Background

[0001 J Radio frequency identification tags (RFID tags) are widely used in several fields for the identification of objects by wireless interrogation. RFfD tags may be passive (without a power source) or active (with a power source).

[0002] Passive RFID lags can, in turn, be divided in two main groups, chipped or chipless. Chipped RFID tags comprise an antenna connected to a silicon chip being the chip adapted to draw enough power from an interrogation signal issued by an RFID reader to communicate with it wirelessiy, Chipless RF!D tags, on the other hand, have a simplified design by removing the use of chips whiie maintaining the ability to communicate with an interrogator through the use of antennas and/or resonators. Chipless RFID tags are easier to manufacture, much cheaper than chipped RFID tags and environmentally friendlier.

B rief P escriD ion of the Drawings

[0003] Examples will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0004] Figure 1A shows a schematic view of the components of a chipless RFID tag according to an example.

[0005] Figure 1 B is an example of design or a conductive track of a chipless RFID tag.

[0006] Figure 2 is a schematic view of an example of a manufacturing method of RFiD tags.

[0007] Figure 3 is a flow diagram of an example of a method of manufacturing RFID tags.

[0008] RFfD tags are widely used in several fields, however, the main drawback for a wider use is the manufacturing complexit and cost. Common RFID tags may be printed on a dielectric substrate by using inks containing silver which makes th manufacturing process too expensive for some applications. Also, the use of dielectric substrates and silver inks increase cost and complexity as special printers may be used. Furthermore, recycling of materials used in such RFiD tags is uncommon.

[0009] Referring to Figure i A an example of chipless RFID tag is shown. In particular a chipless RFID tag 100 is shown that comprises a multiresonator 110, a receiving antenna 122 and a transmitting antenna 121 In an example, the receiving antenna 122 and the transmitting antenna 121 can be replaced by a single dipoSe antenna or, in a further example, lack an antenna as will be shown with reference to Figure 1B. Also, the chipless RFiD tag 100 of figure 1A may be printed on a carbon-based substrate 101 such as, e.g., paper by means of a meta! carbide or metal nitride ink.

[0010] The muitiresonator 1 0 may compris a first resonator 11 , a second resonator 112 and a third resonator 113; however, the quantity of resonators is not limited to three as any other number of resonators may be used depending on the particular application of the chipless RFID tag 100. in particular, the number of resonators may depend on the amount of information to be stored.

[0011} Figure IB shows an example of a chipless RFID tag 1 0 wherein comprising a muitiresonator that has a first resonator 111 , a second resonator 112 and a third resonator 113, in the example of figure 2B the resonators are conductive tracks forming circular rings with radius Ri, 2 and R3, respectsveiy, and having a width w for ail of the rings. As shown in the example of Figure 1B, the circular rings may be concentric.

[0012] Circular resonators are known in the ar and their structure is known to have a substantially constant electromagnetic response that is irrespective of the polarization of the incident wave. The resonance frequency for each of the rings is dependent on the width w of the conductive track and the radius of the ring. For example, for a ring with a radius between 9 and 4 mm with a width v of 0.5 mm, the resonance frequency may be approximately determined, for exampie, by the formula: wherein f _f is the resonance frequency, R is the radius of the ring, c is the speed of light constant, and Ees the effective permittivit for the conductive track with a width w and being a constant dependent mostly on the materia! (or materials) used for the conductive track and the substrate.

[0013] In summary, having a conductive track comprising several rings creates a specific electromagnetic signature in the frequency domain that Is to be used for RFID reading/detection.

[0014] Figure 2 shows an example of a manufacturing method for chipless RFID tags 100 using a chipless RFID printing system 1. In the example of figure 2 a celluiosic substrate is used, e.g., paper as a substrate for the chipless RFID tag 100. A feeder 21 may be included wherein a paper roll 20 is loaded is fed to a printer 2 by means of a feeding roller 22.

[0015] The printer 2 may comprise a printer controller 24 that may be used for controlling the printing processes; for example, the amount of paper to be fed by the feeding roller 22 and its speed. Also, the printer controller 24 may be used to control at least one printhead as to print conductive tracks on the carbon-based substrate, in this example, the paper roil 20.

