Combination EAS and RFID label or tag

A security tag includes an EAS component having a defined surface area, and an RFID component having a defined surface area. The EAS component surface area is configured to at least partially overlap the RFID component surface area. The RFID component includes an antenna which at least partially overlaps the first surface. A substantially planar spacer having a thickness is at least partially disposed between the defined surface areas of the EAS and RFID components. The thickness of the spacer determines a read range between an RFID reader and the RFID component. The RFID reader is capable of activating the RFID component when the RFID component is within the read range. The antenna has a complex impedance, and the EAS component forms a part of an impedance matching network of the antenna.

BACKGROUND

1. Technical Field

The present disclosure relates to an electronic article surveillance (EAS) label or tag for the prevention or deterrence of unauthorized removal of articles from a controlled area. More particularly, the present disclosure relates to an EAS label or tag combined with a radiofrequency identification (RFID) label or tag for recordation of data specific to the article and a novel RFID label or tag.

2. Description of Related Art

Electronic article surveillance (EAS) systems are generally known in the art for the prevention or deterrence of unauthorized removal of articles from a controlled area. In a typical EAS system, EAS markers (tags or labels) are designed to interact with an electromagnetic field located at the exits of the controlled area, such as a retail store. These EAS markers are attached to the articles to be protected. If an EAS tag is brought into the electromagnetic field or “interrogation zone,” the presence of the tag is detected and appropriate action is taken, such as generating an alarm. For authorized removal of the article, the EAS tag can be deactivated, removed or passed around the electromagnetic field to prevent detection by the EAS system.

EAS systems typically employ either reusable EAS tags or disposable EAS tags or labels to monitor articles to prevent shoplifting and unauthorized removal of articles from the store. The reusable EAS tags are normally removed from the articles before the customer exits the store. The disposable tags or labels are generally attached to the packaging by adhesive or are located inside the packaging. These tags typically remain with the articles and must be deactivated before they are removed from the store by the customer. Deactivation devices may use coils which are energized to generate a magnetic field of sufficient magnitude to render the EAS tag inactive. The deactivated tags are no longer responsive to the incident energy of the EAS system so that an alarm is not triggered.

For situations where an article having an EAS tag is to be checked-in or returned to the controlled area, the EAS tag must be activated or re-attached to once again provide theft deterrence. Because of the desirability of source tagging, in which EAS tags are applied to articles at the point of manufacturing or distribution, it is typically preferable that the EAS tags be deactivatable and activatable rather than be removed from the articles. In addition, passing the article around the interrogation zone presents other problems because the EAS tag remains active and can interact with EAS systems in other controlled areas inadvertently activating those systems.

Radio-frequency identification (RFID) systems are also generally known in the art and may be used for a number of applications, such as managing inventory, electronic access control, security systems, and automatic identification of cars on toll roads. An RFID system typically includes an RFID reader and an RFID device. The RFID reader may transmit a radio-frequency carrier signal to the RFID device. The RFID device may respond to the carrier signal with a data signal encoded with information stored by the RFID device.

The market need for combining EAS and RFID functions in the retail environment is rapidly emerging. Many retail stores that now have EAS for shoplifting protection rely on bar code information for inventory control. RFID offers faster and more detailed inventory control over the bar code. Retail stores already pay a considerable amount for hard tags that are re-useable. Adding RFID technology to EAS hard tags could easily pay for the added cost due to improved productivity in inventory control as well as loss prevention.

SUMMARY

It is an object of the present disclosure to provide a tag or label which in one tag or label combines the features of an independent EAS tag or label and an independent RFID tag or label.

More particularly, the present disclosure relates to a security tag which includes an EAS component having a defined surface area, and an RFID component having a defined surface area. The defined surface area of the EAS component is configured to at least partially overlap the defined surface area of the RFID component.

The RFID component includes an antenna and the antenna may at least partially overlap the defined surface area of the EAS component. A substantially planar spacer having a thickness may be at least partially disposed between the defined surface area of the EAS component and the defined surface area of the RFID component. The thickness of the spacer determines a read range between an RFID reader and the RFID component, and the RFID reader is capable of activating the RFID component when the RFID component is within the read range. The antenna and the EAS component may form a part of an impedance matching network of the antenna. The antenna impedance may include loading effects of the EAS component. The RFID component may include the antenna and an application specific integrated circuit (ASIC). The ASIC may have a complex impedance. The complex impedance of the ASIC may match a coupled complex conjugate impedance of the antenna including the loading effects of the EAS component. A material for a base portion of the RFID component may be selected from the group consisting of (a) base paper, (b) polyethylene, (c) polyester; (d) polyethyleneterephthalate (PET); and (e) polyetherimide (PEI). The base portion material may be plastic having a dielectric constant of about 3.3 and a loss tangent of less than about 0.01. The spacer material may be selected from the group consisting of (a) a low loss, low dielectric material; and (b) air.

The present invention relates also to a method of operating a combination of an electronic article surveillance (EAS) component and a radiofrequency identification (RFID) component. The method includes the step of moving the RFID component to be overlapped by the EAS component so as to change the impedance of an antenna coupled to the RFID component. The impedance of the antenna includes the loading effects of the EAS component. The antenna may include an antenna conductor and the antenna is tuned by severing the antenna conductor into at least two segments such that at least one segment point corresponds to an operating frequency for the antenna based upon the length of the at least two antenna segments, and isolating the severed antenna conductor from remaining portions of the conductor.

The method may further include the combination of an electronic article surveillance (EAS) component and a radiofrequency identification (RFID) component having a spacer disposed therebetween, with the spacer having a thickness, and the method may include the step of varying the thickness of the spacer. The step of varying the thickness of the spacer may vary a read range between an RFID reader and the RFID component, and wherein the RFID reader is capable of activating the RFID component when the RFID component is within the read range.

