HK1231602B - Rfid antenna system and method - Google Patents

Description

RFID antenna systems and methods

This application is a divisional application of the invention patent application with Chinese patent application number 200880113956.5 and application date of PCT application PCT/US2008/011303 on September 30, 2008, and entitled "RFID Antenna System and Method".

Technical Field

The present invention relates to the field of radio frequency identification ("RFID") communications, and in particular to RFID transponder configurations.

Background Art

Radio frequency identification (RFID) devices are becoming increasingly popular in a wide variety of industrial, retail, transportation, and other applications. RFID technology uses passive radio frequency signals to provide active identification of any object, person, or similar object carrying an RFID transceiver. In a typical application, an RFID transceiver includes an antenna and an integrated circuit. When a separate RFID reader broadcasts a radio frequency signal, the signal interacts with the RFID transceiver antenna. The transceiver antenna converts a portion of the received RF signal's energy into an electrical current. This current powers the integrated circuit. The integrated circuit then adjusts its impedance to produce a return RF signal. This return RF signal is then detected by the antenna in the RFID reader. This adjusted RF return signal carries encoded data about the transceiver based on data previously stored in the integrated circuit. For example, the transceiver's serial number can be returned to the RFID reader via this adjusted RF signal. Finally, the RFID reader decodes the signal returned from the transceiver to complete the identification.

RFID transceivers are being integrated into a growing number of applications. Employee identification tags, animal identification devices, retail pricing and inventory devices, retail security devices, product manufacturing and material tracking devices, vehicle identification devices, and the like are just a few examples of the expanding areas of application for RFID technology. RFID transceivers are ideally suited for integration with a wide variety of products and in a wide variety of environments. RFID transceivers can be purely passive devices, where all energy for operating the integrated circuit comes from the broadcast RF signal. Alternatively, active RFID systems may include an on-board battery to power the identification chip and/or the transceiver's return RF signal. In fixed systems, such as motor vehicle transceivers used in automated toll collection systems, the added cost of an on-board battery is easily justified by the improved performance of the device. In contrast, in cost-sensitive applications, such as retail pricing and security tags, RFID transceiver devices must be as inexpensive as possible and are therefore typically passive.

The on-board antenna is the key to the technology that implements RFID transceiver devices. The broadcast RF energy can be in the form of a magnetic field, an electric field, or a mixed field, as in a typical wireless signal broadcast. The shape and size of the transceiver antenna are designed based on the characteristics of the broadcast RF energy, such as the type of field and the signal frequency. In addition, the design of the RFID tag typically requires matching the antenna impedance and the load impedance, usually through a matching circuit, to maximize the RF energy from the reader's query or the command signal received by the tag antenna to be transmitted to the RFIC with minimal loss, thereby achieving optimal tag sensitivity. In theory, maximum energy transfer is achieved by conjugating the impedance matching, which requires that the impedance from the antenna is as close as possible to the mathematical conjugate value of the RFID input impedance. This represents an ideal impedance match.

In many applications, it is desirable to reduce the overall size or "footprint" of a particular RFID device. This includes applications where a reduced size may be required on or within retail merchandise having a small footprint. Alternatively, it may simply be desirable to make the RFID device as inconspicuous as possible. While technology exists to significantly reduce the size of the IC components of an RFID device, similar miniaturization of the RFID device's antenna can result in a significant reduction in performance. As discussed above, the particular IC and antenna of an RFID device ideally have matching impedance characteristics. By reducing the overall size of the RFID device, and therefore the overall size of the antenna, it may prove difficult to provide the impedance characteristics sufficiently for effective functioning of the device. Consequently, the RFID may suffer from: inefficient energy transfer to the IC, a reduced operating range relative to the interrogator, and a weak return signal in response.

Furthermore, antennas attached to RFID tags are generally designed to operate within a specific or narrow range of the substrate to which the antenna is attached. Other substrates can cause the antenna's radiation efficiency to degrade from an optimally designed mounting substrate. As a result, the antenna, and therefore the RFID device, will no longer function as expected. This loss in antenna efficiency can be due to a number of variable packaging factors. For example, each substrate has its own dielectric and conductive properties, which typically affect the impedance matching between the wireless communication device and its antenna. Impedance matching ensures the most efficient energy transfer between the antenna and the wireless communication device, as discussed above, and placing an RFID device near a surface with dielectric and conductive properties outside of a specific range can degrade the performance of the RFID device. These adverse effects on RFID device performance can also affect included or integrated electronic article surveillance (EAS) tags or devices. Such EAS devices often include a magneto-acoustic mechanism with one or more metallic components, which can subsequently interfere with or degrade the performance characteristics of a particular RFID device.

