A variable capacitance diode regulated radio frequency identification sensor

Abstract

The application discloses a variable capacitance diode regulated radio frequency identification sensor, which comprises a sensor component, a digital regulation circuit attached to the sensor component and a Bluetooth module connected with the digital regulation circuit; the sensor component comprises a dielectric substrate, a horizontal microstrip line arranged at the middle part of the dielectric substrate, a heterogeneous coding structure fixed on the dielectric substrate and located at one side of the horizontal microstrip line and a strain sensor fixed on the dielectric substrate and located at the other side of the horizontal microstrip line; the heterogeneous coding structure comprises a first epsilon type structure and a second epsilon type structure; the digital regulation circuit, the first epsilon type structure and the second epsilon type structure realize 8-bit digital regulation coding. According to the application, the information amount carried by a single coding structure is significantly increased, the miniaturization of the label is realized, the wireless digital regulation of the coding is realized through the digital regulation circuit and the Bluetooth module, and the flexibility and controllability of the radio frequency identification label coding are greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sensors, in particular to a variable capacitance diode regulated radio frequency identification sensor. BACKGROUND

[0002] RFID is an automatic identification technology, which can work normally without manual help, and the operation is simple, the data is accurate, and it can adapt to various complex environment conditions, so it is widely used in military, logistics, transportation and other fields. RFID technology can identify objects, and can also sense and transmit parameter information in the environment, so it can be applied to detect strain changes in the surrounding environment. However, the traditional chipless RFID sensor has the disadvantages of limited coding information and cannot be flexibly regulated in the field of SHM. At present, there is not enough research on multi-parameter chipless RFID sensors that can detect structural strain and represent codes in the field of structural measurement and control. The amount of information that a single coding structure can carry is small, and there is no effective wireless control strategy for the frequency coding function of the chipless RFID sensor. SUMMARY

[0003] In view of the deficiencies in the prior art, the present application aims to provide a variable capacitance diode regulated radio frequency identification sensor, which significantly increases the amount of information that a single coding structure can carry, realizes the miniaturization of the label, and realizes wireless digital regulation of the code through a digital regulation circuit and a Bluetooth module, greatly improving the flexibility and controllability of the radio frequency identification label code. In order to achieve the above-mentioned purposes and other advantages according to the present application, a variable capacitance diode regulated radio frequency identification sensor is provided, comprising:

[0004] A sensor assembly, a digital regulation circuit attached to the sensor assembly, and a Bluetooth module signal connected to the digital regulation circuit;

[0005] The sensor assembly comprises a dielectric substrate, a horizontal microstrip line arranged at the middle part of the dielectric substrate, a hetero-coding structure based on frequency domain fixed on the dielectric substrate and located on one side of the horizontal microstrip line, and a strain sensor fixed on the dielectric substrate and located on the other side of the horizontal microstrip line;

[0006] The hetero-coding structure based on frequency domain comprises a first ε-type structure and a second ε-type structure, and the lower ends of the first ε-type structure and the second ε-type structure are connected to the horizontal microstrip line through variable capacitance diodes;

[0007] 8-bit digital regulation coding is realized through the digital regulation circuit, the first ε-type structure and the second ε-type structure.

[0008] Preferably, the horizontal microstrip line extends along the length direction of the dielectric substrate, and the horizontal microstrip line divides the dielectric substrate into a first partial interval and a second partial interval, wherein the opposite coding structure is located in the first partial interval, and the rectangular patch strain sensor is located in the second partial interval.

[0009] Preferably, the strain sensor adopts a rectangular microstrip patch, and the relationship between the resonant frequency of the strain sensor and the micro-strain is expressed by formula (1) as follows:

[0010] (1)

[0011] wherein f is the resonant frequency, unit: GHz, and k is the strain factor.

[0012] Preferably, the digital control circuit, the first ε-type structure and the second ε-type structure constitute a digital control coding unit, and the voltages at both ends of the first ε-type structure and the second ε-type structure are controlled by the output port of the digital control circuit.

[0013] The relationship between the varactor diode and the reverse voltage is expressed by formula (2) as follows:

[0014] (2)

[0015] wherein Ct is the capacitance on both sides of the diode, and Vbias is the input DC voltage.