DETAILED DESCRIPTION

Commonly-owned, concurrently filed PCT Application Ser. No. 11/667,742 by R. Copeland entitled “COMBINATION EAS AND RFID LABEL OR TAG WITH CONTROLLABLE READ RANGE” is incorporated by reference herein in its entirety.

The present disclosure will be understood more fully from the detailed description given below and from the accompanying drawings of particular embodiments of the invention which, however, should not be taken to limit the invention to a specific embodiment but are for explanatory purposes.

Numerous specific details may be set forth herein to provide a thorough understanding of a number of possible embodiments of a combination EAS/RFID tag incorporating the present disclosure. It will be understood by those skilled in the art, however, that the embodiments may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the embodiments. It can be appreciated that the specific structural and functional details disclosed herein may be representative and do not necessarily limit the scope of the embodiments.

Turning now to the details of the present disclosure, one manner in which a combination EAS/RFID label (or tag) may be utilized is to put both the EAS related components together with the RFID related components and package them together. However, there may be some electrically or electro-mechanical interacting factors that may affect the performance of either the EAS function and/or the RFID function. Placing the RFID label on top of the EAS label is the most convenient way but may result in substantial de-tuning and signal loss for the RFID label. For example, in a typical RFID device, performance of the RFID label is typically very sensitive to impedance matching of an application specific integrated circuit (ASIC)/lead frame assembly for the RFID device to the effective impedance of an RFID antenna mounted on a substrate. A more detailed description of some possible embodiments of the RFID portion of the device is discussed further below. Other objects surrounding the RFID label may contribute to either the effective impedance or the absorption of electromagnetic energy used to read the RFID label.

Some existing 2450 MHz EAS/RFID combination labels have used a configuration where an RFID label and an EAS label are placed in an overlapped configuration. There may be considerable degradation in RFID label detection with this particular application. Although end-to-end or slight overlap has worked best in such systems, the tag size tends to become prohibitively large in these instances. Also, a side-by-side configuration has been known to create an irregular RFID detection pattern. There are not many designs which have been able to successfully implement a combination EAS/RFID tag in the marketplace. Most applications using combined EAS and RFID of tagged items use separate EAS and RFID labels that are mounted separately so that they occupy considerable space on the tagged item than either one would occupy by itself if mounted separately.

It is envisioned that the solution to this problem is the use of an EAS label portion of the combination tag as part of the impedance matching network for the RFID label. For example, as the RFID label is placed closer and closer to the EAS label, the RFID label antenna impedance is affected, or tuned, by the EAS label. In order to achieve RFID label impedance matching, the RFID antenna geometry may itself be designed so that any resulting electrical effect of the EAS label on the impedance is taken into account. For example, the RFID antenna may be configured to have a highly capacitive impedance and which may be grossly mismatched to the impedance of the logic chip for the device (e.g., an ASIC/lead frame assembly as referred to above). As the RFID label is placed proximate the EAS label e.g., directly underneath, the impedance of the RFID antenna is nearly matched to the ASIC impedance.

When the EAS component1and the RFID component2are disposed adjacent one another as shown in position “P1” ofFIG. 1, there is only a small effect of the EAS component1on the antenna impedance of RFID component2. However, as the RFID—component2is positioned underneath the EAS component1as shown in position “P2”, “P3” and “P4”, i.e., the extent of the overlap shown via a shaded area3, the RFID antenna impedance is progressively affected.

More particularly, the label positions P1-P4of the RFID component2were configured as follows:P1=EAS component1and RFID component2disposed adjacent to each other;P2=RFID component2is disposed ¼ the way across and underneath the EAS component1;P3=RFID component2is disposed ½ the way across and underneath the EAS component1; andP4=RFID component2is disposed directly underneath the EAS component1.

For example,FIGS. 2A and 2Bshow test results of the real and imaginary components of the RFID antenna impedance vs. frequency over the 915 MHz ISM band for a sample security tag which includes EAS component1and RFID component2.

As shown in.FIG. 2A, at the center frequency of 915 MHz, the real impedance R varies from R1=about 6 ohms to R4=about 13 ohms as the RFID label2moves from the position P1to position P4. This apparent increase in the real impedance R represents the effective loss increase due to the EAS label materials. Correspondingly, the imaginary impedance Z changes from Z1=125 ohms to Z4=+195 ohms as the RF1-label2moves from position P1to position P4. Therefore the imaginary impedance Z changes from somewhat capacitive nature to inductive nature.

The RFID component2may be designed so that the antenna impedance is approximately the complex conjugate of the ASIC device. This results in resonance at a target frequency, such as 915 MHz for example. Typical test results for the impedance of the ASIC RFID devices for chips made by ST Microelectronics of Geneva, Switzerland with lead frame used in this example are 5−j 140 ohms, and for chips made by Koninklikje Philips Electronics N.V. of Amsterdam, the Netherlands, with lead frame used in this example, are 20−j 270 ohms. It was necessary for the RFID label antenna imaginary impedance Z to be in the range of +j (140 to 270) ohms for these two RFID devices to achieve resonance at the target frequency.

Therefore, a combination RFID/EAS security tag can be designed using the impedance of the EAS component for matching purposes. In free space, the RFID component antenna can be designed to have a negative imaginary impedance and achieve the correct positive imaginary impedance when placed directly beneath, atop or nearby the EAS component. As can be appreciated by the present disclosure, this configuration may be used with any type of EAS tag or label, such as, for example, various types of adhesive magnetostrictive labels and EAS hard tags, such as the SuperTag® produced by Sensormatic Corporation, a division of Tyco Fire and Security, LLC of Boca Raton, Fla. The types of EAS devices are not limited to these specific examples.

