CA2041827A1 - Electronic article surveillance tag and method for implementing same - Google Patents
Electronic article surveillance tag and method for implementing sameInfo
- Publication number
- CA2041827A1 CA2041827A1 CA002041827A CA2041827A CA2041827A1 CA 2041827 A1 CA2041827 A1 CA 2041827A1 CA 002041827 A CA002041827 A CA 002041827A CA 2041827 A CA2041827 A CA 2041827A CA 2041827 A1 CA2041827 A1 CA 2041827A1
- Authority
- CA
- Canada
- Prior art keywords
- tag
- nonlinear
- reradiator
- circuit
- ground plane
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q23/00—Antennas with active circuits or circuit elements integrated within them or attached to them
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B13/00—Burglar, theft or intruder alarms
- G08B13/22—Electrical actuation
- G08B13/24—Electrical actuation by interference with electromagnetic field distribution
- G08B13/2402—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
- G08B13/2405—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting characterised by the tag technology used
- G08B13/2422—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting characterised by the tag technology used using acoustic or microwave tags
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B13/00—Burglar, theft or intruder alarms
- G08B13/22—Electrical actuation
- G08B13/24—Electrical actuation by interference with electromagnetic field distribution
- G08B13/2402—Electronic Article Surveillance [EAS], i.e. systems using tags for detecting removal of a tagged item from a secure area, e.g. tags for detecting shoplifting
- G08B13/2428—Tag details
- G08B13/2431—Tag circuit details
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/12—Supports; Mounting means
- H01Q1/22—Supports; Mounting means by structural association with other equipment or articles
- H01Q1/2208—Supports; Mounting means by structural association with other equipment or articles associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems
- H01Q1/2225—Supports; Mounting means by structural association with other equipment or articles associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/36—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith
- H01Q1/362—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith for broadside radiating helical antennas
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
- H01Q9/04—Resonant antennas
- H01Q9/16—Resonant antennas with feed intermediate between the extremities of the antenna, e.g. centre-fed dipole
- H01Q9/28—Conical, cylindrical, cage, strip, gauze, or like elements having an extended radiating surface; Elements comprising two conical surfaces having collinear axes and adjacent apices and fed by two-conductor transmission lines
- H01Q9/285—Planar dipole
Abstract
ABSTRACT OF THE DISCLOSURE
In a method for enhancing the performance of tags for use in an electronic article surveillance system of the type comprising a transmitter-receiver arrangement disposed aside an area to be controlled for transmitting a first high-frequency signal into the area, a transmitter disposed aside the area and generating a second frequency signal of substantially lower frequency than the first frequency for establishing in the area an electrostatic field, a tag for attachment to an article to be subject to surveillance, the tag being responsive to the incidence thereon of energy of both the first and second frequencies to transmit a composite thereof and receiver apparatus disposed aside the area for receipt and detection of such composite signal and for generation of an output signal indicative of such detection, the method involving the steps of:
configuring the tag with an antenna for receiving the first and second transmitted signals and for transmitting the composite signal; and a nonlinear circuit for connection electrically with the antenna and responsive to energy derived from the second transmitted signal received by the antenna to exhibit electrical reactance change with change of voltage of the energy; and applying an electrical bias of steady-state nature to the tag dependently on consideration of characteristics of the nonlinear circuit to enhance the electrical reactance change thereof responsively to the energy derived from the second transmitted signal received by the antenna. The considered characteristics of the nonlinear circuit are selected to be a dC/dV slope factor, a l/c2 factor and a DC-impedance factor. The nonlinear circuit is selected to be a diode.
In a method for enhancing the performance of tags for use in an electronic article surveillance system of the type comprising a transmitter-receiver arrangement disposed aside an area to be controlled for transmitting a first high-frequency signal into the area, a transmitter disposed aside the area and generating a second frequency signal of substantially lower frequency than the first frequency for establishing in the area an electrostatic field, a tag for attachment to an article to be subject to surveillance, the tag being responsive to the incidence thereon of energy of both the first and second frequencies to transmit a composite thereof and receiver apparatus disposed aside the area for receipt and detection of such composite signal and for generation of an output signal indicative of such detection, the method involving the steps of:
configuring the tag with an antenna for receiving the first and second transmitted signals and for transmitting the composite signal; and a nonlinear circuit for connection electrically with the antenna and responsive to energy derived from the second transmitted signal received by the antenna to exhibit electrical reactance change with change of voltage of the energy; and applying an electrical bias of steady-state nature to the tag dependently on consideration of characteristics of the nonlinear circuit to enhance the electrical reactance change thereof responsively to the energy derived from the second transmitted signal received by the antenna. The considered characteristics of the nonlinear circuit are selected to be a dC/dV slope factor, a l/c2 factor and a DC-impedance factor. The nonlinear circuit is selected to be a diode.
Description
~~159 EL~CTRONIC ARTICLE SURVEILLANCE TAG
AND METHOD FOR IMPLEM~NTING SAME
FIELD OF T~E INVENTION
This invention relates generally to tag devices ~or use in electronic article surveillance systems and pertains more particularly to the provision of improved tag devices responsive to plural signals of diverse ~requency and to practiaes for fabricating the same.
BACKGROUND OF THE INVEMTION
The electronic article surveillance (EAS~ industry has looked at large to tag devices of a type involving a dipole antenna housed with a diode in a protective e~velope of insulative ~aterialO In some instances, EAS systems have provided ~or the transmi~sion of a high frequency signalt sUch as a 915 m~gahertz carrier, and o~ a lower fre~uency signal, such a~ modulated 100 kilohertz~ Wide~pread understanding, as evidenced i~ Pinneo e~ al. U.S. Pa~ent No. 4,413,Z54, is that such device de~ines a so-call~d "recep~or reradiator", re~urning to the receiver of the EAS sy~tem, ~he 915 ~Hz carrier with con~ent related to the lower ~requency .and it8 modulation characteristic. Upon detection in the reseiver o~ received signals inclusive of the modulation characteristic in g~ven repetitive succession, an alarm indication is provided.
Gen~rall~, detec~io~ taXes pl~ce in a contr~led zon , i.e., an exit area vf a retail e~tablishme,nt,, and output al~rm indication is that o~ a tay device beiny carried therethrouyh without authori~ation (undeactiv~ted).
The art has come to realize substantial analytical evaluation of the activity at hand in EA3 dipole and diode tag devices. Thus, in Woolsey et al. U~S. Patent No~ 4,642,640, there is a recognition o~ the need to establi~h cixcuit parameters which maximize the r~ception of the various ~ignals transmitted, the need ~or establi hing an inductive tag device character at ~he high frequency, where l~ngth parameters otherwise dictate, and the need of having a resonant circuit in the tag device at the high frequency.
In addressing such di~cerned needs, Woolsey et al. looked to the addition of inductance a~ 915 MHz selectively, as by a serpentine inductive path providing same within the length constraint at hand. Woolsey et al. thus looked not to the simple dipole/diode combination but to a discernment o~ specific diversely characterized tag device areas. They pro~ided a generally rectangular tag conPiguration, davoting area to a aircuit ~lement which i5 inductive at the high ~requ~ncy ancl is capacitive up to the lower ~re~uenay and oth~r area to another cirauit element, which is inductive at the high ~requancy, the circuit elements being physically disparate in geometry and . -2-3 ~
arranc~ in elec~rical series circuit with the diode~ There was a part~c~lar reco~nition that the su~ of th~ va~ious reactan~s of the C~Lrcuit e].ements and ~hat of khe diode should give rise to Si~tions wherein the diode is at the cen~er o~ a resonan~
circui~ ~herein the net sum of the various reactances at hand across ~he tag should ~hen be zero and wherein the circuit eleme~s should be addressed generally to different purposes, e.g., ~at one thereof should be such as to maximize second lower ~IY~quency energy receipt and hence voltage applied to the diode~
A f~ her advance in the type of tag device under diccussion is s~en in Siikarla et al. Patent No. 4,736,207 to which incor~ra ing re~erence is hereby made. In i$s prefexred form, the S~i~carla et al. tag devica is of generally rectangular config~rcation and comprises a flrst circuit element extending longi~lxlinally of the de~ice and o~. fir~t transverse dimension, a sec~nd aircuit element extending longitudinally of the deviae at lez~st in part jointly with the ~irst circuit element and of second t~lnsverse dimension substantially exceeding the fi~st trans-~erse dimension and e~feating predominant di~erent raceipt by t~ firsk and second airauit element~ o~ the high and low frequ~cy transmitted signal~ and a ~ur~her circUit element exhi~i~ing voltage depe.ndent capacitive reactance connected in elec ~ ical series circuit with the ~irst and second circuit elem~3r~s~
Th~ third circuit elemen~, which is ~ypically a diode, has applied thereto the v~lt~ge generated in the t~y d~vice irl response to the low frequency signal, which is cyGlic. In practice under the '207 pate~t, one correlates the tag capability for the generation o~ voltage at the low frequency with capacitance change of the third circuit element, and vice versa, to enhance the magnitude of the phase reversals across the third circuit element~ which generate the sideband~ o~ the reradiated signal.
In the '640 patent, the principle underlying the reradiator element is that o~ an ~n-symmetrical dipole, which i~ folded back to conserve length. In the '207 patent tag device, the narrow sections ~orm part of the radiating RF eleme~t of a symmekrical dipoleO Again, as in the '640 patent, part of the pattern is folded back to conserve space.
In a copending and commonly-assigned application, entitled l'Electronic Article Surveillance System and Tag", there i5 provided a tag which incorporatas a reradiator which is configured as a monopole. A monopole antenna typically requires only half as much length as a dipole and encompasses ~ groun~
plane to that ef~ect. In cust.omary monopole configuration~, the ground plane i~ xe~uired to b~ perpendicul~r to the reradiator element of the monopole and o~ considerable ~ize, ~hi~ i~
--at_ "1~
because monopole radi~tor elements are oE length normally near one quarter wavelength and operate at vr closa to their natural resonance~ Per the inventiorl of the xeferenced cop~nding application, however, ~he reradiator element has considerable inductive reactance and a large ground plane is neith~r required nor desirable. The resonant matching condition thus is controlled by impedances of the components o~ the monopole, such as i~s diode and a spiral reradiator element.
