CN113283259A - RFID-based multi-tag radio frequency identification system and method - Google Patents
RFID-based multi-tag radio frequency identification system and method Download PDFInfo
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- CN113283259A CN113283259A CN202110811679.2A CN202110811679A CN113283259A CN 113283259 A CN113283259 A CN 113283259A CN 202110811679 A CN202110811679 A CN 202110811679A CN 113283259 A CN113283259 A CN 113283259A
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- G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
- G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
- G06K7/10009—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
- G06K7/10019—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers.
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- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
- G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
- G06K7/10009—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
- G06K7/10118—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves the sensing being preceded by at least one preliminary step
- G06K7/10128—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves the sensing being preceded by at least one preliminary step the step consisting of detection of the presence of one or more record carriers in the vicinity of the interrogation device
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Abstract
The invention relates to a RFID-based multi-tag radio frequency identification system and a method, wherein the system comprises an RFID reader, a passive coupling antenna and a plurality of RFID tags which are mutually independent, the passive coupling antenna and the RFID tags are arranged in a preset space range, and the RFID reader is respectively coupled with the RFID tags in a radio frequency mode through the passive coupling antenna and is used for simultaneously reading the RFID tags; the RFID tag is specifically an RFID tag with an interface and separated transmitting and receiving antennas; the RFID reader is specifically an RFID reader with an interface and separated transmitting and receiving antennas. The invention can simultaneously read a plurality of RFID labels, improve the reading distance and plug in external equipment.
Description
Technical Field
The invention relates to the technical field of communication, in particular to a multi-label radio frequency identification system and a multi-label radio frequency identification method based on RFID.
Background
The rfid (radio Frequency identification) is a reflective communication technology, and has been widely applied to scenes such as logistics, public transportation, and gate surveillance systems. The RFID comprises an RFID reader and an RFID label (TAG), wherein the RFID reader is an active device and transmits information to the TAG by emitting and modulating a high-frequency carrier; most TAGs are passive devices that accomplish a change in channel conditions by means of load modulation techniques, which change can be detected by the RFID reader and the information of the TAG read out. The existing RFID technology is often limited in reading distance, for example, 15693 protocol is generally only about 10cm, while 14443 protocol is closer, and the 900MHz RFID distance of the "far distance" can only be about 3 m. In addition, the existing TAG end has no sensing capability, and a specific sensor cannot be hung externally to complete the acquisition of specific information, so that the use scenes of the products are greatly limited. If a plurality of same articles exist in a centralized box, when the monitoring of information of the articles, such as temperature, is to be completed in real time, the existing solutions generally need batteries, which brings much pressure to the monitoring cost and may cause secondary pollution.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a multi-tag radio frequency identification system and method based on RFID, which can read a plurality of RFID tags at the same time, improve the reading distance and plug in external equipment.
The technical scheme for solving the technical problems is as follows: a RFID-based multi-tag radio frequency identification system comprises an RFID reader, a passive coupling antenna and a plurality of RFID tags which are mutually independent, wherein the passive coupling antenna and the RFID tags are placed in a preset spatial range, and the RFID reader is respectively coupled with the RFID tags in a radio frequency mode through the passive coupling antenna and is used for reading the RFID tags at the same time;
the RFID tag is specifically an RFID tag with an interface and separated transmitting and receiving antennas; the RFID reader is specifically an RFID reader with an interface and separated transmitting and receiving antennas.
The invention has the beneficial effects that: in an RFID-based multi-tag RFID system of the present invention, one RFID reader needs to communicate with a plurality of RFID tags at the same time, because the placing positions and angles of the plurality of RFID labels are random, each RFID label antenna can not be ensured to be completely parallel to the plane of the RFID antenna of the card reader, when the plane of the RFID tag antenna is not significantly parallel to the plane of the reader RFID antenna, communication failure may result, in order to ensure that one RFID reader communicates with a plurality of RFID tags at the same time, the passive coupling antenna is introduced as a buffer, the magnetic field on the RFID reader antenna can be cut by the passive coupling antenna, so that mutual induction current is generated to form a new magnetic field, these newly generated magnetic fields may couple with the RFID tag antenna at the other end, thereby enabling communication between the RFID reader and the RFID tag, it is thus achieved that one RFID reader can read RFID tags in a plurality of different directions. In addition, the RFID reader and the upper and lower link antennas of the RFID tag are separated, namely, the transmitting antenna and the receiving antenna are separated, so that a high-Q-value circuit is favorably adopted, the communication distance can be greatly improved, and the reading distance is increased. Meanwhile, the RFID reader and the RFID label are provided with interfaces for externally hanging external equipment and communicating with the external equipment, so that the data demodulated from the downlink can be transmitted in a transparent mode, and information transmitted by the external equipment can also be transmitted in a transparent mode.