The RFID component may include, for example, a semiconductor integrated circuit (IC) and a tunable antenna. The tunable antenna may be tuned to a desired operating frequency by adjusting the length of the antenna. The range of operating frequencies may vary, although the embodiments may be particularly useful for ultra-high frequency (UHF) spectrum. Depending upon the application and the size of the area available for the antenna, the antenna may be tuned within several hundred Megahertz (MHz) or higher, such as 868-950 MHz, for example. In one embodiment, for example, the tunable antenna may be tuned to operate within an RFID operating frequency, such as the 868 MHz band used in Europe, the 915 MHz Industrial, Scientific and Medical (ISM) band used in the United States, and the 950 MHz band proposed for Japan. It is again noted that these operating frequencies are given by way of example only, and the embodiments are not limited in this context.

In one embodiment, for example, the tunable antenna may have a unique antenna geometry of an inwardly spiral pattern useful for RFID applications or EAS applications. The inwardly spiral pattern may nest the antenna traces thereby bringing the traces back towards the origin. This may result in an antenna similar in functionality to that of a conventional half-wave dipole antenna, but with a smaller overall size. For example, the size of a conventional half-wave dipole antenna at 915 MHz would be approximately 16.4 centimeters (cm) long. By way of contrast, some embodiments may offer the same performance as the conventional half-wave dipole antenna at the 915 MHz operating frequency with a shorter length of approximately 3.81 cm. Furthermore, the ends of the antenna traces may be modified to tune the antenna to a desired operating frequency. Since the ends of the antenna traces are inward from the perimeter of the antenna, the tuning may be accomplished without changing the geometry of the antenna.

FIG. 3Ashows a first system in accordance with one particularly useful embodiment of the present disclosure.FIG. 3Ashows an RFID system100which may be configured to operate using RFID component2having an operating frequency in the high frequency (HF) band which is considered to be frequencies up to and including 30 MHz. In this frequency range, the primary component of the electromagnetic field is magnetic. RFID system100, however, may also be configured to operate RFID component2using other portions of the RF spectrum as desired for a given implementation. The embodiments are not limited in this context. As illustrated by way of example, RFID component2partially overlaps EAS component1.

RFID system100may include a plurality of nodes. The term “node” as used herein may refer to a system, element, module, component, board or device that may process a signal representing information. The signal type may be, for example but not limited to, electrical, optical, acoustical and/or a chemical in nature. AlthoughFIG. 3Ashows a limited number of nodes, it can be appreciated that any number of nodes may be used in RFID system100. The embodiments are not limited in this context.

Referring first toFIG. 4,FIG. 4illustrates a side view for a security tag200in accordance with one particularly useful embodiment of the present disclosure. RFID component2includes a base portion or substrate202having a first surface or surface area202aand a second surface or surface area202bwhich are typically on opposing sides of base portion or substrate202. An antenna204is disposed on the substrate202. The antenna204has a first surface or surface area204aand a second surface or surface area204bwhich are typically on opposing sides of antenna204. A lead frame206is disposed on the antenna204, and an application specific semiconductor integrated circuit (ASIC)208is disposed on the lead frame206. First and second surfaces or surface areas202aand202b,204aand204bare defined surface areas of RFID component2.

The security tag200includes a substantially planar covering material or spacer210disposed on the RFID component2and EAS component1disposed on the spacer210. The spacer210has surfaces or surface areas210aand210bdisposed on opposite sides thereof.

EAS component1has a first surface or surface area1aand a second surface or surface area1bwhich are typically on opposing sides of EAS component1. First and second surfaces or surface areas1aand1bare defined surfaces or surface areas of EAS component1.

For reference purposes, security tag200is illustrated as being disposed directly underneath EAS component1, i.e., in position P4ofFIG. 1. The security tag200is shown in position P4by way of example only and may be disposed in any position with respect to EAS label1, as discussed previously with respect toFIG. 1. Security tag200may also be utilized completely independently of EAS label1or in conjunction therewith. The embodiments are not limited in this context.

More particularly, security tag200includes an EAS component1having one of the defined surface areas1aand1band an RFID component2having one of the defined surface or surface areas202a,202b,204aand204b.At least one of the defined surface or surface areas1aand1bof the EAS component1is configured to at least partially overlap at least one of the defined surface or surface areas202a,202b,204aand204bof the RFID component2. The RFID component2may include antenna204which at least partially overlaps at least one of the defined surfaces or surface areas1aand1bof the EAS component1.

In one embodiment, the defined surface or surface area of the RFID component2is one of surface or surface area202aand202b.

The substantially planar spacer210has a thickness “t” and is at least partially disposed between at least one of the defined surfaces or surface areas1aand1bof the EAS component1and at least one of the defined surfaces or surface areas202a,202b,204a, and204bof the RFID component2.

AlthoughFIG. 4illustrates a limited number of elements, it may be appreciated that a greater or lesser number of elements may be used for security tag200. For example, an adhesive and release liner may be added to security tag200to assist in attaching security tag200to an object to be monitored. Those skilled in the art will recognize that semiconductor IC208may be directly bonded to antenna204without the lead frame206.

Returning now toFIG. 3A, RFID system100may also include an RFID reader102and security tag200. Security tag200is physically separated from RFID reader102by a distance d1. As is explained below with respect toFIG. 4, security tag200is an RFID security tag, tag or label which differs over the prior art in that it includes an EAS component, i.e., an EAS label or tag. RFID component2includes a resonant circuit112. Resonant circuit112includes inductor coil L2with a resonating capacitor C2across the terminals T1and T2of ASIC208. The capacitance of ASIC208is usually negligible compared to C2. If necessary to add additional capacitance to the resonant circuit112to enable tuning the antenna, i.e., inductor coil112, to the proper frequency, a capacitor C2is connected in parallel to inductor coil L2so that resonant circuit112becomes a parallel resonant circuit having terminals T1and T2across which an induced voltage V1may be formed. As is explained below with respect toFIG. 4, terminals T1and T2are coupled to other portions of the RFID component2. In addition, the inductance value of inductor coil or antenna L2includes the inductance presented by the EAS label or tag.

