Chip-free RFID sensor measuring circuit

Abstract

The invention provides a chipless RFID sensor measuring circuit. The chipless RFID sensor measuring circuit comprises a signal source, a power divider, a humidity sensor tag, a low-noise amplifier, a passive mixer and a low-pass filter, a signal source generates a constant-amplitude sweep frequency signal and transmits the signal to a power divider, the signal is equally divided into two paths by the power divider, one path is transmitted to a humidity sensor label, the humidity sensor label transmits the signal with humidity information to a low-noise amplifier, and the other path is transmitted to an LO end of a passive frequency mixer to serve as a frequency mixing local oscillation signal; a signal of the humidity sensor label enters the low noise amplifier, is amplified and then is transmitted to an RF port of the passive mixer; the passive mixer mixes the signals received by the LO port and the RF port and outputs the mixed signals to the low-pass filter through the IF port, and after high-frequency clutters are filtered out, output signals are generated; output signals are read through an oscilloscope, frequency domain information of the sensor label can be obtained after data processing, and finally the humidity of the environment where the label is located is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit measurement, and in particular to a chipless RFID sensor measurement circuit. Background Art

[0002] The chipless RFID technology framework consists of three parts: tags, readers, and data processing. The reader sends a broadband interrogation signal to the tag through the transmitting antenna. The signal generates an echo signal through the resonant structure of the tag. The echo signal has a difference in amplitude and phase compared to the interrogation signal. It is transmitted to the reader through the receiving antenna. Through data processing, the specific parameters of the tag can be obtained.

[0003] Compared with traditional optical tags, chipless RFID technology has a longer recognition distance and can achieve multiple recognition. Compared with chip-based RFID, it greatly reduces the production cost. These advantages make RFID widely used in logistics, transportation, medical treatment, anti-counterfeiting technology, security protection, management and data statistics.

[0004] Scholars studying chipless RFID technology often focus on the development of tags, and the research field of readers is limited to chip tag readers, such as common access cards, campus cards, archive detectors, etc.; chipless tags are usually read by large and expensive vector network analyzers (VNA), which does not lose the accuracy of the verification process, but the cost performance is very low to be used in production and life. Therefore, the development of chipless tag readers is of research significance and is necessary and significant to promote the development and application of chipless RFID.

[0005] Tag readers can be divided into three categories according to their working methods:

[0006] The tag reader is based on frequency domain SFCW (Stepped-frequency Continuous Wave). The SFCW frequency scanning method is used to obtain the frequency domain coding information of the tag. The frequency of the reader's instantaneous query signal is the same as the received signal frequency, with low noise bandwidth and high spectral resolution. The tag reader based on frequency domain SFCW has a long scanning time, which means that the reading time is also very long, up to tens of seconds. The heterodyne method is used to demodulate the received signal, using two mixers and two voltage-controlled oscillators. In the end, the hardware cost of the entire reader reached thousands of dollars. Although its cost has dropped a lot compared to the vector network analyzer used in the laboratory, this cost price is still at a relatively high level.

[0007] Tag reader based on time-domain IR-UWB (Impulse Radio UWB). This reader uses a sub-nanosecond ultra-wideband pulse interrogation signal to read the tag, and does not require frequency scanning. The noise based on time-domain IR-UWB is high and the frequency resolution performance is not good. Because it requires high input bandwidth and high sampling rate signal processing devices, it is expensive. The Sequential Equivalent Time Approach is used to reduce the sampling rate requirements to reduce costs, but the cost without the antenna is still thousands of dollars.

[0008] Frequency-modulated Continuous Wave (FMCW) tag readers: This type of reader uses FMCW frequency scanning to read tags in the frequency domain, and its structure is similar to FMCW radar. Summary of the invention

[0009] According to the technical problems mentioned in the above background technology, a chipless RFID sensor measurement circuit is provided. The present invention can read the humidity result of the sensor through the device, without relying on the expensive vector network analyzer to measure the sensor result, thereby achieving the main purpose of low cost.

[0010] The technical means adopted by the present invention are as follows:

[0011] A chipless RFID sensor measurement circuit, comprising:

[0012] signal source, power divider, humidity sensor tag, low noise amplifier, passive mixer, and low pass filter;

[0013] The signal source generates a constant amplitude frequency sweep signal and transmits it to the power divider. The power divider divides the signal into two equal paths, one of which is transmitted to the humidity sensor tag. The humidity sensor tag transmits the signal with humidity information to the low noise amplifier, and the other is transmitted to the LO end of the passive mixer as a mixing local oscillator signal. After the signal of the humidity sensor tag enters the low noise amplifier, it is amplified and then transmitted to the RF port of the passive mixer.

