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Publication numberUS3624631 A
Publication typeGrant
Publication dateNov 30, 1971
Filing dateApr 27, 1970
Priority dateApr 27, 1970
Publication numberUS 3624631 A, US 3624631A, US-A-3624631, US3624631 A, US3624631A
InventorsMarc Chomet, Donald E Ellison, Robert F Watterson
Original AssigneeSanders Associates Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Pilferage control system
US 3624631 A
Images(2)
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Description  (OCR text may contain errors)

United States Patent 12 Claims, 3 Drawing Figs.

U.S. Cl 340/280, 340/258 R, 340/258 C, 343/6.5 SS

Int. Cl. ..G08b 13/00, G08b 2 H00 Field of Search 340/258 R,

280; 343/65 SS, 6.8 R

[56] References Cited UNITED STATES PATENTS 3,493,955 2/1970 Minasy 340/258 R 3,363,247 1/1968 Chausse et al. 343/65 SS Primary Examiner-Donald J. Yusko Assistant Examiner-Michael Slobasky Arrorney-Louis Etlinger ABSTRACT: An antipilferage system comprising a cooperating radio frequency transmitter and receiver pair. The trans mitter directs swept radio frequency energy to the cooperating receiver circuit wherein balanced oscillating conditions are maintained in a normally steady state. Passive tuned circuits, preferably in the form of printed circuit elements are placed on the merchandise in a store and if an attempt is made to remove unpurchased merchandise from the store without first destroying a fusible link in the passive tuned circuit an unbalance is caused in the receiver oscillator circuits which operates to actuate a suitable alarm. A fully automatic deactivation circuit is also included as part of the invention.

l DUAL J PASSBAND TIME RECEIVER CONSTANT DETECTOR I 22 l I PASSBAND I FILTER I 32 l l CORRELATION I CIRCUIT I FOOT swn'cn PATENTED nuvso l9?! ANTENNA RECEIVE TR ANSMIT ANTENNA DRIVER PASSBAND RECEIVER DUAL TIME CONSTANT DETECTOR PASSBAND 34 FILTER CORRELATION cmcurr I 28 l l l I SWEEP CONTROL FOOT SWITCH mvsurons MARC CHOMET DONALD E. ELLlSON ROBERT F. WATTERSON .ar y I AGENT PATENTEfluuvaolsn sumenr 2 TRANSMIT ANTENNA r58 RECEIVE ANTENNA 3 se SWEEP POWER R L DRIVER RECEIVER RECEIVER 64 DEACTIVATION IC V c o BUFFER CONTROL so LOGIC MANUAL DESTRUCT 68 FIG. 5

INVENTORS' MARC CHOMET DONALD E. LusoN ROBERT F. WATTERSON AGENT PILFERAGE CONTROL SYSTEM BACKGROUND OF THE INVENTION The present invention relates generally to the field of radiofrequency circuits and more specifically to a radiofrequency antipilferage system.

DESCRIPTION OF THE PRIOR ART Pilferage of merchandise from business establishments has become a matter of great concern and many devices have been devised in an attempt to minimize losses. One such device is a Detecting Means for Stolen Goods described in U.S. Pat. No. 2,774,060 which issued to T. F. Thompson on Dec. 11, 1956. In this system one or more fixed frequency oscillators are employed to set up a radiation field of predetermined shape and size and precision resonant circuits are concealed in sales tags on the merchandise. When merchandise with a resonant circuit is passed through the radiation field the potential of the oscillator is changed and actuation of an alarm results. In order to prevent false alarms by legitimately purchased merchandise it is necessary that the sales tag containing the circuit be physically destroyed.

Several practical problems attend the use of an antipilferage system such as that described by Thompson. The use of a fixed frequency oscillator requires that the resonant tuned circuit be precision tuned to that frequency. In order to prevent actuation of the alarm by an object of appropriate size carried by a legitimate customer it is desirable to use three different fixed frequency oscillators and three precision tuned circuits, one for each frequency. In such an arrangement wherein frequency precision is required a serious problem may arise in detuning of the tuned circuit by body capacity, i.e., the electrical capacity of the human body in close proximity to the tuned circuit is in many cases sufficient to detune the circuit to the extent that detection by a single frequency system is precluded. It will be noted that even in the three oscillator embodiment of the Thompson apparatus detuning of any of the precision circuits will preclude detection. The fact that the Thompson apparatus necessitates a manual destruction of the tuned circuit bearing tag increases the potential for inadvertent and embarrassing triggering of the alarm should an employee forget to remove the tag. An accomplished pilferer may also become aware of the gross nature of the system from observation of consistent removal of such tags and/or the consequences of nonremoval. The apparatus described by Thompson further involves the use of one antenna for both transmitting the radiation pattern and detecting an absorption by the resonant circuit. Such an arrangement has an inherently low-volumetric efiiciency and the tuned circuit must pass in close proximity to the antenna for reliable detection. Many business establishments are not physically laid out such as to assure such proximity.

