MXPA06009458A - Field-shaping shielding for radio frequency identification (rfid) system - Google Patents

Abstract

A radio frequency identification (RFID) system is described that utilizes a substantially-contiguous conductive shield to shape an electromagnetic field formed by an antenna for communication with RFID tags. The antenna and the conductive shield have substantially planar forms, and may be mounted to a surface of a check-in / check-out area. The conductive shield is positioned around the antenna and within a plane parallel to the antenna, e.g., within the same plane. The conductive shield shapes the electromagnetic field to extend substantially in a direction perpendicular to the antenna, and prevents the electromagnetic field from forming substantially over the conductive shield.

Description

PROTECTION OF FIELD FORMATION FOR RADIO FREQUENCY IDENTIFICATION SYSTEM (IDRF) FIELD OF THE INVENTION The invention relates to radiofrequency identification systems (IDRF) for the handling of articles. BACKGROUND OF THE INVENTION Radio Frequency Identification (IDRF) technology has become widely used in ually all industries, including transportation, manufacturing, waste management, postal tracking, airline baggage reconciliation, and toll handling on highways. . A typical IDRF system includes a plurality of IDRF tags, at least one IDRF reader or detection system having an antenna for communication with the IDRF tags, and a computing device for controlling the IDRF tag. The IDRF reader includes a transmitter that can provide power or information to the brands, and a receiver to receive the identity and other information of the brands. The computing device processes the information obtained by the IDRF reader. In general, the information received from an IDRF mark is specific to the particular application, but frequently provides an identification for an item to which the mark is fixed. Exemplary items include Ref .: 175305 manufactured articles, books, files, animals or individuals, or ually any other tangible items. You can also provide additional information for the article. The mark can be used during a manufacturing process, for example, to indicate a paint color of a car chassis during manufacturing or other useful information. The transmitter of the IDRF reader produces RF signals through the antenna to create an electromagnetic field that makes it possible for the marks to return a signal that carries the information. In some configurations, the transmitter initiates communication, and makes use of an amplifier to operate the antenna with a modulated output signal to communicate with the IDRF mark. In other configurations, the IDRF mark receives a continuous wave signal from the IDRF reader and initiates communication by responding immediately with its information. A conventional brand can be an "active" brand that includes an internal power source, or a "passive" brand that is powered by the field created by the IDRF reader. In any case, brands communicate using a pre-defined protocol, allowing the IDRF reader to receive information from one or more brands. The computing device serves as an information management system receiving information from the IDRF reader and performing some action, such as updating a database. In addition, the computing device can serve as a mechanism for programming the data in the marks via the transmitter. Conventional antennas for IDRF readers have a unique inductive circuit and operate in a relatively high frequency range, for example, 3 megahertz (MHz) at 30 MHz. Consequently, these antennas tend to create magnetic fields that suffer from "holes" , ie regions in which an IDRF mark can not be read even though the IDRF mark is located relatively close to the antenna. For example, depending on the orientation and location of the item to which the IDRF mark is set, in some situations the IDRF mark may be centered above a single turn of the inductive antenna circuit during interrogation. In this situation, substantially equal current can be imposed on opposite sides of the IDRF mark, which leads to a cancellation effect. As a result, the IDRF brand may not be able to achieve IDRF communication with the reader. In addition, conventional antennas used with desktop IDRF readers tend to create magnetic fields that extend horizontally beyond the edges of the antennas. In consecuense, items placed next to the antenna, for example, next to the antenna on the desk, can be inadvertently read by the reader, which can lead to unwanted results. For example, books associated with a library pattern and located next to an antenna in a library management system may be inadvertently recalled to another pattern. BRIEF DESCRIPTION OF THE INVENTION In general, a protection component and field formation antenna are described which form the magnetic field in a desirable configuration for use in an IDRF system. More specifically, a dual circuit antenna is described in which the circuits are placed and spaced in a manner that reduces the size of the holes within the resulting magnetic field. In addition, the