CA1241097A - Identification device - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An identification system to be used in association with a set of objects or persons whereby any member of the set may be automatically identified while the member is located within a predetermined interrogation zone, wherein the system has an oscillator and field coils by which an oscillating electromagnetic field is established in the interrogation zone, an identification tag associated with each member of the set of objects or persons, each tag having a core strip of magnetically responsive material of a type which abruptly reaches saturation at a predetermined level of magnetic field , an electromagnetic coil wrapped around the strip, a switch connected with the coil, electronic circuitry for controlling the opening and closing of the switch according to a sequence in timed relation to the halt cycles of the electromagnetic field which sequence defines an identification code for the tag, and a first antenna connected to the circuitry where the circuitry may be operated by power derived from the electromagnetic field, a field detector for detecting and making measurements of the electromagnetic field in the interrogation zone, and a decoder for determining the identity of a tag according to the measurements.

Description

N~'l`U~,h' Uh','l'~,h'_l,N,V~N'l',l~N
'~'his invention relates to a passive electromagnetically activated electronic transponder identilication ta~ and to an identification method and apparatus using such a tag.
B,A~K~tQ,UND OE''l'HE_INVhNT,fON, Many systems are known ~or automatically determining whether an ob~iect or person is passing a predetermined location and whether such ob,~ect or person 1~ is authorized to pass such location. 1~' such passage is alathorized, the ob,ject or person may continue unhindered.
lf such passage is not authorized. action may be taken ~'or its prevention.
~ uch systems are o~'ten u.sed in the~'t security systems. A special security tag is placed upon an object.
such as an article ~or sale in a .store. If a thiet' attempts to remove the article ~'rom the store. detectors located at the store exits will determine the presence o~' the tag. A1arms indicate to security personnel that a theJ`t is being committed and the thie~' may be apprehended.
l~ the article is paid for by a legitimate customer. the tag is removed. deactivated or changed at a check-out station~ so tha-t no tag i5 de-tected by the detector.s at the store exits.
Other applications of such systems may occux in mail or 1uggage handling systems and personnel and livestock detection or countin~ systems.
~ xamples of such applications. systems and associated devices are disclosed in United States ~atents Nc)s. 3.~18.0S9. 3.'7~0.940. 3,7$4.~26. 4.~21.'7~S.

.4~. ~,U~ l'7~ 4,~4~ 4.~:3, ~l.;3:3~.~31 and 4~342~.9U4.
~ ome detection sy.stems make use o~ ta~s having permanent magnets or radioactive mclterial. 'l'ags wit~
permanent ma~nets are bulky and heavy. 'l'a~s using radioactive material pose health risks. ~ther systems ie.g . United ~tates Patent No, 4~242~'71~ m~y require a pieæoelectric tag which re-transmits a delaYed signal. Yet other systems (e.g., ~nited States ~atents Nos. 3~7~0~940 1~ ancl ~021,705) may use a tag having a resonant electronic circuit for retransmitting a generated signal. Some ~aterlts (3.764.22~, 4.~'74.~4~ and 4.2~2.~17) disclose the use o~ electroma~netically activated passive .signal ~--nerator ta~s. All of the, ahove devices Kenerall~ can only be used to determine the presence or non-presence ot a tag. '1'hey cannot determine the speci~ic identitY of the ta~ed ob,~ect.
It is desirable to have a system rlo-t only ~or detectin~ ob~iects or persons~ but a1so for automatically 2U identi~yin~ same. ~uch an automatic identification system makes possible a more flexible. less labour-intensive~
less expensive mail, baggage or material handling system and more reliable livestock and personnel identification.
~ther applications ~or identification systems may be possible.
~xamples of such identification systems are disclosed in United States Letters Patent Nos. 3~ll5~6 :3~l8,0~, 3.832.530. 4~134~3~ and 4.~ .0~3.
Some identification sys-tems (e.~.. United ~tates Patents Nos, 3.11~22, 3~618.~5~ and 4.2'74.~83~ disclose ~ --2-~.c~ Q9~

-t.he use 0~ an active, battery-operated radio -transmitter 'ju~h device~ identi~Y a tagged oh~iect by detection o~` a ll~li~Ue radio siFnal emanatin~ ~rom the transmit-ter on the ~ owever, radio transmitter devices may be exPensiVe.
'I'hev may also be inconvenient and unreliable because of the limited uset'ul battery life.
'l'he s~stem disclo.sed in United ~tates ~atent No.
3.~ 3U depends upon the existence of Gurrent pulses in and the absorption of energy within an electronic circuit lU at~ixed to a ta~. Such current pulses induce voltage pulses in a detector circuit. 'l'he current pulses o~' the tag can be uniquely coded to identi~'y the tagged obiect.
~uch a system re~uires a high degree of sensitivitY so as to be able to distinguish small incremerlts of energy absorption in thè circuit corre~ponding to different identi~'ication codes.
'1'he system disclosed in United ~tates Patent No.
4.13'~.S38 makes use of electromagnetically activated.
passive signal generator tags. Such tags require the selection and dimensioning of magnetic material to provide unique generated signals ~or each tag to. thus. uniquely identify the ta~ged ob~iect. A disadvantage of such system is that it is dif~'icult to select arld size the necessary magnetic material so -that the ta~ will generate a signal capable of being uniquely and reliably distinguishable ~rom the signals of other tags. ~uch a tag may also be somewhat bulky and cumbersome if the system must have the capacity to handle a large number of ob,iects to be identi~`.ied .