RFID reader102may include a tuned circuit108having an inductor L1which serves as an antenna for RFID reader102. Where necessary to add additional capacitance to the tuned circuit108to enable proper tuning of the inductor coil or antenna L1, a capacitor C1is connected in series with inductor coil or antenna L1. RFID reader102is configured to produce a pulsed or continuous wave (CW) RF power across the tuned circuit108which is electro-magnetically coupled by alternating current action to parallel resonant circuit antenna112of RFID component2. The mutually coupled electromagnetic power from RFID component2is coupled to RFID reader102through a magnetic field114.

RFID component2is a power converter circuit that converts some of the coupled CW RF electromagnetic power of magnetic field114into direct current signal power for use by the logic circuits of the semiconductor IC used to implement the RFID operations for RFID component2.

RFID component2may also be a RFID security tag which includes memory to store RFID information and which communicates the stored information in response to an interrogation signal104. RFID information may include any type of information capable of being stored in a memory used by RFID component2. Examples of RFID information include a unique tag identifier, a unique system identifier, an identifier for the monitored object, and so forth. The types and amount of RFID information are not limited in this context.

RFID component2may also be a passive RFID security tag. A passive RFID security tag does not use an external power source, but rather uses interrogation signals104as a power source. A detection zone Z1is defined as an imaginary volume of space bounded by a generally spherical surface having a radius R1generally originating from the inductor L1. The radius R1defines a detection distance or read range R1such that if distance d1is less than or equal to read range R1, the RFID reader102induces a required threshold voltage VTacross terminals T1and T2to activate the RFID component2. The read range R1depends on, among other factors, the strength of the EM field radiation and magnetic field114from the tuned circuit208. Therefore, the strength of the EM field radiation114determines the read range R1.

RFID component2may be activated by a direct current voltage that is developed as a result of rectifying the incoming RF carrier signal including interrogation signals104. Once RFID component2is activated, it may then transmit the information stored in its memory register via response signals110.

In general high frequency (HF) operation, when resonant circuit112of RFID system100is in proximity to tuned circuit108of RFID reader102, an alternating current (AC) voltage Viis developed across the terminals T1and T2of parallel resonant circuit112of RFID component2. The AC voltage Viacross resonant circuit112is rectified by a rectifier to a direct current (DC) voltage and when the magnitude of the rectified voltage reaches a threshold value VT, RFID component2is activated. The rectifier is the aforementioned application specific integrated circuit (ASIC)208. Once activated, the RFID component2sends stored data in its memory register by modulating interrogation signals104of RFID reader102to form response signals110. The RFID device106then transmits the response signals110to the RFID reader102. RFID reader102receives response signals110and converts them into a detected serial data word bitstream of data representative of the information from RFID component2.

The RFID system100as illustrated inFIG. 3Amay be considered to be a high frequency (HF) RFID system because the RFID reader102couples inductively to the RFID component2via magnetic field114. In HF applications, antenna204is typically an inductance coil type antenna as provided by inductance coil L2.

FIG. 3Billustrates an ultrahigh frequency (UHF) RFID system150in which an RFID reader152couples to an RFID device, tag or label156at a distance d2away via an electric field E. The frequency band for UHF is considered herein to range from about 300 MHz to about 3 GHz. The UHF range specifically includes frequencies in the 868 MHz band, the 915 MHz band, and the 950 MHz band.

For UHF applications, antenna204of RFID component2typically includes a UHF open-ended dipole antenna while the RFID reader152typically includes a patch antenna. A coaxial feed line from the reader152is connected to the patch antenna. The UHF antenna may be a simple half-wave dipole or a patch antenna. Many popular designs use an air filled cavity backed patch antenna which can be either linearly polarized or circularly polarized. The electric field vectors E1and E2rotate with equal magnitude for the circularly polarized case. The linearly polarized antenna has higher magnitudes of E field in certain orthogonal orientations, which may be suitable for certain RFID label orientations.

Therefore, in UHF applications, the antenna204of RFID component2includes an open-ended dipole antenna while in HF applications, is typically inductor L2.

In general, when operating in the UHF range, it is not necessary for the RFID component2to include a capacitor such as C2in parallel with the open-ended dipole antenna204to enable tuning to the frequency transmitted by the patch antenna of RFID reader152.

Returning toFIG. 4, as previously noted, RFID component2may include a base portion or substrate202which includes any type of material suitable for mounting antenna204, lead frame206, and IC208. For example, material for substrate202may include base paper, polyethylene, polyester, polyethyleneterephthalate (PET), polyetherimide (PEI) (e.g., ULTEM® amorphous thermoplastic PEI sold by the General Electric Co. of Fairfield, Conn.) and/or other materials. It is known that the particular material implemented for substrate202may impact the RF performance of security tag200and, as such, the dielectric constant and the loss tangent may characterize the dielectric properties of an appropriate substrate material for use as substrate202.

In general, a higher dielectric constant may cause a larger frequency shift of an antenna when compared to free space with no substrate present. Although it may be possible to re-tune the antenna to the original center frequency by physically changing the antenna pattern, it may be desirable to have a material with a high dielectric constant and with a low dielectric loss since usage of such a material results in a smaller tag or label size. The term “read range” may refer to the communication operating distance between RFID reader102and security tag200. An example of a read range for security tag200may range from 1-3 meters, although the embodiments are not limited in this context. The loss tangent may characterize the absorption of RF energy by the dielectric. The absorbed energy may be lost as heat and may be unavailable for use by ASIC208. The lost energy may result in the same effect as reducing the transmitted power and may reduce the read range accordingly. Consequently, it may be desirable to have the lowest loss tangent possible in substrate202since it cannot be “tuned out” by adjusting antenna204. The total frequency shift and RF loss may depend also on the thickness of substrate202. As the thickness increases, the shift and loss may also increase.

