WO2021196118A1 - Système de communication d'identification par radiofréquence à haute fréquence basé sur la résonance - Google Patents

Système de communication d'identification par radiofréquence à haute fréquence basé sur la résonance Download PDF

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Publication number
WO2021196118A1
WO2021196118A1 PCT/CN2020/082944 CN2020082944W WO2021196118A1 WO 2021196118 A1 WO2021196118 A1 WO 2021196118A1 CN 2020082944 W CN2020082944 W CN 2020082944W WO 2021196118 A1 WO2021196118 A1 WO 2021196118A1
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resonator
transmission
receiving
tag
nfc
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PCT/CN2020/082944
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English (en)
Inventor
Yunfei Ma
Xianshang LIN
Pengyu ZHANG
Hongqiang LIU
Renjie ZHAO
Ming Zhang
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Alibaba Group Holding Limited
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Priority to PCT/CN2020/082944 priority Critical patent/WO2021196118A1/fr
Priority to CN202080099479.2A priority patent/CN115380478B/zh
Publication of WO2021196118A1 publication Critical patent/WO2021196118A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B5/00—Near-field transmission systems, e.g. inductive or capacitive transmission systems
    • H04B5/70—Near-field transmission systems, e.g. inductive or capacitive transmission systems specially adapted for specific purposes
    • H04B5/77—Near-field transmission systems, e.g. inductive or capacitive transmission systems specially adapted for specific purposes for interrogation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B5/00—Near-field transmission systems, e.g. inductive or capacitive transmission systems
    • H04B5/70—Near-field transmission systems, e.g. inductive or capacitive transmission systems specially adapted for specific purposes
    • H04B5/72—Near-field transmission systems, e.g. inductive or capacitive transmission systems specially adapted for specific purposes for local intradevice communication

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  • the disclosed embodiments are directed toward near-field communication (NFC) systems and, specifically, to radio-frequency identification systems using improved NFC technologies.
  • NFC near-field communication
  • Radio-frequency identification (RFID) technology is used to identify and track tags attached to objects. These tags consist of a radio receiver and transmitter. An RFID reader device emits an electromagnetic signal, and the tag receives this signal. In response, the tag transmits digital data such as a stocking keeping unit (SKU) value, serial number, or similar digital data.
  • SKU stocking keeping unit
  • Low-frequency (LF) RFID systems generally operate in the 120–150 kHz band and are used for animal tracking, access control, and similar systems.
  • High frequency (HF) RFID systems primarily operate at 13.56 MHz and include NFC as well as ticketing, payment, and data transfer applications.
  • Ultra-high frequency (UHF) RFID systems operate in or around the 433 MHz band and are commonly used for inventory management.
  • UHF RFID systems provide longer distance reading, generally around twelve (12) meters. In contrast, LF and HF RFID systems can only read tags between ten (10) centimeters to one (1) meter away, respectively. However, UHF RFID systems are more prone to interference and misreads than LF and HF RFID systems. Despite the increased costs of UHF RFID tags and interference/misreads, the significantly longer read distance is critical for large scale inventory management. Thus, many manufacturers, retailers, and other entities employ UHF RFID systems and attempt to compensate for the deficiencies of such systems by careful antenna placement.
  • the disclosed embodiments generally describe the use of multiple highly resonant coils to construct magnetic fields that solve the aforementioned problems.
  • the disclosed embodiments utilize magnetic coils with a large, high-quality factor (Q) in contrast to existing systems that specifically emphasize the use of low-quality coils to prevent resonance.
  • Q high-quality factor
  • the disclosed embodiments utilize a Q factor orders of magnitude higher than existing systems. By using such coils, more energy is delivered to a tag under the same transmit power constraints. Further, the use of high Q coils allows a reader to decode weak signals backscattered by a tag.
  • the disclosed embodiments additionally employ a reader designed using a passive self-interference cancellation design to curtail the leakage from the transmit (TX) chain to the receive (RX) chain, such leakage impacting the reader’s sensitivity and read range.
  • the reader By using high-Q coils, the reader generates a sharp degradation for signals that are slightly away from the center frequency. To remedy this degradation, the disclosed embodiments tune the RX coil’s resonance frequency so that it deviates from the TX coil’s frequency.
  • the reader additionally employs a narrow-band notch filter. As a result, the reader-to-tag downlink and tag-to-reader uplink becomes almost orthogonal, thus minimizing the self-interference.
  • the disclosed embodiments additionally include a multi-coil magnetic beamforming apparatus.
  • This apparatus ensures that tags are energized regardless of their orientation, in contrast to existing RFID systems.
  • the beamforming apparatus enables the reader to steer its magnetic field by using two coils with binary phrase configurations (e.g., zero and ⁇ ) .
  • the beamforming apparatus enables the reader to instantaneously scan all orientations at all nearby locations.
  • the disclosed embodiments additionally employ passive magnetic repeaters to improve reading range and reliability.
  • the repeaters comprise battery-free repeaters that are excited by the magnetic field from the TX coil. The repeaters then regenerate a complementary field to diversity the total vector field’s dimensions and enhance its strength.
  • the disclosed embodiments can be combined into a single RFID reader device.
  • This reader device can read standard NFC tags and does not require re-implementation of industry-standard tags.
