RFID detection device for locating stored objects

Abstract

The invention relates to a device for locating (1) objects (21, 22, 23) stored in a compartment (6) comprising a plurality of storage spaces (11, 12, 13, 14, 15, 16); each object (21, 22, 23) being equipped with an RFID tag (210, 220); said object locating device comprising: - a plurality of inhibitor circuits (41, 42, 43, 44) intended to be placed each in an associated storage space and configured to inhibit the reading of the RFID tag of said object by an RFID reader (3), a control unit (5) configured to control the activation of the inhibitor circuits according to a predetermined activation sequence; a locating unit (2) configured to control the RFID reader (3);and to receive, at each step of the activation sequence, a list of identifiers of the objects stored in the locker provided by the RFID reader, and configured to identify the storage space (11, 12, 13, 14) of each object from the identifier lists and the activation sequence. Figure for the abbreviation: Fig.1a;

Description

Title of the invention: Device for locating stored objects by RFID detection

[0001] Scope of application

[0002] The present invention relates to the field of locating objects having RFID tags, stored in a locker, via a sequence of activation / deactivation of the detection of the RFID tags by a dedicated reader.

[0003] Problem raised

[0004] Thus, the radiofrequency communication technique known as RFID can be used for detecting the presence of physical objects in general. This technique is compatible with storage, logistics and object presentation applications.

[0005] Each stored object is provided with an RFID tag in order to retrieve data remotely ("RFID tag" in English). The RFID tags of the stored objects contain an identifier of the object and potentially other useful information on the object such as its nature, its commercial name, its type.

[0006] Standards have been published concerning these devices, for example ISO 14443 for "contactless cards" and ISO 18000-3 for "radio tags" operating at a frequency of 13.56 MHz.

[0007] In these devices, a link is established by radiofrequency magnetic field between the reader and one or more tags. The coupling members are conductive circuits in the form of loops, windings or coils which are called "antenna circuits or antenna windings".

[0008] Thus, reading the RFID tags of the objects stored in the locker can be carried out by an RFID reader comprising an antenna making it possible to read all the Active "radio-tags" of the objects present. The antenna is made of conductive windings constituting an inductive circuit. Reading is carried out by magnetic coupling between the antenna and the RFID tags at a predetermined resonant frequency allowing the exchange of information. Thus, it is possible to have a list of the objects present in the locker. This is particularly useful in inventory activities of stored objects for example.

[0009] The locker comprises a plurality of storage spaces delimited physically (partitions, walls) or virtually (by a signage marker). The disadvantage of known solutions for this type of object storage device is that exploration by RFID communication is limited to the detection and referencing of the objects present without being able to locate the location of each object in the locker.

[0010] There is therefore a need to develop a solution for locating objects stored in a locker comprising a plurality of storage spaces.

[0011] Prior art / State of the art restrictions

[0012] Patent application WO200845075 describes a game board equipped with an array of antennas forming several reading paths for an RFID-type radiofrequency link. Objects equipped with an RFID tag are arranged above this board. This solution is only applicable for high frequencies; it requires that the dimensions of the antenna are not too small compared to the resonance wavelength. Furthermore, this solution is not compatible with an inductive-type RFID radiofrequency link. The major drawback consists of the necessary use of a plurality of reading antennas to achieve localization. This approach places the complexity on the structure of the reader's antenna, in the form of a network of switched antennas. This leads to hardware implementation complexity and high energy consumption. Statement of the invention

[0013] The subject of the invention is a device for locating objects stored in a locker comprising a plurality of storage spaces; each object being equipped with an RFID tag; said object locating device comprising: - a plurality of inhibitor circuits each intended to be placed in an associated storage space and configured to, when one of said objects is stored in the associated storage space and when said inhibitor circuit is activated, inhibit the reading of the RFID tag of said object by an RFID reader, - a control unit configured to control the activation of the inhibitor circuits according to a predetermined activation sequence; - a location unit configured to control the RFID reader; and to receive, at each step of the activation sequence, a list of identifiers of the objects stored in the locker provided by the RFID reader, and configured to identify the storage space of each object from the lists of identifiers and the activation sequence.

[0014] According to a particular aspect of the invention, the inhibitor circuit is capable of transposing the resonance frequency of the RFID tag to a second resonance frequency by magnetic coupling when it is activated.

