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A RADIO FREQUENCY (RF) TAG

BACKGROUND OF THE INVENTION

THIS invention relates to a tag using a radio frequency (RF) or microwave antenna, suitable for use as a RF tag antenna, where the tag-antenna is 0.003 times the free-space wave-length, or less, from a metai surface. Also, where the tag processing chip, or Integrated Circuit (tag IC), is embedded within the tag antenna. Alternatively, when embedding is not a requirement, it can be used as an on-metal RF tag antenna with a 0.0006 free-space wavelength spacing from a metal surface.

RF tags typically operate with a dipofe antenna or variations of dipole antennas in places where the tag-antenna is typically more than 0.05 wavelengths away from metal surfaces. However, in applications where an RF tag is to be attached to a metal surface, the dipole antenna impedance becomes too small and matching becomes problematic.

One example of an application where the tag is to be attached to a metal surface is where the antenna is to be attached to a metal number plate of a motor vehicle or motor cycle, or the body of a motor vehicle or motor cycle.

In such an application the tag also needs to be very thin to fit onto the number plate. For example, in South Africa, the tag needs to be thinner than the embossed letters on the number plate which is 2 mm or less.

The present invention seeks to address this.

SUMMARY OF THE INVENTION

According to a first embodiment, there is provided an RF Tag including:

an integrated circuit (IC) to control the operation and protocol of the tag;

an antenna connected to the tag; and

a matching circuit to match the antenna to the IC connected to the antenna.

The IC and matching circuit may be embedded in the antenna.

The RF tag utilizes stripline, microstrip and/or lumped technologies.

The antenna may be of a nature where stripline, microstrip, patch or an inverted F antenna are used.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an example RF system in which an RF tag is used;

Figure 2 is an example embodiment of a first side of a first part of an RF tag;

Figure 3 is an example embodiment of a second side of the first part of the RF tag;

Figure 4 is an example embodiment of a first side of a second part of the RF tag;

Figure 5 is an example embodiment of a second side of a second part of the RF tag;

Figure 6 is a schematic illustration of how the different parts of Figures 2 to 5 fit together;

Figure 7 is a schematic illustration of an alternative embodiment of an integrated circuit for use as an RF tag;

Figure 8 is an example embodiment of a tamper evident mechanism used with the RF tag.

Figure 9 is a first side of a first part of the RF tag in a second embodiment;

Figure 10 is a second side of a first part of the RF tag in the second embodiment;

Figure 11 is a first side of a second part of the RF tag in the second embodiment;

Figure 12 is a second side of a second part of the RF tag in the second embodiment; and

Figure 13 is a side view of the different layers of the tag of the second embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 is a schematic representation of an example radio frequency identification (RF) system.

The system includes an RF tag 10 that is comprised of an antenna 12, a matching network 14 and an integrated circuit 16. The RF IC is a dedicated

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Radio Frequency Identification Integrated Circuit. The RFID-IC can be from different manufacturers, supporting different protocols.

The RF tag 10 communicates with an RF unit 18 that includes an RF transmitter/receiver 20 that communicates with the RF tag 10 via antennas 22.

The RF transmitter/receiver 20 transmits energy to the RF tag 10 and receives a back-scattered or reradiated signal from the RF tag 10. This RF unit is connected to a decoder 24 to decode the demodulated received signals from the tag 10.

Finally, the decoder 24 is connected to a computer 26.

The tag schematically illustrated in Figure 1 is an example embodiment of the present invention.

The different parts of the tag which are put together are illustrated in Figures 2 to 6.

The tag is comprised of two parts 28 and 30. Each part has two surfaces labelled 28a and 28b and 30a and 30b respectively.

When embedding of the IC is not a requirement, the assembly can be used without part 30.

Figures 2 to 5 show these different sides in more detail.

Although dipole antennas are typically used for RF tags, in the present invention a dipole antenna cannot be used because the Intended application of the tag is too close to a metal substrate as described above. Thus in this application the antenna of the RF tag is one of a stripϋne, a microstrip patch antenna or an inverted F antenna.

Referring first to Figures 2 and 3, the first part of the antenna has a body made from a thin layer of FR4 or any dielectric material, double sided metalised. A typical thickness of this dielectric material is between about 0.2mm and 1mm.

The first side 28a forms the ground plane of the antenna used by the tag and is formed by a copper layer deposited onto the substrate. The copper layer will typically cover most or all of the substrate surface. The typical thickness of the copper layer is 35 μm to 70 μm, although it can be thinner or thicker.

The second side 28b has a metai layer 32 that at least partial covers the body and/or is formed in a specific shape. This metal layer forms the radiator of the tag antenna and the size and shape of the metal layer will be determined by the performance characteristics required from the antenna.

Also embedded in the second side 28b is a matching network 14 for the antenna. The IC and matching network needs to be buried, or embedded, into the embodiment, to protect the IC from external damages. Although the matching network, or feed-line, is illustrated etched into the second side, it could be formed using different components, lumped or distributed. Lumped components refer to discrete components and distributed components refer to etched components. This matching network can also be transferred to surface 30a. The matching network is required to present the correct impedances, simultaneously to the IC and the antenna, in order to enable the tag to generate the optimal re-radiated, backscattered signal.

