Ultra-high conversion efficiency for harmonic RFID tag

Abstract

A radio-frequency identification (RFID) tag including a first antenna configured to receive a reader-to-tag signal having a first frequency; a second antenna configured to transmit a modulated response signal having a second frequency different from the first frequency; a processing unit configured to: extract interrogation information from the reader-to-tag signal; generate the modulated response signal based on tag data and the interrogation information; a first impedance matching circuit operatively coupled between the first antenna and the processing unit, the first impedance matching circuit being configured to substantially match an output impedance of the first antenna to an input impedance of the processing unit; and a second impedance matching circuit coupled between the second antenna and the processing unit, the second impedance matching circuit being configured to substantially match an output impedance of the processing unit to an input impedance of the second antenna.

Description

ULTRA-HIGH CONVERSION EFFICIENCY FOR HARMONIC RFID TAGRELATED APPLICATIONS

[0001] The present application claims priority from United States Provisional Patent Application Serial No. 63 / 617,558 filed on January 4, 2024 and incorporated by reference in its entirety.FIELD

[0002] The present technology pertains to the field of radio-frequency identification (RFID) tags, and more particularly to multi-band passive RFID tags.BACKGROUND

[0003] Passive Radio Frequency Identification (RFID) tags operate without an independent power source, relying on the backscattering principle. According to this principle, when an RFID reader emits a signal, the tag modulates its response onto the reader's signal and reflects it back.

[0004] One of the main practical limitations for conventional RFID tags is that the reader’s signal and the tag’s response share the same carrier frequency. Consequently, the reader’s strong signal can bury or otherwise obscure a tag’s weak backscattered signal such that the backscattered signal may not be readable. This problem is usually referred to as the “self-jamming” problem.

[0005] Further, self-jamming can put practical limitations on the rate at which a reader can successfully read the tag and also the maximum distance at which the reader is able to read the tag.

[0006] To mitigate the self-jamming issue, harmonic RFID tags have been devised. Such a harmonic RFID tag generates a response signal at a frequency that is a harmonic of the frequency of the interrogation signal received by the RFID tag thereby avoiding interference between the response and interrogation signals. However, a notable drawback of harmonic tags lies in their relatively low conversion efficiency. This inefficiency becomes particularly pronounced when the tag is positioned several meters away from the reader. In such cases, the harmonics generated by the tag in response to a low -power signal may be too faint to be detectable by the reader.

[0007] Therefore, there is a need for an improved harmonic RFID tag and RFID system.SUMMARY

[0008] According to a first broad aspect, there is provided a radio-frequency identification (RFID) tag comprising: radio-frequency identification (RFID) tag comprising: a first antenna configured to receive a reader-to-tag signal having a first frequency; a second antenna configured to transmit a modulated response signal having a second frequency different from the first frequency; a storing unit configured to store tag data; a processing unit configured to: extract interrogation information from the reader-to-tag signal; generate the modulated response signal based on the tag data and the interrogation information; a first impedance matching circuit operatively coupled between the first antenna and the processing unit, the first impedance matching circuit being configured to substantially match an output impedance of the first antenna to an input impedance of the processing unit such that a transfer of power associated with the reader-to-tag signal from the first antenna to the processing unit isincreased, wherein the first impedance matching circuit is further configured to prevent at least a portion of the modulated response signal to propagate towards the first antenna; and a second impedance matching circuit coupled between the second antenna and the processing unit, the second impedance matching circuit being configured to substantially match an output impedance of the processing unit to an input impedance of the second antenna such that a transfer of power associated with the modulated response signal from the processing unit to the second antenna is increased, wherein the second impedance matching circuit is further configured to prevent at least a portion of the reader-to-tag signal to propagate towards the second antenna.

[0009] In accordance with any embodiments of the present disclosure, the RFID tag further comprising a substrate and the first antenna, the second antenna, the processing unit, the storing unit, the first impedance matching circuit and the second impedance matching circuit are mounted on the substrate.

[0010] In accordance with any embodiments of the present disclosure, the substrate is made of dielectric material.

[0011] In accordance with any embodiments of the present disclosure, the first impedance matching circuit and the second impedance matching circuit each comprise passive electrical components.

[0012] In accordance with any embodiments of the present disclosure, the passive electrical components comprise at least two of: at least one resistor, at least one inductor, and at least one capacitor.

[0013] In accordance with any embodiments of the present disclosure, the processing unit comprises: a demodulator configured to extract the interrogation information from the reader-to-tag signal; an AC-to-DC convertor configured toconvert a part of the reader-to-tag signal into a DC electrical signal to power the RFID tag; a processor configured to generate a response data signal based on the tag data and the interrogation information; and a modulator and a frequency-shifting unit configured to modulate the reader-to-tag signal according to the response data signal and convert the first frequency to the second frequency.

[0014] In accordance with any embodiments of the present disclosure, the modulator is configured to modulate the reader-to-tag signal to obtain a modulated carrier signal and the frequency-shifting unit is configured to change the first frequency of the modulated carrier signal to the second frequency to obtain the modulated response signal.

[0015] In accordance with any embodiments of the present disclosure, the frequency-shifting unit is configured to change the first frequency of the reader-to-tag signal to the second frequency to obtain a frequency-shifted signal, and the modulator is configured to modulate the frequency-shifted signal according to the response data signal to obtain the modulated response signal.