In the preferred embodiment o~ the invention o~ the referenced application, a tag uses a reradiator element which comprises a spirally wound inductor, which can be both ve~y short and narrow without much loss o~ e~ficiency. The ground plan~ used is a reasonably narrow and short strip o~ conductive material and placed in line with the spiral element. By choosing a diode with suitable impedance characteristics, the limited size of the in-line ground plane can be made an integral part o~ the overall impedance matching system.
A significant and valuable ~eature o~ the i~vention of the ra~erenced application is that all o~ the componQnt~ are ~hort, to conserve length, and narrow, to cons~rve width~ Thua, a v~ry compaat tag deaign is achieved in aaaordance with that invention with pex~ormance comparable with exi~tirlg larg~r tags.
SUMMAR~ OF r~lE INVENTXON
The presen-t invention has ~s i~s primary object the provision of improved EAS t~gs.
A particular ~bject of the invention is to provide improved EAS tags of the type using low ~requency electrostatic energy to reactance-modulate the tag diode capacitance with applied voltage.
In attaining ~his and other objects, the invention darives in part fxom a recognition of an opportunity Por enhancement of the modulation reactance of certain nonlinear elements used as -the third circuit elements or diodes of the above-discussed tag devices. Thuss applicant has determined that high ~requency tag performance is inversely propor*ional to the square of the overall tag c~pacitance. More particularly, it is observed that, where a given nonlinear element exhibits capacitance ~hanye ratio of desired magnitude to provide good ~ideband generation at a high level of capacitance, high freguency perfoxmance deteriorates although low frequency performance is adequate. The invention ~hus looks to a compromise as between high and low ~requency per~ormances~ and paxticularly ob~erve~
that good low ~re~uency per~ormanae can b~ attained without re~uiriny nonlinear element capacitanae which dete~iorates high frequency performance.
.
~ , 3, ~ ~J ~.~Jl In brie~, the invention introduce~, into eith¢r of the above~discussed or other tag devices, a bias volt~g~ addi~ive to the voltage across the nonlinear element derived ~xom inciden~
energy to effectively cause th~ nonlinear element to exhibit voltage change of enhanced magnitude on phase r~versals.
The foregoing and other object~ and features of the invention will be further unders~ood from ~he followiny detailed description of a preferred embodiment thereo~ and from the drawings wherein like reference numerals identify like components and parts throughout.
DESCRIPTION OF THE DRAWINGS
Fig. 1 is a top plan view of a first embodiment o~ a tag device in accordance with the invention Fig. 2 is a right ~ide elevation of the tag device of Fig.
1.
Fig. 3 is a top plan view of a modi~ied version of the Fig.
1 type of tag device in accordance with the invention Fig. 4 is a xight side elevation o~ the tag devi.ce of Fig.
3.
Fig. 5 is a front plan elevation o~ a ~econd ~bodiment o~ a tag device in accordance with the invenkion.
Fig. 6 is a top plan elevation o~ the Fig. 5 tag device.
Fig. 7 is a right ~ide elevation o~ the Fig. 5 tag deviceO
~ ~3 ~ J ~
Fig. 8 is an electrical schematic diayram o~ the Fig. 5 ~ag device.
Fig. 9 is a polar plot of the performance characteristics of the Fig. 5 tag device without bias applied thereto.
Fig. lO is a polar plot of the performance characteris.tics of the Fig. 5 tag device with bias applied thereto.
Fig. 11 is a plok of capacitance change with voltase chanye of an exemplary diode.
Fig. 12 presents ~he gain resulting from increased dC/dV
slope factor vs. bias voltage, computed $rom Fig. 11 measurements and expressed in dB.
Fig. 13 presents xesults from a 1/c2 dB loss calculation.
Fig. 14 shows the calculated dB loss vs. ~orward bias, resulting from desradation of the DC-impedance.
Fig. 15 shows the current V5. volta~e characteristics of an exemplary diode.
Fig. 16 shows the Fig. 15 characteris~i s on a logarithmic scale.
Fig. 17 presents results a5 a ~unation 0~ bias ~ol~age.
Fig. lU present6 results a~ a ~unction o~ bias aurxent~
3 ~ii r~J
DE~CRIP'rION OF PREFET~ED ~MBOD~MENTS ANC~ PRAC'TICES
Re~erring to Figs. 1 and 2, ~ay devicc 10 is o~ yenerally rectangular configuration and comprises an electrically insulative substrate 12 supporting various electrically conductive m~mbers. such members comprise first circuik element~ generally designated as 14 and 16, extending oppositely *rom the center of device 10 and including respectively kransverse wings 18 and 20 and courses 22 and 24 of first tran~vers~ dimension Dl. Courses 2~ and 24 ea~h include longitudinal portions 22a and 24a extending to opposed ends o~
substrate 12, transverse portions 22~ and 24b and terminal portions 22c and 24c. Diode 26 is connected by its leads 26a and 26b in electrical series circuit with first circuit elements 14 and 16.
The conductive me~bers further include second circuit elements designated as 28 and 30 and o~ generally square outline and inclusive of respective tra~sverse interior margin parts 28a and 30a, in spaced parallel relatio~ with wings 18 and 20, respective longitudinal interior margin parts 28b and 30b/ in spaced parallel relation with ~ir~t circuit alemen~ portions 22a and 24a, ~nd respective ~ransver~e outer marginal part~ 28c and 30c, in spaaed parallel relation with ~irst cirauit element portions Z2b and 24b. Second circui~ elements Z8 and 30 are el~ct~ically cont:inuous with terminal por-tions 22c and 24c o~
the first circuit ~lement courses 22 and 2~.
The transverse dimension of second circuik elements 28 and 30, indicated ~t D2, is subs~antially in exc~s~ o~ the transverse dimellsion Dl of first circuit elements 22 and ~4, typically some five or more times D1, the geometric diversities of such circuit elements heing as~igned with ~ view toward providing selective di~ferent ~ixed inductive and capasitive reactances therein at the first and second frequencies received by tag device 10.
The tag device 10 thus far discussed is shown in the '207 patent incorporated by reference above and further details as respect~ circuit element design may be obkained from the '207 patent~ In accordance with the present invention, battery 32 has its negative terminal 34 connected through resistor 36 to irst circuit element 16 at connection location 38 ~nd its ~ositive terminal ~O connected to first circuit elemenk 14 at conneation location 42~
~ urning to ~he modi~ied tag embodimen~ of Figs~ 3 and 4, tag device 60 is o~ generally rectangular ao~iguration and aompri~es an electrically insulative ~ub~rate 6~ suppo:r~ing var.ious eleatrically aonductive member~. Such members comprise first aircuit element~ generally design~ted as 6~ and 66, ex~ending oppositely from the oenter o~ device 60 and including respectively transverse wings 68 and 70 and courses 72 and 74 o~
first ~ransverse dimension D3. Courses 72 and 7~ each include longitudinal portions 7Za and 74a extendiny t~ opp~sed ends oP
substrate 6Z, transverse portions -~2b and 74b and termi~al portions 72c and 74c~ Diode 76 is connected by its leads 76a and 76b in electrical series circuit with first circui~ elemen~s 64 and 66.
The conductive members further include second circuit el~ments designated as 78 and 80 and of generally square outline and inclusive of r~spective transverse interi~r margin parts 78a and 80a, in spaced parallel relation with wings 68 and 70, respective longitudinal interior margin parts 78b and 80b, in spaced parallel relation with first circuit element portions 72a and 74a, and respective transverse outer marginal parts 78b and 80b, in spaced parallel relation with first circuit element portions 72b and 74b. Second circuit elements 78 and ~0 are electrically continuous with terminal portions 72c and 74c of the firsk circuit element courses 72 and 74.
The transverse dimension of second circuit elements 78 and 80, indicated at D4, i5 substantially in excess o~ the transverse dimension D3 o~ ~irsk circui~ elements 72 and 74, typically some ~ive or more times D3, the ge~ometric di.versities of such circuit elements being assigned with a view toward provîding selective different fixed inductive and capacitive ,3 ~ 1 re~ckances therein at the ~irst and second ~recluencie~ receive~
by tag device 60.
The tag dPvice 60 thus ~ar di~cussed is al~o shown in the r207 patent i~co~porated by re~erence ~bove and further detalls as respects circuit element design may be ob~ained fxom the '207 patent. In accordance with the present invention, batkery 82 has its negative terminal 84 connected through re6istor 86 to first circuit element 66 at co~nection location 88 and its positive terminal go ronnected ~hrough resistor 92 to first circuit element 64 ak connection location 94.
Referring to the second embodiment of the inYention shown in Figs. 5-7, tag device 110 includes an elongate; generally planar and electrically conductive member 112, constituting the ground plane of the tag device.
A nonlinear element 114, typi~ally a diode, has one lead 116 thereof connected electrically, as by solde~, to ~round pl~ne 112 adjacent to an end thereof.
Reradiator element 118 has one end 120 thereof ~lectrically connected to a second lead 122 of diode 114 and its other end 124 without electrical connection thereto.
Ground plane 112 i~ typically a rectangulax ~ection v~ a conduati~e sheek, the dimensions o~ which ar~ s~lected to minimize the overall siz~ o~ the tag, yet maintaininy the minimum re~uired perfarmance in a particular applica~ion. The optimum width to minimize the overall tag size i~ ~he same as the outside diameter of the spiral rer~diator element~
Diode 114 is preferably a semiconductor diode, haviny high and low frequency characteristics selected de~ir~bly as described in the referenced '207 patent~
Reradiator element 118 is prefexably a spiral inductor of dimensions selected to optimize tha impedance match to cumulati~e impedance conditions presented by the inductor to the other two components, all such three components being connecked electrically as a series circuit.
The function of reradiator element 118 i~ three-fold, namely, to receive and transmit high frequency energy, to serve as one side of an elementary dipole to capture low frequency electrostatic energy, t~pically 100 kHz, and to provide impedance matching at high frequency between the three components connected in series.
The function of diode 114 is ~at disclosed in the '207 patent, namely, to generate high fre~uency side~ands through reactance-modulation by applied low ~requenay electrostatic energy.