[0014] The passive mixer mixes the signals received by the LO port and the RF port and outputs them to the low-pass filter through the IF port, and generates an output signal after filtering out high-frequency clutter; the output signal is read by an oscilloscope, and the frequency domain information of the sensor tag can be obtained after data processing, and finally the environmental humidity of the tag can be obtained.

[0015] Further, the signal source includes: a sawtooth wave signal generator and a voltage-controlled oscillator;

[0016] The signal source continuously and stably provides a 12V power supply voltage and a 0-12V frequency modulation voltage to the voltage-controlled oscillator, and provides the frequency modulation voltage through the sawtooth wave signal generator, so that the voltage-controlled oscillator generates an amplitude sweep frequency signal;

[0017] The sawtooth wave signal generator is provided with a bias voltage.

[0018] Furthermore, the voltage-controlled oscillator generates a 140 MHz swept frequency signal.

[0019] Furthermore, the chip model of the voltage-controlled oscillator is MAX2623, and the output signal frequency is 800MHz-1025MHz.

[0020] Furthermore, the power divider is an equal-power one-to-two power divider; the power divider couples part of the signal from the chirp signal generated by the voltage-controlled oscillator and uses it for subsequent mixer demodulation of the received signal; the power divider operates in the frequency band of 100M-2700M, and the insertion loss is less than 1dB.

[0021] Furthermore, the humidity sensor tag comprises: a resonator and a humidity-sensitive material; the resonator has an interdigital capacitor microstrip line structure with a FR4 substrate and copper cladding.

[0022] Furthermore, the passive mixer is a device that mixes multiple signals through nonlinear effects to achieve frequency conversion; when two signals with different frequencies are input into the passive mixer, the output frequency will contain the sum frequency, harmonics and difference frequency of the original two frequencies.

[0023] Furthermore, the low-pass filter is used to screen out low-frequency signals and filter out high-frequency signals; the insertion loss of the DC-100KHz working frequency band is less than 2dB, and the filtering power of the 200K-1000MHz working frequency band is greater than 60dB.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] The present invention provides a simple measurement circuit, through which the humidity result of the sensor is read. This measurement circuit has the characteristics of high speed, high precision and high sensitivity, and does not need to rely on an expensive vector network analyzer to measure the sensor result, thereby achieving the main purpose of low cost, and at the same time has the advantages of simple operation and convenient modification. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0027] Figure 1 This is a working principle diagram of the present invention.

[0028] Figure 2 This is the ADS simulation circuit diagram of the present invention.

[0029] Figure 3 It is a schematic diagram of the circuit principle of the present invention.

[0030] Figure 4 A simulation schematic diagram of a sensor tag with an accurate resonance point at 3.48 GHz is designed by HFSS software for the present invention.

[0031] Figure 5 This is a schematic diagram of setting the working bandwidth of the circuit according to the resonant frequency of the sensor tag during simulation of the present invention.

[0032] Figure 6 Under non-humidified conditions, a vector network analyzer was used to measure its S21 parameters, and its resonant frequency was 925MHz.

[0033] Figure 7 The following are the results of reading on an oscilloscope with the operating bandwidth set to 840-980MHz.

[0034] Figure 8 It is a schematic diagram of experimental results of real-time monitoring of the humidity of the experimental environment by the vector network analyzer and the test circuit of the present invention when the humidity is 25-75% RH. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings 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 should fall within the scope of protection of the present invention.

[0036] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0037] like Figure 1-Figure 3 As shown, at the same time, the reader sends and receives signals, which causes the frequencies of the two signals to be different due to the time delay in the transmission process, and then a difference frequency is generated during demodulation. The amplitude and phase information corresponding to the tag are correspondingly included in this difference frequency signal. It can be used to read frequency domain encoded tags. Compared with the other two types of working modes, it has low cost, short scanning time and low noise. The present invention provides a chipless RFID sensor measurement circuit, including: a signal source, a power divider, a humidity sensor tag, a low noise amplifier, a passive mixer and a low-pass filter.

[0038] The signal source generates a constant amplitude swept frequency signal and transmits it to the power divider. The power divider divides the signal into two equal paths, one of which is transmitted to the humidity sensor tag. The humidity sensor tag transmits the signal with humidity information to the low noise amplifier, and the other is transmitted to the LO end of the passive mixer as a mixed local oscillator signal. After the signal of the humidity sensor tag enters the low noise amplifier, it is amplified and transmitted to the RF port of the passive mixer. The passive mixer mixes the signals received by the LO port and the RF port and outputs them to the low-pass filter through the IF port, and generates an output signal after filtering out high-frequency clutter. The output signal is read by an oscilloscope, and the frequency domain information of the sensor tag can be obtained after data processing, and finally the environmental humidity of the tag is obtained.