On the basis of the technical scheme, the invention can be further improved as follows.
Further, the RFID tag comprises a receiving antenna, an energy collecting module, a first modulation and demodulation module, a transmitting antenna, a first interface module and a first data storage module; the receiving antenna is connected with the input end of the energy collecting module, and is also connected with the signal input end of the first modulation and demodulation module; the output end of the energy collection module is connected with the power supply end of the first modulation and demodulation module, the signal output end of the first modulation and demodulation module is connected with the transmitting antenna, the signal output end of the first modulation and demodulation module is also connected with the input end of the first interface module, the output end of the first interface module is connected with the input end of the first data storage module, and the output end of the first data storage module is connected with the signal input end of the first modulation and demodulation module; the front ends of the receiving antenna and the transmitting antenna are respectively provided with a multi-stage adjustable capacitor.
The beneficial effect of adopting the further scheme is that: according to the RFID tag, the upper and lower link antennas are separated, namely, the transmitting antenna and the receiving antenna are separated, so that a high-Q-value circuit is favorably adopted, the communication distance can be greatly improved, and the reading distance is increased. Simultaneously, all set at the front end of transmitting antenna and receiving antenna and be connected with multistage adjustable capacitor for carry out automatic fine setting to Q value or resonance point, this multistage adjustable capacitor has multiple benefit: firstly, the introduction of the multistage adjustable capacitor can ensure that the Q value or the resonance point of an antenna end is unchanged to a certain extent, when the RFID tag is placed in different environments, the resonance point or the Q value of the antenna can be influenced due to the capacitance or inductance effect introduced by the environment, and the influence in the environments can be compensated to a certain extent due to the introduction of the multistage adjustable capacitor, so that the reliability of the tag is ensured; secondly, the introduction of the multi-stage adjustable capacitor can ensure that the communication distance cannot be attenuated due to the change of the Q value to a certain extent, when the Q value or the resonance point caused by the external environment is changed, the energy absorbed from the antenna end can be changed, and the change caused by resonance can cause the sharp reduction of the absorbed energy due to the higher Q value, so that the chip can not work normally, and the introduction of the multi-stage adjustable capacitor can improve the condition. In addition, the RFID tag is provided with a first interface module, the first interface module is used for externally hanging external equipment and communicating with the external equipment, and the first interface module can transmit data demodulated from the downlink and transmit information transmitted by the external equipment.
Further, the resonance points of the receiving antenna and the transmitting antenna are different, and the Q values of the receiving antenna and the transmitting antenna are both larger than 50.
The beneficial effect of adopting the further scheme is that: the resonance points of the receiving antenna and the transmitting antenna are different and are respectively used for a downlink communication link and an uplink communication link.
Furthermore, the RFID tag further comprises a rectification module, and the output end of the energy collection module is connected with the multistage adjustable capacitors of the receiving antenna and the transmitting antenna through the rectification module.
The beneficial effect of adopting the further scheme is that: the energy collection module is used for converting a high-frequency signal of a carrier into a direct current signal to supply power to other parts, and particularly, when the direct current signal of the energy collection module enters the rectification module, the peak voltage of the direct current signal is used as feedback of the antenna so as to adjust the Q value or the resonance point of the antenna to achieve better energy collection efficiency.
Further, the RFID label also comprises a frequency division module, and the first modulation and demodulation module is connected with the transmitting antenna through the frequency division module; the frequency division module is specifically a frequency division circuit with an adjustable frequency division coefficient.
The beneficial effect of adopting the further scheme is that: when the first modulation and demodulation module modulates the local information and is used in an uplink, the frequency division module reduces the frequency of a carrier signal, and the signal after frequency reduction is used for shifting the central frequency of the carrier signal to be consistent with the resonant frequency of a transmitting antenna, so that the optimal transmitting effect is achieved; the frequency division coefficient of the frequency division module can be adjusted, so that when the resonance point of the carrier wave after frequency division and the transmitting antenna is deviated, the frequency division coefficient can be properly changed to relieve the deviation.
Further, the first interface module comprises any one or combination of a plurality of SPI interface, IIC interface and ADC interface.
The beneficial effect of adopting the further scheme is that: the first interface module can be formed by interfaces such as SPI, IIC, ADC and the like, and different interface circuits can be selected according to actual application scenes.
Further, a hardware filtering algorithm is embedded in the first modem module.
The beneficial effect of adopting the further scheme is that: when the first interface module is externally hung on an external device (such as an external sensor) for data reading, the data obtained by the sensor is inevitably subjected to various interferences to generate noise, which inevitably affects the reliability of the read data.