configuration of the described dual circuit antenna achieves increased field size relative to a single circuit antenna with equivalent power and decreases the inter-wind capacitance, thereby decreasing the total reading range achieved by the antenna . In addition, a conductive protection is described that additionally refines and forms the magnetic field produced by the antenna. For example, the antenna can be placed substantially horizontally on a desk or counter. Conductive protection can be oriented parallel to the plane of the antenna, including located in the same plane as the antenna, and generally surrounding the antenna to limit the extent to which the electromagnetic field extends horizontally beyond the edges of the antenna. As a result, an electromagnetic field is produced that generally projects up and down the antenna, thus defining a generally vertical communication zone in which the IDRF marks can be read. In one embodiment, a multi-circuit antenna comprises a plurality of conductive circuits for producing an electromagnetic camp for radio frequency identification (IDRF) communication with the IDRF marks. The conductive circuits are spaced apart at least at a distance that is selected based on a dimension of the IDRF marks with which the antenna communicates. In another embodiment, a radio frequency identification system (IDRF) comprises an IDRF mark associated with an article, and an antenna having a plurality of conductive circuits for producing an electromagnetic field for communication with the IDRF mark. The conductive circuits are spaced at least one distance that is selected based at least in part on a dimension of the IDRF mark. In another embodiment, a radio frequency identification system (IDRF) comprises an antenna that forms an electromagnetic field for communication with IDRF marks, wherein the antenna has a substantially flat shape. A substantially contiguous conductive protection is placed around the antenna and within a plane parallel to the antenna. The details of one or more embodiments of the invention are described in the accompanying figures and the subsequent description. Other features, objects, and advantages of the invention will be apparent from the description and figures of the claims. BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a block diagram illustrating an exemplary IDRF 2 system incorporating the techniques described herein. Fig. 2 is a block diagram further illustrating an embodiment of an antenna of the IDRF system of Fig. 1. Fig. 3 is a plan view of an exemplary dual circuit antenna. Figure 4 is an exploded view of the dual circuit antenna of Figure 3. Figure 5 is a schematic diagram illustrating a dual circuit antenna used in conjunction with a conductive shield to refine and further shape the resulting magnetic field. Figure 6 is a side view perspective diagram illustrating the exemplary effects on a magnetic field from a conductive protection on a single circuit antenna. Figure 7 is another side view perspective diagram illustrating the exemplary field formation effects of a conductive protection. Figure 8A is a perspective diagram illustrating a side view of a mode in which a conductive shield and an antenna are mounted below a work surface. Figure 8B is a perspective diagram illustrating a side view of a mode in which the antenna is mounted on a recessed portion of a work surface, and a conductive protection is mounted on a non-recessed portion of the work surface. DETAILED DESCRIPTION OF THE INVENTION Figure 1 is a block diagram illustrating an exemplary IDRF 2 system embodying the techniques described herein. In the illustrated example of Figure 1, the IDRF 2 system is used to track books, documents, files or other items. The IDRF system can be, for example, deployed within libraries, law offices, government agencies, or other facilities that generate and / or store documents and files, such as business, criminal and medical records. The articles contain IDRF marks that only identify the items. In addition, each IDRF mark may also contain information that describes the article, and status information that indicates whether the removal of the item is authorized. IDRF marks can be embedded within the articles so that the marks are substantially imperceptible, thus reducing or preventing alteration. In general, the IDRF system 2 operates within a frequency range of the electromagnetic spectrum, such as 13.56 MHz, with an allowable frequency variation of +/- 7 KHz. However, other frequencies may be used for IDRF applications, and the invention is not limited in this way. For example, some IDRF systems in large storage areas such as warehouses may use an IDRF system operating at approximately 900 MHz. As illustrated in Figure 1, system 2 includes an output control system 5 that detects unauthorized removal of items from a protected area. For example, the protected area may be a library and the items may be books or other items that are usually removed from and received back into the library. The techniques may also be applied to other types of articles without departing