[0016] Preferably, the digital control circuit includes a microcontroller chip, a first patch capacitor C1 and a second patch capacitor C2 connected in parallel with the microcontroller chip, a first patch resistor R1 and a fourth patch resistor R4, a third patch resistor R3 and a second patch resistor R2 connected in parallel with the first patch resistor R1, a fifth patch resistor R5 and a sixth patch resistor R6 connected in parallel with the fourth patch resistor R4, a first NPN triode D1 connected in series with the second patch resistor R2, a second NPN triode D2 connected in series with the fifth patch resistor R5, a third patch capacitor C3 connected in parallel with the third patch resistor R3, and a fourth patch capacitor C4 connected in parallel with the sixth patch resistor R6, a first patch inductor L1, a second patch inductor L2, a low-voltage linear voltage regulator, a program download port, a serial communication port, a power input end and a voltage output end.

[0017] Preferably, the Bluetooth module includes a Bluetooth chip, a 16MHz patch crystal oscillator, a fifth patch capacitor C5, a sixth patch capacitor C6, a seventh patch capacitor C7, a power input end, a common ground end, an input data RX end and an output data TX end; the serial port RX end of the digital control circuit is connected to the TX end of the Bluetooth module, and the serial port TX end of the digital control circuit is connected to the RX end of the Bluetooth module.

[0018] Preferably, the digital regulation circuit includes four voltage output terminals, two high-level output terminals and two common ground terminals, wherein the two high-level output terminals are led out by the general input and output (GPIO) peripherals of the microcontroller (MCU), and the output voltage values are controlled by the microcontroller (MCU), and each high-level output terminal has four voltage output conditions.

[0019] The two high-level output terminals are connected to the anodes of the two varactor diodes through wires, and the two common ground terminals are connected to the cathodes of the two varactor diodes through wires.

[0020] Compared with the prior art, the sensor tag part of the present application realizes 4-bit coding by means of a single varactor diode, significantly increases the amount of information that can be carried by a single coding structure, and realizes the miniaturization of the tag. Through the combination of the digital regulation circuit and the Bluetooth module with the sensor, wireless digital regulation of the coding is realized, greatly improving the flexibility and controllability of the radio frequency identification tag coding. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 FIG. 1 is a schematic diagram of the overall structure of a varactor diode regulated radio frequency identification sensor according to the present application;

[0022] Figure 2 FIG. 2 is a schematic diagram of the radio frequency identification strain sensor part of a varactor diode regulated radio frequency identification sensor according to the present application;

[0023] Figure 3 FIG. 3 is a schematic diagram of the digital regulation circuit structure of a varactor diode regulated radio frequency identification sensor according to the present application;

[0024] Figure 4 FIG. 4 is a schematic diagram of the digital regulation circuit part and Bluetooth module structure of a varactor diode regulated radio frequency identification sensor according to the present application;

[0025] Figure 5 FIG. 5 is a graph of the equivalent capacitance value of a BBY6502 type varactor diode according to the present application varying with the reverse voltage value on both sides of the diode;

[0026] Figure 6 FIG. 6 is a S21 parameter graph of the sensor under four coding conditions of the middle and low bits of a varactor diode regulated radio frequency identification sensor according to the present application;

[0027] Figure 7 FIG. 7 is a S21 parameter graph of the sensor under four coding conditions of the high bits of a varactor diode regulated radio frequency identification sensor according to the present application;

[0028] Figure 8The diagram shows the S21 parameters of the strain sensor frequency of the radio frequency identification sensor regulated by the varactor diode according to the present invention as the strain factor k changes.

[0029] Figure 9 This is a fitted curve of the strain sensor resonant frequency of the radio frequency identification sensor regulated by the varactor diode according to the present invention as a function of the strain factor k. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Reference Figure 1 A varactor diode-controlled radio frequency identification sensor includes: a sensor assembly, a digital control circuit attached to the sensor assembly, and a Bluetooth module signal-connected to the digital control circuit.

[0032] like Figure 2 As shown, the sensor assembly includes a dielectric substrate, a horizontal microstrip line disposed in the middle of the dielectric substrate, a frequency domain-based anisotropic coding structure fixed on the dielectric substrate and located on one side of the horizontal microstrip line, and a strain sensor fixed on the dielectric substrate and located on the other side of the horizontal microstrip line.

[0033] The frequency domain-based heterogeneous coding structure includes a first ε-type structure and a second ε-type structure. The lower ends of both the first ε-type structure and the second ε-type structure are connected to a horizontal microstrip line through varactor diodes.