[0015] According to a particular aspect of the invention, the activation sequence comprises: - an initialization step in which all the inhibitors are deactivated so as to list all the objects stored in the locker; - a succession of steps in which only part of the inhibitors are activated according to the activation sequence.

[0016] According to a particular aspect of the invention, the location device according to the invention further comprises said locker; such that the storage spaces are dimensioned so that the magnetic coupling coefficient between on the one hand an inhibitor circuit and on the other hand the RFID tag of the object placed in the storage space associated with said inhibitor circuit, is between 0.5 and 1.

[0017] According to a particular aspect of the invention, the second resonant frequency is between 5 MHz and 10 MHz.

[0018] According to a particular aspect of the invention, each inhibitor comprises: - an LC type circuit comprising at least one inductive element connected in series with at least one capacitive element, - a voltage-controlled switch to control the closing of said LC type circuit.

[0019] According to a particular aspect of the invention, the voltage-controlled switch comprises a PIN-type diode having a first electrode connected to a first control voltage and a second electrode, the conductivity state of the PIN-type diode being controlled by a bias circuit.

[0020] According to a particular aspect of the invention, the biasing circuit comprises a trap circuit between the first electrode of the diode and the first control voltage; the trap circuit having a high impedance at the resonant frequency of the RFID tag corresponding to the configuration of a deactivated inhibitor circuit.

[0021] According to a particular aspect of the invention, the voltage-controlled switch is produced by a CMOS type transistor.

[0022] According to a particular aspect of the invention, the inhibitors are produced on a substrate, for each inhibitor circuit, the inductive element is produced by at least one first flat coil comprising a plurality of spiral metal tracks deposited on at least one face of said printed circuit.

[0023] According to a particular aspect of the invention, the inductive element further comprises a second circular planar coil and wherein the first coil is of circular shape having a diameter equal to that of the second planar coil. Brief description of the drawings

[0024] Other characteristics and advantages of the present invention will appear better on reading the description which follows in relation to the following appended drawings:

[0025] [Fig. la] [Fig. la] illustrates a top view of a diagram of the location device according to the invention.

[0026] [Fig.lb] [Fig.lb] illustrates a front view of a part of the location device according to the invention.

[0027] [Fig.2] [Fig.2] illustrates a flowchart of the steps in the control sequence of the operation of the location device according to the invention.

[0028] [Fig.3] [Fig.3] illustrates an inhibitor circuit according to a first embodiment of the invention.

[0029] [Fig.4a] [Fig.4a] illustrates an example of the field response gain curve magnetic of the assembly formed by the RFID tag of an object and the inhibitor circuit when the associated inhibitor circuit is activated and the gain curve of the RFID tag of an object when the associated inhibitor circuit is deactivated.

[0030] [Fig.4b] [Fig.4b] illustrates an example of the voltage gain curve across the antenna circuit of an object's RFID tag when the associated inhibitor circuit is activated and the gain curve of an object's RFID tag when the associated inhibitor circuit is deactivated.

[0031] [Fig.5a] [Fig.5a] illustrates the inhibitor circuit according to a second embodiment of the invention.

[0032] [Fig.5b] [Fig.5b] illustrates the inhibitor circuit according to a third mode of rea lization of the invention.

[0033] [Fig.6a] [Fig.6a] illustrates a top view of an example implementation of the inhibitor circuit according to the invention.

[0034] [Fig.6b] [Fig.6b] illustrates a sectional view of an example implementation of the inhibitor circuit according to the invention.

[0035] [Fig. 1a] illustrates a top view of a diagram of the location device 1 according to the invention. The object location device 1 comprises a locker 6 comprising a plurality of storage spaces for accommodating stored objects; an RFID reader 3; a plurality of inhibitor circuits 41, 42, 43, 44 each intended to be placed in an associated storage space; a control unit 5 and a location unit 2.

[0036] In order to illustrate the invention for informational and non-limiting purposes, we will describe a locker 6 comprising six storage spaces 11 to 16 and in which two objects are stored: the object 21 stored in the storage space 11 and the object 22 stored in the storage space 14. The storage spaces are delimited by physical obstacles (of the wall or partition type) or by a sign to delimit the storage spaces. The object 21 is equipped with an RFID tag 210. The RFID tag 210 stores information making it possible to identify the object 41 such as an identifier noted A. The object 22 is equipped with an RFID tag 220. The RFID tag 220 stores information making it possible to identify the object 22 such as an identifier noted B.

