A wireless passive dual-parameter sensor

Abstract

The present invention relates to the technical field of temperature and humidity detection, and discloses a wireless passive dual-parameter sensor, comprising a spiral inductor, a forked capacitor, a substrate, a through hole, a moisture-sensitive material, and a temperature-sensitive material. The forked capacitor is composed of a first forked capacitor and a second forked capacitor. The first forked capacitor and the second forked capacitor are respectively connected in series with different turns of the same inductor through a through hole arranged on the substrate, so as to form a first resonant circuit and a second LC resonant circuit as a first resonant circuit and a second LC resonant circuit respectively. The temperature-sensitive material and the moisture-sensitive material are respectively coated on the surface of the first forked capacitor and the second forked capacitor in the forked capacitor. When the external environment temperature or humidity changes, the temperature-sensitive material or the moisture-sensitive material causes the dielectric constant to change due to the temperature or humidity change, causing the resonant frequency of the corresponding part to change, and the wireless passive detection of temperature and humidity is realized through the functional relationship between the resonant frequency and the temperature and humidity.

Description

Technical Field

[0001] The invention relates to the technical field of temperature and humidity detection, and mainly to a wireless passive sensor, in particular to a wireless passive dual-parameter sensor. Background Art

[0002] At present, traditional temperature or humidity sensors are mostly single-parameter detection and require an external power supply, which leads to problems such as large sensor size, inconvenience for circuit integration design, limited working time, and frequent battery replacement.

[0003] In order to meet the measurement of temperature and humidity data in the prior art, some studies have proposed wireless passive LC sensors, which can use changes in inductance or capacitance to detect the parameters to be measured. When the LC sensor approaches the target object, the parameter to be measured will cause the value of the inductance or capacitance to change, resulting in a change in the oscillation frequency of the LC circuit. This frequency change can be detected by the receiver by transmitting data through the principle of inductive near-field coupling, thereby achieving the measurement of the distance or other parameters of the target object. The current wireless passive multi-parameter sensor structure combines different capacitors with multiple inductors to achieve multi-parameter measurement.

[0004] However, the structures of the wireless passive multi-parameter sensors reported so far are mostly composed of multiple inductors and multiple capacitors. However, the multiple inductors in the structure will produce mutual inductance and parasitic effects, thus causing electromagnetic interference. This crosstalk will lead to low sensitivity and poor stability of the sensor. The instability of the output signal may even lead to erroneous measurement results or sensor failure to work properly.

[0005] To solve the above problems, the prior art uses a single inductor and multiple different types of capacitors. However, in this structure, due to the use of different types of capacitors, when the measurement environment changes, the corresponding resonant frequency variation range will overlap, and the frequencies corresponding to the measured parameters are difficult to distinguish, resulting in difficulty in decoupling the subsequent reading of some signals. In addition, the use of multiple different types of capacitors cannot take into account the characteristics of each capacitor to optimize performance such as anti-interference or sensitivity. At the same time, it will increase the overall volume of the sensor, limit the application of the sensor in small and enclosed spaces, and reduce the stability and anti-interference ability of the sensor. A single inductor and capacitors of the same type also have problems such as frequency overlap, difficulty in decoupling signals of different parameters, difficulty in manufacturing, and large area.

[0006] In order to solve the above problems, it is urgent to develop dual-parameter LC sensors that can measure temperature and humidity simultaneously to meet the needs of environmental monitoring accuracy and diversity. Such innovations will open up new prospects for the development of sensor technology and enable it to better serve various fields of human production and life. Summary of the invention

[0007] In response to the above problems, the present application proposes a wireless passive dual-parameter sensor, which forms a temperature and humidity sensitive unit by connecting different parts of a bifurcated capacitor in series with different turns of the same inductor. Based on the law of capacitance change caused by the dielectric constant of the temperature-sensitive and humidity-sensitive materials when the temperature and humidity change, the first LC resonant circuit and the second LC resonant circuit respond to changes in ambient temperature and humidity, which solves the crosstalk problem of multi-parameter measurement to a certain extent, realizes the function of measuring the dual parameters of temperature and humidity, and has high test sensitivity.

[0008] The invention discloses a wireless passive dual-parameter sensor, comprising a spiral inductor, a forked capacitor, a substrate, a through hole, a moisture-sensitive material, and a temperature-sensitive material. The forked capacitor is composed of a first forked capacitor and a second forked capacitor, wherein the first forked capacitor and the second forked capacitor have different forked logarithms. The first forked capacitor and the second forked capacitor are respectively connected in series with different turns of the same inductor through a through hole arranged on the substrate, so as to form a first resonant circuit and a second LC resonant circuit as a first resonant circuit and a second LC resonant circuit respectively. The temperature-sensitive material and the moisture-sensitive material are respectively coated on the surface of the first forked capacitor and the second forked capacitor in the forked capacitor. In combination with the method for realizing wireless passive detection of sensitive materials with different dielectric constants under temperature or humidity and LC resonant circuits, the functions of dual-parameter measurement, frequency isolation, etc. are realized by using one inductor, the crosstalk problem generated by the dual inductors in multi-parameter measurement is solved, and the sensitivity and anti-interference ability of the sensor are improved to a certain extent.

[0009] Sensors using this structure can achieve temperature and humidity measurement, high-sensitivity, passive wireless detection and low-power temperature and humidity detection, and solve many problems in materials, reliability, repeatability and production costs, thereby providing support and guarantee for the industrial application of wireless passive multi-parameter sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram of the structure of a wireless passive dual-parameter sensor;

[0011] Figure 2 It is a schematic diagram of the bifurcated capacitor structure;

[0012] Figure 3 A hardware design flow chart of a wireless passive dual-parameter sensor readout system;

[0013] Figure 4 A software design flow chart of a wireless passive dual-parameter sensor readout system;

[0014] Figure 5 It is a schematic diagram of the change of dielectric constant of different formulations of polyimide / molybdenum disulfide composite materials;

[0015] Figure 6It is a schematic diagram of the change of dielectric constant of different formulations of PVDF and PZT ceramic composite materials;

[0016] Figure 7 It is a schematic diagram of the humidity dielectric constant results of different formulations of substrate materials;

[0017] Figure 8 It is a schematic diagram of the temperature dielectric constant results of different formulations of substrate materials;

[0018] Fig. 9 is the number of turns of different inductors S 11 Parameter comparison diagram:

[0019] Fig.10 1. is a logarithmic comparison diagram of different numbers of forks of the first and second interdigital capacitors;

[0020] Fig.11 This is a comparison diagram of the inductance difference between the first and second LC resonant circuits;

[0021] Fig.12 This is a schematic diagram of the test results at different humidity levels at the same temperature;

[0022] Fig.13 This is a schematic diagram of the test results at different temperatures under the same humidity.

[0023] Description of reference numerals:

[0024] 1 spiral inductor, 2 forked capacitor, 3 moisture sensitive material, 4 temperature sensitive material, 5 substrate, 6 through hole, 21 first forked capacitor, 22 second forked capacitor, 200 common plate, 211 first independent plate, 221 second independent plate. DETAILED DESCRIPTION

[0025] The following is a detailed description of the embodiments of the present application in conjunction with the accompanying drawings. In the absence of conflict, the features of the following embodiments and implementations can complement or combine with each other.

[0026] The present invention discloses a wireless passive dual-parameter sensor, comprising a spiral inductor 1, a forked capacitor 2, a substrate 5, a through hole 6, a moisture-sensitive material 3, and a temperature-sensitive material 4. The forked capacitor 2 is composed of a first forked capacitor 21 and a second forked capacitor 22, wherein the number of forked fingers of the first forked capacitor 21 and the second forked capacitor 22 is different. The first forked capacitor 21 and the second forked capacitor 22 share a common plate 200, and the common plate 200 is connected to the end point of the innermost circle of the spiral inductor; the first independent plate 211 of the first forked capacitor 21 is connected to the end point of the outermost circle through the through hole 6 to form a first LC resonant circuit; the second independent plate 221 of the second forked capacitor 22 is connected to part of the inductance of the spiral inductor 1 through the through hole 6 to form a second LC resonant circuit; the temperature-sensitive material 4 and the moisture-sensitive material 3 are respectively coated on the surface of the first forked capacitor 21 and the second forked capacitor 22 in the forked capacitor 2. When the external environment temperature or humidity changes, the dielectric constant of the temperature-sensitive material 4 or the humidity-sensitive material 3 changes due to the change in temperature or water content, causing the capacitance value of the first finger capacitor 21 or the second finger capacitor 22 to change, which in turn causes the resonant frequency of the LC resonant circuit to change, and then wireless passive detection of temperature or humidity is achieved by measuring the resonant frequency.