In one embodiment, for example, substrate202may be configured using base paper having a dielectric constant of about 3.3, and a loss tangent of about 0.135. The base paper may be relatively lossy at 900 MHz. A lossy material has a dielectric loss factor greater than about 0.01. In one embodiment, substrate202may be configured of plastic having a dielectric constant of about 3.3 and a loss tangent of less than about 0.01. The embodiments are not limited in this context.

In one embodiment, security tag200may include IC208having a semiconductor IC, such as an RFID chip or application specific integrated circuit (ASIC) (“RFID chip”). RFID chip208may include, for example, an RF or alternating current (AC) rectifier that converts RF or AC voltage to DC voltage, a modulation circuit that is used to transmit stored data to the RFID reader, a memory circuit that stores information, and a logic circuit that controls overall function of the device. In one embodiment, RFID chip208may be configured to use an I-CODE High Frequency Smart Label (HSL) RFID ASIC or a U-CODE Ultrahigh Frequency Smart Label (USL) RFID ASIC, both of which are made by Philips Semiconductor of Amsterdam, the Netherlands, or an XRA00 RFID chip made by ST Microelectronics of Geneva, Switzerland. The embodiments, however, are not limited in this context.

Lead frames are small connections which enable attaching an RFID chip such as RFID chip208to an antenna such as antenna204. In one embodiment, RFID chip208may be directly bonded to antenna204without including lead frame206. Lead frame206may also include a die mounting paddle or flag, and multiple lead fingers. The die paddle primarily serves to mechanically support the die during package manufacture. The lead fingers connect the die to the circuitry external to the package. One end of each lead finger is typically connected to a bond pad on the die by wire bonds or tape automated bonds. The other end of each lead finger is the lead, which is mechanically and electrically connected to a substrate or circuit board. Lead frame206may be constructed from sheet metal by stamping or etching, often followed by a finish such as plating, downset and taping. In one embodiment, for example, lead frame206may be implemented using a Sensormatic EAS Microlabel™ lead frame made by Sensormatic Corporation, a division of Tyco Fire and Security, LLC, of Boca Raton, Fla., for example. The embodiments, however, are not limited in this context.

In one embodiment, antenna204includes the inductor coil L2, and when required, the capacitor C2, of resonant circuit112of RFID component2. The terminals T1and T2are also included in antenna204to couple to the RFID chip208to enable the induced voltage V1to activate the RFID component2once the threshold voltage VTis reached.

In one embodiment, antenna204includes typically the open ended dipole antenna of RFID component2for UHF applications. Terminals T1and T2may also be included in antenna204to couple to the RFID chip208to enable the electric field E to excite the antenna of reader152

In one embodiment, security tag200may also include covering or spacer material210applied to the top of a finished security tag. As with substrate202, covering or spacer material210may also impact the RF performance of RFID component2. For example, covering material210may be implemented using cover stock material having a dielectric constant of about 3.8 and a loss tangent of about 0.115. The embodiments are not limited in this context.

More particularly, as previously mentioned, the substantially planar spacer210has a thickness “t”. The thickness “t” is generally about 1 mm to 2 mm when the security tag200is a hard combination tag and considerably less than 1 mm when the security tag200is a combination label. As previously mentioned, the spacer210has surfaces or surface areas210aand210bdisposed on opposite sides thereof. In one embodiment, spacer surfaces or surface areas210aand210bare parallel to each other. EAS component1at least partially overlaps at least one of the spacer surfaces or surface areas210aand210b.

An RFID insert is a term common in the art and may be defined herein as the RFID component2, which includes the combination of substrate202, antenna204, lead frame206if applicable, and RFID chip208. RFID component2at least partially overlaps another one of the spacer surfaces210b.Security tag200includes RFID insert or component2and spacer210.

Security tag200may also include antenna204. Antenna204may be representative of, for example, antenna112of RFID device106or antenna204may be formed by a parallel resonant LC circuit, where L is inductance and C is capacitance. Alternatively, antenna204may also be a tunable antenna which is tuned to the carrier signal so that the voltage across the antenna circuit is maximized. As can be appreciated this will increase the read range of antenna204. It is known that the degree of preciseness of the tuning circuit is related to the spectrum width of the carrier signal transmitted by transmitter102. For example, in the United States, the Federal Communication Commission currently (FCC) regulates one band of the RFID security tag spectrum to 915 MHz. Therefore, transmitter102should transmit interrogation signals104at approximately 915 MHz. To receive interrogation signals104, antenna204should be narrowly tuned to the 915 MHz signal. For 915 MHz applications, the RFID tag antenna204may be printed, etched or plated.

The EAS label1creates or presents a constant load impedance to RFID component2. As a result, antenna204of RFID label200uses this constant load of EAS label1for impedance matching. More particularly, antenna204has a complex impedance and the EAS component1forms a part of an impedance matching network of the antenna. Therefore, the impedance of antenna204includes the loading effect of the EAS component1. That is, the loading effects of the EAS component1are the constant load impedance of the EAS component1. The loading effect of EAS component1may be varied by substituting or exchanging one material included within the EAS component1having one dielectric constant and loss tangent for another material having another dielectric constant and loss tangent.