The ~unction o~ ground plane 112 ~ ~wo-~old, name:Ly, ko serve a the yxound agalnst whiah rexadlator element 118 ~orms a monopole antenna and to serve a8 the second part of a dipole for low fre~uency electrost~tic energy, as in the prior ark endeavors described abo~e.
The foreyoing second tag embodiment o~ the invention ~hu.
far described is that o~ the above-re~erenced copending application. In accordance with the present invention baktery 126 is connected between the ground plane and the junction 12 of the diode and the spiral reradiator, with a resistor 130 connected as indicated in the electrical schematic of Fig~ ~.
An evaluation method involves polar plotting of the distance at which a tag response (reradiation~ i~ sensed with respect to a source transmitting-receiving lo~ation~ The graphics programs show the response in the ~orm of a polar diagram, where each circle represents a distance of ten inches. The ~ull scale is o~ thirty inches and plots the response at lO degree increments and computes a total for the readings, from wh~ich it computes an estimated pick rate. Computation is based on tag performance in a reference system installation used for correlation between standard test results and actual s~tem pick rate.
Fig. 9 shows the performance o~ the tag of Figs. 5 7 without bias and Fig. 10 with hias. ~stimated pick rates in the re~erence system ins~allation wexe seven~y-three percent withou~
bias, and ninety-three percent wikh bia~.
Fig. 11 shows that the capacikance~modulation parameter, subsequently reerred to as khe dC/dV ratio, and de~ined as incremental change in capacitance V~. incremental change in diode voltage, increases by the ~orward bias.
-~4-Fi~. 12 presents the gain ~esulting Prom increased dC/dV
slope factor vs. bias voltage, computecl ~om Fig. 11 measurements and expressed in dB. Linear regression takes place in the ki~s range of inter~st to this ir~vention.
As allud~d to above, it has been determined that a high frequency tag performance is inversely proportional to the square of the ovarall capacitance. Conseguently, i~ the diode operating point is shi~ted too far from the zero-bias state, although the dC/dV slope factor is improved, at the same ti~e the square of the overall capacitance value rapidly takes eff~ct and ultimately ruins the performance. Results from a dB loss calculation with respect ~Q this factor ~the 1/C2 factor) for a given diode is shown in Fig. 13~ A gradually increasing loss takes place, until the -6 dB point is reached at around O.28V
bias, above whieh a rapid decline takes e~ect.
The amplitude of the low fre~uency voltage cap~ured by the tag, and resulting tag per~ormance, are directly proportional to the DC-impedance of the diode. As the ~perating point is biased further in forward direction, the current increases wi~h resulting DC-impedance dropping exponentially. ~yain th~ loss o~ low frequency efEiclency becomes ~ominan~ over tha improvement in dC/dV slope factor. Fig. 14 shows the calculated dB loss vs. forward bias, resulting from degradation o~ the DC-i~pedance.
~ S~?J~
Depending on the type o~ diode used, the optimu~ ~c~uard bias varies betweQn various diode types~ As an exa~pl~.
Schottky diodes generally can not be enhanced b~ the p~ice of the inventi~n, due to their inherently low DC impedanc~_ The practice under the subject invention, given th~
above-noted ~indings and recognitions and those furth~c ~tated below, is to sPlect the most suitable diode and to incc~ or~te battery bias in such a manner that an optimum compromi-~- is achieved between bene~icial and detrimental effects o~ ing so.
The benefit of introducing bias is that capacitanc ~
modulation efficiency improves through attaining an i~r~ved dC/dV ratio than would otherwise apply.
The detrimental effects of introducing bias are se~al.
There is a degradation o~ high-frequency performance t~-~ugh increase in overall diode capacitance. Degradation o~
low-frequency impedance ari~e~ through increase in dioc~ ~urrent and increase in overall diode capacitance. Degrada~io~.-~f low-frequency impedance also occurs through the loadinc ~fect o~ the bia~ network which is in parallel with d.iode. ~stly, a source for the bias voltage is needed, namely, a batt~--c-~ and concern of course ex~ts for battery life~
Fig. 15 show~ ~he current vs. vc~ltage charac~eris~3 o~ an exemplary diode. Fi~. 16 shvw~; the same using a loga~--~-~ic scaleO Combined e~fects o~ dC/dV slope factor~ the 1/~
~ ~3 '1 ~ , 7 ractor, and the DC-impedance factor are calculated, based on Fig. 12 slope factor, Fig. 13 1/c2 factor and Fig. 1~1 DC--impedance factor. Fig. 17 presents resul~s, computed as a function of bias voltage, and Fig. 18 presenks ~he same as a function of bias current. The optimum operating point from the two calculations is approximately 0.28V, which ~esult~ in approximately 40 ~egohms as the value of the resistor vr resistors in series with the battery, where the battery terminal voltage i~ 1~5Vo As will be seen, the loading ef~ect of the 40 megohm ~ias resistor is negligibleO
By way of ~ore specific disclosure of practice in accordance with the invention, the following analysi6 is provided. A
reference bias voltage is taken as 0.02V., whera the slope dC/dV
is 0.5 pF/V. The slope factor gain, expressed in dB, is proportional to diode forward bia~ and provides a convenient model from which all AC (alternating current~ char~c~eristics are derived.
The dC/dV gain versus bias voltage (Fig. 12~ ~ollsws the following relationship:
GAIN tdB] - (78.0~2 X Vd) - 1.54 (1) where the two constant~ are e~tabli~hed ~s statistical mean valu~s for a given diode evaluat~d.
~ ,J
The value of ~ias voltage p~oviding optimun~ comprGmise is 0.2~V and a comparison is now ef~ec~ed as between ~he re~erence bias voltage and the optimum bias voltage.
In terms of gain, equati~n ~1) yield~ zero ds ~or the raference and 20.32 for the optimum. Now shown is the remnant dB gain a~ter taking away the dB losses.attributable to the l/c2 factor and the ~C-impedance factor.
The former loss ollow~ the relatio~ship:
LOSS [dBJ = 20 LOG ((1/c2~/(0.542~ ~2) where 0.542 i~ 1/c2 at the reference voltageO
At the reexence voltage, the diode capacitance is 1.358 pF, and at the optimum voltage, the capacitance is 2.052 pF, and equation (23 yields zero loss at the refer~nce vol~age and a loss of 6.09 dB ~ox the opti~um.
The DC-imped~nce loss follows the relation~hip:
LOSS tdB] - 20 LOG (Z/Zo~ . (3) where Zo is the impedance at the reference voltage.
Diode current ~ollows the relationshipq Id = 1o((12.464 x Vd) - 11.6849) (4~
where ~he two constants are astabli~hed a8 sta~ tical mean values o~ the diode under aonsideration.
Disde re~i~tance follow~ the relationship:
R = Vd/Id (5) where Vd i~ the volkage acros~ the diode. For the refarenae voltage, the diode resistance is 5.453 x 109 ohms. with a 4 megohm resistor in parallel with the diode, the effective resistance is 30.71 megohms.
Diode reactance follows the relationship:
X C lt( 2~T ~c~ (6) At the frequency of 100 kilohertz, the reactance ~or the reference voltage is 1.172 x 1o6 ohms.
Diode impedance follows the relationship:
Z = R/ (1 ~ (~2/x2))1J2 which yields 1.172 x 106 ohms for Zo.
For the optimum voltage, the diode resistance is 43.87 x 106 ohms. With a 40 megohm resistor in parallel with the diode, the effective resistance is 20.92 megohms.
At the frequency of 100 kilohertz, the reactance for the optimum voltage is 8.256 x 105 ohms. The diode impedance at the optimum voltage computes as 8.249 x 105 ohms.
The DC impedance loss at the reference voltage is zero and that at the optimum voltage is 3.05 dB.
Considering the gain at the optimum per equation (1) and the ~osses per e~uation~ (2) and (3), a net gain o~ 18 dB is e~fected.
If one e~ects the ~oregoing computatlons ~or O.lV, 0.2V, 0.35V amd 0.4V as the bias voltage, the results în net dB gain are respectively 5.07 dB, 9.73 dB, 10.11 dB and 7.46 dB. As will be appreciated each of these net dB gains are less than that achieved at the optimum bias value.
~, ~J ~ 3 ~ '~
By way Of summary of tlle oreyoing ~nd by way o~
introduction to the e~suing claims, the invention ~ill be seen to have various aspects. In one a~pect, it provides ~ t~g fo~
use in an electronic article surveillance ~ystem o~ the ~ype comprising a transmitter-receiver arrangemenk disposed aside an area to be controlled for transmitting a first high-fre~uency signal into tha area, a transmitter disposed aside ~he area and generating a second frequency signal o~ substantially lower Xxequency than the first frequency for establishing in the area an electrostatic field, a tag for attachment to an arti~le to be su~ject to sur~eillance and responsive to the incidence thereon of energy of both the first and ~econd frequencias to transmit a composite thereof and receiver apparatus disposed aside the area for receipt and det~ction of such composite signal and for generation of an output signal indicati~e o~ ~uch detection, the tag comprising: an antenna for receiviny the ~irst and ~econd transmitted ~ignals and for transmitting the composite signal; a nonlinear circuit for connection electrically with the antenna and responsive to energy derived from the second transmitted signal received by the antenna to e~hibit electriaal reactance change with change of voltage o~ the ener~y; and an electrical power ~upply unit conneat~d to the anten~a ~nd tha nonlinear airauit and opexative to enhance the eleatrical reactance change of the nonlinear circuit.
The anten~a may comprise a reradiator eleme~t ~ 32 ~i electrical ground plane memb~r connected electric~lly to the nonlinear circuit. The r~radiator eleme~k, the nonlinear circuit and the yround plane member are in electrical series circuit connection, the electrical power supply beiny connected betwe~n the ground plane member and a junction connection o~ the reradiator element and the nonlinear ~ircuit, The eletrical power supply may include a battery and a resi~tor connected to a terminal of the battery and to either o~ the reradiator element or the ground plane member. The nonlinear circuit may have capacitive reactance as the electrical reactance and is adapted to generate high frequency sidebands through capacitance-modulation responsiYe to receipt of energy derived from the second transmitted signal. The ground plane member may exhibit a dimension substantially equal to a dimension e~hibited ~y the reradiator ~lement~ The reradiator element may comprise a spiral inductor. The ground plane member may be elongate and have a width dimension sub~tantially equal to ~he out~ide diameter of the spiral induator. ~he tag may be elvngat~, the reradiatox element having a central axis longitudinally diæposed with the tag, the nonlinear ~ir¢ui'c and ~he gxound plane member being di~;posed in general alig~Lment with the central axis. The nonlinear circuit may be a diode. ~he ground plane me~ber may be a conductive sheet.