In view of the foregoing, it would be desirable to provide an RFID device having a reduced footprint while providing efficient operation on various surfaces and/or in conjunction with EAS tags.

Summary of the Invention

The present invention advantageously provides a method and system for an RFID/EAS device. According to a first aspect of the present invention, an RFID device is provided having a dielectric substrate body, an antenna disposed on the substrate body, and a first spacing element, wherein at least a portion of the substrate is wrapped around a portion of the spacing element.

The substrate may be made of a material including at least one of polyimide, polyester, fiberglass, ceramic, plastic, and paper, and the antenna may be made of a material including at least one of copper, aluminum, and conductive ink. The antenna may include a conductive material patterned onto the surface of the substrate body. In particular, the pattern includes a plurality of polygons, such as one or more polygons having a substantially rectangular shape with square or rounded corners. The pattern may also include meanderline (meandering pattern) segments. The plurality of polygonal antennas may be discontinuous and/or include non-conductive openings or breaks therein to thereby provide a single conductive path. In addition, one or more capacitors may be provided on the substrate, and the one or more capacitors may be in electrical communication with the antenna.

In another aspect of the present invention, an RFID/EAS device is provided. The RFID/EAS device may generally include a dielectric substrate body, an antenna disposed on the substrate body, a first spacing element, and a second spacing element. Furthermore, an EAS element may be disposed between the first spacing element and the second spacing element, and at least a portion of the substrate body may be positioned to surround a portion of the first and second spacing elements. The EAS element may include an acousto-magentic device and/or a microwave device.

In another aspect of the present invention, a method of assembling an RFID/EAS device is provided, wherein the method includes the steps of providing an RFID device having a dielectric substrate body and an antenna disposed on the substrate body. The method also includes positioning an EAS element between a first spacing element and a second spacing element, and then wrapping at least a portion of the RFID device around at least a portion of the first spacing element and the second spacing element.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention and its attendant advantages and features will be more readily appreciated by reference to the following detailed description considered in conjunction with the accompanying drawings, in which:

FIG1 illustrates an embodiment of an RFID device constructed in accordance with the present invention;

FIG2 illustrates an alternative embodiment of an antenna pattern for an RFID device constructed in accordance with the present invention;

FIG3 illustrates another embodiment of an antenna pattern for an RFID device constructed in accordance with the present invention;

FIG4 illustrates the use of one or more capacitors electrically connected to an antenna constructed in accordance with the present invention;

FIG5 illustrates the ability of an antenna according to the present invention to be wrapped around a spacer element; and

FIG. 6 illustrates an alternative configuration of spacer elements for use in accordance with the present invention.

DETAILED DESCRIPTION

Referring now to the drawings, wherein like reference numerals represent like elements, FIG. 1 shows a diagram of an exemplary device constructed in accordance with the principles of the present invention and generally designated "10." Device 10 is an RFID device that generally may include a substrate body 12, wherein an integrated circuit ("IC") component 14 is connected to substrate body 12, and an antenna 16 disposed on substrate body 12 in electrical communication with IC component 14. Antenna 16 may generally include a pattern of conductive material. Specifically, antenna 16 may include a plurality of substantially square or rectangular polygons 18 having square or rounded corners, wherein a portion of polygons 18 is hollowed out, i.e., does not contain conductive material. The plurality of polygons 18 may be electrically connected to each other via a strip or portion of conductive material 20 that connects each polygon 18 and further connects the plurality of polygons 18 to IC component 14. Although not shown, it is contemplated that the pattern of antenna 16 may take the form of a meander line segment, such that the overall length of antenna 16 is greater than the distance from the antenna's endpoint connected to IC component 14 to the outer edge of substrate body 12. This can be achieved, for example, by allowing antenna 16 to "meander" back and forth along substrate body 12 as it extends from IC element 14 to the outer edge of substrate body 12. Meander line segments can be used independently or in combination with one or more polygons. Antenna 16 can also include a conductive coupling (not shown) located between a first portion and a second portion of antenna 16 on either side of IC element 14. The coupler can provide a current return path to increase or otherwise optimize the performance characteristics of antenna 16.

