WO2007140800A1

WO2007140800A1 - Metallic shelf

Info

Publication number: WO2007140800A1
Application number: PCT/EP2006/005367
Authority: WO
Inventors: Rafael Pous Andres
Original assignee: Aida Centre, S.L.
Priority date: 2006-06-06
Filing date: 2006-06-06
Publication date: 2007-12-13

Abstract

The invention falls within the technology for Radiofrequency Identification (RFID) applicable for the automatic identification of products, especially those ones stored over punched and folded metal sheets that shape metallic shelves, so often used for logistical warehousing and product displaying in markets. This metallic shelf (1) comprises at least one slot (4, 5, 6, 7, 8) adapted to operate as a slot antenna, which is properly coupled to a RFID reader (9), for identification of each RFID tag (3) attached to the objects (2) supported on said shelf (1). The slot antenna can be fed by a transmission line (10) born in the RFID reader (9) and to which this antenna is electromagnetic closely coupled, without any kind of contacts. The RFID readers (9) can communicate, over a wired or wireless network, from the shelves (1) to a core information system that processes data from the RFID tags (2).

Description

METALLIC SHELF

DESCRIPTION

OBJECT OF THE INVENTION

The invention that is disclosed herein relates to the technology of Radiofrequency Identification (RFID) which can be used for the automatic identification of objects, persons or animals, to which electronic labels, commonly termed RFID tags are attached. Among the numerous fields of application, this technique is frequently applied in the industrial sector of logistics for the tracking of products during their storage and transport, the tracking of inventories, shop lifting prevention, anti-counterfeiting, food traceability, asset tracking and control, etc.

In particular, the present invention merges this RFID technology with the industries of warehousing systems and storage solutions, retail and distribution, and, more specifically, is related with metal shelving.

BACKGROUND OF THE INVENTION

The technology of Radiofrequency Identification (RFID) is based on electronic tags which include an integrated circuit or chip coupled to a micro-antenna. The integrated circuit of the tag stores an exclusive code which can be used as an unequivocal label of an individual, animal or object.

Different implementations of the RFID identifier devices are known, for example, implemented in capsules, coins, cards, badges, etc., but the format most employed in the identification of products is that of self- adhesive labels, comprising several layers of material carrying in the interior thereof the microchip connected to the printed circuit antenna, conforming an RFID electronic tag which can be located on the surface of any product .

To make possible the operation of a system for Radiofrequency Identification, a further two basic elements are also necessary: 1) a core information system wherein the characteristics of each product are previously stored, such as expiry date, material, weight, dimensions, etc., which are important with regard to the proprietary application, and 2) an RFID reader of the RFID electronic tags attached to the products.

Conventionally, he RFID reader incorporates its own antenna, which transmits a series of radiofrequency waves which constitute an interrogation signal, which is picked up, at a distance of up to about 10 metres, by the tiny antenna of the RFID electronic tag. In such an event, the RFID electronic tag transmits automatically to the reader, likewise by means of radiofrequency signals radiated by the micro-antenna, the unique code of the product held in the microchip. Subsequently, the reader sends the code to the information system, whereby it is possible to consult the identity and the data of the products at any time, with which the information system can directly monitor the typical processes of production, distribution or sales in a company.

In the technological development of Radiofrequency Identification, there are RFID devices that operate in a low-frequency band (LF) , around 125 kHz, others in the high-frequency band (HF) at 13.56 MHz and some last ones developed to work in the 900 MHz range, in the ultra-high-frequency (UHF) band. Together with the UHF band, the standard Electronic Product Code (EPC) has been adopted by .the UCC/EAN organization responsible for the bar code standard commonly applied in commerce (although EPC tags are being developed also in the HF band) .

In order to have a real-time inventory of products in a warehouse, store or other places where products are found, the shelves on which the products are stored, may be equipped with RFID readers and antennas, in which case they are commonly referred to as "smart shelves". Since most of the shelves used in logistics and retail are metallic, it is necessary to develop a special kind of antenna suitable to work on metallic surfaces and conformal with a flat surface to be installed in the shelves. An additional requirement is that the antenna integrates well in the manufacturing process of the shelves, if possible adding little or no cost. DESCRIPTION OF THE INVENTION

The present invention is intended to resolve the problem outlined above, constituting a solution perfectly adaptable to the real application environments of Radiofrequency Identification (RFID) , allowing an easy reading of RFID tags attached to objects which are stored in metallic shelves.