In ~ second aspect, the invention Will be seen to provid~, in combin~tion in ~n electronic article surveillance tag: ~
reradiator element; a nonlinear element connected electri~lly to the reradiator element; an ~lec~rical ground plane member connected electrically to the nonline~r element; and an electrical power supply connected to the reradiator element and the nonlinear el~ment, the reradiator element, the nonlinear element and the ground plane member being in electrical series circuit connection, the reradiator element and the yround plane member defining a monopole antenna upon incidence on the tay o~
high ~requency energy for reradiation o~ the high ~requency energy.
In a third aspect, the invention will bP seen to provide a-tag for use in the first aspect system with such ~ower supply wherein the antenna is of generally rectangular con~iguration and comprises first circuit elements ~xkending longitudinally o~
the tag and of first transverse dimension, ~econd circuit elements extending longitudinally of the tag at least in part jointly with a respective Pirst circui~ element and o~ second transverse dimension sub~tantially exa~eding the ~irst transverse dimension and e~eating predominant di~er~nt rea~ipt by the ~lr~t a~d second circuit element~ o~ the ~ransmitted ~ir~t and second signals and wherein th~ nonlinear circu:it i6 connected in electrical ~eries circuit with the ~irs~ and second circuit elements. In this third a~pect, the electriaal power supply may comprise a battery located on one of the second circuit elements and electrically connected thereto and further electrically connected to one of th~ first circuit elements.
The electrical power supply may further include a resistor connected between the battery and one of the first and second circuit elements. Otherwise, the electrical power supply may comprises a battery located in spaced relation to the first and second circuit elements. The battery may have positive and negative terminals which are electrically connected respectively to distinct second cir~uit elaments and the electrical power supply may further include resistors connected betwePn the ba~tery terminals and the second circuit elements~
In a fourth aspect, the in~ention will be seen to provide, in a method for enhancing the performance of tags for use in an electronic article surveillance system of the type comprising a transmitter-receiver arrangement disposed aside an area to b~
controlled for transmitting a first high~frequency signal into the area, a transmitter disposed aside the area and generating a.
second ~requency signal of substantially lower ~re~uerlc.y than the ~irst ~requency ~or es~ablishin~ in the area an electrostatic field, a tag for attachment to an article to be subject to surveillance, the tag being responsive to the incidence thereon of energy of both the f irst and second 3 ~ ;f frequencies to transmit a composite thereo~ ~nd rec~iv~r apparatus disposed aside the area for receipt and d~tec~ion of such composite signal and ~or generation of an outpu~ siynal indicatiYe of such detection, the method involving the steps of:
configuring tha tag with: an antenna for receiving the first and second transmitted signals and for transmitting the composite signal; and a nonlinear circuit for connection electrically with the antenna and xesponsive to energy derived from the second transmitted signal received by the antenna to exhibit electrical r~actance change with change of volta~e o~ the energy; and applying an electrical bias of steady-state nature to the tag dependently on consideration of characteristics of the nonlinear circuit to enhance the electrical reacta~ce change thereof responsively to the energy derived from the second transmitted signal received by the antenna. The considered characteristics of the nonlinear circuit are selected to be a dC/dV slope actor, a 1/c2 factor and a DC-impedance factox. The nonlinear circuit is selected to be a diode.
Various changes may evidently be introduced in the ~oregoing structure without departing from the invention~ Thus, the particularly de8aribed and pre~erred embodiment5 and practices are intended to be illustrative and not limiting of the invention. The true spirit and ~cope o~ the invention i5 set forth in the appended claims.
AND METHOD FOR IMPLEM~NTING SAME
FIELD OF T~E INVENTION
This invention relates generally to tag devices ~or use in electronic article surveillance systems and pertains more particularly to the provision of improved tag devices responsive to plural signals of diverse ~requency and to practiaes for fabricating the same.
BACKGROUND OF THE INVEMTION
The electronic article surveillance (EAS~ industry has looked at large to tag devices of a type involving a dipole antenna housed with a diode in a protective e~velope of insulative ~aterialO In some instances, EAS systems have provided ~or the transmi~sion of a high frequency signalt sUch as a 915 m~gahertz carrier, and o~ a lower fre~uency signal, such a~ modulated 100 kilohertz~ Wide~pread understanding, as evidenced i~ Pinneo e~ al. U.S. Pa~ent No. 4,413,Z54, is that such device de~ines a so-call~d "recep~or reradiator", re~urning to the receiver of the EAS sy~tem, ~he 915 ~Hz carrier with con~ent related to the lower ~requency .and it8 modulation characteristic. Upon detection in the reseiver o~ received signals inclusive of the modulation characteristic in g~ven repetitive succession, an alarm indication is provided.
Gen~rall~, detec~io~ taXes pl~ce in a contr~led zon , i.e., an exit area vf a retail e~tablishme,nt,, and output al~rm indication is that o~ a tay device beiny carried therethrouyh without authori~ation (undeactiv~ted).
The art has come to realize substantial analytical evaluation of the activity at hand in EA3 dipole and diode tag devices. Thus, in Woolsey et al. U~S. Patent No~ 4,642,640, there is a recognition o~ the need to establi~h cixcuit parameters which maximize the r~ception of the various ~ignals transmitted, the need ~or establi hing an inductive tag device character at ~he high frequency, where l~ngth parameters otherwise dictate, and the need of having a resonant circuit in the tag device at the high frequency.
In addressing such di~cerned needs, Woolsey et al. looked to the addition of inductance a~ 915 MHz selectively, as by a serpentine inductive path providing same within the length constraint at hand. Woolsey et al. thus looked not to the simple dipole/diode combination but to a discernment o~ specific diversely characterized tag device areas. They pro~ided a generally rectangular tag conPiguration, davoting area to a aircuit ~lement which i5 inductive at the high ~requ~ncy ancl is capacitive up to the lower ~re~uenay and oth~r area to another cirauit element, which is inductive at the high ~requancy, the circuit elements being physically disparate in geometry and . -2-3 ~
arranc~ in elec~rical series circuit with the diode~ There was a part~c~lar reco~nition that the su~ of th~ va~ious reactan~s of the C~Lrcuit e].ements and ~hat of khe diode should give rise to Si~tions wherein the diode is at the cen~er o~ a resonan~
circui~ ~herein the net sum of the various reactances at hand across ~he tag should ~hen be zero and wherein the circuit eleme~s should be addressed generally to different purposes, e.g., ~at one thereof should be such as to maximize second lower ~IY~quency energy receipt and hence voltage applied to the diode~
A f~ her advance in the type of tag device under diccussion is s~en in Siikarla et al. Patent No. 4,736,207 to which incor~ra ing re~erence is hereby made. In i$s prefexred form, the S~i~carla et al. tag devica is of generally rectangular config~rcation and comprises a flrst circuit element extending longi~lxlinally of the de~ice and o~. fir~t transverse dimension, a sec~nd aircuit element extending longitudinally of the deviae at lez~st in part jointly with the ~irst circuit element and of second t~lnsverse dimension substantially exceeding the fi~st trans-~erse dimension and e~feating predominant di~erent raceipt by t~ firsk and second airauit element~ o~ the high and low frequ~cy transmitted signal~ and a ~ur~her circUit element exhi~i~ing voltage depe.ndent capacitive reactance connected in elec ~ ical series circuit with the ~irst and second circuit elem~3r~s~
Th~ third circuit elemen~, which is ~ypically a diode, has applied thereto the v~lt~ge generated in the t~y d~vice irl response to the low frequency signal, which is cyGlic. In practice under the '207 pate~t, one correlates the tag capability for the generation o~ voltage at the low frequency with capacitance change of the third circuit element, and vice versa, to enhance the magnitude of the phase reversals across the third circuit element~ which generate the sideband~ o~ the reradiated signal.
In the '640 patent, the principle underlying the reradiator element is that o~ an ~n-symmetrical dipole, which i~ folded back to conserve length. In the '207 patent tag device, the narrow sections ~orm part of the radiating RF eleme~t of a symmekrical dipoleO Again, as in the '640 patent, part of the pattern is folded back to conserve space.
In a copending and commonly-assigned application, entitled l'Electronic Article Surveillance System and Tag", there i5 provided a tag which incorporatas a reradiator which is configured as a monopole. A monopole antenna typically requires only half as much length as a dipole and encompasses ~ groun~
plane to that ef~ect. In cust.omary monopole configuration~, the ground plane i~ xe~uired to b~ perpendicul~r to the reradiator element of the monopole and o~ considerable ~ize, ~hi~ i~
--at_ "1~
because monopole radi~tor elements are oE length normally near one quarter wavelength and operate at vr closa to their natural resonance~ Per the inventiorl of the xeferenced cop~nding application, however, ~he reradiator element has considerable inductive reactance and a large ground plane is neith~r required nor desirable. The resonant matching condition thus is controlled by impedances of the components o~ the monopole, such as i~s diode and a spiral reradiator element.
In the preferred embodiment o~ the invention o~ the referenced application, a tag uses a reradiator element which comprises a spirally wound inductor, which can be both ve~y short and narrow without much loss o~ e~ficiency. The ground plan~ used is a reasonably narrow and short strip o~ conductive material and placed in line with the spiral element. By choosing a diode with suitable impedance characteristics, the limited size of the in-line ground plane can be made an integral part o~ the overall impedance matching system.
A significant and valuable ~eature o~ the i~vention of the ra~erenced application is that all o~ the componQnt~ are ~hort, to conserve length, and narrow, to cons~rve width~ Thua, a v~ry compaat tag deaign is achieved in aaaordance with that invention with pex~ormance comparable with exi~tirlg larg~r tags.