[0037] The RFID reader 3 comprises an antenna 32 covering the entire surface of the locker 6 in combination with a processing circuit 31. The antenna is capable of detecting objects present in the locker by magnetic coupling with the associated RFID tags. The processing unit 31 is configured to generate a list L; of identifiers associated with the objects detected by the antenna 32.

[0038] An inhibitor circuit 41 to 46 is placed at the bottom of each storage space 11 to 16 of the locker 6. Each inhibitor circuit is configured to inhibit the reading of the RFID tag of the object stored in its associated storage location by the RFID reader 3. When the inhibitor circuit is deactivated, the detection of the object stored in the storage space associated with said inhibitor circuit is achievable via the RFID reader by magnetic coupling at a first resonant frequency called “working frequency”. Generally speaking, the working frequency is predetermined by construction of the RFID system, RFID reader 3 associated with the RFID tags (210 and 220). The RFID antenna 32 is connected to the processing unit 31 which generates the HF signal applied to the antenna 32 and determines the working frequency. In the illustrated case, when the inhibitor circuit 41 is activated, the detection of the object 21 by the RFID antenna 32 is inhibited.When the inhibitor circuit 41 is deactivated, the detection of the object 21 by the RFID antenna 32 is achievable at the predetermined working frequency. Similarly, when the inhibitor circuit 44 is activated, the detection of the object 22 by the reader 3 via its RFID antenna 32 is inhibited. When the inhibitor circuit 44 is deactivated, the detection of the object 22 by the reader 3 via its RFID antenna 32 is achievable at the predetermined working frequency.

[0039] In order to obtain the effect of inhibiting RFID reading, each inhibitor circuit must be placed in the storage space so as to be close to the RFID tag of the object when the latter is stored in said storage space. The expression "close" means a position in a sphere with a radius of less than 10 mm from the inhibitor. The proximity between the inhibitor circuit and the tag of the stored object makes it possible to maximize the magnetic coupling between these two components. The action of the inhibitor circuit on the reading of a tag is effective when the magnetic coupling coefficient between the two antenna circuits, that of the inhibitor and that of the RFID tag, is between 0.5 and 1. Advantageously, the stored object is placed so as to align its RFID tag with the associated Inhibitor, and so as to minimize the distance between them, in order to maximize the magnetic coupling coefficient. [Fig.lb] illustrates an example with optimization of the magnetic coupling coefficient between each RFID tag and the associated inhibitor circuit. Indeed, the storage spaces 11, 13 and 15 of the locker 6 are delimited by the physical walls 111, 131, 151 and 161. The delimitation by physical walls ensures the alignment between the RFID tag of each object placed with the inhibitor circuit housed at the bottom of the storage space dedicated to said object. The distance separating an inhibitor circuit from the tag of the stored object varies between 0.5 mm and 5 mm along the vertical axis (y). This . allows to maximize the magnetic coupling coefficient between the inhibitor circuit and the RFID tag of a stored object and therefore improve the inhibition performance of each inhibitor circuit.

[0040] The control unit 5 is configured to control the activation of the inhibitor circuits 41, 42, 43 and 44 according to a predetermined activation sequence. An example of a possible activation sequence will be detailed in a later section. Each inhibitor circuit is controlled by its own control signal. This makes it possible to produce several combinations of inhibition configurations by activating at least part of the inhibitor circuits during each step of the activation sequence. For example, the inhibitor circuit 41 associated with the storage space 11 is controlled by the control signal Vcont41 coming from the control unit 5. For example, it is possible to produce the control unit 5 by a programmable microcontroller. The control signals are propagated via wired electrical connections.

[0041] The location unit 2 is configured to receive, at each step of the activation sequence, a list of identifiers of the objects stored in the locker provided by the RFID reader 3. In addition, the location unit is configured to identify the storage space of each object from the lists of identifiers and the activation sequence. This is a data processing operation that can be carried out by a calculation algorithm implemented in a calculator or a computer. The location unit 2 further controls the control unit 5 according to the reading results provided by the processing circuit 3L. Indeed, the location unit 2 sends the reading orders to the processing unit 31 and collects the reading results (for example the list of identifiers of the RFID tags read).

