Temperature sensor with digital coding function

Abstract

The invention belongs to the technical field of sensors, and particularly relates to a temperature sensor with a digital coding function, which is characterized in that a power divider, a quarter-wavelength open-circuit line and a combiner are directly connected to form a structure similar to a cross; the first split-ring resonator, the second split-ring resonator, the third split-ring resonator and the fourth split-ring resonator are located in four directions of the cross-shaped structure respectively, and the four varactors are located at openings of the first split-ring resonator, the second split-ring resonator, the third split-ring resonator and the fourth split-ring resonator. The power divider, the quarter-wavelength open-circuit line, the combiner, the first split-ring resonator, the second split-ring resonator, the third split-ring resonator and the fourth split-ring resonator are arranged on one side of the dielectric substrate, and the metal floor is arranged on the other side of the dielectric substrate.

Description

Technical Field

[0001] The present invention belongs to, but is not limited to, the field of sensor technology, and particularly relates to a temperature sensor with digital encoding function. Background Art

[0002] In industrial production activities, many key devices need to operate within a precisely defined temperature range to ensure their efficient operation and extended service life. Two core requirements have emerged in temperature detection:

[0003] (1) Process control: In process flows such as heat treatment, chemical reactions, and metal smelting that require strict temperature management, real-time monitoring of multi-point temperatures is crucial to ensure the stability and safety of the production process. By promptly detecting and handling abnormal situations, production accidents and product quality problems caused by abnormal temperatures can be avoided;

[0004] (2) Equipment operation monitoring: Given that a large number of devices in industrial production need to operate under specific temperature conditions, continuous monitoring of multi-point temperature changes has become an effective means of promptly detecting overheating or overcooling of equipment. This helps prevent equipment failures and damages caused by improper temperatures, ensures the continuous and stable operation of production equipment, thereby extending the equipment life and reducing maintenance costs.

[0005] In summary, real-time monitoring of multi-point temperatures in industrial production plays a crucial role in ensuring the stability of process flows, enhancing the safety of equipment operation, and extending the service life of equipment. By building an efficient temperature anomaly detection and response mechanism, enterprises can not only significantly improve production efficiency but also effectively reduce production costs and provide a solid guarantee for production safety.

[0006] With the rapid deployment of new wireless devices and applications, the demand for wireless spectrum has been growing continuously in the past decade, and the spectrum for temperature sensing is even scarcer. Currently, most existing articles and products use time-division and frequency-division methods to achieve multi-point temperature measurement, and the utilization efficiency of limited spectrum resources is low: However, both of these methods have problems with low efficiency when using limited spectrum resources: Time-division multiplexing cannot achieve synchronous monitoring of multi-point temperatures, which limits its application in scenarios with high real-time requirements; while frequency-division multiplexing can achieve multi-point temperature measurement to a certain extent, but in large-scale temperature detection tasks, the spectrum resources it occupies are too large, which is not conducive to the efficient use of spectrum resources.

[0007] 2. Existing Technical Solutions

[0008] ① In the paper "Compact Chipless RFID Sensor for Frozen Food Monitoring", a simple, compact, and low-cost chipless RFID sensor tag for frozen food monitoring was proposed. The peak center frequencies of ice and air are 751 MHz and 838 MHz respectively, and the frequency range occupied by a single sensor is at least 87 MHz.

[0009] ② The paper "Wireless Microwave Sensor Network Using Split Ring Resonators for Ice Monitoring Applications" first proposed a portable wireless microwave sensor network for ice monitoring applications. With three sensing nodes, it was successfully tested at 16 discrete frequency points in the temperature range of 40 °C to 20 °C and the frequency range of 1.75 - 2.8 GHz, with a step size of 70 MHz. The frequency range occupied by this sensor exceeds 1 GHz.

[0010] ③ The paper "Metamaterial High-Temperature Sensor Based on All-Planar Substrate Integrated Waveguide" uses a single square complementary split-ring resonator (S-CSRR) as the metamaterial resonator. Three types of metal pastes, Ag, PtRh10, and Pt, are used for sensor fabrication. The temperature test ranges are 30 °C to 800 °C, 30 °C to 1200 °C, and 30 °C to 1600 °C, and the corresponding average sensitivities are 236, 220, and 191 kHz / °C respectively. However, the frequency range occupied by a single sensor is within 200 - 300 MHz.

