Abstract:
An RFID system comprises an intermediate device that includes a first and second antenna coils connected together in a close loop format. The first coil can be optimized for communication with a reader, while the second coil can be optimized for communication with a tag. Thus, the dimension of the first antenna coil and the second antenna coil can be completely independent of each other. The intermediate device can be configured such that it can change the direction of the transmission from either the interrogator or the tag, thereby improving communication when the interrogator and tag are not inline.

Description:
BACKGROUND  
       [0001]     1. Field of the Invention  
         [0002]     The embodiments described herein are directed to radio frequency communication systems, and more particular to systems and methods for extending the communication range in a radio frequency communication system.  
         [0003]     2. Background of the Invention  
         [0004]     Radio Frequency Identification (RFID) systems are a type of radio frequency communication system. RFID systems are gaining attention due to their ability to track and identify moving objects. In an RFID system, remote objects intended to be tracked and identified are equipped with a small RFID tag. The RFID tag contains a transponder and a digital memory chip that is given a unique electronic identification. An interrogator, or a reader can be configured to emit a signal that can activate the RFID tag. When an RFID tag passes within range of the reader, the RFID tag can detect the reader&#39;s signal and provide its identification information. The reader can be configured to decode the identification information, and in certain applications will write data to the RFID tag.  
         [0005]     The signal generated by the reader is a Radio Frequency (RF) signal. RFID systems are generally configured to operate within four main frequency bands. The frequency bands are characterized by the frequency of operation for the RF signal generated by the reader. These bands include a low frequency band, i.e., 125 KHz or 134.2 KHz, a high frequency band, i.e., 13.56 MHz, a UHF frequency band, i.e., 868-956 MHz or 463 MHz, and a microwave frequency band, i.e., 2.4 GHz or 5.8 GHz.  
         [0006]     An RFID reader generally comprises a radio transceiver configured to transmit and receive RF signal. The radio transceiver is coupled with one or more antennas which enable the transceiver to transmit and receive the RF signals. The transceiver is also interfaced with an encoder/decoder configured to decode information contained in the received signals and encode information to be transmitted via the transceiver.  
         [0007]     RFID tags are generally classified as passive or active tags. A passive tag has no internal, or onboard power supply. Instead, a passive tag is powered by energy contained in the RF signal transmitted from the reader. The RF signal transmitted by the reader induces an electrical current in the tag antenna that supplies enough power to allow the tag to power up and transmit a response. Most passive tags signal to the reader by backscattering the RF carrier signal generated by the reader. This means that the tag antenna should be designed to both collect power from the incoming signal and also to transmit the outbound backscatter signal. It should be noted that the response signal generated by the tag can include more than just identification information.  
         [0008]     An active tag, on the other hand, includes its own internal power source, which is used to power the tag in order to generate an outgoing signal. Active tags can have longer operational ranges and larger memories as compared to passive tags, which can allow the tag to store additional information sent by the reader; however, because passive tags do not require an onboard power supply, they can be made smaller and can cost significantly less than active tags. Additionally, due to their simplicity in design, passive tags are suitable for manufacture with conventional printing process for the antenna.  
         [0009]     While passive tags provide many benefits that make them increasingly more popular for new RFID applications, one drawback is the limited operational range, e.g., as compared to active tags. One way to overcome the limited range problem, in certain applications, is to use a range extender. A range extender can be defined as an antenna, or resonator circuit, that can be placed between the reader and the tag and can be configured to receive the RF signal from the reader, amplify it, and rebroadcast it to the tag. Thus, the resonator circuit can be used to extend the range of communication ordinarily achievable between the reader and the tag.  
         [0010]     Conventional range extenders often comprise a single antenna configured for coupling with one of, but not both, the reader or the tag. Consequently, the extension of range can be limited due to the fact that the range extender is not optimized for communication with the other of the reader or the tag. Moreover, conventional range extenders are often only useful for inline communications, i.e., when the reader, the range extender and the tag are all inline with a center orthogonal axis. If the reader and the tag are not so aligned, then conventional range extenders may not provide any advantage.  