[0042] During reading, two tags can transmit their identifiers in the same detection time slot, thus making the message incomprehensible to the reader; it is then said that there is a collision. The location unit 2 according to the invention can use the collision information to locate the location of the objects stored in the locker 6. The collision information can then be used in the context of the invention. The reader 3 is configured according to a mode that does not process collisions. This makes it possible to reduce the execution time of the location operation by the object location device according to the invention. [Fig. 2] illustrates a flowchart of the steps of an example of an activation sequence of the network of inhibitor circuits according to the invention. This is a non-limiting example to illustrate the invention. A person skilled in the art can adapt the sequence according to the precision time constraints of the implementation of the invention.The activation sequence will be applied to the example illustrated in [Fig.1a].

[0043] The first step (100) of the activation sequence SI consists of a step initialization in which the location unit 2 sends a first inhibition command order to the control unit 5 to deactivate all the inhibitor circuits 41 to 46. Then, the location unit 2 sends an inventory reading order to the RFID reader 3. The processing circuit 31 of the RFID reader 3 generates a first list Lo comprising the identifiers of all the objects present in the locker, namely the object 21 and the object 22. We note L0={21,22} with all the inhibition circuits deactivated.

[0044] The second step (200) consists of activating only the inhibitor circuit 41 associated with the storage space 11. Following a reading by the antenna 32, the processing circuit 31 of the RFID reader 3 generates a second list Li comprising only the identifier of the object 22. We note Li={22] with the inhibitor circuit 41 activated. This means that the object 21 which does not appear in the list Li is stored in the storage space 11 associated with the activated inhibitor circuit 4L

[0045] The third step (300) consists of activating only the inhibitor circuit 42 associated with the storage space 12. Following a reading by the antenna 32, the processing circuit 31 of the RFID reader 3 generates a third list L2 identical to the first list Lo. This makes it possible to deduce that no object is stored in the storage space 12 associated with the activated inhibitor circuit 42.

[0046] The fourth step (400) consists of activating only the inhibitor circuit 43 associated with the storage space 13. In the same way as step (200), a list L3 identical to the first list Lo is obtained. This makes it possible to deduce that no object is stored in the storage space 13 associated with the activated inhibitor circuit 43.

[0047] The fifth step (500) consists of activating only the inhibitor circuit 44 associated with the storage space 14. Following a reading by the antenna 32, the processing circuit 31 of the RFID reader 3 generates a fifth list L4 comprising only the identifier of the object 21. This means that the object 22 which does not appear in the list L4 is stored in the storage space 14 associated with the activated inhibitor circuit 44.

[0048] All the objects detected in the initialization step have been located in the locker. It is not necessary to continue to browse the other inhibition configurations. The calculation of the location (by elimination here) from the generated lists L; and the inhibition configuration of each step of the sequence SI, is carried out by the location unit 2. The location unit 2 is carried out by a programmable computer. The lists L; are provided by the RFID reader 3 to the location unit 2, following an exhaustive inventory command.

[0049] The illustrated example makes it possible to precisely locate the location of each stored object by activating (or deactivating) the inhibitors 41 to 46 one by one. However, it is conceivable to activate a group of inhibitor circuits so as to cover a predefined region of the locker for each step. As an example, it is in faceable to activate all the inhibitor circuits belonging to the same row (or column) of locker 6 (in the case of a matrix of storage spaces). This allows for rapid location of the objects stored in locker 6. Indeed, for an identifier present in the inventory list of a row of inactive inhibitor circuits and that of a column, we can deduce that it is present in the intersection box of said row and said column.