  • a device comprising at least one transmission resonator configured to generate a magnetic field; at least one receiving resonator, the at least one receiving resonator physically separated from the transmission resonator and configured to receive data transmission from a near-field communication (NFC) tag using the magnetic field; and a receiving module, the receiving module coupled to the receiving resonator and configured to process the data transmission
  • NFC near-field communication
  • a system comprising a reader device, the reader device comprising at least one transmission resonator configured to generate a magnetic field, at least one receiving resonator, the at least one receiving resonator physically separated from the transmission resonator and configured to receive data transmission from a near-field communication (NFC) tag using the magnetic field, a receiving module, the receiving module coupled to the receiving resonator and configured to process the data transmission a plurality of NFC tags situated between the at least one transmission resonator and the at least one receiving resonator; and at least one repeater situated between the at least one transmission resonator and the at least one receiving resonator.
  • NFC near-field communication
  • a method comprising encoding transmission data on a carrier signal; transmitting the data encoded on the carrier signal to a near-field communication (NFC) tag via at least one transmission resonator configured to generate a magnetic field; receiving, via at least one receiving resonator physically separated from the transmission resonator, a return signal generated by the NFC tag using the magnetic field; removing, via an RF analog front-end, self-interference from the return signal to generate a cleaned signal; and digitizing and transmitting the cleaned signal to a central processing module.
  • NFC near-field communication
  • FIG. 1 is a diagram illustrating the signal strength characteristics of a plurality of RFID systems according to some embodiments of the disclosure.
  • FIG. 2 is a block diagram of a resonating NFC reader-tag system according to some embodiments of the disclosure.
  • FIG. 3 is a block diagram of an improved NFC system according to some embodiments of the disclosure.
  • FIG. 4 are graphs illustrating the frequency response of a coil having a small Q factor and the frequency response of a coil having a large Q factor.
  • FIG. 5 illustrates the measured self-interference characteristics of NFC systems at varying read distances according to some embodiments.
  • FIG. 6 illustrates the suppression of signal due to a passive self-interference cancellation circuit according to some embodiments of the disclosure.
  • FIG. 7 illustrates two perpendicular transmission coils and associated magnetic vector fields according to some embodiments of the disclosure.
  • FIG 8A is a diagram of a repeater excited by a resonator according to some embodiments of the disclosure.
  • FIG 8B is a diagram of a circuit modeling a repeater according to some embodiments of the disclosure.
  • FIG. 8C is a diagram illustrating the current magnitude response of a repeater and the phase difference between a resonator and a repeater according to some embodiments of the disclosure.
  • FIG. 9 is a block diagram of a multi-channel reader according to some embodiments of the disclosure.
  • FIG. 10 is a diagram illustrating test result data of the read distance of a plurality of NFC readers.
  • FIG. 11 is a graph illustrating the improvement in signal strength when using a repeater according to some embodiments of the disclosure.
  • FIG. 12 is a graph illustrating a comparison of signal loss between the disclosed embodiments, standard NFC, and UHF RFID systems according to some embodiments of the disclosure.
  • FIG. 13 is a table illustrating signal strength degradation using the disclosed embodiments and traditional UHF RFID systems.
  • FIGS. 14 and 15 illustrate test results of applying the disclosed embodiments in a simulated warehouse environment.
  • FIG. 16 is a flow diagram illustrating an improved method for reading NFC tags according to some embodiments of the disclosure.
  • FIG. 1 is a diagram illustrating the signal strength characteristics of a plurality of RFID systems according to some embodiments of the disclosure.
  • the strength of a signal received by an RFID reader (vertical axis) is plotted as a function of the distance between the reader and the tag (horizontal axis) .
  • both the vertical and horizontal axes are plotted logarithmically.
  • the illustrated graph plots the strengths of three signals received by an RFID reader: a UHF RFID signal (104) , an NFC RFID signal (106) , and a signal (102) described in more detail herein generated by the disclosed embodiments (the disclosed embodiments are periodically referred to as “NFC+” ) .
  • the graph is divided into three segments: a region of interest (ROI) (110) , a guard region (112) , and an excluded region (114) .
  • the ROI (110) comprises distances where all necessary tags should be read by the reader.
  • the guard region (112) comprises distances where nearly all (e.g., 99.9%) tags are not read by the reader.
  • the excluded region (114) comprises distances where no tags should be read by the reader.
  • This threshold (108) comprises a signal strength required for a tag to retransmit digital data back to the reader and be read by the reader.
  • a signal 102, 104, 106
  • this threshold (108) the tag is not identified by the reader.
  • the received NFC signal (106) falls completely within the ROI (110) .
  • the NFC-based reader does not activate existing UHF-based tags due to its low signal strength.
  • the NFC signal (106) only operates for a short distance and is incapable of reaching the furthest tags in the ROI (110) .
  • NFC-based readers only provide minimal coverage of an ROI (110) .
  • the UHF signal (104) theoretically reaches all tags in the ROI (110) and receives signals therefrom. However, as illustrated, the UHF signal (104) misreads tags (114) and experiences errant cross-readings (116) due to the interference properties of the UHF system.
  • the NFC+ signal (102) receives data from all tags in the ROI (110) and does not receive signals from any tags in the guard region (112) or excluded region (114) . That is, the NFC+ signal (102) is above the tag activation threshold (108) only in the ROI (110) and is below the threshold (108) for all other regions (112, 114) . As will be described, the various embodiments of the reader enable the signal curve (102) depicted in FIG. 1.
  • FIG. 2 is a block diagram of a resonating NFC reader-tag system according to some embodiments of the disclosure.