       SUMMARY  
       [0011]     An RFID system comprises an intermediate device that includes a first and second antenna coils connected together in a close loop format. The first coil can be optimized for communication with a reader, while the second coil can be optimized for communication with a tag.  
         [0012]     In one aspect, the intermediate device can be configured such that it can change the direction of the transmission from either the interrogator or the tag, thus improving communication when the interrogator and tag are not inline.  
         [0013]     In another aspect, the dimension of the first antenna coil and the second antenna coil can be completely independent of each other.  
         [0014]     These and other features, aspects, and embodiments of the invention are described below in the section entitled “Detailed Description.” 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     Features, aspects, and embodiments of the inventions are described in conjunction with the attached drawings, in which:  
         [0016]      FIG. 1  is a diagram illustrating an example wireless communication system comprising an intermediate antenna in accordance with one embodiment;  
         [0017]      FIG. 2  is a diagram illustrating an exemplary wireless communication system;  
         [0018]      FIGS. 3A-3D  are diagrams illustrating example embodiments of intermediate antennas configured in accordance with different embodiments;  
         [0019]      FIG. 4  is a diagram illustrating a wireless communication system comprising an intermediate antenna in more detail;  
         [0020]      FIG. 5A  is a diagram illustrating a wireless communication system comprising an intermediate antenna in accordance with another embodiment;  
         [0021]      FIG. 5B  is a diagram illustrating the schematic equivalent of the a portion of the intermediate antenna; and  
         [0022]      FIG. 6  is a diagram illustrating a wireless communication system comprising an intermediate antenna configured to change the direction of transmission signals in accordance with one embodiment 
     
    
     DETAILED DESCRIPTION  
       [0023]     The embodiments described below are generally directed to RFID systems and devices; however, it will be understood that the systems and methods described herein can apply to other types of RF communication systems. Accordingly, the embodiments described herein should be seen as examples only and should not be seen as limiting the systems and methods described to any particular type of communications system.  
         [0024]     It will also be understood that any dimensions, measurements, ranges, test results, numerical data, etc., are approximate in nature and unless otherwise stated not intended as precise data. The nature of the approximation involved will depend on the nature of the data, the context and the specific embodiments or implementations being discussed.  
         [0025]      FIG. 1  is a diagram illustrating an RFID system  100  configured to allow communication between an RFID reader, or interrogator  102  and an RFID transponder, or tag  114 . As can be seen, RFID interrogator comprises an antenna  104  illustrated as a coil. It will be understood, that an antenna is often represented as an inductive element such as a coil in the manner illustrated in  FIG. 1 . Similarly, RFID transponder  114  comprises an antenna  116 . The dimensions of RFID transponder  114  are often much smaller than interrogator  102 . Consequently, antenna  116  will often comprise smaller dimensions than antenna  104 .  
         [0026]     In operation, RFID interrogator  102  generates a Radio Frequency signal (RF) signal  106  that is transmitted by antenna  104 . Signal  106  will propagate through free space and be received by RFID transponder  114 ; however, under normal operating conditions a signal received by RFID transponder  114  will be attenuated and degraded when it is received.  
         [0027]     This phenomenon can be illustrated with the aid of  FIG. 2  which illustrates a conventional RFID system  200 . In system  200 , RFID interrogator  202  transmits a signal  206  via antenna  204  and RFID transponder  208  receives signal  212  via antenna  210 . Received Signal  212  is attenuated due to dimension mismatch between antenna  204  and antenna  210 . Signal  212  can be further attenuated, or interfered with by other wireless communication systems within range of system  200 , reflection off of objects between RFID interrogator  202  and RFID transponder  208 , etc.  
         [0028]     In system  100 , signal  106  is received by repeater, or range extender  108  and retransmitted to RFID transponder  114 . As can be seen, repeater  108  comprises an antenna  110  configured to receive signal  106 , and antenna  112  configured to transmit signal  118 . By using repeater  108 , signal  106  can be enhanced such that it is a closer replication to signal  106  transmitted via RFID interrogator  102 .  