OBJECTIVES AND SUMMARY OF THE INVENTION From the foregoing it will be understood that among the objectives of the present invention are the following:

To provide a new and novel radiofrequency antipilferage system.

To provide apparatus of the above-described character using a swept radiofrequency.

To provide apparatus of the above-described character having a cooperating transmitter and receiver remotely disposed with respect to one another.

To provide apparatus of the above-described character wherein a passive tuned circuit disposed on merchandise may be automatically and surreptitiously deactivated.

To provide apparatus of the above-described character having improved false alarm rejection.

The foregoing objectives are accomplished through the practice of the present invention by providing a swept radiofrequency oscillator and transmitting antenna and a remotely disposed cooperating broad band radiofrequency receiver and antenna coupled to a post detection signal processor. A passive tuned circuit having a fusible link is affixed to articles of merchandise preferably within a price tag or other item affixed by the store. When pilfered merchandise bearing the tuned circuit is carried between the transmitter and receiver there is absorption of energy from the radiation field and an unbalance is produced in the receiver which is used to actuate a suitable alarm. To preclude actuation of the alarm by tags or legitimately purchased merchandise each passive tuned circuit is provided with a fusible link which is opened when the circuit is exposed to radiofrequency energy above a preselected level. To accomplish the deactivation swept radiofrequency energy above the preselected level is transmitted for example through the surface of a check out counter at which purchased merchandise is wrapped. This energy destroys the fusible link in the passive tuned circuit and automatically checks for the continued presence of an active circuit. Thereafter the merchandise with the tag bearing the deactivated tuned circuit, and in which there has been no change which is readily discemable to the casual observer, may pass between the transmitter and receiver without actuating the alarm. The deactivation portion of the invention is fully automatic in operation and under normal circumstances completely eliminates any requirement for manual participation of sales employees in the deactivation of the tuned circuit.

These and other objects, features and advantages of the present invention will become more apparent from the detailed discussion taken in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a pilferage control system in accordance with the present invention.

FIG. 2 is a schematic diagram of a fusible tuned circuit for use with the present invention.

FIG. 3 is a schematic block diagram of a deactivation circuit for use in the practice of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT Turning now to FIG. 1 here is illustrated a block diagram of the cooperating transmitter and receiver portions of the present invention which would be placed across each exit of a store. The transmitter generally designated 10 comprises a voltage controlled oscillator 12 the output frequency of which is controlled by a sweep control means 14. The swept radiofrequency output signal from the oscillator 12 is coupled through a driver 16 to a transmitter antenna 18. A radiation field 20 over a desired area defined by the characteristics of the transmitter antenna 18 is thus established. The transmitter 10 is preferably placed on one side of the entrance/exit to the place of business.

The receiver designated generally at 22 is placed on the opposite side of the store entrance/exit from the transmitter. A receiver antenna 24 picks up the swept radiofrequency energy and is coupled to a passband radio receiver 26. The output of the receiver 26 is applied to a post detection processor 28 which comprises in sequence a dual time constant detector 30, amplifier 32, passband filter 34 and correlation circuit 36.

The receiver 26 output in the absence of a tuned circuit in the radiation field will be substantially at a continuous level as the transmitter oscillator 12 is swept in frequency. When a tuned circuit enters the radiation field 20 there will result a discemable dip in the receiver 26 output due to energy absorption by the circuit at the frequency for which it is tuned. The dual time constant detector 30 operates to reject false absorption signals of two types; first, that caused by an individual merely passing through the exit and which is manifested as an absorption at all frequencies within the sweep range of the oscillator 12 and second, the random noise within any electronic system which is characterized by very sharp spikes. In that the frequency is swept rather than fixed the dual time constant detector 30 may simply reject any detected absorption which is of too long or short a duration; i.e. corresponding to either too wide or too narrow frequency bands to be produced by a tuned circuit in the radiation field 20.