[0027] Return loss (S 11 ) The smaller the value, the smaller the reflection loss of the signal during transmission and the higher the transmission efficiency.

[0028] Furthermore, the spiral inductor 1 and the bifurcated capacitor 2 in the LC resonant circuit are respectively arranged on both sides of the substrate 5, as shown in FIG. Figure 1 As shown. The main sensitive device of the dual-parameter sensor in this application is designed as a bifurcated capacitor structure, which has the following functions:

[0029] (1) Ensure the contact area during measurement and reduce the response time: Under the two-dimensional structure of the film, the temperature field is relatively uniform, and the temperature-sensitive material 4 can be placed underneath without affecting the actual measurement effect. The humidity-sensitive material 3 needs to have a large enough contact area to fully contact with the water molecules in the external environment. The spiral inductor 1 and the bifurcated capacitor 2 are on the same surface. The spiral inductor 1 will occupy the contact area between the sensitive material and the external environment, which directly affects the response time of the sensor.

[0030] (2) Prevent short circuit and ensure sensor stability: Since the spiral inductor 1 of the present application has important functions such as forming two LC resonant circuits and transmitting signals, and the sensor measures two parameters, temperature and humidity, if the spiral inductor 1 and the bifurcated capacitor 2 are in the same plane, water droplets condense under high humidity and cause the spiral inductor 1 to short circuit, which seriously affects the robustness of the sensor. If the spiral inductor 1 and the bifurcated capacitor 2 are not in the same plane, the sensor can avoid water droplet condensation and extend the service life of the sensor.

[0031] In order to reduce the size of the sensor and improve the anti-interference performance of the sensor, the spiral inductor 1 is optionally a planar spiral structure, and the number of turns of the inductor coil is 9 to 11. Compared with the traditional cylindrical inductor, the planar spiral structure inductor occupies a small space due to the two-dimensional spiral structure, and is suitable for thin-film sensors; compared with the weak coupling inductor, the planar spiral structure inductor does not need to change the spacing to reduce the coupling effect, reduces the height of the reading coil, optimizes the layout of the magnetic field, and makes the magnetic field mainly concentrated inside and above the plane, reducing the magnetic interference to adjacent electronic components.

[0032] The total number of turns of the spiral inductor 1 coil of the sensor of the present application directly affects the quality of the wireless sensing signal of the sensor. Preferably, the number of turns of the planar spiral inductor 1 coil is set to 9 to 11 turns. Since there is parasitic capacitance between the coils that make up the spiral inductor 1, when the number of turns of the spiral inductor 1 coil increases, the parasitic capacitance will increase. Excessive parasitic capacitance will reduce the self-resonant frequency (SRF) of the inductor, limit its high-frequency performance, and cause the resonant frequencies of the two parameters in different detection ranges to overlap, affecting the parameter measurement of the sensor. Too many turns means a longer wire length, resulting in higher resistance, increased power loss and heat generation, and also increases the volume and weight of the inductor, affecting the portability and installation space of the sensor, and affecting the stability and reliability of the inductor and surrounding circuits.

[0033] At the same time, the spiral inductor 1 of the sensor also bears the function of coupling with the external circuit to realize signal transmission, and the inductance value of the spiral inductor 1 is one of the key factors that determine the above functions. Fewer turns will lead to low inductance value and low quality factor (Q), which will increase energy loss during reading, making the sensor exhibit capacitive behavior outside the predetermined operating frequency range, affecting normal signal transmission and processing. Therefore, setting the inductor to a planar spiral inductor and setting the number of coil turns to 9 to 11 turns can effectively reduce parasitic capacitance, enhance signal transmission efficiency, and improve Q and overall inductance stability, which not only reduces the size of the sensor but also improves the stability and anti-interference of the dual-parameter sensor. The inductance value of the spiral inductor 1 with 9 to 11 turns can be flexibly adjusted to ensure the return loss (S 11 ) The parameter temperature frequency varies between 10~150 MHz, and the humidity frequency varies between 200~300MHz.

[0034] Furthermore, the first LC resonant circuit has 6 to 8 more turns of inductance than the second LC resonant circuit. In the measurement of this dual-parameter sensor, the two parameters are connected in series with the spiral inductor 1 through the first forked capacitor 21 and the second forked capacitor 22 respectively with different turns, forming the first LC resonant circuit and the second LC resonant circuit respectively, and the first LC resonant circuit has 6 to 8 more turns of inductance than the second LC resonant circuit. It can not only avoid the mutual inductance effect caused by the two inductors, but also enhance the quality factor of the sensor and enhance the reliability of the sensor. Therefore, the first LC resonant circuit has 6 to 8 more turns of inductance than the second LC resonant circuit, and the wireless passive dual-parameter sensor can more effectively realize the accurate measurement of different environmental parameters while reducing the risk of frequency overlap and parameter cross-interference. This design improves the dual-parameter discrimination capability, accuracy and reliability of the sensor, making it more suitable for application scenarios of multi-parameter monitoring.

[0035] The first LC resonant circuit has 6 to 8 more turns of inductance than the second LC resonant circuit. The purpose is:

[0036] (1) Constructing the first LC resonant circuit and the second LC resonant circuit corresponding to the temperature and humidity: the bifurcated capacitor 2 is connected in series with different turns of the same inductor, so that one spiral inductor 1 can complete the functions of two LC resonant circuits, reducing the volume of the sensor. At the same time, it has the function of wireless coupling and signal transmission from the outside world as an antenna. This structure reduces the length of the wire, reduces resistance and power loss, reduces heat generation, and enhances the quality and stability of the signal.

[0037] (2) Avoid mutual inductance interference: The forked capacitor 2 is connected in series with the spiral inductor 1 with different turns, so that one inductor can complete the functions of two LC resonant circuits, avoiding the interference caused by the mutual inductance effect of multiple inductors. At the same time, the resonant frequency variation range of the first LC resonant circuit and the second LC resonant circuit can be accurately adjusted by controlling the number of turns of the inductance difference in the two LC resonant circuits, avoiding the phenomenon of overlapping measurement ranges caused by changes in temperature and humidity, thereby improving the reliability and accuracy of the sensor.

[0038] (3) Reduce the interference of parasitic effects: Parallel plate-like parasitic capacitance will be generated between metal coils, and multiple inductors will increase the parasitic capacitance exponentially, which will cause the resonant frequency of the temperature and humidity parts to shift, affecting the accuracy of the measurement. By connecting the different turns of the spiral inductor 1 in series with the bifurcated capacitor 2, the number of inductors and the wire length of the bifurcated capacitor 2 can be reduced, thereby reducing the parasitic capacitance between the metal wires and improving the accuracy of the sensor measurement. At the same time, the volume and weight of the sensor are also reduced, which increases the application scenarios of the sensor, such as in small and enclosed environments.

[0039] Furthermore, the forked capacitor 2 is composed of a lower forked electrode of the first forked capacitor 21 and an upper forked electrode of the second forked capacitor 22 to form a common electrode plate 200, such as Figure 2 As shown. The staggered arrangement design of the electrodes helps to reduce the influence of parasitic inductance and parasitic resistance. Parasitic inductance is mainly generated by the current loop between the electrodes. The forked structure generated based on the common electrode plate 200 reduces the influence of parasitic inductance due to shortening the current path length. Since the electrode is made of highly conductive material and the shortest current conduction path, it helps to further reduce the influence of parasitic inductance and parasitic resistance, and enhances the reliability of sensor measurement data. Since the electric fork poles are staggered, the distance between them is closer than that of traditional parallel capacitor elements, which helps to reduce the value of parasitic inductance. At the same time, the staggered electrode arrangement can provide a larger capacitance value in a relatively small physical size. Even under the smallest capacitance change, signal changes can be generated, that is, the sensor has high resolution. And the capacitance value is proportional to the electrode surface area and inversely proportional to the spacing between the forked fingers in the electrode. The forked capacitor 2 can effectively increase the electrode surface area per unit area by optimizing the parameters such as the forked finger quantity and the forked finger spacing of the electrode, thereby increasing the capacitance value, improving the capacitance density, and reducing the volume of the entire LC sensor. The above structure can improve the sensitivity and reliability of the sensor and reduce the volume of the sensor.