from the scope of the present invention. The output control system 5 includes grids 89A and 9B which define an interrogation zone or corridor located near the exit of the protected area. Screens 9A and 9B include antennas to interrogate the IDRF marks as they pass through the corridor to determine if the removal of the item to which the mark is attached is authorized. The output control system 5 can use at least one IDRF reader (not shown) to "-actuate the antennas." To detect a tag, the IDRF reader produces RF energy through the antennas to create an electromagnetic field within the antenna. In general, the terms "electromagnetic field" and "magnetic field" are used interchangeably in the present when the magnetic component is used to couple with the IDRF marks.The RF reader receives information from any of the marks present within the interrogation corridor, and the exit control system 5 determines if the removal of the article is authorized.If the removal of the article is not authorized, the exit control system 5 initiates some appropriate security option, such such as an audible alarm sounding, closing an exit door, etc. In addition, the IDRF 2 system includes a reception / removal area. For example, a library patron or staff member processes items for removal or return. In particular, the receiving / withdrawal area 11 includes an IDRF reader 18 for interrogating the IDRF marks affixed to the articles and changing their status as desired, for example, receipt or removal of the items. In addition, the articles may be placed in a number of storage areas 12, for example, on an open shelf 12A, a booth 12B, a vertical file splitter 12C or another location, as shown 'in Figure 1. Each area Smart Storage 12 includes branding capability which makes it possible to track items throughout an installation. In a "library" environmentFor example, a book can be tracked after reception while it is on the shelf 12. The IDRF marks themselves may take any number of forms without departing from the scope of the present invention. Examples of commercially available IDRF brands include IDRF 3- brands available from 3M Company, St. Paul, MN, or IDRF "Tag-it" transponders available from Texas Instruments, Dallas, TX. An IDRF trademark typically includes an integrated circuit operatively connected to an antenna that receives RF energy from a source and backscatters the RF energy in a manner well known in the art. The IDRF mark modulates RF energy by providing a backscattered signal to communicate information about the IDRF brand and its associated item.

An article management system 14 provides a centralized database of brand information for each item in the facility. The article management system 14 can be interconnected or otherwise coupled to one or more computers so that individuals, such as a librarian, in various locations, can enter data in relation to those items. For example, a user may request the location and status of a particular item, such as a book. The article management system 14 can retrieve article information from a database, and report to the user the last location in which the article was located within one of the intelligent storage areas. Optionally, the article management system 14 can re-obtain or otherwise re-acquire the current location of an article to verify that the article is in the location indicated in the database. As described in further detail below, the IDRF 2 system incorporates the techniques described herein. The reception / removal area 11 and IDRF reader 18, for example, can incorporate a dual field-forming circuit antenna 13 and a conductive protection 16 that produce a magnetic field in a desirable configuration. For example, the IDRF reader 18 may incorporate the dual circuit antenna 13 described herein in which the circuits are placed and spaced in a manner that reduces the size of the holes within the resulting magnetic field. In addition, the configuration of the dual circuit antenna 13 described achieves increased field size relative to a single circuit antenna with equivalent power and decreases the interwinding capacitance, thereby increasing the total read range achieved by the IDRF reader. 18. In addition, the receiving / withdrawing area 11 can use a conductive protection 16 to further refine and form the magnetic field produced by the antenna 13. For example, as illustrated, the antenna 13 can be mounted substantially horizontally on, inside, or under the desk 15. The conductive protection 16 can be located flat and generally surrounding the antenna 13 to prevent the electromagnetic field from extending horizontally beyond the edges of the antenna. As a result, an electromagnetic field is produced which generally projects up and down the antenna 13, thus defining a generally vertical communication zone in which the IDRF marks can be read. Conductive protection 16 can be mounted on the desk 15, or under or inside the desk out of sight of library and personal patterns. Conductive protection 16 need not necessarily be electrically grounded to form the magnetic field as described herein.

