FI95514B - Identification method and identification equipment - Google Patents

Description

, 95514

The present invention relates to an identification method for identifying an object entering a certain area, in which method a first electromagnetic field of a predetermined frequency is produced in the area. The invention further relates to an identification apparatus for identifying an object entering a certain area, which apparatus comprises transmitter means for producing a first predetermined frequency electromagnetic field in said area, and; measuring means for measuring the first field in said area. In this context, field measurement means that both the real and the imaginary part of the field are measured.

This invention relates generally to surveillance systems, and more particularly to burglar alarms for use in stores and shops. Known burglar alarms are based on either 8.2 MHz LC resonators or low frequency readable magnetic tapes. The present invention relates primarily to a burglar alarm that can be used to detect an LC resonator circuit. When an object having a resonator enters the electromagnetic field of a burglar alarm, i.e. an Electronic Article Surveillance System (EAS), which is generated by the transmitter of the system 25 and the associated antenna, the resonator causes a change in the field strength. Based on this change, the alarm system receiver detects the presence of a sensor. The transmitter and receiver of the alarm system are located at a location or locations where it is desired to indicate that the sensor has a product in connection with an unauthorized exit, such as a store exit.

Known burglar alarms are based on scanning, i.e. they are adapted to erase the frequency of the sinusoidal signal past the resonant frequency of the resonator circuit. That is, the transmitter and receiver 35 continuously change the frequency so that in a certain period of time all the frequencies in the frequency range (e.g. 8.0 to 8.8 MHz) become traversed. The signal input and the resulting electromagnetic field activate the oscillation of the nearby resonator circuit 5. The burglar alarm receiver measures the change in field strength (amplitude) caused by the resonant circuit. If the measured change exceeds a certain threshold, the burglar alarm signals the alarm, usually with audible and / or light signals.

10 The most significant weakness of the known burglar alarm described above is its sensitivity to metal objects. That is, if the product to which the resonator circuit is attached is fitted, for example, to a bag or tin box lined with aluminum foil, the burglar alarm will generally not be able to detect it. However, the metal object itself causes a change in the electromagnetic field generated by the burglar alarm, which is detected by the alarm. In most cases, however, the burglar alarms are tuned so that changes in field strength caused by metal objects do not trigger 20 alarms, because otherwise, for example, transporting metal shopping carts through the burglar alarm field would cause continuous false alarms. Thus, thieves have learned that if items to be stolen are concealed in metal cases, bags, or the like, the resonator circuits attached to the items 25 will not trigger the burglar alarms in the store.

The object of the present invention is to obviate the above-mentioned weakness and to provide an identification method by means of which objects 30 entering a predetermined area can be better and more reliably identified, whereby, after identification, the necessary measures can be taken. The identification method according to the invention is characterized in that a second electromagnetic field 35 of a predetermined frequency is produced in the region simultaneously with the first field, the frequency of the second field 3 95514 being selected so as to deviate from the frequency of the first field; monitoring the first and second fields, and; identifying an object entering the area by comparing the changes in the 5 fields caused by it to the first and second fields to predetermined reference values.

The invention is based on the idea that when at least two electromagnetic fields of different frequencies are produced in the area at the same time, objects that have entered the area can be identified by the changes they cause to the different fields. Changes in this context mean that the values of both the real and imaginary parts of the field change. Because different objects produce different changes to the fields in the area, each object has its own "profile" that allows the object to be identified. The more frequencies, i.e. the more electromagnetic fields used for identification, the more individual the profile of each object becomes. The number of frequencies used is preferably about 7 to 15. When objects can be identified very individually, for example, 20 alarm devices no longer need to be adjusted so as not to alert all metal objects, but information about which metal objects should not be alarmed and which it, on the other hand, needs to be alerted.

The most significant advantages of the method according to the invention are the reliability of the identification and the fact that the method is not sensitive to external electrical disturbances.

The identification method according to the invention can be further applied, for example, to access control, in which case, for example, identity cards are made individual by fitting resonator circuits having different resonant frequencies. Each identity card thus has a unique profile, i.e. it causes a different change in the electromagnetic fields prevailing in the area, whereby 35 identity cards can be identified on the basis of the change it causes. By applying the method according to the invention, for example in connection with a door locking mechanism, a locking mechanism can be provided in the door which automatically opens when a certain identity card appears in the electromagnetic fields prevailing in its vicinity.