[0040] Preferably, selecting the interdigital capacitors to form the interdigital capacitor 2 has the following effects:

[0041] (1) Accurate measurement of temperature and humidity: If a parallel plate capacitor is used in the present application, the substrate 5 will expand or contract due to temperature changes, causing changes in the parallel plate capacitor, which will increase the measurement error of the sensor. However, the capacitance value of the bifurcated capacitor 2 is not affected by the volume change of the substrate 5, thereby ensuring the accuracy of the sensor measurement.

[0042] (2) Reduce the response time of the sensor: The sensitive part of the parallel capacitor is placed between the two electrode plates, which causes the contact area of ​​the sensitive material with the external environment to decrease. When the temperature or humidity changes, it cannot respond quickly, resulting in low sensitivity and long response time of this type of sensor. However, the bifurcated capacitor 2 in this application can directly contact the external environment, ensuring that the contact area between the sensitive unit and the external environment is increased by 60%, the temperature unit can change faster, and the humidity unit can combine with water molecules faster, reducing the response time of the sensor. At the same time, it can prevent too many water molecules from contacting the LC resonant circuit, thereby ensuring the stability and life of the LC resonant circuit.

[0043] Preferably, the first forked capacitor 21 and the second forked capacitor 22 of the forked capacitor 2 differ by 1 to 2 pairs. The capacitance value of the forked capacitor 2 is most obviously affected by the dielectric constant of the sensitive material on the forked finger and its own structural parameters. By the difference in the number and dielectric constant of 1 to 2 pairs of forked fingers, the resonant frequencies of the two environmental parameters can be accurately adjusted and distinguished. This distinction allows the sensor to couple with an external reading device at different frequencies to achieve sensitive response to different environmental parameters. Since the circuit composed of each forked capacitor 2 will resonate with a specific frequency signal emitted from the outside according to its capacitance value, effective signal coupling is achieved. Adjusting the number of 1 to 2 pairs of forked fingers changes the difference in capacitance value between the first forked capacitor 21 and the second forked capacitor 22, which can achieve minimized error and lowest cross-sensitivity (a change in one parameter is mistakenly considered to be a change in another parameter), causing a change in the resonant frequency, and can ensure a high degree of accuracy and reliability during the measurement process. In addition, by changing the number of 1-2 pairs of interdigital pairs, the parasitic parameters in the capacitor are affected, especially the parasitic resistance and parasitic inductance in the loop are reduced, thereby reducing energy loss and improving the efficiency of signal coupling, and improving the Q factor of the LC circuit, thereby achieving higher efficiency and clearer signal recognition during signal coupling. Therefore, the dual parameter differentiation capability and sensor transmission efficiency can be enhanced.

[0044] Preferably, the function of the bifurcated capacitor 2 is:

[0045] (1) Further realize the isolation of temperature and humidity frequency for subsequent reading: In this application, it can avoid the mixing of resonant frequency when the temperature decreases and the humidity increases, that is, the temperature resonant frequency variation range and the humidity variation range have an overlapping part, so as to ensure the normal operation of the sensor and ensure the S 11 The parameter temperature frequency varies between 10 and 150 MHz, and the humidity frequency varies between 200 and 300 MHz, which is convenient for the readout system to read out.

[0046] (2) Reduce resistance and improve signal quality. This application reduces the requirement for two different capacitors in dual-parameter measurement, shortens the length of the wire in the circuit, reduces the total resistance in the sensor, reduces the energy consumption of signal transmission, and improves the signal transmission quality of the sensor.

[0047] Optionally, the spiral inductor 1 and the forked capacitor 2 are made of silver, and a protective film is coated on their surface. In wireless sensors, the conductivity of the material directly affects the quality of energy transmission and signals. Silver has a very high electrical conductivity. When the spiral inductor 1 and the forked capacitor 2 are made of silver, the parasitic resistance in the circuit is reduced, the quality factor of the sensor is improved, and thus the efficiency and response speed of the sensor are improved. At the same time, silver has good thermal stability. Under changing ambient temperatures, compared with commonly used copper materials, the electrical conductivity and low resistance properties of silver materials remain relatively stable, which is critical to ensure that the sensor can work reliably under different environmental conditions.

[0048] In order to extend the life and corrosion resistance of the sensor, a protective film is applied on the surface of silver to reduce the influence of humidity and temperature on the physical properties of the circuit such as conductivity and resistance, and resist the corrosion of the circuit by acid, alkali and other environments, thereby improving the anti-interference performance and corrosion resistance of the sensor and extending the life of the sensor. The spiral inductor 1 of the dual-parameter sensor in this application has the important role of signal transmission and forming two LC resonant circuits. This component is exposed to an environment with frequent changes in humidity and temperature, and the circuit is easily corroded. The application of a protective film can protect the inductor device, improve the corrosion resistance, and extend the life and stability of the sensor.

[0049] Optionally, the humidity sensitive material 3 is made of a polyimide (PI) / molybdenum disulfide (MoS2) composite material. This solution proposes a humidity sensitive sensor based on a polyimide / molybdenum disulfide composite material, which is specially designed for a dual-parameter sensor with a bifurcated capacitor 2 structure, and can effectively meet the requirements of dielectric constant changing with humidity and strong temperature stability. In order to achieve this goal, the humidity sensitive material 3 must have high humidity sensitivity, temperature stability, and appropriate and uniform thickness, and at the same time have high process repeatability to reduce production costs and improve measurement accuracy, and is suitable for mass production.

[0050] In order to achieve the temperature stability of the humidity-sensitive material 3, polyimide is used as a humidity-sensitive unit, which has the characteristics of small temperature coefficient, chemical corrosion resistance, heat resistance, and good high-temperature dielectric stability. Its coating process is compatible with the photoresist process of silicon materials. The film thickness and uniformity can be precisely controlled by adjusting the spin coating speed and time, thereby ensuring that the humidity-sensitive material 3 can fully cover the surface of the second interdigital capacitor 22.

[0051] Furthermore, in order to enhance the humidity-sensitive properties of the humidity-sensitive material 3, its humidity-sensitive performance is improved by doping MoS2. There are a large number of dangling bond defects in the edge atoms of MoS2, which enable it to combine with oxygen atoms in water molecules. At the same time, the internal porous structure of polyimide absorbs water molecules in the air through the capillary effect, increasing the volume and surface area of ​​the nanocomposite material. As the humidity increases, the adsorbed water molecules gradually aggregate and condense into droplets, entering the gap between the bifurcated electrodes. Under the action of the internal electric field, the water molecules are polarized and decomposed into protons (H+) and hydroxide ions (OH-), thereby inducing electrolytic conduction, resulting in an increase in the relative dielectric constant (ε) of the humidity-sensitive material 3.

[0052] The molecular structure of polyimide contains benzene rings and imide bonds, which provide rigidity and chemical stability, and reduce the influence of temperature on the dielectric constant of humidity-sensitive material 3. In addition, during the preparation of polyimide, the step-by-step temperature increase treatment of the polyimide precursor polyamic acid film can fully dehumidify the water molecules between the MoS2 molecular layers, while increasing the molecular layer spacing, ensuring that the final MoS2 polyimide composite humidity-sensitive film has excellent hygroscopic properties.

[0053] Compared with the MoS2-doped graphene oxide-based humidity-sensitive material 3 in the prior art, the polyimide-based composite film of this solution has the advantages of high sensitivity and low cost in humidity measurement. The preparation methods of traditional graphene oxide, such as the Hummers and Offman methods, are complex, time-consuming and dangerous, which limits their large-scale production. The MoS2-doped polyimide-based composite film takes into account the dielectric humidity-sensitive properties, low cost and repeatable and highly consistent manufacturing process, so that the humidity-sensitive unit of the sensor has fast response, fast recovery and high measurement accuracy. To ensure the S of the sensor 11 The parameter temperature frequency varies between 10 and 150 MHz, and the humidity frequency varies between 200 and 300 MHz, which is convenient for the readout system to read out.

