Device for the electromagnetic shielding of a radio frequency tag, assembly comprising an electromagnetic shielding device and a radio frequency tag and method for electromagnetically shielding a radio frequency tag

Abstract

The invention relates to a device (8) for the electromagnetic shielding of a HF radio frequency tag, forming a low-pass filter for frequencies below 100 MHz, the frequencies between 2 and 4 GHz being filtered by more than 50%, preferably by more than 90%, which device comprises a protective layer (9) protecting against mechanical and chemical attacks and comprising a first surface for cooperating with the tag, and a second surface opposite the first surface, which device further comprises a metal conductive pattern (10) with a thickness of less than 20 microns, in contact with the first or the second surface and protected by the protective layer (9), the conductive pattern (10) being periodic, the conductive pattern (10) having a line width of less than 2 mm, and the conductive pattern having a minimum convex radius of at least 0.30 mm.

Description

Description Title of the invention: ELECTROMAGNETIC SHIELDING DEVICE FOR RADIO FREQUENCY LABEL, ASSEMBLY COMPRISING AN ELECTROMAGNETIC SHIELDING DEVICE AND A RADIO FREQUENCY LABEL AND METHOD FOR ELECTROMAGNETIC SHIELDING OF RADIO FREQUENCY LABEL

[0001] The invention relates to the field of tableware or kitchenware made of durable material. Tableware includes plates, platters, hollow containers such as soup tureens or vegetable bowls, glasses, carafes, pitchers, ramekins, etc. Kitchenware partly overlaps with tableware. Kitchenware includes containers in which food is prepared, in particular cut, ground or cooked.

[0002] Disposable tableware made from petrochemical materials was used until recently. The high consumption of energy and raw materials, as well as the generation of polluting waste, is leading to a reconsideration, or even a ban, of disposable tableware.

[0003] There is a need to efficiently manage a fleet of tableware in a professional catering establishment, particularly a mass catering establishment. From another perspective, contactless payment without cashiers is growing.

[0004] The emergence of self-service canteens with a need for tableware connected to contactless payment terminals has led to numerous proposals for reusable glass containers (dishes, plates, ramekins) that can be digitally traced or tracked using contactless solutions such as RFID.

[0005] However, the connected tableware item could be damaged when put in the dishwasher or microwave.

[0006] Furthermore, the price of a tableware item requires the use of a standard RFID tag produced in large quantities. However, the applicant observed that a standard RFID tag does not withstand being placed in a microwave oven due to the occurrence of short circuits or thermal destruction likely to cause a fire.

[0007] FR3125149 describes an RFID tag device equipped on one side with a layer of silicone material and having a dielectric permittivity greater than at least three times the dielectric permittivity of Pair and having a thickness of at least 6 millimeters. A waveguide is formed by 3D stacking. The RFID tag is provided on one side with a layer of copper plate with a thickness of at least 3 times, or even 10 times, the depth of Microwave penetration at 2.45 GHz. The RFID tag has an operating frequency of 868 MHz. However, the figures show an antenna unsuitable for this frequency. The overall thickness is very high.

[0008] The Applicant also noticed that certain prior art devices boasting microwave resistance were in reality content with preserving the external appearance of the RFID tag after being subjected to microwaves but did not offer multiple uses with a succession of a large number of microwave heating and washing cycles of the tableware item.

[0009] The applicant sought to offer real benefits to consumers with the reuse of containers made of durable material allowing repeated use, the durability of the communication function of said containers, and the quality of remote transmission.

[0010] The invention improves the situation.

[0011] The invention proposes an electromagnetic shielding device for an HF radio frequency tag, forming a low-pass filter for frequencies below 100 MHz, frequencies between 2 and 4 GHz being filtered at more than 50%, preferably at more than 90%, comprising a protective layer against mechanical and chemical attacks comprising a first surface for cooperating with the tag and a second surface opposite the first surface, and a metallic conductive pattern with a thickness of less than 20 microns, in contact with the first or second surface and protected by the protective layer. The conductive pattern is periodic. The conductive pattern has a line width of less than 2 mm. The conductive pattern has a minimum convex radius of at least 0.30 mm. The electromagnetic shielding is dishwasher-resistant, microwave-resistant, generates little heat under the effect of microwaves and is durable.Thus, the functions offered at first use are retained for subsequent uses.