         [0029]     As will be described in more detail below, antenna  110  can be designed such that it can optimally couple with antenna  104  in order to optimally receive signals  106 . Similarly, antenna  112  can be configured so as to optimally couple with antenna  116  in order to ensure that the an optimum signal  118  is received by RFID transponder  114 . By using repeater  108 , the power contained in signal  118  can be improved several times compared to a conventional RFID system such as system  200 . The improved power can improve error rates and/or increase communication ranges between interrogator  102  and RFID transponder  114 .  
         [0030]      FIG. 3A  is a diagram illustrating an intermediate antenna  302  comprising a first coil  304  and a second coil  306 . Antenna  302  can be used as a repeater such as repeater  108 . Coils  304  and  306  can be formed, for example, on a substrate  301 . For example, coils  304  and  306  can be formed from conductive material deposited or formed on substrate  301 . The conductive material comprising coils  304  and  306  can be formed on substrate  301  using conventional printed wiring board processing techniques. For example, in embodiments where coils  304  and  306  are fabricated from metal formed on substrate  301 , conventional printed wiring board processing techniques can be used. In other embodiments, the conductive material comprising coils  304  and  306  can be formed on substrate  301  using conventional printing processes, such as silk screening.  
         [0031]     Substrate  301  can comprise of flexible substrate such as a flexible plastic or metal foil. By using a flexible substrate, antenna  302  can be configured so that it can flex, or bend. For example, antenna  302  can be configured to bend so that the “direction” of communication between a reader and a tag can be changed. This is described in more detail below.  
         [0032]     Accordingly, substrate  301  can be constructed from a flexible material and can comprise a thin region  312  and antenna  302  can be configured so as to bend around the axis AA′. In other embodiments, a substrate  301  can comprise a rigid substrate beneath coils  304  and  306  and a flexible substrate in region  312  joining the two more rigid regions.  
         [0033]     Substrate  301  can also comprise multiple conductive layers. For example, the top of substrate  301  is clearly a conductive layer comprising coils  304  and  306  and a connection  308  between the two; however, coils  304  and  306  also comprised second terminals that must be connected. These terminals cannot be directly connected on top of substrate  301  because the conductive connection running between the two would cross coils  304  and  306 , shorting them out and impairing their performance. Thus, the second terminals of coils  304  and  306  can be connected via a conductive line  310  on the back of substrate  301 . In this case, substrate  301  will comprise two conductive layers the top and the back.  
         [0034]     It will be understood that in order to connect the terminals of antennas  304  and  306  via conductive line  310  on the back of substrate  301 , conductive holes, or vias extending down through substrate  301  and in contact with coils  304  and  306  must be formed. On the back of substrate  301 , conductive line  310  can also contact the vias and thereby electrically connect antennas  304  and  306 .  
         [0035]     In other embodiments, substrate  301  can actually comprised multiple laminated substrates and conductive line  310  can be formed from a conductive layer internal to substrate  301 ; however, it will be understood that for cost and ease of manufacturing, it is preferable that the only conductive layers on substrate  301  be on the top and bottom of substrate  301 .  
         [0036]     Coils  304  and  306  are configured so as to comprise two resonant circuits that can receive and transmit RF signal at the appropriate frequencies. Accordingly, the number of turns and dimensions associated with coils  304  and  306  must be configured so that each coil can receive and transmit RF signals at the appropriate frequency.  
         [0037]     Further, coils  304  and  306  are configured so that one of the coils, e.g., coil  304  is optimized for coupling with the interrogator, while the other antenna, e.g., is optimized for coupling with the tag. Accordingly, the dimensions of coil  304  can be close to the dimensions of the coil, or antenna included in the reader, while the dimension of coil  306  can be close to the dimensions of the coil, or antenna in the tag. Accordingly, in certain embodiments the dimension of the two coils will differ as seen in some of the embodiments described below.  
         [0038]     Coils  304  and  306  are electrically connected via connectors  308  and  310 . Thus, when, e.g., an RF signal is impinged upon coil  304 , coil  304  will produce an electrical signal that will be coupled via connectors  308  and  310  to coil  306 . If coil  306  is constructed properly, then coil  306  will resonate at the appropriate frequency and fully take over the RF signal received by coil  304 . In this manner, antenna  302  can act as a range extender.  
