Abstract:
An RFID system comprises an intermediate device that includes a first and second antenna coils connected together in a close loop format. The coils are formed on a flexible substrate that can be folded around a magnetic flux blocker such that one loop is on side of the blocker and the other loop is on the other side of the blocker. The intermediate device can then improve communication between a reader on one side of the blocker and a tag on the other. The coil on the reader side of the blocker can receive RF signals being generated by the reader and convert them to an electrical signal that can be passed to the coil on the tag side of the blockage. The second coil can then generate an RF signal that can be transmitted to the tag.

Description:
BACKGROUND 
   1. Field of the Invention 
   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. 
   2. Background of the Invention 
   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. 
   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. 
   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 that 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. 
   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. 
   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. 
   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. 
   Conventional range extenders do not necessarily help, however, when the limited range is due to some impediment to the RF signal being produced by the reader. RF signals are electromagnetic signals. Accordingly, the ability for a reader to communicate with the tag is dependent on the degree to which the RF signals produced by the reader and transmitted by the reader antenna magnetically coupled with the tag antenna. This means that the magnetic strength, or magnetic flux of the RF signal as seen by the tag is an important parameter. 
   Many materials act as magnetic flux blockers, i.e., they block the electromagnetic RF signals being generated by the reader. When limited communication range is the result of a magnetic flux blocker, a range extender will not necessarily overcome the problem. This is because the magnetic flux blocker will block the RF signals being generated and retransmitted by the range extender in the same manner that it will block the signals being generated by the reader. 
   As the applications for RFID technology grow, RFID tags are being included, or embedded in devices that are housed or contained in material that can act as a magnetic flux blocker. Accordingly, communication range can be limited for many of these new applications. Unfortunately, conventional range extenders will not necessarily be able to overcome some of the limited communication ranges for these new applications. 
   SUMMARY 
   An RFID system comprises an intermediate device that includes a first and second antenna coils connected together in a close loop format. The coils are formed on a flexible substrate that can be folded around a magnetic flux blocker such that one loop is on side of the blocker and the other loop is on the other side of the blocker. The intermediate device can then improve communication between a reader on one side of the blocker and a tag on the other. The coil on the reader side of the blocker can receive RF signals being generated by the reader and convert them to an electrical signal that can be passed to the coil on the tag side of the blockage. The second coil can then generate an RF signal that can be transmitted to the tag. 
   In one aspect, the intermediate device can be folded around a cellphone battery in order to enable a tag, e.g., disposed on a SIM card within the cellphone behind the battery, to communicate with the reader external to the cellphone. 
   In another aspect, the first antenna coil and the second antenna coil can comprise different dimensions. 
   These and other features, aspects, and embodiments of the invention are described below in the section entitled “Detailed Description.” 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Features, aspects, and embodiments of the inventions are described in conjunction with the attached drawings, in which: 
       FIGS. 1A-1D  are diagrams illustrating example embodiments of intermediate antennas configured in accordance with different embodiments; 
       FIG. 2  is a diagram illustrating one of the antennas of  FIGS. 1A-1D ; 
       FIG. 3  is a diagram illustrating the antenna of  FIG. 2  formed around a magnetic flux blocker; 
       FIG. 4  is a diagram illustrating an RFID system comprising the intermediate antenna of  FIG. 2  in accordance with one embodiment; and 
       FIG. 5  is a diagram illustrating a mobile communication device comprising an intermediate antenna in accordance with one embodiment. 
   

   DETAILED DESCRIPTION 
   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. 
   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. 
     FIG. 1  is a diagram illustrating an antenna  102  comprising a first coil  104  and a second coil  106 . Coils  104  and  106  can be formed, for example, on a substrate  101 . For example, coils  104  and  106  can be formed from conductive material deposited or formed on substrate  101 . The conductive material comprising coils  104  and  106  can be formed on substrate  101  using conventional printed wiring board processing techniques. For example, in embodiments where coils  104  and  106  and are fabricated from metal formed on substrate  101 , conventional, printed wiring board processing techniques can be used. In other embodiments, the conductive material comprising coils  104  and  106  can be formed on substrate  101  using conventional printing processes, such as silk screening. 
   Substrate  101  can comprise of flexible substrate such as a flexible plastic or metal foil. By using a flexible substrate, antenna  102  can be configured so that it can flex, or bend around a object. For example, antenna  102  can be configured to bend around a magnetic flux blocker in order to enable communication between a reader and a tag even given the presence of the blocker. 
   Accordingly, substrate  101  can be constructed from a flexible material and can comprise a thin region  112  and antenna  102  can be configured so as to bend around the axis AA′. In other embodiments, a substrate  101  can comprise a rigid substrate beneath coils  104  and  106  and a flexible substrate in region  112  joining the two more rigid regions. 