[0011] ④ The paper "High Sensitivity SIW-CSRR Temperature Sensor Based on Microwave Scattering" designed a wireless passive high-sensitivity temperature sensor with a semi-circular complementary split-ring resonator (CSRR) structure and fabricated it using laser cutting. The sensitivity of the sensor is 106.67 kHz / °C in the low-temperature range of 25 °C to 400 °C and 437.5 kHz / °C in the high-temperature range of 400 °C to 1200 °C. This structure has a wide temperature measurement range but only occupies a 400 MHz bandwidth.

[0012] ⑤ The paper "Performance of PDC-SiBCN Ceramic-based Wireless Passive Temperature Sensor" prepared a wireless passive temperature sensor integrating a slotted antenna and a resonator to achieve wireless passive transmission of temperature information. The dielectric constant of PDC-SiBCN ceramic increases monotonically with the increase of temperature. The sensor with a pyrolysis temperature of 1000 °C has a test temperature up to 1100 °C, showing excellent high-temperature resistance and dielectric-temperature characteristics. Its temperature measurement range is 20 °C to 1100 °C, occupying a bandwidth of about 300 MHz.

[0013] ⑥ The paper "Simulation and Verification of the Method of Increasing the Wireless Detection Distance of Resonant Cavity Temperature Sensor by Integrated Patch Antenna" designed two types of polymer-derived sialcn ceramic resonant cavity wireless passive temperature sensors with and without patch antennas. Compared with the sensor without a patch antenna, the maximum detection distance of the sensor with a patch antenna increased from 18 mm to 32 mm. Its temperature measurement range is 25 °C to 1100 °C, occupying a bandwidth of about 400 MHz.

[0014] In view of the above analysis, the technical problems that urgently need to be solved in the existing technology are as follows: both of the existing two methods have low efficiency when using limited spectrum resources: time-division multiplexing cannot achieve synchronous monitoring of multiple-point temperatures, restricting its application in scenarios with high real-time requirements; while frequency-division multiplexing can achieve multi-point temperature measurement to a certain extent, but in large-scale temperature detection tasks, the spectrum resources it occupies are too large, which is not conducive to the efficient use of spectrum resources. Summary of the Invention

[0015] Aiming at the problems existing in the prior art, the present invention provides a temperature sensor with digital coding function.

[0016] The present invention is implemented as follows. A temperature sensor with digital encoding function includes seven parts: a power divider, a quarter-wavelength open circuit line, a combiner, a first split ring resonator, a second split ring resonator, a third split ring resonator, a fourth split ring resonator, four varactor diodes, a dielectric substrate, and a metal floor. The power divider, the quarter-wavelength open circuit line, and the combiner are directly connected to form a structure similar to a cross. The first split ring resonator, the second split ring resonator, the third split ring resonator, and the fourth split ring resonator are respectively located at the four directions of the cross-shaped structure. The four varactor diodes are located at the openings of the first split ring resonator, the second split ring resonator, the third split ring resonator, and the fourth split ring resonator. The power divider, the quarter-wavelength open circuit line, the combiner, the first split ring resonator, the second split ring resonator, the third split ring resonator, the fourth split ring resonator, and the four varactor diodes are located on one side of the dielectric substrate, and the metal floor is located on the other side of the dielectric substrate.

[0017] Furthermore, the power divider, the quarter-wavelength open circuit line, and the combiner are made of copper, with a thickness of 1 ounce, that is, 0.035 mm. The power divider and the combiner are symmetrically distributed with respect to the quarter-wavelength open circuit line.

[0018] Furthermore, the first split ring resonator, the second split ring resonator, the third split ring resonator, and the fourth split ring resonator are made of copper, with a thickness of 1 ounce, that is, 0.035 mm. The gap distances between the first split ring resonator, the second split ring resonator, the third split ring resonator, the fourth split ring resonator and the power divider, the quarter-wavelength open circuit line, and the combiner are the same. The lengths and widths of the first split ring resonator, the second split ring resonator, the third split ring resonator, and the fourth split ring resonator are slightly different.

[0019] Furthermore, the four varactor diodes have exactly the same model size, and are respectively located at the openings of the first split ring resonator, the second split ring resonator, the third split ring resonator, and the fourth split ring resonator and are connected to the rings.

