HK1149122A - Rfid antenna for use adjacent to conductive elements - Google Patents

Description

RFID antenna for use adjacent to conductive element

Technical Field

The present invention relates to Radio Frequency Identification (RFID) tag antennas, and more particularly to RFID tag antennas that are operable when in proximity to metal and other conductive elements.

Background

It is a challenge to accurately monitor the location and flow of objects related to inventory, product manufacturing, sales, and related operations. There is a need to continuously determine the location of these objects and track relevant information about the objects. A tag, identification, or marking device suitably configured to be associated with any form of object, including goods, merchandise, people or animals, or substantially any moving or stationary and animate or inanimate object, may be used to facilitate location and data tracking. One such tag tracking system is an electrical identification system, such as RFID. An RFID tag is affixed to, attached to, or in some way associated with an object to track the object and store and retrieve information about the object.

The RFID tag stores data related to the object. The RFID reader may scan for RFID tags by sending an interrogation signal at a known frequency. The RFID tag may respond to the interrogation signal, the response including, for example, data related to the object or an RFID tag ID. The RFID reader detects the response signal and decodes the data or RFID tag ID. The RFID reader may be a handheld reader or a fixed reader through which the goods with RFID tags pass. The fixed reader may be configured as an antenna located on a pedestal similar to that used in electronic article surveillance ("EAS") systems.

The antenna collects and transmits energy in the form of electromagnetic waves. The unit for this transmission is in the form of power per unit area. Many tags used in such tag detection systems have a single favored (distorted) direction with respect to the excitation field in which they show the maximum response, i.e. they are directional. Most tags are somewhat rectangular in shape and vary from a dipole antenna, having a large aspect ratio. These tags give the maximum response when they are oriented within an incident field orthogonal to the long axis of the tag. This property is commonly referred to as "reading direction sensitivity".

For example, fig. 1 shows one example of an RFID tag 100 having an antenna 102 disposed on a substrate 104. The substrate 104 is substantially rectangular in shape. Antenna 102 includes multiple antenna portions, i.e., antenna 102 has a first antenna portion 106 and a second antenna portion 108. The first antenna portion 106 is connected to a first side 112A of the lead frame 112. Second antenna portion 108 may be connected to a second side 112B of lead frame 112. The RFID chip 110 may be connected to the lead frame 112 by ultrasonically bonding the lead frame 112 to a conductive pad on the RFID chip 110. The RFID chip 110 and lead frame 112 are placed directly in the geometric center of the dielectric substrate material of the substrate 104. The ends of the lead frame 112 may be physically and electrically bonded to the foil (foil) antenna pattern of the antenna 102. The RFID chip may also be bonded directly to the antenna 102 by using a conductive adhesive to eliminate the need for the lead frame 112.

The first antenna portion 106 has a first antenna end 106A and a second antenna end 106B. Likewise, second antenna portion 108 has a first antenna end 108A and a second antenna end 108B. The first antenna end 106A of the first antenna portion 106 is connected to the lead frame 112A. The first antenna portion 106 is disposed on the substrate 104 and forms an inwardly spiraling pattern (pattern) from the RFID chip 110 in a first direction, and the second antenna end 106B terminates in an inner loop of the inwardly spiraling pattern on one half of the substrate 104. Likewise, first antenna terminal 108A of second antenna portion 108 is connected to lead frame 112B. Second antenna portion 108 is disposed on substrate 104 and forms a pattern spiraling inward from RFID chip 110 in a second direction, with second antenna end 108B terminating in an inner loop of the pattern spiraling inward on the other half of substrate 104. As shown in fig. 1, the two clockwise helical portions 106, 108 of the antenna 102 are substantially rotationally symmetric with respect to each other. RFID tag 100 produces a radiation pattern 200 (fig. 2) similar to that of a conventional dipole antenna.