Furthermore, the RFID reader comprises a multi-transmitting antenna array, a multi-receiving antenna array, a second modulation and demodulation module, a second interface module, a second data storage module and a control module; the multi-receiving antenna array is connected with the signal input end of the second modulation and demodulation module, the signal output end of the second modulation and demodulation module is connected with the multi-transmitting antenna array, the signal output end of the second modulation and demodulation module is also connected with the input end of the second interface module, the output end of the second interface module is connected with the input end of the second data storage module, the output end of the second data storage module is connected with the signal input end of the second modulation and demodulation module, and the control module is bidirectionally connected with the second interface module; the front end of the multi-receiving antenna array is connected with a multi-stage adjustable capacitor in a matched mode.
The beneficial effect of adopting the further scheme is that: in the RFID reader, as the RFID reader is an active device, a beam forming technology can be introduced at a transmitting end and a receiving end to improve the SNR of signals, and equivalently, the communication distance can be increased; meanwhile, the introduction of the multi-antenna technology is beneficial to solving the problem of the reading directivity.
Based on the RFID-based multi-tag radio frequency identification system, the invention also provides a RFID-based multi-tag radio frequency identification method.
An RFID-based multi-tag radio frequency identification method is applied to the RFID-based multi-tag radio frequency identification system, and comprises the following steps,
s1, when the RFID reader detects the change of the impedance of the RFID label and before the RFID reader sends an inventory instruction, tuning between the RFID label and the RFID reader;
s2, after the tuning between the RFID label and the RFID reader is completed, the data transmission between the RFID label and the RFID reader is carried out based on the load modulation method of full duplex communication;
in the above-mentioned S1, the method,
the tuning process of the RFID tag is as follows:
adjusting a multistage adjustable capacitor at the front end of the receiving antenna to enable the feedback voltage of the receiving antenna to be maximum;
tuning the transmitting antenna by adjusting a multistage adjustable capacitor at the front end of the transmitting antenna according to the strength of the signal read by the RFID reader as a feedback value, so that the transmitting antenna reaches an optimal matching point;
the tuning process of the RFID reader is as follows:
based on an ALOHA algorithm, the extreme value of the signal strength received by the multi-receiving antenna array is used as a tuning target value, the energy of a carrier signal generated by the RFID reader is gradually increased from low to high according to multiple stages, and when any one RFID label in the plurality of RFID labels completes self tuning under the corresponding energy, the RFID label is in a silent state until all the RFID labels complete tuning.
The invention has the beneficial effects that: in the RFID-based multi-tag radio frequency identification method, after an RFID reader detects the impedance change of an RFID tag and before the RFID reader sends an inventory instruction, the RFID tag and the RFID reader are tuned to ensure normal and stable communication between the RFID tag and the RFID reader; in addition, the feedback time can be reduced by adopting a full-duplex communication mode.
On the basis of the technical scheme, the invention can be further improved as follows.
Further, in S2, the load modulation method of full duplex communication is specifically that amplitude modulation is used for a downlink between the RFID tag and the RFID reader, and phase modulation is used for an uplink between the RFID tag and the RFID reader;
specifically, the method for implementing amplitude modulation in the downlink and phase modulation in the uplink between the RFID tag and the RFID reader is,
the real impedance part of the load element and the real impedance part of the load modulation element are set to be consistent in magnitude and opposite in sign, and the imaginary impedance part of the load element and the imaginary impedance part of the load modulation element are set to be consistent in magnitude and opposite in sign.
Drawings
FIG. 1 is a block diagram of a RFID-based multi-tag RFID system according to the present invention;
FIG. 2 is a schematic diagram of an arrangement of an RFID reader antenna, an RFID tag antenna, and a passive coupling antenna;
FIG. 3 is a block diagram of an RFID tag;
FIG. 4 is a schematic diagram of a receiving antenna or a transmitting antenna in the RFID tag;
FIG. 5 is a schematic diagram of a circuit structure of a multi-stage tunable capacitor in an RFID tag;
FIG. 6 is a schematic diagram of a circuit configuration of an energy harvesting module in an RFID tag;
FIG. 7 is a block diagram of an RFID reader;
FIG. 8 is a structural schematic diagram of an arrangement of multiple transmit antenna arrays or multiple receive antenna arrays in an RFID reader;
fig. 9 is an equivalent circuit diagram of load modulation.
Detailed Description
The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.
As shown in fig. 1, an RFID-based multi-tag radio frequency identification system includes an RFID reader, a passive coupling antenna, and a plurality of RFID tags, which are independent of each other, the passive coupling antenna and the plurality of RFID tags are disposed in a preset spatial range, and the RFID reader is respectively radio-frequency coupled with the plurality of RFID tags through the passive coupling antenna and is configured to simultaneously read the plurality of RFID tags;
the RFID tag is specifically an RFID tag with an interface and separated transmitting and receiving antennas; the RFID reader is specifically an RFID reader with an interface and separated transmitting and receiving antennas.