[0054] Optionally, the temperature-sensitive material 4 is a composite material made of polyvinylidene fluoride (PVDF) and lead zirconate titanate (PZT) powder. The present application proposes a composite temperature-sensitive material based on PVDF and PZT powder, which is specially designed for a temperature-sensitive unit with a bifurcated capacitor 2 structure and can effectively meet the requirements of dielectric constant changing with temperature and strong humidity stability.

[0055] In order to achieve this goal, the temperature-sensitive material 4 must have high temperature sensitivity, humidity stability and appropriate and uniform thickness, and at the same time have high process repeatability to reduce production costs and improve measurement accuracy, and is suitable for mass production. In order to realize the temperature unit by high temperature sensitivity, further enhance the effective isolation of the temperature change range and humidity change range. The composite material of PVDF and PZT powder is selected, because PZT powder realizes polarization through the displacement of ions and electrons. When the temperature rises, the internal thermal energy of the material increases, and the movement speed of molecules, ions and electrons also increases, resulting in changes in the dielectric constant. PVDF is a polymer with a high dielectric constant and a natural dipole. The rise in temperature will cause the thermal vibration of its polymer chain to increase, further increase the change in the dielectric constant, can effectively realize the resonant frequency separation of temperature and humidity, and ensure sensitivity to temperature, and enhance the sensitivity of the sensor. At the same time, the PVDF matrix provides structural support and flexibility, while the PZT powder gives the material excellent piezoelectric properties. By mixing these two materials in a specific ratio, not only can they exert high temperature sensitivity, but also produce a synergistic effect, which can effectively reduce the impact of humidity on the temperature-sensitive material 4, thereby improving the measurement accuracy, stability and anti-interference ability of the temperature-sensitive unit of the sensor. 11 The parameter temperature frequency varies between 10 and 150 MHz, and the humidity frequency varies between 200 and 300 MHz, which is convenient for subsequent readout systems to read out.

[0056] The PVDF / PZT composite material is coated on the temperature sensitive unit of the present application, i.e., the first interdigital capacitor 21, by spin coating, spray coating, hot pressing, etc. The PVDF / PZT composite material maintains stable performance over a wide temperature range, which enables it to work under extreme environmental conditions, such as high or low temperature environments. At the same time, the material is insensitive to humidity changes, further improving its adaptability in different environments.

[0057] Optionally, the substrate 5 is made of a composite material whose dielectric constant changes very little or even zero with respect to temperature changes or humidity changes, which can ensure the stability and accuracy of the sensor output. Based on the working principle of the LC sensor, its resonant frequency is determined by the inductance (L) and capacitance (C) in the circuit. In the present application, the forked capacitor 2 is in direct contact with the substrate 5, and the capacitance value (C) is directly affected by the dielectric constant (ε) of the substrate 5, which is closely related to the electrical properties of the material. If the dielectric constant of the substrate 5 changes with temperature or humidity, the capacitance value will also change accordingly.

[0058] The substrate 5 is made of a composite material whose dielectric constant changes very little or even zero with respect to temperature changes or humidity changes. Its functions are as follows:

[0059] (1) Ensure the measurement accuracy of the sensor: This application detects the temperature or humidity parameters by changing the resonant frequency. If the dielectric constant of the substrate 5 fluctuates greatly with temperature or humidity, the resonant frequencies of the first and second resonant circuits will change, increasing the measurement error of the sensor. A composite material whose dielectric constant changes very little or even zero with temperature or humidity changes is used to reduce the measurement error of the sensor.

[0060] (2) It can protect circuit safety and extend the life of the sensor: The circuit inside the sensor is particularly sensitive to temperature changes. The increase or decrease in temperature may cause the voltage and current inside the circuit to be unstable, which in turn causes circuit failure or damage. For example, capacitors may experience dielectric breakdown at high temperatures, while inductors may change their magnetic properties due to heat diffusion. Using materials with a temperature coefficient close to zero can effectively control the fluctuations of these electrical parameters caused by temperature changes. When the electrical properties of the substrate 5 (such as the dielectric constant) remain stable, the voltage and current in the circuit will also be more stable, thereby reducing the failure rate and improving the reliability and durability of the circuit.

[0061] In order to realize the effective readout of the sensor of this application, a wireless passive dual-parameter sensor readout system is designed, including hardware and software parts:

[0062] The hardware part includes a single-chip microcomputer control module, a direct digital frequency synthesis (DDS) sweep signal generation module, a reading coil, a signal decoupling module, a data cache module, a solution module, and a display module.

[0063] The single-chip control module controls the DDS sweep frequency signal generation module to generate a sweep frequency signal, which is coupled to the wireless passive dual-parameter sensor through the reading coil. The coupled signal is decoupled by the signal decoupling module to obtain the temperature and humidity frequency signals, which are converted by analog-to-digital converters (AD) respectively. The temperature and humidity are calculated by the data cache module and the solution module and displayed by the display module, such as Figure 3 shown.

[0064] (1) Single-chip microcomputer control module: The signal generation module is controlled by the MSP430F149 main control chip to cyclically generate a 0~350MHz sweep frequency signal.

[0065] (2) DDS frequency sweep signal generation module: Using the AD9011 signal generation module, it can generate a 0~500 MHz frequency signal, which is suitable for the sensor resonant frequency variation range of 10~300 MHz in this application.

[0066] (3) The reading coil is a cylindrical coil with 2 to 4 turns and a length of 10 to 12 cm, which is made of copper wire and connected to bandpass filter 1 and bandpass filter 2 through a small precision A-type connector (SMA) interface.

[0067] (4) Signal decoupling module: A temperature band-pass filter and a humidity band-pass filter are used to filter out the resonant frequency band of 10-150 MHz with temperature information and the resonant frequency band of 200-300 MHz with humidity information, respectively, to extract and distinguish the information of the two parameters. The extracted frequency bands are then sampled by AD according to the following formula and converted into voltage values.

[0068]

[0069] V IN V is the analog voltage value to be converted by the AD module. R+ V is the reference positive voltage value of the AD module. R− is the negative reference voltage value of the AD module. The formula can be understood as dividing the reference voltage into 4095 parts. The input voltage can account for as many parts as possible. The reference voltage is selected by default as V R+ is AVCC, V R− Take 0 V. This is convenient for subsequent solution modules to process.

[0070] The signal decoupling module is the core component of this reading system. It can distinguish the temperature resonance change range and the humidity resonance change range. At the same time, this also requires that the temperature and humidity change ranges of the dual-parameter sensor must be clearly distinguished, further highlighting the importance of the forked capacitor 2, the different number of turns of the same spiral inductor 1 in series, the temperature-sensitive material 4, and the dielectric properties of the humidity-sensitive material 3 for subsequent readings.

[0071] (5) Data cache module: The circuit is designed using an external FIFOIDT7207 as a data buffer. The FIFOIDT7207 chip usually has a timing control interface that can help synchronize data transmission and avoid data loss or errors during data transmission. At the same time, the data transmission processing task can be transferred from the main processor to the FIFOIDT7207 chip, which can reduce the burden on the main processor and enable it to focus more on other tasks, improving the overall performance of the system. FIFOIDT7207 can smooth data traffic and avoid data loss or overflow during data transmission. When the data source generates data at a rate that temporarily exceeds the receiver's processing rate, the FIFOIDT7207 can temporarily store excess data to prevent data loss.

[0072] (6) Calculation module: The digital signal processor (DSP) chip Texas Instruments TMS320 series has powerful arithmetic and signal processing capabilities and is suitable for various complex signal processing algorithms. The algorithm is used to compare the voltage values ​​after AD sampling at adjacent frequencies to obtain the maximum voltage and the corresponding frequency, and the resonant frequency is brought into the corresponding temperature or humidity and frequency fitting function (the frequency within 10~150 MHz belongs to the temperature detection range, and the frequency within 200~300MHz belongs to the humidity detection range).