[0034] An 8-bit digital control encoding is achieved through a digital control circuit, a first ε-type structure, and a second ε-type structure. The dielectric substrate is a 0.787mm thick Rogers RO3003 material with a dielectric constant of 3.003, a loss tangent of 0.002, a length of 45mm, and a width of 42mm. The first ε-type encoding structure 1 is connected to the horizontal microstrip line 4 via a first varactor diode 5, and the second ε-type encoding structure 2 is connected to the horizontal microstrip line 4 via a second varactor diode 6. The first varactor diode 5 and the second varactor diode 6 are BBY6502 type varactor diodes, which can be equivalent to a small resistor and a capacitor in parallel. The equivalent resistance is approximately 0.8Ω, and the equivalent capacitance changes with the reverse voltage across the diodes, as shown in the graph below. Figure 5 As shown, the relationship is:

[0035] (1)

[0036] where C t is the capacitance on both sides of the diode, and Vbias is the input DC voltage.

[0037] Further, the horizontal microstrip line extends along the length direction of the dielectric substrate, and the horizontal microstrip line divides the dielectric substrate into a first partial interval and a second partial interval, wherein the opposite coding structure is located in the first partial interval, and the rectangular patch strain sensor is located in the second partial interval.

[0038] Further, the strain sensor adopts a rectangular microstrip patch, and a relationship between the resonant frequency of the strain sensor and the micro-strain is expressed by formula (1) as follows:

[0039] (2)

[0040] where f is the resonant frequency, the unit is GHz, and k is the strain factor.

[0041] Further, the digital control circuit, the first ε-type structure, and the second ε-type structure constitute a digital control coding unit, and the voltages at both ends of the first ε-type structure and the second ε-type structure are controlled by the output port of the digital control circuit.

[0042] A relationship between the varactor diode and the reverse voltage is expressed by formula (3) as follows:

[0043] (3)

[0044] where Ct is the capacitance on both sides of the diode, and Vbias is the input DC voltage.

[0045] where Ct is the capacitance on both sides of the diode, and Vbias is the input DC voltage.

[0046] As Figure 3As shown, the digital control circuit includes a microcontroller chip, a first patch capacitor C1 connected in parallel with the microcontroller chip, a second patch capacitor C2, a first patch resistor R1 and a fourth patch resistor R4, a third patch resistor R3 and a second patch resistor R2 connected in parallel with the first patch resistor R1, a fifth patch resistor R5 and a sixth patch resistor R6 connected in parallel with the fourth patch resistor R4, a first NPN triode D1 connected in series with the second patch resistor R2, a second NPN triode D2 connected in series with the fifth patch resistor R5, a third patch capacitor C3 connected in parallel with the third patch resistor R3, and a fourth patch capacitor C4 connected in parallel with the sixth patch resistor R6, a first patch inductor L1, a second patch inductor L2, a low-voltage linear voltage regulator, a program download port, a serial communication port, a power input terminal, and a voltage output terminal. The digital control circuit includes four voltage output terminals, two high-level output terminals and two common ground terminals. The two high-level output terminals are connected to the general input and output GPIO peripherals of the microcontroller MCU, and the output voltage value is controlled by the microcontroller MCU. Each high-level output terminal has four voltage output conditions.

[0047] The two high-level output terminals are connected to the anodes of the two varactor diodes through wires, and the two common ground terminals are connected to the cathodes of the two varactor diodes through wires. The digital control circuit uses external power supply, and converts the external 10V DC power supply into 3.3V DC voltage through TLV76033 type low-voltage linear voltage regulator, which is supplied to the microcontroller, Bluetooth module and NPN triode collector as excitation voltage. The digital control circuit is attached to the sensor shape and reduces the influence on the sensor. The circuit adopts the form of narrow at the bottom and wide at the top, and leads wires at the bottom to control the voltage across the varactor diodes in the coding structure. The MCU is designed in QFN20 package, which has the advantages of small size, low power consumption and low cost. The first patch inductor L1 and the second patch inductor L2 are used in the two high-level output terminals to isolate high-frequency signals, so as to avoid the inflow of high-frequency signals into the digital control circuit, which causes unexpected frequency response of the metal wires and affects the normal work of the sensor.