[0016] In accordance with any embodiments of the present disclosure, the frequency-shifting unit comprises a non-linear component.

[0017] In accordance with any embodiments of the present disclosure, the nonlinear component comprises at least one of a varactor diode and a variable capacitor.

[0018] In accordance with any embodiments of the present disclosure, the first antenna and the second antenna each comprise a dipole antenna.

[0019] In accordance with any embodiments of the present disclosure, the second frequency comprises one of a harmonic and a subharmonic of the first frequency.

[0020] In accordance with any embodiments of the present disclosure, the first frequency is within ISM UHF band and the second frequency is twice the first frequency,

[0021] According to another broad aspect, there is provided a radio -frequency identification (RFID) system comprising: a reader comprising at least one antenna, a reader processing unit and a reader storing unit, the reader processing unit being configured for generating a reader-to-tag signal having a first frequency, and receiving a modulated response signal having a second frequency, the second frequency different from the first frequency; and the above-described RFID tag.

[0022] According to a further broad aspect, there is provided a method for operating a radio-frequency identification (RFID) tag, comprising: receiving, by a first antenna, a reader-to-tag signal having a first frequency; extracting, by a processing unit, interrogation information from the reader-to-tag signal; generating, by the processing unit, a modulated response signal based the interrogation information, the modulated response signal having a second frequency different from the first frequency; and transmitting, by a second antenna, the modulated response signal, wherein: a first impedance matching circuit is operatively coupled between the first antenna and the processing unit, the first impedance matching circuit being configured to substantially match an output impedance of the first antenna to an input impedance of the processing unit such that a transfer of power associated with the reader-to-tag signal from the first antenna to the processing unit is increased, wherein the first impedance matching circuit is further configured to prevent at least a portion of the modulated response signal to propagate towards the first antenna; and a second impedance matching circuit is coupled between the second antenna and the processing unit, the second impedance matching circuit being configured to substantially matchan output impedance of the processing unit to an input impedance of the second antenna such that a transfer of power associated with the modulated response signal from the processing unit to the second antenna is increased, wherein the second impedance matching circuit is further configured to prevent at least a portion of the reader-to-tag signal to propagate towards the second antenna.

[0023] According to a further broad aspect, there is provided a method radiofrequency identification (RFID) tag comprising: a first antenna configured to receive a reader-to-tag signal having a first frequency; a second antenna configured to transmit a modulated response signal having a second frequency different from the first frequency; a storing unit configured to store tag data; a processing unit configured to: extract interrogation information from the reader-to-tag signal, and generate the modulated response signal based on the tag data and the interrogation information; a first matching circuit operatively coupled between the first antenna and the processing unit; a second matching circuit operatively coupled between the second antenna and the processing unit; and a switching unit operatively coupled between the first and second matching circuits for selectively changing the RFID tag between a backscatter mode and a non-backscatter mode.

[0024] In accordance with some embodiments of the present disclosure, the switching unit includes a first switch circuit including a varactor diode (or similar nonlinear elements) and a second switch circuit including a capacitor conjugate- matched to an inductance of the second matching circuit.

[0025] In accordance with some embodiments of the present disclosure, upon closing the first switch circuit while the second switch circuit is open, the second frequency is doubled relative to the first frequency thereby enabling the RFID tag to operate in the backscatter mode.

[0026] In accordance with some embodiments of the present disclosure, upon closing the second switch circuit while the first switch circuit is open, maximum power is provided to the processing unit thereby enabling the RFID tag to operation in the non-backscatter mode.

[0027] Implementations of the present technology each have at least one of the above-mentioned objects and / or aspects, but do not necessarily have all of them. It should be understood that some aspects of the present technology that have resulted from attempting to attain the above-mentioned object may not satisfy this object and / or may satisfy other objects not specifically recited herein.

[0028] Additional, and / or alternative features, aspects and advantages of implementations of the present technology will become apparent from the following description, the accompanying drawings and the appended claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0029] For a better understanding of the present technology, as well as other aspects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawings, where:

[0030] FIG. 1 schematically illustrates a radio-frequency identification (RFID) system comprising an RFID reader and an RFID tag, in accordance with various nonlimiting embodiments of the present disclosure;

[0031] FIG. 2 illustrates a high-level functional block diagram of the RFID tag, in accordance with various non-limiting embodiments of the present disclosure;

[0032] FIG. 3 illustrates a high-level functional block diagram of a processing unit, in accordance with various non-limiting embodiments of the present disclosure;

[0033] FIG. 4 illustrates an integrated circuit (IC) representing at least some components of the RFID tag, in accordance with various non-limiting embodiments of the present disclosure;

[0034] FIG. 5 illustrates an equivalent RLC circuit diagram of the IC, in accordance with various non-limiting embodiments of the present disclosure;

[0035] FIG. 6 illustrates an alternative equivalent RLC circuit diagram of the IC, in accordance with various non-limiting embodiments of the present disclosure;

[0036] FIG. 7 and FIG. 8 illustrate conversion efficiency curves for the alternative equivalent RLC circuit diagram of FIG. 6. in both backscatter and non-backscatter modes, respectively;

[0037] FIG. 9 illustrates a flowchart of a process for operating the RFID tag, in accordance with various non-limiting embodiments of the present disclosure.DETAILED DESCRIPTION

[0038] The examples and conditional language recited herein are principally intended to aid the reader in understanding the principles of the present technology and not to limit its scope to such specifically recited examples and conditions. It will be appreciated that those skilled in the art may devise various arrangements which, although not explicitly described or shown herein, nonetheless embody the principles of the present technology and are included within its spirit and scope.