In the RFID-based multi-tag radio frequency identification system, one RFID reader needs to communicate with a plurality of RFID tags at the same time, and the placement positions and angles of the RFID tags are random, so that each RFID tag antenna cannot be guaranteed to be completely parallel to the plane of the RFID antenna of the card reader, when the planes of the RFID tag antenna and the RFID antenna of the card reader are seriously not parallel, communication failure can be caused, in order to guarantee that one RFID reader communicates with the RFID tags at the same time, a passive coupling antenna is introduced as a buffer, and the problem of reading direction is solved; the magnetic field on the antenna of the RFID reader can be cut by the passive coupling antenna, so that mutual inductive current is generated to form a new magnetic field, the newly generated magnetic field can be coupled with the antenna of the RFID tag at the other end, and further, the communication between the RFID reader and the RFID tag is realized, so that the RFID tags in a plurality of different directions can be read by one RFID reader.
For example, in a complex multi-card scenario where the RFID tag antenna is not necessarily perfectly parallel to the plane of the RFID reader antenna, as in the extreme scenario shown in fig. 2, where the RFID reader antenna 1 is perfectly perpendicular to the RFID tag antenna 3, card face reading in such an arrangement is most difficult, in which case communication will fail. With this arrangement, the magnetic field generated by the RFID reader cannot generate a mutual inductive current on the RFID tag antenna 3, and thus cannot activate the RFID tag, and even more, cannot achieve reliable communication. After the passive coupling antenna 2 is introduced, the passive coupling antenna 2 can be used as an intermediate medium, a magnetic field on the RFID reader antenna 1 can be cut by the passive coupling antenna 2, so that mutual induction current is generated to form a new magnetic field, the newly generated magnetic field can be coupled with the RFID tag antenna 3 at the other end, and information transmitted by a card reader is transmitted to the card end.
In the present invention: the RFID tag antenna 3 specifically includes a receiving antenna and a transmitting antenna described below in the RFID tag, and the RFID reader antenna 1 specifically includes a multi-transmitting antenna array and a multi-receiving antenna array described below in the RFID reader.
In this particular embodiment: as shown in fig. 3, the RFID tag includes a receiving antenna, an energy collecting module, a first modulation and demodulation module, a transmitting antenna, a first interface module and a first data storage module; the receiving antenna is connected with the input end of the energy collecting module, and is also connected with the signal input end of the first modulation and demodulation module; the output end of the energy collection module is connected with the power supply end of the first modulation and demodulation module, the signal output end of the first modulation and demodulation module is connected with the transmitting antenna, the signal output end of the first modulation and demodulation module is also connected with the input end of the first interface module, the output end of the first interface module is connected with the input end of the first data storage module, and the output end of the first data storage module is connected with the signal input end of the first modulation and demodulation module; the front ends of the receiving antenna and the transmitting antenna are respectively provided with a multi-stage adjustable capacitor.
The working principle of the RFID tag is as follows: when the RFID tag enters the reading range of the RFID reader, a receiving antenna of the RFID tag receives a carrier wave sent by the RFID reader, the receiving antenna transmits a high-frequency signal of the received carrier wave to an energy collecting module, the energy collecting module converts the high-frequency signal of the carrier wave into a direct-current signal to supply power to a first modulation and demodulation module, the receiving antenna transmits the received signal in the carrier wave to the first modulation and demodulation module, the first modulation and demodulation module demodulates the signal in the carrier wave, and when the RFID tag is matched with the RFID reader, the first modulation and demodulation module acquires pre-stored tag data from a first data storage module and transmits the pre-stored tag data to the RFID reader through a transmitting antenna after modulating the tag data. The first interface module is used for externally hanging external equipment, and the first interface module can transmit data demodulated from the first modulation and demodulation module to the first data storage module in a transparent mode and can also transmit information transmitted by the external equipment to the first data storage module in a transparent mode.
The traditional RFID tag adopts the same antenna for the uplink and the downlink, and the invention separates the antennas of the uplink and the downlink, thereby being beneficial to adopting a high-Q-value circuit, greatly improving the communication distance and ensuring the feasibility of reliable communication under the condition of high Q value. The resonance points of the receiving antenna and the transmitting antenna are different, and the Q values of the receiving antenna and the transmitting antenna are both greater than 50 (the Q value is specifically a quality factor, and the Q value greater than 50 is called a high Q value). The resonance points of the receiving antenna and the transmitting antenna are different and are respectively used for a downlink communication link and an uplink communication link.