In short, the present invention relates to a metallic shelf that integrates an antenna which may be used for identification of RFID tags when Operating in collaboration with an RFID reader.

In electromagnetic theory, there is a principle, which is called the Babinet principle, that apertures and obstacles have complementary diffraction properties. On the other hand, it is known that the impedance loads of complementary radiating structures supported in a medium (metal support) , such as a dipole antenna and a slot antenna, need to be in a relationship of the same form as the determined by the well known Booker relationship. Hence, according to Babinet-Booker principle, the radiation pattern and characteristics of a dipole antenna are analogous to a slot antenna of the same dimension. Thus, swapping the metal and free space parts of the dipole by free space and metal, respectively, this results in swapping the electric and magnetic field, but maintains the power radiation pattern. The same holds for other kinds of antennas such as folded dipoles, patches, etc.

This invention proposes the use of slot-based antennas directly on the surface of a metallic shelf. The design of the antenna allows its integration in the shelf within the manufacturing process, at no additional cost, because the antennas are built just by defining at least one slot directly in the metal surface that constitutes the shelf itself.

These slot antennas may be combined with an RFID reader in order to scan the overall surface of the shelves, supporting products with corresponding RFID tags, so that information in real time of the exact contents of a warehouse, supermarket, etc., including the position of every reference, is provided to a core system.

Slot antennas are excited by a coaxial cable or, instead and often, by electromagnetic close coupling (which can be capacitive or inductive coupling, depending on the geometry) to a feeder transmission line such as microstrip, slot line, coplanar waveguide, etc. In this case, the feeder line is electromagnetically coupled to the RFID reader, which means that a back-mounted modular reader would not require any electrical connection to the shelf. That way all shelves could be equipped with the slot antennas, and the optional reader could be assembled at any time, as and add-on option, at any of the two faces of the shelf without the need for a specialized technician.

By simple fixing means, the installer of the shelves can easily add the RFID reader attaching it to one face of the shelf, for example, the lower face so that the reader circuit is not in the way to be occupied by the objects on the shelf, and at a determined distance from the slot. The distance is such that the antenna structure is indirectly or reactively coupled to the feeder transmission line of said RFID reader. Only fastening screws or some adhesive would be required to quickly install the RFID reader, preferably under the slot so that the antenna can be electromagnetic closely coupled to its feeder line.

The full set of RFID readers of all the shelves can communicate with the core system via a Local Area Network (LAN) specifically implemented for the application in question, as for example by using a wired Ethernet network or a wireless network such as, WiFi, Bluetooth, Zigbee, etc.

In summary, the main advantage of this invention,- is that it provides for an essentially free way to equip metallic shelves with integrated antennas, that can, without the intervention of any specialised technician, be converted into RFID smart shelves by just snapping a modular RFID reader that feeds the slot antenna through an electromagnetic close-coupling mechanism that does not require soldering, just simple mechanical assembly. If the reader communicates wirelessly with the core information system, only a power cable needs to be installed to power up the RFID reader, and no RF or network cables will be necessary.

The number of steps in the manufacturing process of this metallic shelf incorporating the RFID antenna is reduced because no external pieces have to be assembled on the surface since the antenna is, actually, a part of the shelf surface. Also the cost of the shelf is not increased thanks to simplified manufacturing process, which involves only cutting a metal sheet with a die, folding it and finishing it with paint of other coatings, remains the same; it only requires a modification in die that cuts the metal sheet.

