DE2263905B2 - DEVICE FOR DETERMINING UNAUTHORIZED REMOVAL OF OBJECTS FROM A PROTECTED OR MONITORED AREA - Google Patents

Description

i £ 569 1

deten deactivation system,

15 shows a schematic representation of an embodiment the invention using a single resonance antenna system,

Fig. 16 is a schematic representation in which a non-resonant single antenna system is used an embodiment,

17 shows a schematic representation of an embodiment the invention, in which antennas closely spaced apart are used,

F i g. 18 is a block diagram of an alternative embodiment of an interference level rejection circuit shown in FIG is shown, and

19 is a schematic representation of signals for explaining the operation of the 15 shown in FIG th circuit.

A device according to the invention is shown in the form of a block diagram in FIG. 1 and includes a transmitter 10 connected to an antenna 12 which generates an electromagnetic field within a predetermined space that is to be monitored. A receiving antenna 14 is arranged in the monitored space and receives energy that is radiated from the transmitter antenna 12, and this energy is fed to the input of an RF device which has an RF bandpass filter 16 and an RF amplifier 18. The output of amplifier 18 is fed to a detector 20 and the output of that detector is fed to a low pass filter 22 which removes the carrier frequency components and high frequency noise. The output of the filter 22 is fed to a high-pass filter 24 which only allows the higher frequency segment of the signal spectrum to pass. The high-pass filter is preferably a sharp-cut filter, such as a multipole Chebyshev filter. The output signals of the filter 24 are amplified by an amplifier 26 and then fed to a jamming signal blocking circuit 28 which is operative to generate an output signal according to the received signal of the correct amplitude, pulse duration. To maintain pulse spacing, polarity and pulse sequence, so that output pulses are only generated for real useful signals that are generated by a resonance tag in the surveillance zone . The pulses generated by the jamming signal blocking circuit 28 are applied to a second jamming signal blocking circuit 30 which is responsive to the received signals at a predetermined pulse train rate at the modulation frequency to produce output signals to actuate an alarm 32 or other output device.

The transmitter 10 is shown in detail in Figure 2 and includes an oscillator 34 which supplies a modulation signal to a voltage controlled oscillator 36, which in turn drives an amplifier 38, which the transmitting antenna input 12 of the oscillator 34 generates a regularly again hold waveform with a predetermined frequency, which typically has the value of 1 kHz.The voltage-controlled oscillator 36 generates a carrier signal which changes in frequency under the influence of the modulation signal from oscillator 34. As a typical example, the carrier frequency can have a center frequency of 5 MHz, which is only 15% Frequency deviation is changed at a rate of IkHz. The modulation signal generated by the oscillator 34 is usually a sinusoidal changing wave. However, it can also be a repetitive weave , for example a ramp wave, such as a triangular wave or a sawtooth wave, or an exponential signal. The amplifier 38 preferably supplies the transmitting antenna 12 with a current, the strength of which changes inversely proportional to the frequency.

In the absence of a resonance circuit in the monitored space, that generated by the antenna 12 is generated electromagnetic field picked up by the receiver antenna 14, but no output display generated by the receiving system and there is no pulse to trigger the alarm. When a Resonance circle pendant is located in the monitored room, this pendant speaks at most to that transmitted signal every time the transmitted frequency changes through the Resonant frequency of the trailer passes through it, causing a palpable change in electrical characteristics is generated at the receiver antenna, thereby determining the presence of a trailer will. However, spurious signals are present under numerous operating conditions, leading to undesired Signals can rise that could be processed to trigger a false alarm. Through the Invention, the possibility of triggering alarms is essentially switched off, namely at other than real resonance trailer signals.

A resonance circuit with multiple resonance points is provided on a card or on a tag that can be attached to merchandise and the like. Such a circle is shown in FIG. 3 shown. The circuit is fabricated by printed circuit or etched circuit technology and has a first conductive path 40, generally rectangular in shape, on one surface of a substrate 42 of insulating material, and this line terminates at one end in a conductive surface 44 spaced near an edge of the beam 42. The other end of the line 40 terminates in a conductive surface 46 which is disposed in the vicinity of a corner of the carrier 42. A second line 48 is designed as a rectangular spiral on the carrier 42 and has a connection point 50 with the conductive surface 44 at the outer end. At the inner end of this second line is a conductive surface 52, in the center of the spiral.

The opposite surface of the carrier 42 is shown in FIG. 4, and has a conductive surface 54 that coincides with the conductive surface 52 on the surface shown in FIG. 3 is aligned and is generally of the same dimensions. Two conductive surfaces 56 and 58 are provided which are aligned with surfaces 44 and 46 on the other surface of the carrier and are generally of the same dimensions. The conductive surfaces 54 and 56 are connected to one another by means of a line 60 , while the conductive surfaces 56 and 58 are connected to one another by a line 62. As will be described later, the line 62 is dimensioned such that it melts when excited by a predetermined electromagnetic field in order to change the resonance properties of the trailer circuit. An electrical connection 63 is made between surfaces 46 and 58 by a conductive pin or the like extending through support 42

The lines 40 and 48 serve as inductances of the Resonance circuit, these lines raid are in the same Meaning coiled to make a positive between them

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Generate coupling coefficients. The conductive surfaces 52 and 54 are separated from one another by the intermediate carrier 42 and serve as a first capacitor, while a second capacitor is formed by the conductive surface 44 which cooperates with the surface 56 on the opposite carrier surface. The equivalent circuit diagram of the carrier is shown schematically in FIG. 5, and this circuit has two resonance frequencies. One is used to determine the presence of a trailer and the other is used to change or destroy the trailer response at the monitoring frequency. Induction L 1 is outer loop 40 while induction L 2 is inner loop 48. The capacitor C2 is formed by the conductive surfaces 52 and 54, while the capacitor C 1 is formed by the conductive surfaces 44 and 56.