The invention further relates to an identification device with which the method according to the invention can be applied. The apparatus according to the invention is characterized in that the apparatus further comprises transmitter means for producing an electromagnetic field of a second predetermined frequency in said region simultaneously with the first field, the frequencies of the first and second fields differing from each other; measuring means for measuring a second electromagnetic field in said region, 15 and; a control unit for comparing the values measured by the measuring means with predetermined reference values and for identifying an object entering the area on the basis of said comparison.

Preferred embodiments of the method and apparatus according to the invention appear from the appended dependent claims 2 to 3 and 5 to 8. The invention will now be described in more detail by way of example with reference to the accompanying figures, in which Figure 1 shows a block diagram of a first preferred embodiment of an identification apparatus according to the invention. 2 illustrates the signals to be applied to the antenna of Figure 1, Figures 3a to 3d illustrate measurement results obtained from various objects, and Figure 4 illustrates the sum signal to be applied to the antenna of Figure 1.

Figure 1 shows a block diagram of a first preferred embodiment of an identification apparatus according to the invention. The identification device 5 95514 shown in Fig. 1 is suitable for use, for example, as a burglar alarm in stores. The burglar alarm of Figure 1 has a common transmitting and receiving antenna ANT, which is shaped as a gate through which a person can pass. The burglar alarm can also be implemented with two separate antennas, if necessary. The gate of Figure 1 can be adapted, for example, to the exits of stores, whereby customers have to walk through an antenna loop when leaving the store. In the case of Figure 1, two 10 LC / C circuits are mounted on the antenna to reduce the electric field. Depending on the location and number of LC / C circuits, the electric field of the antenna is distributed differently in the center of the antenna loop ANT.

In connection with the antenna ANT, a switch S and a known component 4 (coil or resistor 15) are further arranged in Fig. 1. By means of a known component, the measuring and control unit 3 obtains a reference for both the amplitude and the phase. This makes it easier to calibrate the port at the installation site.

The transmitter part of the burglar alarm of Figure 1 has a signal generator 1 consisting of a D / A converter adapted to produce a sum signal consisting of seven different frequency components, the lowest f1 being, for example, about 1 MHz and the remaining six f2 to f7 evenly 8.2 MHz in the neighborhood of. The signal generator 1 of the sum signal produced produces its output B via the control component 7 to the antenna ANT. The control component 7 preferably consists of a coil connected in parallel and an adjustable capacitor. With said component 7, the effect of the metal on the antenna ANT can be "simulated". If a large metal object comes into the immediate vicinity of the antenna, the measuring and control unit 3 can quickly compensate for the effect of the metal object by means of the control component 7. Thus, the AMP gain of the amplifier can be increased, and thus the sensitivity of the equipment with respect to the detection of resonant circuits is improved in situations where a large metal object makes detection difficult.

6 95514

The antenna ANT generates an electromagnetic field consisting of seven sub-components of different frequencies from the sum signal applied to it. The different frequency components of the sum signal are synchronized with each other so that the peak value of the sum-5 signal is as small as possible. Minimizing the peak value allows for the highest possible value of the individual signal components, which in turn results in good sensitivity without the field strength of the field produced by the burglar alarm exceeding the limits set by the authorities 10. In the optimal situation, the sum signal resembles noise (compare Figure 4).

The burglar alarm of Figure 1 receives signals from its antenna ANT regardless of whether or not there are objects inside the antenna loop ANT (i.e., the gate). The signal received by the antenna-15 depends on the port itself and nearby metal objects. In the case of Fig. 1, a compensation signal resembling the sum signal to be fed to the antenna is input to the second input of the summing member 6 from the output G of the signal generator 1. Thanks to the compensation signal, a signal is supplied from the AMP output of the amplifier to the mixer 2, which compensates for the inductance of the antenna, the resistance and the nearby solid metal objects. The necessary compensation signal is obtained by installing the gate in its place of use, after which the measuring and control unit 3 measures the signal coming from the antenna, and ** controls the signal generator 1 to produce this corresponding compensation signal. This arrangement allows the amplifier AMP (and, for example, the mixer may be placed after the two amplifiers), the gain may be 30 to increase by a factor of 10 - 100, wherein the .. received downside to the sensitivity is improved. This improves the dynamics of the device.

The mixer 2 is supplied with signals from the output of the amplifier AMP and the signals from the output 35 R of the signal generator 1 with frequencies fl + fa, ..,

II

7 95514 f7 + 7fa. Thus, signals with frequencies fa, 2fa, 3fa, ..., 7fa are obtained from the output of the mixer. By selecting the frequency f a low enough, for example 1 kHz, the output signals of the mixer 2 can be compressed into the audio frequency band 5, whereby the information contained therein can be read by the audio A / D converter preceding the measuring and control unit 3. The measuring and control unit 3 measures the amplitude and phase (real and imaginary part) of each signal, for example by utilizing FFT (Fast Fourier Transform) technology 10. The measuring and control unit 3 then compares the reference values stored in the memory 4 with the measured values and identifies the object in the gate on the basis of the comparison.

Once the measuring and control unit 3 has identified the object in the port 15 by means of the reference values in the memory 4, it reads the operation data for that object from the memory 4 and inputs this operation data to the detection unit 5. The detection unit 5 then operates based on the operation data content. That is, if the identified object is, for example, a resonator circuit (product protection sensor), the detection unit performs an alarm with, for example, audible and visual signals in response to the content of the operation data. If, on the other hand, the identified object is, for example, a combination of a human and a metal object (e.g. a thief with a beer can in his pocket), * the detection unit 5 can trigger an alarm by sending a radio message to the store detector radio receiver unit in response to the action data content.

The burglar alarm of Figure 1 can be calibrated, for example, so that each identifiable object (shopping cart, human, product protection sensor, human + beer can, etc.) is taken alternately to the antenna loop ANT, i.e. the port, after which the values measured by the measuring and control unit ( compare Figures 3a to 3d), i.e. the values describing the profile of the object in question are stored in the memory medium 4 together with the action data for the object 3 95514 in question. The objects listed above, as well as the measures involved in identifying them, are, of course, only exemplary, as there are a large number of identifiable objects and object combinations.

Figure 2 illustrates the signals to be applied to the antenna of Figure 1, i.e. the sub-components of the sum signal. In Figure 2, the signals are shown in frequency space. The frequency of the signal f1 is about 1 MHz, so that it can be used to expose the metal. The frequencies of the signals f2 to f7 used to identify the resonant circuit are about 7.5 to 9.0 MHz. If there is a resonator-circuit near the antenna, the real part Asin (9) of the measured frequency components (A = signal amplitude, φ «signal phase) and the imaginary part Acos (p) behave as shown in Figures 3a. If the measured signals form the curves according to Fig. 3a with sufficient accuracy and several times in succession, the measuring and control unit 3 concludes that there is a resonator near the gate, whereupon it performs an alarm. The reasoning algorithm of the measuring and control unit is preferably made in such a way that it only accepts curve measures corresponding to the goodness number (Q value) of the resonant circuit, whereby sharp changes or tilts are not interpreted as caused by the resonant circuit.

Figures 3a to 3d illustrate the measurement results obtained from »different objects, i.e. the profile of the objects.

Figures 3a to 3d show the behavior of the real part of the measurement result in the top row, and the behavior of the imaginary part in the bottom row, respectively. The horizontal axes 30 of Figures 3a to 3d illustrate the frequency. Figures 3a -3d illustrate the measured values with dots. The dot on the left to the left illustrates the measurement in the 1 MHz frequency range, and the remaining six points illustrate the measurements in the 7.5 to 9.0 MHz frequency range.

Fig. 3a shows a situation in which the gate of Fig. 1 has a resonator circuit with a resonant frequency of 9,95514 about 8.2 MHz. It can be seen from Figure 3a that the sensor affects both the real and imaginary part in the 8.2 MHz environment.

Fig. 3b shows a situation in which a metal object is located in the gate of Fig. 1. It can be seen from Figure 3b that the metal object affects the imaginary part at both low and high frequencies.

Figure 3c shows a situation where a human is located in the gate of Figure 1. Figure 3c shows that man has little effect on the imaginary-10 part at low frequencies. At high frequencies, on the other hand, man affects both the real and imaginary parts.

Figure 3d shows a situation where a sensor and a human are located in the gate of Figure 1.

On the basis of the curves according to Figures 3a to 3d, it is thus possible to identify the object in the field relatively unambiguously, after which the necessary measures can be taken.

Figure 4 illustrates the sum signal to be applied to the antenna of Figure 1. The horizontal axis of Figure 4 represents time and the vertical axis 20 the signal amplitude. It can be seen from Figure 4 that the phases of the individual frequency components of the sum signal are synchronized with each other so that the sum signal resembles noise.

It is to be understood that the foregoing description and the accompanying drawings are intended to illustrate the present invention only. Various variations and modifications of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention as set forth in the appended claims. 1 ·

Claims (9)

Identification method for identifying an object in a given region, in which a first electromagnetic field of predetermined frequency is generated in the region, characterized in that a second electromagnetic field of predetermined frequency is generated in the region simultaneously with the first field the frequency of the second field is chosen so that it deviates from the frequency of the first field, the first and second fields are monitored, and the object arriving at the range is identified by comparing the changes it causes in the first and second fields with predetermined reference values. 2. A method according to claim 1, characterized in that the frequency of the first field is chosen such that the presence of a predetermined resonator circuit in the field 20 causes a measurable change in the first field, and the frequency of the second field is chosen to deviate substantially from said one. resonator frequency resonators. Method according to Claim 1 or 2, characterized in that in addition to the first and second electromagnetic fields, several other electromagnetic fields are also generated in the region, the frequencies of which are selected when said resonant frequency of the resonator circuit, said other fields are monitored and the area of interest mentioned is identified by comparing the changes it causes in said electromagnetic field with predetermined reference; - cleaning values. 4. Identification device for identifying an object arriving at a given range, which device comprises transmitter means (1, 7, ANT) for generating a first electromagnetic field of predetermined frequency at said ... region and measuring means (ANT) , AMP, 2, 3, 6, 7) to measure the first field of said region, characterized in that it further comprises transmitter means (1, 7, ANT) for generating, at the same time as the first field, a second electromagnetic field of predetermined frequency in said region, wherein the first and second fields have deviating frequencies from each other, measuring means (ANT, AMP, 2, 3, 6, 7) for measuring the second electromagnetic field in said region and a controller (3) for comparing the values measured by the measuring means with predetermined reference values and to identify an object coming to the area on the basis of said comparison. 5. Device according to claim 4, characterized in that the transmitting means comprise a signal generator (1) arranged to generate a sum signal consisting of at least two sinusoidal signal components of different frequencies synchronized with each other to minimize the peak value of the sum signal. , and antenna means (ANT) for generating a first and second electromagnetic field in response to the sum signal. Device according to claim 4 or 5, characterized in that a memory means (4) is arranged adjacent to the control unit (3), in which memory means 25 reference values and operation data for several predetermined objects are stored, that the control unit (3) is arranged to input measure data for a given item into an indicator unit (5), where the values measured by the measuring means correspond to the reference values stored in the memory means (4) for the subject in question and the indicator unit (5) is arranged to in response to the action data, indicate an identified item. Device according to any of claims 4-6, characterized in that said identification device is a pointer alarm, the first electromagnetic field produced by transmitter means 95514 (1, 7, ANT) having a frequency of about 7.5 - 9. , 0 MHz, and the second electromagnetic field has a frequency of about 1 MHz, and the indicator unit (5) is arranged to indicate in response to the action data 5 an alarm, preferably by means of audio and / or light signals, where the values measured by the measuring means (ANT, AMP, 2, 3, 6, 7) correspond to the reference values stored in the memory means (4) for a predetermined resonator circuit or a metal object of a given size. 10 Device according to any of claims 4-7, characterized in that the transmitting means (1, 7, ANT) are arranged to produce, in addition to the first and second electromagnetic fields, several other electromagnetic fields of different frequencies in the area, that the measuring means (ANT, AMP, 2, 3, 6, 7) are arranged to measure all fields generated in the range, and that the controller (3) is arranged to identify an object coming to the range by comparing the values measured by the measuring means with predetermined reference values. 9