Optionally, for a greater output, the shelf incorporates a metallic cavity behind the slot, so that it can operate as a cavity-backed slot antenna, i.e., the slot antenna can radiate only in a half because the cavity prevents it to radiate in the backwards direction. This technique can be used with any configuration of slot antenna, not only with a dipole slot antenna, and the geometry of this cavity may be rectangular, cylindrical, or shaped otherwise. Therefore, the metallic shelf integrating the cavity-backed slot antenna achieves a more efficient identification of the supported objects for several reasons: i) the cavity-backed slot antenna reduces interference to/from other adjacent shelves, ii) it assures to identify only the products in a defined region (e.g. the products placed on the shelf and not the ones below it) . iii) the cavity helps to reduce the coupling to other electronic parts (as instance, the RFID reader that is placed under the antenna) . iv) the antenna has a higher gain, which means that to cover the same area it will be needed less amount of power. v) the antenna gets restrictions in the maximum beam-width, conveniently adapted for RFID applications.

To the advantageous characteristics of the invention must be added the benefits that its application implies in a complete RFID system for warehousing and selling, which can be summarized as follows:

The RFID tags facilitate the tracking of the products, mandatory in those for foodstuffs and pharmaceuticals, achieving identification and continuous monitoring during the stage of storage and exhibition for selling. A reduction in the inevitable human errors, as neither specific personnel in attendance to read the identifying tags and to make an inventory nor a special qualified installer of the shelves are needed.

Hundreds of readings are carried out per second, which implies a considerable saving in time and is reflected in a substantial reduction in the overall cost of the products. The network connection allows the communication of the RFID readers from the very location of the products (the shelves in the warehouse or shopping centre) with the proprietary information systems of the user, for example, a corporate intranet.

DESCRIPTION OF THE DRAWINGS

To complete the description being made and to assist in a better understanding of the characteristics of the invention, in accordance with a preferred example of practical embodiment, this description is accompanied, as an integral part of the same, with a set of drawings which illustrates but does not restrict, in which the following has been represented:

Figure 1. - It shows a perspective view of a plurality of the metallic shelves, forming a storage rack, with slot-based antenna in each shelf object of this invention, according to a posible embodiment.

Figure 2. - It shows a plan view of the lower face of one metallic shelf with its slot antenna coupled to the feeder line from a RFID reader (not drawn) .

Figure 3. - It shows an oblique view of the shelf drawn in figure 2 showing the contactless coupling between the slot antenna and the feeder line.

Figure 4. - It shows a perspective view of the metallic shelf with a RFID reader attached below.

Figure 5. - It shows a plan view of the metallic shelf with a bow-tie slot antenna, according to another possible embodiment of the invention.

Figure 6. - It shows a plan view of the metallic shelf with a folded-dipole slot antenna, according to an alternate embodiment of the invention.

Figure 7. - It shows a plan view of the metallic shelf with a meander-dipole slot antenna, according to another alternate embodiment of the invention.

Figure 8. - It shows a plan view of the metallic shelf with a cross-dipole slot antenna, according to yet another alternate embodiment of the invention.

Figure 9. - It shows a perspective view of a storage rack formed by metallic shelves with cavity-backed slot antennas radiating upwards, according to a last example for embodiment of the invention.

Figure 10. - It shows in more detail the cavity- backed slot antenna that works on each shelf drawn in figure 9, in the way determined by a metallic cavity.

Figure 11. - It shows a schematic representation of the known in the state of the art radiation pattern from a dipole antenna.

PREFERRED EMBODIMENT OF THE INVENTION

In the light of the aforesaid figures 1-4, it is possible to describe one of the possible embodiments of the invention as a shelf (1) that constitutes a metal surface for supporting objects (2) that have associated at least one RFID tag (3) . A group of such shelves (1) are mounted to build a storage rack (11). Each shelf (1) comprises at least one slot (4) whose configuration is adapted to operate as a single-dipole slot antenna when is coupled to a RFID reader (9) . As seen in figure 3, this coupling is preferred to be contactless, without requiring electric direct connection with the RFID reader (9), due to the fact that the slot antenna is fed by electromagnetic close coupling with a transmission line (10) included in said RFID reader (9) . For this coupling and in order to no substraction of loading capacity from the shelf as well as for security reasons, the RFID reader (9) is attached to the lower face of the shelf (1), just under the slot (4), according to the illustration of figure 2. This layout positioning avoids the RFID reader (9) to be a hindrance for the objects (2) stored on the upper face of the shelf (1) and results in more protection for the whole circuit. There is neither welding nor cables between the shelf (1) and the RFID reader (9), which can be plugged by screwing, adhering or other simple attaching mechanism. The RFID reader is connected or supplied with a feeding source.

