Radio frequency identification sensor regulated and controlled by variable capacitance diode

Abstract

The invention discloses a radio frequency identification sensor regulated and controlled by a variable capacitance diode. The radio frequency identification sensor comprises a sensor assembly, a digital regulation and control circuit attached to the sensor assembly and a Bluetooth module in signal connection with the digital regulation and control circuit, the sensor assembly comprises a dielectric substrate, a horizontal microstrip line arranged in the middle of the dielectric substrate, a heterogenous 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. The anisotropic coding structure comprises a first epsilon-type structure and a second epsilon-type structure; and the digital regulation and control circuit, the first epsilon-type structure and the second epsilon-type structure realize 8-bit digital regulation and control coding. According to the radio frequency identification tag, the amount of information which can be carried by a single coding structure is remarkably increased, miniaturization of the tag is achieved, wireless digital regulation and control of coding are achieved through the digital regulation and control circuit and the Bluetooth module, and flexibility and controllability of coding of the radio frequency identification tag are greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of sensors, and in particular to a radio frequency identification sensor controlled by a varactor diode. Background Art

[0002] RFID is an automatic identification technology that can work normally without human help. It is simple to operate and has accurate data during detection. It can adapt to a variety of complex environmental conditions. Therefore, it is widely used in military, logistics, transportation and other fields. RFID technology can identify objects and sense and transmit parameter information in the environment. Therefore, it can be used to detect strain changes in the surrounding environment. However, traditional chipless RFID sensors have the disadvantages of limited coding information and inability to flexibly adjust in the SHM field. At present, there is insufficient research on multi-parameter chipless RFID sensors that can simultaneously detect structural strain and characterize coding in the field of structural measurement and control. The amount of information that can be carried by a single coding structure is small, and there is no effective wireless control strategy for the frequency coding function of chipless RFID sensors. Summary of the invention

[0003] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a radio frequency identification sensor controlled by a varactor diode, which significantly increases the amount of information that can be carried by a single coding structure, realizes the miniaturization of the tag, and realizes wireless digital control of the coding through a digital control circuit and a Bluetooth module, greatly improving the flexibility and controllability of the radio frequency identification tag coding. In order to achieve the above-mentioned purpose and other advantages according to the present invention, a radio frequency identification sensor controlled by a varactor diode is provided, comprising:

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

[0005] The sensor assembly includes a dielectric substrate, a horizontal microstrip line arranged in the middle of the dielectric substrate, a frequency domain-based heterosexual 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;

[0006] The frequency domain-based heterogeneous coding structure includes 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 both connected to the horizontal microstrip line through a varactor diode;

[0007] 8-bit digital control coding is achieved through the digital control 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 heterosexual 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 and microstrain of the strain sensor is expressed by Formula 1:

[0010] f=-488k+1027.22222 (1)

[0011] Where f is the resonant frequency in GHz and k is the gauge 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:

[0014]

[0015] Where 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 chip capacitor C1 connected in parallel with the microcontroller chip, a second chip capacitor C2, a first chip resistor R1 and a fourth chip resistor R4, a third chip resistor R3 and a second chip resistor R2 connected in parallel with the first chip resistor R1, a fifth chip resistor R5 and a sixth chip resistor R6 connected in parallel with the fourth chip resistor R4, a first NPN transistor D1 connected in series with the second chip resistor R2, a second NPN transistor D2 connected in series with the fifth chip resistor R5, a third chip capacitor C3 connected in parallel with the third chip resistor R3 and a fourth chip capacitor C4 connected in parallel with the sixth chip resistor R6, a first chip inductor L1, a second chip inductor L2, a low-voltage linear regulator, a program download port, a serial communication port, a power input terminal and a voltage output terminal.

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

[0018] Preferably, the digital control circuit has a total of 4 voltage output terminals, which are 2 high-level output terminals and 2 common ground terminals, wherein the 2 high-level output terminals are led out by the general purpose input and output GPIO peripherals of the microcontroller MCU, and the output voltage values ​​thereof are controlled by the microcontroller MCU, and each high-level output terminal has 4 voltage output conditions;

[0019] The two high-level output terminals are connected to the positive electrodes of the two variable-capacitance diodes through metal wires, and the two common ground terminals are connected to the negative electrodes of the two variable-capacitance diodes through metal wires.