The two series-connected conductor loops, which form the inductances L 1 and L 2 and the capacitor C2 , are tuned to a resonance frequency which can lie in any section of the spectrum. For example, a locking frequency of 5 MHz is used. The outer loop, which consists of the induction L 1 and the capacitor C1, is tuned to a destruction frequency, which is preferably one of the frequencies that have been approved for industrial, scientific and medical purposes. Such frequencies have the advantage that they can be broadcast with unlimited power without a special operating license being required. For example, the frequencies in the United States of America are 13.56; 27.12; 40.00 and 905 MHz. In the illustrated embodiment, a frequency of 27.12 MHz is used. The destruction of the resonant properties of the trailer is simply effected by applying energy at the destruction frequency to melt the connecting line 62 so that the trailer is no longer detectable by the receiver system. Sufficient power can be provided to the resonant trailer the destruction frequency are supplied to destroy the connection line in the trailer, even if the actual resonance point of the trailer circuit is slightly different from the nominal destruction frequency.

The trailer circuit can be fabricated using various printed circuit and etched circuit techniques. Extremely low manufacturing costs result from the use of a continuous manufacturing process in which a strip of tags is made which can be severed for use. In such a continuous process, a strip of insulation material is used which has a conductive foil extruded or coated on each side. The tag circuit is repeatedly printed on the respective sides of the strip and unprinted areas are etched to form a continuous roll Trailers formed which can then be cut from the strip or separated in some other way. The connection 63 between the surfaces 46 and 58 can be made by known printed circuit manufacturing techniques such as lead pins or eyes extending through the carrier, or by means of a plated through hole or the like. The strip may be a high density polyethylene 0.025-0.05 mm thick with an aluminum foil 0.025 mm thick on each side. The thin carrier enables the connection point 63 to be produced easily, for example by pressing a conductive eye through the carrier or by spot welding the opposing surfaces.

It has been found that the in Figs. 3 to 5 shown resonance circuit in the inventive System is very effective. It should be noted, however, that the resonant circuit can have a variety of shapes can to give the desired destruction and detector frequencies. As an alternative, a Trailer circuit use where three capacitors are used to make a manufacture of the trailer without allowing an electrical connection between the sides of the circuit board. This embodiment makes a larger support area necessary for the third capacitor take up, which can be formed, for example, by a widened design of the surfaces 46 and 58.

The fusible connecting line 62 can in

other way than shown in the circuit to deactivate the Follower to perform at the detector frequency or alternatively to completely deactivate the To effect resonance circuit. The coupling coefficient

Efficient M between the coils of the resonance circuit can be either positive or negative. When the coupling coefficient is negative, the respective tuned circles making up the trailer can be tuned separately, and this simplifies the design of the particular trailer circuits having the respective resonance characteristics. Since the sensitivity of a tuned circuit is related to the total number of coil turns of the inductors, the formation of a positive coupling coefficient leads to greater sensitivity, since the number of turns of the circuit inductors wound in the same direction is additive. If, for example, the coupling coefficient M

If is negative, the locking frequency is determined by the coil L 1, which is connected in series with the coil L 2 and the capacitor C2 , while the deactivation frequency is determined by the coil L 1, which is connected in series with the capacitor Ci

however the coupling coefficient is positive so will the resonance frequencies due to the overall interactions determined by the various inductors and capacitors

The fusible connecting line can be in the

Trailer circuit can be arranged in such a way that, if it is destroyed by an applied electromagnetic field, the trailer becomes completely ineffective.

shafts of the trailer are destroyed at the locking frequency, the trailer then at a third frequency takes effect again, both of the detection frequency and the destruction frequency is different. This third frequency can be used at

Operation of the system when this system is inconsistent with the third frequency works ignored. At a alternative embodiment, the third frequency, if the fusible link is destroyed

Management line is used to determine if there is a trailer that is being monitored Space is located, has been changed electrically.

This embodiment can be used, for example, at the exit of a store where the System is in place to detect the presence of a trailer by means of the locking frequency, to check whether there are any objects in the room that have been illegally removed from the store became. The detection of a trailer at the third frequency is an indication of an electric modified trailer, and the lack of detection of the third frequency may indicate that a Item is present from which a tag has been removed. The use of this third Trailer frequency can be used as an additional safety precaution.