[0012] In one embodiment, the conductive pattern is made from silver or copper and the protective layer comprises a vitreous enamel. Conduction is high. Heating is low. Protection against chemical agents is effective.

[0013] In one embodiment, the conductive pattern has a thickness of less than 15 microns, the protective layer has a thickness of less than 20 microns. The electromagnetic shielding is permeable to HF radio waves and effective against waves beyond 1 GHz. Thus, the electromagnetic shielding is sufficiently permeable in NFC mode and sufficiently impermeable in UHF mode. Said permeability allows communication with an electronic tag. Said impermeability allows the electronic tag to withstand heating microwaves.

[0014] In one embodiment, the conductive pattern has a line width of less than 0.5 mm and a width between lines of less than 4 mm, preferably less than 1 mm. Heating is low.

[0015] In one embodiment, the conductive pattern is single-layer and the shielding layer is single-layer. The electromagnetic shield is very thin and compact. The thickness of the electromagnetic shield is less than 40 microns.

[0016] In one embodiment, the conductive pattern is continuous in the form of closed meshes or open patterns, in particular spirals. The risk of short circuiting is low.

[0017] In one embodiment, the electromagnetic shield is attached to a microwave oven tray, on the upper side. The electromagnetic shield is thus positioned to protect an electronic tag attached to the lower side of a piece of crockery that is placed on the tray for the purpose of heating food placed on or in the piece of crockery.

[0018] In one embodiment, the electromagnetic shield has rounded, tetrasceles-shaped closed meshes.

[0019] In one embodiment, the electromagnetic shield has rounded closed meshes in the shape of a trisceles, pentasceles or hexasceles.

[0020] In one embodiment, an assembly comprises an HF radio frequency tag electromagnetic shielding device and an HF radio frequency tag, wherein the maximum dimension of the conductive pattern is at least equal to the maximum dimension of the tag, preferably at least equal to 1.2 times the maximum dimension of the tag. The assembly may be attached to a small tableware item, for example, a tumbler or drinking glass.

[0021] In one embodiment, a piece of tableware for household or professional use comprises an assembly as above. The electromagnetic shielding device and the radio frequency tag are arranged in a concavity provided in the piece of tableware. The assembly may be affixed to a tableware item, for example to an existing hollow on the underside of said tableware item.

[0022] In one embodiment, a dinnerware item includes a body made of ceramic, soda-lime glass, borosilicate glass, crystalline, stoneware, earthenware, porcelain, wood, or plastic. The dinnerware item is durable. The dinnerware item may be returnable.

[0023] In one embodiment, a method for electromagnetically shielding an HF radio frequency tag is provided, comprising providing a piece of tableware, affixing an electromagnetic shielding device to the piece of tableware, and attaching an HF radio frequency tag to said device. The electromagnetic shielding may be formed at elevated temperature, for example at least 600° and the RFID tag may be disposed after cooling.

[0024] In one embodiment, the electromagnetic shielding may be formed at low temperature, in particular less than 100°, for example at room temperature. The electromagnetic shielding may comprise a pattern affixed to a plastic wall, in particular food-grade plastic. The electromagnetic shielding may comprise a pattern affixed to a plastic film.

[0025] In one embodiment, the electromagnetic shielding device is deposited by pad printing, screen printing, inkjet or metal film deposition. The yield is high for articles having non-planar surfaces.

[0026] In one embodiment, the conductive pattern is provided in the form of a metallic ink. The metallic ink is suitable for pad printing and for flat or non-flat surfaces.

[0027] In one embodiment, a method for electromagnetically shielding an HF radio frequency tag is provided, comprising providing an HF radio frequency tag, affixing an electromagnetic shielding device to the HF radio frequency tag, and affixing a protective varnish. The method is simple to implement.

[0028] Other characteristics and advantages of the invention will appear on examining the detailed description below, and the attached drawings, in which:

[0029] [Fig.1 ] . is a top view of radio frequency tags according to one aspect of the invention.

