a plan view of an electromagnetic sensor of the present invention with portions cut away to show interior construction;

Fig. 2 is an enlarged fragmentary perspective view of the sensor of Fig. 1 with portions cut away to show interior construction;

Fig. 3A is an enlarged perspective view of a bit indicator included in the sensor of Fig. 1 and magneti~ed in a ~irst stable remanent state;

Fig. 3B 1s a graph of a hysteresis loop indicating .

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.. ' . . . . ' , ' ' . " ,: ' . ' . ' . ' ' ' . . ' . . " , , ~4~5 the magnetic characteristics of the bit indicator of Fig. 3A, Fig. 3C is an enlarged perspective view of the bit indicator of Figo 3A magnetized in a second stable remanent state, Fig, 4 is an enlarged perspective view of the bit indicator of Fig. 3A adjacent a magnetized bit of a magnetically encoded card;
Fig. 5 is an enlarged perspective view of the bit indicator of Fig. 3A interposed between a magnetic field source and a magnetlzed bit o~ a magnetically encoded card, Fig. 6A is an enlarged perspective view of a bit indicator that may be utilized in the sensor of Fig. 1 in substitution for the indicator of Fig. 3A;
Fig. 6B is an enlarged perspective view of another type~of bit indicator construction that may be utilized in the~sensor of Fig. l, Fig. 6C is an enlarged perspective view o~ yet another type of bit indicator that may be utilized in the sensor of Fig. l;
:
Figo 7 is an enlarged perspective view of a complex -. .
~ bit indicator that may be utilized in the sensor of Fig. l;
. .
and Fig. 8 is a perspective view of a magnetically ., .
encoded card having a plurality of magnetized regionsO
Referring now to the drawings and with reference flrst to Figso 1 and 2, an electromagnetic sensor 1 is shown that represents a preferred embodiment of the present in-ventlon. ~he sensor 1 is particularly advantageous ~or : .

~079~4~5 employment with a card reader that detects the presence of data bits located in regions of a magnetically encoded cardO
Such bits may each be in the form of a s1ngle magnetized section~ or of a pair of magnetized sectlons interfaced together at a common boundary~ The sensor 1 is shown as having a self cont~ined housing 2, but for practical consid-erations it may be desirable to build the sensor 1 as an integral part of a card reader with which it is employed.

The sensor housing 2 has a relatively thin rectangu-lar configuration and is formed of a top wall 3, a bottom wall 4, sidewalls 8 and 9, and end walls 10 and 11. A backing card 12 is positioned in the housing 2 and is parallel to the top wall 3. Mount.ed on the card 12 in close proximity to the top wall 3 is a planar array of a plurality of minute bit indicators 13 arranged in a number of rows and columns, but such arrange-ment is not essential to the present invention. Instead, the indicators 13 may be positioned in various arrangements to con-form with the location of magnetized bits in the encoded cards that the sensor 1 may be utilized for reading.

As indicated in Flg. 3A, the bit indicators 13 each include a toroidal, ferrite core 14 through which a control means -16 is disposed. A palr of electrlcal conductors 17 and 18 form the control means 16 and serve respectively as a drive means and a sense means. ~ather than using two conductors in the control means it may be desirable to use a single conductor that acts as both the drive and sense means. It would also be ~ -possible to employ more than one of the conductors 17 to form the drive means such as presently used in addressing computer memories. The core 14 is preferably formed from a ferromag~
netic, ceramic material such as magnesium-manganese ferrites -~

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~)7~4~i or other spinel ferri~es and has a rectangular hysteresis loop l9, of the type shown in the graph of ~ig. 3B, with two remanent magnetized stable states 20 and 21. The term "ferro-magnetic" is used here~n to include both ~erromagnetic and ferrimagnetic.

Referring now to Fig. 3B in conJunction with Fig.
3A, directing a d-c pulse, represented by the arrow 22, through the drive conductor 17 results in a magnetic ~ield Hm of the ~orm of closed loop concentric lines that induce a similarly configured stable remanent magnetized state that circles the conductor 17. The magnetic flux 23 resulting from this mag-netization state is substantially confined in the core 14.
Upon termination of the pulse 22 through the drive conductor 17, the magnetic field Hm relaxes and the magnetic flux density decreases a small amount to the stable state 20.