The RFID component chip208may be represented as an equivalent series RC circuit, where R represents a resistor and C represents a capacitor. This circuit is represented by a complex impedance Zchipas
Zchip=Z1−jZ2,

where Z1and Z2are the real and imaginary components of the impedance of the chip208. The RFID device tag or label antenna204may be represented by a complex impedance Zantennaas
Zantenna=Z3+jZ4(1)

where Z3and Z4are the real and imaginary components of the impedance of the antenna204. When the chip208is mounted on the antenna204, the complex impedance of chip208is matched to the coupled conjugate impedance of the RFID antenna204, including the impedance matching effect or loading effect of the EAS component or label1. This allows maximum power coupling to the RFID chip208which results in the greatest read range R1.

In one embodiment, thickness “t” of spacer210may be varied to vary with respect to either the RFID reader device102or to the RFID reader device152in order to vary the read range R1, respectively. More particularly, thickness “t” determines the read range, i.e., the maximum distance R1between the security tag200and the EAS/RFID reader102or the EAS/RFID reader152at which the reader102or152may interrogate the security tag200. The read range R1is affected adversely as thickness “t” decreases. Conversely, the read range R1increases as thickness “t” increases. It should be noted that reader102for HF applications and reader152for UHF either read only the EAS component1or only the RFID component2such that the EAS component1is read by a dedicated EAS reader while RFID component2is read by a dedicated RFID reader. Alternatively, reader102and reader152may be combined in the same housing or their functions integrated to be performed by the same hardware. Undesirable interference between the reading of EAS component1and the reading of RFID component2is prevented or minimized because of the wide discrepancy between the range of read frequencies common to EAS components as opposed the range of read frequencies common to RFID components, with the EAS components typically being read at frequencies in the range of less than or equal to 8.2 KHz, whereas RFID components are typically being read at frequencies in the range of 13 MHz or greater.

However, it is envisioned that since security tags200and400are stand alone devices, security tags200and400provide an EAS function and an RFID function independently of the type of reader or readers or particular frequencies to which security tags200or400are subjected.

The spacer210is made using a low loss, low dielectric material such as ECCOSTOCK® RH rigid foam, made by Emerson Cuming Microwave Products, Inc. of Randolph, Mass., or any other similar material. The embodiments are not limited in this context. When made from one of the foregoing materials, the read range is about 30.5 to 61.0 cm (1 to 2 feet) when the thickness “t” of spacer902is about 0.0762 mm (0.003 inches). Similarly, the read range is about 127 cm (5 feet) when the thickness “t” of spacer210is at least 1.02 mm (0.040 inches).

In one embodiment, the spacer210may be a thin film having a thickness “t” of about 0.05 mm where EAS component1directly overlaps RFID component2.

In one embodiment, the spacer may be air where the EAS label1is supported mechanically away from the RFID component2.

As a result, security tag200provides significant advantages over the prior art by enabling a combined EAS/RFID devices of significantly lower space or volume and lower cost.

In one embodiment, security tag200may use an induced voltage from a coil antenna for operation. This induced AC voltage may be rectified to result in a DC voltage. As the DC voltage reaches a certain level, the RFID component2begins operating. By providing an energizing RF signal via transmitter102, RFID reader102can communicate with a remotely located security tag200that has no external power source such as a battery.

Since the energizing and communication between the RFID reader and RFID component2is accomplished through antenna204, antenna204may be tuned for improved RFID applications. An RF signal can be radiated or received effectively if the linear dimension of the antenna is comparable with the wavelength of the operating frequency. The linear dimension, however, may be greater than the available surface area available for antenna204. Therefore, it may prove difficult to utilize a true full size antenna in a limited space which is true for most RFID systems in HF applications. Accordingly, it is contemplated that RFID component2may use a smaller LC loop antenna circuit that is arranged to resonate at a given operating frequency. The LC loop antenna may include, for example, a spiral coil and a capacitor. The spiral coil is typically formed by n-turns of wire, or n-turns of a printed or etched inductor on a dielectric substrate.

For HF applications, in order to achieve good RFID coupling, the loop area*turns product and resonant frequency need to be optimized. In one embodiment of the present disclosure illustrated inFIG. 3A, the resonant frequency can be effected by tuning the parallel capacitor C2of the resonant circuit112including the effects on impedance of the EAS label1and of the RFID chip208.

In either HF or UHF applications, for the particular frequency of interest, the RFID chip complex impedance must be matched by the complex conjugate impedance of the antenna including the loading effects on impedance of the EAS label. In the HF case, a resonating capacitor is commonly used to tune the frequency. This capacitor is usually larger than the RFID chip capacitance and will dominate the response. For the UHF case, the RFID chip complex impedance contains only the chip capacitance for tuning.

In another embodiment according to the present disclosure, antenna204may be designed so that the complex conjugate of the overall antenna matches the impedance to the complex impedance of lead frame206and IC208at the desired operating frequency, e.g., 915 MHz. When RFID security tag200is placed on an object to be monitored, however, it has been observed that the resulting operating frequency may change, i.e., each object may have a substrate material with dielectric properties affecting the RF performance of antenna204. In other words and as with substrate202, the object substrate may cause frequency shifts and RF losses determined by the dielectric constant, loss tangent, and material thickness. Examples of different object substrates may include so called “chip board” (i.e., material used for item-level cartons, corrugated fiber board which is material used for corrugated boxes), video cassette and digital video disc (DVD) cases, glass, metal, etc. It is contemplated that each object substrate may have a significant effect on the read range R1for security tag200.

Antenna204may be tunable to compensate for such variations. In other words, since the dielectric constant for many materials is greater than one, the operating frequency is typically lowered when security tag200is attached to an object substrate. In order to establish the original frequency, antenna204is typically altered in some manner, otherwise detection performance and read range may be reduced. As such, antenna204may be altered by trimming the ends of antenna204by severing the antenna conductor and isolating the resultant trimmed antenna segment from the ends that were cut away. The trimmed ends do not necessarily have to be removed to allow the tuning operation. Consequently, continuous tuning of antenna204to the desired operating frequency is possible to allow operation of security tag200when security tag200is attached to different objects. Security tag200in general, and antenna204in particular, are described in more detail below with reference toFIGS. 5-7.