The reception and transmission of RFID tag 100 is best when RFID tag 100 is perpendicular to its y-axis (i.e., along the z-axis) and not at all along the y-axis (also referred to as the "dipole axis"), as illustrated graphically in fig. 2 by radiation pattern 200. The dead space in the radiation pattern 200 of the antenna 102 is referred to as null 202. Antenna directivity is important for RFID tags because if the tag 100 is oriented with its null 202 pointing to the tag reader, the tag 100 receives no power for excitation and therefore cannot read. In general, a radiation pattern describes the sensitivity of a receiving antenna to the direction of travel or propagation of an Electromagnetic (EM) wave. Since an electromagnetic wave is a transverse wave, the electric field component of the electromagnetic wave is perpendicular to the propagation direction of the wave.

Another situation that results in additional empty areas in the radiation pattern 200 of the tag antenna 102 is where the RFID tag 100 is used on a conductive surface, such as a metal surface. In order to couple energy into a "dipole-like" antenna, an excitation field (electric field) parallel to the length of the dipole-like antenna and having an appropriate frequency is required. The conductive properties of the metal indicate that the tangential electric field (which is aligned with the length of the dipole antenna) will be zero at the metal surface. This effect prevents energy from coupling into the RFID tag 100, resulting in a full or partial reduction in the detection performance of the RFID tag 100.

Once removed from the metal surface, the electric field may be non-zero. Thus, a separate dielectric spacer is provided between the dipole antenna and the metal surface, to the extent that the excitation field reaches the RFID tag 100. However, even for Ultra High Frequency (UHF) RFID tags, large spacers (e.g., greater than 10 millimeters) are required to obtain comparable radiation exposure to the excitation field, thus making practical packaging and applications impractical. In addition, typical dielectric spacers are relatively expensive.

In view of the above, it would be desirable to provide an RFID device having a radiation pattern that is minimally affected by conductive surfaces, such as metal surfaces, EAS tags, and the like.

Disclosure of Invention

The present invention advantageously provides a Radio Frequency Identification (RFID) system and RFID tag that operate in conjunction with a conductive element.

According to one aspect, the present invention provides an RFID tag for use with a conductive element, the RFID tag comprising a substrate body having a surface and defining a plane of the tag. An RFID integrated circuit is disposed on a surface of the substrate body. An antenna having an antenna pattern is disposed on the base body and in electrical communication with the RFID integrated circuit. The antenna produces a radiation pattern having a maximum gain along an axis substantially coplanar with the tag. The antenna may include a first antenna portion and a second antenna portion. The first antenna portion has a first antenna end and a second antenna end. A first antenna end of the first antenna portion is in electrical communication with the RFID integrated circuit. The second antenna portion forms an antenna pattern in a clockwise direction. The second antenna portion has a first antenna end and a second antenna end. The first antenna end of the second antenna portion is in electrical communication with the RFID integrated circuit. The second antenna portion forms an antenna pattern in a clockwise direction. The second antenna portion has a first antenna end and a second antenna end, the first antenna end of the second antenna portion in electrical communication with the RFID integrated circuit. The second antenna portion forms an antenna pattern in a clockwise direction.

According to another aspect, the present invention provides an RFID system for use with a conductive element, the system comprising an RFID reader that generates an interrogation signal, and a security tag that receives the interrogation signal and transmits a response signal. The security tag includes a substrate body having a surface and defining a plane of the tag. An RFID integrated circuit is disposed on a surface of the substrate body. An antenna having an antenna pattern is disposed on the base body and electrically connected to the RFID integrated circuit. The antenna is arranged to produce a radiation pattern having a maximum gain along an axis substantially coplanar with the tag.

According to another aspect, the present invention provides an RFID tag for use with a conductive element, the RFID tag comprising a base body having a surface and defining a plane of the tag, an RFID integrated circuit disposed on the surface of the base body, a conductive element disposed proximate the base body, and an antenna having an antenna pattern. The antenna is disposed on the substrate body and in electrical communication with the RFID integrated circuit, the antenna being arranged to produce a radiation pattern having a maximum gain along an axis substantially coplanar with the tag.

Additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The aspects of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

Drawings

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

FIG. 1 is an illustration of a conventional RFID tag;

FIG. 2 is a diagram illustrating an example of a three-dimensional radiation pattern of the conventional tag antenna of FIG. 1;

FIG. 3 is a diagrammatic view of an RFID system constructed in accordance with the principles of the present invention;

FIG. 4 is a diagram of another embodiment of an RFID system constructed in accordance with the principles of the present invention;

FIG. 5 is an illustration of an exemplary tag having an antenna constructed in accordance with the principles of the present invention;

FIG. 6 is a diagram illustrating an example of a three-dimensional radiation pattern of the antenna of the tag of FIG. 5 constructed in accordance with the principles of the present invention;

FIG. 7 is an illustration of another exemplary tag having an antenna constructed in accordance with the principles of the present invention; and

fig. 8 is a diagram illustrating an example of a three-dimensional power gain radiation pattern of the antenna of the tag of fig. 7, constructed in accordance with the principles of the present invention.

Detailed Description

Referring now to the drawings in which like reference designators refer to like elements, there is shown in FIG. 3 a diagram of an exemplary system constructed in accordance with the principles of the present invention and designated generally as "300". The communication system 300 in the embodiments described herein provides an electrical identification system. Further, as described in the following detailed description, the described communication system 300 is configured for backscatter communication. It is contemplated that other communication protocols may be used in other embodiments.

The depicted communication system 300 includes at least one reader 302, the reader 302 having at least one electronic wireless telecommunication device 306. Radio Frequency (RF) communication may occur between the reader 302 and the remote communication device 306 for use in identification systems and product monitoring systems, as an exemplary application.

In the embodiments described herein, the remote communication device 306 comprises a Radio Frequency Identification (RFID) device. Although only one such device 306 is shown in fig. 3, multiple wireless telecommunication devices 306 may typically communicate with the reader 302.

Although multiple communication devices 306 may be employed in communication system 300, there is typically no communication between the multiple communication devices 306. Instead of communicating with the reader 302 with a plurality of communication devices 306. Multiple communication devices 306 may be used in the same area of the reader 302, i.e., multiple communication devices 306 are within communication range of the reader 302. Likewise, multiple readers 302 may be in proximity to one or more devices 306.

The remote communication device 306 is configured to couple with the reader 302, in one embodiment, using a wireless medium. More specifically, communication between communication device 306 and reader 302 occurs via an electromagnetic link, such as a radio frequency of microwave frequency in the depicted embodiment. The reader 302 is configured to output a forward link wireless communication signal 308. In addition, the reader 302 is operable to receive a return link wireless communication signal 310, such as an acknowledgement signal from the device 306 in response to the forward link communication signal 308. In accordance with the above, the forward link communication signals and the return link communication signals are wireless signals, such as radio frequency signals. Other forms of communication signals are contemplated, such as infrared, acoustic, and the like.

The reader unit 302 includes at least one antenna 312, as well as transmit and receive circuitry, similar to that implemented in the device 306. The antenna 312 includes a transmit/receive antenna connected to the reader 302. In an alternative embodiment, the reader 302 may have separate transmit and receive antennas.

In operation, reader 302 transmits a forward link communication signal 308, such as an interrogation command signal, via antenna 312. The communication device 306 is operable to receive an arriving forward signal 308. Upon receiving the signal 308, the communication device 306 responds by sending a responsive return link communication signal 310, such as a response acknowledgement signal. Communications within system 300 are described in more detail below.

In one embodiment, the response return link communication signal 310, such as the response reply signal, is encoded with information that uniquely identifies or tags the particular device 306, which signal is transmitted to identify any object, animal or human, with which the communication device 306 is associated. The communication device 306 may be RFID tags attached to objects or persons, where each tag is programmed with information about the object or person to which it is to be attached. The information may take many forms and may be more or less detailed depending on the needs served by the information. For example, the information may include article identification information, such as a universal product code. The tag may include identification information and security check information (security clearance information) for the person authorized to issue the tag. The tag also has a unique serial number to uniquely identify the object or person of interest. Alternatively, the tag may include more detailed information about the object or person, such as a complete description of the object or person. As alternative other examples, the tag may store a single bit to provide theft control or simply track by detecting the entry or exit of an object or person at a particular reader without specifically identifying the object or person.