The squareness ratio of the core 14 is high in order that the magnetization of the core 14 remains virtually un-changed from the state state 20 even in the presence o~ a reverse magnetizing force approaching the coercive force. As lndicated by Figso 3B and 3C, however~ application of a second d~c pulse 24 in the drive conductor 17 (such pulse being equal ~ ;
in magnitude but opposite in direction to the pulse 22) pro-duces a reverse magnetizing field ~Hm in the directlon 29 that abruptly reverses the magnetization state o~ the core 14 in the same direction 29 to result in a magnetic flux density ~Bm~ also in the direction 29.

The re~erse magnetic field -Hm falls to zero at the termination of the current pulse 24 and the negative magnetic flux denslty ~Bm decreases slightly to the stable remanent state 210 A second d-c pulse 22 will therea~ter cause ~7~ S
another abrupt reversal in the magnetization of the core 14 and return it back to the magnetic flux densi~y BmO Thus, by directing d-c pulses through the drive conductor 17 -first in one direction and then in the opposite direction- the magnet-ized stable states of the core 14 are abruptly reversed. Eachabrupt reversal of the magnetic flux in the core 14 induces an easily detectable short duration discrete output pulse represented in Fig. 3C by the arrow 28 in the sense conductor 18, and standard electronic circuitry (not shown) may be employed to receive the pulses 28 for detecting the flux reversals that occur. In contrast to using d-c pulses in the drive conductor 17, a-c pulses may be applied to the drive conductor 17 to produce a series of abrupt reversals bekween the two stable magnetized states 20 and 21.

The pulses 28 that are induced in the sense con-ductor 18 are utilized in the present invention to indicate that the bit indicator 13 of Plg. 3A is not in close proximity ~ ~-to a magnetized bit of a magnetically encoded cardO Referring now to Figo 4, one of the bit lndicators 13 is shown ad~acent a por~lon of a magnetically encoded card 30 having a magnetized ~-encoded bit 31 of the type normally employed to form a mag-netized region of an encoded card. The bit 31 may be magnetized such that the direction of its internal magnetic field will be either perpendicular to the planar surface of the card or parallel thereto, but for purposes of clarity the following description of the operation o~ the present invention is made assuming a perpendicular internal magnetic field, indicated in directlon by the arrow 32, is presentO

Due to the close pro~imity of the indicato~ 13 to the magnetized bit 31,the magnetic fleld of khe bit 31 induces .

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magnetization o~ the indicator core 14 with what is substaht-ially a unidirectional ~ield resulting in magnetizat~on as represented by the arrows 33O The bit field is stronger ln magnitude than that induced by drive pulses in the conductor 17O Accordingl~, the bit ~ield dominates in determining the resultlng magnetized state of the core 14. Only a relatively weak magnetic field is required to induce the sta~le states 20 or 21 in the core 14 in the absence o~ a bit ~ield. A
typical .125 inch (3 mm) magnetic bit that is normally employed lU in present magnetically encoded cards produces an external magnetic density o~ 300 oersteds, whereas the external magnetic ` .
~ield necessary to induce the stable remanent states 20 or 21 in the absence o~ a bit field is developed as a result o~ a .:
one amp current pulse that ~ypically produces peak fields o~
approximately 3-15 oersteds ak the core 14.
The magnetic field associated with the bit 31 locks the core 14 in a nonremanent magnetized third state and pre-vents ~lux reversal from the stable state 20 to the sta~le state 21, or vice versa regardless of the number o~ dr~ve .
pulses ln the drive conductor 17. This means that the mag- ~
netized bits of a magnetically encoded card placed on the top .. -wall 3 o~ the sensor 1 can be readily ascertained by inter-rogating each lndioator 13 with an a-c drive pulse or no more than two oppositely directed d-c drive pulses in their associated drive conductors 17. I~ one o~ the indicators is not ad~acent a magnetized bit 31, it provides sensing pulses in lts respective sensing conductor 18 in response to the drlve pulses, but i~ it is near a magnetized bit 31 it will be held in a magnetically locked up condition wherein no si~nal pul.ses are induced in its sense conductor 18. Thus, the LS
present lnvention provldes a magnetized bit sensor ~ith an operation that furnishes two clearly discern$ble condltlons to indicate the presence orr absence of magnetized bl~s of an encoded card As a result, the sensing operation of the present invention is highl.y reliable, but yet involves structure that is relatively simplistic and inexpensiveO