[0039] As a preferred embodiment, in the present application, the signal source includes: a sawtooth wave signal generator and a voltage-controlled oscillator; the signal source continuously and stably provides a 12V power supply voltage and a 0-12V frequency modulation voltage to the voltage-controlled oscillator, and provides the frequency modulation voltage through the sawtooth wave signal generator, so that the voltage-controlled oscillator generates an amplitude sweep signal; the sawtooth wave signal generator is provided with a bias voltage. In the present application, the amplitude sweep signal generated by the voltage-controlled oscillator is a 140MHz sweep signal. As a preferred embodiment, in the present application, the chip model of the voltage-controlled oscillator is MAX2623, and the output signal frequency is 800MHz-1025MHz. It can be understood that in other embodiments, the output signal of the signal source can also be adjusted as needed during use.

[0040] As a preferred embodiment, in the present application, the power divider is a device that divides power, and the distribution ratio can be arbitrarily designed. On the contrary, it can also be used in the synthesis of multiple powers. The power divider is an equal power one-to-two power divider; the power divider couples part of the chirp signal generated by the voltage-controlled oscillator and uses it for subsequent mixer demodulation of the received signal; the power divider operates in the frequency band of 100M-2700M, and the insertion loss is less than 1dB.

[0041] As a preferred embodiment, in the present application, the humidity sensor tag includes: a resonator and a humidity-sensitive material; the resonator has a cross-finger capacitor microstrip line structure with a copper-clad FR4 substrate. The resonance point is set near 915M, and the S21 parameter amplitude is -10dB. Graphene oxide with a concentration of 5% is used as a humidity-sensitive material to cover the cross-finger capacitor of the resonator. Due to the special humidity-sensitive characteristics of graphene oxide, the resonance point of the sensor tag changes with the ambient humidity. After the humidity calibration is completed, the ambient humidity can be understood by reading the resonance point of the sensor tag.

[0042] Preferably, the passive mixer is a device that mixes multiple signals through nonlinear effects to achieve frequency conversion; when two signals with different frequencies are input into the passive mixer, the output frequency will contain the sum frequency, harmonics and difference frequency of the original two frequencies. In this application, it is used to convert the received high-frequency RF signal into a low-frequency signal. The double-balanced passive mixer produced by Shenghaiwei Company is selected here, model SHWFM-003100S. Its local oscillator (LO) and radio frequency (RF) input end operating frequency band is 300KHz-1000MHz, the intermediate frequency band is DC-1000MHz, and the typical frequency conversion loss is 6dB. At the same time, the reader sends and receives signals, which causes the frequencies of the two signals to be different due to the time delay in the transmission process, and then a difference frequency is generated during demodulation. The amplitude and phase information corresponding to the tag are correspondingly contained in this difference frequency signal.

[0043] As a preferred embodiment, in the present application, the low-pass filter is used to screen out low-frequency signals while filtering out high-frequency signals; the insertion loss of the DC-100KHz working frequency band is less than 2dB, and the filtering power of the 200K-1000MHz working frequency band is greater than 60dB.

[0044] Example 1

[0045] The sensor tag with precise resonance point at 3.48GHz is designed by HFSS software, and its S21 parameters are obtained by simulation as follows: Figure 4 As shown, export it to generate an S2P file; import the S2P file into the design circuit of the ADS software, and obtain the output signal of the sensor tag after it is imported into the circuit of the present invention through joint simulation; read the time point of the distortion notch of the output signal, and use the formula to deduce the location of the sensor tag resonance point. During the simulation, the working bandwidth of the circuit is set according to the resonance frequency of the sensor tag. We set it to 1-5GHz, such as Figure 5 The time point of the lowest distortion notch voltage is 16.2us, 10us is the starting point of the cycle, (16.2-10) / 10=0.62, that is, the resonance time point is at 0.62 of the working cycle 10us. The sweep frequency of the signal source is of equal amplitude, so we can determine that the resonance point is at 0.62 of 1-5GHz, 4*0.62+1=3.48, that is, the resonance point of the sensor tag is 3.48GHz. Through this simulation process, it can be proved that during the simulation process of this circuit, the circuit of the present invention can accurately read the resonance point in the S parameter to obtain the humidity information carried by the sensor tag.

[0046] Example 2

[0047] The humidity sensor tag was made and its S21 parameter was measured using a vector network analyzer under non-humidified conditions. Its resonant frequency was 925MHz, as shown in Figure 6 As shown; the humidity sensor tag is connected to the reading circuit of the present invention, and the working bandwidth is set to 840-980MHz. The result read from the oscilloscope is as follows Figure 7 As shown. The starting point of the cycle is selected as the voltage rise starting point 448us. The resonance time point is the lowest point of the distortion notch voltage 752us, the difference is 304us, accounting for 0.608 of a working cycle of 500us, and the working bandwidth is 140MHz. The resonance point of the sensor is calculated to be 840+140*0.608=925.12, which is only 0.12MHz error from the measurement result of the vector network analyzer;