3~ It is there~ore desirable to provide an ~ 2~9~

iclerlti~icatic)n system WhiCll i5 inexpensive. reliable.
conYenient to use. uses a tag ot` convenient siæe. has long li~e. and has the capacity to handle various numbers ot`
ob.iects that are likely to ~e required -to be handled.
~TA'1'~,~3~N,1,1 0~,'',,,'l',~h_,1,Ny,hN,'~'l,(~
With a view to overcoming the above-noted problems and to providing the advantages discussed. the invention comprises a method, a sys-tem and a device for the automatic identification of` any member o~ a set of lU objects or persons to be identi~`ied. The device is an identification tag to be used on an object or person to be identi~'ied~ in as,sociation with an identification system which system establishes an oscillating electromagnetic field within a predetermined interrogation zone~ said tag comprisin~ a core strip of rnagnetically resPonsiVe material o~` a type which abruptly reaches saturation at a predetermined level ot` ma~netic ~ield . an electroma~netic masking coil wrapped around said strip~ switch means in circuit with said coil~ electronic circuitry means for controlling opening and closin~ o~' said switch means according to a predetermined sequence in timed relation to the oscillations of the electromagnetic field~ which se~uence defines an identification code ~`or the tag~ and first antenna means connected to said circuitry wherebY
said circuitry may be operated by power derived ~'rom the electromagnetic ~`ield.
The system comprises an oscillator~ ~`ield coils connec-ted to the oscillator whereby at least one oscillating electromagnetic ~ield is established in an 3~ interrogation zone~ an identi~'ication tag as described r ~
-~ ~ ~ 4 9'7 above associated with each member o~ the set of ob~iects or persons, ~'ield detection means for detecting and measurin~
the electromagnetic ~ield. and decoder means to determine the iclentity o~' a tag according to the measurements.
The method comprises -the operation of the system described above to identi~`y tags~ and thus ob~iects or persons and distinguish them from each other.
Accordingly, it is an obiect of the invention to provide an identification system which is inexpensive, 1~ reliable and convenient to use.
lt is a further obiect of the invention to provide an identificatiorl system which utilizes a durable identi~'ication tag of convenient size which has long life.
~ t i5 a further ob,ject of the invention to provide an identification system which has the capacity to handle various numbers of objects or persons that are likely to be required to be handled.
In accordance with the invention, the magIIetically responsive material in the tag is a material which i5 saturable, magnetically in a magnetic field of a predetermined streng-th. When sub~iected to a magrletic ~'ield o~' this strength. the material undergoes a sudden transition to saturation, and thus a sudden c~lange in its response. 'l'his abrupt or sudden change or response can be detected by measuring the overall magnetic field in the interrogation zone. l'he abrupt changeover produced by saturation o~'-the material will produce a "blip", which is detectable in the presence o~' the primary field.
ln accordance with the invention, the response of the saturable member may be maskedl by the ef~ect of b-o~

the electromagnetic masking coil~ when the switch in its circuit is closed.
When the switch is open. and there is there~ore rlo circuit. the masking coil is not in circuit. and thus no masking ot the core strip takes place.
The masking coil is switched in and out o~
circuit in a predetermined sequence. thereby producing a predetermined number of "blips". interspersed with an absence of such "blips".
1~ It is thus possible to provide a unique code of "blips", and absences of "blips". which code can be identitied with a particular objec-t or individual unique to the wearer of the tag.
'The various ~eatures oY the novelty which characterize the invention are pointed out with particularity in the claims annexed to and formin~ a part of this disclosure. E`or a better understanding of the invention, its operating advantages and speci~ic objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described pre~erred embodiments ot` the invention.
lN_THE ~
Figure 1 is a schematic drawin~ o~ an identification system according to the invention;
Figure 2 is a schematic diagram of one embodiment of an identification tag according to -the invention;
Figure 3 is a schematic diagram ot` the 3~ electronic circuitxy of the tag of ~'igure ~;

Q9~7 ~ `igure ~l is a graphical representation ot the electromagnetic ~ield prior to passage o~` a tag according t,o the invention;
E'igure b is a graphical representation o~ the electromagnetic field durin~ passage o~ a piece o~ a response member as userl in a tag according to the invention;
E`igure ~ is a ~raphical representation ot the electroma~netic ~ield durin~ passage ot a tag according to 1U the invention; and.
~ 'igure I is a schematic represe~ltation ot a portion of an a.lternate embodiment.
,rl'IO,,N O~,l'.,A _P,~.'1E~ .M~ "IJ~,UT
~ eferrin~ to ~'igure 1, an identi~:ication sys-tem according to the invention is indicated generally as 10.
An ob.,iect or a package 1~ passes through system 1~.
Identi~ication tag 14 is attached to an ob.ject or a package 1~ and passes through system 10 with packagè 1~.
'I'ag 14 and. thus. package 1~. are detected and identified by system 10. The system 1~ uses such identity in~`ormation as required. Eor instance, such intormation may be used to operate conveyor belts (not shown) ~o tha-t package 12 is directed to the appropriate des-ti.nation.
Sys-tem lV may mere:Ly record the in~ormation that a particular package 12 has pa.ssed a speci~ic locat.ion. Sl~ch in~orination rnay be important to trace the path of an ob~iect through a proce.ssing system and to determine whether certain operations have been carried out orl the ob~iect.
Such a system wou.ld be suitable ~or handling ., .