[0030] [Fig.2] . is a side elevational view of a piece of tableware equipped with a radio frequency tag and electromagnetic shielding device assembly according to one aspect of the invention.

[0031] [Fig.3] is a bottom elevation view of a piece of tableware equipped with a radio frequency tag and electromagnetic shielding device assembly according to another aspect of the invention.

[0032] [Fig.4] is a bottom elevation view of a piece of tableware equipped with a radio frequency tag and electromagnetic shielding device assembly according to another aspect of the invention.

[0033] [Fig.5] is a detail view of Figure 4.

[0034] The attached drawings may not only serve to complete the invention, but also contribute to its definition, where appropriate.

[0035] The Applicant realized that there was a need to produce a durable, traceable and reusable piece of tableware. The resistance of the radio frequency label to washing and microwaves used for heating or cooking presents major difficulties. Microwaves generate surges in the radio frequency label leading to a breakdown by short circuit or destruction by heating.

[0036] The Applicant has carried out tests on electromagnetic shielding against common frequency microwaves, i.e. 2.45 GHz. The electromagnetic shielding intercepts part of the useful signal of the radio frequency tag, both in transmission and reception.

[0037] Applying the electromagnetic shielding to one side and the radio frequency label to the other side of the tableware may lead to the destruction of the radio frequency label depending on the wall thickness between the sides of the tableware and other parameters. It is desirable that the electromagnetic shielding and the radio frequency label are placed on the same side of the tableware.

[0038] In one embodiment, the electromagnetic shielding is affixed to a top face of a microwave oven tray. The microwave oven tray may be made of glass.

[0039] As illustrated in Figure 1, radio frequency tags 1 are available being provided on a carrier strip 2. The carrier strip 2 is common to several tags radio frequency. The radio frequency tags 1 are HF, i.e. in the 3 to 30 MHz band. The radio frequency tags 1 are flexible and may be flat. The radio frequency tags 1 comprise an antenna 3 and an electronic chip 4. In the embodiment shown, the antenna 3 is wound around the electronic chip 4. The antenna 3 comprises a plurality of turns, with an inner turn connected to the electronic chip 4 directly, and an outer turn connected to the electronic chip 4 by an electrical bridge passing over the other turns and electrically insulated from the other turns. Alternatively, the antenna has a rectangular shape. Alternatively, the antenna has a square shape.

[0040] In Figure 2, a piece of tableware 5 is shown. Here, the piece of tableware 5 is a cup with a handle. The piece of tableware 5 can be made of earthenware, glass, in particular soda-lime, borosilicate, fluosilicate, crystalline, stoneware, earthenware, porcelain, wood or plastic.

[0041] . The piece of crockery 5 has a cylindrical wall 6 having an outer surface. The piece of crockery 5 carries a shielded radio frequency tag assembly 7. The shielded radio frequency tag assembly 7 is arranged on the outer surface of the cylindrical wall 6. The shielded radio frequency tag assembly 7 is thus supported by a convex surface.

[0042] In another embodiment, the shielded radio frequency tag assembly 7 is supported by a concave surface of a piece of crockery, for example a plate bottom, see figure 3.

[0043] The shielded radio frequency tag assembly 7 comprises a radio frequency tag 1 and an electromagnetic shielding device 8. The electromagnetic shielding device 8 is affixed to the outer surface of the cylindrical wall 6. The electromagnetic shielding device 8 is fixed by adhesion. Here, the electromagnetic shielding device 8 is circular. Here, the electromagnetic shielding device 8 has a diameter of between 30 mm and 120 mm. The electromagnetic shielding device 8 has a thickness of between 0.03 mm and 0.1 mm.

[0044] The radio frequency label 1 is affixed to the surface of the electromagnetic shielding device 8. The radio frequency label 1 is fixed by adhesion. The radio frequency label 1 has a surface area smaller than the surface area of ​​the shielding device electromagnetic 8. The radio frequency label 1 is centered on the electromagnetic shielding device 8. Alternatively, the radio frequency label 1 is off-center relative to the electromagnetic shielding device 8. The radio frequency label 1 is circular, in particular with a diameter of between 9 mm and 40 mm. The radio frequency label 1 has a thickness of between 0.075 mm and 0.200 mm.