[0073] (7) Display module: The temperature and humidity values ​​obtained in the solution module are displayed through the LCD1602 display module.

[0074] The software algorithm is deployed on the TMS320 series of DSP chips from Texas Instruments. The algorithm-related processes are as follows: Figure 4 shown.

[0075] Software part: Start to initialize the ADC module, AD9910 module, LCD1602 module, and then display the temperature unit and humidity unit and prompts. Then continue to give the control word to the AD9910 module for frequency sweeping. After completing the 0~400 MHz frequency sweep, start the ADC once, use the ADC single channel for multiple sampling, and sample 64 times in the range of 10~150 MHz and 200~300 MHz respectively, and obtain the voltage value corresponding to the sampling point in each range. Then compare the voltage values ​​at adjacent frequencies in each range to obtain the frequency corresponding to the maximum voltage, and substitute the corresponding frequency into the fitted frequency and temperature (10~150MHz), humidity (200~300 MHz) function to obtain the corresponding temperature and humidity values. LCD1602 displays the corresponding temperature and humidity. The above process from displaying the temperature unit and humidity unit and prompts to displaying the corresponding temperature and humidity is continuously cycled until the measurement is stopped.

[0076] The working principle of the present application is: when the external environment temperature and humidity change, the dielectric constant of the sensitive material changes due to the change in temperature or water content, causing the capacitance values ​​of the first fork-finger capacitor 21 and the second fork-finger capacitor 22 to change accordingly, causing the resonant frequency of the LC resonant circuit to change. Since the fork index pairs of the first fork-finger capacitor 21 and the second fork-finger capacitor 22 of the forked capacitor 2 are different, the number of turns of the inductor connected in series is different, and the dielectric constant of the coated sensitive material is different, the effect of dual parameter measurement and frequency isolation can be effectively achieved, and then the wireless passive detection of temperature and humidity can be achieved by measuring the resonant frequency.

[0077] The method of using this application is: place the sensor of this application in the environment to be tested, and place the reading coil in the reading system directly above the sensor of this application, with a distance of 0.5~1.5 cm between the two. After 10~30 seconds, the current temperature and humidity can be directly read through LCD1602.

[0078] In order to illustrate the best effect that can be achieved by the parameters of the sensor of the present application, and to effectively solve the problems of crosstalk and poor signal quality existing in the existing technology of multi-inductance and multi-parameter measurement, Example 1 and Comparative Examples 1 to 6 are set up for comparison. The above sensors are all printed on a new substrate 5 by a microelectronic circuit printer, and sensors with different structural parameters are obtained after drying on a heating table.

[0079] Embodiment 1:

[0080] In this embodiment, the parameter design of the sensor has an important influence on the anti-interference, sensitivity and other performances of the sensor. The specific parameters of the sensor are as follows:

[0081] (1) Parameters of spiral inductor 1: outer diameter is 27.9 mm, inner diameter is 12.7 mm, line width is 0.2 mm, line spacing is 0.4 mm, thickness is 0.03 mm, and number of turns is 10.

[0082] (2) Parameters of the forked capacitor 2: The fork length of the first forked capacitor 21 is 10 mm, the fork width of the first forked capacitor 21 is 0.1 mm, the fork thickness of the first forked capacitor 21 is 0.03 mm, the distance between the two forks of the first forked capacitor 21 is 0.025 mm, the number of fork pairs of the first forked capacitor 21 is 9 pairs, and the first independent electrode plate 211 is 22.3 mm; the common electrode plate 200 is 22.3 mm; the fork length of the second forked capacitor 22 is 10 mm, the fork width of the second forked capacitor 22 is 0.4 mm, the fork thickness of the second forked capacitor 22 is 0.03 mm, the distance between the two forks of the second forked capacitor 22 is 0.025 mm, the number of fork pairs of the second forked capacitor 22 is 7 pairs, and the second independent electrode plate 221 is 18.3 mm.

[0083] (3) Number of turns of the same inductor connected in series: the common electrode 200 is connected to the innermost turn end point of the spiral inductor 1; the first independent electrode plate 211 of the first interdigital capacitor 21 is connected to the outermost turn end point of the spiral inductor 1 through a through hole to form a first LC resonant circuit; the second independent electrode plate of the second interdigital capacitor is connected to the spiral inductor through a through hole and the third turn (counting from the inside to the outside) of the spiral inductor 1 to form a second LC resonant circuit; the first LC resonant circuit has 7 more turns than the second LC resonant circuit.

[0084] (4) Substrate 5: Made of 6.5 g of barium sulfate (BaSO4), 2 g of titanium dioxide (TiO2) powder and 6 g of glass (BaO-B2O3-SiO2-Al2O3) powder.

[0085] (5) Humidity-sensitive material 3: made of 0.1 g polyimide and 0.2 g molybdenum disulfide nanosheet powder.

[0086] (6) Thermosensitive material 4: A composite material made of PVDF powder and PZT powder in a mass ratio of 1:4.

[0087] In order to improve the sensitivity of humidity test in dual-parameter sensor and ensure that the resonant frequency of humidity varies within 200-300 MHz, the configuration of humidity-sensitive material 3 was debugged, such as Figure 5 shown.

[0088] The inventors have found through research that when the humidity ranges from 10 to 90% RH and PI:MoS2 is 1:0, the dielectric constant changes little, making it difficult to detect slight humidity changes, resulting in low sensor resolution; when PI:MoS2 is 0:1, the starting frequency of the dielectric constant is low and cannot reach the humidity starting frequency, i.e., 200 MHz, and the sensor humidity module cannot complete the full range measurement of 10 to 90% RH; when PI:MoS2 is 1:1, the dielectric constant only changes from 35 to 55, with little change, and the starting humidity resonance frequency can only reach 100 MHz, and the humidity resonance frequency varies from 100 to 180 MHz, which overlaps with the temperature variation range, and humidity detection cannot be completed; when PI:MoS2 is 1:3, the humidity ranges from 50 to 90% RH, the dielectric constant remains basically unchanged, and humidity testing cannot be completed; when PI:MoS2 is 1:2, the humidity ranges from 10 to 90 %RH, the dielectric constant changes from 50 to 85, and the change trend is nearly linear. The initial dielectric constant of 50 can ensure that the starting resonant frequency of humidity reaches 200 MHz, and the change range is within 200~300 MHz.

[0089] The configuration process of the above-mentioned humidity sensitive material 3 is composed of PI / MoS2 composite material:

[0090] (1) Weigh 0.1 g PI and 0.2 g MoS2 powder respectively and place them in 20 mL N,N-dimethylformamide (DMF) mixed solvent. Stir the solution at 40 °C and 1000 r / min for 30 min until they are completely fused.

[0091] (2) The uniformly mixed PI / MoS2 composite material obtained above is spin-coated onto the surface of the second interdigital capacitor 22 by spin coating, and then dried at 100°C for 30 min.

[0092] In order to improve the sensitivity of temperature test in dual parameter sensor and ensure the resonant frequency of temperature varies within 10~150 MHz, the configuration of temperature sensitive materials is debugged, such as Figure 6 shown.

[0093] The inventors found that when the temperature ranges from 20 to 80 °C, the ratio of PVDF to PZT is 1:1, the dielectric constant only changes from 400 to 100, and the temperature sensitivity of the sensor is only 2.7 KHz / °C. When the ratio of PVDF to PZT is 1:1, the dielectric constant only changes from 800 to 2000, and the temperature sensitivity of the sensor is only 9.3 KHz / °C. When the ratio of PVDF to PZT is 1:4, the dielectric constant ranges from 1000 to 7000, but when the ratio of PVDF to PZT is 1:4, the dielectric constant ranges from 1000 to 9000, and a higher dielectric constant change can be achieved with a small ratio of PVDF to PZT. When the ratio of PVDF to PZT is 1:4, the temperature sensitivity of the sensor can be 345.67 KHz / °C, which is 128 times higher than the sensitivity of other formulas, and its range of change is within 10 to 150 MHz.