[0050] [Fig. 3] illustrates an inhibitor circuit according to a first embodiment of the invention. Each inhibitor circuit comprises an LC-type circuit comprising at least one inductive element L1 connected in series with at least one capacitive element C1 and a voltage-controlled CCT switch for controlling the closing of said LC-type circuit. When the CCT switch is in the blocking state (high impedance), the series LC circuit is in an open circuit. When the CCT switch is in the conducting state, the LC circuit is a closed circuit. The CCT switch is controlled by the signal Vcont coming from the control unit 5. Control with an electrical voltage offers better performance, reduced energy consumption, reduced size and better technological robustness compared to a mechanical switch.The sizing of the capacitive element Cl and the inductive element Ll is chosen so as to transpose the resonant frequency fi of the RFID tag of the object stored in the associated storage space, to a second resonant frequency f2 by magnetic coupling when the LC circuit is closed. The voltage at the working frequency (for example 13.56 MHz) at the terminals of the antenna circuit of the tag subjected to the electromagnetic field of the RFID reader can thus go from a few volts allowing the operation of the RFID chip of the tag, to a residual voltage of a few hundred mV insufficient for the RFID chip to be able to operate.

[0051] As an example, the inductance of the inductive element is equal to 2.2pH and the capacitance of the capacitive element Cl is equal to 120pF. This makes it possible to shift the voltage resonant frequency of the tag antenna circuit from an initial value fi= 13.6MHz to a second resonant frequency f2=7.9MHz when the inhibitor circuit is activated (CCT switch on). The previous dimensioning example has a quality factor of 40. Generally, in the context of the invention, the second resonant frequency f2 is between 5MHz and 10MHz.

[0052] Generally speaking, when the inhibitor circuit is activated, the voltage gain across the associated RFID tag is divided by 10 at the initial working frequency compared to the configuration without inhibition.

[0053] [Fig.4a] illustrates an example of the gain curve Cl in magnetic field response of the assembly formed by the RFID tag of an object and the inhibitor circuit when the associated inhibitor circuit is deactivated and the gain curve C2 in response to the magnetic field of the assembly formed by the RFID tag of an object and the inhibitor circuit when the associated inhibitor circuit is activated. The RFID tag 210 (or 220) of the object 21 (or 22) is detectable by the RFID reader 3 at a working frequency around the first resonance frequency fl. The energy exchanged between the antenna 32 and the RFID tag 210 during a reading is maximum at this frequency as illustrated by the peak of the curve CL. Activation of the LC circuit of the inhibitor circuit shifts the gain curve to obtain the curve C2 corresponding to the assembly formed by the inhibitor and the RFID tag seen by the antenna 32. Activation of the LC circuit thus transposes the resonance frequency to a value f2 different from the working frequency fl of the RFID antenna 32.Thus, the detection of the object 21 (or 22) by the RFID reader 3 is inhibited by frequency shift between the antenna 32 (designed for fl detection) and the target to be read having a frequency shifted by magnetic coupling with the activated inhibitor circuit.

[0054] [Fig.4b] illustrates an example of the gain curve C' 1 in voltage across the antenna circuit of the RFID tag of an object when the associated inhibitor circuit is deactivated and the gain curve C'2 in voltage across the antenna circuit of the RFID tag of an object when the associated inhibitor circuit is activated. The RFID tag 210 (or 220) of the object 21 (or 22) is detectable by the RFID reader 3 at a working frequency around the first resonance frequency fb The energy exchanged between the antenna 32 and the RFID tag 210 during a reading is maximum at this frequency as illustrated by the peak of the curve C' 1. The activation of the LC circuit of the inhibitor circuit shifts the gain curve to obtain the curve C'2 corresponding to the voltage across the antenna circuit of the RFID tag that the antenna 32 can induce.In the illustrated case, the gain curve C'2 has a first resonance peak A corresponding to the frequency f2A and a second peak B at a frequency f2B higher than the resonance frequency f2A. The activation of the LC circuit thus causes a voltage gain curve with a first resonance frequency f2A lower than the working frequency C and a second resonance frequency f2B higher than the working frequency fb. The voltage gain around the frequency C is divided by 10 compared to the configuration without inhibition (curve C' 1). Thus, the detection of the object 21 (or 22) by the RFID reader 3 is inhibited by frequency shift between the antenna 32 (designed for detection at C) and the target to be read having a frequency shifted by magnetic coupling with the activated inhibitor circuit.