Thus receiver signals which have the proper frequency (and thus time) characteristics are coupled to amplifier 32 and thence through a passband filter 34 to a correlation circuit 36. The correlation circuit 36 may, for example, comprise a plurality of one shot multivibrators or any other of the recognized means for dividing the frequency sweep of oscillator 12 into a given number of bins or windows. Once the presence of a tuned circuit is detected in the radiation field 20 by a proper absorption characteristic the correlation circuit 36 establishes a frequency window or bin; eg percent of the total frequency sweep range, within which the absorption was detected. Only after a predetermined number of sequential detections have occurred in that frequency window will the correlation circuit 39 produce an output signal. A transient signal in the system is thus rejected since it would not appear in the requisite number of successive sweeps and random signals would not have the frequency stability to appear in the same window for a long enough period to actuate the alarm. The correlation circuit output signal could be coupled directly to a suitable alarm 40, however, as an added false alarm rejection feature this signal may be applied to an AND-gate 38 to which is also coupled a signal from a foot switch (not shown) concealed for example under a floor mat in an exit doorway. In this fashion the alarm 40 would only be actuated by a person in the radiation field who was carrying merchandise bearing an active tuned circuit.

FIG. 2 is a schematic illustration of a passive tuned circuit which is useful in the practice of the present invention. The circuit is essentially a simple tank circuit comprising a coil 42 and capacitors 44 and 46. A significant difference, however, which is of great practical utility in the practice of this invention is the incorporation of a fusible link 48 in the circuit. This link is shown for the purpose of illustration as being disposed between capacitors 44 and 46, however, it is to be understood that disposition anywhere in the circuit is equally suitable in the practice of the invention. The link 48, when placed in series in the tuned circuit, has negligible current induced therein by the radiation field across the entrance/exit of the store and thus has substantially no effect upon the detection process discussed above. The fusible link 48 is formed of a fine conductor such as steel wire which may be burned out" by a preselected level of radiofrequency energy. The passive tuned circuit may be formed using printed circuit techniques well known in the art and incorporated into any of the variety of cards, tags or the like which are normally found in or on merchandise displayed for sale. Initially the circuit is complete and when placed in a radiation field 20 operates to absorb energy in the field. On the application of a relatively higher power RF field the induction field overloads the fusible link, opening the circuit and thus rendering it ineffective as an absorber.

FIG. 3 is a schematic block diagram of a fully automatic deactivation circuit which is preferred in the practice of the present invention. This circuit may be placed beneath the checkout and wrapping counter usually found in business establishments and operates to detect the tuned circuit carried by merchandise being legitimately purchased, switch to an output power sufficient to burnout or open the fusible link and check to assure that deactivation has actually been accomplished. A voltage controlled oscillator 50 having substantially the same frequency range as oscillator 12 of FIG. 1 and which is controlled by a frequency sweep control means 52 is coupled through a buffer amplifier 54 to a power driver 56. The power driver 56 is coupled to a transmitter antenna 58 which may be flush-mounted in or under the wrapping counter. Mounted concentrically with the transmitter antenna 58 is a receiver antenna 60. When a piece of merchandise bearing a tuned circuit is placed on the wrapping counter an unbalance is produced in the receiver 62 to which the receiver antenna 60 is coupled. The receiver output is coupled through receiver logic circuitry 64 to a deactivation control logic circuit 66. When the presence of a tuned circuit is detected the receiver logic circuit 64 generates an output signal which is applied to the deactivation control logic circuit 66 which operates to switch the power driver 56 into a relatively highpower mode (e.g., I00 mw.) for a predetermined period of time. At the end of this time the power drive 56 is returned to its normal lower level output. If the continued presence of a tuned circuit is indicated the deactivation process is automatically repeated. If, after a predetermined number of deactivation cycles, as determined by feeding back the output of the deactivation control logic circuit 66 to the receiver logic circuit 64, a tuned circuit continues to be detected a manual destruct indicator 68 such as a light, buzzer or the like, may be activated to instruct the employee to manually remove and destroy the circuit-bearing tag or label. To further discourage the employee from simply ignoring the manual tag destruction indicator a reset switch (not shown) may be provided which must be closed by the employee before the indicator will be deactivated. The deactivation circuit is thus both fully automatic and self-checking in operation, and substantially precludes the actuation of the entrance/exit alarm by legitimately purchased merchandise. It is only in rare instances that the manual involvement of an employee is required and even in this event the employee need have little if any knowledge of what the under-counter unit is or how it operates.