Remote device 306 is configured to output an acknowledgement signal within an acknowledgement link communication 310 in response to receiving forward link wireless communication 308. The reader 302 is configured to receive and distinguish (recognize) reply signals, such as return signals, within the reply link communication signal 310. The reply signal may be used to identify the particular transmitting communication device 306 and may include different types of information corresponding to the communication device 306 including, but not limited to, stored data, structured data, or other command information.

An exemplary embodiment of the reader 302 is explained with reference to fig. 4. In this embodiment, reader 302 has an RF module or unit 400 and a controller module or unit 402. RF module 400 includes a radio signal source 404 for synthesizing a radio frequency signal, such as an interrogating RF signal, with radio signal source 404 outputting an RF signal to a transceiver 406 of reader 302. The interrogating RF signal from source 404 uses a suitable frequency, for example 915 MHz. When the radio signal source 404 is energized, the transceiver 406 transmits an interrogating RF signal (typically after the RF signal is modulated with an information signal) through the antenna 312 to a suitable antenna 314, such as a dipole antenna at the wireless communication device 306.

The modulated signal is received from the communication device 306 via the antenna 312 and passed to the transceiver 406. The control module 402 of the reader 302 receives a digital signal corresponding to the modulated signal. In one embodiment, the control module 402 generates a sequence of signals having a pattern that identifies a pattern of 1's and a pattern of 0's in a read only memory ("ROM") 408 of the communication device 306. For example, the received and processed sequence may be compared in the reader 302 with an expected sequence to determine whether the identified object is searched by the reader 302.

With continued reference to fig. 4, an embodiment of the remote communication device 306 is explained. The depicted communication device 306 includes a modulator 410, the modulator 410 having a receiver/transmitter as described below and a data source, such as a ROM 408, that provides a sequence of binary 1's and 0's in different patterns to identify an object. In this embodiment, a binary "1" in ROM 408 causes modulator 410 to generate a first plurality of signal cycles, and a binary "0" in ROM 408 causes modulator 410 to generate a second plurality of signal cycles that are different from the first plurality of signals. The modulator sequentially generates a plurality of signal cycles to represent a pattern of binary "1" and binary "0" identifying the object and is introduced into the dipole antenna 314 for transmission to the antenna 312 of the reader 302. In another embodiment, the communication device 306 may have separate receive and transmit antennas. The communication device 306 may also include an optional power source (not shown) connected to the modulator 410 to provide operating power to the modulator 410.

Fig. 5 illustrates an RFID tag 500 constructed in accordance with the principles of the present invention. In this embodiment, the antenna 502 may be disposed on a substrate 504. The substrate 504 may be substantially rectangular in shape, but may also have various other geometries to meet packaging and performance parameters. The substrate 504 may define a transverse axis 503, the transverse axis 503 being parallel to the proximal and distal longer sides of the substrate 504 and intersecting a center point of the substrate 504. Transverse axis 503 thus extends along the y-axis and divides substrate 504 into a proximal half and a distal half. The substrate 504 may also define a longitudinal axis 505, the longitudinal axis 505 being parallel to the left and right short sides of the substrate 504 and intersecting the center point of the substrate 504. Longitudinal axis 505 thus extends along the x-axis and divides substrate 504 into a left half and a right half. Substrate 504 may include any type of material suitable for mounting antenna 502, optional lead frame 512, and RFID chip 510. For example, the material of the substrate 504 may include base paper, polyethylene, polyester, and the like. The particular material applied to the substrate 504 may affect the RF performance of the RFID tag 500. More particularly, the dielectric constant and loss tangent may characterize the dielectric properties of a suitable substrate material for use as substrate 504.