  • the illustrated system employs a reader device having a high-quality coil and a shunt inductor/capacitor for increasing the resonance effect.
  • the coils may utilize a Q factor that exceeds a pre-configured threshold.
  • this threshold comprises a numerical value that represents a lower bound of floor for the Q factor.
  • an upper bound may also be used.
  • the Q factor may be tunable to optimize the coils.
  • the threshold may be tuned configured to meet a specific bandwidth requirement of the system.
  • a reader (202) includes a signal generator (206) connected to a resonator (212) via circuit paths (208, 216) .
  • the resonator generates a magnetic field (218) that is detected by a passive or active tag (204) .
  • the signal generator (206) comprises an alternating current (AC) source.
  • the AC source operates at a fixed frequency. In some embodiments, this fixed frequency comprises a 13.56 MHz frequency.
  • the generator (206) supplies an input current i (208) to the resonator (212) . In return, the resonator provides a resonant current Q i (216) back to the signal generator (206) .
  • the resonator (212) comprises an inductive coil (210) and a parallel capacitor (232) .
  • the size of the coil (210) is significantly smaller than the wavelength of the signal generator, which, when operating at 13.56 MHz, is 22 meters. Given the discrepancy between the input current frequency and the size of the coil, the input current (218) is evenly distributed on the coil (210) .
  • the coil (210) operates as a discrete inductor and resistor device.
  • a capacitor (232) in parallel with the coil (210) a resonator (212) is formed.
  • energy in the resonator (212) is stored in two different ways: (1) as electrical energy as charges accumulate at the capacitor (232) electrodes and (2) magnetic energy (218) as currents flow through the inductor.
  • the tag (204) detects the field (218) via a second antenna (220) .
  • the tag (204) includes a resonating capacitor (224) to amplify the received signal. In some embodiments, multiple such resonating capacitors may be included in parallel.
  • the tag (204) circuitry additionally includes a shunting diode (226) in parallel with the capacitor (224) connected to the load (228) .
  • the load (228) comprises a dedicated application-specific integrated circuit (ASIC) or similar processing element. Details of the tag (204) are not included herein as standard NFC or RFID tags may be used as tag (204) .
  • the coupling coefficient k (230) comprises the ratio of the open-circuit actual voltage ratio to the ratio that would obtain if all the flux coupled from one circuit to the other.
  • L represents the value of the inductance of the coil (210) and C represents the capacitance of the capacitor (232) .
  • the value of the capacitance (C) of the capacitor (232) can be adjusted.
  • the value of the capacitance (C) of the capacitor (232) is set such that the value of f 0 is equal to the frequency of the generated input current (208) .
  • the value of f 0 is equal to the generating frequency (e.g., 13.56 MHz) , a resonating effect is created.
  • the strength of the oscillation above is measured by the quality factor (Q) of the coil.
  • the quality factor (Q) is defined as the ratio of the peak energy stored in the resonator (212) in a cycle of oscillation to the energy lost per radian of the cycle.
  • Q can be calculated using the following equation:
  • R is the internal resistance of the coil.
  • the resonant current (216) passing through the coil (210) will be Q times larger than the input current (208) , which means that magnetic field strength is amplified by Q times compared to a resistive load even though the input power source (206) stays the same.
  • bandwidth (BW) of the resulting field (218) can be represented by the following equation, which relates the frequency (f 0 ) and quality factor (Q) :
  • FIG. 3 is a block diagram of an improved NFC system according to some embodiments of the disclosure.
  • a plurality of transmission resonators (302a, 302b, 302c; collectively, 302) is situated in an environment.
  • the structure of the resonators (302) is described in the description of FIG. 2 and, specifically, resonator (212) and is not repeated herein.
  • Each resonator (302) generates a magnetic field (320) that passes through the environment and is received by passive or active tags (318a, 318b, 318c; collectively, 318) .
  • Various repeaters (314a, 314b; collectively, 314) are installed in the environment for amplifying the magnetic flux (as will be described) .
  • each of the tags (318) generates a responsive magnetic field upon detecting a signal from the reader and modulates data in this field.
  • a receiving resonator (316) is configured to receive this modulated data.
  • the receiving resonator (316) is configured in the same manner as the transmission resonators (302) , however, it may be tuned to a different resonant frequency as will be discussed.
  • the transmission resonators (302) and receiving resonator (316) are connected to a system-level application platform.
  • This platform includes a beamformer (304) , which directs the magnetic fields of the resonators (302) , an application-layer stack (306) , which may comprise an ISO 15693 stack, and a passive self-interference cancellation circuit (322) .
  • the passive self-interference cancellation circuit (322) includes an optional notch filter (312) , a radio-frequency (RF) analog front-end (310) , and a digital back-end (308) .
  • the range of NFC signals is extended by physically separating the transmission and reception resonators. Further, high-quality factor coils are used for both transmission and reception, which increases the range of the NFC signals.
  • the resonators (302) are tuned to resonate around 13.56 MHz while the receiving resonator (316) resonates around 13.11 MHz or 14.01 MHz.
  • the system includes a passive self-interference cancellation circuit (322) to enable the application-layer stack (306) to receive and decode very weak backscattered signals from tags (318) that are far away from the reader.
  • the system employs multiple resonators (302) to do efficient magnetic beamforming to ensure tags (318) with undesired orientations can also obtain sufficient power for their operation.
  • passive (e.g., battery-less) repeaters (314) are deployed at locations close to the tags (318) , which can aid in the reading of tags (318) far away from the resonators (302) or with undesired orientations.