[0016] The conductive tracks may be printed by using a particular type of ink, e.g., carbide mefai, boride metal or nitride metal inks. Examples of carbide mefai inks can be; gCf¾ ₂ C¾ Y ₂ Cs, o ₃ C ₂ , LaNiCa, oaAfeC, SiC, TIC, VC, WC, W ₂ C, ZrC, oC, N C or any combination between them. Examples of nitride metal inks can be: TiN, VN, BN, AIN, CrN, gSiNs. These inks may be stored in a ink supply 23 fiuid!y connected to th printer 2.

[001 ?] Metal carbide and metal nitride inks have specific properties that allow the printing of RFID fags 100 on carbon or carbon fiter-based substrates, like paper. In partic- u!ar, metal carbides and metal nitrides are good electric conductors and have the particularity of having ref ractory properties which protects the substrate upon the presence of a heating source. Paper electronics are normally very susceptible to heating and the use of metal carbides and metal nitride as inks not only reduces the cost of printing (in comparison to expensive silver-based inks) but also, the refractory properties protect at some extent the substrate in further heating processes.

[0018J Paper is a thin material produced by pressing together moist fibers of cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets, it is a versatile material with many uses, including writing, printing, packaging, cleaning, and a number of industrial and construction processes. Furthermore, it is carbon-based substrates which are a source of carbon that wiil help to provide carbon to be sintered or carbonized with the ink solution as well as certain amounts of gra hene, carbide, etc. to be mixed with metal carbide for the enhancement of the conductivity during a subsequent heating process, !n particular, soot is known to include buckminsterfuller- ene which is conductive under some reactions with carbon-based substrates. The buckminsterfuiierene may provide the conductive sections of the substrate with improved conductivity.

[0019] The printer 2 for carrying out the printing of the conductive track may be any type of ink-based printer; for example, an Inkjet printer or an offset printer like, for example, a web press.

[0020] After printing, a printed substrate 25 is obtained. The printed substrate 25 is subsequently subject to a heating treatment by means of a heater, in particular, a laser source 3 configured to selectively heat at least the parts of the printed substrate that comprise conductive tracks. The laser 3 may be connected to peripheral devices 31 such as a controlle to control the position and power of the laser or a CCD camera to determine the parts of the substrate comprising conductive tracks,

[0021 Once the printed substrate 25 is heated, a conductive substrate 32 is obtained wherein, at this stage, the substrate already comprises a chipSess RF!D tag 100. [0022] In another example, the printer 2 may also comprise ^' a prfnthead to be fed with dielectric ink in order to print with non-conductive material, at least, the surroundings of the conductive track or, alternatively, the complementary parts of the substrate, i.e., portions of the substrate that do not comprise conductive tracks printed. Also, the dielectric ink may be activated by the laser 3, so that the laser may selectively heat, not only the conductive tracks, but also the portions of the substrate comprising the dielectric ink.

[0023] Even though the conductive substrate 32 already comprises a chipless RFID tag 100 that would work, in some cases, post-processing of the conductive substrate 32 may be performed. The post-processing can be performed in a post-processing unit 4 wherein the conductive substrate can be subject, for example, to a cooling process by depositing sprinkling droplets 40 of water over the substrate. Alternatively, the postprocessing may comprise depositing a top sealed layer for surface protection, such a an overprint coating,

[0024] As a result, a finished substrate 41 is obtained and may be stored again as a roil of chipless RFID tags 10.

[00253 Overprint coatings ma be applied to the conductive substrate 32 for different purposes. These coatings may be, for example, a dielectric coating, oleoresins, or binding coatings (e.g. , styneric or acrylic coatings). In an example, the overprint coating may be used for increasing the conductivity on the conductive tracks, for example, by using nanographite or nanoceliu!ose coatings which, in addition to conductivity, improves the water retention of the finished substrate 41.

[0026] The roll of chipless RFID tags 10 may comprise several RFID tags that may each comprise a different configuration of conductive track, such as different configurations either in width v of the tracks or in the pattern used.

[0027] It is to be noted that, even though in the example of figure 2 the paper feeder, the printer, the heater and the prost-processing unit are shown as separate devices, they could also be enclosed in a single device and share some elements; for example, by using a shared controller.