Antenna 502 may have multiple antenna portions, such as a first antenna portion 506 and a second antenna portion 508. The first antenna portion 506 may be connected to a first side 512A of a leadframe 512. The second antenna portion 508 may be connected to a second side 512B of the lead frame 512. The RFID chip 510 may be connected to the lead frame 512 by ultrasonically bonding the lead frame 512 to a conductive pad on the RFID chip 510. As shown in fig. 5, the RFID chip 510 and lead frame 512 may be placed proximate the proximal longer side of the insulative substrate material of the substrate 504. In this embodiment, RFID chip 510 and lead frame 512 may be placed 1-5mm from the proximal longer side of substrate 504. An end of the lead frame 512 may be physically and electrically bonded to the antenna pattern of the antenna 502.

The first antenna portion 506 may have a first antenna end 506A and a second antenna end 506B. Likewise, the second antenna portion 508 may have a first antenna end 508A and a second antenna end 508B. The first antenna end 506A of the first antenna portion 506 is connected to the lead frame 512A. First antenna portion 506 may include segments 514A, 514B, 514C, and 514D to define a portion of an antenna pattern of antenna 502. The second antenna portion 508 may include segments 516A, 516B, and 516C to define a second portion of the antenna pattern of the antenna 502. In this embodiment, the segment 514A is disposed on the substrate 504 and extends outwardly from the RFID chip 510 toward the right short side of the substrate 504 in a direction substantially parallel to the proximal longer side of the substrate 504. The segment 514B is disposed on the substrate 504 and extends outwardly from the tip of the segment 514A toward the distal longer side of the substrate 504 in a direction substantially parallel to the right side of the substrate 504. The segment 514C is disposed on the base 504 and extends inwardly from the end of the segment 514B toward the left short side of the base 504 in a direction substantially parallel to the distal longer side of the base 504. The segment 514D is disposed on the substrate 504 and extends inwardly from the end of the segment 514C toward the proximal longer side of the substrate 504 in a direction substantially parallel to the left short side of the substrate 504.

With continued reference to fig. 5, segment 516A is disposed on substrate 504 and extends outwardly from RFID chip 510 toward the left short side of substrate 504 in a direction substantially parallel to the proximal longer side of substrate 504. The segments 516B are disposed on the substrate 504 and extend outwardly from the ends of the segments 516A toward the distal longer side of the substrate 504 in a direction substantially parallel to the left short side of the substrate 504. The segments 516C are disposed on the substrate 504 and extend inwardly from the ends of the segments 516B toward the right side of the substrate 504 in a direction substantially parallel to the distal longer side of the substrate 504. In this embodiment, the length of segment 516C extending from the left short side of substrate 504 to the right side of substrate 504 may be substantially the entire length of substrate 504. In this embodiment, the segment 516C of the second antenna portion 508 may be placed closer to the distal longer side of the substrate 504 than the segment 514C of the first antenna portion 506 and at least partially surround the second end 506B of the first antenna portion 506. Segment 516C may be further modified to lengthen and coil or further to narrow to achieve the appropriate resonant frequency for wireless communication.

The antenna pattern of fig. 5 advantageously results in an antenna radiation pattern 600 as shown in fig. 6. The antenna radiation pattern 600 of the tag 500 has directional sensitivity in a direction (e.g., z-axis) orthogonal to the plane (e.g., y-axis) of the substrate 504. A comparison of the graph of fig. 6 with the graph of fig. 2 shows that the radiation pattern 600 of the tag 500 is rotated about 90 degrees left about the x-axis relative to the radiation pattern 200 of the tag 100. That is, the blank of the radiation pattern 600 is orthogonal to the plane defined by the substrate 504. Thus, unlike the radiation pattern 200 of the conventional label 100, the directional sensitivity of the label 500, as indicated by the spaces 602, is orthogonal or perpendicular to the plane of the label. Thus, the influence of the conductive element or surface to which the tag 500 is attached, such as a metal surface or an EAS tag (not shown), is minimal because the external excitation field is coupled into the tag 500 along orthogonal axes perpendicular to the plane defined by the conductive element or surface.

Fig. 7 illustrates one embodiment of an RFID tag 700 constructed in accordance with the principles of the present invention. In this embodiment, antenna 702 may be disposed on substrate 704. Substrate 704 may be similar to the material and geometry of substrate 504 as described above with respect to substrate 504. Substrate 704 may define a transverse axis 703, transverse axis 703 being parallel to the proximal and distal longer edges of substrate 704 and intersecting a center point of substrate 704. Transverse axis 703 thus extends along the y-axis and divides base 704 into a distal half and a proximal half. The substrate 704 may also define a longitudinal axis 705, the longitudinal axis 705 being parallel to the left and right short sides of the substrate 704 and intersecting the center point of the substrate 704. Longitudinal axis 703 thus extends along the x-axis and divides substrate 704 into a left half and a right half.

The antenna 702 may have multiple antenna portions, such as a first antenna portion 706 and a second antenna portion 708. The first antenna portion 706 may be connected to a first side 712A of a lead frame 712. The second antenna portion 708 may be connected to a second side 712B of the lead frame 712. The RFID chip 710 may be connected to the lead frame 712 by ultrasonically bonding the lead frame 712 to conductive pads on the RFID chip 710. As shown in fig. 7, the RFID chip 710 and lead frame 712 may be placed proximate the proximal longer side of the insulative substrate material of the substrate 704. In this embodiment, RFID chip 710 and lead frame 712 may be placed 1-5mm from the proximal longer side of substrate 704. The end of lead frame 712 may be physically and electrically bonded to the antenna pattern of antenna 702.

The first antenna portion 706 may have a first antenna end 706A and a second antenna end 706B. Likewise, the second antenna portion 708 may have a first antenna end 708A and a second antenna end 708B. The first antenna end 706A of the first antenna portion 706 is connected to a lead frame 712A. First antenna portion 706 may include 714A, 714B, 714C, 714D, and 714E segments to define a portion of the antenna pattern of antenna 702. The second antenna portion 708 may include several segments 716A, 716B, 716C, 716D, and 716E to define a second portion of the antenna pattern of the antenna 702. In this embodiment, the segment 714A is disposed on the substrate 704 and extends outwardly from the RFID chip 710 toward the right side of the substrate 704 in a direction substantially parallel to the proximal longer side of the substrate 704. The segment 714B is disposed on the base 704 and extends outwardly from the tip of the segment 714A toward the distal longer side of the base 704 in a direction substantially parallel to the right side of the base 704. The segments 714C are disposed on the base 704 and extend inwardly from the ends of the segments 714B toward a central portion of the base 704 in a direction substantially parallel to the distal longer sides of the base 704. Segment 714D is disposed on substrate 704 and extends inwardly from the end of segment 714C toward the proximal longer side of substrate 704 and segment 714A in a direction substantially parallel to the left short side of substrate 704. The segment 714E is disposed on the base 704 and extends outward from the end of the segment 714D toward the right side of the base 704.

With continued reference to fig. 7, the segment 716A is disposed on the substrate 704 and extends outward from the RFID chip 710 toward the left short side of the substrate 704 in a direction substantially parallel to the proximal longer side of the substrate 704. The segment 716B is disposed on the substrate 704 and extends outwardly from the tip of the segment 716A toward the distal longer side of the substrate 704 in a direction substantially parallel to the left short side of the substrate 704. The segment 716C is disposed on the substrate 704 and extends inwardly from the end of the segment 716B toward a central portion of the substrate 704 in a direction substantially parallel to the distal longer side of the substrate 704. Segment 716D is disposed on substrate 704 and extends inwardly from the end of segment 716C toward the proximal longer side of substrate 704 and segment 716A in a direction substantially parallel to the left short side of substrate 704. Segment 716E is disposed on substrate 704 and extends outward from the end of segment 716D toward the left short side of substrate 704. In this embodiment, the first antenna portion 706 and the second antenna portion 708 are substantially symmetrical.