[0020] Compared with the prior art, the present invention has the following beneficial effects: the sensor tag of the present application realizes 4-bit coding of a single structure by means of a varactor diode, significantly increases the amount of information that can be carried by a single coding structure, and realizes the miniaturization of the tag. Wireless digital control of the coding is realized by combining the digital control circuit and the Bluetooth module with the sensor, which greatly improves the flexibility and controllability of the RFID tag coding. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the overall structure of the radio frequency identification sensor controlled by the varactor diode according to the present invention;

[0022] Figure 2 A schematic diagram of the structure of a radio frequency identification strain sensor portion of a radio frequency identification sensor controlled by a varactor diode according to the present invention;

[0023] Figure 3 A schematic diagram of the structure of a digital control circuit of a radio frequency identification sensor controlled by a varactor diode according to the present invention;

[0024] Figure 4 A schematic diagram of the digital control circuit part and the Bluetooth module structure of the RFID sensor controlled by the varactor diode according to the present invention;

[0025] Figure 5 A graph showing the change in the equivalent capacitance value of the BBY6502 type varactor diode of the RFID sensor controlled by the varactor diode according to the present invention as a function of the reverse voltage value on both sides of the diode;

[0026] Figure 6 The S21 parameter diagram of the sensor under four encoding conditions of the middle and low bits of the RFID sensor controlled by the varactor diode according to the present invention;

[0027] Figure 7 The S21 parameter diagram of the sensor under four high-order coding conditions of the RFID sensor controlled by the varactor diode according to the present invention;

[0028] Figure 8It is a S21 parameter diagram of the strain sensor frequency of the RFID sensor controlled by the varactor diode according to the present invention when the strain factor k changes;

[0029] Fig. 9 The figure is a fitting curve diagram showing the variation of the resonant frequency of the strain sensor of the RFID sensor controlled by the varactor diode according to the present invention with the strain factor k. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Reference Figure 1 , a variable capacitance diode controlled radio frequency identification sensor, comprising: a sensor component, a digital control circuit attached to the sensor component, and a Bluetooth module connected to the digital control circuit signal;

[0032] like Figure 2 As shown, the sensor assembly includes a dielectric substrate, a horizontal microstrip line arranged in the middle of the dielectric substrate, a frequency domain-based heterosexual 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, and the lower ends of the first ε-type structure and the second ε-type structure are both connected to the horizontal microstrip line through a varactor diode;

[0034] 8-bit digital control coding is achieved through digital control circuits, the first ε-type structure and the second ε-type structure. The dielectric substrate uses Rogers RO3003 plate with a thickness of 0.787mm, a dielectric constant of 3.003, a loss tangent ratio of 0.002, a length of 45mm and a width of 42mm. The first ε-type coding structure 1 is connected to the horizontal microstrip line 4 through the first varactor 5, and the second ε-type coding structure 2 is connected to the horizontal microstrip line 4 through the second varactor 6. The first varactor 5 and the second varactor 6 use BBY6502 type varactors, which can be equivalent to a small resistor and a capacitor in parallel. The equivalent resistance value is about 0.8Ω, and the equivalent capacitance value changes with the reverse voltage value on both sides of the diode. The relationship image is as shown Figure 5 As shown, the relationship is:

[0035]

[0036] Among them Ct is the capacitance on both sides of the diode, and Vbias is the input DC voltage.

[0037] Furthermore, 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 section and a second section, wherein the heterosexual coding structure is located in the first section, and the rectangular patch strain sensor is located in the second section.

[0038] Furthermore, the strain sensor adopts a rectangular microstrip patch, and the relationship between the resonant frequency and microstrain of the strain sensor is expressed by formula (1):

[0039] f=-488k+1027.22222 (2)

[0040] Where f is the resonant frequency in GHz and k is the gauge factor.

[0041] Furthermore, 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] The relationship between the varactor diode and the reverse voltage is expressed by formula (2):

[0043]

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

[0045] like Figure 3 As shown, the digital control circuit includes a microcontroller chip, a first chip capacitor C1 connected in parallel with the microcontroller chip, a second chip capacitor C2, a first chip resistor R1 and a fourth chip resistor R4, a third chip resistor R3 and a second chip resistor R2 connected in parallel with the first chip resistor R1, a fifth chip resistor R5 and a sixth chip resistor R6 connected in parallel with the fourth chip resistor R4, a first NPN transistor D1 connected in series with the second chip resistor R2, a second NPN transistor D2 connected in series with the fifth chip resistor R5, a third chip capacitor C3 connected in parallel with the third chip resistor R3 and a fourth chip capacitor C4 connected in parallel with the sixth chip resistor R6, a first chip inductor L1, a second chip inductor L2, a low-voltage linear regulator, a program download port, a serial communication port, a power input terminal and a voltage output terminal. The digital control circuit contains 4 voltage output terminals, including 2 high-level output terminals and 2 common ground terminals. The 2 high-level output terminals are led out by the general-purpose input and output GPIO peripherals of the microcontroller MCU. The output voltage value is controlled by the microcontroller MCU. Each high-level output terminal has 4 voltage output conditions.

[0046] The two high-level output terminals are connected to the positive electrodes of the two varactor diodes through metal wires, and the two common ground terminals are connected to the negative electrodes of the two varactor diodes through metal wires. The digital control circuit uses an external power supply, and converts the external 10V DC power supply into a 3.3V DC voltage through a TLV76033 low-voltage linear regulator, which is supplied to the microcontroller, Bluetooth module and the collector of the NPN transistor as an excitation voltage. In order to fit the shape of the sensor and reduce the impact on the sensor, the digital control circuit adopts a narrow bottom and wide top form, and leads out a wire at the lower end to control the voltage at both ends of the varactor diode in the encoding structure. The MCU packaged in QFN20 is used for design, which has the advantages of small size, low power consumption and low cost as a whole. The first chip inductor L1 and the second chip inductor L2 are used at the two high-level output terminals to isolate the high-frequency signal, so as to prevent the high-frequency signal from flowing into the digital control circuit and causing the metal wire therein to produce an unexpected frequency response, affecting the normal operation of the sensor.

[0047] like Figure 4 As shown, the Bluetooth module includes a Bluetooth chip, a 16MHz chip crystal oscillator, a fifth chip capacitor C5, a sixth chip capacitor C6, a seventh chip capacitor C7, a power input terminal, a common ground terminal, an input data RX terminal and an output data TX terminal; the serial port RX terminal of the digital control circuit is connected to the TX terminal of the Bluetooth module, and the serial port TX terminal of the digital control circuit is connected to the RX terminal of the Bluetooth module. The first chip capacitor C1 filters the input external power supply, and the second chip capacitor C2 filters the voltage output by the low-voltage linear regulator (LDO). The low-voltage linear regulator (LDO) model 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 a pulse width modulation module (PWM), and then raises the voltage to 10V through an NPN transistor, and then outputs a DC voltage through a low-pass filter. The output DC voltage range is 0 to 10V. The Bluetooth module includes an ECB01H2 Bluetooth chip, a 16MHz chip crystal oscillator, a fifth chip capacitor C5, a sixth chip capacitor C6, a seventh chip capacitor C7, a power input terminal, a common ground terminal, an input data RX terminal and an output data TX terminal. The serial port RX terminal of the FPC digital control circuit is connected to the TX terminal of the Bluetooth module, and the serial port TX terminal of the FPC digital control circuit is connected to the RX terminal of the Bluetooth module.

[0048] Furthermore, the microcontroller is supplied with a voltage signal with a peak-to-peak value of 3.3 volts and an adjustable duty cycle through a pulse width modulation module, the voltage is raised to 10 V through an NPN transistor SS8050, and a DC voltage between 0 V and 10 V is obtained through a low-pass filter, which is output to the positive electrode of the varactor diode through a high-level output port to control the capacitance value of the varactor diode.

[0049] The present invention utilizes the characteristic that the capacitance value of a varactor diode is controlled by the voltage value at both ends thereof, connects the varactor diode in series in the coding structure, and changes its capacitance value by changing the voltage value at both ends of the diode, thereby changing the resonant frequency of the coding structure. Figure 5 As shown in the figure, when the voltage value on both sides of the diode increases, the capacitance value decreases, and the resonant frequency of the encoding unit increases; when the voltage value on both sides of the diode decreases, the capacitance value increases, and the resonant frequency of the encoding unit decreases. There is a one-to-one correspondence between the voltage value on both sides of the diode and the resonant frequency of the encoding unit. Therefore, four suitable output voltage values ​​can be obtained to correspond to the four encoding states of a single encoding structure. The S21 parameter image of the sensor under different encoding conditions is shown in the figure. Figure 6 , 7 shown.

[0050] Table 1 shows the capacitance values ​​of the varactor diodes and the resonant frequencies of the encoding structures corresponding to the four output voltages.

[0051] Table 1 Output voltage corresponding to the capacitance value of the varactor diode and the resonant frequency of the coding structure

[0052]

[0053]

[0054] In the present invention, the rectangular patch strain sensor 3 is 16.2 mm long and 7.9 mm wide, and the bottom edge is connected to the horizontal microstrip line 5 through a feeder 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, its width will change. When the width increases, the resonant frequency decreases, and when the width decreases, the resonant frequency increases. Since the resonant frequency and width of the strain sensor are monotonically related, 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 k changes is as follows: Figure 8 As shown in the figure, the fitting curve of the resonant frequency changing with the gauge factor k is as follows Fig. 9 As shown, the relationship between the two is:

[0055] f=-0.43133k+1.03389

[0056] Where f is the resonant frequency in GHz and k is the gauge factor.

[0057] The number of devices and processing scales described here are used to simplify the description of the present invention, and the application, modification and variation of the present invention will be obvious to those skilled in the art.

[0058] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A radio frequency identification sensor controlled by a varactor diode, characterized in that: include: A sensor component, a digital control circuit attached to the sensor component, and a Bluetooth module connected to the digital control circuit signal; The sensor assembly includes a dielectric substrate, a horizontal microstrip line arranged in the middle of the dielectric substrate, a frequency domain-based heterosexual 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; The frequency domain-based heterogeneous coding structure includes 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 both connected to the horizontal microstrip line through a varactor diode; 8-bit digital control coding is achieved through the digital control circuit, the first ε-type structure and the second ε-type structure.

2. The RFID sensor controlled by a varactor diode as claimed in claim 1, characterized in that: 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 section and a second section, wherein the heterosexual coding structure is located in the first section, and the rectangular patch strain sensor is located in the second section.

3. The RFID sensor controlled by a varactor diode as claimed in claim 1, characterized in that: The strain sensor adopts a rectangular microstrip patch, and the relationship between the resonant frequency and microstrain of the strain sensor is expressed by formula 1: f=-488k+1027.22222 (1) Where f is the resonant frequency in GHz and k is the gauge factor.

4. The RFID sensor controlled by a varactor diode as claimed in claim 1, characterized in that: 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; The relationship between the varactor diode and the reverse voltage is expressed by formula 2: Where Ct is the capacitance on both sides of the diode, and Vbias is the input DC voltage.

5. The RFID sensor controlled by a varactor diode as claimed in claim 4, characterized in that: The digital control circuit includes a microcontroller chip, a first SMD capacitor C1 arranged between a common ground and an input power supply, a second SMD capacitor C2 arranged between the common ground and an input end of the microcontroller chip, a low voltage linear regulator LDO arranged between the first SMD capacitor C1 and the second SMD capacitor C2, a first SMD resistor R1 and a fourth SMD resistor R4 connected to an output end of the low voltage linear regulator LDO, a third SMD resistor R3 connected in parallel with the first SMD resistor R1 and the second SMD resistor R4 connected in parallel with the first SMD resistor R1, and a fourth SMD resistor R4 connected in parallel with the second SMD resistor R3. The chip resistor R2, the fifth chip resistor R5 and the sixth chip resistor R6 connected in parallel with the fourth chip resistor R4, the first NPN transistor D1 connected in series with the second chip resistor R2, the second NPN transistor D2 connected in series with the fifth chip resistor R5, the third chip capacitor C3 connected in parallel with the third chip resistor R3, the fourth chip capacitor C4 connected in parallel with the sixth chip resistor R6, and the first chip inductor L1 and the second chip inductor L2 connected in series with the two voltage output ports respectively.

6. The variable capacitance diode controlled radio frequency identification sensor as claimed in claim 5, characterized in that: The Bluetooth module includes a Bluetooth chip, a fifth chip capacitor C5 arranged between a power supply and a common ground, a sixth chip capacitor C6 and a seventh chip capacitor C7 respectively arranged between two output ports of the Bluetooth chip and the common ground, a 16MHz chip crystal oscillator arranged between the sixth chip capacitor C6 and the seventh chip capacitor C7, a TX-end output serial port connected to the serial port RX end of the digital control circuit, and an RX-end output serial port connected to the serial port TX end of the digital control circuit.

7. The RFID sensor controlled by a varactor diode as claimed in claim 6, characterized in that: The digital control circuit contains 4 voltage output terminals, including 2 high-level output terminals and 2 common ground terminals. The 2 high-level output terminals are led out by the general-purpose input and output GPIO peripherals of the microcontroller MCU. The output voltage value is controlled by the microcontroller MCU. Each high-level output terminal has 4 voltage output conditions. The two high-level output terminals are connected to the positive electrodes of the two variable-capacitance diodes through metal wires, and the two common ground terminals are connected to the negative electrodes of the two variable-capacitance diodes through metal wires.

8. The variable capacitance diode controlled radio frequency identification sensor according to claim 7, characterized in that: The digital control circuit uses an external power supply, and converts the external 10V DC power supply into a 3.3V DC voltage through a TLV76033 low-voltage linear regulator, which is then supplied to the microcontroller, Bluetooth module, and the collector of the NPN transistor as an excitation voltage.

9. The variable capacitance diode controlled radio frequency identification sensor according to claim 8, characterized in that: The microcontroller is supplied with a voltage signal with a peak-to-peak value of 3.3 volts and an adjustable duty cycle through a pulse width modulation module. The voltage is raised to 10V through the NPN transistor SS8050, and then a DC voltage between 0V and 10V is obtained through a low-pass filter. The voltage is output to the positive electrode of the varactor diode through a high-level output port to control the capacitance value of the varactor diode.

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