[0045] The electromagnetic shielding device 8 comprises a conductive pattern 10. The conductive pattern 10 may have a thickness of less than 15 microns, for example between 5 and 13 microns. The conductive pattern 10 is made from a conductive metal, in particular from silver or copper. The conductive pattern 10 may be single-layer. The conductive pattern 10 may be deposited by pad printing, screen printing or metal film deposition. The conductive pattern 10 may be provided in the form of conductive metallized ink by an industrial inkjet printer. In contrast to a continuous conductive layer which would filter the microwaves and radio frequency waves of the radio frequency label, the conductive pattern 10 aims to allow the radio frequency waves of the radio frequency label to pass through and to filter the microwaves. For this purpose, the conductive pattern 10 has conductive zones and non-conductive zones according to a chosen design.The conductive pattern 10 is resistant to a temperature of more than 600°C in order to be able to undergo a ceramization step. The ceramization ensures that the conductive pattern 10 lasts over time and is resistant to washing and common rubbing when using a piece of tableware.

[0046] In one variant, the conductive pattern 10 is produced by low-temperature polymerization of an organic metallized ink. The polymerization ensures that the conductive pattern 10 lasts over time and is resistant to washing and common rubbing when using a piece of tableware. The electromagnetic shielding device 8 comprises a protective layer 9. The protective layer 9 is designed to resist mechanical and chemical attack. The protective layer 9 comprises an enamel, in particular a vitreous enamel. The protective layer 9 may be single-layer. The protective layer has a thickness of less than 20 microns, in particular between 5 and 15 microns. The protective layer 9 may be wider than the conductive pattern 10. The protective layer 9 is electrically insulating. The conductive pattern 10 is entirely covered by the protective layer 9.

[0047] The conductive pattern 10 may be formed by a conductive track. The conductive pattern 10 may have an outline shape of tetrasceles neighboring each other, see Figure 2 for a cup and Figure 3 for a plate. Said outline is continuous. The outline of the tetrasceles is conductive. The tetrasceles are distant from each other. The conductive pattern 10 is closed mesh while each tetrascele is insulating. The conductive pattern 10 is continuous. Said conductive track surrounds each tetrascele. A space of constant width, formed by the conductive track, is provided between two neighboring tetrasceles. In other words, the tetrasceles are insulating, due to the absence of conductive material. Said conductive track has a constant width or line width. The width is less than 2 mm, preferably less than 0.50 mm.

[0048] Said conductive track has a minimum convex radius of at least 0.35 mm, preferably at least 0.40 mm, in a local plane of the conductive track in FIG. 2, in a plane of the conductive pattern 10 in FIG. 3. Thus, sharp convex conductive track angles are absent to reduce the risks of short-circuiting while sharp concave conductive track angles are permitted.

[0049] Each tetrasceles is inscribed in a square with sides between 3 mm and 8 mm. Tetrasceles have four branches extending over an angle between 30 and less than 60°. This angle is defined between the hypotenuse and the adjacent short side of a right triangle in which one branch of the tetrasceles is inscribed. Tetrasceles are arranged in a rhombus.

[0050] The electromagnetic shielding device 8 has a diameter between 1.5 and 3 times the diameter of the radio frequency tag 1.

[0051] The 10-tetrasceles conductor pattern of Figure 2 filters more than 85% of the 2.45 GHz microwaves with a track width of 0.42 mm and passes more than 40% of the signal from radio frequency tag 1 at 13.56 MHz.

[0052] In the embodiment of Figures 3 and 4, the piece of tableware 5 is a plate or a dish. The piece of tableware 5 has an upper face for receiving food and a lower face 15. The lower face 15 comprises a peripheral rim 16 on which the piece of tableware 5 rests during use and a hollow 17. The peripheral rim 16 surrounds the hollow 17. The shielded radio frequency tag assembly 7 is affixed in the hollow 17. Alternatively, the hollow is partially or completely filled with resin. having a refractive index or color similar to that of the structural material of the piece of tableware 5. Alternatively, the shielded radio frequency tag assembly 7 is affixed to a flat lower face.

