US3707711A - Electronic surveillance system - Google Patents

Electronic surveillance system Download PDF

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US3707711A
US3707711A US3707711DA US3707711A US 3707711 A US3707711 A US 3707711A US 3707711D A US3707711D A US 3707711DA US 3707711 A US3707711 A US 3707711A
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frequency
means
system
receiver
signal
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Peter Harold Cole
Richard Vaughn
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RICHARD VAUGHAN
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RICHARD VAUGHAN
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    • GPHYSICS
    • G08SIGNALLING
    • G08BSIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00Burglar, theft or intruder alarms
    • G08B13/22Electrical actuation
    • G08B13/24Electrical actuation by interference with electromagnetic field distribution
    • G08B13/2402Electronic 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
    • G08B13/2405Electronic 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
    • G08B13/2422Electronic 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
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/74Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
    • G01S13/75Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems using transponders powered from received waves, e.g. using passive transponders, or using passive reflectors
    • G01S13/751Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems using transponders powered from received waves, e.g. using passive transponders, or using passive reflectors wherein the responder or reflector radiates a coded signal
    • G01S13/753Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems using transponders powered from received waves, e.g. using passive transponders, or using passive reflectors wherein the responder or reflector radiates a coded signal using frequency selective elements, e.g. resonator
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/74Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
    • G01S13/75Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems using transponders powered from received waves, e.g. using passive transponders, or using passive reflectors
    • G01S13/751Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems using transponders powered from received waves, e.g. using passive transponders, or using passive reflectors wherein the responder or reflector radiates a coded signal
    • G01S13/755Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems using transponders powered from received waves, e.g. using passive transponders, or using passive reflectors wherein the responder or reflector radiates a coded signal using delay lines, e.g. acoustic delay lines
    • GPHYSICS
    • G06COMPUTING; CALCULATING; COUNTING
    • G06KRECOGNITION OF DATA; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K7/00Methods or arrangements for sensing record carriers, e.g. for reading patterns
    • G06K7/0008General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
    • GPHYSICS
    • G08SIGNALLING
    • G08BSIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00Burglar, theft or intruder alarms
    • G08B13/22Electrical actuation
    • G08B13/24Electrical actuation by interference with electromagnetic field distribution
    • G08B13/2402Electronic 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
    • G08B13/2428Tag details
    • G08B13/2431Tag circuit details
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01QANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00Details of, or arrangements associated with, antennas
    • H01Q1/36Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith
    • H01Q1/38Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith formed by a conductive layer on an insulating support

Abstract

An electronic surveillance system in which a passive label is attached to goods to be placed under surveillance and the label is interrogated by electromagnetic signals from a transmitter, the label acting to transmit a reply signal to a receiver which gives a characteristic response in the presence of a label, the transmitter being arranged to transmit signals, preferably two, at widely different frequencies and the label acts to mix these frequencies to produce a reply signal which is distinct from the original transmitted signal. The receiver is provided with a signal processing system which analyses and compares characteristics of the transmitted signal and the reply signal and produces different responses in the presence or absence of a label.

Description

343-100 MS AU 25 E- r v in; 3.101.111 s r D xsfi/ when states 1'2 x 3 w 3,707,711 l et 1, ew /me H Dec.26,1972

[54] ELECTRONIC SURVEILLANCE SYSTEM Primary Examiner.lohn W. Caldwell Assistant Examiner-Michael Slobasky 72 l t P te Herold C Stran a l 1 nvcn on i North g gj AltOTnEY-MCGICW and TOI'QU Vaughn, 6 Taylor Street, Maroubra, New South Wales, both of Australia [571 AESTRACT [22] Filed; April 2 1970 An electronic surveillance system in which a passive label is attached to goods to be placed under siirveil- 1 PP N04 25332 lance and the label is interrogated by electromagnetic I signals from a transmitter, the label acting to transmit 521 Us. c1. ..340/280, 340/258 c a p y signal to 8 which gives a characteristic [51] Int. Cl. ..G08b 21/00 p in the Prewm of a label, the transmitter {58] Field of Search...340/258 R, 258 C, 258 D, 280; being arranged to transmit signals, pr ly BI 343/65 R, 6.5 LC, 6.8; 325/8, 51 widely difierent frequencies and the label acts to mix these frequencies to produce a reply signal which is [56] References Cited distinct from the original transmitted signal. The receiver is provided with a signal processing system UNITED STATES PATENTS which analyses and compares characteristics of the 3,467,962 9/1969 Laplume ..325/8 transmitted Signal and the p y Signal and PmdwtS 3,500,373 3/1970 Minasy ..340,'280X different responses in the presence or absence of a 2,899,546 8/1959 Hollmzmn ..343/6.8 R label. 2,l93,l02 3ll940 Koch ..325/8 3.518.546 6/l970 Augenblick ..325/8 16 Claims, 6 Drawing Figures 7 A.G.C. -5 T l Moin 1' Transmitter ll I Label r--'- Receiver 4 Auxiliary Transmitter i 2 i Signal Analyser PATENTED w w I 3. 7 07 71 1 SHEET 1 OF 2 Receive 4 Main Transmitter i 2 l I I r Lobel I Auxlhury 1 Transmitter 3 F! G. l I

I Main V Transmitter Auxiliary Transmitter 2 Signal r Analyser 6 F|G.2

4 A J c F B .A L J F] (5 3 INVENTORS PETER HAROLD COLE RICHARD VAUGHN PATENTEU DEC 2 5 i972 SHEET 2 UF 2 Microwave Transmitter Auxiliary Transmitter FIGA Microwave Transmitter Auxiliary Transmitter FIG.