[0048] After setting the humidity environment, the humidification experiment was started, and the humidity was controlled at 25-75% RH. In order to compare the vector network analyzer with the test circuit in the present invention, a humidity sensor tag was connected to both sets of equipment at the same time, and a hygrometer was used to monitor the humidity of the experimental environment in real time. The experimental results are shown in Figure 2. Figure 8 As shown;

[0049] At humidity values ​​(unit: %RH): 27, 33, 41, 55, 62, 66 and 72, the S values ​​are read from the vector network analyzer and the measurement circuit of the present invention respectively. 21 The maximum error of the parameter resonance point does not exceed 3MHz. The figure shows a phenomenon: the error is large in a high humidity environment and small in a low humidity environment. The reason for this phenomenon is that as the humidity increases, the resonance characteristics of the sensor deteriorate, the amplitude of the resonance point decreases, the distortion notch of the output signal of the measurement circuit decreases, and the difficulty of reading increases.

[0050] After the simulation and experiment are completed, it is proved that the measurement circuit of the present invention is feasible in two aspects:

[0051] 1. When the humidity environment is static and unchanged, the measurement circuit of the present invention can accurately measure the resonance point frequency of the sensor tag;

[0052] 2. When the humidity environment changes dynamically, the measurement circuit of the present invention can measure the changing resonance point frequency of the sensor tag in real time, and complete the dynamic reading and humidity monitoring of the humidity sensor after humidity calibration.

[0053] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0054] In the above embodiments of the present invention, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0055] In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. Among them, the device embodiments described above are only schematic. For example, the division of the units can be a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of units or modules, which can be electrical or other forms.

[0056] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple units. Some or all of the units may be selected according to actual needs to achieve the purpose of the present embodiment.

[0057] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0058] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions for a computer device (which can be a personal computer, a server or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), mobile hard disk, magnetic disk or optical disk and other media that can store program codes.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A chipless RFID sensor measurement circuit, characterized in that: include: signal source, power divider, humidity sensor tag, low noise amplifier, passive mixer, and low pass filter; The signal source generates a constant amplitude frequency sweep signal and transmits it to the power divider. The power divider divides the signal into two equal paths, one of which is transmitted to the humidity sensor tag. The humidity sensor tag transmits the signal with humidity information to the low noise amplifier, and the other is transmitted to the LO end of the passive mixer as a mixing local oscillator signal. After the signal of the humidity sensor tag enters the low noise amplifier, it is amplified and then transmitted to the RF port of the passive mixer. The passive mixer mixes the signals received by the LO port and the RF port and outputs them to the low-pass filter through the IF port, and generates an output signal after filtering out high-frequency clutter; the output signal is read by an oscilloscope, and the frequency domain information of the sensor tag can be obtained after data processing, and finally the environmental humidity of the tag can be obtained.

2. A chipless RFID sensor measurement circuit according to claim 1, characterized in that: The signal source includes: a sawtooth wave signal generator and a voltage-controlled oscillator; The signal source continuously and stably provides a 12V power supply voltage and a 0-12V frequency modulation voltage to the voltage-controlled oscillator, and provides the frequency modulation voltage through the sawtooth wave signal generator, so that the voltage-controlled oscillator generates an amplitude sweep frequency signal; The sawtooth wave signal generator is provided with a bias voltage.

3. A chipless RFID sensor measurement circuit according to claim 2, characterized in that: The voltage-controlled oscillator generates a 140 MHz sweep frequency signal.

4. A chipless RFID sensor measurement circuit according to claim 2 or 3, characterized in that: The chip model of the voltage-controlled oscillator is MAX2623, and the output signal frequency is 800MHz-1025MHz.

5. The chipless RFID sensor measurement circuit according to claim 1, characterized in that: The power divider is an equal-power one-to-two power divider; the power divider couples part of the chirp signal generated by the voltage-controlled oscillator and uses it for subsequent mixer demodulation of the received signal; the power divider operates in the frequency band of 100M-2700M, and the insertion loss is less than 1dB.

6. The chipless RFID sensor measurement circuit according to claim 1, characterized in that: The humidity sensor tag comprises: a resonator and a humidity-sensitive material; the resonator has an interdigital capacitor microstrip line structure with a FR4 substrate and copper cladding.

7. The chipless RFID sensor measurement circuit according to claim 1, characterized in that: The passive mixer is a device that mixes multiple signals through nonlinear effects to achieve frequency conversion; when two signals with different frequencies are input into the passive mixer, the output frequency will contain the sum frequency, harmonics and difference frequency of the original two frequencies.

8. The chipless RFID sensor measurement circuit according to claim 1, characterized in that: The low-pass filter is used to screen out low-frequency signals and filter out high-frequency signals; the insertion loss of the DC-100KHz working frequency band is less than 2dB, and the filtering power of the 200K-1000MHz working frequency band is greater than 60dB.

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