In this embodiment, both the transmitting antenna and the receiving antenna may adopt a loop antenna formed by PCB traces, such as the antenna structure shown in fig. 4. In fig. 4, a plurality of adjustable capacitors C are connected to the front end of the antenna, that is, a plurality of adjustable capacitors C are connected to the front ends of the receiving antenna and the transmitting antenna, and a specific circuit structure of the plurality of adjustable capacitors C is as shown in fig. 5, and the plurality of adjustable capacitors C (the adjustable capacitors C1 ', the adjustable capacitors C2 ', … …, and the adjustable capacitors CK ') are connected in parallel, and the number of the adjustable capacitors is set according to actual conditions. All dispose at the front end of transmitting antenna and receiving antenna and be connected with multistage adjustable capacitor for carry out automatic fine setting to Q value or resonance point, this multistage adjustable capacitor has multiple benefit: firstly, the introduction of the multistage adjustable capacitor can ensure that the Q value or the resonance point of an antenna end is unchanged to a certain extent, when the RFID tag is placed in different environments, the resonance point or the Q value of the antenna can be influenced due to the capacitance or inductance effect introduced by the environment, and the influence in the environments can be compensated to a certain extent due to the introduction of the multistage adjustable capacitor, so that the reliability of the tag is ensured; secondly, the introduction of the multi-stage adjustable capacitor can ensure that the communication distance cannot be attenuated due to the change of the Q value to a certain extent, when the Q value or the resonance point caused by the external environment is changed, the energy absorbed from the antenna end can be changed, and the change caused by resonance can cause the sharp reduction of the absorbed energy due to the higher Q value, so that the chip can not work normally, and the introduction of the multi-stage adjustable capacitor can improve the condition. The RFID tag can self-adaptively and dynamically adjust the Q value or the resonant frequency of the antenna end, and the adjustment of the dynamic Q value is beneficial to ensuring higher energy collection efficiency and better communication distance than the traditional RFID by the circuit part.
In this embodiment, the energy collection module may adopt a circuit structure as shown in fig. 6, and the energy collection module is configured to convert a high-frequency signal in a carrier received by the receiving antenna into a direct-current signal through a voltage boosting circuit formed by a diode and a capacitor, so as to supply power to another part (e.g., the first modem module). The energy collection module comprises a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a diode D1, a diode D2, a diode D3 and a diode D4; an input end of the energy collection module is arranged between one end of the capacitor C1 and the anode of the diode D2, the other end of the capacitor C1 is connected to the cathode of the diode D2 and one end of the capacitor C2, the other end of the capacitor C2 is connected to the cathode of the diode D3 and the anode of the diode D4, the cathode of the diode D4 is connected to one end of the capacitor C4, the other end of the capacitor C4 is connected to the anode of the diode D3 and the cathode of the diode D1, the anode of the diode D1 is connected to the cathode of the diode D2, one end of the capacitor C3 is connected to the cathode of the diode D1, the other end of the capacitor C3 is connected to the anode of the diode D2, the anode of the diode D2 is also connected to the digital ground, the output end of the energy collection module is arranged between the anode of the diode D2 and the cathode of the diode D4; wherein, in fig. 6, EP represents digital ground, Vin represents an input terminal of the energy collection module, and Vout represents an output terminal of the energy collection module. In addition, the RFID label also comprises a rectification module, and the output end of the energy collection module is also connected with the multistage adjustable capacitors of the receiving antenna and the transmitting antenna through the rectification module. When the direct current signal of the energy collection module enters the rectification module, the peak voltage of the direct current signal is used as the feedback of the antenna, so that the Q value or the resonance point of the antenna is adjusted to achieve better energy collection efficiency. The RFID label of the invention adopts the self-adaptive adjustment of the transmitting frequency point, and achieves the purpose of changing the transmitting frequency point by changing the step coefficient, so that the transmitting frequency point is consistent with the resonance frequency point of the transmitting antenna, and the communication distance of the uplink is optimal.
In this particular embodiment, the first modem module is used to demodulate a signal in a carrier or modulate a signal to be transmitted. Particularly, the RFID tag further comprises a frequency division module, and the first modulation and demodulation module is connected with the transmitting antenna through the frequency division module; specifically, the frequency division module is a frequency division circuit with an adjustable frequency division coefficient. When the first modulation and demodulation module modulates the local information to be used in the uplink, the frequency division module reduces the frequency of the carrier signal, and the signal after frequency reduction is used for shifting the central frequency of the carrier signal to be consistent with the resonant frequency of the transmitting antenna, so that the optimal transmitting effect is achieved. The frequency division coefficient of the frequency division module can be adjusted, so that when the resonance point of the carrier wave after frequency division and the transmitting antenna is deviated, the frequency division coefficient can be properly changed to relieve the deviation.
In this embodiment, the first interface module is used for external devices to communicate with the external devices, and may transmit data demodulated from the downlink or information transmitted by the external devices. The interface circuit can be formed by interfaces such as SPI, IIC, ADC, and different interface circuits can be selected according to actual application scenes. The first interface module is used for expanding the functions of the tag, such as an analog or digital temperature sensor which is externally hung with an IIC interface through an ADC interface and used for passive temperature sensing; and a Flash chip is hung externally through the SPI interface and is used for event recording and the like.