FIG. 5illustrates a top view of a partial security tag200with an antenna in accordance with one embodiment according to the present disclosure which is particularly suitable for UHF applications. Security tag200includes antenna204disposed upon substrate202which is substantially rectangular in shapes. In one envisioned embodiment, antenna204is disposed on substrate202by die-cutting the label antenna pattern onto substrate202.

RFID chip208may be connected to lead frame206by ultrasonically bonding lead frame206to the conductive pads on RFID chip208. In the particular embodiment ofFIG. 5, RFID chip208and lead frame206are placed in the geometric center of the dielectric substrate material of substrate202. The ends of lead frame206are mechanically and electrically bonded to the foil antenna pattern of antenna204. A covering material (not shown) may be applied over the entire top surface of security tag200to protect the assembly and provide a surface for printing indicia if desired. It is known in the art to use an anisotropic electrically conductive thermally setting adhesive to bond the RFID chip208to the antenna204. An example of such an adhesive is Loctite 383® made by the Henkel Loctite Corporation of Rocky Hill, Conn. Antenna204may also include multiple antenna portions. For example, antenna204may include a first antenna portion306and a second antenna portion308, the first antenna portion306being connected to a first side206A of lead frame206, and the second antenna portion308connected to a second side206B of lead frame206. Therefore, antenna204is the entire RFID tag antenna which is subdivided into first antenna portion306and second antenna portion308.

First antenna portion306may have a first antenna end306A and a second antenna end306B. Similarly, second antenna portion308may have a first antenna end308A and a second antenna end308B. In one embodiment and as shown inFIG. 5, first antenna end306A of first antenna portion306is connected to lead frame206A. First antenna portion306is disposed on substrate202to form an inwardly spiral pattern from RFID chip208in a first direction, with second antenna end306B positioned to terminate on the inner loop of the inwardly spiral pattern. Similarly, first antenna end308A of second antenna portion308may be connected to lead frame206B. Second antenna portion308is also disposed on substrate202to form an inwardly spiral pattern from RFID chip208in a second direction, with second antenna end308B positioned to terminate on the inner loop of the inwardly spiral pattern.

In one embodiment, the antenna geometry of antenna204is configured to traverse around the perimeter of substrate202and spiral inwardly. It is envisioned that the inwardly directed spiral antenna pattern may provide several advantages:

(1) The ends of antenna204may be placed well inside the perimeter of substrate202. Placing the ends of antenna204within the perimeter of substrate202may allow the ends to be trimmed without changing the amount of area used by antenna204;

(2) The Q factor of antenna204may be optimized so that the response of security tag200, including the effects of spacer210and EAS label1, only varies by approximately −3 dB at the ISM band limits. Using the Chu-Harrington limit of Q=1/(kα)3+1/(kα), where k=2π/λ and “α” is a characteristic dimension of antenna204, it can be seen that a sphere of radius “α” could just enclose security tag200. For a high Q factor, then “kα” should be <<1. Therefore, by maximizing Q, “a” is minimized to fall within the operating frequency band limits. The tuning of antenna204for UHF applications is disclosed in further detail in co-pending, commonly owned U.S. patent application Ser. No. 10/917,752 filed on Aug. 13, 2004 entitled “TUNABLE ANTENNA” by R. Copeland and G. M. Shafer, the entire contents of which are incorporated herein by reference.

Antenna204may also be tuned particularly for UHF applications to a desired operating frequency by modifying a first length for first antenna portion306, and a second length for second antenna portion308, after these antenna portions are disposed on substrate202. For example, each antenna portion may be divided into multiple antenna segments at multiple segment points. The first and second antenna lengths may be modified by electrically isolating at least a first antenna segment from a second antenna segment. The antenna length may be modified by severing each antenna portion at one of multiple segment points, with each segment point to correspond to an operating frequency for antenna204. Dividing first antenna portion306and second antenna portion308into multiple antenna segments results in shortening the length of each antenna portion, and thereby effectively changes the total inductance of antenna204. The antenna segments and segment points are described in more detail with reference toFIG. 6.

FIG. 6illustrates a diagram of a security tag400with an antenna having segment points in accordance with one embodiment. In particular,FIG. 6illustrates a top view of portions of security tag400with multiple segment points SP1, SP2, SP3and SP4. In a similar manner as shown inFIG. 4with respect to security tag200, security tag400may include EAS component1, spacer210and RFID component2. Antenna204may be tuned also to a desired operating frequency by modifying a first length for first antenna portion306, and a second length for second antenna portion308, after these antenna portions are disposed on substrate202. For example, it is contemplated that each antenna portion may be divided into multiple antenna segments at multiple segment points SP1-SP4. Multiple segment points SP1through SP4represent end tuning positions where the antenna204may be cut or trimmed in order to be tuned to various objects. SP1is the free space position where the length of original free space antenna204is tuned to 868 MHz. SP2is the free space position where the length of antenna portions306and308is tuned to 915 MHz. SP3and SP4are the free space positions where the length of antenna portions306and308is tuned to the various objects. The various objects include, for example and are not limited to, retail and/or wholesale merchandise.

The first and second antenna lengths may be modified by electrically isolating at least a first antenna segment from a second antenna segment. The antenna length may be modified by severing each antenna portion at one of multiple segment points, with each segment to correspond to an operating frequency for antenna204. The severing may be achieved in a number of different ways, such as cutting or punching the antenna trace at a given segment point SP1-SP4. The severing may create a slot at the segment point, such as slots402,404,406,408,410, and412.