The device according to the invention is effective to determine amplitude, frequency, or phase modulation which are generated by the presence of a resonance tag within the monitored space. In one embodiment of the invention using amplitude modulation, demodulator 20 (Fig. 1) includes a full wave rectifier to detect amplitude changes caused by the presence of a trailer loop in the field generated by the transmitter. The mode of operation of such an amplitude demodulator can best be seen in conjunction with the spectral diagrams in FIG. 6 and the signal diagrams in FIG. 7 will be explained. The carrier frequency, which is shown in FIG. 6A, changes in a regularly recurring manner through a predetermined frequency range which is usually ± 15% of the carrier center frequency. After processing by the high frequency band pass filter 16 (FIG. 1), the received signal has a spectral envelope 70. as shown in FIG. 6A, this envelope curve being centered around the carrier frequency f _c . After full-wave demodulation by the demodulator 20, the spectrum has the spectrum shown in FIG. 6B, and there is a carrier spectrum 72 which is centered around twice the carrier frequency 2f _c . Furthermore, a signal spectrum 74 is present which contains the modulation frequency f _m . Noise signal components 76 are also present as shown and extend from the frequencies of the signal spectrum to frequencies higher than twice the carrier spectrum. The signal output from demodulator 20 is a series of bipolar pulses shown in Figure 7B. Each pulse occurs as the carrier signal passes through the trailer circuit's resonant detection frequency. It should be noted that adjacent pulses have opposite directions because of the corresponding passage of the carrier frequency through the resonance detection frequency in the positive and negative directions.

The low-pass filter 22 has the effect that the carrier spectrum 72 around the frequency 2f _c and the noise level components above the signal spectrum are removed, as shown in FIG i g. 6D shows the low pass range of this high-pass filter for the illustrated embodiment is in the range from 20 to 100 kHz, the modulation frequency being 1 kHz can be determined much more easily than the less abrupt impulses that are generated by background noise or by objects that do not vibrate in resonance or that vibrate only slightly in resonance. In practice, the spectral content of pulses generated by interfering conditions is usually insufficient within the bandwidth of the high-pass filter to enable further processing. The pulse signals generated by the high pass filter 24 are amplified by the amplifier 26 and then fed to the noise blocking circuits 28 and 30 to operate an alarm system 32.

The noise blocking circuit 28 is shown in FIG. 8 pulse signals from amplifier 26 are shown positive pulse height threshold detector 78 supplied and a negative pulse height threshold detector 80. Each detector produces an output signal according to FIG a received signal which exceeds the corresponding threshold The output signals of the threshold circuits 78 and 80 are pulse duration discriminators 82 and 84 fed to the outputs of these Discriminators are fed to an OR circuit 86. The output of OR circuit 86 becomes a flip-flop 88, a monostable multivibrator 90 and a counter 92. The output of the Multivibrator 90 generates a reset pulse for counter 92 and flip-flop 88. The (^ output of the Flip-flops 88 are used to apply a lock signal to the discriminator 84 during the ζί output of the flip-flop 88 is used to supply the discriminator 82 with an inhibit signal. The outcome of the Noise blocking circuit occurs at the output terminal of the counter 92.

After being processed by the high pass filter 24, the signal is both in time and in The amplitude is symmetrical and always takes the form of a positive-negative-positive pulse, the negative-positive-negative pulse follows as shown in Fig. 9A. The maximum time between zero crossings of these Signals is fixed and is determined by the cutoff frequency of the high-pass filter instead of the variable Properties of the resonance tag itself. After the signal passes through the high pass filter, becomes this by a series of alternating positive and negative pulses of a predetermined maximum Pulse duration, pulse height and interval sequence are determined, and the interference signal blocking circuit 28 is effective to output pulses only to be given if certain precise conditions are met during the positive passage of a received signal must meet the conditions of the positive threshold detector 78 and the pulse duration discriminator 82 are satisfied to have an output signal at the OR circuit 86 produce. During the negative passage of the received signal, the negative threshold and the Pulse duration can be achieved, which are determined by the detector 80 and the discriminator 84 to a Signal to the OR circuit 86 to be supplied. The flip-flop 88 is effective to one or the other of the To block outputs of the discriminators 82 and 84 and to alternate between the two circuit polarities, wherefore the circuit only works for signals from alternating polarity for each pass of the signals coming from amplifier 26

The mode of operation of the interference signal blocking circuit should be shown in

V. 569

13 14

Connection with the signal diagrams of Fig.9 is used to trigger an alarm device 32. Of the explained. The operation of this circuit from amplifier 26 is intended in conjunction with the Signal looks like it in Fig. 9A is shown, and signal diagrams of FIG. 11 are described,

Each pulse received by the jamming signal trap circuit 28 has a pair during a scan of the transmitter frequency of positive pulse sections with a 5 gene and the one shown in FIG. 1IA is shown, triggers the

middle negative section between and multivibrator 96, d ^ r has a period that is slightly during an opposite sweep, a pair is less than the period of the modulation frequency,

from negative sections with a mean The multivibrator is effective at glitching higher

positive section The positive and negative repetition rate lock, being the repetition rate

Threshold level which is higher than the modulation frequency by detectors 78 and 80. The initial formed are shown in dashed lines in Fig. 9A signal of the multivibrator, which is shown in Fig. HB

After the received signal is positive there is a gate pulse, which is sent to the leading edge of the

Threshold level exceeds, the detector generates 78 pulse signal (Fig. HA) begins and just before the

a pulse for a time interval in which the leading edge of the next repeating pulse

received signal the positive threshold level 15 ses ends This gate pulse is the mean value and

As Fig. 9B shows, two pulses are supplied to the integration circuit 98, which is

formed according to the received signal, which can act two a /? C circuit,

have positive sections, and a single pulse for the A predetermined reference threshold is through the

second signal which formed a single positive section detector 100 and is shown as a dashed line in FIG

has negative pulses are represented by the negative 20 Fig. HC. After exceeding the