  • elements 302, 304, 306, 308, 310, 312, 316, and 322 are collectively referred to as a “reader. ”
  • the magnetic field (320) passing through the tags (318) is represented by the following equation, which is derived from Biot-Savart law:
  • H represents the magnetic field strength
  • P represents the transmission power
  • R represents the radius of a transmission coil
  • Q represents the coil quality factor
  • a represents the coil wire radius
  • d represents the distance where the magnetic field is measured.
  • the values of P, R, a or Q should be increased which additionally increases the field strength H.
  • the value of Q is the ideal factor to increase the read distance of the system.
  • the value of R may be adjusted to obtain the desired distance (d) .
  • An optimal value of R can be calculated by taking the derivative of Equation 4 to zero, which leads to a value of R comparable to d.
  • optimizing R is often infeasible for two reasons. First, a large coil has a high self-inductance, which can only function with small resonating capacitance when the coil is tuned to 13.56 MHz as shown in Equation 1. The small capacitance can be easily changed by parasitic capacitance experienced in deployment. As a result, a coil with a large R value would get detuned from the desired 13.56 MHz even though it has been carefully calibrated in the lab environment.
  • the loop currents should be evenly distributed along the coil to avoid spurious electromagnetic emission at far-field, which implies that the maximum circumference of the coil can only be a small fraction of the wavelength.
  • a maximum value of R equal to approximately 0.5 meters can be selected.
  • the quality factor (Q) is selected to increase the read distance of the resonators (302) .
  • existing NFC readers employ a quality factor of eight (8) to enable both wireless power transfer as well as data communication functionality.
  • FIG. 4 are graphs illustrating the frequency response (402) of a coil having a small Q factor and the frequency response (404) of a coil having a large Q factor.
  • the frequency response (402) comprises a response similar to existing NFC readers, while the frequency response (404) illustrates a response generated by the disclosed embodiments.
  • a tag e.g., 318a, 318b, 318c talks to a reader using a sub-carrier of 423.75 kHz or 484.25 kHz.
  • a sampling bandwidth of around 1 MHz is needed (2 ⁇ 484.25 kHz) .
  • the Q of the coil should be no more than 13.56 (13.56 MHz divided by 1 MHz) .
  • Current readers employ a Q factor 86. Using such a small Q factor, the frequency response of the coil is not sharp, and its bandwidth (406) is wide. Therefore, tag-to-reader data communication can survive.
  • Equation 4 indicates that a large Q factor improves the magnetic strength, the frequency response of the coil becomes sharp as shown by the middle curve (408) of the improved frequency response graph (404) .
  • the frequency response of the coil becomes sharp as shown by the middle curve (408) of the improved frequency response graph (404) .
  • tag-to-reader communication can suffer because the frequency of the backscattered signal is outside of the bandwidth of the coil.
  • the system depicted in FIG. 3 narrows the bandwidth of a given coil, which excludes the coil from performing data communication with a tag while simultaneously increasing the transmit distance of the system.
  • the system in FIG. 3 separates resonators (302) from a receiving resonator (316) .
  • the reader-to-tag (e.g., transmission coil to tag) tag downlink transmission utilizes pulse position modulation with a pre-configured slot value.
  • this slot value comprises an 18.88 ⁇ s slot according to the ISO-15693 protocol.
  • the bandwidth required for the reader-to-tag link is around 53 kHz. Since the center frequency of the resonators (302) is around 13.56 MHz, the Q of the resonators (302) can be increased to 256 (13.56 MHz divided by 53 kHz) , 32 times larger than that of a standard commercial NFC reader.
  • the disclosed embodiments tune the receiving resonator (316) to operate at or around 13.11 MHz or 14.01 MHz, corresponding to the lower/upper sideband frequencies (410) used in the tag-to-reader communication link.
  • the tag performs frequency-shift keying (FSK) modulation at 6.7 kbps with a 423 kHz or 484 kHz subcarrier.
  • the minimum sampling bandwidth required by the reader to decode the information is 74.4kHz ( (484-423) +2 ⁇ 6.7) .
  • the receiving resonator (316) can have a Q factor of 188 (14.01 MHz divided by 74.4 kHz) .
  • resonators (302) having a Q factor of 256 and a receiving resonator (316) having a Q factor of 188 can extend the reader-to-tag link range by 1.8 times and tag-to-reader link range by 1.7 times compared to the coils used by state-of-the-art commercial NFC readers having a Q factor of eight (8) .
  • the use of separated high Q factor coils can support significantly longer distances than existing NFC readers.
  • coils used in the resonators (302) comprise aluminum gamma-loops.
  • each coil has a 0.9 meter by 1.1 meter dimension.
  • the coils have a high-power rating and a tunable Q factor value, which can tune up to 300.
  • the system includes a passive self-interference cancellation circuit (322) .
  • this circuit (322) is optional.
  • signal will leak from the transmission device to the receiving device. This leakage is generally referred to as self-interference.
  • This self-interference limits the operational range of current systems (such as standard NFC) and results in a small read distance of a maximum of ten (10) centimeters. Current NFC systems provide no solution for addressing self-interference and instead require a small read distance.
  • the system in FIG. 3 includes a passive self-interference cancellation circuit (322) that compensates for self-interference that occurs due to longer read distances.
  • FIG. 5 illustrates the measured self-interference characteristics of NFC systems at varying read distances according to some embodiments.
  • both measured characteristics (502, 504) include the same self-interference signal (506) generated by a transmission coil.