Referring to Figures 4 and 5, the second part of the antenna has a body made from a similar dielectric material as the body of the first part 28, but with a thickness at least the thickness of the tag IC (or tag die if the bare die, of flip chip, is used). A typical thickness of this will be between about 0.8mm and 1.6mm.

Note that the thicknesses of 28 and 30 can be interchanged

The first side 30a includes a metal layer 34 which couples to surface 32. The function of this layer is to get as small an impedance contact as possible between the different layers, with or without soldering.

The second part 30a has a recess or cut-out 36a cut into the substrate wherein the integrated circuit 16 (not shown in Figures 2 to 6) fits when the two parts of the RF tag are placed together. 36b is a metal free area to avoid short circuits to the matching network.

The second side 30b includes a metal layer 38 which forms a parasitic radiator of the antenna.

It will be noticed from the drawings that the metal layer 38 is typically larger than the metal layer 34. The relationship between layers 32 and 34, and 38 can vary with respect to each other as part of the matching network.

Figure 6 illustrates the two parts of the RF tag 10 put together to form the RF tag. The parts can be glued or soldered together. Note that 28, 30 and 36 can vary in shape and/or thickness.

Typically, the RF tag 10 is covered with a thin layer, epoxy or cαnformal coating, so that the whole tag is encapsulated in a coating which protects the tag in the use of it. Opening 36a can be covered with epoxy, silicone or any suitable dielectric material.

In an alternative embodiment illustrated in Figure 7, the assembly is formed using a three layer structure, including an upper layer 40, a mid layer 44 and a lower layer 42. Layers 42 and 44 are the same layers as in Figures 2 - 5. Layer 40 is a thin layer used to cover opening 44a and the tag IC 42a. The tag IC, matching network and radiator will then be embedded and protected.

Figure 8 illustrates a tamper evidence mechanism whereby a cut-out 46 is formed in the first part 28 to which the integrated circuit 16 is connected.

The first part 28 is the part which is glued to the surface onto which the RF tag 10 is to be mounted in use. If a user attempts to remove the RF tag from the surface to which it is glued, the first part 28 wiil break around the cut-out 46 thereby leaving the integrated circuit located on the surface.

Figures 9 to 13 illustrate another embodiment of the tag in which like reference numerals have been used to identify like parts.

Referring first to Figures 9 and 10, the first part 28 of the antenna has a body made from a thin layer FR4 or any dielectric material, double sided metalised. A typical thickness of the dielectric material is between about 0.2mm and 1mm.

The first side 28a has a copper layer deposited onto the substrate. The copper layer will typically be etched away, leaving only copper for through- hole plating purposes. This side, in this alternative embodiment, will act as the radome (or protected layer) of the radiator.

The second side 28b has a metal layer 32 that at least partially covers the body and/or is formed in a specific shape. This metal layer forms the radiator of the tag antenna and the size and shape of the metal layer will be determined by the performance characteristics required from the antenna.

Also embedded in the second side 28b is a matching network 14 for the antenna. Although the matching network, or feed-line, is illustrated etched into the second side, as with the first embodiment, it could be formed using different components, lumped or distributed. Lumped components refer to discrete components and distributed components refers to etched components This matching network can also be transferred to surface 30a.

Referring to Figures 11 and 12, the second part of the antenna has a body made from similar material as 28, but with a thickness at least the thickness of the tag IC (or tag die if the bare die, of flip chip, is used). A typical thickness will be between about 0.8mm and 1.6mm.

Note that the thicknesses of 28 and 30 in this embodiment can also be interchanged

The first side 30a in this embodiment does not include a metal layer coupled to the surface as in the previous embodiment.

The second part 30b is covered with a copper layer 48. This layer has the function of the antenna assembly ground plane.

A cut-out 50 is formed through the whole substrate wherein the integrated circuit and matching network fits when the two parts of the RF tag are placed together.

Figure 13 illustrates the two parts of the RF tag put together to form the RF tag with a layer of pre-preg 52. Pre-preg is PCB material used to glue layers of FR4 together.

In this embodiment, the tag includes a plurality of holes 54 that are formed through all of the layers of the tag. The holes allow copper to partially fill the holes and join the copper of the different layers together. The holes 54 are thus trough hole plated. Opening 50 is formed by control depth routing.

Typically, the RF tag 10 is covered with a thin layer, epoxy or conformal coating, so that the whole tag is encapsulated in a coating which protects the tag in the use of it. Opening 50 can be covered with epoxy, silicone or any suitable dielectric material.

It will be appreciated that RF tags have until now mostly been used with dipole antennas, or antennas that are not as dose as 0.005 to 0.05 wavelengths from a metal surface.

The tag antenna described above is suitable for applications where RF tags need to be manufactured in a thin embodiment, close to a metal surface, but not limited to be close to a metal surface.

Also, the tag in the illustrated embodiments is 2mm thick or less than 2mm thick.

Finally, it will be appreciated that the microstrip patch antenna and the inverted-F antenna, for example, were selected due to the fact that they use their own ground plane and will thus operate on a bigger ground plane being the metal surface to which the tag is connected.