SUMMAR~ OF r~lE INVENTXON
The presen-t invention has ~s i~s primary object the provision of improved EAS t~gs.
A particular ~bject of the invention is to provide improved EAS tags of the type using low ~requency electrostatic energy to reactance-modulate the tag diode capacitance with applied voltage.
In attaining ~his and other objects, the invention darives in part fxom a recognition of an opportunity Por enhancement of the modulation reactance of certain nonlinear elements used as -the third circuit elements or diodes of the above-discussed tag devices. Thuss applicant has determined that high ~requency tag performance is inversely propor*ional to the square of the overall tag c~pacitance. More particularly, it is observed that, where a given nonlinear element exhibits capacitance ~hanye ratio of desired magnitude to provide good ~ideband generation at a high level of capacitance, high freguency perfoxmance deteriorates although low frequency performance is adequate. The invention ~hus looks to a compromise as between high and low ~requency per~ormances~ and paxticularly ob~erve~
that good low ~re~uency per~ormanae can b~ attained without re~uiriny nonlinear element capacitanae which dete~iorates high frequency performance.
.
~ , 3, ~ ~J ~.~Jl In brie~, the invention introduce~, into eith¢r of the above~discussed or other tag devices, a bias volt~g~ addi~ive to the voltage across the nonlinear element derived ~xom inciden~
energy to effectively cause th~ nonlinear element to exhibit voltage change of enhanced magnitude on phase r~versals.
The foregoing and other object~ and features of the invention will be further unders~ood from ~he followiny detailed description of a preferred embodiment thereo~ and from the drawings wherein like reference numerals identify like components and parts throughout.
DESCRIPTION OF THE DRAWINGS
Fig. 1 is a top plan view of a first embodiment o~ a tag device in accordance with the invention Fig. 2 is a right ~ide elevation of the tag device of Fig.
1.
Fig. 3 is a top plan view of a modi~ied version of the Fig.
1 type of tag device in accordance with the invention Fig. 4 is a xight side elevation o~ the tag devi.ce of Fig.
3.
Fig. 5 is a front plan elevation o~ a ~econd ~bodiment o~ a tag device in accordance with the invenkion.
Fig. 6 is a top plan elevation o~ the Fig. 5 tag device.
Fig. 7 is a right ~ide elevation o~ the Fig. 5 tag deviceO
~ ~3 ~ J ~
Fig. 8 is an electrical schematic diayram o~ the Fig. 5 ~ag device.
Fig. 9 is a polar plot of the performance characteristics of the Fig. 5 tag device without bias applied thereto.
Fig. lO is a polar plot of the performance characteris.tics of the Fig. 5 tag device with bias applied thereto.
Fig. 11 is a plok of capacitance change with voltase chanye of an exemplary diode.
Fig. 12 presents ~he gain resulting from increased dC/dV
slope factor vs. bias voltage, computed $rom Fig. 11 measurements and expressed in dB.
Fig. 13 presents xesults from a 1/c2 dB loss calculation.
Fig. 14 shows the calculated dB loss vs. ~orward bias, resulting from desradation of the DC-impedance.
Fig. 15 shows the current V5. volta~e characteristics of an exemplary diode.
Fig. 16 shows the Fig. 15 characteris~i s on a logarithmic scale.
Fig. 17 presents results a5 a ~unation 0~ bias ~ol~age.
Fig. lU present6 results a~ a ~unction o~ bias aurxent~
3 ~ii r~J
DE~CRIP'rION OF PREFET~ED ~MBOD~MENTS ANC~ PRAC'TICES
Re~erring to Figs. 1 and 2, ~ay devicc 10 is o~ yenerally rectangular configuration and comprises an electrically insulative substrate 12 supporting various electrically conductive m~mbers. such members comprise first circuik element~ generally designated as 14 and 16, extending oppositely *rom the center of device 10 and including respectively kransverse wings 18 and 20 and courses 22 and 24 of first tran~vers~ dimension Dl. Courses 2~ and 24 ea~h include longitudinal portions 22a and 24a extending to opposed ends o~
substrate 12, transverse portions 22~ and 24b and terminal portions 22c and 24c. Diode 26 is connected by its leads 26a and 26b in electrical series circuit with first circuit elements 14 and 16.
The conductive me~bers further include second circuit elements designated as 28 and 30 and o~ generally square outline and inclusive of respective tra~sverse interior margin parts 28a and 30a, in spaced parallel relatio~ with wings 18 and 20, respective longitudinal interior margin parts 28b and 30b/ in spaced parallel relation with ~ir~t circuit alemen~ portions 22a and 24a, ~nd respective ~ransver~e outer marginal part~ 28c and 30c, in spaaed parallel relation with ~irst cirauit element portions Z2b and 24b. Second circui~ elements Z8 and 30 are el~ct~ically cont:inuous with terminal por-tions 22c and 24c o~
the first circuit ~lement courses 22 and 2~.
The transverse dimension of second circuik elements 28 and 30, indicated ~t D2, is subs~antially in exc~s~ o~ the transverse dimellsion Dl of first circuit elements 22 and ~4, typically some five or more times D1, the geometric diversities of such circuit elements heing as~igned with ~ view toward providing selective di~ferent ~ixed inductive and capasitive reactances therein at the first and second frequencies received by tag device 10.
The tag device 10 thus far discussed is shown in the '207 patent incorporated by reference above and further details as respect~ circuit element design may be obkained from the '207 patent~ In accordance with the present invention, battery 32 has its negative terminal 34 connected through resistor 36 to irst circuit element 16 at connection location 38 ~nd its ~ositive terminal ~O connected to first circuit elemenk 14 at conneation location 42~
~ urning to ~he modi~ied tag embodimen~ of Figs~ 3 and 4, tag device 60 is o~ generally rectangular ao~iguration and aompri~es an electrically insulative ~ub~rate 6~ suppo:r~ing var.ious eleatrically aonductive member~. Such members comprise first aircuit element~ generally design~ted as 6~ and 66, ex~ending oppositely from the oenter o~ device 60 and including respectively transverse wings 68 and 70 and courses 72 and 74 o~
first ~ransverse dimension D3. Courses 72 and 7~ each include longitudinal portions 7Za and 74a extendiny t~ opp~sed ends oP
substrate 6Z, transverse portions -~2b and 74b and termi~al portions 72c and 74c~ Diode 76 is connected by its leads 76a and 76b in electrical series circuit with first circui~ elemen~s 64 and 66.
The conductive members further include second circuit el~ments designated as 78 and 80 and of generally square outline and inclusive of r~spective transverse interi~r margin parts 78a and 80a, in spaced parallel relation with wings 68 and 70, respective longitudinal interior margin parts 78b and 80b, in spaced parallel relation with first circuit element portions 72a and 74a, and respective transverse outer marginal parts 78b and 80b, in spaced parallel relation with first circuit element portions 72b and 74b. Second circuit elements 78 and ~0 are electrically continuous with terminal portions 72c and 74c of the firsk circuit element courses 72 and 74.
The transverse dimension of second circuit elements 78 and 80, indicated at D4, i5 substantially in excess o~ the transverse dimension D3 o~ ~irsk circui~ elements 72 and 74, typically some ~ive or more times D3, the ge~ometric di.versities of such circuit elements being assigned with a view toward provîding selective different fixed inductive and capacitive ,3 ~ 1 re~ckances therein at the ~irst and second ~recluencie~ receive~
by tag device 60.
The tag dPvice 60 thus ~ar di~cussed is al~o shown in the r207 patent i~co~porated by re~erence ~bove and further detalls as respects circuit element design may be ob~ained fxom the '207 patent. In accordance with the present invention, batkery 82 has its negative terminal 84 connected through re6istor 86 to first circuit element 66 at co~nection location 88 and its positive terminal go ronnected ~hrough resistor 92 to first circuit element 64 ak connection location 94.
Referring to the second embodiment of the inYention shown in Figs. 5-7, tag device 110 includes an elongate; generally planar and electrically conductive member 112, constituting the ground plane of the tag device.
A nonlinear element 114, typi~ally a diode, has one lead 116 thereof connected electrically, as by solde~, to ~round pl~ne 112 adjacent to an end thereof.
Reradiator element 118 has one end 120 thereof ~lectrically connected to a second lead 122 of diode 114 and its other end 124 without electrical connection thereto.
Ground plane 112 i~ typically a rectangulax ~ection v~ a conduati~e sheek, the dimensions o~ which ar~ s~lected to minimize the overall siz~ o~ the tag, yet maintaininy the minimum re~uired perfarmance in a particular applica~ion. The optimum width to minimize the overall tag size i~ ~he same as the outside diameter of the spiral rer~diator element~
Diode 114 is preferably a semiconductor diode, haviny high and low frequency characteristics selected de~ir~bly as described in the referenced '207 patent~
Reradiator element 118 is prefexably a spiral inductor of dimensions selected to optimize tha impedance match to cumulati~e impedance conditions presented by the inductor to the other two components, all such three components being connecked electrically as a series circuit.
The function of reradiator element 118 i~ three-fold, namely, to receive and transmit high frequency energy, to serve as one side of an elementary dipole to capture low frequency electrostatic energy, t~pically 100 kHz, and to provide impedance matching at high frequency between the three components connected in series.
The function of diode 114 is ~at disclosed in the '207 patent, namely, to generate high fre~uency side~ands through reactance-modulation by applied low ~requenay electrostatic energy.
The ~unction o~ ground plane 112 ~ ~wo-~old, name:Ly, ko serve a the yxound agalnst whiah rexadlator element 118 ~orms a monopole antenna and to serve a8 the second part of a dipole for low fre~uency electrost~tic energy, as in the prior ark endeavors described abo~e.
The foreyoing second tag embodiment o~ the invention ~hu.
far described is that o~ the above-re~erenced copending application. In accordance with the present invention baktery 126 is connected between the ground plane and the junction 12 of the diode and the spiral reradiator, with a resistor 130 connected as indicated in the electrical schematic of Fig~ ~.