Threshold circuit generated as shown in FIG. 9C by the integritor output

is. The in the F i g. 9B, 9C shown pulse output signal (F i g. HC), the detector 100 becomes effective,

are the pulse duration discriminators 82 and 84 to generate an output pulse (Fig. HD) to

which generate an output signal when the actuate an alarm circuit. Glitches with

pulses 25 supplied by the threshold circuits occur at a repetition frequency which is greater than that

are equal to at least the predetermined pulse duration. Modulation frequency, affect the operation of the

The output signals of the positive pulse duration circuit do not, as the monostable multivibrator does not

nators 82 are shown in Fig.9D while the can be triggered faster than that with the

Output signal of the negative pulse duration discriminative modulation frequency. An alarm is therefore triggered when to

gate 84 in FIG. 9E is shown. 30 fast glitch inputs not generated For real

The pulses that are fed to the OR circuit 86 are useful signals that occur with the modulation frequency,

have the correct amplitude and duration so that the voltage output of the integrator exceeds the

from then corresponding threshold detectors 78 and threshold level within a time interval, in

80 and pulse duration discriminators 82 and 84 processed a predetermined number of signal pulses for the

to become. The flip-flop 88 is set alternately 35 processing is received. With others

and reset, by pulses from the words, this means that an alarm display is only

OR circuit 86 ei are generated, and the output occurs when a predetermined number of

Signals are used to alternately receive the positive impulses that were received from the resonance

ven and negative channels of the interfering signal blocking circuit were generated. The number of pulses that

to dine. The output pulse from the OR switch 40 is required to trigger an alarm is through

device 86 are also fed to a counter 92, which the time constant of the integration circuit 98 and the

is effective, after receiving three input impulses, mean value of the multivibrator output determined interference

sen to generate an output signal. The input im- signals that have a lesser consequence than the

pulses for the counter 92 must occur within the modulation frequency, have no mean

Time interval occur, which is due to the multivibra value, which is greater than the threshold level, and it

gate 90 is determined, otherwise the output signal of the will not generate an alarm.

Multivibrators the counter 92 and the flip-flop 88 The interference signal blocking circuit 30 can alternatively so resets. The switching timing of the multivibrator 90 is as shown in Fig. 18 signals Shown in Fig.9F, set and slightly longer than the interference signal blocking circuit 28 are a first the time between the maximum signal peaks of the 50 monostable multivibrator 81 supplied to the output received video signal. The interfering signal blocking circuit of this multivibrator is generated at the same time as a staircase Output signals for further processing generator and comparator 83 fed to a second only if the received signals have a monostable multivibrator 85 and a third predetermined pulse height, a predetermined pulse monostable multivibrator 87. The output of the have a duration and a predetermined sequence. The 55 multivibrators 85 are fed to a counter 89 Incorrect processing of interfering signals, such as the output of which is a series of pulses that is used for triggering it is used, for example, by disruptive conditions of the alarm device 32. The staircase generator 83 is is substantially reduced and it is effective to give a reset signal to the counter 89 and the unlikely to introduce noise to the various multivibrators 87. The multivibrator 87 leads Meet criteria that are determined by the in F i g. 8, a reset signal is sent to the counter 89 and the staircase circuit are required. generator 83 closed.

The interference signal trap circuit 30 shown in FIG. 10 The mode of operation of the one shown in FIG

receives pulses from the interfering signal trap circuit 28. The circuit is intended in conjunction with the signal diagrams

The output of this trap circuit 28 is a monostatic the F i g. 19 will be described. The input pulses

The multivibrator 96 is connected to 65, which in turn is connected to the circuit 2 ”are shown in FIG. 19A

a mean value and integration circuit 98 connected. Pulses are fed to the multivibrator 81, the

that is. The output of circuit 98 is generated as an output pulse as shown in FIG. 19B.

Threshold level detector 100 is supplied whose output provides. These output pulses have a pre-

correct duration Tl ₁ . which is selected in such a way that it exceeds the duration of the expected received signals when using the frequency modulation fixed position of a resonance trailer within a room monitored by the detector 20 (Fig. 1) 81 are the inputs dzs staircase generator and usually a Analysis circuit, whose output comparator 83 and the Mulüvibratoren 85 and 87 ₅ signals is a series of de-modulated pulses that are supplied to the multivibrator 85 has a period that occurs each time the transmitted carrier frequency is approximately equal to the modulation rate, and generated by the The resonance detection frequency of the trailer in response to the pulses from the multivibrator 81 passes. The phase shift caused by pulses as shown in Fig. 19D, by which the presence of the trailer indicates, is compared _{by counter 89 to a payment for each applied pulse Io} the phase of received signals with vorzufellea The pulses 72 from the multivibrator 85 compared to that of a receiving oscillator, which is synchronized to the start at the leading edge of the corresponding transmitted signal phases.In a pulse from the multivibrator 81 and end shortly before the analyzer circuit, the received signal is the beginning of a subsequent pulse of the multivibra automatically synchronized with the local oscillator tor 81 and are effective to prevent interference input signals from being ₅ and the phase of the transmitted signal is compared with that of the counter 89 with a rate local oscillator to introduce an error signal that is faster than that of the expected generate, which is the phase deviation between signals. d _em received and represents the receiver signal.