Instead of indicating the absence of a magnetized bit with a sensing pulse, as descr$bed above~ the sensor 1 may be modified to include a plurality of bias magnetic field sources 34 (one of which is shown in Fig~ 5) that are dis- .
posed in the sensor 1 so that one field source 34 is positioned immediately beneath each indicator 13. The field sources 34 can be provided by using permanent magnets or current carrying conductors that may be adapted to change bias field direction or magnitude when necessary to sense bits of different polarity ~ .
or slze. The purpose of the sources 34 is to blas the cores 14 ~;
with a sufficiently strong unidirectional field, indicated by the arrows 38 in Fig. 5, so that the cores 14 are normally in a nonremanent or unstable magnetized third state that inhibits magnetization in the cores 14 from existing in the stable state 20 or 21, or switchlng therebetween.

The strength of the magnetic fields o~ the field sources 34 should be care~ully selected in order that they .:
approximately equal the magnitude of the magnetic fields o~
the bits 31 in the magnetically encoded cards 30 with which the sensor 1 is to be employed. As indicated by Figo 5, khe magnetic fields of the bits 31 and the field sources 34 are opposite $~ n dlrection and serve to cancel one anotherO Upon such field cancellation, app:ropriate electrical pulses in the drive conductor 17 of the indictor 13 therea~ter induce one ' . . ,, ~ :, ~0~ 45i o~ the magnetized stable states 20 or 21 and subsequent trans-itions therebetween ln the core 14~ Thus, with the addition of the field sources 34 the bit indicators 13 signal the presence of an encoded bit by induced electrical pulses in the sense conductor 18.

Although the use of the field sources 34 allows the sensor 1 to provide electrical sense pulses in the conductor 18 only when detecking encoded bits 31 of one type o~ magnetic polarity, the bias field provided by the field sources 34 may be reversed to detect bits of opposite polarities and, thus, the use of the field sources 34 is highly advantageous in the present invention. Furthermore, the sources 34 permit the indicators 13 to operate within a range of magnetic fields that may be designed to allow normal variations in bit sl~e, to permit the sensing of encoded cards with unmagnetized or oppositely magnetized background areas, and also to provide a means for ignoring bits 31 of the wrong size and polarity in an encoded card where it is desirabIe to conceal the encoded data.

In addition to the use of the field source 34 the -sensor 1 may be modified by employing other types o~ bit ~-indlcators as an alternative to the above construction of the ~-indicators 13. As shown in Fig. 6A bit indicators may be formed with two relatively thin layers 39 and 40 of the ferromagnetic ~ilm employed as a core 41 to encircle a control means 42g or the bit indicators may be formed with a magnetic foll core 43, as shown in Fig. 6B. A third form of bit indicators (shown in Fig. 6C) may include a control means 44 that is plated with a ferromagnetic core material 45.
In some instances, it may be desirable to have . .

~(~'7~5 larger output sensing pulses in the sense conductors 18 or a greater sensitivity to small bit fields than provided by the use of a bit indicator 13 with a single core 14 ~or each magnetized bit o~ an encoded cardr Such increased per~ormance may be achieved through the use o~ a complex bit indicator 46 shown in Fig. 7 together with the magnetically encoded card 30O The indicator 46 has three toroidal ceramic cores 47, but any number of cores 47 may be employed to obtain the desired output voltages or sensitivity. Similar to the bit indicators 13, the indicator 46 has a control means 48 formed o~ a drive conductor 49 and a sense conductor 50 that are directed through the cores 47 so that the pulses induced in the sense conductors 50 are additive. Greater sensitivity results from lengthening one direction of the core member because the permeability of the core member increases in that direction.