Referring finally to figures 5-8, there are different suitable configurations of slot antennas in order to achieve better characteristics of bandwidth, polarization and isotropy of the radiation pattern, compared to the single dipole slot antenna initially proposed.

The bow-tie slot (5), folded dipole slot (6) and meander dipole slot (7) antennas provide a higher bandwidth than a single dipole slot (4) antenna. Also slot antennas as the meander dipole (7) or the cross- dipole (8) are less sensitive to the polarization than the single dipole slot (4) antenna. In addition, the cross-dipole slot (8) antenna has a more isotropic radiation pattern. The reason of such improvement is that, whilst antenna structure as the single dipole does not radiate at all in the axis direction, the result from combining two dipoles forming a crossed dipole is a combined radiation pattern without this problem, because of the diversity provided by the two dipoles.

Independently of the slot profile, in order to achieve half of the radiation pattern, which is especially useful for the application in smart shelving as well as to have more degrees of freedom to control the antenna parameters, the slot antenna has a resonant metallic cavity (12) behind, that draws its radiation pattern to forwards direction solely, as figure 9 shows. This cavity-backed slot antenna, depicted in figure 10, is basically the same slot antenna but with higher gain and directivity, which interests in this application, and a better tuning. Indeed, as said before, returning to the Babinet principle, a slot antenna emits the same radiation pattern of its counterpart "positive" antenna of the same dimensions, i.e. if a dipole antenna (A) has an omni-directional radiation pattern (R) as the one shown in figure 11, a slot dipole antenna will also be omni-directional. In the case of shelving, only half of the radiation pattern is profitable, towards the direction defined for storing the objects, that is, upwards. This directional radiation pattern which covers a limited area (C) , shown in figure 9, is obtained just adding such cavity (12) to the metallic shelf, covering the back side of the slot (4), but without involving costly steps in the usual manufacturing process.

Some preferred embodiments of the invention are described in the dependent claims which are included next.

Claims

1. - Metallic shelf (1) for supporting objects (2) having at least one RFID tag (3), characterised in that it comprises at least one slot (4, 5, 6, 7, 8) adapted to operate as a slot antenna for identification of each RFID tag (3) of the objects (2) .

2. - Metallic shelf according to claim 1, comprising an upper face and a lower face, and which is provided with an RFID reader (9) attached to one of said faces and coupled to the slot antenna.

3. - Metallic shelf according to claim 2, wherein the coupling between the slot antenna and the RFID reader

(9) is contactless by means of a feed transmission line.

(10) included in said RFID reader (9) .

4. - Metallic shelf according to claim 3, wherein the RFID reader (9) is attached at a distance from the slot antenna which is determined to electromagnetic closely couple to the feed transmission line (10).

5. - Metallic shelf according to claim 4, wherein the RFID reader (9) is attached by fastening screws .

6. - Metallic shelf according to claim 4, wherein the RFID reader (9) is attached by adhesive material.

7. - Metallic shelf according to any claim from 2 to 6, wherein the RFID reader (9) includes means of communication with a LAN.

8. - Metallic shelf according to claim 7, wherein the means of communication consists of an Ethernet network connector.

9. - Metallic shelf according to claim 7, wherein the means of communication consists of a Wi-Fi transmitter.

10. - Metallic shelf according to claim 7, wherein the means of communication consists of a Bluetooth transmitter.

11. - Metallic shelf according to claim 7, wherein the means of communication consists of a Zigbee transmitter.

12.- Metallic shelf according to any preceding claim, wherein the configuration of the slot antenna is selected among simple dipole, folded dipole, meander dipole, cross dipole and bow-tie slot antenna.

13. - Metallic shelf according to any preceding claim, further comprising a resonant metallic cavity (12) defined in a side of the slot antenna.