The device 10 may further include a spacing element 22, wherein at least a portion of the substrate body 12 surrounds at least a portion of the spacing element 22. As described in detail below, the RFID device 10 may further include an EAS element, such as an acousto-optic-magnetic device (not shown in FIG. 1 ), coupled to at least one of the substrate body 12 and/or the spacing element 22.

In particular, substrate body 12 may generally define a first surface 13a and a second surface 13b opposite first surface 13a, wherein first surface 13a may receive IC component 14 and at least a portion of antenna 16. First surface 13a may include dielectric properties to reduce or eliminate the possibility of interference with antenna 16 or otherwise prevent shorting of antenna 16 and/or IC component 14. Second surface 13b may be suitable for securing or otherwise attaching to a particular object, packaging, or the like. For example, second surface 13b may include adhesive or similar properties to facilitate placement of RFID device 10. Furthermore, second surface 13b may have dielectric properties similar to those of the first surface. Substrate body 12 may include one or more substrate layers made of a flexible material, such as an organic material such as polyimide or polyester. Substrate body 12 may have an elongated rectangular shape with dimensions appropriately designed for a given application, although a myriad of shapes and sizes may be used for different environments.

The IC component 14 of the RFID device 10 may be connected to or otherwise positioned on the first surface 13a of the substrate body 12. The IC component 14 may generally include an integrated circuit device capable of storing multiple bits of data and may further be capable of regulating current in the antenna of the RFID device 10 to thereby encode data into an RF signal. In particular, the IC component 14 may include a semiconductor-based device, such as a silicon chip, and may also include active and/or passive components integrated thereon, such as transistors, resistors, capacitors, and the like. For example, the IC component 14 may include a passive network of resistors, capacitors, and/or inductors that exhibits a resonant response to an input RF signal. Additionally, the IC component 14 may include a diode device to simply rectify the input RF signal. The IC component 14 may also include a fixed response frequency and/or identifying data pattern, and may optionally include a programmable and/or preprogrammable response frequency and/or identifying data pattern.

The RFID device 10 of the present invention also includes an antenna 16 disposed on the first surface 13a of the substrate body 12, wherein the antenna 16 is capable of conducting RF signals. The antenna 16 may comprise a patterned configuration of conductive material in electrical communication with the IC component 14 to transmit signals to and from the IC component 14. The pattern of the antenna 16 may be varied and/or selected to provide a desired impedance characteristic to match the electrical characteristics of the IC component 14 for optimal use and performance of the RFID device 10. The antenna 16 may comprise a material having sufficiently high electrical conductivity, such as a metallic material including copper (Cu) or aluminum (Al), or microwave-conductive carbon fiber. The antenna 16 may be patterned onto the first surface 13a of the substrate body 12 using any commonly known patterning method, such as, but not limited to, photolithography, ion etching, chemical etching, or vapor deposition. The antenna 16 may generally comprise a dipole configuration with the IC component 14, although the present invention is equally applicable to monopole configurations.

Furthermore, antenna 16 can be patterned to provide a single conductive path or, alternatively, multiple, serially connected electrical paths. For example, an antenna pattern can include multiple connected polygons 18 that provide a path for conducting a desired signal. Each polygon 18 can have a substantially continuous shape, with multiple polygons 18 connected to each other to define a series of conductive paths therethrough. The polygons of a particular antenna pattern can be "hollowed out" or have conductive material of varying diameters or thicknesses to provide the desired impedance for a particular application.