It will thus be seen that the objectives set forth hereinabove, among those made apparent from the preceding description are efficiently attained and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the appended drawings shall be interpreted as illustrative and not in a limiting sense.

Having described what is new and novel and desired to secure by Letters Patent, what is claimed is:

I. A pilferage control system for detecting the unauthorized removal of goods from an area comprising a passive tank circuit affixed to said goods, tuned such as to have predetermined radiofrequency absorption characteristics in the presence of a radiation field, and having fusible link disposed in series therein,

means for transmitting a field of swept radiofrequency radiation of a preselected first level into a volume of space including an exit from said area, means disposed remotely with respect to said transmitting means for detecting said swept radiofrequency radiation and responsive to a selected change in said radiation level to produce an electrical output signal indicative thereof,

tuned circuit deactivation means for selectively applying swept radiofrequency frequency radiation of a preselected second level higher than said first level to said passive tank circuit said second level being sufficiently high to destroy said fusible link, and

indicating means coupled to said detecting means and responsive to said electrical output signal therefrom to indicate the presence ofa passive tuned tank circuit having a complete fusible link therein within said radiation field.

2. Apparatus as recited in claim I wherein said transmitting means comprises a variable radiofrequency oscillator,

means coupled to said oscillator for varying the frequency thereof as a preselected function of time,

a planar radiofreqnecy transmitting antenna, and

means for driving said antenna coupled between said oscillator and said antenna.

3. Apparatus as recited in claim 1 wherein said detecting means comprises a planar radiofrequency receiving antenna,

a radiofrequency passband receiver coupled to said receiving antenna, and

means coupled to said receiver for rejecting detected changes in said radiation level which correspond to other than absorption produced by a passive tank circuit in said radiation field.

4. Apparatus as recited in claim 3 wherein said rejecting means includes a dual time constant detector means operative to produce an electrical output signal only in response to detected changes in said radiation level which correspond to the presence of a passive tuned tank circuit having a complete fusible link in said radiation field, and to reject detected changes both above and below a preselected frequency bandwidth.

5. Apparatus as recited in claim 4 wherein said rejecting means includes correlation means coupled to said dual time constant detector means comprising means for establishing a plurality of frequency bands within the frequency range of said transmitting means,

means for determining in which one of said plurality of frequency bands a change in said radiation level corresponding to the presence of a passive tuned tank circuit is produced,

means for detecting only changes in said radiation level which occur in said one frequency band for a predetermined number of sequential sweeps through said frequency range of said transmitting means, and

means for producing an electrical output signal only in response to said predetermined number of sequential detections in said one frequency band.

6. Apparatus as recited in claim 1 further including means coupled between said detecting means and said indicating means for sensing the presence of a person in said radiation field and producing an electrical signal indicative thereof and wherein said indicating means is responsive only to the combined electrical signals from said detecting means and said sensing means.

7. Apparatus as recited in claim 1 wherein said passive tuned tank circuit comprises in series an inductance element,

first and second capacitive elements, and

a fusible link disposed in said circuit and susceptible to destruction by the application of radiofrcquency energy above a preselected level.

8. Apparatus as recited in claim 1 wherein said tuned circuit deactivation means comprises means for transmitting swept radio frequency radiation at selectable first and second levels into a preselected volume of space,

means colocated with said transmitting means for detecting said swept radiofrcquency radiation and responsive to a selected change in said radiation level to produce an electrical output signal indicative of the presence of said tuned circuit, and

means coupled to said detecting means and to transmitting means for selecting the higher of said first and second transmitting means output radiation levels for a preselected period of time said higher level being sufficiently high to burnout said fusible link in said tuned circuit.

9. Apparatus as recited in claim 8 further including means for indicating complete destruction of said fusible link.

10. A tuned passive tank circuit for use with a radiofrcquency pilferage control system comprising in series an inductance element,

first and second capacitive elements, and

a fusible link disposed in said circuit and susceptible to destruction by the application of radiofrequency radiation above a preselected level.