[0094] The configuration process of the temperature-sensitive material 4 made of PVDF and PZT into a composite material:

[0095] (1) Weigh 5 g of PZT powder and 1 g of PVDF powder, add them to 30 mL of DMF solution, and stir them magnetically at 1500 r / min for 30 min at 50 °C to obtain a PZT-based / PVDF composite solution;

[0096] (2) The prepared PZT-based / PVDF composite solution was spin-coated onto the surface of the first interdigital capacitor 21 (temperature-sensitive unit) and then placed in a drying oven at 100° C. for 30 min.

[0097] In order to stabilize the dielectric constant of the substrate 5 in the dual-parameter sensor, the configuration of the substrate material was debugged and the humidity stability test was performed. Figure 7 Temperature stability test, such as Figure 8 shown.

[0098] The inventors have found through research that when the temperature ranges from 20 to 80°C and the humidity ranges from 10 to 90%RH, and the ratio of barium sulfate, titanium dioxide powder and glass powder is 65:20:6 (by mass), the dielectric constant temperature stability and humidity stability of the substrate 5 are better than those of other configurations, and the influence of the substrate 5 on the parameter test of the sensor can be minimized.

[0099] The above substrate 5 is a composite material made of barium sulfate, titanium dioxide powder and glass powder.

[0100] (1) Weigh 6.5 g of barium sulfate, 2 g of titanium dioxide powder and 6 g of glass powder respectively, add the weighed raw materials into 100 mL of anhydrous ethanol to dissolve, add the mixture into a sand mill and wet grind for 1-2 hours until the particle size D50 is about 2.5 um, and then dry it in a vacuum drying oven at 150 °C for 30 min;

[0101] (2) adding 5 wt% (weight percentage) of polyvinyl butyral (PVB) solution as a binder for granulation and molding;

[0102] (3) The substrate 5 is manufactured by sintering at a temperature of 850°C in an air atmosphere for 20 min.

[0103] In order to illustrate the influence of the difference in the number of turns of the inductor on the signal quality and anti-interference ability of the present application, comparative examples 1 and 2 are set for comparison, and the relevant data are as follows.

[0104] Comparative Example 1:

[0105] (1) Parameters of spiral inductor 1: outer diameter is 31.1 mm, inner diameter is 12.7 mm, line width is 0.2 mm, line spacing is 0.4 mm, thickness is 0.03 mm, and number of turns is 12.

[0106] (2) Parameters of the forked capacitor 2: The fork length of the first forked capacitor 21 is 10 mm, the fork width of the first forked capacitor 21 is 0.1 mm, the fork thickness of the first forked capacitor 21 is 0.03 mm, the distance between the two forks of the first forked capacitor 21 is 0.025 mm, the number of fork pairs of the first forked capacitor 21 is 9 pairs, and the first independent electrode plate 211 is 22.3 mm; the common electrode plate 200 is 22.3 mm; the fork length of the second forked capacitor 22 is 10 mm, the fork width of the second forked capacitor 22 is 0.4 mm, the fork thickness of the second forked capacitor 22 is 0.03 mm, the distance between the two forks of the second forked capacitor 22 is 0.025 mm, the number of fork pairs of the second forked capacitor 22 is 7 pairs, and the second independent electrode plate 221 is 18.3 mm.

[0107] (3) Number of turns of the same inductor connected in series: the common electrode 200 is connected to the innermost turn end point of the spiral inductor 1; the first independent electrode plate 211 of the first interdigital capacitor 21 is connected to the outermost turn end point of the spiral inductor 1 through a through hole to form a first LC resonant circuit; the second independent electrode plate of the second interdigital capacitor is connected to the spiral inductor through a through hole and the fifth turn (counted from the inside to the outside) of the spiral inductor 1 to form a second LC resonant circuit; the first LC resonant circuit has 7 more turns than the second LC resonant circuit.

[0108] (4) Substrate 5: Made of 6.5 g of barium sulfate, 2 g of titanium dioxide powder and 6 g of glass powder.

[0109] (5) Humidity-sensitive material 3: made of 0.1 g polyimide and 0.2 g molybdenum disulfide nanosheet powder.

[0110] (6) Thermosensitive material 4: A composite material made of PVDF powder and PZT powder in a mass ratio of 1:4.

[0111] Comparative Example 2:

[0112] (1) Parameters of spiral inductor 1: outer diameter is 24.7 mm, inner diameter is 12.7 mm, line width is 0.2 mm, line spacing is 0.4 mm, thickness is 0.03 mm, and number of turns is 8.

[0113] (2) Parameters of the forked capacitor 2: The fork length of the first forked capacitor 21 is 10 mm, the fork width of the first forked capacitor 21 is 0.1 mm, the fork thickness of the first forked capacitor 21 is 0.03 mm, the distance between the two forks of the first forked capacitor 21 is 0.025 mm, the number of fork pairs of the first forked capacitor 21 is 9 pairs, and the first independent electrode plate 211 is 22.3 mm; the common electrode plate 200 is 22.3 mm; the fork length of the second forked capacitor 22 is 10 mm, the fork width of the second forked capacitor 22 is 0.4 mm, the fork thickness of the second forked capacitor 22 is 0.03 mm, the distance between the two forks of the second forked capacitor 22 is 0.025 mm, the number of fork pairs of the second forked capacitor 22 is 7 pairs, and the second independent electrode plate 221 is 18.3 mm.

[0114] (3) Number of turns of the same inductor connected in series: the common electrode 200 is connected to the innermost turn end point of the spiral inductor 1; the first independent electrode plate 211 of the first interdigital capacitor 21 is connected to the outermost turn end point of the spiral inductor 1 through a through hole to form a first LC resonant circuit; the second independent electrode plate of the second interdigital capacitor is connected to the spiral inductor through a through hole and the first turn (counted from the inside to the outside) of the spiral inductor 1 to form a second LC resonant circuit; the first LC resonant circuit has 7 more turns than the second LC resonant circuit.

[0115] (4) Substrate 5: Made of 6.5 g of barium sulfate, 2 g of titanium dioxide powder and 6 g of glass powder.

[0116] (5) Humidity-sensitive material 3: made of 0.1 g polyimide and 0.2 g molybdenum disulfide nanosheet powder.

[0117] (6) Thermosensitive material 4: A composite material made of PVDF powder and PZT powder in a mass ratio of 1:4.

[0118] The inventor has found through research that when the number of inductor turns is set to different numbers, the S 11 Parameters have an impact on Fig. 9 As shown (S 11 When the inductor turns are 8, the inductance value is too small, the frequencies of the two parameters overlap, and S 11 The parameter only shows a single peak, and dual parameter reading is impossible. At the same time, the inductance value is too small, resulting in higher energy loss when reading, and the sensor will show capacitive behavior outside the predetermined operating frequency range, affecting normal signal transmission and processing. When the number of turns of the inductor is 10, the inductance value distinction in the first LC resonant circuit and the second LC resonant circuit is increased, the self-resonant frequency is increased, and the dual parameters can be clearly read, and S 11 When the number of turns of the inductor is 12, the inductance value increases and the series resistance and parasitic capacitance also increase. Excessive resistance and parasitic capacitance will reduce the self-resonant frequency (SRF) and quality factor of the inductor, limit its high-frequency performance and signal transmission efficiency, and cause the resonant frequencies of the two parameters to overlap in different detection ranges. 11 Parameters reduced.

[0119] When the number of turns of the inductor is 10, the inductor works effectively over a wider frequency range, which helps to reduce signal attenuation and phase delay, thereby maintaining signal integrity and improving transmission efficiency.

[0120] In order to illustrate the difference in the number of fork pairs in the forked capacitor 2 and the importance of realizing dual parameter measurement and frequency separation in the present application, comparative examples 3 and 4 are set for comparison, and the relevant data results are as follows.

[0121] Comparative Example 3:

[0122] (1) Parameters of spiral inductor 1: outer diameter is 27.9 mm, inner diameter is 12.7 mm, line width is 0.2 mm, line spacing is 0.4 mm, thickness is 0.03 mm, and number of turns is 10.