Alternatively, as shown in FIG2 , the antenna 16 may include a pattern of “open” polygons 18 that provide a single conductive flow path. The pattern of polygons 18 in FIG2 is non-continuous, i.e., one side or portion of each polygon 18 is non-conductive, thereby providing a single conductive flow path through the length of the antenna 12. In FIG2 , the polygons 18 are configured in an alternating pattern. Similar to the above-described antenna arrangement depicted in FIG1 , multiple non-continuous polygons 18 may be in electrical communication with each other via connections or deposits of conductive material connecting the multiple polygons 18 together and connecting the antenna pattern to the IC element 14. Additionally, if the antenna 16 includes a dipole configuration extending on either side of the IC element 14, there may be a conductive strip or portion 23 connecting the two sides of the antenna to each other to form a current loop or electrical path external to or independent of the IC element 14, as shown in FIG2 .

FIG3 illustrates another antenna configuration in which each polygon 18 is non-continuous, as in the embodiment shown in FIG2 . However, in this configuration, the orientation of each polygon 18 is repeated. The present invention is not limited to any particular orientation of polygons 18 and may include combinations of patterns, not just the orientations depicted in FIG2 and FIG3 . By varying the pattern (or meandering line) of polygons 18, different overall impedances can be achieved.

2 and 3 show symmetrical antenna segments on each side of IC chip 14, the invention is not limited thereto. It is contemplated that asymmetrical antenna segments may be implemented, for example, by having a different number of polygons 18 on each side of IC chip 14.

Similarly, as shown in the exemplary embodiments of Figures 1-3, the capacitive and inductive portions of the impedance used to match the antenna to the IC chip 14 can be derived from the antenna 16 itself, without the need for external discrete devices. By changing the length of the conductive path of the antenna 16, the capacitive and inductive portions of the impedance can be changed. By way of non-limiting example, extending the length of the antenna 16 results in an increase in the capacitive and inductive portions of the impedance. In a situation such as that shown in Figure 1, where the resulting length of the antenna 16 exceeds the length of the spacer 22 (or EAS element), as described in detail below, the substrate body 12 (together with the antenna 16) can be wrapped around the spacer to minimize the overall package size.

In FIG4 , one or more discrete capacitors 26 may be electrically connected to either or both ends of the antenna 16 to provide the desired electrical capacitance characteristics of the RFID device. As used herein, the term “capacitor” is intended to include any element or structure that exhibits capacitive properties. For example, it may include an extension of the antenna 16 or the like, and is not limited to the construction of a discrete “capacitor” element consisting of two charged conducting surfaces having opposite polarities separated by a dielectric. Although it is not necessary to create matching impedance based on the use of the conductive path length of the antenna 16 itself, discrete capacitors 26 and/or discrete inductors (not shown) may be implemented in any of the antenna arrangements described herein.

As described above, the RFID device 10 of the present invention may also include one or more spacer elements 22 connected to the substrate body 12 to bias or otherwise manipulate the position of the substrate body 12, or any portion thereof, relative to one another. Each spacer element 22 may define a substantially planar body having non-conductive and/or dielectric properties and may be made of a non-conductive plastic, polymer, or other suitable insulating material. For example, the spacer element 22 may comprise a substantially rectangular portion of insulating foam, wherein the spacer element has a thickness of less than approximately 3 mm.

FIG5 illustrates an exemplary configuration of an RFID device 10 of the present invention utilizing any of the aforementioned antenna configurations. As discussed above, IC component 14 is connected to a non-conductive surface of substrate body 12. Antenna 16 extends from and is in electrical communication with IC component 14 on substrate body 12 to provide a desired impedance characteristic, as described above. At least a portion of substrate body 12 of RFID device 10 can then be positioned around the periphery or exterior portion of spacer element 22. Substrate body 12 can then be substantially wrapped, folded, or otherwise positioned around spacer element 22 such that IC component 14 and antenna 16 face or are otherwise proximate to spacer element 22. Note that while FIG5 illustrates spacer element 22 as separate from substrate body 12, it is contemplated that cover stock (not shown) can be positioned over substrate body 12 such that, when substrate body 12 is wrapped around itself, the cover stock functions as spacer element 22. The thickness of the cover stock, e.g., cardboard, paper, plastic, etc., can be varied to establish the desired resulting spacing when substrate body 12 is wrapped around itself.