An evaluation method involves polar plotting of the distance at which a tag response (reradiation~ i~ sensed with respect to a source transmitting-receiving lo~ation~ The graphics programs show the response in the ~orm of a polar diagram, where each circle represents a distance of ten inches. The ~ull scale is o~ thirty inches and plots the response at lO degree increments and computes a total for the readings, from wh~ich it computes an estimated pick rate. Computation is based on tag performance in a reference system installation used for correlation between standard test results and actual s~tem pick rate.
Fig. 9 shows the performance o~ the tag of Figs. 5 7 without bias and Fig. 10 with hias. ~stimated pick rates in the re~erence system ins~allation wexe seven~y-three percent withou~
bias, and ninety-three percent wikh bia~.
Fig. 11 shows that the capacikance~modulation parameter, subsequently reerred to as khe dC/dV ratio, and de~ined as incremental change in capacitance V~. incremental change in diode voltage, increases by the ~orward bias.
-~4-Fi~. 12 presents the gain ~esulting Prom increased dC/dV
slope factor vs. bias voltage, computecl ~om Fig. 11 measurements and expressed in dB. Linear regression takes place in the ki~s range of inter~st to this ir~vention.
As allud~d to above, it has been determined that a high frequency tag performance is inversely proportional to the square of the ovarall capacitance. Conseguently, i~ the diode operating point is shi~ted too far from the zero-bias state, although the dC/dV slope factor is improved, at the same ti~e the square of the overall capacitance value rapidly takes eff~ct and ultimately ruins the performance. Results from a dB loss calculation with respect ~Q this factor ~the 1/C2 factor) for a given diode is shown in Fig. 13~ A gradually increasing loss takes place, until the -6 dB point is reached at around O.28V
bias, above whieh a rapid decline takes e~ect.
The amplitude of the low fre~uency voltage cap~ured by the tag, and resulting tag per~ormance, are directly proportional to the DC-impedance of the diode. As the ~perating point is biased further in forward direction, the current increases wi~h resulting DC-impedance dropping exponentially. ~yain th~ loss o~ low frequency efEiclency becomes ~ominan~ over tha improvement in dC/dV slope factor. Fig. 14 shows the calculated dB loss vs. forward bias, resulting from degradation o~ the DC-i~pedance.
~ S~?J~
Depending on the type o~ diode used, the optimu~ ~c~uard bias varies betweQn various diode types~ As an exa~pl~.
Schottky diodes generally can not be enhanced b~ the p~ice of the inventi~n, due to their inherently low DC impedanc~_ The practice under the subject invention, given th~
above-noted ~indings and recognitions and those furth~c ~tated below, is to sPlect the most suitable diode and to incc~ or~te battery bias in such a manner that an optimum compromi-~- is achieved between bene~icial and detrimental effects o~ ing so.
The benefit of introducing bias is that capacitanc ~
modulation efficiency improves through attaining an i~r~ved dC/dV ratio than would otherwise apply.
The detrimental effects of introducing bias are se~al.
There is a degradation o~ high-frequency performance t~-~ugh increase in overall diode capacitance. Degradation o~
low-frequency impedance ari~e~ through increase in dioc~ ~urrent and increase in overall diode capacitance. Degrada~io~.-~f low-frequency impedance also occurs through the loadinc ~fect o~ the bia~ network which is in parallel with d.iode. ~stly, a source for the bias voltage is needed, namely, a batt~--c-~ and concern of course ex~ts for battery life~
Fig. 15 show~ ~he current vs. vc~ltage charac~eris~3 o~ an exemplary diode. Fi~. 16 shvw~; the same using a loga~--~-~ic scaleO Combined e~fects o~ dC/dV slope factor~ the 1/~
~ ~3 '1 ~ , 7 ractor, and the DC-impedance factor are calculated, based on Fig. 12 slope factor, Fig. 13 1/c2 factor and Fig. 1~1 DC--impedance factor. Fig. 17 presents resul~s, computed as a function of bias voltage, and Fig. 18 presenks ~he same as a function of bias current. The optimum operating point from the two calculations is approximately 0.28V, which ~esult~ in approximately 40 ~egohms as the value of the resistor vr resistors in series with the battery, where the battery terminal voltage i~ 1~5Vo As will be seen, the loading ef~ect of the 40 megohm ~ias resistor is negligibleO
By way of ~ore specific disclosure of practice in accordance with the invention, the following analysi6 is provided. A
reference bias voltage is taken as 0.02V., whera the slope dC/dV
is 0.5 pF/V. The slope factor gain, expressed in dB, is proportional to diode forward bia~ and provides a convenient model from which all AC (alternating current~ char~c~eristics are derived.
The dC/dV gain versus bias voltage (Fig. 12~ ~ollsws the following relationship:
GAIN tdB] - (78.0~2 X Vd) - 1.54 (1) where the two constant~ are e~tabli~hed ~s statistical mean valu~s for a given diode evaluat~d.
~ ,J
The value of ~ias voltage p~oviding optimun~ comprGmise is 0.2~V and a comparison is now ef~ec~ed as between ~he re~erence bias voltage and the optimum bias voltage.
In terms of gain, equati~n ~1) yield~ zero ds ~or the raference and 20.32 for the optimum. Now shown is the remnant dB gain a~ter taking away the dB losses.attributable to the l/c2 factor and the ~C-impedance factor.
The former loss ollow~ the relatio~ship:
LOSS [dBJ = 20 LOG ((1/c2~/(0.542~ ~2) where 0.542 i~ 1/c2 at the reference voltageO
At the reexence voltage, the diode capacitance is 1.358 pF, and at the optimum voltage, the capacitance is 2.052 pF, and equation (23 yields zero loss at the refer~nce vol~age and a loss of 6.09 dB ~ox the opti~um.
The DC-imped~nce loss follows the relation~hip:
LOSS tdB] - 20 LOG (Z/Zo~ . (3) where Zo is the impedance at the reference voltage.
Diode current ~ollows the relationshipq Id = 1o((12.464 x Vd) - 11.6849) (4~
where ~he two constants are astabli~hed a8 sta~ tical mean values o~ the diode under aonsideration.
Disde re~i~tance follow~ the relationship:
R = Vd/Id (5) where Vd i~ the volkage acros~ the diode. For the refarenae voltage, the diode resistance is 5.453 x 109 ohms. with a 4 megohm resistor in parallel with the diode, the effective resistance is 30.71 megohms.
Diode reactance follows the relationship:
X C lt( 2~T ~c~ (6) At the frequency of 100 kilohertz, the reactance ~or the reference voltage is 1.172 x 1o6 ohms.
Diode impedance follows the relationship:
Z = R/ (1 ~ (~2/x2))1J2 which yields 1.172 x 106 ohms for Zo.
For the optimum voltage, the diode resistance is 43.87 x 106 ohms. With a 40 megohm resistor in parallel with the diode, the effective resistance is 20.92 megohms.
At the frequency of 100 kilohertz, the reactance for the optimum voltage is 8.256 x 105 ohms. The diode impedance at the optimum voltage computes as 8.249 x 105 ohms.
The DC impedance loss at the reference voltage is zero and that at the optimum voltage is 3.05 dB.
Considering the gain at the optimum per equation (1) and the ~osses per e~uation~ (2) and (3), a net gain o~ 18 dB is e~fected.
If one e~ects the ~oregoing computatlons ~or O.lV, 0.2V, 0.35V amd 0.4V as the bias voltage, the results în net dB gain are respectively 5.07 dB, 9.73 dB, 10.11 dB and 7.46 dB. As will be appreciated each of these net dB gains are less than that achieved at the optimum bias value.
~, ~J ~ 3 ~ '~
By way Of summary of tlle oreyoing ~nd by way o~
introduction to the e~suing claims, the invention ~ill be seen to have various aspects. In one a~pect, it provides ~ t~g fo~
use in an electronic article surveillance ~ystem o~ the ~ype comprising a transmitter-receiver arrangemenk disposed aside an area to be controlled for transmitting a first high-fre~uency signal into tha area, a transmitter disposed aside ~he area and generating a second frequency signal o~ substantially lower Xxequency than the first frequency for establishing in the area an electrostatic field, a tag for attachment to an arti~le to be su~ject to sur~eillance and responsive to the incidence thereon of energy of both the first and ~econd frequencias to transmit a composite thereof and receiver apparatus disposed aside the area for receipt and det~ction of such composite signal and for generation of an output signal indicati~e o~ ~uch detection, the tag comprising: an antenna for receiviny the ~irst and ~econd transmitted ~ignals and for transmitting the composite signal; a nonlinear circuit for connection electrically with the antenna and responsive to energy derived from the second transmitted signal received by the antenna to e~hibit electriaal reactance change with change of voltage o~ the ener~y; and an electrical power ~upply unit conneat~d to the anten~a ~nd tha nonlinear airauit and opexative to enhance the eleatrical reactance change of the nonlinear circuit.
The anten~a may comprise a reradiator eleme~t ~ 32 ~i electrical ground plane memb~r connected electric~lly to the nonlinear circuit. The r~radiator eleme~k, the nonlinear circuit and the yround plane member are in electrical series circuit connection, the electrical power supply beiny connected betwe~n the ground plane member and a junction connection o~ the reradiator element and the nonlinear ~ircuit, The eletrical power supply may include a battery and a resi~tor connected to a terminal of the battery and to either o~ the reradiator element or the ground plane member. The nonlinear circuit may have capacitive reactance as the electrical reactance and is adapted to generate high frequency sidebands through capacitance-modulation responsiYe to receipt of energy derived from the second transmitted signal. The ground plane member may exhibit a dimension substantially equal to a dimension e~hibited ~y the reradiator ~lement~ The reradiator element may comprise a spiral inductor. The ground plane member may be elongate and have a width dimension sub~tantially equal to ~he out~ide diameter of the spiral induator. ~he tag may be elvngat~, the reradiatox element having a central axis longitudinally diæposed with the tag, the nonlinear ~ir¢ui'c and ~he gxound plane member being di~;posed in general alig~Lment with the central axis. The nonlinear circuit may be a diode. ~he ground plane me~ber may be a conductive sheet.