'7 bag~Jage. 'l'he ob~iect may o~ course be an animal. vr a person. 'l'he tag would then Iunction to identi~`y the :indivi~ual. lt could be used to trace individuals in a buildirlg. or the pas.sage ot individuals through a il.it,Y.
'I'he identitication system 10 includes an interrogation gate l~. comprising two pedestals 18 between Wtlich package 1~ must pass. ~ate 16 de~`ines an interrogation zone within which packa~e 12 may be 1~ identi~`ied. Gate 16 includes at .least one pair of electromagnetic field coils 20. ~ne each of coils 2~ is located in each pedestal 18. Such coils and pedestals are well-known in the art. More detailed descriptions of such coils as used in identi~ication systems may be ~ourld in United ~-tates Pa-tents Nos. 3,'7b4.22~. 3,832.S30 and 4.~'l4,~49. In order to improve the detection capabilities of system 1~ to the passage of a tag at dif~erent orient~tions relative to the coils. gate 1~ may include two or three mutually orthogonal pairs of electromagnetic tield coils 20.
Field coils ~0 are electrically connected to ~ield oscillatvr 22. Oscilla-tor 2~ takes power ~rom a ~ower source (not .shown) and establishes an oscillating electromagnetic field between pairs of coils 20.
~enerally. such an oscillator 22 will establish an electromagnetic field which oscillates at a predetermined ~requency. ~uch oscillators ~2 are conventional devices well~known in the electrical ar-ts. hligure 4 presents a graphical representation of the electromagnetic ~ieJ.d, as 3U i-t may be established br osciLla-tor ~2.

o~
~ ate 1~ ~`urther includes an antenna coil 24 ~`or rec:ei~ing signals ~rom ~ield coils 2~ and responses which may be emitted by tag 14 as it passes through the electromagnetic tie.ld. Antenna ~4 is elec-trically connected to a signal amplifier ~. which in turn is connected to decoder ~8. Antenna ~4. amplifier ~ and decoder ~8 may all be standard components~ well understood in the art~
The output of decoder 28 is an electrical 1U signal~ corresponding to the identity o~ package 1~. ~uch a signal~ and other signals (such as~ ~'or example~ a time signal)~ may be inputted to computer 3CJ. C,omputer ~u may simply store such information or computer 3() may.
accordi.ng to its programming, issue instructions to other devi,ces (not showrl) to control ~`urther movement of package 1~. C')~ course~ the output o~ decoder ~ may be fed to a suitable indicator (not shownJ for visually displaying the identity of package 12. Appropriate manual action could then be taken. either in con,junction with or to over-ride an~ action taken by computer 3C).
.All of the above components~ except ta~ 14~ o~`
identi~ication system lC) are essen-tially standard and are well. known in the.art. Such components are described only in order that the invention may be better understood~ and not in order to limit the scope o~ the invention in any way. Kather. it is the intention that the scope o~' the invention covers any detection or identi~'ication system using an identifica~ion tag according to the invention.
~eferring to ~igure ~ tag 14 comprises a base 3C) .3~ to which is affixed or in which is embedded a strip 34 ~;
1 _g_ ~ .~p,,~ Q9~7 oi ma~netically responsive material. ~uch material may cc>nveniently be a t`erromagnetic alloy ot nickel.
molvbderlum, iron and manganese (commonly referred to as supermalloy~. ~ther lerromagnetic materials having a coercivity ranging betwesn 0.1 Oersteds and U~Ol Oersteds may be equally suitable.
This type o~` ma-terial has the property of high permeability in a magnetic field.lt further has the property o~` reaching an abrupt level o~` magnetic saturation at a predetermined level of magnetic ~ield within the material.
When it reaches saturation there is an abrupt chan~e in permeability. ~ermeability rises suddenly to a peak and then ~all~ of sharply. Li'or the purposes of this explanation, the precise level or intensitY of magnetic ~ield is not relevant, and is refered to herein as ~
~auss. 'l'his is the level oi ma~netic field at which a given sample o~ the material abruptly becomes saturated.
'l'he level will vary ~rom one material to another~ and also depending upon the size and shape of the strip 'i4. as is well understood in the art.
The abrupt transition to saturation. at the saturation point of the material results in ~ measurable electromagnetic response. which will produce a measurable signal in the presence of the primary oscillating field. A
response signal would normally be ~letectable on each hal~
cycle of the field.
Wrapped around strip 34 is electromagnetic masking coil 36. Coil 36 is electrically connected by ~i~ line 3'1 to solid state maskin~ relay switch. indicated -lIJ-o~
~enerally as 3~.
When switch 38 is open. no cuxrent can flow in mlasking coil 36. ~witch 38 is operated by electronic circuitry, indicated ~enerally as .3~. which in turn is electrically connected to a tag antenna 40. The oscillating electromagnetic field through which tag 14 passes induces corresponding alternating current in the tag antenna 40. ~uch current is used to power circuitry :~9 .