  • this signal (506) is generated at 13.56 MHz, as discussed above.
  • the graphs additionally illustrate the tag signals (508a, 508b) generated by the respective tags.
  • the tag signals (508a) of characteristics (502) are generated by tags that are ten (10) centimeters away from the receiving coil
  • the tag signals (508b) of characteristics (504) are generated by tags that are one (1) meter away from the receiving coil.
  • the difference between the self-interference signal (506) and the tag signals (508a) are approximately 50 dB. Further, the tag signals (508a) are above the NFC reader sensitivity level (510) and well above the noise floor (512) . By surpassing both these limits (510, 512) , the reader can generally successfully decode the tag signals (508a) even without cancellation of the self-interference signal.
  • Characteristics (504) illustrates a traditional NFC system where the tags are moved to approximately one (1) meter from the reader. As illustrated, when placed at one (1) meter, the backscattered tag signals (508b) become significantly weaker while the self-interference signal (506) remains the same. As indicated in Equation 4, the movement of a tag from ten (10) centimeters to one (1) meter results in a signal decrease of 40 dB. Thus, the resulting tag signals (508b) are significantly lower than the self-interference (506) signal. Further, the tag signals (508b) are much closer to the noise floor (512) and are below the NFC reader's sensitivity (510) , resulting in misreads.
  • the system in FIG. 3 employs a passive self-interference cancellation circuit (322) .
  • the receiving resonator (316) comprises a coil having a high Q factor. Further, the receiving resonator (316) is tuned to 14.01 MHz or 13.11 MHz. Following from Equation 3 (illustrated in the bandwidth and Q factor tradeoff) , the high Q factor of the receiving resonator (316) suppresses signal outside the tuned band (e.g., 14.01 MHz or 13.11 MHz) . As a result of this tuning, the self-interference signal from the resonators (302) , which is at a different frequency such as 13.56 MHz, is suppressed.
  • the use of high Q factor transmission and receiving coils (302, 316) results in a 19 dB suppression of the self-interference signal, as illustrated in FIG. 6. As illustrated in FIG. 6, however, the reduction of 19 dB still results in self-interference, and the self-interference signal is still above the component rating power, which would result in damage to the front-end components of the receiver.
  • the system can employ active cancellation techniques as described in UHF RFID combined with a full-duplex communication system. In this embodiment, active cancellation can be achieved by controlling the phase and amplitude of a copy of the signal from the resonators (302) , which results in a signal exactly opposite the self-interference signal.
  • the passive self-interference cancellation circuit (322) includes a notch filter (312) .
  • the notch filter (312) comprises a crystal notch filter.
  • the notch filter (312) has a 15 dB sharp rejection around the transmission frequency (e.g., 13.56 MHz) and a very low loss (less than 1 dB) near the receiving frequency (e.g., 13.10 MHz or 14.01Mhz) .
  • the notch filter (312) includes a cascading array of multiple notch filters.
  • the notch filter (312) results in additional interference reduction. As illustrated in FIG. 6, measurements indicate that this reduction is approximately 32 dB. Thus, when combined with high Q factor coils, the notch filter and coils provide approximately 50dB of interference reduction.
  • the passive self-interference cancellation circuit (322) additionally includes radio-frequency (RF) analog front-end (310) and a digital back-end (308) . As illustrated in FIG. 6, these components further reduce the self-interference signal by 60 dB and 30 dB, respectively.
  • the front-end (310) comprises an intermediate frequency (IF) filter.
  • the IF filter may a single, two-, or three-stage IF filter.
  • the digital back-end (308) may comprise a digital baseband processor that performed further digital filtering on the received signal.
  • the system of FIG. 3 includes multiple resonators (302) controlled by a magnetic beamformer (304) . These components are described in more detail herein.
  • the magnetic signal produced by a resonant coil comprises a vector field.
  • FIG. 7 illustrates two perpendicular transmission coils and associated magnetic vector fields according to some embodiments of the disclosure.
  • the vector fields produced by transmission coils TX1 and TX2 at a given tag can be represented as follows:
  • the magnetic beamformer (304) optimizes an angle ( ⁇ ) of the magnetic field normal to the plane of the tag.
  • the power of the combined signal can be represented as:
  • P B2 (a 1 cos ( ⁇ 1 - ⁇ ) +a 2 cos ( ⁇ 2 - ⁇ ) cos ( ⁇ 2 - ⁇ 1 ) ) 2 + (a 2 cos ( ⁇ 2 - ⁇ ) sin ( ⁇ 2 - ⁇ 1 ) ) 2
  • the optimal ⁇ configuration in a multiple transmission coil system (e.g., as depicted in FIG. 3) is independent of the tag location and orientation.
  • any number (N) of resonators (302) may be used.
  • the phase value of the coil is set to either 0 or 180 degrees.
  • the power received at the tags (318) can be represented as:
  • N resonators (302) can deliver the maximum amount of power to tags (318) by setting the phase of each resonator (302) to either 0 or ⁇ .
  • the number of resonators (302) is less than or equal to six (6) , which is sufficient for activating the tags (318) in the region of interest.
  • the searching complexity for the beamformer (304) is 2N-1 ⁇ 32, which is quickly executed during startup.
  • the system additionally includes one or more repeaters (314) .
  • these repeaters (314) comprise passive magnetic repeaters that compensate range and angle coverage and eliminate “dead spots” within an environment. These repeaters (314) are described in more detail below.