Figure 2 is a block diagram further illustrating the antenna 13. As illustrated, the antenna 13 generally includes dual circuits 20 which, as described in additional detail below, are placed and spaced in a manner that reduces the size of the antenna. holes within the resulting magnetic field and achieve increased strength and field size. Although it is generally discussed that it has dual circuits, the antenna 13 may have additional circuits that are spaced based on the desired size of the brand communication zone as well as the dimensions of the individual brands. The tuning circuit 22 tunes dual circuits 20 to a resonant frequency, and provides impedance equalization and signal conversion between the circuit structure and cable 26, which may be a coaxial cable. The reader 18 is coupled to the tuning circuit 22 via the cable 26 and uses the antenna 13 to both transmit and receive IDRF operations. Accordingly, the reader 18 may include a directional coupler for interpreting the returned signal from the tuning circuit 22. Figure 3 is a plan view of an exemplary dual circuit antenna 30. In an exemplary mode, the dual circuit antenna 30 includes an internal circuit 32 and an external circuit 34 that reside on the parallel layers of a printed circuit board. In another embodiment, the internal circuit 32 and the external circuit 34 reside in a co-planar relationship. Due to the configuration of the dual circuit antenna 30, the current (I) of the reader 18 (FIGS. 1, 2) flows through each conductive edge of the circuits 32, 34 in the same direction. As a result, the electromagnetic fields created by the parallel conductive edges of the circuits 32, 34 are additive in nature and achieve a resulting field having an increased field size relative to a single circuit antenna with equivalent power. In addition, the internal circuit 32 and external circuit 34 are positioned and spaced to reduce the number and / or size of any of the potential holes within the resulting magnetic field. For example, different from conventional single circuit antennas, the reader 18 may be able to achieve successful communication with an IDRF mark placed directly above a conductive edge of the antenna. More specifically, in this situation a conventional single circuit IDRF antenna can produce substantially equal current on opposite sides of the IDRF mark, which leads to a cancellation effect. In contrast, an IDRF mark centered above one edge of the external circuit 34, for example, will achieve increased current on the inner side of the IDRF mark due to the internal circuit 32. Similarly, an IDRF mark centered above a internal circuit edge 32, for example, will achieve increased current on the outer side of the IDRF mark due to external circuit 34. In either case, the increased current achieves increased energy within the IDRF mark, allowing the IDRF mark communicates successfully with the IDRF reader 18. In this manner, the described configuration of the dual circuit antenna 30 can reduce the number and / or size of any of the holes within the resulting electromagnetic field. In one embodiment, the internal circuit 32 and external circuit 34 may be placed at least at a separate distance D, where D is selected based on a dimension of an IDRF mark for use within the system. For example, sizes for many conventional 13.56 MHz IDRF brands vary in dimension from 0.5"x 1" (1.27 cm x 2.54 cm) to 2"x 3" (5.08 cm x 7.62 cm). Accordingly, in a D mode it may be selected to exceed a maximum dimension of the IDRF mark to ensure that no IDRF mark can be placed through both the internal circuit 32 and the external circuit 34, which may be advantageous in the increase of the ability of reader 18 to achieve successful communication with brands without considering the location of the brand. Consequently, in a D >modality; 2.54 cm. In another embodiment, D > 5.08 cm.

Although illustrated for exemplary purposes with respect to the generally rectangular dual circuits, other forms of circuits can be easily used, such as round, oval and other geometric configurations. Figure 4 is an exploded view of the antenna 30 of Figure 3. As described above, antenna 30 comprises a first layer 40 containing internal circuit 32 and a second layer 42 containing external circuit 34. Layers 40, 42 , for example, layers can be stacked on top of each other to form a multilayer printed circuit board. Figure 5 is a schematic diagram illustrating a dual circuit antenna 60 used in conjunction with a conductive shield 66 to refine and further shape the resulting magnetic field. Although illustrated for exemplary purposes with respect to a dual circuit antenna, the conductive protection 66 may be used with other forms of antennas, such as single-circuit antennas or multiple of square, round or other configurations. Conductive protection 66 can be seen as four conductive flat regions 65A-65D which form an almost contiguous conductive protection having an unprotected internal region 61 around antenna 60. Conductive protection 66 prevents the passage of an electromagnetic field, limiting hence the magnetic field created by antenna 60 to the inner region. In other words, the magnetic field created by the antenna 60 extends vertically (eg, in and out of Figure 6) into the inner region 61, but is prevented from substantially forming on the conductive shield 66 due to the Conductive nature of conductive protection. The conductive protection 66 includes a disconnection area 63 which prevents a closed circuit from being formed around the antenna 60, thereby preventing the current from forming within the conductive protection. In general, the disconnection area 63 may have an opening of a minimum distance D4 of sufficient minimum to create an electrical disconnection within the conductive protection 66 and not substantially reduce the protective effect of the conductive protection. For example, the conductive protection 66 may be conventional or other copper conductive protection, and the distance D4 need not be more than a few millimeters. In general, the conductive protection 66 is located at a distance D3 from the external circuit 64, and the distance D3 therefore defines