[0053] The 10-tetrasceles conductor pattern in Figure 3 filters more than 90% of the microwaves at 2.45 GHz with a track width of 0.42 mm and allows more than 40% of the signal from the radio frequency tag 1 at 13.56 MHz to pass, or even more than 50%.

[0054] The electromagnetic shielding device 8 has a diameter between 4 and 8 times the diameter of the radio frequency tag 1 in the mode shown.

[0055] The conductive pattern 10 may have a shape of triskelions adjacent to each other, see figures 4 and 5. The conductive pattern 10 is discontinuous. The conductive pattern 10 is open mesh. Each triskelion comprises three spirals 11 each formed of a wire. The wire or line has a width of less than 2 mm, for example between 0.2 mm and 1.6 mm. The spirals are nested two by two between neighboring triskelions. Double spirals are thus formed. The wires of a double spiral are disjointed at the center of the spiral and diametrically opposed outside the spiral. At the center of the double spiral, each wire has a free end formed in an arc of a circle. The free end in an arc of a circle is opposite the free end in an arc of a circle of the other wire. Preferably, the salient angle between said arc of a circle and the chord of said arc of a circle is at most 90°.Depending on the graphic resolution of the manufacturing process, the free end in an arc of a circle can be left raw as shown or can be formed with a fillet. On the outside of the spiral, each wire is connected to the wires of two neighboring spirals forming a triscele. The connection between said wire and the wires of the two neighboring spirals in the center of the triscele is formed into a triangle with concave rounded sides. The two wires of a double spiral are spaced 0.2 to 2 mm apart.

[0056] Each triskelion is electrically independent. Three neighboring triskelions leave an interior space free of conductive pattern 10. The interior space has a six-pointed star shape with a small diameter close to the diameter of a spiral. The triskelions have a minimum radius of at least 5 mm, preferably at least 6 mm. The triskelions are inscribed in a triangle with a side length between 13 mm and 17 mm, preferably 14.5 mm and 15.5 mm. The side length of the triangle to minimum radius ratio is of the order of 2.48. The conductive pattern 10 has the general shape of a hexagon. The spirals of the outer edges of the conductive pattern 10 are simple spirals, i.e. not nested with another spiral of another triscel. A spiral is wound over two turns. Figure 5 shows a detail of an outer edge spiral. The 10-conductor triscel pattern provides inductive-capacitive coupling. The 10-conductor triscel pattern in Figures 4 and 5 filters more than 70% of microwaves at 2.45 GHz, or even more than 80%.

[0057] In an embodiment not shown, each spiral is adjacent to six spirals. Said six spirals are arranged in a hexagon around said spiral.

[0058] In a non-shown embodiment, each spiral comprises six independent wires. The hexafilar trisceles conductive pattern 10 filters more than 90% of microwaves at 2.45 GHz with a track width of 1 mm, in particular with a turn angle of between more than 215° and 230°. The hexafilar trisceles conductive pattern 10 filters more than 90% of microwaves at 2.45 GHz with a track width of 0.5 mm, in particular with a turn angle of between more than 415° and less than 420°.

[0059] The tetrasceles motif is superior to the trisceles motif in terms of limiting warming.

[0060] In one embodiment not shown, the tetrasceles comprise spirals wound at an angle between 180 and 540°.

[0061] The electromagnetic shielding device 8 has a diameter between 4 and 8 times the diameter of the radio frequency tag 1 in the mode shown. The electromagnetic shielding device 8 complies with standard EN15284.

[0062] Tests were conducted on plates that had previously been exposed to the same domestic microwave oven set to the same cooking parameters in order to eliminate the case of defective plates whose structure or decoration may overheat or arc in a microwave oven.

[0063] Tests conducted with a radio frequency tag 1 of frequency 13.56 MHz, i.e. in the HF band, with the electromagnetic shielding device 8, in a household microwave oven have shown that the radio frequency tag 1 and its functionality are preserved. Thus, the radio frequency tag 1 is operational after several dozen passages in the household microwave oven of frequency 2.45 GHz.