  • the repeaters (314) used in the system are battery-less and passive devices.
  • the repeaters (314) comprise one-turn coils that are remotely coupled to either the resonators (302) or receiving resonator (316) .
  • the repeaters (314) form slave-master relationships with the reader and spontaneously repeats a reader’s action even though it does not have a battery. The passive nature of the repeaters (314) allows them to be easily deployed in various harsh environments.
  • FIG 8A is a diagram of a repeater excited by a resonator according to some embodiments of the disclosure.
  • the resonator (302) generates a magnetic field flux (802) that passes through a one-turn circular repeater coil (314) .
  • the radius of the coil of the repeater (314) is denoted as R rep .
  • the wavelength of the transmitted signal is larger (e.g., 22 meters at 13.56 MHz)
  • the phase of the magnetic field (802) remains nearly constant within the operating range of the resonator (302) .
  • the magnetic flux produced at the repeater by an input current (208) Isin ⁇ c t on the resonator (302) can be denoted as ⁇ sin ⁇ c t , where the value of B TX representing the average magnetic field strength passing through the coil of the repeater (314) .
  • the magnetic flux at the repeater (314) is dependent on time, and thus the time-varying magnetic flux induces an electromotive force in the coil of the repeater (314) .
  • the electromotive force e of the repeater (314) can be represented as:
  • Equation 11 The electromotive force denoted in Equation 11 is equivalent to a signal source.
  • the repeater (314) can be modeled as the RLC circuit depicted in FIG. 8B.
  • the current through the repeater (314) can be represented by the following formula:
  • ⁇ c is the resonant frequency of the repeater (314) .
  • FIG. 8C is a diagram illustrating the current magnitude response of a repeater and the phase difference between a resonator and a repeater according to some embodiments of the disclosure.
  • the resonator resonates at a frequency of 13.56 MHz.
  • the elicited current amplitude in a repeater (314) attains maximum when it’s the resonant frequency is equal to that of a resonator coil, but the response will quickly drop if the repeater’s resonant frequency deviates from 13.56 MHz.
  • the graph (806) illustrates that the phase of the signal elicited by the repeater has a 90° phase difference compared to the 13.56 MHz signal from the resonator coil.
  • the signal from the resonator and the one elicited from the repeater do not destructively add on top of each other.
  • the repeater if the repeater is located in an appropriate region with a sufficient Q factor, its elicited currents can be as large as that in the original resonator coil (several amperes) , which subsequently generates strong magnetic fields. Therefore, the passive repeater acts equivalently as a resonator transmission coil, introducing more diversity and helping eliminate “dead spots” undiscovered by the system.
  • the repeater loop is a one-turn loop comprising a copper tube with a diameter of 9.42 millimeters, although other materials and sizes may be used.
  • each repeater is connected to a printed circuit board (PCB) that includes external, variable shunt and series capacitors for tuning and impedance-matching.
  • PCB printed circuit board
  • FIG. 9 is a block diagram of a multi-channel reader according to some embodiments of the disclosure.
  • a multi-channel reader includes a transmission (TX) module (906) , a central processing module (910) , and a receiving (RX) module (908) .
  • the multi-channel reader (902) is communicatively coupled to multiple resonators (904a–d) .
  • the resonators (904a–d) generate a magnetic field that passes through one or more tags (940) and is amplified via repeaters (942) .
  • the tags (940) generate a magnetic field in response that is received via a receiving resonator (938) . Details of resonators (904a–d, 938) , tags (940) , and repeaters (942) are described more fully in the preceding sections, and details of those elements are not repeated herein.
  • the TX module (906) includes a clock signal generator (916) , a phase controller (912) , and an amplitude key-shifting (ASK) modulator (918) .
  • the TX module (906) supports four (4) concurrent transmission paths, as indicated in the connection between the ASK modulator (918) and the four resonators (904a–d) .
  • the specific number of resonators (904a–d) is not limiting. However, in most embodiments, the number of resonators (904a–d) may be limited to six or fewer.
  • the phase controller (912) is configured to tune phases independently in each transmission path and perform the magnetic beamforming described previously with respect to beamformer (304) .
  • the phase controller (912) comprises four (4) flip-flop-based quadrature phase-shift keying (QPSK) modulators (941a–d) .
  • the number of QPSK modulators (941a–d) is equal to the number of resonators (904a–d) .
  • the QPSK modulators (941a–d) run on a clock at a cycle rate of the transmission frequency times the number of resonators (904a–d) .
  • the clock (916) runs as 54.25 MHz (4 x 13.56 MHz) .
  • the clock (916) comprises a programmable logic device (PLD) such as an ATF16V8A PLD used to obtain different phase values.
  • PLD programmable logic device
  • the ASK modulator (918) encodes downlink data received from the central processing module (910) using an RF switch.
  • the output signal power delivered to the resonators (904a–d) is set at a preconfigured power level. In some embodiments, this power level is five watts.
  • the multi-channel reader (902) further includes an RX module (908) .
  • the RX module (908) includes a notch filter (926) .
  • the notch filter (926) comprises a two-stage crystal notch filter.
  • the notch filter (926) is selected to have a nulling frequency equal to the transmission frequency. As described above, in some embodiments, this transmission frequency is 13.56 MHz.
  • the notch filter (926) is placed before an amplifier (928) .
  • the placement of the notch filter (926) prior to an amplifier (928) in the receiving chain results in the suppression of the large, self-jamming frequency from the TX module (906) .