[0055] [Fig.5a] illustrates an inhibitor circuit according to a second embodiment of the invention; and more particularly an example of implementation of the voltage-controlled CCT switch. The CCT switch comprises a PIN type diode (from the English Positive Intrinsic Negative diode) 410 having a first electrode El and a second electrode E2. The second electrode E2 is connected to ground through a control transistor T1. The first electrode El is connected to the inductive element L1 of the LC circuit. The second electrode E2 is connected to the capacitive element Cl of the LC circuit. The electrical potential on the first electrode El and on the second electrode E2 are controlled by a biasing circuit CL. When the PIN diode is biased in the forward direction, its impedance is low and it is in an on state. When the PIN diode is biased in the indirect direction, its impedance is high and it is in a off state. The biasing circuit CL includes a logic gate log1 which receives the control signal Vcont from the control unit 5. The logic gate adapts the input signal Vcont (digital signal) to be compatible with the biasing of the PIN diode.The bias circuit CL further comprises a resistor R connected in series between the output of the logic gate log1 and the node El in order to control the current flowing through the PIN diode in its on state. The intensity of the current flowing through the PIN diode is between 1mA and 10mA. When the signal Vcont is in a high logic state, the node El is at a high electrical potential received through the logic gate log1 and the resistor R, and the transistor Tl is on so as to bring the electrical potential of the node E2 to ground. This induces a forward bias of the PIN diode 410. This induces the closing of the LC circuit and therefore the activation of the inhibitor circuit.

[0056] The advantage of using the PIN type diode is that the low impedance effect in the on state is accentuated for RF radiofrequency electrical signals. In addition, by adapting the currents and voltages to the bias points of the diode, the reliability and technical robustness of the CCT switch are improved compared to other switching solutions (mechanical switching for example).

[0057] [Fig.5b] illustrates an inhibitor circuit according to a third embodiment of the invention; and more particularly an alternative example of implementation of the voltage-controlled switch CCT. The bias circuit CL comprises an inverter INV in place of the transistor TL. The inverter is capable of inverting the logic state of the control signal Vcont towards the electrode E2. The bias circuit CL further comprises a trap circuit CBn mounted between the first electrode El and the resistor R. The trap circuit CBn comprises a capacitive element Cn mounted in parallel with an inductance Lu. The trap circuit CBn is sized to have a high impedance at the working frequency fb. This makes it possible to isolate the bias circuit CL from the circuit LiCi of the inhibitor circuit. More particularly, the trap circuit makes it possible to separate the direct electrical signals (DC) biasing the PIN diode from the high-frequency signals (HF and more particularly 13).56MHz) of the resonant circuit Ll, CL.

[0058] [Fig.6a] illustrates a top view of an example implementation of the circuit in inhibitor according to the invention. [Fig.6b] illustrates a sectional view of an exemplary implementation of the inhibitor circuit according to the invention. The illustrated exemplary implementation is carried out on a PCB-type printed circuit. The PCB-type printed circuit is called a “selection board” and can be mounted below the compartment 6.

[0059] The inductive element L1 is made by two flat coils B1 and B2. Each coil comprises a plurality of spiral metal tracks. The first coil B1 is deposited on a first face of the printed circuit PCB. The second coil B2 is deposited on the opposite face of the printed circuit PCB. The two coils B1 and B2 may be identical. For example, each coil comprises six circular turns for an overall diameter of 14 mm. The turns are metal tracks with a width of 0.2 mm spaced at a pitch of 0.4 mm. The two coils B1 and B2 are connected in series across the capacitive element CL. The capacitive element Cl is implemented on one face of the PCB substrate.

[0060] The first end of the first coil B1 is connected to the first electrode El of the PIN diode not shown here (or to the first electrode of the switch in general). The second end of the first coil B1 is connected to a terminal of the capacitive element CL

[0061] The first end of the second coil B2 is connected to the second electrode E2 of the PIN diode not shown here through a via not shown here (or to the second electrode of the switch in general). The second end of the second coil B2 is connected to the other terminal of the capacitive element C1 through a via VIA1.

[0062] Alternatively, the capacitive element C1 is placed in an area inside the circle defined by the coil B1. The PIN diode 410 is placed in an area outside the circle defined by the coil B1. The electrical connections between the coils B1, B2 and the capacitive element C1 are made by vias passing through the PCB substrate.