In ~ second aspect, the invention Will be seen to provid~, in combin~tion in ~n electronic article surveillance tag: ~
reradiator element; a nonlinear element connected electri~lly to the reradiator element; an ~lec~rical ground plane member connected electrically to the nonline~r element; and an electrical power supply connected to the reradiator element and the nonlinear el~ment, the reradiator element, the nonlinear element and the ground plane member being in electrical series circuit connection, the reradiator element and the yround plane member defining a monopole antenna upon incidence on the tay o~
high ~requency energy for reradiation o~ the high ~requency energy.
In a third aspect, the invention will bP seen to provide a-tag for use in the first aspect system with such ~ower supply wherein the antenna is of generally rectangular con~iguration and comprises first circuit elements ~xkending longitudinally o~
the tag and of first transverse dimension, ~econd circuit elements extending longitudinally of the tag at least in part jointly with a respective Pirst circui~ element and o~ second transverse dimension sub~tantially exa~eding the ~irst transverse dimension and e~eating predominant di~er~nt rea~ipt by the ~lr~t a~d second circuit element~ o~ the ~ransmitted ~ir~t and second signals and wherein th~ nonlinear circu:it i6 connected in electrical ~eries circuit with the ~irs~ and second circuit elements. In this third a~pect, the electriaal power supply may comprise a battery located on one of the second circuit elements and electrically connected thereto and further electrically connected to one of th~ first circuit elements.
The electrical power supply may further include a resistor connected between the battery and one of the first and second circuit elements. Otherwise, the electrical power supply may comprises a battery located in spaced relation to the first and second circuit elements. The battery may have positive and negative terminals which are electrically connected respectively to distinct second cir~uit elaments and the electrical power supply may further include resistors connected betwePn the ba~tery terminals and the second circuit elements~
In a fourth aspect, the in~ention will be seen to provide, in a method for enhancing the performance of tags for use in an electronic article surveillance system of the type comprising a transmitter-receiver arrangement disposed aside an area to b~
controlled for transmitting a first high~frequency signal into the area, a transmitter disposed aside the area and generating a.
second ~requency signal of substantially lower ~re~uerlc.y than the ~irst ~requency ~or es~ablishin~ in the area an electrostatic field, a tag for attachment to an article to be subject to surveillance, the tag being responsive to the incidence thereon of energy of both the f irst and second 3 ~ ;f frequencies to transmit a composite thereo~ ~nd rec~iv~r apparatus disposed aside the area for receipt and d~tec~ion of such composite signal and ~or generation of an outpu~ siynal indicatiYe of such detection, the method involving the steps of:
configuring tha tag with: an antenna for receiving the first and second transmitted signals and for transmitting the composite signal; and a nonlinear circuit for connection electrically with the antenna and xesponsive to energy derived from the second transmitted signal received by the antenna to exhibit electrical r~actance change with change of volta~e o~ the energy; and applying an electrical bias of steady-state nature to the tag dependently on consideration of characteristics of the nonlinear circuit to enhance the electrical reacta~ce change thereof responsively to the energy derived from the second transmitted signal received by the antenna. The considered characteristics of the nonlinear circuit are selected to be a dC/dV slope actor, a 1/c2 factor and a DC-impedance factox. The nonlinear circuit is selected to be a diode.
Various changes may evidently be introduced in the ~oregoing structure without departing from the invention~ Thus, the particularly de8aribed and pre~erred embodiment5 and practices are intended to be illustrative and not limiting of the invention. The true spirit and ~cope o~ the invention i5 set forth in the appended claims.
Claims (35)
1. A tag for use in an electronic article surveillance system of the type comprising a transmitter-receiver arrangement disposed aside an area to be controlled for transmitting a first high-frequency signal into said area, a transmitter disposed aside said area and generating a second frequency signal of substantially lower frequency than said first frequency for establishing in said area an electrostatic field, a tag for attachment to an article to be subject to surveillance, said tag being responsive to the incidence thereon of energy of both said first and second frequencies to transmit a composite thereof and receiver apparatus disposed aside said area for receipt and detection of such composite signal and for generation of an output signal indicative of such detection, said tag comprising:
(a) antenna means for receiving said first and second transmitted signals and for transmitting said composite signal;
(b) nonlinear circuit means for connection electrically with said antenna means and responsive to energy derived from said second transmitted signal received by said antenna means to exhibit electrical reactance change with change of voltage of said energy; and (c) electrical power supply means connected to said antenna means and said nonlinear circuit means and operative to enhance said electrical reactance change of said nonlinear circuit means.
(a) antenna means for receiving said first and second transmitted signals and for transmitting said composite signal;
(b) nonlinear circuit means for connection electrically with said antenna means and responsive to energy derived from said second transmitted signal received by said antenna means to exhibit electrical reactance change with change of voltage of said energy; and (c) electrical power supply means connected to said antenna means and said nonlinear circuit means and operative to enhance said electrical reactance change of said nonlinear circuit means.
2. The invention claimed in claim 1 wherein said antenna means comprises a reradiator element and an electrical ground plane member connected electrically to said nonlinear circuit means.
3. The invention claimed in claim 2 wherein said reradiator element, said nonlinear circuit means and said ground plane member are in electrical series circuit connection, said electrical power supply means being connected between said ground plane member and a junction connection of said reradiator element and said nonlinear circuit means.
4. The invention claimed in claim 3 wherein said electrical power supply means includes a battery and a resistor connected to a terminal of said battery and to either of said reradiator element or said ground plane member.
5. The invention claimed in claim 2 wherein said nonlinear circuit means has capacitive reactance as said electrical reactance and is adapted to generate high frequency sidebands through capacitance-modulation responsive to receipt of energy derived from said second transmitted signal.
6. The invention claimed in claim 2 wherein said ground plane member exhibits a dimension substantially equal to a dimension exhibited by said reradiator element.
7. The invention claimed in claim 2 wherein said reradiator element comprises a spiral inductor.
8. The invention claimed in claim 7 wherein said ground plane member is elongate and has a width dimension substantially equal to the outside diameter of said spiral inductor.
9. The invention claimed in claim 2 wherein said tag is elongate, said reradiator element having a central axis longitudinally disposed With said tag, said nonlinear circuit means and said ground plane member being disposed in general alignment With said central axis.
10. The invention claimed in claim 2 wherein said nonlinear circuit means is a diode.
11. The invention claimed in claim 2 wherein said ground plane member is a conductive sheet.
12. In combination in an electronic article surveillance tag:
(a) a reradiator element;
(b) a nonlinear element connected electrically to said reradiator element;
(c) an electrical ground plane member connected electrically to said nonlinear element; and (d) electrical power supply means connected to said reradiator element and said nonlinear element, said reradiator element, said nonlinear element and said ground plane member being in electrical series circuit connection, said reradiator element and said ground plane member defining a monopole antenna upon incidence on said tag of high frequency energy for reradiation of said high frequency energy.
(a) a reradiator element;
(b) a nonlinear element connected electrically to said reradiator element;
(c) an electrical ground plane member connected electrically to said nonlinear element; and (d) electrical power supply means connected to said reradiator element and said nonlinear element, said reradiator element, said nonlinear element and said ground plane member being in electrical series circuit connection, said reradiator element and said ground plane member defining a monopole antenna upon incidence on said tag of high frequency energy for reradiation of said high frequency energy.
13. The invention claimed in claim 12 wherein said reradiator element, said nonlinear circuit means and said ground plane member are in electrical series circuit connection, said electrical power supply means being connected between said ground plane member and a junction connection of said reradiator element and said nonlinear circuit means.
14. The invention claimed in claim 13 wherein said electrical power supply means includes a battery and a resistor connected to a terminal of said battery and to either of said reradiator element or said ground plane member.
15. The invention claimed in claim 12 wherein said ground plane member exhibits a dimension substantially equal to a dimension exhibited by said reradiator element.
16. The invention claimed in claim 12 wherein said reradiator element comprises a spiral inductor.
17. The invention claimed in claim 16 wherein said ground plane member is elongate and has a width dimension substantially equal to the outside diameter of said spiral inductor.
18. The invention claimed in claim 12 wherein said tag is elongate, said reradiator having a central axis longitudinally disposed with said tag, said nonlinear element and said ground plane member being disposed in general alignment with said central axis.
19. The invention claimed in claim 12 wherein said nonlinear element is a diode.
20. The invention claimed in claim 12 wherein said ground plane member is a conductive sheet.
21. The invention claimed in claim 1 wherein said antenna means is of generally rectangular configuration and comprises first circuit elements extending longitudinally of the tag and of first transverse dimension, second circuit elements extending longitudinally of the tag at least in part jointly with a respective first circuit element and of second transverse dimension substantially exceeding the first transverse dimension and effecting predominant different receipt by the first and second circuit elements of the transmitted first and second signals and wherein said nonlinear circuit means is connected in electrical series circuit with the first and second circuit elements.
22. The invention claimed in claim 21 wherein said electrical power supply means comprises a battery located on one of said second circuit elements and electrically connected thereto and further electrically connected to one of said first circuit elements.
23. The invention claimed in claim 22 wherein said electrical power supply means further includes a resistor connected between said battery and one of said first and second circuit elements.
24. The invention claimed in claim 21 wherein said electrical power supply means comprises a battery located in spaced relation to said first and second circuit elements.
25. The invention claimed in claim 24 wherein said battery has positive and negative terminals which are electrically connected respectively to distinct said second circuit elements.
26. The invention claimed in claim 25 wherein said electrical power supply further includes resistors connected between said battery terminals and said second circuit elements.
27.In combination in an electronic article surveillance tag:
(a) antenna means of generally reatangular configuration comprising first circuit elements extending longitudinally of the tag and of first transverse dimension, second circuit elements extending longitudinally of the tag at least in part jointly with a respective first circuit element and of second transverse dimension substantially exceeding the first transverse dimension;
(b) nonlinear circuit means connected in electrical series circuit with the first and second circuit elements; and (c) electrical power supply means electrically connected with said nonlinear circuit means for imparting bias thereto.
(a) antenna means of generally reatangular configuration comprising first circuit elements extending longitudinally of the tag and of first transverse dimension, second circuit elements extending longitudinally of the tag at least in part jointly with a respective first circuit element and of second transverse dimension substantially exceeding the first transverse dimension;
(b) nonlinear circuit means connected in electrical series circuit with the first and second circuit elements; and (c) electrical power supply means electrically connected with said nonlinear circuit means for imparting bias thereto.