FIG.

Label Receiver Receiver IN VE/V T0195 1 ELECTRONIC SURVEILLANCE SYSTEM in certain electronic surveillance systems, for example those devoted to the control of merchandise in shops and warehouses by the extraction of information from prepared passive labels by electromagnetic interrogation.

The basic principle of operation of any interrogating system for passive labels, is as follows: Energy is some form is transmitted to the label by a transmitter and transmitting antenna unit. This energy is then processed in some way by the label, and the resulting energy retransmitted by the label as a reply signal. This reply" energy is then detected, suitably processed and information extracted therefrom by a sensitive receiver and receiving antenna unit. It is basic to all interrogation systems that'the very small reply energy from the label be distinguished from the very much larger transmitter or "interrogation" energy, and provision must be made in the design of the system to enable it to distinguish unwanted responses from the desired reply signals. These undesired responses are of two main kinds:

a. Unwanted responses from labels located outside the scanning area which are accidentally interrogated by the system,

b. Spurious responses from naturally occurring 'objects, located inside the scanning area, which produce signals capable of being confused with the desired label response.

Each of these two problems may be dealt with by the techniques discussed in general terms in turn below, and described in particular form later in this document. The general form of the surveillance system to which the invention relates is shown in FIG. 1. The principal components are a set (perhaps only one) of transmitting units 1, a coded label 2 located inside the scanning area 3, and a set (perhaps only one) of receiver units 4, which detect and process the output signals from the label. The receiver units 4 also contain whatever signal processing systems are needed to distinguish between genuine reply signals and undesired signals. Certain direct interconnections (shown as a solid line in FIG. 1) between the transmitter and receiver units may be necessary to enable the receiver to perform this function.

The elimination of the first class of undesired responses described above involves the restriction of the area scanned by the transmitter receiver system to the required region There are four basic principles on which this restriction may be based, any number of which can be used in combination.

1. Use of high frequency radiation for some of the information carrying signals (of which there may be one or several) so that directionally sensitive transmitting and receiving antennas of reasonable proportions became possible. 1

2. Employ time gating in the receiver adjusted in such a way that the time width and time position of the receiver gate determine, in conjunction with the propogation velocity of the signals being used, a spatial location an extension of the area being scanned.

3. Select at least one of the signal frequencies to be sufiiciently low that the scanning area lies in the near field of the transmitter and receiver antennas. The discrimination against distant spurious responses is enhanced by the rapid decay with distance which the near fields possess as compared with propogating fields.

4. Select at least one of the signal frequencies so that the natural attenuation of the propogating medium (generally air)at that frequency contribuites to the discrimination against distant responses. If signals are propogated by electromagnetic means, one such suitable frequency occurs at the oxygen molecular resonance absorption band at about 60 Gi-lz.

An important difference between the last two methods and between those methods which employ the natural decrease with distance of propagating fields lies in the mathematical form of the attenuation loss encountered. in the propagating case the fields undergo a l/r decrease with distance, in the near field case a l/r or higher power law may be achieved depending upon complexity of the antenna system, and when attenuation in the propogating medium is made use of, the fields decay exponentially with distance. This last effect will always predominate at sufficiently large distances.

In extreme situations when a large degree of discrimination is required, the shortcomings of one system may be overcome by using several of these principles in conjunction as their characteristics are in a sense complementary. For example a highly directive microwave antenna pattern may be disturbed by reflections from objects or persons moving through the scanning area, but a low frequency signal for which the scanning area is in the near field region is not so disturbed.

For the discrimination against spurious responses produced by naturally occurring objects sited within the scanning area, the general approach is to use a combination of propogation means to the label, physical processes within the label, and subsequent signal analysis techniques which are unlikely to be duplicated in nature. A general discussion of the various means and combinations is included immediately below.

The sensing signals may be carried between the transmitter and the label, and from there back to the receiver by any combination of the following means.

a. Electromagnetic radiation at wave lengths comparable with or less than the dimensions of the scanning region, which therefore produce both electric and magnetic radio frequency fields in that region.

b. Electromagnetic radiation at much longer wave lengths designed to produce magnetic fields with negligible electric field in the scanning region.

0. Electromagnetic radiation at long wave lengths arranged to produce electric fields with negligible magnetic fields in the scanning region.

The sensing signals, once they have been received by the label, may be processed in several ways by making use of the following physical processes.

a. Frequency selective transmission of energy in its various forms by the use of resonant systems.

b. Harmonic and subharmonic frequency generation.

c. Generation of new frequencies by mixing techniques.

d. Creation of unusual and possibly anharmonic frequency or part time patterns in the response produced by the label.

The signals which reach the receiver can be analyzed in various ways. Two techniques which are important in this connection are: t

1060;: Your g s a. Synchronous detection keyed, both in carrier phase and modulation envelope phase to the several kinds of signal transmitted.

b. Use of automatic gain control derived from signals in some of the receiver channels to control the gain of others, in such a way as to compensate for variations in the transmission losses between the labels and the transmitter and receiver antennas. Both these techniques are used in the particular embodiment of the present invention described below.

An electronic surveillance system having means to transmit electromagnetic signals, a passive label for attachment to an article to be placed under surveillance, the label having means to receive a signal from said transmitting means and transmit a reply signal and a receiver to receive and process said reply signal, the system being characterized in that the transmitting means is constructed and arranged to transmit signals simultaneously at widely spaced frequencies, the label has means to receive signals at said frequencies, means to mix the frequencies and means to transmit a reply signal produced by mixing those frequencies which is distinct from the original transmitted signal and the receiver having a signal processing system responsive both tothe original transmitted signal and the reply signal and mean to analyze characteristics of the reply signal by reference to characteristics of the transmitted signal to produce different responses in the presence or absence of a label.

The invention further consists in a label for use in a system as defined above.

in order that the invention may be better understood and put into practice preferred forms thereof are hereinafter described, by way of example with reference to the accompanying drawings in which:

FIG. 1 is a block diagram showing the main elements constituting an electronic surveillance system of the kind with which the present invention is concerned,

PK). 2 is a block diagram illustrating a first system according to the invention,

P16. 3 illustrates the constructional features of a label for use in the system,

FIG. 4 is a block diagram illustrating a second system,

FIG. 5 is a block diagram illustrating a third system and a FIG. 6 illustrates the constructional features of a label for use in the third system.

The general form of a first surveillance system according to the present invention with a high degree of rejection of unwanted responses from prepared labels located outside the scanning area, and from spurious signals produced within the scanning area by means other than the labels, is shown in FIG. 2.

The principle components comprise:

1. Main transmitter and antenna system operating at a carrier frequency of 9 l SMHz, a peak power output of 10 watts, a pulse length of lO/p sec and a pulse repetition rate of 5 ,000 pulses per second.

2. An auxiliary transmitter and magnetic coil antenas system operating at a carrier frequency of 100 KHz, a pulse length of l in sec, and a pulse repetition rate of 93 per second. A

3. A prepared label which contains the following elements A. A strip line microwave antenna which is capable of operating at frequencies of 9 l5 and 1,830 MHz.

8. A microwave semi-conductor diode capable of frequency doubling and frequency mixing.

C. A magnetic loop antenna operating at KHZ which receives energy from the auxiliary transmitter and couples this to the diode.

These elements and the details of their interconnections are shown in FIG. 3. The two sections of the antenna A are separated by a thin di-electric film in the region where they overlap. The resulting capacitance provides isolation at the 100 KHz frequency and an rf bypass at the 915 MHZ frequency.

4. A receiver system tuned to 1,830 MHz with a 300/u pass band, and a high level of rejection of both the 915 MHz and 100 KHz carrier frequencies.

5. An AGC system which controls the receiver gain. This system accepts signals from the receiver and from the two transmitters and acts only on the signals received while the main transmitter is on and the auxiliary transmitter is off. The function of the AGC system is to bring the 1,830 MHz received signal to a standard level, in order to compensate by changes of receiver gain for variations in the propagation path losses between the transmitter, the label, and the receiver.

6. A signal analyzer system. This unit processes the output of the receiver, and has the task of distinguishing genuine from spurious responses. The signal analyzer processes only those signals which are produced by the receiver while the auxiliary transmitter pulse is on. During these periods, the output from a label will contain the normal 1,830 Ml-lz second harmonic signal, as well as the 1,830 i 0.1. MHz sidebands of this signal in a substantial proportion. The signal analyzer examines the receiver output and passes as genuine those responses which contain the sidebands in sufficient proportion.

Because the system employs a 100 KHz signal in the near field region, it discriminates well against responses from coded labels located outside the scanning region.

it is unlikely that naturally occurring objects in the scanning area, such as non-linear magnetic materials, will possess in sufficient degree all the characteristics needed to produce by accident an acceptable response. The essential characteristics are:

a. Coupling to electromagnetic fields at 915 and 1,830 MHz b. Coupling to magnetic fields at 100 KHz.

e. Harmonic generation and frequency mixing at microwave frequencies.

The system may be varied by constructing the receiver to detect simply the 100 kc/s sidebands on reradiated 915 Mc/s carrier. Such a system would avoid the added losses associated with frequency doubling in the label to 1,830 Mc/s. On the other hand it would have the disadvantages of combining fewer processes unlikely to be duplicated in nature in the label also receiver design would have to reject the unmodulated 915 Mc/s carrier either direct or reradiated; such a system is described in more detail below.

Potential problems arising from variations in transmission path losses at the microwave frequencies are avoided by the use of an AGC system. There are no significant variations in the propogation path loss at 100 Kill which can be introduced by the interpolation of common body, clothing, or packaging materials.

The general arrangement of the second form of the invention is shown in block diagram form in FIG. 4. The principal components are:

1. A microwave transmitter and antenna system operating at a frequency of 915 MHz, a peak power level of l0 watts, a pulse length of l0/p. sec and a pulse repetition frequency of 1 MHz.

2. An auxiliary transmitter and magnetic coil antenna system 16 operating at a frequency of lOOKHz with a power level of 10 watts delivered to the internal losses of the coil.

3. The coded label 17 which is the same label as used for the first form of the invention, and is shown in FIG. 3. 3 X 10 4. A receiver system 18 which is tuned to receive the 915.1 Mldz sideband generated by frequency mixing between the two transmitted signals, and which employs high selectivity to reject the 915 MHz carrier. The receiver can employ the technique of synchronous detection to advantage to achieve ahigh sensitivity and a law noise bandwidth. The direct connections shown in FIG. 4 from the two transmitter units to the receiver carry the phase information which makes this possible.

The signal processing in the receiver consists in part of ensuring that sufficient side band energy exists in a suitably narrow band width centered on the sum of the two transmitter frequencies before a response is considered genuine Further signal processing which is designed to diseniminate against responses from labels located outside the scanning area is implemented in the receiver by incorporation of a time gate, adjusted in time position in relation to the microwave transmitter gate, so as to define in conjunction with the velocity of propogation of electromagnetic signals (3Xl0rneter sec a definite spatial volume from which the responses will be accepted by the receiver.

The general arrangement of the third form of the invention is shown in block diagram form in FIG. 5. The principle components comprise:

l. A microwave transmitter and antenna system 19 operating at a carrier frequency of 915 MHz, a peak power output of 10 watts, a pulse length of 250; sec and a pulse repetition frequency of 400 KHz.

2. An auxiliary transmitter and magnetic coil antenna system 20 operating at a CW frequency of 100KB: with a power of 10 watts, delivered to the internal losses in the coil.

3. A prepared label 21, shown in more detail in FIG. 6 containing the following elements:

a. A single turn magnetic dipole antenna 24 which receives the microwave pulses from the transmitter.

b. A surface accoustic wave delay line 25 which produces after a time of approximately SOD/p. sec an electroaccoustic echo, of each transmitter pulse, which is reradiated by the microwave antenna.

c. A modulation diode 26 connected in parallel with the delay line, which can amplitude modulate at a frequency of 100 KHz the return signal from the delay line. A

d. A multitum magnetic antenna 27, designed to receive the 100 KHz signal but whose inductame is sufficiently large that it produces a negligible admittance across the delay line at the microwave frequencies. 4. A time gated receiver and signal processor system 5 22 which receives the modulated echo from the label 21 as well as reference signals directly from the two transmitters. The time position of the receiver gate is set in relation to the transmitted pulse envelope so that the receiver responds only to the electroaccoustic echo signal, and has a high degree of disenimination against the transmitted signal, part of which will unavoidably be present in the receiver antenna. A high degree of isolation in the receiver gate is required.

The significant signals received by the receiver system 2 consist of:

l. Pulses of 915 MHz energy retarded by the SOD/p.

sec time delay provided by the surface wave delay line. 2. Pulses of 9l5.l MHz and 914.9 MHz energy, resulting by the modulation provided by diode 26, which however, are delayed by the same 500/p. sec as are the carrier echo pulses in l above.

The essential signal processing functions performed by the receiver consist of measuring the absolute and relative proportions of the return signals described above. Responses for which the relative magnitudes of all signals fall simultaneously within their respective preassigned acceptance levels are regarded as genuine.

All three forms described above of the invention involve the use of two widely separated frequencies in the transmitted signal, which combined with the use of signal analysis technique in the receiver, provides both improved definition of the scanning area (over the prior art), and also detailed identification of the characteristics of the non-linear elements in the coded label as a means of distinguishing between genuine and spurious responses from objects located within the scanning area.

Particulars of the actual circuits used in the various parts of these systems are not given in the interests of brevity and clarity as the design of the circuitry involved in conventional and obvious to those skilled in the art.

We claim:

1. An electronic surveillance system, comprising electronic interrogating means for transmitting interrogating signals, passive means attachable to an article under surveillance for sensing the interrogating signals and retransmitting reply signals, receiver means for responding to the reply signals, said interrogating means including zone defining means for establishing a surveillance zone outside of which said passive means and said receiver means are together substantially unresponsive to the interrogating signals, said zone defining means including first transmitter means for transmitting a first portion of the interrogating signals at a first frequency at which the first portion of the signals decays rapidly, said interrogating means including second transmitter means for transmitting a second portion of the interrogating signals at a second frequency substantially higher than the first frequency, said passive means including signal mixing means for forming a reply signal so that the reply signal includes beat frequency components, said passive means being sufficiently small to be attachable to an article under surveillance and to form a label on the article, said passive means including an antenna, said secondfrequency being sufficiently high to be coupled to said antenna and to allow coupling of said antenna to said receiver means, said receiver means including discriminator means for responding substantially only to a beat frequency component.

2. A system as in ciairn 1, wherein said receiver means is tuned to frequencies including a beat frequency and at least one of the fundamental and harmonics of the second frequency.

3. A system as in claim 1, wherein said second frequency exceeds said first frequency by at least two orders of magnitude.

4. A system as in claim 2, wherein said second frequency exceeds said first frequency by at least two orders of magnitude.

5. A system as in claim I, wherein said receiver means is tuned over a passhand including a beat frequency and one of the fundamentals and harmonics of said second frequency.

6. A s stem as in claim 1, wherein the second frequency exceeds the first frequency by at least three orders of magnitude.

7. A system as in claim 1, wherein the second frequency is of the order of 1,000 MB: and the first frequency is of the order of 0.1 MHz.

8. A system as in claim 1, wherein said passive means inciudes harmonic generating means for producing a second harmonic of the second frequency and a beat frequency of said second harmonic and said first frequency.

9. A system as in claim 8, wherein the second frequency exceeds the first frequency by at least three orders of magnitude.

10. A system as in claim 1, wherein said discrimination means produces a response only when a beat frequency has a predetermined strength in relation to the strength of said second frequency.

11. A system as in claim 10, wherein the higher frequency is of the order of 1,000 MHz and the lower frequency is of the order of 0.l MHz.

12. A system as in claim 1, wherein one of said transmitter means transmits the signals in the form of pulses, and wherein said receiver means includes a synchronized detector. and connecting means connecting said one of transmitter means to carry phase information from said one of said transmitter means to said synchronous detector.

13 A system as in claim 11, wherein said passive means includes time delay means.

14. A system as in claim 1, wherein said passive means includes a first antenna responsive to signals of the first frequency, a second antenna responsive to signals of the second frequency, said second antenna having a first part and a second part, a capacitance coupling said first part to said second part and pro iding isolation of the first frequency and a bypass at the second frequency, and a non-linear circuit element connected between the two parts of said second anten- 15. A system as in claim 1, wherein said passive means includes a'first antenna responsive to signals at said first frequency, a second antenna responsive to signals at the second frequency, a surface accoustic dela l ige connected to said first antenna and arranged to gr uce an electroaccoustic echo of a signal

Claims (15)

1. An electronic surveillance system, comprising electronic interrogating means for transmitting interrogating signals, passive means attachable to an article under surveillance for sensing the interrogating signals and retransmitting reply signals, receiver means for responding to the reply signals, said interrogating means including zone defining means for establishing a surveillance zone outside of which said passive means and said receiver means are together substantially unresponsive to the interrogating signals, said zone defining means including first transmitter means for transmitting a first portion of the interrogating signals at a first frequency at which the first portion of the signals decays rapidly, said interrogating means including second transmitter means for transmitting a second portion of the interrogating signals at a second frequency substantially higher than the first frequency, said passive means including signal mixing means for forming a reply signal so that the reply signal includes beat frequency components, said passive means being sufficiently small to be attachable to an article under surveillance and to form a label on the article, said passive means including an antenna, said second frequency being sufficiently high to be coupled to said antenna and to allow coupling of said antenna to said receiver means, said receiver means including discriminator means for responding substantially only to a beat frequency component.
2. A system as in claim 1, wherein said receiver means is tuned to frequencies including a beat frequency and at least one of the fundamental and harmonics of the second frequency.
3. A system as in claim 1, wherein said second frequency exceeds said first frequency by at least two orders of magnitude.
4. A system as in claim 2, wherein said second frequency exceeds said first frequency by at least two orders of magnitude.
5. A system as in claim 1, wherein said receiver means is tuned over a passband including a beat frequency and one of the fundamentals and harmonics of said second frequency.
6. A system as in claim 1, wherein the second frequency exceeds the first frequency by at least three orders of magnitude.
7. A system as in claim 1, wherein the second frequency is of the order of 1,000 MHz and the first frequency is of the order of 0.1 MHz.
8. A system as in claim 1, wherein said passive means includes harmonic generating means for producing a second harmonic of the second frequency and a beat frequency of said second harmonic and said first frequency.
9. A system as in claim 8, wherein the second frequency exceeds the first frequency by at least three orders of magnitude.
10. A system as in claim 1, wherein said discrimination means produces a response only when a beat frequency has a predetermined strength in relation to the strength of said second frequency.
11. A system as in claim 10, wherein the higher frequency is of the order of 1,000 MHz and the lower frequency is of the order of 0.1 MHz.
12. A system as in claim 1, wherein one of said transmitter means transmits the signals in the form of pulses, and wherein said receiver means includes a synchronized detector, and connecting means connecting said one of transmitter means to carry phase information from said one of said transmitter means to said synchronous detector. 13 A system as in claim 11, wherein said passive means includes time delay means.
14. A system as in claim 1, wherein said passive means includes a first antenna responsive to signals of the first frequency, a second antenna responsive to signals of the second frequency, said second antenna having a first part and a second part, a capacitance coupling said first part to said second part and providing isolation of the first frequency and a bypass at the second frequency, and a non-linear circuit element connected between the two parts Of said second antenna.
15. A system as in claim 1, wherein said passive means includes a first antenna responsive to signals at said first frequency, a second antenna responsive to signals at the second frequency, a surface accoustic delay line connected to said first antenna and arranged to produce an electroaccoustic echo of a signal received by said second antenna after a predetermined delay, and a non-linear circuit element connected in parallel with said delay line and connected to said first antenna.
16. A system as in claim 15 wherein said non-linear circuit element includes a semiconductor diode.
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Cited By (56)

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Publication number Priority date Publication date Assignee Title
US3816708A (en) * 1973-05-25 1974-06-11 Proximity Devices Electronic recognition and identification system
US3842246A (en) * 1973-09-27 1974-10-15 Proximity Devices Recognition and identification system with noise rejection capabilities
US3859652A (en) * 1972-06-26 1975-01-07 North American Systems Corp Method and apparatus for detecting the theft of articles
US3895368A (en) * 1972-08-09 1975-07-15 Sensormatic Electronics Corp Surveillance system and method utilizing both electrostatic and electromagnetic fields
DE2612996A1 (en) * 1975-03-27 1976-10-07 Stiftelsen Inst Mikrovags Means for register of objects
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US4118693A (en) * 1977-05-09 1978-10-03 Knogo Corporation Method and apparatus for producing uniform electromagnetic fields in an article detection system
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EP0002595A1 (en) * 1977-12-09 1979-06-27 Lintech Instruments Limited Transponders
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US4308530A (en) * 1977-07-19 1981-12-29 N.V. Nederlandsche Apparatenfabriek Nedap Detection system forming wide gates with superior spatial selectivity
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EP0066403A1 (en) * 1981-05-19 1982-12-08 Automated Security (Holdings) PLC Batteryless, portable, frequency divider
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EP0451059A1 (en) * 1990-04-06 1991-10-09 Valeo Securite Habitacle Circuit for transmission of radioelectric high-frequency radiation, especially for a portable electronic device included in a remote control system for motor vehicles
US5099227A (en) * 1989-07-18 1992-03-24 Indala Corporation Proximity detecting apparatus
US5115160A (en) * 1989-08-28 1992-05-19 Gte Products Easily encodable surface acoustic wave (SAW) security devices
US5241923A (en) * 1992-07-23 1993-09-07 Pole/Zero Corporation Transponder control of animal whereabouts
EP0583084A1 (en) * 1992-07-20 1994-02-16 Mitsubishi Denki Kabushiki Kaisha Non-contact IC card, non-contact IC card reader/writer and data transmission method
US5386214A (en) * 1989-02-14 1995-01-31 Fujitsu Limited Electronic circuit device
US5465099A (en) * 1991-09-25 1995-11-07 Nippon Information Industry Corporation Detectable device and movable item detecting system
US5570082A (en) * 1995-10-13 1996-10-29 Mahgerefteh; Nasser Remote wetness sensor for diapers
US5838253A (en) * 1995-05-17 1998-11-17 Accu-Sort Systems, Inc. Radio frequency identification label
US5970393A (en) * 1997-02-25 1999-10-19 Polytechnic University Integrated micro-strip antenna apparatus and a system utilizing the same for wireless communications for sensing and actuation purposes
US6064308A (en) * 1996-10-25 2000-05-16 Pole/Zero Corporation RF signaling system and system for controlling the whereabouts of animals using same
US6150921A (en) * 1996-10-17 2000-11-21 Pinpoint Corporation Article tracking system
US6166643A (en) * 1997-10-23 2000-12-26 Janning; Joseph J. Method and apparatus for controlling the whereabouts of an animal
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
US20030076263A1 (en) * 2001-10-24 2003-04-24 Datamars Sa Identifying assembly comprising an interrogator and a transponder
US6667092B1 (en) 2002-09-26 2003-12-23 International Paper Company RFID enabled corrugated structures
US6700544B2 (en) 2002-02-05 2004-03-02 Theodore R. Anderson Near-field plasma reader
US20040102870A1 (en) * 2002-11-26 2004-05-27 Andersen Scott Paul RFID enabled paper rolls and system and method for tracking inventory
US6812824B1 (en) 1996-10-17 2004-11-02 Rf Technologies, Inc. Method and apparatus combining a tracking system and a wireless communication system
US20040227682A1 (en) * 2002-02-05 2004-11-18 Anderson Theodore R. Reconfigurable scanner and RFID system using the scanner
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BE1015990A3 (en) 2004-04-21 2006-01-10 Bf Engineering APPARATUS FOR MONITORING bed-ridden persons.
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US20060058913A1 (en) * 2002-11-26 2006-03-16 Andersen Scott P Inventory tracking
US20060097874A1 (en) * 2004-11-08 2006-05-11 Checkpoint Systems, Inc. System and method for detecting EAS/RFID tags using step listen
US20070187496A1 (en) * 2006-02-10 2007-08-16 Andersen Scott P Inventory tracking system and method
USRE43699E1 (en) 2002-02-05 2012-10-02 Theodore R. Anderson Reconfigurable scanner and RFID system using the scanner

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Cited By (74)

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US3859652A (en) * 1972-06-26 1975-01-07 North American Systems Corp Method and apparatus for detecting the theft of articles
US3895368A (en) * 1972-08-09 1975-07-15 Sensormatic Electronics Corp Surveillance system and method utilizing both electrostatic and electromagnetic fields
US3816708A (en) * 1973-05-25 1974-06-11 Proximity Devices Electronic recognition and identification system
US3842246A (en) * 1973-09-27 1974-10-15 Proximity Devices Recognition and identification system with noise rejection capabilities
US3990065A (en) * 1975-02-20 1976-11-02 The Magnavox Company Theft detection system
DE2612996A1 (en) * 1975-03-27 1976-10-07 Stiftelsen Inst Mikrovags Means for register of objects
US4087802A (en) * 1976-05-24 1978-05-02 Williamson Robert D Method and apparatus for electronic surveillance of precisely defined control zone
US4212002A (en) * 1976-05-24 1980-07-08 Williamson Robert D Method and apparatus for selective electronic surveillance
US4206453A (en) * 1976-05-24 1980-06-03 Williamson Robert D Method and apparatus for electronic surveillance
US4118693A (en) * 1977-05-09 1978-10-03 Knogo Corporation Method and apparatus for producing uniform electromagnetic fields in an article detection system
US4308530A (en) * 1977-07-19 1981-12-29 N.V. Nederlandsche Apparatenfabriek Nedap Detection system forming wide gates with superior spatial selectivity
US4139844A (en) * 1977-10-07 1979-02-13 Sensormatic Electronics Corporation Surveillance method and system with electromagnetic carrier and plural range limiting signals
FR2405528A1 (en) * 1977-10-07 1979-05-04 Sensormatic Electronics Corp Method and space limit monitoring device
EP0002595A1 (en) * 1977-12-09 1979-06-27 Lintech Instruments Limited Transponders
FR2416514A1 (en) * 1978-02-03 1979-08-31 Williamson Robert Electronic surveillance of precisely defined control zone - using HF generator projecting wave to establish first field and FM generator for second field
EP0020062A1 (en) * 1979-05-18 1980-12-10 Parmeko Limited Method and surveillance system for detecting the presence of an e.m. wave receptor reradiator
US4249167A (en) * 1979-06-05 1981-02-03 Magnavox Government And Industrial Electronics Company Apparatus and method for theft detection system having different frequencies
US4319248A (en) * 1980-01-14 1982-03-09 American Electronic Laboratories, Inc. Integrated spiral antenna-detector device
US4274090A (en) * 1980-02-19 1981-06-16 Knogo Corporation Detection of articles in adjacent passageways
EP0035660A2 (en) * 1980-02-19 1981-09-16 Knogo Corporation Detection of articles in adjacent passageways
EP0035660A3 (en) * 1980-02-19 1981-09-23 Knogo Corporation Detection of articles in adjacent passageways
US4320402A (en) * 1980-07-07 1982-03-16 General Dynamics Corp./Electronics Division Multiple ring microstrip antenna
US4471344A (en) * 1980-10-09 1984-09-11 Ici Americas Inc. Dual frequency anti-theft system
WO1982001437A1 (en) * 1980-10-09 1982-04-29 Deterrent Tech Corp Dual frequency anti-theft system
EP0066403A1 (en) * 1981-05-19 1982-12-08 Automated Security (Holdings) PLC Batteryless, portable, frequency divider
US4475108A (en) * 1982-08-04 1984-10-02 Allied Corporation Electronically tunable microstrip antenna
US4862160A (en) * 1983-12-29 1989-08-29 Revlon, Inc. Item identification tag for rapid inventory data acquisition system
FR2557714A1 (en) * 1983-12-29 1985-07-05 Revlon Method and device identification stored articles, and labels for identifying articles, allowing automatic maintenance of inventories
DE3447599A1 (en) * 1983-12-29 1985-09-12 Revlon Method and apparatus for inventory data acquisition
US4673932A (en) * 1983-12-29 1987-06-16 Revlon, Inc. Rapid inventory data acquistion system
US4704602A (en) * 1984-02-15 1987-11-03 Intermodulation And Safety System Ab Method and system for detecting an indicating device
US4798175A (en) * 1986-10-09 1989-01-17 Alfa-Laval Agri, Inc. Electronic identification system
WO1988005546A1 (en) * 1987-01-19 1988-07-28 Midi Robots Societe Anonyme Identification and/or localization system and beacon
US4855583A (en) * 1987-08-17 1989-08-08 Figgie International, Inc. Structure and method of making combination proximity/insertion identification cards
US5386214A (en) * 1989-02-14 1995-01-31 Fujitsu Limited Electronic circuit device
US5099227A (en) * 1989-07-18 1992-03-24 Indala Corporation Proximity detecting apparatus
US5115160A (en) * 1989-08-28 1992-05-19 Gte Products Easily encodable surface acoustic wave (SAW) security devices