In this embodiment, a hardware filtering algorithm is embedded in the first modem module. When the first interface module is externally hung on an external device (such as an external sensor) for data reading, the data obtained by the sensor is inevitably subjected to various interferences to generate noise, which inevitably affects the reliability of the read data. The filtering maximum and minimum value algorithm, the mean filtering algorithm, the median filtering algorithm and the low-pass filtering algorithm are mainly introduced, and relevant parameters of the algorithms can be configured in a wireless mode, such as the data length of the mean filtering algorithm or the median filtering algorithm.
As shown in fig. 7, the RFID reader includes a multi-transmitting antenna array, a multi-receiving antenna array, a second modulation and demodulation module, a second interface module, a second data storage module, and a control module; the multi-receiving antenna array is connected with the signal input end of the second modulation and demodulation module, the signal output end of the second modulation and demodulation module is connected with the multi-transmitting antenna array, the signal output end of the second modulation and demodulation module is also connected with the input end of the second interface module, the output end of the second interface module is connected with the input end of the second data storage module, the output end of the second data storage module is connected with the signal input end of the second modulation and demodulation module, and the control module is bidirectionally connected with the second interface module; the front end of the multi-receiving antenna array is connected with a multi-stage adjustable capacitor in a matched mode.
The basic functional module of the RFID reader is similar to the RFID label, namely, a receiving and transmitting antenna separation technology and a high-Q-value circuit are adopted, and meanwhile, an adjustable capacitor is introduced into an antenna end to tune. In contrast, since the RFID reader is an active device (power supply of the RFID reader is not shown in fig. 7), a beam forming technique can be introduced at the transceiving end to improve SNR of the signal, and equivalently, the communication distance can be increased; meanwhile, the introduction of a multi-antenna technology (the multi-antenna technology is a technology of adding signals received by multiple antennas, and the signal-to-noise ratio is enhanced by utilizing the characteristic that coherent superposition can enhance the signal strength) is favorable for solving the problem of reading directivity. For example, as shown in FIG. 8, when the multi-receive antenna array includes two square antennas, namely a first antenna A and a second antenna B, which are arranged in a mutually perpendicular manner as shown in FIG. 8 (if conditions allow that the area of the PCB surface can be increased by several antennas), the RFID tag is difficult to have a directional blind spot regardless of the manner in which the RFID tag appears in the field of view (if the two antennas are arranged vertically as shown in FIG. 8, the problem of reading at two angles can be solved). If more antennas are introduced, multi-angle RFID tag reading can be easily realized, so that the application scene of the RFID tag is greatly expanded, for example, automatic settlement of commodities in a shopping column is realized through the RFID tag; the real-time collection of the temperature in a plurality of vaccine bottles in the container is realized through the RFID tag. Thereby realizing support of multi-card reading.
In this embodiment, the control module may be a programmable control chip, which is a control center of the RFID reader.
Based on the RFID-based multi-tag radio frequency identification system, the invention also provides a RFID-based multi-tag radio frequency identification method.
An RFID-based multi-tag radio frequency identification method is applied to the RFID-based multi-tag radio frequency identification system, and comprises the following steps,
s1, when the RFID reader detects the change of the impedance of the RFID label and before the RFID reader sends an inventory instruction, tuning between the RFID label and the RFID reader;
s2, after the tuning between the RFID label and the RFID reader is completed, the data transmission between the RFID label and the RFID reader is carried out based on the load modulation method of full duplex communication;
in the above-mentioned S1, the method,
the tuning process of the RFID tag is as follows:
adjusting a multistage adjustable capacitor at the front end of the receiving antenna to enable the feedback voltage of the receiving antenna to be maximum;
tuning the transmitting antenna by adjusting a multistage adjustable capacitor at the front end of the transmitting antenna according to the strength of the signal read by the RFID reader as a feedback value, so that the transmitting antenna reaches an optimal matching point;
the tuning process of the RFID reader is as follows:
based on an ALOHA algorithm, the extreme value of the signal strength received by the multi-receiving antenna array is used as a tuning target value, the energy of a carrier signal generated by the RFID reader is gradually increased from low to high according to multiple stages, and when any one RFID label in the plurality of RFID labels completes self tuning under the corresponding energy, the RFID label is in a silent state until all the RFID labels complete tuning.
In the RFID-based multi-tag radio frequency identification method, after an RFID reader detects the impedance change of an RFID tag and before the RFID reader sends an inventory instruction, the RFID tag and the RFID reader are tuned to ensure normal and stable communication between the RFID tag and the RFID reader; in addition, the feedback time can be reduced by adopting a full-duplex communication mode.