[0063] This implementation has a planar structure of the inhibitor circuit allowing simple integration into the object location device according to the invention. The plurality of inhibitor circuits can be produced on a single “selection plate” which is mounted below the plane of the locker 6. This compact integration makes it possible to ensure better magnetic coupling between the inhibitor circuits and the RFID tags of the objects placed in the associated storage spaces. Indeed, only the thickness of the bottom of the locker, of the order of a few millimeters, separates the inhibitor circuit from the RFID tag of the stored object.

[0064] Alternatively, it is possible to produce each inhibitor circuit on a dedicated printed circuit. This allows the same inhibitor circuit design to be reproduced several times depending on manufacturing needs.

Claims

Claims

1. Device (1) for locating objects (21, 22, 23) stored in a locker (6) comprising a plurality of storage spaces (11, 12, 13, 14, 15, 16); each object (21, 22, 23) being equipped with an RFID tag (210, 220); said object locating device (21, 22, 23) comprising: - a plurality of inhibitor circuits (41, 42, 43, 44) each intended to be placed in an associated storage space and configured to, when one of said objects is stored in the associated storage space and when said inhibitor circuit (41, 42, 43, 44) is activated, inhibit the reading of the RFID tag (210, 220, 230) of said object by an RFID reader (3), - a control unit (5) configured to control the activation of the inhibitor circuits (41, 42, 43, 44) according to a predetermined activation sequence; - a locating unit (2) configured to control the RFID reader (3);and to receive, at each step of the activation sequence, a list of identifiers of the objects stored in the locker provided by the RFID reader (3), and configured to identify the storage space (11, 12, 13, 14) of each object from the lists of identifiers and the activation sequence.;

2. Device (1) for locating objects (21, 22, 23) according to claim 1, in which the inhibitor circuit is capable of transposing the resonant frequency of the RFID tag to a second resonant frequency by magnetic coupling when it is (41, 42, 43, 44) activated.

3. A locating device (1) according to claim 2 wherein the second resonant frequency (f2) is between 5MHz and 10MHz.

4. Location device (1) according to any one of claims 1 to 3 in which the activation sequence comprises: - an initialization step in which all the inhibitors are deactivated so as to list all the objects stored in the locker; - a succession of steps in which only some of the inhibitors are activated according to the activation sequence.

5. Location device (1) according to any one of the preceding claims further comprising said locker; such that the storage spaces (11, 12, 13, 14) are dimensioned so that the magnetic coupling coefficient between on the one hand an inhibitor circuit (41, 42, 43, 44) and on the other hand the RFID tag (210, 220, 230) of the object placed in the storage space (11, 12, 13, 14) associated with said inhibitor circuit, is between 0.5 and 1.

6. Location device (1) according to any one of the preceding claims in which each inhibitor (41, 42, 43, 44) comprises: - an LC type circuit comprising at least one inductive element (Ll) connected in series with at least one capacitive element (Cl), - a voltage-controlled switch (CCT) for controlling the closing of said LC type circuit;

7. Locating device (1) according to the preceding claim wherein the voltage controlled switch (CCT) comprises a PIN type diode (410) having a first electrode (El) connected to a first control voltage (VI) and a second electrode (E2), the conductivity state of the PIN type diode (410) being controlled by a bias circuit (CL).

8. Location device (1) according to the preceding claim wherein the bias circuit (CL) comprises: - a logic gate (logl) configured to adapt a digital control signal (Vcont) to the bias of the PIN type diode (410); - a resistor (R) connected in series with the logic gate (logl); - a trap circuit (CBn) connected between the first electrode (El) of the diode (410) and the resistor (R); the trap circuit (CBn) having a high impedance at the resonant frequency of the RFID tag corresponding to the configuration of a deactivated inhibitor circuit.

9. Location device (1) according to claim 6 wherein the voltage-controlled switch (CCT) is produced by a CMOS type transistor.

10. A locating device (1) according to any one of the claims 6 to 8 in which the inhibitors are made on a printed circuit board (PCB), for each inhibitor circuit, the inductive element (Ll) is produced by at least one first flat coil (Bl) comprising a plurality of spiral metal tracks deposited on at least one face of said printed circuit.

11. A locating device (1) according to the preceding claim wherein the inductive element further comprises a second circular planar coil (B2) and wherein the first coil is circular in shape having a diameter equal to that of the second planar coil.

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