[0064] In comparative tests, an identical radio frequency label 1, affixed to the same piece of crockery, but without the electromagnetic shielding device, is destroyed almost instantly with the appearance of electric arcs in the same microwave oven. household set with the same cooking parameters. In other comparative tests, an identical radio frequency label 1, affixed to the same piece of crockery, and with an electromagnetic shielding device 8 affixed to the same piece of crockery but on an opposite side, i.e. 2-3 mm apart, is destroyed after a few seconds with the appearance of electric arcs in the same household microwave oven set with the same cooking parameters.

[0065] The tests were carried out with identical plates with the electromagnetic shielding device 8 and the radio frequency tag 1 in mutual contact and arranged in a hollow of the plate. The tests carried out on fluosilicate glass plates with a fluorine content of at least 1% by mass and on soda-lime glass plates comprising 1 to 20% Ca, 5 to 20% Na and 50 to 80% Si showed identical results in terms of filtering.

[0066] The electromagnetic shielding device 8 attached to the radio frequency label 1 forms a low-pass filter for frequencies below 100 MHz, in particular with high transmission for the frequency 13.56 MHz. The electromagnetic shielding device 8 attached to the radio frequency label 1 forms a filter for frequencies above 1 GHz, in particular for frequencies between 2 and 4 GHz being filtered at more than 50%. The patterns shown in Figures 2 to 5 provide filtering of the 2.45 GHz frequency at more than 90%.

[0067] The plates with tetrasceles patterns on the bottom of the plate withstood a 2-minute cycle in the same domestic microwave oven. The tests were carried out with 7 sets of shielded radio frequency tags with Ag conductive pattern of diameters 39 mm, 48 mm, 60 mm, 73.3 mm, 93.6 mm and 139.2 mm and a 1 radio frequency tag of 25 mm diameter without highlighting any difference in behavior. The temperatures of the plate at the outlet of the domestic microwave oven were between 32 and 48°C, increasing with the diameter of the 7 sets of shielded radio frequency tags. No electric arc occurred. The presence or absence of an ornamental decoration in the plate did not generate any difference in the test results.

[0068] Then the same tetrasceles patterned plates withstood a long cycle according to EN 15284 of 12 minutes in the same domestic microwave oven. The temperatures of the plates at the outlet of the domestic microwave oven were 52°C regardless of the diameter of the 7 sets of shielded radio frequency label. No electric arc occurred.

[0069] Fatigue tests with 50 microwave ovens for 2 minutes showed satisfaction of the two criteria of absence of electric arc during microwave ovens and reading of the radio frequency label 1 at the end.

[0070] In one embodiment, the shielded communicating crockery piece is manufactured as follows. A commercially available crockery piece is supplied. An electromagnetic shielding device 8 is applied by pad printing to the underside of the crockery piece. The conductive pattern is provided in the form of a metallic ink, in particular silver-based. The protective layer is provided in the form of a vitreous mineral enamel. In another embodiment, the protective layer is provided in the form of an organic ink based on epoxy, silicone or polyurethane followed by polymerization. A ceramization step at at least 600°C may be provided. A radio frequency label 1 is applied to the electromagnetic shielding device 8. The radio frequency label 1 is fixed.

[0071] In another embodiment, the shielded communicating tableware piece is manufactured as follows. A commercially available tableware piece is supplied. A radio frequency label 1 is affixed to the underside of the tableware piece. An electromagnetic shielding device 8 is applied by pad printing to the same underside of the tableware piece, covering the radio frequency label 1. The conductive pattern is provided in the form of a metallized ink, in particular silver-based. The protective layer is provided in the form of organic ink or organic protective varnish. The organic ink can be applied by screen printing or pad printing. The organic varnish can be applied by spraying. The electromagnetic shielding device 8 is applied to the radio frequency label 1. A polymerization step can be provided by heating to less than 250° or UV or drying.