The output of the staircase generator and comparator 83 is shown in FIG. 19C, and it can be seen, ₂ o reference. The output of a phase detector, which is a staircase voltage, which is like an analyzer circuit, is shown in FIG. A threshold circuit is modulation frequency f _m which together with Störinnerhalb the staircase generator and! Comparators 83 components above and below the signal Spek arranged, and if it exceeds a vorbestimm- ₂₅ spectrum. After a low-pass filtering by the filter 22 th threshold value through the staircase signal, the interference components above the Signalspek circuit 83 are effective to an output pulse trums removed, and the signal spectrum remains, as to be output, which is used to output the counter 89 and it in Fig. 12B is shown. Of the low-pass filters filtered multivibrator reset 87, and the output is then filtered in a high pass filter 24, staircase generator itself. Glitches that that of the repetition frequency occurring at a ₃ o, only the high frequency section 104 which is larger passes as the signal spectrum as shown in Figure Modulation frequency shown in Figure 12C, cause the staircase span to be. This final spectrum is essentially the voltage to a level above the threshold as it rises in connection with the above in order to reset the system. The counter amplitude modulation system has been described, and is reset in this way before it is counted up to its 35 processing as described above, so that a set to real useful signals of interfering signals to alarm at these too fast interfering signal inputs do not distinguish and an alarm is only triggered. For real useful signals that occur with the trigger when the presence of a trailer modulation frequency exceeds the staircase- is determined.

voltage threshold within the programmable time _40, the circuit may be formed as a phase detector

valles not in which a predetermined number of, as shown in Fig. 13, the signal from

Signal pulses for processing is received. RF amplifier 18 becomes a phase detector 106

The multivibrator 87 determines the maximum time, in and also fed to an analysis circuit 108,

receiving the predetermined number of pulses generating a reference signal for the phase detector,

must be to send an output pulse to the 45 The output of the phase detector 106 is a

To issue an alarm circuit. For the purpose of the display low-pass filter 22 is supplied and the output of this

It should be noted that the embodiment low-pass filter shown is in turn a high-pass filter 24

example 32 pulses are used to generate an alarm and then fed to the subsequent circuit, such as

trigger. The output signal from the multivibrator 86 is shown in FIG. 1 is shown. The outcome of the

is shown in FIG. 19E and is a long gate pulse, 50 phase detector circuit 106 is similar to that of FIG

that shown for an analyzer circuit upon receipt of the first pulse from FIG. 12A

Trailer circuit begins and leads to a pre- output with the exception that the signal component

right time after the occurrence of the 32nd with the modulation frequency / _{m is} not shifted like

Impulse ends. The multivibrator 87 has a period in the case where the analyzing circuit is used

that is longer than 32 times the modulation rate, 55, and the phase detector generates a spectrum with

and the output pulses of this multivibrator are double the carrier frequency. As an alternative you can

effective to the counter 89 in its initial stage the reference signal for the phase detector 106 by the

postpone. The counter does not generate an output transmitter 10 instead of the analyzer circuit 108

pulse for the alarm circuit if 32 pulses are generated by the. Regardless of whether it is an amplitude module multivibrator 85 not within the interval reception, frequency modulation or phase modulation at

gen, which is determined by the gate pulse, is used system according to the invention, takes that

which is generated by the multivibrator 87. The demodulated signal has a frequency spectrum, which

Counter 89 generates an output pulse that ranges from the modulation frequency up to about the

19F, and upon receipt of 32, extends hundreds of times this modulation frequency. Pulses from the multivibrator 85 with the modulation frequency 65 In the illustrated embodiment extends

frequency, and as shown above, interference signals are the frequency spectrum from 1 kHz to 100 kHz. That

statistically ineffective, a counter output for low-pass filters removed the carrier frequency and the

generate an alarm actuation. High frequency noise while the high pass filter

17 18

Removed all frequencies that are lower than the coupling of the trailer circuit with the antenna

twenty times the modulation frequency. cause a reflection of the trailer circuit impedance

The device for generating an electromagnetic radiation into the non-resonant antenna, and this

table field to the destruction or change of leads to a decreasing increase of the apparent

Resonance circuit of the trailer is in Fig. 14 5 resistance of the antenna and therefore to one

This device has a transmitter 101 abrupt change in the current in the antenna. the

on, the one output with the destruction frequency of the change in current is connected to the resistor R with a

Circuit of the trailer generated This transmitter is with detector, as in F i g. 14, established to have a locking

a balanced loop antenna 103, signal for subsequent processing in the

which generate the destruction field for a trailer in the manner described in FIG.

Surrounding this field generated The transmitter 101 has As a further alternative, separate transmission and

Usually an output power of 100 to 150 receiving antennas are used, which are closer together

Watt and is working on the loop antenna 103 by means of neighborhood, the distance between

adapted to matched lines An output line - the antennae is essentially smaller than about 5 cm,

The transmitter should be equipped with one line of frame length 15 to achieve maximum sensitivity. In which

antenna 103 connected. The other output terminal of the FIG. 1 illustrated embodiment are the

The transmitter is generally connected to the antenna on loop antennas via a line 105 in a considerable

a selected location 107 connected. These lines are spaced apart and a person

105 serves as an impedance matching loop and follows which carries a resonance tag that is detected

the configuration of the loop antenna, to be a ₂ o, passes between the antennas that

Leak flow between the input lines and the opposite one another. In a system where

associated antenna. The other end uses antennas that are placed side by side

the antenna 103 is to be via a variable capacitor, a person who goes a resonance pendant

109 grounded The geometry of the input lines carries through both loop antennas. Because

results in a branched coil that has a predetermined 25 of the short distance between the transmit and

The input impedance of the transmitter 101 for the input IM receiving antenna is the voltage in the

Pedance of the antenna 103 has. Receiving antenna is induced, partially compensated,

In the embodiment described above, to prevent receiver saturation while it

Example are separate sending and receiving - it is still possible that a full signal from the trailer

Terminals 12 and 14 are present, each receiving a 30.