11. Apparatus as recited in claim 10 wherein said fusible link is formed of an electrically conductive material wherein an electrical overload adequate to destroy said link is induced by a radiofrcquency radiation level of one hundred milliwatts.

12. Apparatus as recited in claim 10 wherein:

said radio frequency pilferage control system employs swept radio frequency radiation, and

said tuned passive tank circuit is tuned such as to absorb radiation over a frequency range less than and within the range of radiofrequencies frequencies over which said pilferage control system is swept.

l t l I?

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3363247 *May 5, 1967Jan 9, 1968Gen ElectricIdentification system
US3493955 *Apr 17, 1968Feb 3, 1970Monere CorpMethod and apparatus for detecting the unauthorized movement of articles
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3732555 *Mar 13, 1972May 8, 1973Sperry Rand CorpSelective intrusion alarm system
US3810147 *Dec 30, 1971May 7, 1974G LichtblauElectronic security system
US3828337 *Aug 20, 1973Aug 6, 1974G LichtblauNoise rejection circuitry
US3828341 *Jan 20, 1972Aug 6, 1974Ici America IncAlarm apparatus for facilitating the detection of an unauthorized removal of property
US3859652 *Jun 26, 1972Jan 7, 1975North American Systems CorpMethod and apparatus for detecting the theft of articles
US3863244 *Jun 14, 1972Jan 28, 1975Lichtblau G JElectronic security system having improved noise discrimination
US3938044 *Nov 14, 1973Feb 10, 1976Lichtblau G JAntenna apparatus for an electronic security system
US4012583 *Mar 3, 1975Mar 15, 1977Motorola, Inc.Pay TV control system
US4321586 *Aug 21, 1980Mar 23, 1982Knogo CorporationArticle theft detection
US4498076 *May 10, 1982Feb 5, 1985Lichtblau G JResonant tag and deactivator for use in an electronic security system
US4567473 *Nov 20, 1984Jan 28, 1986Lichtblau G JResonant tag and deactivator for use in an electronic security system
US4717438 *Sep 29, 1986Jan 5, 1988Monarch Marking Systems, Inc.Method of making tags
US4778552 *Apr 22, 1987Oct 18, 1988Monarch Marking Systems, Inc.Alarm tag and method of making and deactivating it
US4818312 *Oct 28, 1987Apr 4, 1989Monarch Marking Systems, Inc.Method of making electronic tags
US4846922 *Nov 24, 1987Jul 11, 1989Monarch Marking Systems, Inc.Method of making deactivatable tags
US4920335 *Jan 31, 1989Apr 24, 1990Interamerican Industrial CompanyElectronic article surveillance device with remote deactivation
US5027106 *Dec 27, 1989Jun 25, 1991Checkpoint Systems, Inc.Method and apparatus for electronic article surveillance
US5059950 *Sep 4, 1990Oct 22, 1991Monarch Marking Systems, Inc.Deactivatable electronic article surveillance tags, tag webs and method of making tag webs
US5103210 *Jun 27, 1990Apr 7, 1992Checkpoint Systems, Inc.Activatable/deactivatable security tag for use with an electronic security system
US5182544 *Oct 23, 1991Jan 26, 1993Checkpoint Systems, Inc.Security tag with electrostatic protection
US5218189 *Sep 9, 1991Jun 8, 1993Checkpoint Systems, Inc.Binary encoded multiple frequency rf indentification tag
US5367290 *Dec 19, 1990Nov 22, 1994Actron Entwicklungs AgDeactivatable resonance label
US5447779 *Jan 27, 1993Sep 5, 1995Tokai Electronics Co., Ltd.Resonant tag and method of manufacturing the same
US5510770 *Mar 30, 1994Apr 23, 1996Checkpoint Systems, Inc.Surface deactivateable tag
US5574431 *Aug 29, 1995Nov 12, 1996Checkpoint Systems, Inc.For use with an electronic security system
US5589251 *Aug 22, 1995Dec 31, 1996Tokai Electronics Co., Ltd.Resonant tag and method of manufacturing the same
US5682814 *Aug 22, 1995Nov 4, 1997Tokai Electronics Co., Ltd.Apparatus for manufacturing resonant tag