[0048] The Bluetooth module includes a Bluetooth chip, a 16MHz patch crystal oscillator, a fifth patch capacitor C5, a sixth patch capacitor C6, a seventh patch capacitor C7, a power input end, a common ground end, an input data RX end and an output data TX end; the serial port RX end of the digital control circuit is connected with the TX end of the Bluetooth module, and the serial port TX end of the digital control circuit is connected with the RX end of the Bluetooth module. The first patch capacitor C1 filters the input external power supply, the second patch capacitor C2 filters the voltage output by the low-voltage linear voltage regulator (LDO), the model of the low-voltage linear voltage regulator (LDO) is TLV76033, which can convert the external 10V DC power supply into a 3.3V DC voltage for use as an excitation voltage in the circuit. The MCU outputs a voltage signal with a peak-to-peak value of 3.3 volts and an adjustable duty cycle through the pulse width modulation module (PWM), then raises the voltage to 10V through the NPN transistor, and then outputs a DC voltage through the low-pass filter, and the output DC voltage ranges from 0 to 10V. The Bluetooth module includes an ECB01H2 Bluetooth chip, a 16MHz patch crystal oscillator, a fifth patch capacitor C5, a sixth patch capacitor C6, a seventh patch capacitor C7, a power input end, a common ground end, an input data RX end and an output data TX end, the serial port RX end of the FPC digital control circuit is connected with the TX end of the Bluetooth module, and the serial port TX end of the FPC digital control circuit is connected with the RX end of the Bluetooth module.

[0049] Further, the supply microcontroller outputs a voltage signal with a peak-to-peak value of 3.3 volts and an adjustable duty cycle through the pulse width modulation module, raises the voltage to 10V through the NPN transistor SS8050, and then obtains a DC voltage between 0V and 10V through the low-pass filter, and outputs the DC voltage through the high-level output port to the positive electrode of the varactor diode to control the capacitance value of the varactor diode.

[0050] The application utilizes the characteristic that the capacitance value of the varactor diode is controlled by the voltage value across the two ends of the varactor diode, connects the varactor diode in series in the encoding structure, changes the capacitance value of the diode by changing the voltage value across the two ends of the diode, and further changes the resonant frequency of the encoding structure. Figure 5 As shown in the figure, when the voltage value across the two ends of the diode increases, the capacitance value decreases, and the resonant frequency of the encoding unit increases; when the voltage value across the two ends of the diode decreases, the capacitance value increases, and the resonant frequency of the encoding unit decreases, and the voltage value across the two ends of the diode and the resonant frequency of the encoding unit have a one-to-one correspondence, so four encoding states of a single encoding structure can be obtained by obtaining four appropriate output voltage values. The S21 parameter image of the sensor under different encoding conditions is shown in Figure 6 、 7 .

[0051] Table 1 is the capacitance value of the varactor diode corresponding to the four output voltages and the resonant frequency of the encoding structure.

[0052] Table 1 Resonant frequency of varactor diode corresponding to output voltage and code structure

[0053] Encoding 0001 0010 0100 1000 voltage V bias (V)]]> 3.42 3.02 2.17 1.3 Diode capacitance C t (pF) 6 7 10 15 High encoding resonance frequency (GHz) 1.7925 1.8450 1.9050 1.9425 Low encoding resonance frequency (GHz) 2.6625 2.6250 2.5725 2.5275

[0054] The rectangular patch strain sensor 3 in the present application has a length of 16.2 mm and a width of 7.9 mm, and the bottom edge is connected to the horizontal microstrip line 4 through a feed line with a length of 8 mm and a width of 0.5 mm. There is a good linear relationship between the resonant frequency of the strain sensor and its width. When the sensor is subjected to stress along the width direction, the width will change. When the width increases, the resonant frequency decreases, and when the width decreases, the resonant frequency increases. Since the resonant frequency of the strain sensor and the width are in a monotonic relationship, that is, there is a one-to-one correspondence between the resonant frequency and the strain, the current strain can be obtained by detecting the resonant frequency of the strain sensor. The S21 image of the strain sensor frequency when the strain factor changes is as shown in k Figure 8 k Figure 9

[0055] ;

[0056] wherein f is the resonant frequency, unit: GHz; k is the strain factor.

[0057] The number of devices and the scale of processing described herein are used to simplify the present application, and the application, modification and change of the present application are obvious to those skilled in the art.