         [0039]      FIG. 3B  is a diagram illustrating another example antenna  120  configured in accordance with another embodiment of the systems and methods describe herein. Antenna  320  comprises a first coil  322  and a second coil  324  formed on a substrate  319 . As with substrate  301 , substrate  319  can be a flexible substrate, or can at least comprise a flexible region  329 . In the example of  FIG. 3B , the terminals of antenna  322  and  324  are each connected via a conductive connector on top of substrate  319  and a conductive connector on the bottom of substrate  319 , wherein the conductive connectors on top and bottom are connected by vias.  
         [0040]     Thus, the first terminal of antenna  322  can be connected to a first terminal of antenna  324  through a conductive connecting line  326  on top of substrate  319  in a conductive connecting line  323  on the bottom of substrate  319 . Conductor line  326  and conductor line  323  can then be connected by a via  321 . Similarly, a second terminal of antenna  322  can be connected with the second terminal of antenna  324  by a conductive connecting line  328  on the bottom of substrate  319  and a conductive connecting line  325  on the top of substrate  319 . Connecting line  328  and connecting line  325  can be connected by via  327 .  
         [0041]      FIG. 3C  is a diagram illustrating an example antenna  330  that comprises coils of different dimensions in accordance with another embodiment of the systems and methods described herein. As can be seen, coil  332  is smaller in dimension than coil  334 . It must be kept in mind, however, that the number of coils and dimensions of each coil must still be sufficient to transmit and receive RF signals at the appropriate frequency. Further, the dimension of coil  332  can be configured so as to ensure optimal coupling with a tag, or transponder, while the dimensions of coil  334  can be configured so as to ensure optimal coupling with a reader. Accordingly, the dimension of coil  332  can close to the dimension of an antenna included in the tag, while the dimensions of coil  334  can be close to the dimensions of the antenna included in the reader.  
         [0042]     In the example of  FIG. 3C , the first terminal of coil  332  is connected with the first terminal of coil  334  via connecting line  336  on top of substrate  331 . The second terminal of coil  332  is connected to a second terminal of coil  334  by a connecting line  338  on the bottom of substrate  331 . Connecting line  338  can be connected with the terminals of coils  332  and  334  by vias extending through substrate  331 .  
         [0043]      FIG. 3D  is a diagram illustrating an example embodiment of antenna  340  comprising coils of different dimensions configured in accordance with another embodiment of the systems and methods described herein. In the example of  FIG. 3D , coil  342 , which is smaller than coil  344 , is interfaced with the terminals of coil  344  by connecting line  346  on top of substrate  341 , via  347 , and connecting line  348  on the bottom of substrate  341 . The other terminal of coil  342  is connected with the other terminal of coil  344  by conducting line  345  on the bottom of substrate  341 , via  343 , and connecting line  345  on the top of substrate  341 .  
         [0044]     Again the dimension of coil  342  can be selected so as to ensure optimal coupling with a tag, while the dimensions of coil  334  can be selected to ensure optimal coupling with a reader.  
         [0045]     The examples on  FIGS. 3A-3D  illustrate several examples of embodiments of intermediate antennas configured in accordance with the systems and methods described herein. It will be understood, however, that other embodiments are possible. For example, in other embodiments antennas configured in accordance with the systems and methods described herein can comprise coils of varying dimensions and shapes. Again, however, the shapes and dimensions should be selected so as to ensure optimal coupling with the associated reader and tag.  
         [0046]      FIG. 4  is a diagram illustrating an RFID system  400  configured to allow communication between an interrogator  402  and a tag  418 . Interrogator  402  comprises a transceiver circuit coupled with an antenna  404 . Interrogator  402  can be configured to transmit RF signals  420  via antenna  404 . RF signals  420  are intended for tag  418 ; however, RF signals  420  would normally experience attenuation. An intermediate antenna  408  has been placed inline with reader  402 .  
         [0047]     Intermediate antenna  408  comprises a first coil  410  configured to optimally couple with antenna  404 , and a coil  412  configured to be optimally coupled with antenna  424  on tag  418 . Thus, RF signals  420  will be impinged upon coil  410 , which will cause an electric signal to flow in coil  410  that will be coupled with coil  412 . The current will cause coil  412  to resonate and generate an RF signal  422  that can be transmitted to and received by antenna  424 .  