  • the notch filter (926) uses air-core inductors to avoid saturation, thereby achieving a low insertion loss of about 0.3 dB total.
  • the signal output from the notch filter (926) is amplified by an amplifier (928) .
  • the amplifier (928) comprises a low noise amplifier (LNA) .
  • the output of the amplifier (928) is then fed into LC (inductor/capacitor) filter (930) .
  • LC filter (930) comprises an image-rejection LC bandstop filter.
  • a standard NFC tag modulates on both sidebands at 13.11 MHz and 14.01 MHz. Therefore, in some embodiments, the RX module (908) is reconfigurable such that it can support two sets of configurations (e.g., 13.11 MHz and 14.01 MHz) .
  • these uplink sidebands are down-converted to an IF for IF processing.
  • the IF is at 10.7 MHz.
  • the output of the LC filter (930) is routed to one or more ceramic filters (932) .
  • the ceramic filters comprise two 10.7 ⁇ 0.18 MHz ceramic filters.
  • the ceramic filters (932) further attenuate interference and reduce noise bandwidth.
  • the output of the ceramic filters (932) is then output to an analog to digital converter (ADC) (934) .
  • ADC analog to digital converter
  • the ADC (934) samples the received IF signals.
  • the ADC (934) comprises a 16-bit ADC.
  • the samples generated by the ADC (934) are then transmitted to the controller (936) .
  • the controller (936) performs digital filtering, frame synchronization, and coherent demodulation on the received samples before transmitting the processed signals to the central processing module (910) .
  • the multi-channel reader (902) includes a central processing module (910) .
  • the central processing module (910) includes a dedicated microcontroller unit (MCU) .
  • the MCU may comprise an STM32 ARM Cortex-M7 manufactured by STMicroelectronics of Geneva, Switzerland.
  • the central processing module (910) performs ISO-15693 layer processing (920) as the physical layer processing of the reader (902) .
  • the central processing module (910) additionally implements a MAC layer protocol (924) in a high-level programming language such as C++.
  • the MAC protocol (924) implements collision detection and supports a greater than 50 tags per second read-rate.
  • all modules (906, 910, and 902) may be clocked from single PLL-DLL (phase-locked loop, delay-locked loop) clock generator, which provides multiple clock frequencies derived from one crystal reference.
  • PLL-DLL phase-locked loop, delay-locked loop
  • clock sharing avoids the carrier frequency offset issue that can occur during tag signal decoding.
  • the aforementioned NFC reader design provides significant advantages over existing NFC and RFID systems.
  • FIG. 10 is a diagram illustrating test result data of the read distance of a plurality of NFC readers.
  • a plurality of devices was tested including a smartphone (1002) , an open-source NFC reader (1004) , a commercial NFC reader (1006) , a system implementing the disclosed embodiments without repeaters (1008) , and a system implementing the disclosed embodiments with repeaters (1010) .
  • the smartphone (1002) , open-source reader (1004) , and commercial reader (1006) only use one coil for both transmission and reception, while the disclosed systems use multiple coils.
  • a tag was placed parallel to the coil (i.e., the most favorable orientation) and gradually moved away. Then, measurements were taken to determine whether the tag can be read as the tag was moved.
  • the smartphone (1002) can only read tags approximately 1 centimeter away.
  • the open-source NFC reader (1004) read tags at a distance of no more than 15 centimeters.
  • the commercial reader (1006) extended its read range beyond a few centimeters.
  • the tested commercial reader (1006) uses an eight (8) watt power smartphone and an 80cm ⁇ 50cm coil.
  • the reader (1006) was capable of reading tags up to 90 cm away.
  • none of the existing readers (1002, 1004, 1006) were capable of reading tags beyond 90 centimeters, far short of the ranges needed in logistics management (e.g., up to 2.5 meters) .
  • one RX resonator was placed three (3) meters away from the TX resonator. Then, a tag was placed between the TX and RX resonators and moved away from the TX resonator. As illustrated, when repeaters were not used, the tag was read when it is 0–170 cm and 200–300 cm away from the TX resonator. As illustrated with the system (1008) , tag reading failed between 170–200 cm due to the summation of downlink and uplink budgets were smallest at these locations.
  • FIG. 11 is a graph illustrating the improvement in signal strength when using a repeater according to some embodiments of the disclosure.
  • a repeater was placed a 0.5 m, 0.8 m, and 1.0 m away from a TX resonator.
  • the TX resonator to tag distance was increased and the power received by the tag was measured using a pickup loop.
  • the received power decreases monotonically over distance.
  • the received power is improved by 16–23 dB and maximized when the tag is close to the repeater.
  • the use of a repeater in the disclosed embodiments can improve both signal strength and read distance for applications requiring such characteristics.
  • FIG. 12 is a graph illustrating a comparison of signal loss between the disclosed embodiments, standard NFC, and UHF RFID systems according to some embodiments of the disclosure.
  • tags were placed in different orientations (i.e., non-ideal orientations relative to the magnetic field) .
  • two TX resonators were placed perpendicular to each other and separated by 50 cm. Then, one RX resonator was placed parallel to the first TX resonator and one repeater was placed parallel to the second TX resonator. The distances from both resonators was 1.5 m. Then, an NFC tag was placed in the center.
  • FIG. 12 shows the loss of signal experienced by a tag compared to its optimum orientation.