The antenna pattern 702 shown in fig. 7 may be overlaid onto or incorporated with a conductive element or surface 718, such as an electronic article surveillance ("EAS") tag, e.g., the UltraMax manufactured by Sensormatic electronicsTo form the RFID tag 700, the antenna pattern 702 advantageously produces an antenna radiation pattern 800 as shown in fig. 8. In this embodiment, the electronic article surveillance device may be, for example, a magneto-acoustic device. The antenna radiation pattern 800 of the antenna pattern 702, overlaid on the conductive element or surface 718, has directional sensitivity in a direction (e.g., z-axis) orthogonal to the plane (e.g., y-axis) of the substrate 704. The first antenna portion 706 and second antenna portion 708 are intermixed with an RFID chip 710 and optional lead frame 712, optional lead frame 712 being placed near the proximal longer side of substrate 704, the field effect of the symmetric geometry of first antenna portion 706 and second antenna portion 708 producing a radiation pattern with maximum gain coplanar with the tag. A comparison of the graphs in fig. 8 and fig. 6 shows that the radiation pattern of tag 600 and the radiation pattern of tag 800 have similar field strengths and rotational directions.

A comparison of the graph of fig. 8 and the graph of fig. 2 shows that the radiation pattern 800 of the label 700 is rotated about 90 degrees left about the x-axis relative to the radiation pattern 200 of the label 100. That is, the blank of the radiation pattern 800 is orthogonal to the plane defined by the substrate 704. Thus, unlike the radiation pattern 200 of the conventional tag 100, the directional sensitivity of the tag 700, as evidenced by the margin 802, is orthogonal or perpendicular to the plane of the tag and the plane of the conductive element or surface 718. Thus, the influence of a conductive element or surface that the tag antenna 702 may incorporate, such as a metallic surface or the influence of an EAS tag, is used to produce the desired radiation pattern 800 with maximum gain coplanar with the tag.

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Moreover, it should be noted that, unless stated to the contrary above, all of the accompanying drawings are not to scale. Many modifications and variations are possible in light of the above teaching without departing from the scope and spirit of the invention, which is limited only by the following claims.

Claims (4)

1. A Radio Frequency Identification (RFID) tag, the tag comprising:

a substrate body having a surface, the substrate body defining a plane of the label, the substrate body having a first edge, a second edge opposite the first edge, a third edge, and a fourth edge opposite the third edge, the third and fourth edges being longer than the first and second edges;

a conductive element adjacent to the base body;

an RFID integrated circuit (710) disposed at a midpoint of the fourth edge on the surface of the substrate body; and

an antenna having an antenna pattern, the antenna disposed on the base body and in electrical communication with the RFID integrated circuit,

wherein the antenna has a first clockwise dipole element (708) forming a first helix and a second counter-clockwise dipole element (706) forming a second helix, the first and second counter-clockwise dipole elements being symmetrical to each other,

a first antenna end (708A) of the first clockwise dipole element (708) is connected to the RFID integrated circuit, a second antenna end (708B) terminates in an inner loop of the pattern of the first spiral, the first clockwise dipole element comprising a plurality of segments: a first segment (716A) arranged in a direction parallel to the fourth edge, extending outwardly from the first antenna end (708A) towards the first edge, a second segment (716B) arranged in a direction parallel to the first edge, extending outwardly from an end of the first segment towards the third edge, a third segment (716C) arranged in a direction parallel to the third edge, extending inwardly from an end of the second segment towards a central portion of the third edge, a fourth segment (716D) arranged in a direction parallel to the first edge, extending inwardly from a central portion of the third edge towards the fourth edge, a fifth segment (716E) arranged in a direction parallel to the fourth edge inside the first segment (716A), extending outwardly from an end of the fourth segment towards the first edge and terminating at the second antenna end (708B),