In a conventional RFID protocol, an inventory command is issued when an RFID reader detects a change in impedance to begin reading a card. In the present invention, before inventoryy, automatic adjustment processing of the Q value or the resonance frequency is first performed. For the label, the receiving antenna can automatically adjust the capacitance to enable the feedback voltage to reach the maximum, so that the aim of resonance is fulfilled; the tuning of the transmitting antenna needs the matching of the RFID reader, and whether the transmitting end is tuned to reach the optimal matching point is based on the feedback information of the RFID reader: specifically, the RFID reader transmits the read signal strength back to the tag as a feedback value. For the RFID reader, it only needs to tune the receiving end: the extreme value of the received signal strength is used as the target value of tuning. Because the tuning is aimed at a mismatched circuit, namely the carrier frequency deviates from a resonance point, the tag in the invention adopts a high-Q-value circuit, when the circuit is detuned, the situation that the receiving end energy of the circuit is too small to work due to the fact that the Q value is too high and the resonance point deviates too far is likely to happen. To this end, the energy of the carrier signal generated by the RFID reader is continuously increased from low to high in several stages during the tuning process. When tuning of a certain tag is completed under a certain energy condition, the certain tag can be in a silent state and does not participate in the tuning process any more. The whole tuning process is completed by matching with an ALOHA algorithm so as to complete the calibration of multiple labels; the whole calibration process is completed in a short time; when needed, the antenna can be manually excited again to tune once after the antenna is detuned due to the situation of the position change of the label and the like.
In the tuning method between the RFID tag and the RFID reader, after the RFID reader detects the impedance change of the RFID tag and before the RFID reader sends an inventory instruction, the tuning is carried out between the RFID tag and the RFID reader, so that the normal and stable communication between the RFID tag and the RFID reader is ensured.
In S2, the load modulation method of full duplex communication is specifically that amplitude modulation is used for a downlink between the RFID tag and the RFID reader, and phase modulation is used for an uplink between the RFID tag and the RFID reader;
specifically, the method for implementing amplitude modulation in the downlink and phase modulation in the uplink between the RFID tag and the RFID reader is,
the real impedance part of the load element and the real impedance part of the load modulation element are set to be consistent in magnitude and opposite in sign, and the imaginary impedance part of the load element and the imaginary impedance part of the load modulation element are set to be consistent in magnitude and opposite in sign.
In the conventional load modulation technology, the load modulation element mostly adopts pure resistive elements, for example, one of the pure resistive elements is a 50 ohm resistor, and the other pure resistive element is open-circuited, the conventional modulation mode is amplitude modulation, which is influenced by the complexity of a signal demodulation circuit, and the configuration mode cannot realize full-duplex communication. To solve this problem, the present invention employs amplitude modulation for the downlink and phase modulation for the uplink. As shown in fig. 9, one end of the first load modulation element Z1 is connected to an antenna (which may be a transmitting antenna and a receiving antenna in an RFID tag, and may also be a multi-receiving antenna array and a multi-transmitting antenna array in an RFID reader), one end of the second load modulation element Z2 is open, the other ends of the first load modulation element Z1 and the second load modulation element Z2 are connected to GND, which represents the ground, and the specific implementation method is that the real parts of the first load modulation element Z1 and the second load modulation element Z2 are kept consistent, and the imaginary parts are opposite in sign (which can be conveniently realized by tuning), such as Z1= S + jG, Z2= S-jG (admittance form); wherein S is a real part and G is an imaginary part. Thus, at the receiving end, the decoding of the uplink can be completed by detecting the phase of the reflected signal.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (9)
1. A RFID-based multi-tag radio frequency identification system is characterized in that: the RFID reader is in radio frequency coupling with the RFID tags through the passive coupling antenna and is used for reading the RFID tags simultaneously;
the RFID tag is specifically an RFID tag with an interface and separated transmitting and receiving antennas; the RFID reader is specifically an RFID reader with an interface and separated transmitting and receiving antennas;
any RFID label comprises a receiving antenna, an energy collecting module, a first modulation and demodulation module, a transmitting antenna, a first interface module and a first data storage module; in any RFID tag, the receiving antenna is connected with the input end of the energy collecting module, and the receiving antenna is also connected with the signal input end of the first modulation and demodulation module; the output end of the energy collection module is connected with the power supply end of the first modulation and demodulation module, the signal output end of the first modulation and demodulation module is connected with the transmitting antenna, the signal output end of the first modulation and demodulation module is also connected with the input end of the first interface module, the output end of the first interface module is connected with the input end of the first data storage module, and the output end of the first data storage module is connected with the signal input end of the first modulation and demodulation module; the front ends of the receiving antenna and the transmitting antenna are respectively provided with a multi-stage adjustable capacitor.