[0039] Furthermore, as an aid to understanding, the following description may describe relatively simplified implementations of the present technology. As persons skilled in the art would understand, various implementations of the present technology may be of a greater complexity.

[0040] In some cases, what are believed to be helpful examples of modifications to the present technology may also be set forth. This is done merely as an aid to understanding, and, again, not to define the scope or set forth the bounds of the present technology. These modifications are not an exhaustive list, and a person skilled in the art may make other modifications while nonetheless remaining within the scope of the present technology. Further, where no examples of modifications have been set forth, it should not be interpreted that no modifications are possible and / or that what is described is the sole manner of implementing that element of the present technology.

[0041] In the description herein, it is important to note that the terms "comprise", "include" and / or contain may be used interchangeably. These terms indicate that the list or elements following them is not exhaustive, and the scope of the present disclosure encompasses the listed elements as well as any additional elements or variations that are similar or related in function or purpose.

[0042] FIG. 1 illustrates a radio-frequency identification (RFID) system, in accordance with various embodiments of the present disclosure. As shown, the RFID system comprises an RFID reader 12 and at least one RFID tag 14.

[0043] The RFID reader 12 transmits both modulated and unmodulated signals.The modulated signal generated by the RFID reader 12 may be referred to as a reader- to-tag signal / frequency. When the RFID tag 14 is selected to reply back to the RFID reader 12, the RFID reader 12 starts to transmit unmodulated signal. The RFID tag 14, then modulates its response on the received unmodulated signal. In some embodiments, the RFID tag 14 may operate on ISM UHF band (902 MHz to 928 MHz). The RFID reader 12 is configured to generate and emit the reader-to-tag signal 40 and receive a modulated response signal 42 from the RFID tag 14. It is to be notedthat the reader-to-tag signal 40 and the modulated response signal 42 are radiofrequency (RF) signals. The RFID reader 12 is configured to generate the reader- to-tag signal 40 at a first frequency that may be selected in a first frequency band (for example, 902 to 928 MHz). The reader-to-tag signal 40 includes information / data encoded therein such as interrogation data corresponding to a request.

[0044] The RFID reader 12 is configured to emit the reader-to-tag signal 40 at a first frequency which may be received by the RFID tag 14. In response, the RFID tag 14 that receives the reader-to-tag signal 40 generates a modulated response signal 42 at a second frequency being different from the first frequency. The second frequency may be a harmonic or subharmonic frequency of the first frequency so that the modulated response signal 42 may be a harmonic or subharmonic signal of the reader- to-tag signal 40. The RFID tag 14 emits the modulated response signal 42 and the RFID reader 12 detects the modulated response signal 42. As described in greater detail below and in some non-limiting embodiments, the RFID tag 14 may rely on a part of the reader-to-tag signal 40 to power its internal components.

[0045] The RFID reader 12 may be coupled to a power source (not shown) and comprises a processing unit 20, a storing unit or memory unit 22 and at least one antenna 24. It is contemplated that the RFID reader 12 may include other components, however for the sake of illustrative clarity, such components have been omitted from FIG. 1. Information about the RFID reader 12 and / or the RFID tag 14 is be stored in the memory unit 22. The memory unit 22 may be used in situations when the RFID reader 12 may be required to keep track of tags locally, before transmitting the information to the users, for example. The processing unit 20 is configured to generate the signal 40 to be transmitted to the RFID tag 14. A person skilled in the art will readily understand that the signal 40 may be inclusive of a command and / or a query ora continuous wave to be used by the RFID tag 14 for backscattering its reply. The signal 40 may be any mandatory, optional, or proprietary commands, provided by standard RFID protocols. The processing unit 20 is further configured to transmit the reader-to-tag signal 40 via the antenna 24. The antenna 24 may be any suitable antenna such as, but not limited to, a bipolar antenna.

[0046] It is contemplated that the number of antennas contained in the RFID reader 12 may vary as long as the RFID reader 12 includes at least one antenna. In some embodiments, the RFID reader 12 includes a single antenna so that the reader- to-tag signal 40 is transmitted by the single antenna and the modulated response signal 42 is also received by the single antenna. In another embodiment, the RFID reader 12 includes two antennas. In this case, a first antenna may be dedicated to transmitting the reader-to-tag signal 40 and a second antenna may be dedicated to receiving the modulated response signal 42.

[0047] In some embodiments, the RFID reader 12 comprises a mono-static RFID reader. In other embodiments, the RFID reader 12 comprises a bi-static RFID reader.