   Substrate  101  can also comprise multiple conductive layers. For example, the top of substrate  101  is clearly a conductive layer comprising coils  104  and  106  and a connection  108  between the two; however, coils  104  and  106  also comprised second terminals that must be connected. These terminals cannot be directly connected on top of substrate  101  because the conductive connection running between the two would cross coils  104  and  106 , shorting them out and impairing their performance. Thus, the second terminals of coils  104  and  106  can be connected via a conductive line  110  on the back of substrate  101 . In this case, substrate  101  will comprise two conductive layers the top and the back. 
   It will be understood that in order to connect the terminals of antennas  104  and  106  via conductive line  110  on the back of substrate  101 , conductive holes, or vias extending down through substrate  101  and in contact with coils  104  and  106  must be formed. On the back of substrate  101 , conductive line  110  can also contact the vias and thereby electrically connect antennas  104  and  106 . 
   In other embodiments, substrate  101  can actually comprised multiple laminated substrates and conductive line  110  can be formed from a conductive layer internal to substrate  101 ; however, it will be understood that for cost and ease of manufacturing, it is preferable that the only conductive layers on substrate  101  be on the top and bottom of substrate  101 . 
   Coils  104  and  106  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  104  and  106  must be configured so that each coil can receive and transmit RF signals at the appropriate frequency. 
   Coils  104  and  106  are electrically connected via connectors  108  and  110 . Thus, when, e.g., an RF signal is impinged upon coil  104 , coil  104  will produce an electrical signal that will be coupled via connectors  108  and  110  to coil  106 . If coil  106  is constructed properly, then coil  106  will resonate at the appropriate frequency and reproduce an amplified version of the RF signal received by coil  104 . In this manner, antenna  102  can act as a range extender; however, due to the flexible nature of substrate  101 , antenna  102  can act as a range extender even in the presence of a magnetic flux blocker. This will be described in more detail below. 
     FIG. 1B  is a diagram illustrating another example antenna  120  configured in accordance with another embodiment of the systems and methods describe herein. Antenna  120  comprises a first coil  122  and a second coil  124  formed on a substrate  119 . As with substrate  101 , substrate  119  can be a flexible substrate, or can at least comprise a flexible region  129 . In the example of  FIG. 1B , the terminals of antenna  122  and  124  are each connected via a conductive connector on top of substrate  119  and a conductive connector on the bottom of substrate  119 , wherein the conductive connectors on top and bottom are connected by vias. 
   Thus, the first terminal of antenna  122  can be connected to a first terminal of antenna  124  through a conductive connecting line  126  on top of substrate  119  in a conductive connecting line  123  on the bottom of substrate  119 . Conductor line  126  and conductor line  123  can then be connected by a via  121 . Similarly, a second terminal of antenna  122  can be connected with the second terminal of antenna  124  by a conductive connecting line  128  on the bottom of substrate  119  and a conductive connecting line  125  on the top of substrate  119 . Connecting line  128  and connecting line  125  can be connected by via  127 . 
     FIG. 1C  is a diagram illustrating an example antenna  130  that comprises coils of different dimensions in accordance with another embodiment of the systems and methods described herein. As can be seen, coil  132  is smaller in dimension than coil  134 . 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. In the example of  FIG. 1C , the first terminal of coil  132  is connected with the first terminal of coil  134  via connecting line  136  on top of substrate  131 . The second terminal of coil  132  is connected to a second terminal of coil  134  by a connecting line  138  on the bottom of substrate  131 . Connecting line  138  can be connected with the terminals of coils  132  and  134  by vias extending through substrate  131 . 
     FIG. 1D  is a diagram illustrating an example embodiment of antenna  140  comprising coils of different dimensions configured in accordance with another embodiment of the systems and methods described herein. In the example of  FIG. 1D , coil  142 , which is smaller than coil  144 , is interfaced with the terminals of coil  144  by connecting line  146  on top of substrate  141 , via  147 , and connecting line  148  on the bottom of substrate  141 . The other terminal of coil  142  is connected with the other terminal of coil  144  by conducting line  145  on the bottom of substrate  141 , via  143 , and connecting line  145  on the top of substrate  141 . 
   The examples on  FIGS. 1A-1D  illustrate several examples of embodiments of 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. 