[0058] Although the embodiments of the present application have been disclosed as above, it is not limited to the application and modification listed in the specification and embodiments, and can be fully applied to various fields suitable for the present application, and other modifications can be easily realized by those skilled in the art, therefore the present application is not limited to specific details and the figures shown and described herein, without departing from the general concept defined by the claims and the equivalent scope.​​​​

Claims

1. A varactor diode regulated radio frequency identification sensor, characterized by, The application relates to a sensor assembly, a digital control circuit attached to the sensor assembly, and a Bluetooth module connected to the digital control circuit. The sensor assembly comprises a medium substrate, a horizontal microstrip line arranged at a middle part of the medium substrate, a frequency-domain-based opposite coding structure fixed to the medium substrate and located at one side of the horizontal microstrip line, and a strain sensor fixed to the medium substrate and located at the other side of the horizontal microstrip line. The Bluetooth module comprises a Bluetooth chip, a fifth chip capacitor C5 arranged between a power supply and a common ground, sixth and seventh chip capacitors C6 and C7 respectively arranged between two output ports of the Bluetooth chip and the common ground, a 16 MHz chip crystal oscillator arranged between the sixth and seventh chip capacitors C6 and C7, a TX end output serial port connected to a RX end of the digital control circuit, and an RX end output serial port connected to a TX end of the digital control circuit. The digital control circuit comprises four voltage output ends, two high-level output ends and two common ground ends, wherein the two high-level output ends are led out from a general input and output GPIO peripheral of a microcontroller MCU, the voltage values output by the two high-level output ends are controlled by the microcontroller MCU, and each high-level output end has four voltage output conditions. The two high-level output ends are connected to the anodes of two varactor diodes through metal wires, and the two common ground ends are connected to the cathodes of the two varactor diodes through metal wires. The microcontroller outputs a voltage signal with a peak-to-peak value of 3.3 volts and a duty cycle that can be adjusted through a pulse width modulation module, the voltage is lifted to 10 V through an NPN triode SS8050, a direct current voltage between 0 V and 10 V is obtained through a low-pass filter, and the voltage is output to the anode of the varactor diode through the high-level output port to control the capacitance value of the varactor diode. The frequency-domain-based opposite coding structure comprises a first epsilon structure and a second epsilon structure, and the lower ends of the first and second epsilon structures are connected to the horizontal microstrip line through the varactor diodes. The 8-bit digital control coding is realized through the digital control circuit, the first and second epsilon structures. The horizontal microstrip line extends along the length direction of the medium substrate, and the horizontal microstrip line divides the medium substrate into a first partial interval and a second partial interval, wherein the opposite coding structure is located in the first partial interval, and the rectangular patch strain sensor is located in the second partial interval.

2. A varactor diode regulated radio frequency identification sensor as claimed in claim 1, characterized in that, The strain sensor adopts a rectangular microstrip patch, and the relationship between the resonant frequency of the strain sensor and the micro-strain is expressed by formula one as follows:

3. The varactor diode regulated RF identification sensor of claim 1, wherein, Wherein f is the resonant frequency, the unit is GHz, and k is the strain factor. （1） The digital control circuit, the first and second epsilon structures constitute a digital control coding unit, and the voltages at the two ends of the first and second epsilon structures are controlled by the output port of the digital control circuit.

4. The varactor diode regulated RF identification sensor of claim 1, wherein, The relationship between the varactor diode and the reverse voltage is expressed by formula two as follows: Wherein Ct is the capacitance on both sides of the diode, and Vbias is the input direct current voltage. （2） ​ 5. A varactor diode regulated radio frequency identification sensor as claimed in claim 4, characterized in that, The digital regulation circuit includes a microcontroller chip, a first patch capacitor C1 arranged between a common ground and an input power supply, a second patch capacitor C2 arranged between the common ground and an input end of the microcontroller chip, a low-voltage linear voltage regulator LDO arranged between the first patch capacitor C1 and the second patch capacitor C2, a first patch resistor R1 and a fourth patch resistor R4 connected to an output end of the low-voltage linear voltage regulator LDO, a third patch resistor R3 and a second patch resistor R2 connected in parallel with the first patch resistor R1, a fifth patch resistor R5 and a sixth patch resistor R6 connected in parallel with the fourth patch resistor R4, a first NPN triode D1 connected in series with the second patch resistor R2, a second NPN triode D2 connected in series with the fifth patch resistor R5, a third patch capacitor C3 connected in parallel with the third patch resistor R3, a fourth patch capacitor C4 connected in parallel with the sixth patch resistor R6, and a first patch inductor L1 and a second patch inductor L2 connected in series with two voltage output ports respectively.

6. The varactor diode regulated RF identification sensor of claim 1, wherein, The digital regulation circuit uses external power supply, converts an external 10V DC power supply into a 3.3V DC voltage through a TLV76033 type low-voltage linear voltage regulator, and supplies the microcontroller, the Bluetooth module and the NPN triode collector as an excitation voltage.

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