~uch current is induced solely as a reponse to the oscillating field. and will o~' course cease as soon as the tag is removed ~rom the field. or if the field should be switched off Yor some reason.
Normally the oscillating electromagnetic is on continuously.
Xeferring to Figure 3, circuitry 3~ includes a rectifier and voltage stabilizer circuit 42 which is connected to antenna 40. Circuit 42 establishes a substantially constant voltage output across two output terminals. The circuitry 3g of tag 14 cannot conveniently be grounded. ~owever, circuitry 3~ may define a common point. which, insofar as the operation o~ circuitry 39 is concerned. acts in a fashion similar to a ground. E'or convenience. one of the two output terminals o~' recti~'ier and stabilizer 42 is defined -to 'be such a common point and is named voltage source terminal 44. l'~e other of the two output terminals of circuit 4~ is de~ined to be a voltage drain terminal 46.
Recti~ier and stabilizer 42 also defines a clock 3~ signal. A voltage pulse is ~enerated for each half-cycle Y ' !--`` -11-j ~2~9~

oscillation of the current in antenna 40. ~uch voltage is le~irled across volta~e source terminal 44 and a third output terminal o~ rectifier and stabilizer 4~. namely clock termin~l ~8.
Voltage drain terminal 46 and clock terminal 48 are electricall~ connected to integrated circuitry decade counter chip ~ hip 50 is also connected to voltage source terminal 44. ~hip 50 functions similarlY to a series of ten electronic switches (not shown). Each such 1~ switch connects volta~e drain terminal 46 to one o~ ten counter chip output terminals 52a to 52j. A single voltage pulse of the clock sigr~ rom clock termlnal 48 cause,s one o~ such switche.s to close and~ m~re or less simultaneous1y, a previouslY closed switch to open.
allowing the volta&~e drain si~nal to pass to th~
particular output terminal ~ associated with such swi-tch.
A subsecluent voltage pulse from clock terminal 48 will cause the same switch to open and a subsequen-t switch to close. A further clock si~nal will cause a next switch to operate in identical fashion. A series o~ ten voltage pulses will cause each o~ the switches to close and open once. A subse~uent pulse will cause the switch last closed to open and the first switch to close a second time. The entire sequence will subseguentlY be repeated.
Each of counter chip output terminals 5~a to 5~i is connected to a column line 54 o~ identification code matrix 56~ Matrix 56 also includes a series o~ row lines 58, the ends of which define matrix output terminals 6U.
~olumn lines 54 and row lines ~8 may be electrically 3~ connected bY one or more diodes 6~. but otherwise are not ,~, .