Loop antenna is. According to the invention, the embodiment with the closely spaced

Single antenna systems are used, namely arrayed antennas, is shown in FIG. A

The transmitter 128 is provided with an antenna loop 130 for both emitting and receiving

electromagnetic energy. A single antenna network connected in series with a winding 132 of a

Sonanzsystem is in Fig. 15 and has a 35 transformer 134 is connected. The other winding

Antenna loop HO in resonance circuit with a 136 of the transformer is in series with one

variable voltage capacitor 112 . An Aiitennenschleife 138 connected and that with the

Oscillator 114 feeds antenna loop 110 and the receiving antenna loop, to which a detector 140

generates the carrier signal. The modulation signal is connected to the transformer 134 has a

generated by a modulation source 116, the 40 variable transformer coupling Mi on, and, there

The control input of the capacitor 112 is connected to the received signal by a negative feedback

to change the capacitance of the capacitor and thus between the transmitter and the trailer circuit and then between

The resonance of the matched circle that creates the trailer circle and detector is the

Includes antenna. The antenna circuit acts in the wesentli coupling coefficient adjusted so that an extreme

chen as an oscillator circuit, and if a ₄₅ sensitive trailer detection without overload

The resonance tag is located close to the antenna of the receiver.

and magnetically coupled thereto, the invention is not intended to be used with any

Antenna circuit with the reflected impedance of the electronically changeable trailer resonance circuit

Trailer circle burdened, and the low series impe- limited, but can also with trailer circles

danz the trailer circuit will be used in the antenna circuit 50, which does not have a fusible line

have a high real series resistance at resonance section. For some purposes it is desirable

reflects and causes an abrupt change in what is worth seeing a reusable trailer too

Q factor of the oscillator and leads to a sharp use of the one or more frequencies

Voltage drop on the oscillator circuit. This has a resonance which is determined to be the

A voltage drop is detected by a detector 118. The presence of a trailer. Of the

which provides an output signal for a further group of followers, alternatively, for example one

Processing produces such as they have in conjunction with the simple resonance circuit of a single

F i g. 1 was described. Frequency has a circle of followers can also

The invention can also have several resonance points in the case of a non-resonance, whereby the resotes Single antenna system can be used as it is in 60 nanzfrequenzen all in the frequency range of the transmission

F i g. 16 is shown This system has an oscillator th electromagnetic field. These frequencies

120 on, the voltage controlled oscillator 122 zen are determined according to the invention to the

who in turn is testing a // F-amplifier 124 with the presence of a trailer. The invention

low output impedance, which can also be used using different

det is realized around a non-resonant loop antenna 126 65 circles with which the desired

to dine. The presence of a trailer circuit system operation can be carried out
near the antenna and a magnetic

In addition 8 sheets of drawings

Claims (20)