[0072] In another embodiment, a self-adhesive assembly comprises an electromagnetic shielding device 8, a flexible plastic support supporting the device, and a radio frequency label 1. The electromagnetic shielding device 8 and the flexible plastic support are fixed together, for example by gluing. Said self-adhesive assembly is provided with an adhesive on an external face and a peelable film for protecting the adhesive. Preferably, the electromagnetic shielding device 8, the radio frequency label 1 and the flexible plastic support have dimensions, diameter or width and length, close. Thus the electromagnetic shielding device 8 has a diameter between 1 and 1.5 times the diameter of the radio frequency tag 1.

[0073] Thus, a resonant system with respect to microwave blocking is formed. This corresponds to a minimum impedance of the printed circuit forming the electromagnetic shield at the microwave frequency. In the vicinity of the electromagnetic shield, the electric field caused by the microwaves vanishes, giving rise to significant electric currents in the electromagnetic shield, which acts as a quasi-short circuit. The RFID tag attached to the electromagnetic shield is then protected against the polarizing electrical effects, which disappear with the disappearing electric field. The electromagnetic shield behaves like a broadband resonant circuit. At the RFID frequency, the electromagnetic shield has a sufficiently high impedance not to absorb the entire RFID signal, so that a portion of it remains sufficient to operate with the RFID tag.

Claims

Claims

1. Electromagnetic shielding device (8) for an HF radio frequency tag on a piece of crockery, forming a low-pass filter for frequencies below 100 MHz, frequencies between 2 and 4 GHz being filtered at more than 50%, comprising a protective layer (9) against mechanical and chemical attacks comprising a first surface for cooperating with the tag and a second surface opposite the first surface, and a metallic conductive pattern (10) with a thickness of less than 20 microns, in contact with the first or second surface and protected by the protective layer (9), the conductive pattern (10) being periodic, the conductive pattern (10) having a line width of less than 2 mm, the conductive pattern (10) having a minimum convex radius of at least 0.30 mm.

2. Device according to claim 1, in which the conductive pattern (10) is made from silver or copper and the protective layer (9) comprises a vitreous enamel.

3. Device according to claim 1 or 2, in which the conductive pattern (10) has a thickness of less than 15 microns, the protective layer (9) has a thickness of less than 20 microns and the frequencies between 2 and 4 GHz are filtered at more than 90%.

4. Device according to one of the preceding claims, in which the conductive pattern (10) has a line width of less than 0.5 mm and a width between lines of less than 4 mm, preferably less than 1 mm.

5. Device according to one of the preceding claims, in which the conductive pattern (10) is single-layer and the protective layer (9) is single-layer.

6. Device according to one of the preceding claims, in which the conductive pattern (10) is continuous in the form of closed meshes or open patterns, in particular spirals.

7. Assembly (7) comprising a device according to one of the preceding claims and a radio frequency tag (1) HF, the maximum dimension of the conductive pattern (10) being at least equal to the maximum dimension of the tag, preferably at least equal to 1.2 times the maximum dimension of the tag.

8. A piece of tableware (5) for household or professional use comprising an assembly (7) according to claim 7, the electromagnetic shielding device (8) and the radio frequency tag (1) being arranged in a concavity made in the piece of crockery (5).

9. A piece of tableware according to claim 8, comprising a body made of ceramic, soda-lime glass, borosilicate glass, crystalline, stoneware, earthenware, porcelain, wood or plastic.

10. A method of electromagnetic shielding of an HF radio frequency tag, comprising providing a piece of tableware (5), affixing an electromagnetic shielding device (8) according to one of claims 1 to 6 to the piece of tableware, and attaching an HF radio frequency tag (1) to said device.

11. A method according to claim 10, wherein the electromagnetic shielding device (8) is deposited by pad printing, screen printing, inkjet or metal film deposition.

12. A method according to claim 10 or 11, wherein the conductive pattern (10) is provided in the form of metallic ink.

13. Method according to one of claims 10 to 12, comprising providing an HF radio frequency label on a piece of crockery (5), affixing a device according to one of claims 1 to 6 on the HF radio frequency label and affixing a protective varnish completely covering the conductive pattern (10).

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