~.2r~3L0~37 conn~ct~d. l'he speci~`ic posi-tionin~ o~ such diodes ~ to .ioin certain column lines h~1 and row lines 58 define a particular identi~ication code. as explained below. Each o1 ~latrix row lines ~ is connec-ted through resistors ~3 to volta~e source terminal 44 in order to provide a path to source terminal 44 for stray currents when no voltage drain signal is present in row lines ~8. --The remaining counter chip output terminal 52.ii5 connected to index terminal 64 to integrated circuitry data .selector chip ~. Matrix output terminals 60 are conrlected to a serie.s of selector chip input terminals 68.
Selector chip ~6 is also connected to voltage source terminal 44. Selector chip ~ ~unctiorls in simi.lar ~ashion to counter chip bO. ~'hip 66 ~unctions similarly to a series o~ electronic switches (not shown7 each connectin~ a selector chip input terminal 68 to selector chip output terminal 7~. A signal from counter chip output terminal 5~j causes one o~ such switches to close and. more or less simultaneously. a previously closed switch to open. A subsequent signal ~rom terminal ~
causes such first switch to open and a subse~uen-t switch to close. l'hus. signals arriving from terminal b~j will cause the switches of selector chip ~ to consecutively close and open. After the last switch is opened. the cycle will commence again at -the ~irst switch.
~elector chip output terminal 70 is conrlected to solid state relay switch 38 in line 3'1. ~ach time a si~nal (which will correspond to the signal in voltage drai.n terminal 46) appears at output terminal 70 switch 38 3~ will c1ose. thus allowing alternating current induced in -1.3-)97 coil :~fi by the passage v-~ tag 14 through -ttle eleclromagnetic ~`ield to ~ w. Line 37 is also connected to voltage source termiIlal 44.
ALl o~ the above cornponents. namely the recti~`ier and s-tabiliæer 4~ the decade counter chip b~.
the identi~'ication code matrix ~6~ the selector chip 66 and switch 38 are well-known and understood in the art.
ln operation. the tag 14 will be passed through the oscillating electromagnetic field generated at gate 16 1~ between pedestals 18. l'he peaks o~ each half' cycle of the magnetic field in this zone are greater than the intensitY
required to produce abrupt saturation o~ strip 34. When switch 38 is open, current cannot be induced in coil 3~
and response strip .34 i5 ~'re~ to respond unhirldered to the iniluence o~ the electromagnetic field. Each hal~' cycle o~' the slectromagnetic Y'ield thus causes both a rever.sal o~ the magnetic polarization o~' response strip ~4 and also causes an abrupt saturation of the stxip 34. Each such reversal and saturation af~'ects the elec-tromagnetic field itself in a gradual and then abrupt manner. As the ~'ield intensity rises from zero the strip causes a gradual distortion ot` the ~ield. When the abrupt saturation takes place there is an abrupt distortion which has the ei~'ect o~' adding an impul.se signal or "blip" to the field (see E'igures 4 and ~). Such "blips" are detectable by the ~'ield detection system. namely antenna 24. ampli~'ier 26 and decoder 28. It will be appreciated such impulse .si~nals or "blips" will occur only during the existence of the primary oscillating electroma~netic f'ield.
3~ Accordingly~ it is o~ partlcular signii'icance to the ~ -14-0~'7 invention that such signals are detectable by the ~`ield detection system during the presence ~` the primary field.
'l'he signals detected by the detection coil will be processed so as to as ~ar as possible cancel ou-t the primary ~ield response and enhance the coded pulses or blips" ~rom the response member 34.
It will of course be appreciated that the generation ot such signals or "blips" in accordance with the invention is dependant upon the continued oscillation o~ the primary ~ield, which in turn is responsible ~or the generation both of the alternating current in the tag antena 4~ and a1so ~`or the gerleration o~ a response in the strip 34 itsel~.
1'hus assurning the SWitCtl remain.s open, therl each hall cycle o~ the primary field will produce a complimentary response signal or "blip" caused by the strip 34 However, when switch 38 is c10sed, alternating current is induced in coil 36, by the primarY
electromagnetic field. 'I'he alternating current in turn induces its own electromagnetic Yield which ef~ective1Y
cancels or at least reduces the primary ~ield. in the region of the strip 34, below that necessary to reach saturation. 'l'hus. if switch .38 is closed. coil 36 acts as a shield or mask between response strip ~4 and the primary electromagnetic field. ~trip 34 is isolated from the influence of the electromagnetic field. There will be no signal or "blip" caused by abrupt saturation o~ the strip 34. ~onsequently, the primaxy electromagnetic field is 3~ no-t a~ected. No impulse signal i~ added to the ~'2.~ac~37 oscillating primary i`ie,ld signal. as would be the case if t,he switch ~ and circuit to coil 36 were open.
onsequently, a graphical represen-tati~n o~ the ti.eld in t,llis c:ondition woulcl look similar to tha-t when J10 tag was present (see ~igure 4).
'l'he tag 14 according to the invention thus al.lows certain impulse signals to be added to particular half cycles oJ the ~ield. Thus~ the presence ot` a specific tag 14 in the field results in a specific train o~ tag impulses being superimposed on the field oscillations, 'l'his ~unction is accomplished by opening and closin~ oY switch 38 and the circuit to coil 36 in a predetermined sequence. which se~uence de~ines the identi~ication cocle oY tag lA. As explained below. the sequence for the opening and elosing o~ switch 38 is controlled by the positioning of diocles in matrix 5~.
I'he operation of matrix ~6 in con~iunc-tion with counter chip 50 and selector chip ~6 is explained with reference to the embodiment illustrated in E'igure 3. It will be appreciated that such embodiment represents only one identification code pa-ttern out of a multiplicity of po.ssible patterns~ It will also be appreciated that the numbsr o~ possible code patterns is dependent on the number oJ column lines and courlter chip output terminals and the number o~ row lines and selector chip input terminals. Although in the illustrated embodiment there are nine column lines and eight row lines, the principle oJ: the invention may be applied with varyin~ numbers of co.Lumn lines and row :lines. It will also be appreciated that although chip 5~ counts by tens ancl chip ~ counts by ei~hts, other chips counting by other numbers may also be us~
~ th~r circuits might be used in place of the rna~rix. E'or example a ring counter. or a series of ring counters (not shown), could be used in place of the matrix. 'l'he circuitry might be more complex to achieve a Large number of unique codes. but in some circumstances this might be acceptable.
For the purposes of this description. it is lu assumed that the first switch of counter chip 5~ to be closed is the switch connecting voltage drain terminal 46 to counter chip output terminal 52a. lt is also assumed t~la-t the t'irst swi.-tch ot' selector chip 6~ to be closed is the switch connecting selector chip input terminal ~8a to c:elector chip output terminal 7~.
As the switch to terminal 5~a is closed, the voltage drain signal is passed to column line 54a and through diode 62aa to row line 58a and terminal ~8a.
Because column line 54a and row line 58a are not connected to any other column lines 5~ or row lines 58. the volta~e drain signal does not reach any other terminal 68. As the switch between terminal 68a and -terminal '70 is closed, the voltage drain signal passes to switch 38 and the circuit to coil 3~ is closed. Thus .strip ~4 is masked and does not at'fect the t'ield during such halt cycle. As a second ha.Lf cycle of the field commences, -the clock signal opens the terminal 52a switch and closes the terminal 52b switch, energizin~ column line 54b.
~'olumn line 54a is no lon~er connected to voltage drain terminal 4~. Consequently, row line 5~a is ., ~2~19~