         [0048]     In the example of  FIG. 4 , antenna  404 , intermediate antenna  408 , and tag  418  can be said to be aligned with a center orthogonal axis  406 . It will be understood that the alignment pictured in  FIG. 4  can be preferred as it can result in the optimal magnetic coupling of RF signals  420  with coil  410  and RF signals  422  with antenna  424  included on tag  418 . In other embodiments, the various antennas are not necessarily aligned as illustrated in  FIG. 4 , but it will be understood that the various antennas must be aligned sufficiently to ensure that enough magnetic energy in the various RF signals are sufficiently coupled with the various antennas. Further, as explained in relation to  FIG. 6 , in certain embodiments intermediate antenna  408  can be configured to bend so that is can change the direction of communication an provide enhanced communication capability when reader  402  and tag  418  are not aligned along a center orthogonal axis as in  FIG. 4 .  
         [0049]     In the example of  FIG. 4 , communications from interrogator  402  to tag  418  is illustrated but it will be understood that communication from tag  418  to interrogator  402  will operate in a similar manner.  
         [0050]     As noted above, coils  410  and  412  must be configured so as to act as resonators at the appropriate frequency. It will be understood, that in order to act as a resonator additional components may need to be coupled with one or both of antennas  410  and  412 . For example,  FIG. 5A  is a diagram illustrating an embodiment of system  400  in which a parallel capacitor  502  and a parallel resistor  504  are coupled with coil  410  in order to create a resonant circuit as required.  FIG. 5B  is illustrates the schematic equivalent of the resonant circuit formed when capacitor  502  and resistor  504  are coupled with antenna  410 . It will be understood that the value of capacitor  502  and resistor  504  will depend on a specific implementation and must be chosen so as to produce a tuned resonant circuit configured to resonate at the appropriate frequency.  
         [0051]     In other embodiments, a parallel resistor and/or capacitor can also be coupled with coil  412  in order to produce a resonant circuit tuned to resonate at the appropriate frequency. In certain other embodiments, resistor  504  can be omitted from the tuned resonant circuit coupled with coil  410  and/or coil  412 .  
         [0052]     As illustrated in  FIG. 6 , in certain embodiments interrogator  402  and transponder  418  are not aligned along an orthogonal axis. In such embodiments, intermediate antenna  408  can be configured to bend so that it can communicate with interrogator  402  along an axis  602  and with tag  408  along an axis  604 . For example, intermediate antenna  408  can be configured to bend around a structure  606  which can be configured to align coil  410  with antenna  404  and coil  412  with antenna  424 . This can be achieved via a flexible substrate such as in the embodiments described above.  
         [0053]     Thus, antenna  408  can be said to be able to change the direction of communication because it can receive signals from antenna  404  along axis  602  and then retransmit those signals to antenna  424  along axis  604 .  
         [0054]     It will be understood, that in certain embodiments signals are broadcast from antenna  404  meaning that they travel in all or many directions; however, the portion of the signals broadcast by antenna  404  traveling along axis  602  will be optimally received by coil  410 . Similarly, signals broadcast by antenna  424  traveling along axis  604  will be optimally received by antenna  412 . Accordingly, antenna  408  configured as illustrated in  FIG. 6  can still improve communication between interrogator  402  and tag  418  by redirecting and optimizing the transmissions between the two.  
         [0055]     In other embodiments, beam forming or beam shaping can be used so that most, or a significant portion of the transmit energy from antenna  404  travels in the direction defined by axis  602 . Similarly, antenna  424  can be configured such that all or a substantial portion of the energy transmitted from antenna  424  travels in the direction defined by axis  604 . In such embodiments, communication can be optimized even further.  
         [0056]     While certain embodiments of the inventions have been described above, it will be understood that the embodiments described are by way of example only. Accordingly, the inventions should not be limited based on the described embodiments. Rather, the scope of the inventions described herein should only be limited in light of the claims that follow when taken in conjunction with the above description and accompanying drawings.