  • the tag in the disclosed embodiments 1202 harvests a strong magnetic flux from TX resonators and repeater. Even in the worst case, the tag only experiences around 3 dB signal strength degradation (i.e., the signal quality is almost invariant to the tag orientation) .
  • FIG. 13 summarizes the signal strength difference when the tag is or is not attached to a product between the disclosed embodiments (NFC+) and UHF RID.
  • NFC+ liquid products
  • UHF RID UHF RID
  • FIGS. 14 and 15 illustrate the results of this test.
  • the NFC+ reader’s coils were embedded on the left, right, and top part of the scanning gate, while the repeater was integrated into a moving cart.
  • Over 10,000 tags were attached to various products stored and shipped in the warehouse, including water, milk, cans, beer, bread, oil, etc. Then, these products were placed on the moving cart. The number of products per cart varied depending on the shipping volume, and their orientations were random.
  • the cart was pushed through the scanning gate, and the products read by the disclosed embodiments were recorded.
  • a standard NFC and UHF RFID system were also used to scan products. These systems were configured in the manners described above.
  • FIG. 14 shows the performance of the disclosed embodiments (NFC+) along with the performance of standard NFC and UHF RFID systems.
  • Graph (1402) illustrates the misread rate of the systems. As illustrated in graph (1402) , NFC+ can read over 99.97%of the tags passing through the gate. In contrast, a standard NFC system only reads 60%of the same tags. When UHF tags are intentionally placed (i.e., all tags have LoS with the reader) , the UHF RFID system can read 98.46%of the products. Even though the reading rate of the UHF RFID system is close to the 99.9%requirement of many logistic applications, such minor tailing error may translate into non-trivial revenue loss for the big warehouses.
  • the disclosed embodiments are the only system that can achieve over 99.9%accuracy when reading desired tags placed within the ROI while not reading any undesired tags outside the ROI.
  • the disclosed embodiments achieve less than 0.1%miss-reading rate (i.e., over 99.9%accuracy) within around 2.8 seconds.
  • the disclosed embodiments can achieve less than 0.01%miss-reading rate (over 99.99%accuracy) within around 3.6 seconds.
  • slower-moving speed helps reduce the misreading rate because the reader can sample the tags multiple times with more orientation diversity.
  • the disclosed embodiments misread rate is still much lower than standard NFC and UHF RFID systems.
  • FIG. 15 shows the signal strength degradation when the tag is immersed at different levels of depth (in water) , in comparison with an empty tank.
  • the disclosed embodiments’ magnetic signal does not significantly degrade as water depth increases. For example, when a tag is 15 cm away from the edge of the water tank, the signal degradation is only 3dB, close to its airborne path loss. However, a UHF tag at the same location experiences more than 30dB signal degradation which causes RFID operation to fail.
  • FIG. 16 is a flow diagram illustrating an improved method for reading NFC tags according to some embodiments of the disclosure.
  • the method phase tunes a plurality of transmission resonators.
  • a resonator comprises a high Q factor coil and parallel capacitor.
  • the carrier signal being phase tuned is a 13.56 MHz signal.
  • the number of resonators is between one and six and, in some embodiments, is four.
  • the phase is tuned to either zero or ⁇ .
  • the method encodes transmission data on the carrier signal.
  • this data can comprise any data used in an NFC or RFID system.
  • the data may include an instruction or command or may comprise user data.
  • the method transmits the encoded signal.
  • the signal may be transmitted through one or more repeaters.
  • the transmission resonator is situated apart from a receiving resonator, and the repeaters are situated between the two resonators.
  • step 1608 the method receives the transmitted signal and transmits a return signal.
  • step 1608 is performed by the NFC tag and is not described in more detail herein. Indeed, as discussed above, any NFC tag may be used.
  • step 1610 the method removes self-interference from the return signal to generate a cleaned signal.
  • the method receives the return signal via a receiving resonator.
  • the high Q factor coil of the receiving resonator filters a portion of the self-interference.
  • the method transmits the signal through an RF front end, which removes the remainder of any interference as described more fully in the preceding figures.
  • step 1612 the method digitizes (e.g., samples) the signal and transmits the digital signal to a central processing module. This process was described more fully in the description of FIG. 9 and that detail is not repeated herein.
  • a module is a software, hardware, or firmware (or combinations thereof) system, process or functionality, or component thereof, that performs or facilitates the processes, features, and functions described herein (with or without human interaction or augmentation) .
  • a module can include sub-modules.
  • Software components of a module may be stored on a computer-readable medium for execution by a processor. Modules may be integral to one or more servers, or be loaded and executed by one or more servers. One or more modules may be grouped into an engine or an application.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
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Abstract

L'invention concerne des dispositifs, des systèmes et des procédés destinés à améliorer les systèmes de communication en champ proche. Dans un mode de réalisation, l'invention concerne un dispositif comprenant au moins un résonateur de transmission configuré pour générer un champ magnétique; au moins un résonateur de réception, le au moins un résonateur de réception étant physiquement séparé du résonateur de transmission et configuré pour recevoir une transmission de données depuis une étiquette de communication en champ proche (NFC) en utilisant le champ magnétique; et un module de réception, le module de réception étant couplé au résonateur de réception et configuré pour traiter la transmission de données.
PCT/CN2020/082944 2020-04-02 2020-04-02 Système de communication d'identification par radiofréquence à haute fréquence basé sur la résonance WO2021196118A1 (fr)

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CN202080099479.2A CN115380478B (zh) 2020-04-02 2020-04-02 基于谐振的高频射频识别通信系统

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