When the substrate 12 is substantially wrapped around and over the spacer element 22, the resulting RFID device 10 has substantially the same physical dimensions as the spacer element, without compromising or reducing the actual length of the antenna 16. The spacer element 22 prevents the antenna 16 from shorting because it provides a buffer between opposing portions of the antenna 16. As a result, when the antenna 16 is wrapped over the spacer element 22, the overall impedance of the antenna 16 matches the impedance of the IC component 14, while the size of the RFID device 10 is significantly reduced due to the ability of the substrate 12 to be folded over the spacer element 22. Thus, because the substrate 12 is "wrapped" over the spacer element 22, the RFID device 10 achieves impedance matching between the IC component 14 and the appropriate antenna pattern while significantly reducing its overall size, while at the same time preventing shorts in the antenna or circuitry on the device 10 due to the spacer element 22.

The device of the present invention may also include an electronic article surveillance ("EAS") element 24 connected to the substrate body 12. The EAS element 24 may include an acousto-optical-magnetic device having amorphous ferromagnetic metal strips that are free to mechanically oscillate and are identified by their resonant response to an induced magnetic field.

Alternatively, the EAS element may comprise a microwave device having a nonlinear element (e.g., a diode) connected to microwave and electrostatic antennas. One antenna emits a low-frequency (approximately 100 kHz) field, while the other emits a microwave field, with the device acting as a mixer that re-emits the combined signal from the two fields to trigger the alarm. Additional suitable EAS devices and/or tags known in the art may be equally suitable for use with the present invention.

6 , the EAS element 24 can be embedded or otherwise disposed between one or more spacer elements 22, while the substrate body 12 remains disposed around the perimeter of the one or more spacer elements 22. Specifically, the EAS element 24 can be disposed between a first spacer element 22a and a second spacer element 22b (collectively referred to herein as “spacer elements 22”), with the substrate body 12 having the IC element 14 and antenna 16 disposed around a portion of the perimeter of the first and second spacer elements 22, thereby resulting in the folded configuration shown in FIG5 . Because the substrate body 12 and the EAS element 24 are not in electrical communication with each other, the desired impedance characteristics of the antenna/IC element pairing remain intact, while allowing the RFID device 10 to provide both identification and article theft prevention functions.

In an exemplary use of the RFID device 10, the RFID device 10 can be attached to or otherwise positioned on merchandise or items. The RFID device 10 can include an EAS element 24 embedded within one or more spacer elements. Furthermore, by wrapping at least a portion of the device around the one or more spacer elements, the overall footprint of the RFID device is greatly reduced.

It will be understood by those skilled in the art that the present invention is not limited to what has been particularly shown and described herein. Furthermore, it should be noted that unless otherwise indicated above, all of the accompanying drawings are not drawn to scale. In light of the above teachings, various modifications and variations are possible without departing from the scope and spirit of the present invention, which is limited only by the following claims.

Claims (17)