[0048] In some embodiments, the RFID tag 14 comprises a processing unit 30, a storing unit or memory unit 32 and at least two antennas 34 and 36, a first impedance matching circuit 44, and a second impedance matching circuit 46. The RFID tag 14 may further comprise components such as circulators, diplexers, and / or the like (not shown) to split and / or direct signals. It is contemplated that the RFID reader 12 may include other components, however for the sake of illustrative clarity, such components have been omitted from FIG. 1.

[0049] The RFID tag’s antenna 34 is configured to detect signals having the first frequency so that the antenna 34 may receive reader-to-tag signal 40. The signal 40 is transmitted to the processing unit 30 of the RFID tag 14. To improve the transfer ofpower of the reader-to-tag signal 40 from the antenna 34 to the processing unit 30, the first impedance matching circuit 44 is operatively coupled between the antenna 34 and the processing unit 30. The details of the first impedance matching circuit 44 are provided below.

[0050] Tag information such as tag identification (ID), information on the product to which the RFID tag 14 is associated with, information received from the RFID reader 12, etc. is stored on the memory unit 32. The processing unit 30 is configured to generate the modulated response signal 42 having the second frequency and comprising response data encoded therein based on the reception of the reader-to-tag signal 40 and to transmit the modulated response signal 42 via the antenna 36. It should be understood that the antenna 36 is configured to emit signals having the second frequency. In some embodiments, the processing unit 32 is configured to extract information from the received reader-to-tag signal 40, generate the modulated response signal 42 based on the extracted information and / or the tag information and transmit the modulated response signal 42 via the antenna 36. In the same or other embodiments, the processing unit 30 is further configured to convert a part of the received reader-to-tag signal 40 into electrical power for powering the RFID tag 14. To improve a transfer of power of the modulated response signal 42 from the processing unit 30 to the antenna 36, the second impedance matching circuit 46 is operatively coupled between the processing unit 30 and the antenna 36. The details of the second impedance matching circuit 46 are presented below.

[0051] In some embodiments, the modulated response signal 42 is generated by modulating at least a part of the received reader-to-tag signal 40 to encode response information or data therein and changing the frequency of the received reader-to-tagsignal 40 to a harmonic or subharmonic of its initial frequency, i.e., to a harmonic or subharmonic of the received reader-to-tag signal 40.

[0052] In other embodiments in which the signal 40 is indicative of a command or a query, the modulated signal response 42 is generated based on the information extracted from the reader-to-tag signal 40 and / or tag information.

[0053] In some embodiments, the processing unit 30 is configured to first modulate the reader-to-tag signal 40, thereby obtaining a modulated signal, and then to change the frequency of the modulated signal. In other embodiments, the processing unit 30 is configured to first change the frequency of the reader-to-tag signal 40, thereby obtaining a frequency-changed signal, and then modulate the frequency-changed signal.

[0054] In some embodiments, the processing unit 30 comprises an alternating current (AC) to direct current (DC) converter such as a rectifier for converting a part of the reader-to-tag signal 40 into an electrical power signal that is then used for powering the RFID tag 14.

[0055] In some embodiments, the processing unit 30 comprises a modulator for modulating the reader-to-tag signal 40 and a frequency-shifting unit configured to change the frequency of the reader-to-tag signal 40 to a harmonic or subharmonic frequency. For example, the frequency-shifting unit may be a non-linear component that causes nonlinearity. In one embodiment the non-linear component is a passive non-linear component such as a diode or a rectifier. In another embodiment, the nonlinear component is at least one of a varactor diode and a variable capacitor.

[0056] In one embodiment, the AC-to-DC conversion and the frequency shifting is performed by a single component such as a rectifier. In this case, the rectifier may receive the reader-to-tag signal 40 from the antenna 34 and generates two signals, i.e.,a DC electrical signal for powering the RFID tag 14 and an unmodulated carrier signal of which the frequency is a harmonic or subharmonic of the frequency of the reader-to-tag signal 40. A first filter may be used for extracting the DC electrical signal from the output of the rectifier and a second filter may be used for extracting the unmodulated carrier signal from the output of the rectifier. The unmodulated carrier signal may be then modulated to generate the modulated response signal.

[0057] The RFID tag 14 may further comprise a substrate on which the different components constituting the RFID tag 14 such as the processing unit 30, the memory unit 32, the antennas 34 and 36, the first impedance matching circuit 44, the second impedance matching circuit 46 and additional tag components, if any, are mounted.

[0058] FIG. 2 illustrates a high-level functional block diagram of the RFID tag 14, in accordance with various non-limiting embodiments. As illustrated, the first impedance matching circuit 44 is operatively coupled between the antenna 34 and the processing unit 30. Also, the second impedance matching circuit 46 is operatively coupled between the processing unit 30 and the antenna 36.

[0059] The first impedance matching circuit 44 is designed to substantially match the output impedance of the antenna 34 to the input impedance of the processing unit 30. In doing so, the transfer of power of the reader-to-tag signal 40 from the antenna 34 to the processing unit 30 may be improved. In other words, the transfer of power of the signal 40 from the antenna 34 to the processing unit 30 may be increased by virtue of the first impedance matching circuit 44. The first impedance matching circuit 44 is frequency dependant. The first impedance matching circuit 44 effectively transfers the power from antenna 34 to the signal processing unit 30. In addition, the first impedance matching circuit 44 provides a high impedance to the modulated response signal 42 at the second frequency, thereby reducing a propagation of the modulatedresponse signal 42 towards the antenna 34 resulting in efficient power transfer of the modulated response signal 42 towards the antenna 36.

[0060] Also, the second impedance matching circuit 46 is designed to substantially match the output impedance of the processing unit 30 to the input impedance of the antenna 36. In doing so, the transfer of power of the modulated response signal 42 from the processing unit 30 to the antenna 36 may be improved. In other words, the transfer of power of the modulated response signal 42 may be increased by virtue of the second impedance matching circuit 46. In addition, the second impedance matching circuit 46 provides a high impedance to reader-to-tag signal 40 at the first frequency, thereby reducing a propagation of the reader-to-tag signal 40 towards the antenna 36 resulting in efficient power transfer of the reader-to- tag signal 40 towards the processing unit 30.

[0061] In the context of the present disclosure, with respect to the first impedance matching circuit 44, the term 'substantially match' may be referred to that the impedance of the first impedance matching circuit 44 may be adjusted or configured to closely approximate, within a reasonable tolerance, the output impedance of the antenna 34. Such that the power of the reader-to-tag signal 40 is efficiently transferred from the antenna 34 to the processing unit 30. Similarly, with respect to the second impedance matching circuit 46, the term 'substantially match' may refer to the impedance of the second impedance matching circuit 46 being adjusted or configured to closely approximate, within a reasonable tolerance, the input impedance of the antenna 36. Accordingly, the power of the modulated response signal 42 is efficiently transferred from the processing unit 30 to the antenna 36. 'Substantially match' shall not be interpreted to require an exact or perfect impedance match but rather denotes adegree of impedance alignment that may enable effective operation and minimizes reflections or losses as described in various embodiments of the present disclosure.

[0062] The design of the first impedance matching circuit 44 may depend on the type of the antenna 34 and more particularly to an output impedance of the antenna 34. Similarly, the design of the second impedance matching circuit 46 may depend on the type of the antenna 36 and more particularly to an input impedance of the antenna 36. Without limiting the scope of the present disclosure, the antenna 34 and the antenna 36 may be any suitable antenna such as, but not limited to, a dipole antenna.

[0063] The first impedance matching circuit 44 and the second impedance matching circuit 46 may each comprise a respective electrical network of passive electrical components such as resistors, capacitors, and / or inductors. A selection of the passive electrical components and the associated values may depend on the specific impedance transformation required and the frequency range of operation. The design of the first impedance matching circuit 44 and the second impedance matching circuit 46 may be based on any suitable impedance matching techniques. In some embodiments, the impedance matching may be based on traces. The traces may be designed in terms of their width, length, and other parameters to match the impedance. In other embodiments, the impedance matching may be based on L- Section Matching Circuit, Pi-Section Matching Circuit, T-Section Matching Circuit, or the like.

[0064] FIG. 3 illustrates a high-level functional block diagram of the processing unit 30 of the RFID tag 14, in accordance with various embodiments of the present disclosure. As shown, the processing unit 30 includes an AC-to-DC convertor 52, a demodulator 54, a processor 56, a modulator 58, and a non-linear component 60. It is to be noted that the processing unit 30 may include other elements, however suchcomponents have been omitted from FIG. 3 for the sake of illustrative clarity. Various components of the processing unit 30, the memory unit 32, the antennas 34 and 36, the first impedance matching circuit 44 and the second impedance matching circuit 46 may be mounted on a substrate. In some embodiments, the substrate may be made of a dielectric material.

[0065] The AC-to-DC convertor 52 is configured to receive a part of the reader- to-tag signal 40 and convert the part to a DC electrical signal. The DC electrical signal is then utilized to power various components of the RFID tag 14. The AC-to-DC convertor 52 may be implemented using any suitable technique without limiting the scope of present disclosure. Some of the non-limiting examples of the AC-to-DC convertor 52 may include a rectifier, such as, half-wave rectifier, full-wave rectifier, bridge rectifier, or the like.

[0066] In some embodiment, the demodulator 54 is operatively coupled to the first impedance matching circuit 44 to receive the reader-to-tag signal 40 therefrom. Further, the demodulator 54 is operatively coupled to the processor 56. The demodulator 54 is configured to extract interrogation information or data from the reader-to-tag signal 40 and transmit the extracted interrogation data to the processor 56. The interrogation information may include for example, electronic product code (EPC), tag identification (TID) code, and any other information related to the RFID tag 14 stored in the memory unit 32.

[0067] In addition to the tag information or tag data such as an identification of the RFID tag 14 and information received from the RFID reader 12, the memory unit 32 is further configured to store therein interrogation information or data received from the demodulator 54. The memory unit 32 is operatively coupled to the processor56.

[0068] The processor 56 is configured to interpret interrogation information, take required action, such as, generate a response data signal (i.e., a response to the reader- to-tag signal 40) based on information contained in the memory unit 32 such as the tag ID and the interpreted interrogation information.

[0069] In some embodiments, the modulator 58 is operatively coupled to the processor 56 to receive response data signal therefrom. Further, in some embodiments, the modulator 58 is operatively coupled to the first impedance matching circuit 44 to receive the reader-to-tag signal 40 therefrom. In some embodiments, the modulator 58, uses the reader-to-tag signal 40 as the carrier signal to modulate the respective data.

[0070] In some embodiments, the non-linear component 60 is operatively connected to the modulator 58 for receiving the modulated signal therefrom. The nonlinear component 60 is configured to change the carrier frequency of the modulated signal received from the modulator 58 to a harmonic or subharmonic frequency, thereby obtaining the modulated response signal 42 in which a response to the interrogation is encoded. The modulated response signal 42 is then provided to the second impedance matching circuit 46.

[0071] In another embodiment, the non-linear component 60 is configured to receive the reader-to-tag signal 40 and change the frequency of this signal to a harmonic or subharmonic frequency, thereby obtaining a frequency shifted signal. The modulator 58 is operatively coupled to the non-linear component 60 to receive the frequency-shifted signal therefrom and to the processor 56 to receive the response data signal therefrom. The modulator 58 is configured to modulate the frequency- shifted signal based on the received response data signal to generate the modulatedresponse signal 42. The modulated response signal 42 is then provided to the second impedance matching circuit 46.

[0072] Returning to FIG. 2, the modulated response signal 42 may propagate from the second impedance matching circuit 46 thereupon to the antenna 36 for emission therefrom.

[0073] There may be certain scenarios where, in addition to the processing unit 30, the reader-to-tag signal 40 may propagate towards the antenna 36. Also, in addition to the antenna 36, the modulated response signal 42 may propagate towards the antenna 34. This may result in a degradation of the power of the modulated response signal 42.

[0074] To further improve the performance of the RFID tag 14 and in some embodiments, the first impedance matching circuit 44 is further configured to prevent at least a portion of the modulated response signal 42 to propagate towards the antenna 34. The second impedance matching circuit 46 is further configured to prevent at least a portion of the reader-to-tag signal 40 to propagate towards the antenna 36.

[0075] The first impedance matching circuit 44 is configured to provide a high impedance to the frequency components associated with the modulated response signal 42. Similarly, the second impedance matching circuit 46 is configured to provide a high impedance to the frequency components associated with the reader-to- tag signal 40. In doing so, the power associated with the modulated response signal 42 as emitted by the antenna 36 may be significantly improved.

[0076] FIG. 4 illustrates one possible implementation of an integrated circuit (IC) 70 representing at least some components of the RFID tag 14 in accordance with various non-limiting embodiments of the present disclosure. In the IC 70, two dipoleantennas 72 and 76 are operatively coupled to a processing unit (not shown) using traces 73 and 74. It should be understood that the physical representation of antennas 72 and 76 in FIG. 4 are functionally equivalent to the antennas 34 and 36, respectively, in the high level diagram FIG. 2. The trace 73 may represent the first impedance matching circuit 44 and the trace 74 may represent the second impedance matching circuit 46. The traces 73 and 74 may be constructed from any standard conducting material such as copper or aluminum. The IC 70 further includes a nonlinear element 75. Most of the components of the IC 70 may be mounted on a substrate 77. The substrate 77 may be made of any suitable dielectric material, such as, Flame Retardant 4 or Rogers PCB.

[0077] FIG. 5 illustrates an equivalent RLC circuit diagram 80 of the IC 70, in accordance with various non-limiting embodiments of the present disclosure. As shown, an antenna circuit 81 may represent RLC equivalent components of the dipole antenna 72. The antenna circuit 81 may be energised by a receiving signal 82, such as, the reader-to-tag signal 40 which is represented by Vinpeak. An antenna circuit 85 may represent RLC equivalent components of the dipole antenna 76. A non-linear circuit 84 may represent RLC equivalent components of the non-linear element 75. The non-linear element may include a diode 86. The non-linear circuit 84 may represent RL equivalent components of the traces 73 and 74. The non-linear circuits 84, 86 may be coupled to the antenna circuits 81 and 85. The trace circuit 84 may receive an input voltage at Prl 83 corresponding to the receiving signal 82 from the antenna circuit 81. The trace circuit 84 may provide an output voltage at Pr2 94 corresponding to the input voltage. The output voltage at Pr2 94 may be provided to the antenna circuit 85 for emission.

[0078] FIG. 6 illustrates an alternative equivalent RLC circuit diagram 600 of the IC 70, in accordance with various non-limiting embodiments of the present disclosure. In this additional embodiment, the alternative equivalent RLC circuit diagram 600 provides the selective capability of either backscatter mode or non-backscatter mode. It should be understood that when the RFID tag is in backscatter mode, the maximum transmission power at 2f„ through the 2f„ antenna (e.g., antenna 76 in FIG. 4) should be ensured. Whereas the transmission at the 2f„ frequency should be minimized as much as possible in non-backscatter mode. Advantageously, maximizing the difference in transmission power between backscatter and non-backscatter modes enables the RFID reader’s successful reading of the RFID tags. In the embodiment shown in FIG. 6, the configuration shown may be used to increase the difference in the transmission power at 2f„ in backscatter mode versus non-backscatter mode.

[0079] In FIG. 6, Rf, 602 and R2f„ 611 represent the radiation resistance for the f„ antenna (e.g., antenna 72 in FIG. 4) and 2f„ antenna (e.g., antenna 76 in FIG. 4), respectively. The f„ antenna on the input side of the RFID tag (i.e., left side of FIG. 6) is connected to a 2f„ filter 603 as shown which blocks any 2f„ radiation through the f„ antenna at Prl 604. As mentioned earlier, this 2f„ filter 603 is achieved through the physical antenna and trace configurations connecting the ft antenna to the IC (e.g., IC 70 in FIG. 4). Similarly, on the output side of the RFID tag, the 2f„ antenna and its connecting trace blocks the transmission of fi, and its harmonics via the filters 607, 608, 609 which include 3rdand 4thharmonics filtering as shown thereby allowing only the 2f„ frequency signals to pass through at Pr2 610. Effectively, this provides a highly efficient frequency doubler.

[0080] As further shown in FIG. 6, Lmatchl 605 and Lmatch2 606 form first and second matching circuits and which represent the inductances formed by thephysicality of the traces, while SI 612 and S2 613 are two switches (shown closed and open, respectively, in the embodiment of FIG. 6) that are controlled by the digital core of the IC through the modulator (e.g., the processing unit 30 and its modulator as previously discussed). It should be understood that Cs represents the leakage capacitance of the switches 612, 613.

[0081] In operation between backscatter and non-backscatter modes, the switches51 612 and S2 613 form a switching unit and are configured to correspondingly open and close. When the tag is in backscatter mode, SI 612 is closed, and S2 613 is open. In this mode, the maximum current passes through the varactor diode (or similar nonlinear elements) when S 1 612 is closed, which generates a signal at the 2fo frequency. This generated signal is then radiated through the 2fo antenna.

[0082] In non-backscatter mode of operation, the SI switch 612 is open, and the52 switch 613 is closed. The capacitor following the S2 switch is conjugate-matched with the inductance Lmatchl 605. This allows maximum power to be delivered to the IC without generating any signal at the 2fo frequency.

[0083] With regard to FIG. 7 and FIG. 8, there are shown the conversion efficiency curves for the alternative equivalent RLC circuit diagram 600 in both backscatter and non-backscatter modes, respectively. It should be understood that conversion gain is defined as the ratio of the output power on the 2fo antenna at 2fo frequency relative to the input power on the fo antenna at fo frequency, reported in dB. As may be observed in FIG. 7 and FIG. 8, the alternative equivalent RLC circuit diagram 600 in backscatter mode may advantageously convert a substantial amount of the input power into the second harmonic 2fo, whereas the alternative equivalent RLC circuit diagram 600 in non-backscatter mode provides nearly zero transmission of the second harmonic 2fo.

[0084] In all embodiments discussed herein, the present RFID system provides a practical solution for ultra-long range and high read-yield passive RFID systems. The use of a first impedance matching circuit (e.g., 44 in FIG. 2) and a second impedance matching circuit (e.g., 46 in FIG. 2) may improve a power associated with the modulated response signal 42 resolving the inherent inefficiency of harmonic RFID tags and improve signal-to-interference and noise ratios.

[0085] FIG. 9 illustrates a flowchart of a process 100 for operating the RFID tag 14, in accordance with various non-limiting embodiments of the present disclosure.As shown, the process 100 commences at step 102 where the first antenna 34 receives a reader-to-tag signal 40. As previously noted, the first antenna 34 is included in the RFID tag 14 and the reader-to-tag signal 40 may be generated by the RFID reader 12.

[0086] The process 100 advances to step 104 where the processing unit 30 extracts interrogation information from the reader-to-tag signal 40. As previously noted that the interrogation information may include electronic product code (EPC), tag identification (TID) code, and any other information related to the RFID tag 14 stored in the memory unit 32.

[0087] At step 106, the processing unit 30 generates the modulated response signal 42 based on the interrogation information. It is to be noted that the modulated response signal 42 has a frequency that is different from the frequency of the reader- to-tag signal 40.

[0088] Finally, at step 108, the second antenna 36 transmits the modulated response signal 42. In some embodiments, the second antenna 36 may broadcast the modulated response signal 42. In other embodiments, the second antenna 36 may transmit the modulated response signal 42 towards the RFID reader 12.

[0089] Modifications and improvements to the above-described implementations of the present technology may become apparent to those skilled in the art. The foregoing description is intended to be exemplary rather than limiting.

Claims

CLAIMSWhat is claimed is:

1. A radio-frequency identification (RFID) tag comprising: a first antenna configured to receive a reader-to-tag signal having a first frequency; a second antenna configured to transmit a modulated response signal having a second frequency different from the first frequency; a storing unit configured to store tag data; a processing unit configured to: extract interrogation information from the reader-to-tag signal, and generate the modulated response signal based on the tag data and the interrogation information; a first impedance matching circuit operatively coupled between the first antenna and the processing unit, the first impedance matching circuit being configured to substantially match an output impedance of the first antenna to an input impedance of the processing unit such that a transfer of power associated with the reader-to-tag signal from the first antenna to the processing unit is increased, wherein the first impedance matching circuit is further configured to prevent at least a portion of the modulated response signal to propagate towards the first antenna; and a second impedance matching circuit operatively coupled between the second antenna and the processing unit, the second impedance matching circuit being configured to substantially match an output impedance of the processing unit to an input impedance of the second antenna such that a transfer of power associated with the modulated response signal from the processing unit to the second antenna is increased, wherein the second impedance matching circuit is further configured to prevent at least a portion of the reader-to-tag signal to propagate towards the second antenna.

2. The RFID tag of claim 1, further comprising a substrate and the first antenna, the second antenna, the processing unit, the storing unit, the first impedance matching circuit and the second impedance matching circuit are mounted on the substrate.

3. The RFID tag of claim 2, wherein the substrate is made of dielectric material.

4. The RFID tag of any one of claims 1 to 3, wherein the first impedance matching circuit and the second impedance matching circuit each comprise passive electrical components.

5. The RFID tag of claim 4, the passive electrical components comprise at least two of: at least one resistor, at least one inductor, and at least one capacitor.

6. The RFID tag of any one of claims 1 to 5, wherein the processing unit comprises: a demodulator configured to extract the interrogation information from the reader-to- tag signal; an AC-to-DC convertor configured to convert a part of the reader-to-tag signal into a DC electrical signal to power the RFID tag; a processor configured to generate a response data signal based on the tag data and the interrogation information; and a modulator and a frequency-shifting unit configured to modulate the reader-to-tag signal according to the response data signal and convert the first frequency to the second frequency.

7. The RFID tag of claim 6, wherein the modulator is configured to modulate the reader- to-tag signal to obtain a modulated carrier signal and the frequency-shifting unit is configured to change the first frequency of the modulated carrier signal to the second frequency to obtain the modulated response signal.

8. The RFID tag of claim 6, wherein the frequency-shifting unit is configured to change the first frequency of the reader-to-tag signal to the second frequency to obtain a frequency-shifted signal, and the modulator is configured to modulate the frequency- shifted signal according to the response data signal to obtain the modulated response signal.

9. The RFID tag of any one of claims 6 to 8, wherein the frequency-shifting unit comprises a non-linear component.

10. The RFID tag of claim 9, wherein the non-linear component comprises at least one of a varactor diode and a variable capacitor.

11. The RFID tag of any one of claims 1 to 10, wherein the first antenna and the second antenna each comprise a dipole antenna.

12. The RFID tag of any one of claims 1 to 11, wherein the second frequency comprises one of a harmonic and a subharmonic of the first frequency.

13. The RFID tag of any one of claims 1 to 12, wherein the first frequency is within ISM UHF band and the second frequency is twice the first frequency.

14. A radio-frequency identification (RFID) system comprising: a reader comprising at least one antenna, a reader processing unit and a reader storing unit, the reader processing unit being configured for generating a reader-to-tag signal having a first frequency, and receiving a modulated response signal having a second frequency, the second frequency different from the first frequency; and the RFID tag of any one of claims 1 to 9.

15. A method for operating a radio-frequency identification (RFID) tag, comprising: receiving, by a first antenna, a reader-to-tag signal having a first frequency; extracting, by a processing unit, interrogation information from the reader-to-tag signal;generating, by the processing unit, a modulated response signal based the interrogation information, the modulated response signal having a second frequency different from the first frequency; and transmitting, by a second antenna, the modulated response signal, wherein: a first impedance matching circuit is operatively coupled between the first antenna and the processing unit, the first impedance matching circuit being configured to substantially match an output impedance of the first antenna to an input impedance of the processing unit such that a transfer of power associated with the reader-to-tag signal from the first antenna to the processing unit is increased, wherein the first impedance matching circuit is further configured to prevent at least a portion of the modulated response signal to propagate towards the first antenna; and a second impedance matching circuit is coupled between the second antenna and the processing unit, the second impedance matching circuit being configured to substantially match an output impedance of the processing unit to an input impedance of the second antenna such that a transfer of power associated with the modulated response signal from the processing unit to the second antenna is increased, wherein the second impedance matching circuit is further configured to prevent at least a portion of the reader-to-tag signal to propagate towards the second antenna.

16. A radio-frequency identification (RFID) tag comprising: a first antenna configured to receive a reader-to-tag signal having a first frequency; a second antenna configured to transmit a modulated response signal having a second frequency different from the first frequency; a storing unit configured to store tag data; a processing unit configured to: extract interrogation information from the reader-to-tag signal, and generate the modulated response signal based on the tag data and the interrogation information; a first matching circuit operatively coupled between the first antenna and the processing unit;a second matching circuit operatively coupled between the second antenna and the processing unit; and a switching unit operatively coupled between the first and second matching circuits for selectively changing the RFID tag between a backscatter mode and a nonbackscatter mode.

17. The RFID tag of claim 16, wherein the switching unit includes a first switch circuit including a varactor diode and a second switch circuit including a capacitor conjugate-matched to an inductance of the second matching circuit.

18. The RFID tag of any one of claims 16 to 17, wherein, upon closing the first switch circuit while the second switch circuit is open, the second frequency is doubled relative to the first frequency thereby enabling the RFID tag to operate in the backscatter mode.

19. The RFID tag of any one of claims 16 to 18, wherein, upon closing the second switch circuit while the first switch circuit is open, maximum power is provided to the processing unit thereby enabling the RFID tag to operation in the non-backscatter mode.

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