28. The invention claimed in claim 27 wherein said electrical power supply means comprises a battery located on one of said second circuit elements and electrically connected thereto and further electrically connected to one of said first circuit elements.
29. The invention claimed in claim 28 wherein said electrical power supply means further includes a resistor connected between said battery and one of said first and second circuit elements.
30. The invention claimed in claim 27 wherein said electrical power supply means comprises a battery located in spaced relation to said first and second circuit elements.
31. The invention claimed in claim 30 wherein said battery has positive and negative terminals which are electrically connected respectively to distinct said second circuit elements.
32. The invention claimed in claim 31 wherein said electrical power supply further includes resistors connected between said battery terminals and said second circuit elements.
33. A method for enhancing the performance of tags for use in an electronic article surveillance system of the type comprising a transmitter-receiver arrangement disposed aside an area to be controlled for transmitting a first high-frequency signal into said area, a transmitter disposed aside said area and generating a second frequency signal of substantially lower frequency than said first frequency for establishing in said area an electrostatic field, a tag for attachment to an article to be subject to surveillance, said tag being responsive to the incidence thereon of energy of both said first and second frequencies to transmit a composite thereof and receiver apparatus disposed aside said area for receipt and detection of such composite signal and for generation of an output signal indicative of such detection, involving the steps of:
(a) configuring said tag with:
(1) antenna means for receiving said first and second transmitted signals and for transmitting said composite signal; and (2) nonlinear circuit means for connection electrically with said antenna means and responsive to energy derived from said second transmitted signal received by said antenna means to exhibit electrical reactance change with change of voltage of said energy ; and (b) applying an electrical bias of steady-state nature to said tag dependently on consideration of characteristics of said nonlinear circuit means to enhance said electrical reactance change thereof responsively to said energy derived from said second transmitted signal received by said antenna means.
(a) configuring said tag with:
(1) antenna means for receiving said first and second transmitted signals and for transmitting said composite signal; and (2) nonlinear circuit means for connection electrically with said antenna means and responsive to energy derived from said second transmitted signal received by said antenna means to exhibit electrical reactance change with change of voltage of said energy ; and (b) applying an electrical bias of steady-state nature to said tag dependently on consideration of characteristics of said nonlinear circuit means to enhance said electrical reactance change thereof responsively to said energy derived from said second transmitted signal received by said antenna means.
34. The invention claimed in claim 33 wherein said considered characteristics of said nonlinear circuit means are selected to be a dC/dV slope factor, a l/c2 factor and a DC-impedance factor,
35. The invention claimed in claim 34 wherein said nonlinear circuit means is selected to be a diode.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/561,787 US5030940A (en) | 1990-08-02 | 1990-08-02 | Electronic article surveillance tag and method for implementing same |
| US07/561,787 | 1990-08-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2041827A1 true CA2041827A1 (en) | 1992-02-03 |
Family
ID=24243472
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002041827A Abandoned CA2041827A1 (en) | 1990-08-02 | 1991-05-03 | Electronic article surveillance tag and method for implementing same |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US5030940A (en) |
| EP (1) | EP0472932A1 (en) |
| JP (1) | JPH04250392A (en) |
| AR (1) | AR245839A1 (en) |
| BR (1) | BR9102873A (en) |
| CA (1) | CA2041827A1 (en) |
Families Citing this family (31)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5278573A (en) * | 1990-08-06 | 1994-01-11 | Sensormatic Electronics Corporation | Electronic article surveillance system and tag circuit components therefor |
| US5109217A (en) * | 1990-08-09 | 1992-04-28 | Sensormatic Electronics Corporation | Method and apparatus for enhancing detection of electronic article surveillance tags in close proximity to electrically conductive objects |
| US5206626A (en) * | 1991-12-24 | 1993-04-27 | Knogo Corporation | Stabilized article surveillance responder |
| US6144859A (en) * | 1993-08-27 | 2000-11-07 | Aeris Communications, Inc. | Wireless cellular communicator system and apparatus |
| US5889474A (en) * | 1992-05-18 | 1999-03-30 | Aeris Communications, Inc. | Method and apparatus for transmitting subject status information over a wireless communications network |
| US5241923A (en) * | 1992-07-23 | 1993-09-07 | Pole/Zero Corporation | Transponder control of animal whereabouts |
| US7158031B2 (en) | 1992-08-12 | 2007-01-02 | Micron Technology, Inc. | Thin, flexible, RFID label and system for use |
| US5594740A (en) | 1993-08-27 | 1997-01-14 | Axion Logistics Corporation | Wireless communications application specific enabling method and apparatus |
| EP0646983B1 (en) * | 1993-10-04 | 1998-09-02 | Amtech Corporation | Modulated backscatter microstrip patch antenna |
| WO1997014112A1 (en) * | 1995-10-11 | 1997-04-17 | Motorola Inc. | Remotely powered electronic tag and associated exciter/reader and related method |
| US5999808A (en) * | 1995-12-12 | 1999-12-07 | Aeris Communications, Inc. | Wireless gaming method |
| US5845203A (en) * | 1996-01-25 | 1998-12-01 | Aertis Cormmunications | Remote access application messaging wireless method |
| SE506449C2 (en) * | 1996-02-12 | 1997-12-15 | Rso Corp | Article Surveillance systems |
| SE506167C2 (en) | 1996-02-12 | 1997-11-17 | Rso Corp | Sensor for contactless detection of objects |
| US5874902A (en) * | 1996-07-29 | 1999-02-23 | International Business Machines Corporation | Radio frequency identification transponder with electronic circuit enabling/disabling capability |
| US6446049B1 (en) | 1996-10-25 | 2002-09-03 | Pole/Zero Corporation | Method and apparatus for transmitting a digital information signal and vending system incorporating same |
| US6064308A (en) * | 1996-10-25 | 2000-05-16 | Pole/Zero Corporation | RF signaling system and system for controlling the whereabouts of animals using same |
| EP0863087A1 (en) * | 1997-03-07 | 1998-09-09 | The Procter & Gamble Company | Anti-slip layer for a package or for an anti-slip sheet |
| US6980085B1 (en) | 1997-08-18 | 2005-12-27 | Micron Technology, Inc. | Wireless communication devices and methods of forming and operating the same |
| US6339385B1 (en) * | 1997-08-20 | 2002-01-15 | Micron Technology, Inc. | Electronic communication devices, methods of forming electrical communication devices, and communication methods |
| US5990791A (en) * | 1997-10-22 | 1999-11-23 | William B. Spargur | Anti-theft detection system |
| US6166643A (en) * | 1997-10-23 | 2000-12-26 | Janning; Joseph J. | Method and apparatus for controlling the whereabouts of an animal |
| US6057765A (en) * | 1998-10-07 | 2000-05-02 | Research Electronics International | Non-linear junction detector |
| US6285342B1 (en) * | 1998-10-30 | 2001-09-04 | Intermec Ip Corp. | Radio frequency tag with miniaturized resonant antenna |
| US6356197B1 (en) * | 2000-04-03 | 2002-03-12 | Sensormatic Electronics Corporation | Electronic article surveillance and identification device, system, and method |
| US6714136B1 (en) * | 2000-08-14 | 2004-03-30 | Computime, Ltd. | Alarm clock with remote control function |
| US6750768B2 (en) | 2002-04-15 | 2004-06-15 | Wg Security Products, Inc. | EAS system employing pseudorandom coding system and method |
| US7336243B2 (en) * | 2003-05-29 | 2008-02-26 | Sky Cross, Inc. | Radio frequency identification tag |
| US7152804B1 (en) | 2004-03-15 | 2006-12-26 | Kovlo, Inc. | MOS electronic article surveillance, RF and/or RF identification tag/device, and methods for making and using the same |
| US7034687B2 (en) * | 2004-04-29 | 2006-04-25 | Comm-Engines | Error-avoiding anti-theft surveillance system |
| US7286053B1 (en) | 2004-07-31 | 2007-10-23 | Kovio, Inc. | Electronic article surveillance (EAS) tag/device with coplanar and/or multiple coil circuits, an EAS tag/device with two or more memory bits, and methods for tuning the resonant frequency of an RLC EAS tag/device |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1604219A (en) * | 1977-04-28 | 1981-12-02 | Parmeko Ltd | Detection systems |
| US4387379A (en) * | 1980-10-14 | 1983-06-07 | Raytheon Company | Radio frequency antenna |
| US4413254A (en) * | 1981-09-04 | 1983-11-01 | Sensormatic Electronics Corporation | Combined radio and magnetic energy responsive surveillance marker and system |
| US4642640A (en) * | 1983-04-25 | 1987-02-10 | Sensormatic Electronics Corporation | Signal receptor-reradiator and surveillance tag using the same |
| US4736207A (en) * | 1986-01-31 | 1988-04-05 | Sensormatic Electronics Corporation | Tag device and method for electronic article surveillance |
| US4783646A (en) * | 1986-03-07 | 1988-11-08 | Kabushiki Kaisha Toshiba | Stolen article detection tag sheet, and method for manufacturing the same |
| CA1335676C (en) * | 1988-01-14 | 1995-05-23 | Akira Iga | Portable data transmitter device and a system using the same |
-
1990
- 1990-08-02 US US07/561,787 patent/US5030940A/en not_active Expired - Lifetime
-
1991
- 1991-05-03 CA CA002041827A patent/CA2041827A1/en not_active Abandoned
- 1991-07-02 AR AR91320078A patent/AR245839A1/en active
- 1991-07-09 BR BR919102873A patent/BR9102873A/en not_active Application Discontinuation
- 1991-07-30 JP JP3189768A patent/JPH04250392A/en not_active Withdrawn
- 1991-07-30 EP EP91112755A patent/EP0472932A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| BR9102873A (en) | 1992-04-28 |
| US5030940A (en) | 1991-07-09 |
| AR245839A1 (en) | 1994-02-28 |
| EP0472932A1 (en) | 1992-03-04 |
| JPH04250392A (en) | 1992-09-07 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |