EP1315135A1 - Antenna for detection of tags - Google Patents

Abstract

The RF label detection method has a detection antenna (10) with two loops (1,2) connected to an HF head (21,22). The heads are connected to a multiplexer (5), providing common processing for each loop. The alarm (8) is set when a label is detected in either of the loops.

Description

The present invention relates to the field of the detection of radio frequency labels, in particular for the fight against theft of goods from stores.

The present invention relates more particularly to a label detection process radio frequency using at least one detection antenna having at least two loops.

The prior art already knows methods of radio frequency tag detection using an antenna detection.

The prior art knows, for example the demand French patent FR 2 402 255.

In this document, the antenna device is consisting of conductors connected in series so as to form a single closed circuit. This unique closed circuit is connected to a single transmitter or a single receiver.

In the processes of the prior art, the label detection is performed using a electronic device forming a whole.

An important drawback of these methods is that when the device fails, for example example an antenna loop that does not work, no detection is performed by the antenna.

The present invention intends to remedy the disadvantages of the prior art by proposing a method simple, inexpensive and efficient in which a failure in a detection loop does not cause failure of the whole detection antenna.

So part of the detection antenna can still work, even if another part of the detection antenna is out of order.

In addition, the method according to the invention allows optimization of the antenna detection field, so to remove any area of least sensitivity.

To do this, the present invention is type described above and it is remarkable, in its widest meaning, in that each loop is connected to an HF head, said HF heads themselves all connected to a single analog multiplexer for said antenna to allow common processing signal from each loop and an implementation of a alarm if a label is detected by at least one said loops.

Said signal processing for each loop is preferably operated at different times.

Said signal processing preferably includes digital filtering.

Said antenna preferably comprises a plurality of loops arranged so that their respective detection fields overlap and overlap complete.

The present invention also relates to an antenna for implementing the method according to the invention comprising at least two loops and at one device for implementing the method according to the invention comprising at least one detection antenna having at least two loops.

Advantageously, all the settings of sensitivity and tuning of each loop can be as well independently of each other and each loop can thus be adapted in a very specific way to the environment in which the detection device is implanted.

The detection carried out by the method according to the invention is only slightly influenced by the signals parasites.

Advantageously also, the method according to the invention makes it possible to carry out “hole-free” detection, that is to say without zone of least sensitivity, and this, whatever the position of the label vis-à-vis the antenna.

• la figure 1 illustre un schéma de principe du procédé selon l'invention ;
• la figure 2 illustre un schéma de principe d'un exemple de réalisation d'une antenne à deux boucles pour la mise en oeuvre du procédé selon l'invention ;
• la figure 3 illustre un schéma de principe d'un exemple de réalisation du filtrage digital pour la mise en oeuvre du procédé selon l'invention ;
• les figures 4, 5 et 6 illustrent respectivement des signaux lors de la détection d'une étiquette sur le milieu d'une antenne, lors de la détection d'une étiquette dans le bas d'une antenne et sans étiquette dans le champ de détection d'une antenne ; et
• les figures 7 et 8 illustrent respectivement une vue de face et une vue de côte d'une antenne selon l'invention.

The invention will be better understood using the description, given below for purely explanatory purposes, of an embodiment of the invention, with reference to the appended figures:

• Figure 1 illustrates a block diagram of the method according to the invention;
• FIG. 2 illustrates a block diagram of an exemplary embodiment of a two-loop antenna for implementing the method according to the invention;
• FIG. 3 illustrates a block diagram of an exemplary embodiment of digital filtering for the implementation of the method according to the invention;
• Figures 4, 5 and 6 respectively illustrate signals when detecting a label on the middle of an antenna, when detecting a label at the bottom of an antenna and without a label in the detection field an antenna; and
• Figures 7 and 8 respectively illustrate a front view and a side view of an antenna according to the invention.

The label detection process radio frequency according to the invention, illustrated in FIG. 1, is a radio frequency tag detection method using at least one detection antenna (10) comprising at least minus two loops (1, 2).

According to the method of the invention, each loop (1, 2) is connected to an HF head (20, 21), said HF heads (20, 21) being themselves all connected to a single analog multiplexer (5) for said antenna (10) to enable common processing of the signal of each loop (1, 2) and an implementation an alarm (8) if a label is detected by the at least one of said loops (1, 2).

Each loop (1, 2) is connected to a head high frequency HF (21, 22).

Each HF high frequency head (21, 22) includes tuning circuits, filters and demodulation of the signal of each loop.

The demodulated signal of each loop is sent in a single analog multiplexer (5) for a signal processing common to all loops the antenna, but performed at different times, operating in synchronization with time.

Processing includes the digital filter and the alarm (8) is triggered by the presence of a signal label for at least one of the loops (1, 2).

The alarm (8) can be an audible alarm and / or visual. It can be included in the antenna or remote outside the antenna and common to all the antennas of the detection device.

Each loop (1, 2) is connected to a head high frequency HF (21, 22), itself connected to the ground (20) of the antenna (10), as illustrated in FIG. 2.

In this figure, the loop (1) is in eight and the interlaced loop (2) in double eight, connected by the central part. These two loops (1, 2) can be juxtaposed in the antenna (10) so that their lower and lateral upper ends coincide and their respective detection fields overlap and to complement each other.

The filtering, illustrated in Figure 3, consists of add to the input signal, the delayed output signal of a period. This assumes that the signal is periodic with a period strictly equal to the delay used.

So the signal is amplified because it is at the good period; however, all spurious signals are eliminated because they are generally not at the right period. The transmitter scan signal must have a period strictly equal to the period caused by the analog delay.

To adjust the antenna (10) illustrated Figure 2, each HF head must be adjusted separately (21, 22) starting with the double loop, then the triple loop, then visualize on the oscilloscope (9) two successive periods in T3.

You have to put the sensitivity of the two HF heads (21, 22) at zero, then locate where the signal is corresponding to the double loop by playing on the sensitivity of the associated HF head (21), adjust the tuning antenna and sensitivity by presenting a label towards the middle of the antenna (10). Figure 4 illustrates the signal then obtained.

Then, it is advisable to carry out a test overall by moving the label from top to bottom and observing the signal. At the bottom of the antenna, the signal obtained is illustrated in Figure 5.

Figure 6 illustrates the signal obtained without label in the antenna reception field.

In T3, the signal obtained by the loop (1) or the signal obtained by loop (2) always has a sufficient amplitude to ensure the triggering of the alarm (8), one taking over from the other for effectively cover the entire detection area of the antenna.

The antenna (10) illustrated in FIGS. 7 and 8 presents, for example a height of 1420 centimeters for a width of 290 centimeters and a thickness of 3 centimeters.

The antenna (10) has a base (11), vertical (12) and horizontal (13) uprights, as well that a housing (14).

This configuration allows you to include inside the uprights (12, 13), the loop (1) in eight and the interlaced double eight loop (2), such as illustrated in figure 2, so that their detection fields respective overlap and complement each other. The housing (14) protects the electronic circuit including demodulation and filtering the signal from each loop and the multiplexing, digital filtering and processing of these signals, as well as the alarm (8).

The antenna (10) can be transmitting and receiving, or only receiving.

The invention is described in the foregoing to as an example. It is understood that the skilled person is at even to realize different variants of the invention without however, outside the scope of the patent.

Claims (6)

Method for detecting a radio frequency tag using at least one detection antenna (10) comprising at least two loops (1, 2), characterized in that each loop (1, 2) is connected to an HF head (20, 21), said HF heads (20, 21) being themselves all connected to a single analog multiplexer (5) for said antenna (10), in order to allow a common processing of the signal of each loop (1, 2 ) and an implementation of an alarm (8) in the event of detection of a label by at least one of said loops (1, 2). A radio frequency tag detection method according to claim 1, characterized in that said processing of the signal of each loop (1, 2) is carried out at different times. A method of detecting a radio frequency label according to claim 1 or claim 2, characterized in that said signal processing includes digital filtering. Method for detecting a radio frequency label according to any one of Claims 1 to 3, characterized in that the said antenna (10) has a plurality of loops (1, 2) arranged in such a way that their respective detection fields overlap and to complement each other. Label detection antenna (10) radio frequency for implementing the method according to one any of claims 1 to 4, comprising at least two loops (1, 2). Label detection device radio frequency for implementing the method according to one any of claims 1 to 4, comprising at least a detection antenna (10) comprising at least two loops (1, 2).

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