Patent claims: 1. Device for determining the unauthorized removal of objects from a protected area or monitored area with a transmitter that generates an electromagnetic field in a predetermined Space is created with a receiver, which the presence of a certain predetermined Frequency determines, and with a resonance circuit, which when introduced into the predetermined Addresses space, characterized in that the transmitter (10, 12) is designed such that the electromagnetic field it generates repeats a given frequency range runs through that the resonance circuit has several resonance points (Fig.5) that a first Resonance frequency (loops 40 + 48) within the given frequency range and beyond a second resonance frequency (loop 40) lies outside the predetermined frequency range that the receiver (14, 16) detects the presence of the first resonance frequency and that continues a device (Fig. 14) is provided, which serves to the resonance circuit by supplying to deactivate electromagnetic energy with the second resonance frequency, namely in the Way that its resonance properties are destroyed at the first resonance frequency. 2. Device according to claim 1, characterized in that the resonance circuit has a third resonance frequency which responds when the resonance properties of the oscillator circuit at the first resonance frequency were destroyed by the application of an electromagnetic field, and that there is a device serving to sample the third resonance frequency. 3. Device according to claim 1, characterized in that that the transmitter has the following parts: an oscillator (34), the a modulation signal generated with a predetermined frequency, a voltage controlled oscillator (36), which as Response to the operation of the oscillator (34) generates a carrier frequency which is differentiated by a predetermined frequency range changes, as a result of the modulation signal of the oscillator (34), an amplifier (38) connected to the voltage controlled oscillator (36) and an antenna (12) which is connected to the amplifier (38) to generate the electromagnetic field. 4. Device according to claim 1, characterized in that the receiver has the following parts comprises: a high frequency input stage (16, 18), which the electromagnetic field of the transmitter receives and in response thereto generates a radio frequency output signal, a detector circuit (20), which responds to this output signal and output pulses in the presence of the first Resonant frequency of the oscillator circuit generated in the electromagnetic field, an interference suppression device (6, 22, 24, 28, 30), which suppresses interference signals received with the output pulses and means (32) responsive to these output pulses to provide an output display to produce which the presence of an oscillator circuit at the first resonance frequency in this given area. 5. Device according to claim 4, characterized in that the interference suppression device has devices (16) which only allow the signal spectrum of the high-frequency output signal to pass, and devices (28,30), which process the pulses of the detector in a digital manner, to only produce output pulses to be generated when pulses of a given sequence and duration occur. 6. Device according to claim 1, characterized in that the receiver has the following parts: a detector (20) which generates output pulses in the presence of a resonance circuit with the first resonance frequency in the electromagnetic field, devices (24) which between relatively steep Pulses coming from the detector, which are generated by the presence of a resonant circuit in the electromagnetic field, and the less steep pulses which are caused by disturbances , distinguish a noise signal suppression circuit (28, 30), which in response to the pulses from the suppression circuits Output signals generated on received pulses of corresponding predetermined properties such as pulse height, pulse duration, pulse spacing, pulse polarity, pulse train and pulse repetition frequency, and means (32) which, in response to the output pulses of these interference signal suppression circuits, an output indicator for an alarm actuation generating a predetermined number of pulses received. 7. Device according to claim 6, characterized in that the transmitter has an antenna (110) which generates the electromagnetic field in the given space, and that the detector (116) is connected to this antenna (110). 8. Device according to claim 6, characterized in that the pulse discrimination device Filter (22, 24) having a part of the signal spectrum of the output pulses of the detector which has a higher frequency than twice the modulation frequency of the transmitter. 9. Device according to claim 6, characterized in that the interference signal suppression circuit means (82, 84) responsive to pulses from the pulse discriminating device originate to the first output pulses of the specified pulse height and pulse duration to generate, in response to the received pulses of one polarity, and second Pulses of a given height and duration, in response to those received Pulses of opposite polarity, means (86, 88) generating third pulses, and although in response to received pulses of alternating polarity, a device (92), which counts the third pulses and an output display at a given count of these Pulses generated, and a device that generates a gate signal representing a time interval, within which the third pulse must be received in order to get the output display produce. 10. Device according to claim 9, characterized in that the interference signal suppression circuit comprises the following parts: a multivibrator circuit (98), which is supplied with Input pulses Output pulses of a specified duration generated, which is slightly less than the Period of the modulation frequency of the transmitter, an integration circuit (98) acting on the output pulses of the multivibrator responds to generate an output signal, the signal level of which is the mean value represents the multivibrator output pulses, s a switching device (100; which a threshold level of a predetermined amplitude, and a device which generates an output signal, when this threshold level is exceeded by the integrator output, the The integration circuit has such a time constant that it generates an output signal having a level which only exceeds the threshold level if a predetermined minimum number of Multivibrator output pulses were received. 11. Device according to claim 6, characterized in that the receiver has a high-frequency input stage (16, 18), which receives the electromagnetic field from the transmitter and a high frequency output signal! in response to generates this field, the detector (20) being responsive to the high frequency output signal. 12. Device according to claim 11, characterized characterized in that the transmitter (10, 12) and the high-frequency input stage (16, 18) have an antenna (12,14) have in order to emit or receive the electromagnetic field. 13. Device according to claim 6, characterized in that the interference level suppression circuit comprises: a first threshold detector (28) which has an output pulse in response to a received pulse of positive polarity and predetermined pulse height generates a second threshold detector (80) which generates an output pulse upon a received Impulse of negative polarity and predetermined height generated, a first pulse duration discriminator (72), responsive to pulses received from the first threshold detector, to To generate output pulses of predetermined duration, a second pulse duration discriminator (84), the is responsive to pulses received from the second threshold detector to to generate corresponding output pulses of predetermined duration, a gate circuit (82, 88), the corresponding to the output pulses received from the first and second pulse duration discriminators a device (92), alternately blocks the first and second discriminator, with which the output pulses are counted from the first and second pulse duration discriminator and to receive a predetermined number of pulses therefrom Discriminators to generate an output indicator, and a circuit that generates a time interval within which the output display from the counter must appear, and the blocking device and the Resets counter at the end of the time interval. 