2. The RFID-based multi-tag radio frequency identification system of claim 1, wherein: the resonance points of the receiving antenna and the transmitting antenna are different, and the Q values of the receiving antenna and the transmitting antenna are both larger than 50.
3. The RFID-based multi-tag radio frequency identification system of claim 1, wherein: the RFID tag further comprises a rectification module, and the output end of the energy collection module is also connected with the multistage adjustable capacitors of the receiving antenna and the transmitting antenna through the rectification module;
the energy collection module comprises a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a diode D1, a diode D2, a diode D3 and a diode D4; an input end of the energy collection module is arranged between one end of the capacitor C1 and the anode of the diode D2, the other end of the capacitor C1 is connected to the cathode of the diode D2 and one end of the capacitor C2, the other end of the capacitor C2 is connected to the cathode of the diode D3 and the anode of the diode D4, the cathode of the diode D4 is connected to one end of the capacitor C4, the other end of the capacitor C4 is connected to the anode of the diode D3 and the cathode of the diode D1, the anode of the diode D1 is connected to the cathode of the diode D2, one end of the capacitor C3 is connected to the cathode of the diode D1, the other end of the capacitor C3 is connected to the anode of the diode D2, the anode of the diode D2 is also connected to the digital ground, between the anode of the diode D2 and the cathode of the diode D4 is the output of the energy harvesting module.
4. The RFID-based multi-tag radio frequency identification system of claim 1, wherein: the RFID label also comprises a frequency division module, and the first modulation and demodulation module is connected with the transmitting antenna through the frequency division module; the frequency division module is specifically a frequency division circuit with an adjustable frequency division coefficient.
5. The RFID-based multi-tag radio frequency identification system of any of claims 1 to 4, wherein: the first interface module comprises any one or combination of multiple of SPI interface, IIC interface and ADC interface.
6. The RFID-based multi-tag radio frequency identification system of any of claims 1 to 4, wherein: and a hardware filtering algorithm is embedded in the first modulation and demodulation module.
7. The RFID-based multi-tag radio frequency identification system of any of claims 1 to 4, wherein: the RFID reader comprises a multi-transmitting antenna array, a multi-receiving antenna array, a second modulation and demodulation module, a second interface module, a second data storage module and a control module; the multi-receiving antenna array is connected with the signal input end of the second modulation and demodulation module, the signal output end of the second modulation and demodulation module is connected with the multi-transmitting antenna array, the signal output end of the second modulation and demodulation module is also connected with the input end of the second interface module, the output end of the second interface module is connected with the input end of the second data storage module, the output end of the second data storage module is connected with the signal input end of the second modulation and demodulation module, and the control module is bidirectionally connected with the second interface module; the front end of the multi-receiving antenna array is connected with a multi-stage adjustable capacitor in a matched mode.
8. A RFID-based multi-tag radio frequency identification method is characterized in that: applied to the RFID-based multi-tag radio frequency identification system according to any of claims 1 to 7, comprising the steps of,
s1, when the RFID reader detects the change of the impedance of the RFID label and before the RFID reader sends an inventory instruction, tuning between the RFID label and the RFID reader;
s2, after the tuning between the RFID label and the RFID reader is completed, the data transmission between the RFID label and the RFID reader is carried out based on the load modulation method of full duplex communication;
in the above-mentioned S1, the method,
the tuning process of the RFID tag is as follows:
adjusting a multistage adjustable capacitor at the front end of the receiving antenna to enable the feedback voltage of the receiving antenna to be maximum;
tuning the transmitting antenna by adjusting a multistage adjustable capacitor at the front end of the transmitting antenna according to the strength of the signal read by the RFID reader as a feedback value, so that the transmitting antenna reaches an optimal matching point;
the tuning process of the RFID reader is as follows:
based on an ALOHA algorithm, the extreme value of the signal strength received by the multi-receiving antenna array is used as a tuning target value, the energy of a carrier signal generated by the RFID reader is gradually increased from low to high according to multiple stages, and when any one RFID label in the plurality of RFID labels completes self tuning under the corresponding energy, the RFID label is in a silent state until all the RFID labels complete tuning.
9. The RFID-based multi-tag radio frequency identification method of claim 8, wherein: in S2, the load modulation method of full duplex communication is specifically that amplitude modulation is used for a downlink between the RFID tag and the RFID reader, and phase modulation is used for an uplink between the RFID tag and the RFID reader;
specifically, the method for implementing amplitude modulation in the downlink and phase modulation in the uplink between the RFID tag and the RFID reader is,
the real impedance part of the load element and the real impedance part of the load modulation element are set to be consistent in magnitude and opposite in sign, and the imaginary impedance part of the load element and the imaginary impedance part of the load modulation element are set to be consistent in magnitude and opposite in sign.
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