[0123] (2) Parameters of the forked capacitor 2: The fork length of the first forked capacitor 21 is 10 mm, the fork width of the first forked capacitor 21 is 0.1 mm, the fork thickness of the first forked capacitor 21 is 0.03 mm, the distance between the two forks of the first forked capacitor 21 is 0.025 mm, the number of fork pairs of the first forked capacitor 21 is 9 pairs, the first independent electrode plate 211 is 22.3 mm; the common electrode plate 200 is 22.3 mm; the fork length of the second forked capacitor 22 is 10 mm, the fork width of the second forked capacitor 22 is 0.4 mm, the fork thickness of the second forked capacitor 22 is 0.03 mm, the distance between the two forks of the second forked capacitor 22 is 0.025 mm, the number of fork pairs of the second forked capacitor 22 is 6 pairs, and the second independent electrode plate 221 is 14.8 mm.

[0124] (3) Number of turns of the same inductor connected in series: the common electrode 200 is connected to the innermost turn end point of the spiral inductor 1; the first independent electrode plate 211 of the first interdigital capacitor 21 is connected to the outermost turn end point of the spiral inductor 1 through a through hole to form a first LC resonant circuit; the second independent electrode plate of the second interdigital capacitor is connected to the spiral inductor through a through hole and the third turn (counting from the inside to the outside) of the spiral inductor 1 to form a second LC resonant circuit; the first LC resonant circuit has 7 more turns than the second LC resonant circuit.

[0125] (4) Substrate 5: Made of 6.5 g of barium sulfate, 2 g of titanium dioxide powder and 6 g of glass powder.

[0126] (5) Humidity-sensitive material 3: made of 0.1 g polyimide and 0.2 g molybdenum disulfide nanosheet powder.

[0127] (6) Thermosensitive material 4: A composite material made of PVDF powder and PZT powder in a mass ratio of 1:4.

[0128] Comparative Example 4:

[0129] (1) Parameters of spiral inductor 1: outer diameter is 27.9 mm, inner diameter is 12.7 mm, line width is 0.2 mm, line spacing is 0.4 mm, thickness is 0.03 mm, and number of turns is 10.

[0130] (2) Parameters of the forked capacitor 2: The fork length of the first forked capacitor 21 is 10 mm, the fork width of the first forked capacitor 21 is 0.1 mm, the fork thickness of the first forked capacitor 21 is 0.03 mm, the distance between the two forks of the first forked capacitor 21 is 0.025 mm, the number of fork pairs of the first forked capacitor 21 is 9 pairs, and the first independent electrode plate 211 is 22.3 mm; the common electrode plate 200 is 22.3 mm; the fork length of the second forked capacitor 22 is 10 mm, the fork width of the second forked capacitor 22 is 0.4 mm, the fork thickness of the second forked capacitor 22 is 0.03 mm, the distance between the two forks of the second forked capacitor 22 is 0.025 mm, the number of fork pairs of the second forked capacitor 22 is 9 pairs, and the second independent electrode plate 221 is 22.3 mm.

[0131] (3) Number of turns of the same inductor connected in series: the common electrode 200 is connected to the innermost turn end point of the spiral inductor 1; the first independent electrode plate 211 of the first interdigital capacitor 21 is connected to the outermost turn end point of the spiral inductor 1 through a through hole to form a first LC resonant circuit; the second independent electrode plate of the second interdigital capacitor is connected to the spiral inductor through a through hole and the third turn (counting from the inside to the outside) of the spiral inductor 1 to form a second LC resonant circuit; the first LC resonant circuit has 7 more turns than the second LC resonant circuit.

[0132] (4) Substrate 5: Made of 6.5 g of barium sulfate, 2 g of titanium dioxide powder and 6 g of glass powder.

[0133] (5) Humidity-sensitive material 3: made of 0.1 g polyimide and 0.2 g molybdenum disulfide nanosheet powder.

[0134] (6) Thermosensitive material 4: A composite material made of PVDF powder and PZT powder in a mass ratio of 1:4.

[0135] The number of interdigital pairs of the first interdigital capacitor 21 and the second interdigital capacitor 22 is one of the key parameters for realizing dual parameter distinction in the present invention, and plays an important role in the sensitivity and reliability of the sensor of the present invention. 11 Parameter tests, such as Fig.10 shown.

[0136] The inventor has found through research that when the first finger capacitor 21 and the second finger capacitor 22 in the forked capacitor 22 are arranged in different finger pairs, the S 11 Parameters have an impact (S 11 When the parameters are measured, the sensor sensitivity, response time and other performance are indirectly reflected through the reflection characteristics). When the finger pairs of the first interdigital capacitor 21 and the second interdigital capacitor 22 differ by 0 pairs, the resonance frequency differs by only 60 MHz, and the two temperature resonance peaks and humidity resonance peaks are both in the temperature range (10-150 MHz), so dual parameter reading cannot be performed, and temperature measurement is interfered. When the finger pairs of the first interdigital capacitor 21 and the second interdigital capacitor 22 differ by 2 pairs, the self-resonance frequency is increased by the difference in the number of interdigital pairs, and dual parameters can be clearly read, and the difference is about 200 MHz. In actual applications, mixing is not likely to occur during the measurement process, S 11 The parameters are strong, and a temperature resonance peak (within the temperature detection range) and a humidity resonance peak (within the humidity detection range) appear. When the difference between the first fork finger capacitor 21 and the second fork finger capacitor 22 is 3 pairs, the difference between the temperature resonance peak and the humidity resonance peak is more than 400MHz, but within the detection range (0~400 MHz), only a single peak appears, and dual-parameter measurement cannot be achieved in practical applications. In summary, when the difference between the first fork finger capacitor 21 and the second fork finger capacitor 22 is 2 pairs, which is the best difference parameter between the first fork finger capacitor 21 and the second fork finger capacitor 22 in this embodiment, the sensor can work effectively in a wider frequency range, which helps to distinguish the dual-parameter resonance peak, can clearly read and maintain signal integrity, and improve transmission efficiency.

[0137] In order to illustrate the different numbers of turns of the same inductor connected in series, and the importance of realizing dual parameter measurement, frequency separation, low frequency mixing, high sensitivity, and strong anti-interference ability in the present application, comparative examples 5 and 6 are set for comparison, and the relevant data results are as follows.

[0138] Comparative Example 5:

[0139] (1) Parameters of spiral inductor 1: outer diameter is 27.9 mm, inner diameter is 12.7 mm, line width is 0.2 mm, line spacing is 0.4 mm, thickness is 0.03 mm, and number of turns is 10.

[0140] (2) Parameters of the forked capacitor 2: The fork length of the first forked capacitor 21 is 10 mm, the fork width of the first forked capacitor 21 is 0.1 mm, the fork thickness of the first forked capacitor 21 is 0.03 mm, the distance between the two forks of the first forked capacitor 21 is 0.025 mm, the number of fork pairs of the first forked capacitor 21 is 9 pairs, and the first independent electrode plate 211 is 22.3 mm; the common electrode plate 200 is 22.3 mm; the fork length of the second forked capacitor 22 is 10 mm, the fork width of the second forked capacitor 22 is 0.4 mm, the fork thickness of the second forked capacitor 22 is 0.03 mm, the distance between the two forks of the second forked capacitor 22 is 0.025 mm, the number of fork pairs of the second forked capacitor 22 is 7 pairs, and the second independent electrode plate 221 is 18.3 mm.

[0141] (3) Number of turns of the same inductor connected in series: the common electrode 200 is connected to the innermost turn end point of the spiral inductor 1; the first independent electrode plate 211 of the first interdigital capacitor 21 is connected to the outermost turn end point of the spiral inductor 1 through a through hole to form a first LC resonant circuit; the second independent electrode plate of the second interdigital capacitor is connected to the spiral inductor through a through hole and the first turn (counted from the inside to the outside) of the spiral inductor 1 to form a second LC resonant circuit; the first LC resonant circuit has 9 more turns than the second LC resonant circuit.

[0142] (4) Substrate 5: Made of 6.5 g of barium sulfate, 2 g of titanium dioxide powder and 6 g of glass powder.

[0143] (5) Humidity-sensitive material 3: made of 0.1 g polyimide and 0.2 g molybdenum disulfide nanosheet powder.

[0144] (6) Thermosensitive material 4: A composite material made of PVDF powder and PZT powder in a mass ratio of 1:4.