     FIG. 2  is a diagram illustrating antenna  130  which comprises of flexible portion  135  such that antenna  130  can flex or bend ground access AA′. A flexible portion  135  can be used in order to bend antenna  130  around a magnetic flux blocker. For example, as illustrated in  FIG. 3 , a magnetic flux blocker  302  can be disposed in the RF signaling path between a reader and tag. Without antenna  130 , blocker  302  can prevent, or degrade communication between the reader and the tag. In order to overcome the effects of blocker  302 , antenna  130  can be bent around battery  302  so that coil  132  is on one side of object  302  and coil  134  is on the other side of object  302 . 
   Accordingly, signals, e.g., transmitted by the reader can be impinge on coil  134 , which will cause an electrical signal to flow in coil  134 . This electrical signal will be coupled with coil  132  via connecting lines  136  and  138  connecting the terminals of coils  134  and  132 . The electrical signal will cause coil  132  to resonate and transmit an RF signal that is a recreation of the RF signal impinged upon coil  134 . The signal transmitted by coil  132  can then be receive by the tag. Similarly, signals transmitted from the tag can be impinged on coil  132 , which can create an electrical signal on coil  132  that would be passed to coil  134  via connectors  138  and  136 . The electrical signals will cause coil  134  to resonate and transmit an RF signal that can be received by the interrogator. 
   It can be seen, therefore, that the magnetic flux blocker  302  can be overcome by the use of antenna  130 . 
   This can be illustrated with the aide of  FIG. 4 , which illustrates an RFID system  400  configured to allow communication between an interrogator  401  and a tag  406  even in the presence of a magnetic flux blocker  302 . Interrogator  401  comprises a transceiver circuit  402  coupled with an antenna  404 . Interrogator  401  can be configured to transmit RF signals  410  via antenna  404 . RF signals  410  are intended for tag  406 ; however, magnetic flux blocker  302  is inline between antenna  404  and tag  406 , and would otherwise block or degrade RF signal  410  in manner that can inhibit communication between interrogator  401  and tag  406 . An antenna, such as antenna  130  has been folded around magnetic flux blocker  302 . Thus, RF signals  410  will be impinged upon coil  134 , which will cause an electric signal to flow on coil  134  that will be coupled with coil  132  on the back of magnetic flux blocker  302 . The current will cause coil  132  to resonate and generate an RF signal  412  that can be transmitted to and received by tag  406 . 
   In the example of  FIG. 4 , antenna  404 , antenna  130 , and tag  406  can be said to be aligned with a center orthogonal access  408 . 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  410  with coil  134  and RF signals  412  with the antenna included on tag  406 . 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. 
   In the example of  FIG. 4 , communications from interrogator  401  to tag  406  is illustrated but it will be understood that communication from tag  406  to interrogator  401  will operate in a similar manner. 
   It should be noted that communication in the face of a magnetic flux blocker can be achieved without the need to modify the tag or the reader. This can allow the reader and tag to manufactured for any application and avoids the need to make custom, or modified readers and tags, which can increase the cost of the reader, tag, and/or overall system. 
   As applications for RFID systems expands, RFID tags are being included, or affixed to more and smaller items. For example, it is anticipated that SIM cards included in wireless communication devices will include an RFID tag. The tag will need to be read by a reader external to the mobile communication device, but as it will be understood the SIM card is installed, or inserted internal to a mobile communication device. As a result, the many layers of the mobile communication device housing, and even the battery can act as magnetic flux blockers that can inhibit communication between an RFID tag included on a SIM card and an external reader. 
   An antenna, such as those illustrated in  FIGS. 1A-1D , can be used to enable, or augment communication between an RFID tag on a SIM card internal to a mobile communication device and an external reader. This can be illustrated with the aide of  FIG. 5 , which illustrates an RFID reader  401  configured to communicate with an RFID tag  506  included on a SIM card  504  internal to a mobile communication device  502 . 
   In addition to possibly the layers comprising the housing of mobile communication device  502 , battery  510  is disposed between tag  504  and reader  401  and will act as a magnetic flux blocker. Accordingly, an antenna  512  is disposed around battery  510  in order to enable communication between reader  401  and tag  506 . Accordingly, antenna  512  comprises a coil  514  on the outside of battery  510  and a coil  516  on the inside of battery  510  connected by conductive connecting lines  518  and  520 . As with the embodiments described above, antenna  512  can be configured on a flexible, or partially flexible substrate such that it can be bent around battery  510  as illustrated. 
   It will be understood that the example embodiment of  FIG. 5  is just one possible practical application of an antenna configured in accordance with the systems and methods described herein. It will be further understood that many more practical applications are possible in order to allow a reader and a tag to communicate even in the presence of a magnetic flux blocker such as a battery or housing. Accordingly, the example on  FIG. 5  should not be seen as limiting the systems and methods described herein to any particular application. 
   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.