14. Device according to claim 13, characterized in that the interference signal suppression circuit comprises the following parts: a device (81) which acts on the output display of the counter responds to generate first output pulses of a predetermined duration which is greater than that Duration of the expected received pulses, wherein a staircase generator (73) is provided which on responsive to the first output pulses to generate a staircase signal the amplitude of which increases increased in the presence of each first output pulse, a device (85), which on the responds to the first output pulses to generate counting pulses that have a duration that is somewhat is less than the penode of the expected signals, a circuit (81) that responds to the first output pulses responds to generate a gate signal for the counter which determines a time interval within which a predetermined number of counter pulses must be received, a counter (89) responsive to the counter pulses to generate an output indication given the presence of a predetermined number of Counter pulses within a time interval generated by the gate signal of the circuits is, the staircase generator a reset signal when exceeding a predetermined Threshold level generated by the staircase signal to the counter, the staircase generator and the Reset circuits. 15. The device according to claim 1, characterized in that the device for electrical Elimination of the resonance circuit comprises the following parts: an antenna (12), which the electromagnetic energy generated at the second resonance frequency, and a transmitter (10). the the Antenna (12) feeds to generate the electromagnetic energy. 16. The device according to claim 15, characterized in that the antenna is a balanced Loop antenna (110) is connected to the output of the transmitter (10) by means of a balanced line is adapted. 17. Device according to claim 1, characterized in that the resonance circuit having a plurality of resonance frequencies has the following parts: a first resonance circuit (Li, L2, C2), the resonance frequency of which is within the predetermined range at the most frequency, a second resonance circuit ( L I. C 1) whose resonance frequency is the second frequency outside the predetermined range and a fusible link line (62) in the circuit of the resonant circuits, the at predetermined det ¹ feeding of electromagnetic energy power at the second frequency melts. 18. Device according to claim 17, characterized in that the resonance circuit has a third Has resonance frequency, which responds when the resonance characteristics of the resonance circuit at the first resonance frequency by applying an electromagnetic field with the second Frequency were destroyed. 19. Device according to claim 17, characterized in that the several resonance frequencies having a resonance circle a flat base (42) made of an electrically insulating material having, with first and second resonance circles on this base in a planar configurator are trained. 20. Device according to claim 1, characterized in that the plurality of resonance frequencies zen having resonance circuit a flat Unterla ge (42) made of an electrically insulating material has that a first conduction path (40) on a surface of this base ir. such a ' Configuration is designed that a first inductance is formed that a second line 5 6 create way (48) on this base in such a way, which is formed with an extremely simple construction configuration that a second one requires particularly little energy.
Inductance is formed in that first and second pairs. To achieve this object, the invention provides for conductive areas (52, 54; 44, 56) to be provided so that the transmitter is designed to be of it, with each pair of conductive areas 5 generated electromagnetic field repeats an opposite sides of said base aligned, predetermined frequency range passes through that of the said conducting areas having on the surface of the resonant circuit a plurality of resonance points that support the first and second conduction paths, a first resonant frequency within the voirgegebeaufw iron and using this electrically are connected at selected NEN frequency range and further a second point to form the first and second io resonance frequency outside the predetermined frequency range for these circuits, that the receiver detects the presence of a conduction path (62) of predetermined being the first resonance frequency t and that shape and size in the resonance circuit on a further a device is provided, which is provided for the surface of the base and serves to melt the resonance circuit by supplying electrical supply of electromagnetic energy at 15 magnetic energy with the second resonance frequency and wherein to deactivate the resonance frequency in such a way that a conduction path (63) through the substrate is provided so that its resonance properties are provided at the first and one of the first and second resonance frequencies are destroyed.
Conduction paths and one of the conductive surfaces. Advantageous developments and preferred connections to close the circuit. 20 lead forms of the subject matter of the invention result from the subclaims. The arrangement according to the invention is not just great simple and robust in its construction, so that it can also be produced extremely inexpensively , rather it comes The invention relates to a device for locking 25 even with an extremely low level of energy. development of the unauthorized removal of objects from In addition, let the arrangement according to the invention work a protected or monitored area with particularly reliable operation, because an alarm is only then Transmitter that can trigger an electromagnetic field in you if that is used as an alarm criterion predetermined space generated, with a receiver, serving signal different predetermined conditions which fulfills the presence of a certain pre-set, through which it is clear from interfering signals with a resonance circuit that is distinguishable. The arrangement according to the invention continues to be actuated when it is introduced into the predetermined space. the advantage that with such small Strahlungslei- Such devices are stungen particular for supply manages that to prevent the operation of the entsprekaufläden expedient stands to the theft of counter 35 sponding circuit means no approval from the store to the required is The invention is intended in the following description zen caused by shoplifting. Such with reference to the figures of the drawing Facilities generally have an electromagnetic field. It shows: table field, which in a monitored area 40 F i g. 1 is a block diagram of an inventive is created through which the goods at the establishment, Leaving the shop must be transported. F1 g. 2 is a block diagram of the in FIG. 1 shown A resonance circuit is attached to the goods, and the transmitter, Presence of the resonance circuit in the monitored F i g. 3 is a view of a location of a resonance circuit area is scanned by a receiving system, 4} trailer, the unauthorized removal of objects Fig.4 is a view of the other side of the in Fig.3 ascertain. The resonance circuit is represented by the sales resonance circuit trailer, staff removed or can be electronically shown in Fig. 5 a schematic representation of the electrical be changed that an object that can be seen in the correct equivalent circuit of the in Figs Way leaves the store, through the monitored 50 represented resonance circuit, Can pass area without an alarm 6 is a representation of signal spectra for is triggered. Explanation of the operation of an embodiment with A circuit arrangement of the amplitude modulation mentioned at the beginning, Art is known from British patent specification 12 12 504 Fig.7 a Sigiialdarstellung to explain the. In this known arrangement, a 53 operation with amplitude modulation, the resonant circuit is used with a diode, g to har- F i. 8 is a block diagram of a noise niche used to generate, in response to a field signal blocking circuit,
given frequency. F i g. 9 shows a representation of signals for the purpose of explanation Furthermore, from the German exploratory document of the company in Fig. 8 circuit used, 1944653 a circuit arrangement is known, which to Fig. 10 a block diagram of an additional interference also has a resonance circuit with a diode, signal blocking circuit, which serves as a non-linear circuit element in FIG. 11 is a diagram of signals for explanation Reaction to an electromagnetic operation of the Emriclitnng shown in Fig. 10, which is used for querying, table field to generate harmonics. The field is Fig. 12 a schematic representation of a signal nrit created with the help of a transmitter, which with a fixed «3 spectrum to explain the operation with phase- ' Frequency works modulation, The invention is based on the object of a Fig. 13 a block diagram of a phase detector, To be sure, of the type mentioned in connection with FIG. 14, a schematic representation of a . »- jfr.