the outermost regions of the mark communication zone created by the antenna 60. In other words, D3 defines the outermost boundaries of the unprotected internal region 61 in which the marks can be read when the antenna 60 is driven with sufficient power to generate a magnetic field that has sufficient strength to achieve successful communication throughout the inner region. Each of the conductive regions 65A-65D has a width of D5, which is generally determined based on the strength of the magnetic field formed by the antenna 60. For example, the width D5 of each of the conductive regions 65A-65D should it suffices that the field resistance in any region beyond, eg, external, conductive protection 66 is below a threshold level necessary for IDRF communication. In this way, the conductive protection 66 substantially prevents IDRF communication in areas above the conductive protection 66 until the field itself has reached an insufficient field strength insufficient for the IDRF communication, which can be anywhere between inner edges and the outer edges of the conductive regions 65. Accordingly, D5 can be seen as a minimum width of the conductive regions 65, and the conductive regions can have larger widths. For example, conductive regions 65 may extend beyond distance D5 for other reasons, for example, -simplicity of manufacturing. In addition, the conductive regions 65 need not be of uniform widths, but rather each preferably exceeds the minimum distance D5. Figure 6 is a side-view perspective diagram illustrating the effects on a magnetic field from a conductive shield for which a left portion 70 and a right portion 72 are shown. For simplicity, a single circuit antenna is illustrated in Figure 6 by the conductive traces 74 and 76. It should be understood that with respect to the effects of a conductive protection, a dual circuit antenna can logically be viewed as a circuit antenna only one that has a radius equal to an average between the radios associated with the dual circuits. As illustrated in FIG. 6, the current I within the conductive traces 74 and 76 creates respective magnetic fields 82 and 84. Notably, the magnetic fields 82, 84 may extend to the regions 78, 80, respectively, but for the protection the left portion 70 and right portion 72 are affected, respectively. Accordingly, it should be understood that the location of the left portion 70 and right portion 72 closest to the conductive traces 74 and 76 could further limit the outward extension to which the resulting magnetic field is formed. In addition, the location of the left portion 70 and right portion 72 closest to the conductive traces 74 and 76 could further limit the extent to which the fields 82, 84 extend inwardly to the opposite conductive tracing. The total communication zone for this single circuit antenna is the approximate sum of the magnetic fields 82 and 84.

For this reason, D3 (Figure 5) is selected to exceed a minimum distance necessary for the magnetic fields 82, 84 (Figure 6) to overlap to ensure that a field resistance is achieved within the circuits sufficient for the IDRF communication. . In one embodiment, for example, D3 is selected to approximately equal the average of Di and D2 as follows: D3 > (DI + D2) / 2. (1) In addition, D2 is selected to approximately equal 1.5 * Dl. For example, Di, D2 and D3 can equal 2"(5.08 cm), 3.5" (8.89 cm), and 2.75"(6.98 cm) respectively.This particular selection for distance D3 allows the resulting magnetic field created by the circuit internal 62 and external circuit 64 (Figure 5) extends from these circuits both in the inward and outward directions to completely cover the antenna 60 with sufficient resistance to achieve IDRF communication.Figure 7 is another perspective view diagram • Lateral illustrating the effects of field formation of a conductive protection. In particular, Figure 7 illustrates a resultant electromagnetic field 90 produced by the antenna 94 and formed by a conductive protection, of which a left portion 92A and a right portion 92B are shown. As illustrated, the conductive protection limits the extent to which the electromagnetic field 90 extends externally of the antenna 94, thereby preventing inadvertent reading of the IDRF marks located beyond the horizontal edges of a defined communication zone. Figure 8A is a perspective diagram illustrating a side view of an embodiment of a reception / removal area 100 in which an antenna 102 and conductive protection 104 are mounted below a surface 106. In this example, the antenna 102 and conductive protection 104 creates an IDRF mark communication zone 107 above the surface 106. The surface -106 may include visual identification of the edges of the communication zone. In this way, the conductive protection 104 prevents inadvertent reading of the IDRF marks in the areas 108 beyond the defined communication zone 107. Figure 8B is a perspective diagram illustrating a side view of another embodiment of a reception / removal area 110. In this example, the desk 116 forms a recess 120, below which the antenna 112 is mounted. The conductive protection 114 is mounted to surround the antenna 112, in the non-recessed portion of the desk 116. In this example, the antenna 112 and conductive protection 114 create a dial-up communication zone of IDRF 117, and the conductive protection prevents reading inadvertent of the IDRF marks in areas 118 beyond the defined communication zone. In another embodiment, the desk 116 does not form the recess 120, and the antenna 112 is mounted below the desk. Several embodiments of the invention have been described. These and other modalities are within the scope of the following claims. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (16)

1. Having described the invention as above, the content of the following claims is claimed as property: 1. Radio Frequency Identification System (IDRF), characterized by comprising: an antenna that forms an electromagnetic field for communication with IDRF markers, in where the antenna has a substantially flat shape; and substantially contiguous conductive protection placed around the antenna and within a plane parallel to the antenna.