[0028] In essence, figure 2 shows a process wherein a conductive track Is first printed by means of a metal bohde, a metal nitride, a metal carbide or a combination between at least two of them on a cartoon-based substrate. Then, a sintering, annealing or curing of the ink is performed by means, e.g., of a laser to selectively heat the portions of the substrate comprising the conductive track. Finally, an optional step of post-processing is performed, e.g., by coating the substrate.

[0029] Figure 3 shows a flowchart of the chipless RF!D tag printing process. In the example of figure 3 a shared controller 1 1 is used to control the process. In particular, a substrate is received from a feeder 21 to a printer and the shared controller controls the suppiy of substrate 28 to the printer 2.

[0030] Once the substrate is located on the printer 2 the printer prints a conductive track 27 on the substrate, in particular, the printing is made by use of a metal carbide or metal nitride ink stored in the ink supply 23. Also, the substrate may be carbon- based substrate, e.g., ce!lulosic substrate, like paper or cardboard, in case the substrate is cardboard, the cardboard may be a box and the chipless RFSD tag 100 may be printed directly on the cardboard that is to form the box, thereby reducing the cost of boxes, e.g., in supply chains wherein boxes and RFSD tags are normally printed separately.

[0031 J Subsequently, heat is applied 33, at least, on the parts of the substrate comprising the conductive track. The heat ma be selectively applied on the parts comprising the conductive track by using a laser controlled to heat only the parts comprising the conductive track. The identification of which parts comprise the conductive track may be performed, e.g., by defecting such parts by using a camera.

[0032] Finally, the method comprises a post-processing 42 of the substrate. This postprocessing may be, e.g., cooling the paper by air blowing or droplet sprinkling. Also, the post processing may comprise depositing a protective layer over the chipless RFID tag. [0033] in essence, it is disclosed a method of manufacturing of a chipSess RF1D tag comprising:

* printing a conduciive track on a carbon-based substrate; and

* selectively heating the substrate on the parts comprising the conduciive track;

wherein the printing of the conductive track comprises using an ink comprising at least one of a metal carbide, a metal boride or a metal nitride.

The selectiv heating of the substrate may be performed by directing a iaser towards the conductive track

As for the substrate, the carbon-based substrate may be a cel!uSosic substrate, e.g., paper or cardboard, wherein cardboard is especially usefui as the RFiD tags may be printed directly on a cardboard packaging.

[0034] in an example, the conductive track comprises an antenna. Trie antenna may ^¬ be a passive antenna and, in an example, may comprise a receiving antenna and a transmitting antenna. Alternatively a single dipole antenna may be used.

[0035] i an example, the conductive track comprises a resonator.

[0036] in a further example, the inks envisaged may be metal carbide inks comprising a material selected from gCNi3, La2C3, Y2C3, Sv1o3C2, LaNiC2, Mo3AI2C, SiC, TiC, VC, WC, W2C, ZrC, MoC, or NbC. Also, the inks may be metal nitride inks comprising a material selected from: TiN, VN, BN, ASM, CrN or MgSiN2.

[0037] Furthermore, it is envisaged a post-processing of the RFID tag, in an example, this post-processing may comprise adding a top layer surface on the substrate, at least, over the conductive track. This post-processing may be selected to improve water retention, improve water repelling, increase the resistance to tearing of the substrate and/or improve the conductivity of the conductive tracks. [0038] Additionally, it is disclosed a chip!ess FID tag manufacturing system comprising:

• an ink-based printer

# a selectively heating mechanism

wherein the prinier is to use an ink comprising at least one of a metal carbide, a metai boride or a metai nitride to print a conductive track on a carbon-based substrate and the selectively heating mechanism is to selectively heat the portions of the substrate comprising the conductive track.

100303 As mentioned above, examples of metai carbide inks to be used by the system may comprise a material selected from: Mi3, La2C3, Y2G3, fv1o3C2, LaNIC2, o3AI2C, SiC, TiC, VC, WC, W2C, ZrC, MoC, or NbC. Alternatively, metal nitride inks are envisaged wherein the inks may comprise a material selected from: TiN, VN, BN, AIN, CrN or MgSiN2.

[0040] in an example, the conductive track comprises an antenna. This antenna may be a unipoie or dipole antenna.

[0041] In a further example, the conductive track comprises a resonator.

[0042] Furthermore, the printer may be any type of ink-based printer e.g., the printer may be an offset printer, like a press.