[0145] Comparative Example 6:

[0146] (1) Parameters of spiral inductor 1: outer diameter is 27.9 mm, inner diameter is 12.7 mm, line width is 0.2 mm, line spacing is 0.4 mm, thickness is 0.03 mm, and number of turns is 10.

[0147] (2) Parameters of the forked capacitor 2: The fork length of the first forked capacitor 21 is 10 mm, the fork width of the first forked capacitor 21 is 0.1 mm, the fork thickness of the first forked capacitor 21 is 0.03 mm, the distance between the two forks of the first forked capacitor 21 is 0.025 mm, the number of fork pairs of the first forked capacitor 21 is 9 pairs, and the first independent electrode plate 211 is 22.3 mm; the common electrode plate 200 is 22.3 mm; the fork length of the second forked capacitor 22 is 10 mm, the fork width of the second forked capacitor 22 is 0.4 mm, the fork thickness of the second forked capacitor 22 is 0.03 mm, the distance between the two forks of the second forked capacitor 22 is 0.025 mm, the number of fork pairs of the second forked capacitor 22 is 7 pairs, and the second independent electrode plate 221 is 18.3 mm.

[0148] (3) Number of turns of the same inductor connected in series: the common electrode 200 is connected to the innermost turn end point of the spiral inductor 1; the first independent electrode plate 211 of the first interdigital capacitor 21 is connected to the outermost turn end point of the spiral inductor 1 through a through hole to form a first LC resonant circuit; the second independent electrode plate of the second interdigital capacitor is connected to the spiral inductor through a through hole and the fifth turn (counted from the inside to the outside) of the spiral inductor 1 to form a second LC resonant circuit; the first LC resonant circuit has 5 more turns than the second LC resonant circuit.

[0149] (4) Substrate 5: Made of 6.5 g of barium sulfate, 2 g of titanium dioxide powder and 6 g of glass powder.

[0150] (5) Humidity-sensitive material 3: made of 0.1 g polyimide and 0.2 g molybdenum disulfide nanosheet powder.

[0151] (6) Thermosensitive material 4: A composite material made of PVDF powder and PZT powder in a mass ratio of 1:4.

[0152] The results of sensors with different structural parameters of Example 1 and Comparative Examples 1 to 6 are analyzed.

[0153] In order to further enhance the dual parameter distinguishing capability and the reliability of the sensor, the first interdigital capacitor 21 and the second interdigital capacitor 22 in the interdigital capacitor 2 are respectively connected in series with different turns of the same inductor through the through hole set on the substrate 5. The difference in the number of turns of the inductor connected in series plays an important role in the dual parameter distinguishing capability and reliability of the sensor. The inventors have found through research that the first interdigital capacitor 21 and the second interdigital capacitor 22 are respectively connected in series with different turns of the same inductor, and the difference in the number of turns has an important impact on the S of the sensor.11 Parameters have an impact on Fig.11 As shown (S 11 When the number of turns of the same inductor is 5 turns different, the first interdigital capacitor 21 and the second interdigital capacitor 22 are connected in series with different numbers of turns of the same inductor, and the difference in inductance value is too small, resulting in the overlap of the frequencies of the two parameters, S 11 The parameters have a single peak and cannot be read for dual parameters. When the number of turns differs by 7 turns, the difference in inductance values ​​of different numbers of turns of the same inductor is increased by adding the first interdigital capacitor 21 and the second interdigital capacitor 22, which reduces the influence of frequency overlap and increases the self-resonant frequency. The dual parameters can be read clearly and differ by 320 MHz. In actual applications, the measurement process is not prone to frequency mixing, and S 11 The parameters are strong, and the dual-parameter resonance peaks that are easy to distinguish appear. When the number of turns differs by 9 turns, the inductance value increases while the series resistance also increases, resulting in S 11 The parameters are reduced, which reduces the transmission efficiency of the sensor.

[0154] When the first fork-finger capacitor 21 and the second fork-finger capacitor 22 are respectively connected in series with different numbers of turns of the same inductor, the number of turns differs by 7 turns, which is the parameter with the best difference in turns in this embodiment. It ensures that the two inductors have sufficient inductance values, balances the effects of resistance and frequency overlap, and enables the sensor to more effectively achieve accurate measurement of different environmental parameters within a wider frequency range, maintain signal integrity, and clearly read dual parameters. At the same time, it reduces the risks of frequency overlap and parameter cross-interference, thereby maximizing the sensitivity, accuracy, reliability and transmission efficiency of the sensor, making it suitable for application scenarios of multi-parameter monitoring.

[0155] In order to reflect the sensitivity of the humidity unit of the present application, the change of the resonant frequency of the LC circuit between the temperature of 50°C and the relative humidity of 40% to 70%RH is as follows: Fig.12 As shown in the figure, it can be seen that when the relative humidity increases from 40%RH to 70%RH, the resonant frequency decreases from 259.65 MHz to 256.88 MHz. The sensitivity of the resonant frequency reaches 92.33 KHz / %RH.

[0156] In order to reflect the sensitivity of the temperature unit of the present application, the change of the resonant frequency of the LC circuit at a humidity of 40% RH and a temperature of 50-70°C is as follows: Fig.13 As shown in the figure, it can be seen that when the temperature rises from 50 ℃ to 70 ℃, the resonant frequency drops from 108.19 MHz to 97.82 MHz. The sensitivity of the resonant frequency reaches 345.67KHz / ℃.

[0157] The above is a specific description of the preferred implementation of the present invention, but the present invention is not limited to the above-mentioned implementation mode. Technical personnel familiar with the field can also make various equivalent deformations or substitutions without violating the spirit of the present invention. These equivalent deformations or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A wireless passive dual-parameter sensor, characterized in that: include: Spiral inductor, bifurcated capacitor, substrate, moisture-sensitive material, temperature-sensitive material; The spiral inductor is a planar single spiral structure, and the number of coil turns is 9 to 11 turns; The spiral inductor and the bifurcated capacitor are respectively arranged on two sides of the substrate; The interdigitated capacitor comprises a first interdigitated capacitor and a second interdigitated capacitor, wherein the number of interdigitated pairs of the first interdigitated capacitor and the second interdigitated capacitor differs by 1 to 2 pairs, and the surface of the first interdigitated capacitor is at least partially coated with the temperature-sensitive material, and the surface of the second interdigitated capacitor is at least partially coated with the moisture-sensitive material; The first interdigital capacitor and the second interdigital capacitor share a common electrode plate, and the common electrode plate is connected to the innermost circle end point of the spiral inductor; the first independent electrode plate of the first interdigital capacitor is connected to the outermost circle end point of the spiral inductor to form a first LC resonant circuit; the second independent electrode plate of the second interdigital capacitor is connected to part of the inductance of the spiral inductor to form a second LC resonant circuit, and the first LC resonant circuit has 6 to 8 more turns of inductance than the second LC resonant circuit.

2. A wireless passive dual-parameter sensor according to claim 1, characterized in that: The substrate comprises a composite material made of barium sulfate, titanium dioxide powder and glass powder.

3. A wireless passive dual-parameter sensor according to claim 1, characterized in that: The humidity sensitive material comprises a composite material made of polyimide / molybdenum disulfide.

4. A wireless passive dual-parameter sensor according to claim 1, characterized in that: The temperature-sensitive material comprises a composite material made of PVDF powder and PZT powder.

5. A wireless passive dual-parameter sensor according to any one of claims 1 to 4, characterized in that: The readout system includes: single chip control module, DDS frequency sweep signal generation module, reading coil, signal decoupling module, data buffer module, solution module and display module; The single-chip control module controls the DDS sweep frequency signal generating module to generate a sweep frequency signal which is coupled with the wireless passive dual-parameter sensor through a reading coil. The coupled signal is decoupled by a signal decoupling module to obtain temperature and humidity frequency signals which are respectively subjected to AD conversion. The temperature and humidity are calculated by the data cache module and the solution module and displayed by the display module.

6. A wireless passive dual-parameter sensor according to claim 5, characterized in that: The signal decoupling module extracts temperature and humidity resonance information through a temperature bandpass filter and a humidity bandpass filter.

Images