a first antenna end (706A) of the second counter-clockwise dipole element (706) is connected to the RFID integrated circuit, a second antenna end (706B) terminates at an inner loop of the pattern of the second spiral, the second counter-clockwise dipole element comprising a plurality of segments: a first segment (714A) arranged in a direction parallel to the fourth edge extending outwardly from the first antenna end (706A) towards the second edge, a second segment (714B) arranged in a direction parallel to the second edge extending outwardly from an end of the first segment towards the third edge, a third segment (714C) arranged in a direction parallel to the third edge extending inwardly from an end of the second segment towards a central portion of the third edge, a fourth segment (714D) arranged in a direction parallel to the second edge extending inwardly from a central portion of the third edge towards the fourth edge, a fifth segment (714E) arranged inside the first segment (714A) in a direction parallel to the fourth edge extending outwardly from an end of the fourth segment towards the second edge and terminating at the second antenna end (706B),

the antenna and the conductive element are arranged to produce a radiation pattern having a maximum gain along an axis substantially coplanar with the plane of the tag that is greater than a maximum gain along an axis substantially orthogonal to the plane of the tag, the radiation pattern exhibiting nulls at and near the axis orthogonal to the plane of the tag.

2. The RFID tag of claim 1, wherein the RFID integrated circuit is 1-5mm from the fourth edge of the substrate body.

3. An RFID system, the system comprising:

a radio frequency identification reader that generates an interrogation signal; and

a security tag that receives the interrogation signal and transmits a response signal, the security tag comprising:

a substrate body having a surface, the substrate body defining a plane of the label, the substrate body having a first edge, a second edge opposite the first edge, a third edge, and a fourth edge opposite the third edge, the third and fourth edges being longer than the first and second edges;

a conductive element adjacent to the base body;

an RFID integrated circuit (710) disposed at a midpoint of the fourth edge on the surface of the substrate body; and

an antenna having an antenna pattern, the antenna disposed on the base body and in electrical communication with the RFID integrated circuit,

wherein the antenna has a first clockwise dipole element (708) forming a first helix and a second counter-clockwise dipole element (706) forming a second helix, the first and second counter-clockwise dipole elements being symmetrical to each other,

a first antenna end (708A) of the first clockwise dipole element (708) is connected to the RFID integrated circuit, a second antenna end (708B) terminates in an inner loop of the pattern of the first spiral, the first clockwise dipole element comprising a plurality of segments: a first segment (716A) arranged in a direction parallel to the fourth edge, extending outwardly from the first antenna end (708A) towards the first edge, a second segment (716B) arranged in a direction parallel to the first edge, extending outwardly from an end of the first segment towards the third edge, a third segment (716C) arranged in a direction parallel to the third edge, extending inwardly from an end of the second segment towards a central portion of the third edge, a fourth segment (716D) arranged in a direction parallel to the first edge, extending inwardly from a central portion of the third edge towards the fourth edge, a fifth segment (716E) arranged in a direction parallel to the fourth edge inside the first segment (716A), extending outwardly from an end of the fourth segment towards the first edge and terminating at the second antenna end (708B),

a first antenna end (706A) of the second counter-clockwise dipole element (706) is connected to the RFID integrated circuit, a second antenna end (706B) terminates at an inner loop of the pattern of the second spiral, the second counter-clockwise dipole element comprising a plurality of segments: a first segment (714A) arranged in a direction parallel to the fourth edge extending outwardly from the first antenna end (706A) towards the second edge, a second segment (714B) arranged in a direction parallel to the second edge extending outwardly from an end of the first segment towards the third edge, a third segment (714C) arranged in a direction parallel to the third edge extending inwardly from an end of the second segment towards a central portion of the third edge, a fourth segment (714D) arranged in a direction parallel to the second edge extending inwardly from a central portion of the third edge towards the fourth edge, a fifth segment (714E) arranged inside the first segment (714A) in a direction parallel to the fourth edge extending outwardly from an end of the fourth segment towards the second edge and terminating at the second antenna end (706B),

the antenna and the conductive element are arranged to produce a radiation pattern having a maximum gain along an axis substantially coplanar with the plane of the tag that is greater than a maximum gain along an axis substantially orthogonal to the plane of the tag, the radiation pattern exhibiting nulls at and near the axis orthogonal to the plane of the tag.

4. The RFID system of claim 3, wherein the RFID integrated circuit is 1-5mm from the fourth edge of the substrate body.