1. An RFID/EAS device, comprising: A dielectric substrate body having a rectangular shape with a predetermined thickness and having a first surface and a second surface opposite to each other, wherein the rectangular shape of the dielectric substrate body defines the direction of the long side; An RFID integrated circuit is disposed on a first surface of the dielectric substrate body; A bipolar antenna is disposed on a first surface of the dielectric substrate body and electrically connected to the RFID integrated circuit. The bipolar antenna includes a first antenna portion and a second antenna portion, both of which are connected to the RFID integrated circuit and extend from the RFID integrated circuit along the long side of the dielectric substrate body in opposite first and second directions. A spacer element, formed separately from the dielectric substrate body, the spacer element comprising a planar body having a predetermined thickness and having a first surface and a second surface opposite to each other; and EAS element, which is embedded within the spacer element. The dielectric substrate body is wrapped around the spacer element with embedded EAS elements along the long side direction, such that the bipolar antenna contacts the first and second surfaces of the spacer element, and the RFID integrated circuit and the portions of the first and second antenna portions closest to the RFID integrated circuit contact the first surface of the spacer element, while the portions of the first and second antenna portions farther from the RFID integrated circuit along the long side direction contact the second surface of the spacer element. 2. The RFID/EAS device as claimed in claim 1, wherein the first antenna portion and the second antenna portion are respectively composed of conductive material patterned onto the surface of the dielectric substrate body. 3. The RFID/EAS device of claim 2, wherein the pattern of the conductive material includes at least one of a plurality of polygons and zigzag lines. 4. The RFID/EAS device of claim 3, wherein each of the plurality of polygons has a substantially rectangular shape. 5. The RFID/EAS device of claim 3, wherein each of the plurality of polygons is discontinuous, thereby providing a single conductive path. 6. The RFID/EAS device as claimed in claim 1, wherein the spacer element is substantially non-conductive. 7. The RFID/EAS device as claimed in claim 1, wherein the EAS element is an acousto-optic-magnetic device. 8. The RFID/EAS device as claimed in claim 1, wherein the EAS element is a microwave device. 9. The RFID/EAS device of claim 1, wherein the dielectric substrate body is made of at least one material selected from polyimide, polyester, glass fiber, ceramic, plastic and paper. 10. The RFID/EAS device of claim 1, wherein the bipolar antenna is made of a material comprising at least one of copper, aluminum, and conductive ink. 11. An RFID/EAS device, comprising: A dielectric substrate body having a rectangular shape with a predetermined thickness and having a first surface and a second surface opposite to each other, wherein the rectangular shape of the dielectric substrate body defines the direction of the long side; An RFID integrated circuit is disposed on a first surface of the dielectric substrate body; A bipolar antenna is disposed on a first surface of the dielectric substrate body and electrically connected to the RFID integrated circuit. The bipolar antenna includes a first antenna portion and a second antenna portion, both of which are connected to the RFID integrated circuit and extend from the RFID integrated circuit along the long side of the dielectric substrate body in opposite first and second directions. A spacer element comprising a first spacer element portion and a second spacer element portion is formed separately from the dielectric substrate body. The spacer element comprises a planar body having a predetermined thickness and having a first surface and a second surface opposite to each other. An EAS element is disposed between the first spacer element portion and the second spacer element portion of the spacer element. Wherein, the dielectric substrate body is wrapped around the EAS and the spacer element including the first spacer element and the second spacer element along the long side direction, such that the bipolar antenna contacts the first surface and the second surface of the spacer element, and the RFID integrated circuit and the portions of the first antenna portion and the second antenna portion closer to the RFID integrated circuit contact the first surface of the spacer element, while the portions of the first antenna portion and the second antenna portion farther from the RFID integrated circuit along the long side direction contact the second surface of the spacer element. 12. The RFID/EAS device of claim 11, wherein the first antenna portion and the second antenna portion are each composed of a conductive material patterned onto the surface of the dielectric substrate body. 13. The RFID/EAS device of claim 12, wherein the pattern of the conductive material comprises at least one of a plurality of polygons and zigzag lines. 14. The RFID/EAS device of claim 13, wherein each of the plurality of polygons has a substantially rectangular shape. 15. The RFID/EAS device of claim 13, wherein each of the plurality of polygons is discontinuous, thereby providing a single conductive path. 16. The RFID/EAS device of claim 11, wherein the bipolar antenna further includes a third antenna portion, the third antenna portion forming an electrical connection between the first antenna portion and the second antenna portion. 17. A method for assembling an RFID/EAS device, comprising the following steps: An RFID device is provided, comprising a dielectric substrate body having a rectangular shape with a predetermined thickness and having opposing first and second surfaces, and a bipolar antenna disposed on the first surface of the dielectric substrate body, the rectangular shape of the dielectric substrate body defining the long side direction, and the bipolar antenna comprising a first antenna portion and a second antenna portion. An isolation element is provided by positioning an EAS element between a first spacer element portion and a second spacer element portion, the first spacer element portion and the second spacer element portion being formed separately from the dielectric substrate body. The isolation element includes a planar body having a predetermined thickness and spacer elements having a first surface and a second surface opposite to each other. An RFID integrated circuit is disposed on a first surface of the dielectric substrate body, such that both the first antenna portion and the second antenna portion are connected to the RFID integrated circuit and extend from the RFID integrated circuit along the long side of the dielectric substrate body in opposite first and second directions, respectively; and The dielectric substrate body is wrapped around at least a portion of the spacer element along the long side direction, such that the bipolar antenna contacts the first and second surfaces of the spacer element, and the RFID integrated circuit and portions of the first and second antenna portions closest to the RFID integrated circuit contact the first surface of the spacer element, while portions of the first and second antenna portions farther from the RFID integrated circuit along the long side direction contact the second surface of the spacer element.