It should be noted that for HF applications, antenna204is tuned by changing the inductance or capacitance parameters but not the lengths of the segments.

In one embodiment, and as shown inFIG. 6, each segment point SP1-SP4corresponds to an operating frequency for antenna204. In one example, SP1may tune antenna204for an operating frequency of approximately 868 MHz when security tag400is in free space and unattached to an object. SP2may tune antenna204for an operating frequency of approximately 915 MHz when security tag400is in free space and unattached to an object. SP3may tune antenna204for an operating frequency of approximately 915 MHz when security tag400is attached to a VHS cassette housing. SP4may tune antenna204for an operating frequency of approximately 915 MHz when security tag400is attached to a chip board. As can be appreciated, the number of segment points and corresponding operating frequencies for antenna204may vary according to a given implementation. The embodiments are not limited in this context.

FIG. 7illustrates a block flow diagram500in accordance with another embodiment of the present invention. As mentioned above, security tag200may be configured in a number of different ways. For example: 1) an integrated circuit may be connected to a lead frame at block502; 2) an antenna may be disposed on a substrate at block504; 3) the lead frame may be connected to the antenna at block506.

In one particular embodiment, the antenna is tuned for use with an operating frequency at block508. The tuning may be performed by modifying a length for the antenna by severing the antenna into multiple antenna segments at a segment point corresponding to the operating frequency. The severing may electrically disconnect a first antenna segment from a second antenna segment, thereby effectively shortening the length of the antenna.

As described above, the unique antenna geometry of an inwardly spiral pattern may be useful for RFID applications when connected to an RFID chip. As previously noted, the unique antenna geometry shown inFIGS. 5 and 6, however, may also be useful for an EAS system where security tag200and security tag400, respectively, each include EAS component1and spacer210. In one embodiment, RFID chip208may be replaced with a diode or other non-linear passive device where the voltage and current characteristics are nonlinear. The antenna for the diode or other passive non-linear EAS device may have the same geometry as shown inFIGS. 5 and 6, and may be trimmed to tune the antenna to the operating frequency of the transmitter used to transmit interrogation signals for the EAS system. Similar to RFID system100, the range of operating frequencies may vary, although the embodiments may be particularly useful for the UHF spectrum, such as 868-950 MHz. The embodiments are not limited in this context.

It is also contemplated that some embodiments of the present disclosure may be configured using an architecture that may vary in accordance with any number of factors, such as: 1) desired computational rate; 2) power levels; 3) heat tolerances; 4) processing cycle budget; 5) input data rates; 6) output data rates; 7) memory resources; 8) data bus speeds and other performance constraints. For example, an embodiment may be configured using software executed by a general-purpose or special-purpose processor. In another example, an embodiment may be configured as dedicated hardware, such as a circuit, an ASIC, Programmable Logic Device (PLD) or a digital signal processor (DSP). In yet another example, an embodiment may be configured by any combination of programmed general-purpose computer components and custom hardware components. The embodiments are not limited in this context.

Examples of security tags200and400, which are combination EAS and RFID labels/tags, are shown inFIGS. 8A to 8Dwhich show various types of adhesive magnetostrictive labels and EAS hard tags, such as the SuperTag® produced by Sensormatic, a division of Tyco Fire and Security, LLC of Boca Raton, Fla.FIG. 8Aillustrates an EAS label804adjacent to an RFID label806in a co-planar configuration. This configuration of adjacent labels804and806is known in the prior art.FIG. 8Billustrates a variation of the co-planar configuration of EAS label804and RFID label806ofFIG. 8Awherein the EAS label804and the RFID label806are separated from each other by a gap805having a distance “g”. This configuration of804and806being separated by gap805is also known in the prior art.

In both the configuration ofFIGS. 8A and 8B, the EAS label804and the RFID label806act independently of one another with respect to matching of impedance values. As “g” increases, the read range increases. As a result, the size of gap “g” controls the impedance load. However, this is not a desirable effect because although the read range increases, the total area occupied by the EAS label804and RFID label806increases, necessarily occupying more space or area on an object to be identified.

FIG. 8Cillustrates an embodiment of the present disclosure of a security tag200or400showing an EAS component or label1. An RFID component or insert2is mounted directly underneath the EAS component or label1. A dummy bar code802is printed on the EAS component or label1and is just for visual purposes only. Dummy bar code802has no EAS or RFID function. As compared to the prior art, the configuration of security tag200or400as a combination EAS component or label or tag1with RFID component or insert2mounted directly underneath the EAS component or label1(as shown inFIG. 4) provides a minimal separation between the RFID component or insert2and the EAS label1.

FIG. 8Dillustrates one embodiment of the present disclosure of one portion812of a housing for combination EAS component or label1with RFID component or insert2. The RFID component or insert2is defined as including RFID chip208mounted on antenna204. However, spacer210or an adhesive layer are not visible (SeeFIG. 4).

FIG. 8Eis an elevation view of the combination EAS component or label1with RFID component or insert2disclosed inFIG. 8D, but showing spacer210disposed between the EAS component or label1and the RFID component or insert2.

FIG. 8Fillustrates one embodiment of the present disclosure of one portion818of a housing for a combination EAS label816similar to EAS component or label1with an RFID insert814which is similar to RFID component or insert2. The RFID insert814is defined as another RFID chip820mounted on antenna204. Again, spacer210or an adhesive layer are not visible (SeeFIG. 4).

FIG. 8Gis an elevation view of the combination EAS label816with RFID insert814disclosed inFIG. 8F, but showing spacer210disposed between the EAS label816and the REID insert814.

The types of EAS devices and RFID combinations are not limited to the EAS and RFID devices described herein.