US5695860 *Sep 1, 1995Dec 9, 1997Tokai Electronics Co., Ltd.Resonant tag and method of manufacturing the same
US5767772 *Aug 8, 1996Jun 16, 1998Lemaire; GerardMarker for an article which is detected when it passes through a surveillance zone
US5786764 *Mar 4, 1997Jul 28, 1998Engellenner; Thomas J.Voice activated electronic locating systems
US5796339 *Dec 2, 1996Aug 18, 1998Sensormatic Electronics CorporationShoplifting detection label deactivator with combined excitation-deactivation coil
US5798693 *Jun 7, 1995Aug 25, 1998Engellenner; Thomas J.Electronic locating systems
US6057756 *Aug 14, 1998May 2, 2000Engellenner; Thomas J.Electronic locating systems
US6333692Jul 5, 2000Dec 25, 2001Ats Money Systems Inc.Security tag deactivation system
US6388569 *May 2, 2000May 14, 2002Thomas J. EngellennerElectronic locating methods
US6476720Oct 2, 2001Nov 5, 2002Ats Money Systems, Inc.Security tag deactivation system
US6592037 *Sep 16, 1998Jul 15, 2003Meto International GmbhMethod and device for the detection and deactivation of a deactivatable security element
US6891469 *May 14, 2002May 10, 2005Thomas J. EngellennerElectronic locating systems
US6946963Oct 16, 2002Sep 20, 2005Spectra Research, Inc.Secure storage disc and disc surveillance system
US7012531 *Jun 7, 2002Mar 14, 2006Infineon Technologies AgProduct label, method of producing product labels and method for identifying products in a contactless and forgery-proof manner
US7095311 *Nov 25, 2003Aug 22, 2006The Regents Of The University Of CaliforniaIdentification coding schemes for modulated reflectance systems
US7321296May 9, 2005Jan 22, 2008Thomas J. EngellennerElectronic locating systems
US7481178 *Jun 20, 2005Jan 27, 2009Infineon Technologies AgRadio-interrogable data storage medium
US7527198 *Jul 2, 2003May 5, 2009Datalogic Scanning, Inc.Operation monitoring and enhanced host communications in systems employing electronic article surveillance and RFID tags
US7902971Jan 18, 2008Mar 8, 2011Xalotroff Fund V, Limtied Liability CompanyElectronic locating systems
US8006904May 5, 2009Aug 30, 2011Datalogic Scanning, Inc.Operation monitoring and enhanced host communications in systems employing electronic article surveillance and RFID tags
US8358211Oct 24, 2011Jan 22, 2013Datalogic ADC, Inc.Integrated data reader and electronic article surveillance (EAS) system
CN1098511C *Aug 22, 1996Jan 8, 2003检验点系统公司Detachable anti-theft tag
DE3128980A1 *Jul 22, 1981Apr 8, 1982Knogo CorpVerfahren und vorrichtung zum schutz von gegenstaenden gegen diebstahl
DE3490695C2 *Apr 23, 1984Mar 15, 2001Lichtblau G JResonant tag and deactivator for electronic security system
DE3546642C2 *Nov 25, 1985Feb 8, 1990Sensormatic Electronics Corp., Deerfield Beach, Fla., UsTitle not available
DE3546746C2 *Nov 25, 1985Feb 15, 1990Sensormatic Electronics Corp., Deerfield Beach, Fla., UsTitle not available
EP0252975A1 *Jan 8, 1987Jan 20, 1988Checkpoint Systems IncSecurity tag deactivation system.
WO1985004975A1 *Apr 23, 1984Nov 7, 1985Little Inc AResonant tag and deactivator for use in an electronic security system
WO1990009011A1 *Dec 29, 1989Aug 9, 1990Interamerican Ind CoElectronic article surveillance device with remote deactivation
WO1992000578A1 *May 29, 1991Dec 28, 1991Checkpoint Systems IncActivatable-deactivatable security tag for use with an electronic security system
WO1998025244A1 *Oct 29, 1997Jun 11, 1998Sensormatic Electronics CorpShoplifting detection label deactivator with combined excitation-deactivation coil
WO2005057794A2 *Sep 7, 2004Jun 23, 2005Univ CaliforniaIdentification coding schemes for modulated reflectance systems
Classifications
U.S. Classification340/568.1, 340/572.3, 340/572.5, 334/39
International ClassificationG08B13/24
Cooperative ClassificationG08B13/2414, G08B13/2431
European ClassificationG08B13/24B1G, G08B13/24B3C