nc longer ener~ized via diode 6~aa. ~eGaUSe there is no diode connection between column lirle 54b and row line ~8a, row line ~8a is no longer energized at aLl. ~owever.
~lere is a cliode ~ cb connec-ting column line ~4b and r~w line ~c. 'l'hus, row line ~8c and terminaL ~8c are ener~i~ed by the voltage d.rain si~nal. ~owever. because only the switch between terminals 68a and '7~ is open~ the signal at terminal 68c is not passed to switch 38. Thus the circuit to coil 36 is open and strip 34 reacts to add 1~ an impulse signal to the second hal~' cycle o~' the field.
Similarly, the third hal~ cycle adds an impulse to the field sigrlal.
On the ~ourth half cycle, row line 58a is again energized, but through diode 62ad. A voltage drain signal is pas.sed to termina.l 70 and switch 38 is closed. No impulse is added to the Yield signal.
On thc ~i~th to ninth hal~' cycles impulses are added to the ~ield signal.
On the tenth half cycle, the switch between ~0 terminal b2~i and volta~e drain terminal 46 closes. thus sending a signal to index terminal 64. ~uch signal causes the terminal 68a switch to open and the terminal ~8b switch to close. No other action occurs, thus on every tenth hal~ cycle no signal passes to switch 38 and an impulse signal is added to the ~ield signal.
On the eleventh hal~ cycle, the terminal ~a switch closed ~'or a second time, thus energizin~ column line 54a a second time. Again, the voltage drain si~nal is passed thxough diode 6~aa to row line 58a. ~owever, now the terminal 68a switch is open. -thus no si~na.l can -l8-q r~ach switch ~8 and an impulse is added~
~ n the twel~th to fourteenth hal~ cycles. no sigllals reach switch 38.
~ n the ~i~'teenth half cycle~ column line ~4e is energized as is row line 58b via diode ~be. ~ecause the terminal ~8b switch is closed. the voltage drain signal is passed to switch 38 and coil 36 is closed. ~hus. the ~ `teenth hal~ cycle o~ the 1`ield possesses no added impulse~
1~ ~imilarly, on the sixteenth half cycle. column line ~4r is energized. as is row line 58b via diode 6~br.
'I'hus~ the sixteenth half cycle of the tield possesses no added impulses.
With each ~'urther halY cycle, the electronic switches of counter chip b~ and selector chip ~ con-tinue to open and close. A train of impulses passes to switch 3~ in the fa,shion described above. A corresponding train of irnpulses or "blips" is superimposed on the primarY
field. The initial half cycles of such primary field are illustrated in figure 6. After the final hal~ cycle.
corresponding to the closed position of the column line b3i switch and o~ the input terminal 68h switch. the entire irnpulse train of "blips" will be repeated. l'hus.
tag 14 will continue to generate its particular irnpulse train and af~'ect the electromagnetic field for as long as tag 14 is within the ~ield. that is, passing through or near Kate 1~.
~y positioning diodes ~ in dirt`erent positions in rnatrix 5~ dif~'erent impulse trains may be generated.
3~ E'or any given number of counter chip output terminals and --lg-6)9~7 ol selector chip input terminals~ the number of possible identi~'ication codes which may be utilized are determined bl,Y the ~'ollowing relatinship:
N = ~mn where N = number o~' possible codes n = number of matrix column lines m = number of matrix row lines Di~des ~2 may be installed within matrix 56 to d~fine a particular code at the time tag 14 is 1~ manufactured. It may also be possible to allow the operator to choose his own codes. in this case. the manufacturer will manufacture a tag 14 in which diodes 6~
are installed to connect each column line b4 with each row line ~ (.see E'igure 7). lrl such an embodiment, each line '/4 from a column line 54 to a diode ~ and a row line 58 is provided with a removable electrical connection 'l~.
~uch a connection 7~ may be easily removed or broken by the the oper~tor, thus preventing an electrical connection between a particular column line and a particular row line. The removal or breaking o~' connections '7~ thereby defines an identification code. ln such an embodiment it may be n~cessary to increase the physical size o~ tag 14 in order to allow sufficient space for the operator to conveniently remove or break particular COïlneCtiOnS.
In a further embodiment it may be possible for ta~ 14 to .include a con-trol strip (not shown) o~' ferromagnetic material in proximity to strip 34. Such a con-trol strip may be used to deactivate the identification capabilities of tag 14. ~uch control strips are well known in the art (for example see United States ~a-ten-t No.

2~5l'i). `I'he ferromagne-tic material ol the control s~rip ~las a coercivity signi~icantlY greater -than tha-t o~`
strip :j~. 'l'he material o~' the control strip may cooveniently be a terromagrletic alloy o~ iron. cobalt. and vanadium (co~monly referred to as vical:Loy~. At'ter the control strip is magnetized in a deactivation unit.. the control strip prevents the reversal of the magnetic polarization of strip 34 under the influellce of the electromagnetic fie1d. In such a condition. tag 14 cannot 1~ emit a unique identification code.
It wil:l be appreciated that an identi~'ication tag according to the invention may be used not only in material handling applications. but a1so in any other application wher.e identiYicati.Qrl of objects or per.40rlne1 i.s required. E'or instance, without limiting the gellerality o~ the foregoirlg, an identification tag may be conveniently used for livestock identification. A tag may be a~'~'ixed to an animal at birth. Breeding, ~'eedin~, health treatment and other information may be more converliently recorded with the automatic idsntification of the animal concerned. A tag may even remain with an animal carcass after the animal has been slaughtered.
'rhus, meat bu~ers may be provided w1th a reliable means of i.dentifying and obtaining the history of an animal.
Identification tags according to the invention may be used in personnel identi~ication and security systems. A computer connected to a series of interrogation gates placed within a high securj.ty area may record the pa-th of an individual through such area.

3~ ~ertain doors may be locked or unlocked by the computer 09~7 according to whether an individual is authorized to pass through such door.
'rhe tag may also be used to identi~'y library books, or ~'iLes in an automated ~'ilin~J system. 'l'he ga-tes 1~ may be fabricated on a reduced scale and used as a "tag reader". In this way security o~ filing systems couLd be increased. Handlin~ o~` ~'iles in a computerised word processing or accounting facility could be automated to a much higher degree.
1~ lt will be appreciated that although an identification tag according to the invention has been described using solid state or electronic circuity. other electrical parts or components may be used without departing ~rom the principle of the invention. Slach an embodiment may have application where small tag size is not a requirement.
Having described what is believed to be the best mode by which the invention may be per~'ormed, it will be seen that the invention may be particularly defined as Yollows:
An identification system ~or use in association with a set of ob~iects ! such as persons, animals, packages or the like, whereby any member o~ said set may be identified while said member is located within a predetermined interrogation zone, wherein said system comprises;
interrogation ~'ield means whereby at least one oscillating electromagnetic interrogation field may be established in said interrogation zone;
~U response si~nal detection means operable to i ~l~4109~