FR2660779A1 (en) * 1990-04-06 1991-10-11 Neiman Sa The transmission circuit of a radio radiation at high frequency, in particular for a portable electronic device included in an interactive remote control system for a motor vehicle.
EP0451059A1 (en) * 1990-04-06 1991-10-09 Valeo Securite Habitacle Circuit for transmission of radioelectric high-frequency radiation, especially for a portable electronic device included in a remote control system for motor vehicles
US5465099A (en) * 1991-09-25 1995-11-07 Nippon Information Industry Corporation Detectable device and movable item detecting system
EP0583084A1 (en) * 1992-07-20 1994-02-16 Mitsubishi Denki Kabushiki Kaisha Non-contact IC card, non-contact IC card reader/writer and data transmission method
US5619529A (en) * 1992-07-20 1997-04-08 Mitsubishi Denki Kabushiki Kaisha Non-contact IC card and non-contact IC card reader/writer
US5241923A (en) * 1992-07-23 1993-09-07 Pole/Zero Corporation Transponder control of animal whereabouts
US5838253A (en) * 1995-05-17 1998-11-17 Accu-Sort Systems, Inc. Radio frequency identification label
US5570082A (en) * 1995-10-13 1996-10-29 Mahgerefteh; Nasser Remote wetness sensor for diapers
US6483427B1 (en) 1996-10-17 2002-11-19 Rf Technologies, Inc. Article tracking system
US6812824B1 (en) 1996-10-17 2004-11-02 Rf Technologies, Inc. Method and apparatus combining a tracking system and a wireless communication system
US6150921A (en) * 1996-10-17 2000-11-21 Pinpoint Corporation Article tracking system
US6064308A (en) * 1996-10-25 2000-05-16 Pole/Zero Corporation RF signaling system and system for controlling the whereabouts of animals using same
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
US5970393A (en) * 1997-02-25 1999-10-19 Polytechnic University Integrated micro-strip antenna apparatus and a system utilizing the same for wireless communications for sensing and actuation purposes
US7058362B1 (en) * 1997-02-25 2006-06-06 Polytechnic University Integrated micro-strip antenna apparatus and a system utilizing the same for wireless communications for sensing and actuation purposes
US6166643A (en) * 1997-10-23 2000-12-26 Janning; Joseph J. Method and apparatus for controlling the whereabouts of an animal
US20030076263A1 (en) * 2001-10-24 2003-04-24 Datamars Sa Identifying assembly comprising an interrogator and a transponder
US6700544B2 (en) 2002-02-05 2004-03-02 Theodore R. Anderson Near-field plasma reader
US20040227682A1 (en) * 2002-02-05 2004-11-18 Anderson Theodore R. Reconfigurable scanner and RFID system using the scanner
US6922173B2 (en) 2002-02-05 2005-07-26 Theodore R. Anderson Reconfigurable scanner and RFID system using the scanner
USRE43699E1 (en) 2002-02-05 2012-10-02 Theodore R. Anderson Reconfigurable scanner and RFID system using the scanner
US6667092B1 (en) 2002-09-26 2003-12-23 International Paper Company RFID enabled corrugated structures
US20040102870A1 (en) * 2002-11-26 2004-05-27 Andersen Scott Paul RFID enabled paper rolls and system and method for tracking inventory
US8295974B2 (en) 2002-11-26 2012-10-23 Rush Tracking Systems, Llc System and method for tracking inventory
US20060036346A1 (en) * 2002-11-26 2006-02-16 Andersen Scott P System and method for tracking inventory
US20060058913A1 (en) * 2002-11-26 2006-03-16 Andersen Scott P Inventory tracking
US20110015780A1 (en) * 2002-11-26 2011-01-20 Scott Paul Andersen System And Method For Tracking Inventory
US7818088B2 (en) 2002-11-26 2010-10-19 Rush Tracking Systems, Llc System and method for tracking inventory
US8774960B2 (en) 2002-11-26 2014-07-08 Totaltrax, Inc. System and method for tracking inventory
US7151979B2 (en) 2002-11-26 2006-12-19 International Paper Company System and method for tracking inventory
BE1015990A3 (en) 2004-04-21 2006-01-10 Bf Engineering APPARATUS FOR MONITORING bed-ridden persons.
US8154388B2 (en) * 2004-06-16 2012-04-10 Gemalto Sa Synchronous-phase contactless demodulation method, and associated demodulator and reader
US20050280510A1 (en) * 2004-06-16 2005-12-22 Gemplus Synchronous-phase contactless demodulation method, and associated demodulator and reader
US7148804B2 (en) * 2004-11-08 2006-12-12 Checkpoint Systems, Inc. System and method for detecting EAS/RFID tags using step listen
US20060097874A1 (en) * 2004-11-08 2006-05-11 Checkpoint Systems, Inc. System and method for detecting EAS/RFID tags using step listen
US20060220872A1 (en) * 2005-03-01 2006-10-05 Brown Mark A Mounting bracket
US20070187496A1 (en) * 2006-02-10 2007-08-16 Andersen Scott P Inventory tracking system and method

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