2. 2. An IDRF system according to claim 1, characterized in that the conductive protection forms the magnetic field to extend substantially in a direction perpendicular to the antenna, and prevents the electromagnetic field from being formed substantially over the conductive protection.
3. An IDRF system according to claim 1, characterized in that the conductive protection comprises flat conductive regions oriented to form an unprotected internal region, and further where the antenna is placed within the unprotected internal region and parallel to the regions flat conductive
4. 4. IDRF system according to claim 3, characterized in that the conductive regions define at least one disconnection area which prevents the conductive field from forming a closed conductive circuit around the antenna.
5. 5. IDRF system according to claim 3, characterized in that the antenna comprises one or more conductive circuits including an external circuit, and the conductive regions of the conductive protection are located at least at a distance D3 from an external circuit of the antenna that is selected based on a radio of the external circuit.
6. 6. IDRF system according to claim 3, characterized in that the antenna has a first conductive circuit having a radius Di and a second concentric conductive circuit having a radius D2, and the conductive regions of the conductive protection are located at less at a distance D3 from the external circuit, and where D3 is selected as approximately the average of Di and D2.
7. 7. IDRF system according to claim 3, characterized in that each of the conductive regions has respective widths extended outwardly from the antenna, and further where the widths are selected based at least in part on a field threshold level. necessary for the IDRF communication between the antenna and the IDRF marks.
8. An IDRF system according to claim 7, characterized in that the widths are selected to extend sufficiently in the parallel and outward directions of the antenna to prevent the electromagnetic field from forming inside or above the conductive regions until the Magnetic field strength is reduced below the communication threshold.
9. 9. IDRF system according to claim 1, characterized in that. the antenna and the
10. "conductive protection are mounted to a work surface of an IDRF reception / removal area ..
11. IDRF system according to claim 9, characterized in that the work surface has a recessed area and a non-recessed area, and additionally wherein the antenna is mounted to the recessed area of the work surface and the conductive protection is mounted to the non-recessed area 11.
12. IDRF system in accordance with claim 1, characterized in that the conductive protection and the antenna are Planar IDRF system according to claim 1, characterized in that the conductive protection and the antenna are located in two different parallel planes.
13. 13. IDRF system according to claim 1, characterized in that it additionally comprises: an IDRF interrogation device coupled to the antenna, wherein the interrogation device interrogates the IDRF marks to obtain information with respect to the selected articles; and a computing device for processing information retrieved from the IDRF interrogation device.
14. An IDRF system according to claim 1, characterized in that the antenna comprises a plurality of conductive circuits for producing the electromagnetic field, and wherein the conductive circuits are spaced apart at least one distance D that is selected based on a dimension of the IDRF marks with which the antenna communicates.
15. 15. IDRF system according to claim 14, characterized in that the distance D is selected to exceed a maximum dimension of the IDRF marks.
16. 16. IDRF system according to claim 14, characterized in that the IDRF marks have a length dimension M, and the distance D between each of the plurality of conductive circuits is selected so that D > M.