morlitor said interroga-tion zone;
an identit`ication tag associated with each merll~er o~' said set. each tag comprising;
a response member formed of a magnetical:ly permeable material adapted to reach saturation abruptly at a predetermined level of magnetic flux and responsive to halY cycles of said interrogation field when present in said interrogation zone. upon abrupt magnetic saturation thereo~, to abruptly distort said field thereby generating 1~ a series of Yield distortion pulses correspondin~ to successive hal~ cycles of said interrogation Yield and detectable during said half cycles;
an electromagrletic maskirlg coil around the said response member selectively operabl,e to magnetica1ly mask the same and thereby prevent saturation of said response member and adapted to be rendered inoperable whereby no such masking takes place;
switch means in circuit with said masking coil selectively operable during a half cycle to control said masking coi.l;
circuitry means connected with sai~ switch means and operable to control opening and closing of said switch means according to a predetermined sequence in timed reLation to said half cycles o~ said interrogation Yield thereby establishing during the presence ot' said interro~ation field a series of interrogation field distortion pulses caused by abrupt saturation o~' said res~ponse member, said series of interrogation :~ield distortion pulses being interrupted by a unique series o~
3~ discontinuities in said series of distortion pulses which r A ~ _ 3~! t'~

deiines a~l identi~ication code ~or said ta~;
power means ~or said circuitry means whereby the sarne may be operatecl. and, signal pro-essing mean.s connected to said detection means ~or processing and decoding said series of distortion pulses.
Additionally. the invention provides an identi~'ication tag which may particularly de~ined as ~`ollows:
1~ An identi~`ication tag to be used in association wi1;h an ob,ject such as a person, animal, package or the like to be icientit'ied~ and an identi~ication system which system establishes an oscillating electromagne-tic interrogation t'ield within a prsdeterMirled interrogation ZO~le, said tag coMprising, a response signal member responsive to said continuou~ interrogation t'ield to abruptly reach ma~netic saturation thereby generatin~ a series ot' response signal pulses correspon~ing to successive hal~ cYcles o~ said interrogatiorl l'ield and detectable during said half cycles, electromagne-tic masking coil means around said response si~nal member selectively operable to magnetically mask the same and adapted to be rendered inoperable whereby no such masking takes place. switch means in circuit with said masking coil meansl and selectively operable during a .saicl hal~' cycle to control said masking coil means. electronic circuitry means connected with said switch rneans ancl operable -to control the opening and clos:in~ ot' said switch ~eans according to a predetermined sequence in timecl relation to the oscillations ot' said interrogation t'ield ~ 24-14~ 3~7 t~l~reby establishing during tlle presence ol said int~rrogation tield a series o.t re~ponse signal pulses ~enera-te(i by said response signal rnember~ said series beirlLt i~lterrupted by selective op~ration o~ said maskin~
coil means to produce a unique sequence oi' discontinuities in said series o~ respon.se si~nal pulses, which sequerlce de~'ines an identi~'ication co~e for said tag. and! power means to power said circuitry means.
Additionally, the inven-tion also embraces a 1~l method ~`or identi~'ying each member o~` a set and which method is broadly defined as folLows:
A method for identit'ying each member o~ a set of obiects such a,s persons, animals, packages or the like said method comprising:
establishing a contirluous oscillating interrogation field, at an interrogation zone;
providing each said member ot` said set with an identifieation -tag. said tag comprising a response signal member responsive to continuous oscillations o-t said ~U in~errogation ~`ield to abruptly reach magnetie saturàtion on each half cycle thereby ~enerating a series o~ response signal pulses eorresponding to successive hal~' cycles of said interrogation ~ield and detectable during said half cycles. and further comprising masking coil means around said re.sponse signal member. switch means in circuit with said masking coil means. whereby said maskirlg coil means is selectively operable by said switch means to mask said response signal member durin~ the presence of a said half c~cle o~' said inte:rrogation -~`ield. elec1,ronic circuitry 3~ means connected with said switch means and operable to J~ 2~-Q9~

contlol opening and closin~ of said switch means according to a predetermined sequence in timed relation to the os-illations of said continuous interrogation field thereby establishing during the presence o~` said continuous interrogation signal a response si~nal cc>nsistin~ of a series of response signal pulses ~enerated by said response signal member. said series of response signal pulses being interrupted by a unique series o~
discontinuities in said series o~' response signal pulses, 1~ which sequence defines an iden-ti~'ication code for said tag, and said tag having pick up means responsive to said continuous interrogation field to power from said continuous interrogation ~`ield, for powering said circuitry means;
placing a member of said .set, with a tag. in said continuous interrogation field established in said interrogation zone;
detecting the electroma~netic field in said intcrrogation zone whereby to detect said sequence of response signals in the presence of said continuous interrogation field; and.
processing and decoding said sequence of response signals to determine the identity of said tag and said member o~` said set.
The ~oregoing is a description of a preferred embodiment of the invention which is given here by way of example onl,-~. The invention is not to be taken as limited to any of the specific features as described, but comprehends all such variations thereof as come within the 3V scope o~ the appended claims.