Thus, as shown and described~ the present invention provides a sensor l that is simplistic in construction but yet provides an improved capability for detecting magnetic bits in magnetically encoded cards. In the above described embodiment, the sensor l is adapted to provide an indication o~ the pre sence of a magnetic bit without regard to holding such data in memoryO However, the sensor l may also be empIoyed as a ~ ;
programable memory sensor that records in memory the particular data obtained from a magnetically encoded card and stores such data until processing of it can begin. Such recording in memcry is produced by the sensor 1 as described following below~
Referring again to Figs. 2 and 3A, each o~ the drive conductors 17 o~ the bit indicators 13 is pulsed with a ~7~45 su~ficient d-c pulse to induce magnetizatlon oP their respec-tive cores 14 in the first magnetized stable state 200 A
magnetically encoded card 519 shown in Fig. 8, ls then posi-tioned on ~he top wall 3 of the sensor housing 2 to be in close proximity to the planar array oP the indicators 13.
The card 51 is composed of a plurality of bit regions 52 equal to the number of bit indicators 13 in the sensor 1. Each bit region 52 is aligned directly above one of the indicators 13 and may or may not include a magnetized data bit.

Certain o~ the bit locations 52 are magnetized to represent one type of digital information such as a "1", and -~:
the remaining bit locations 52 are left unmagnetized to rep ::~
resent a "0". With the card 51 positioned on the housing top ~ -wall 3 of the sensor 1, the field Or each magnetize~ bit location magnetically induces the core 14 of its corresponding bit indicator 13 in a nonremanent third magnetized state, such as indicated in Figo 40 During the time the card is retained in close proxlmity to the indicator 13, subthreshold electrical pulses that tend to induce the magnetized stable state 21 in the cores 14 are supplied to all the drive conductors 17 and persist until after removal of the card 51 Prom the sensor lo Such pulses are subthreshold pulses in that they are not sufficient by themselves to produce a re-versal of the magnetized stable states of the cores 14 from the remanent state 20 to the state 210 Nevertheless, when 0 the card 51 is removed from the sensor 1, the persistent sub-threshold pulses provide a sufficient magnetic Pield to induce the cores 14 that are in the third nonremanent magnetized . .
state to the stable state 21 because less energy is required to induce the stable state 21 in the cores 14 as the , ' ,'` ' : , :"
- .~,,, . ~ , ' 3L~7'~5 nonremanent state is relaxed than is required to switch the cores 14 from the stable state 20 to the stable state 21.
Accordingly, the persistent subthreshold pulses do not effect switching in the cores 14 that were not induced with the non-remanent field. In this way, an information pattern isestablished in the sensor 1 and such information may be later processed. Therefore, not only does the present invention provide an improved magnetic bit senslng operation but also provides memory capabilities that make the present invention a versatile dual function sensor.

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Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A sensor device that is comprised of a housing with at least one planar surface area and is employed for providing an electronic indication of data encoded in a magnetically encoded document disposed in surface-to-surface contact with said surface area, which data is represented by a plurality of magnetic data bits located in various bit regions arranged in a two dimensional pattern and said sensor device further comprises a two dimensional planar array of bit indicators disposed in said housing in a parallel relationship to said surface area of said housing, said planar array including at least one bit indicator aligned with each of said bit regions in a sufficiently close relation-ship to said encoded document that said bit indicators are magnetically influenced by said data bits, which bit indicators each include at least one ferromagnetic core that is magnetizable to one of two alternative stable remanent magnetized states; a control member centrally disposed through said core and including drive means that provides a magnetic field for switching the magnetization of said ferromagnetic core from one stable remanent state to the other when said core is not magnetically influenced by one of said data bits and also including sense means in which an electrical signal is induced during each stable state transition; and said sensor is characterized by the feature of also having a plurality of magnetized bias field sources, each of said field sources being disposed in said sensor in a close proximity to one of said cores to magnetize said cores in a magnetized state that prevents the inducement of the stable remanent magnetized states and transitions therebetween only when said cores are not magnetically influenced by the magnetized bits of said encoded card.

2. A sensor device as recited in claim 1 wherein said cores each comprise a substantially toroidal member having an open center through which said control means is disposed.

3. A sensor device as recited in claim 1 wherein said cores each comprise two layers of ferromagnetic film between which said control means is disposed.

4. A sensor device as recited in claim 1 wherein each of said cores comprise a ring of ferromagnetic foil.