Claims (8)

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

1. An identification system for use in association with a set of objects, such as persons, animals, packages or the like, whereby any member of said set may be identified while said member is located within a predetermined interrogation zone, wherein said system comprises;
interrogation field means whereby at least one oscillating electromagnetic interrogation field may be established in said interrogation zone;
response signal detection means operable to monitor said interrogation zone;
an identification tag associated with each member of said set, each tag comprising;
a response member formed of a magnetically permeable material adapted to reach saturation abruptly at a predetermined level of magnetic flux and responsive to half cycles of said interrogation field when present in said interrogation zone, upon abrupt magnetic saturation thereof, to abruptly distort said field thereby generating a series of field distortion pulses corresponding to successive half cycles of said interrogation field and detectable during said half cycles;
an electromagnetic masking coil around the said response member selectively operable to magnetically mask the same and thereby prevent saturation of said response member and adapted to be rendered inoperable whereby no such masking takes place;
switch means in circuit with said masking coil selectively operable during a half cycle to control said masking coil;
circuitry means connected with said switch means and operable to control opening and closing of said switch means according to a predetermined sequence in timed relation to said half cycles of said interrogation field thereby establishing during the presence of said interrogation field a series of interrogation field distortion pulses caused by abrupt saturation of said response member, said series of interrogation field distortion pulses being interrupted by a unique series of discontinuities in said series of distortion pulses which defines an identification code for said tag;
power means for said circuitry means whereby the same may be operated, and, signal processing means connected to said detection means for processing and decoding said series of distortion pulses.

2. An identification system as claimed in Claim 1 wherein said power means is responsive to said interrogation field to generate power therefrom, for said circuitry means.

3. An identification system as claimed in Claim 1 wherein said system further includes a computer connected to said response signal detection means whereby information concerning the identified member of said set may be stored.

4. An identification tag to be used in association with an object such as a person, animal, package or the like to be identified and an identification system which system establishes an oscillating electromagnetic interrogation field within a predetermined interrogation zone, said tag comprising, a response signal member responsive to said continuous interrogation field to abruptly reach magnetic saturation thereby generating a series of response signal pulses corresponding to successive half cycles of said interrogation field and detectable during said half cycles, electromagnetic masking coil means around said response signal member selectively operable to magnetically mask the same and adapted to be rendered inoperable whereby no such masking takes place, switch means in circuit with said masking coil means, and selectively operable during a said half cycle to control said masking coil means, electronic circuitry means connected with said switch means and operable to control the opening and closing of said switch means according to a predetermined sequence in timed relation to the oscillations of said interrogation field thereby establishing during the presence of said interrogation field a series of response signal pulses generated by said response signal member, said series being interrupted by selective operation of said masking coil means to produce a unique sequence of discontinuities in said series of response signal pulses, which sequence defines an identification code for said tag, and, power means to power said circuitry means.

5. An identification tag as claimed in Claim 4 wherein said power means is responsive to said interrogation field to generate power therefrom, for said circuitry means.

6. An identification tag as claimed in Claim 4 wherein said power means comprises;
a rectifier and voltage stabilizer circuit, connected to said power means, said rectifier and voltage stabilizer circuit defining a more or less constant voltage signal, and a clock signal, said clock signal defining essentially a series of pulses corresponding to said half cycles of said electromagnetic field;
and wherein said electronic circuitry means comprises:
an integrated circuitry counter receiving said voltage and clock signals and having at least two counter output terminals whereby said voltage may be passed to a different counter output terminal with each said pulse of said clock signal;
an identification code matrix comprising a grid of at least two electrically insulated column lines and at least two electically electrically insulated row lines, in which a particular column line may be electrically connected to a particular row line via a diode, whereby the positioning of said diodes in said grid defines an identification code, each said column line being electrically connected to a respective counter output terminal, and each said row line defining a matrix output terminal;
an integrated circuitry data selector having at least two counter input terminals, a selector output terminal, and at least two matrix input terminals. each said matrix input terminal being electrically connected to a respective one of said matrix output terminals, each said counter input terminal being electrically connected to a respective one of said counter output terminals, whereby a different said matrix input terminal may be electrically connected to said selector output terminal each time said voltage signal appears at a said counter input terminal;
said switch means being electrically connected to said selector output terminal whereby each time said voltage signal appears at said selector output terminal said switch means will close.

7. An identification tag as claimed in Claim 6 wherein said matrix includes diodes connecting each said column line to each said row line, and breakable electrical connections associated with each said diode whereby an operator may break particular breakable electrical connections thereby defining an identification code.

8. A method for identifying each member of a set of objects such as persons, animals, packages or the like said method comprising:
establishing a continuous oscillating interrogation field, at an interrogation zone;
providing each said member of said set with an identification tag, said tag comprising a response signal member responsive to continuous oscillations of said interrogation field to abruptly reach magnetic saturation on each half cycle thereby generating a series of response signal pulses corresponding to successive half cycles of said interrogation field and detectable during said half cycles, and further comprising masking coil means around said response signal member, switch means in circuit with said masking coil means, whereby said masking coil means is selectively operable by said switch means to mask said response signal member during the presence of a said half cycle of said interrogation field, electronic circuitry means connected with said switch means and operable to control opening and closing of said switch means according to a predetermined sequence in timed relation to the oscillations of said continuous interrogation field thereby establishing during the presence of said continuous interrogation signal a response signal consisting of a series of response signal pulses generated by said response signal member, said series of response signal pulses being interrupted by a unique series of discontinuities in said series of response signal pulses which sequence defines an identification code for said tag, and said tag having pick up means responsive to said continuous interrogation field to power from said continuous interrogation field, for powering said circuitry means;
placing a member of said set, with a tag, in said continuous interrogation field established in said interrogation zone;
detecting the electromagnetic field in said interrogation zone whereby to detect said sequence of response signals in the presence of said continuous interrogation field; and.
processing and decoding said sequence of response signals to determine the identity of said tag and said member of said set.