[0020] Furthermore, the dielectric substrate is Rogers RT / duroid 5880(tm), with a dielectric constant of 2.2, a substrate thickness of 0.254 mm, and a loss tangent of 0.0009.

[0021] Furthermore, the metal floor is made of copper, with a thickness of 1 ounce, that is, 0.035 mm.

[0022] Combining the above technical solutions and the solved technical problems, the advantages and positive effects of the technical solution to be protected by the present invention are:

[0023] First, the 4-bit digital encoded temperature sensor studied in the present invention has a temperature measurement range of -10°C to 80°C. The sensitivity of temperature sensing is 0.114 MHz / °C in the range of -10°C to 25°C and 0.073 MHz / °C in the range of 25°C to 80°C. Compared with the performance of existing temperature sensors, the difference is not significant. However, the frequency range occupied by each encoded sensor on average is 6.67 MHz, which is much smaller than the bandwidth resources occupied by existing sensors. It can perform high-precision temperature sensing at a large number of points within a limited bandwidth, which is of great significance.

[0024] The present invention generates the electromagnetic induced transparency effect through the split ring resonator and the quarter-wavelength microstrip open stub line. A varactor diode SMV1405-079LF is introduced at the opening of the split ring resonator. When the temperature changes, the diode capacitance generates a temperature drift, causing the frequency of the split ring resonator to change, thereby realizing temperature sensing. The present invention uses four split ring resonators to achieve four group delay peaks, and digital encoding is performed by whether a varactor diode is loaded at the opening, achieving a coding effect of 15 types in total with 4 bits within a limited frequency band. The size of the digital encoded temperature sensor designed in the present invention is 140 mm × 70 mm × 0.254 mm, operating in the ISM band of 915 MHz from 850 to 950 MHz. The frequency range occupied by each encoded sensor on average is 6.67 MHz, and the temperature measurement range is -10°C to 85°C; the sensitivity of temperature sensing is 0.114 MHz / °C in the range of -10°C to 25°C and 0.073 MHz / °C in the range of 25°C to 85°C, realizing high-precision temperature sensing at more points to be measured within a limited bandwidth.

[0025] Second, as the creative auxiliary evidence of the claims of the present invention, it is also reflected in the following important aspects:

[0026] (1) The expected benefits and commercial value after the transformation of the technical solution of the present invention are:

[0027] After the transformation of the technical solution of the present invention, the utilization efficiency of spectrum resources for temperature sensing will be greatly improved. On the one hand, the innovation of this solution provides a new idea for subsequent work. On the other hand, it can improve production efficiency, reduce costs, open up new markets, enhance user experience, etc., and is expected to generate significant economic benefits in applications such as industry, agriculture, medical care, and smart home.

[0028] (2) The technical solution of the present invention fills the technical gaps in the domestic and international industries:

[0029] The technical solution of the present invention was first proposed by the author, innovatively using a varactor diode for digital encoding and achieving high-precision temperature sensing through the electromagnetically induced transparency (EIT) effect, filling the domestic and foreign technical gaps in temperature sensing using varactor diodes and the EIT effect.

[0030] (3) The technical solution of the present invention solves the technical problems that people have been eager to solve but have never succeeded in:

[0031] With the increasing demand for the wireless spectrum today, it is extremely urgent to be able to perform high-precision temperature sensing for more points to be measured within a limited bandwidth. This solution provides a brand-new solution for realizing large-scale temperature detection under the condition of limited spectrum resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a schematic structural diagram of a temperature sensor with digital encoding function provided by an embodiment of the present invention;

[0033] Figure 2 is a schematic diagram of a three-level system provided by an embodiment of the present invention;

[0034] Figure 3 is a schematic diagram of the simulation result of the transmission coefficient generated by the electromagnetically induced transparency effect provided by an embodiment of the present invention;

[0035] Figure 4 is a schematic diagram of the simulation result of the group delay generated by the electromagnetically induced transparency effect provided by an embodiment of the present invention;

[0036] Figure 5 is a schematic diagram of the equivalent circuit model of the SMV1405-079LF varactor diode provided by an embodiment of the present invention;

[0037] Figure 6 is a graph of the capacitance-frequency variation relationship of the group delay peak provided by an embodiment of the present invention;

[0038] Figure 7 is a schematic diagram of the temperature drift characteristic of the SMV1405-079LF varactor diode provided by an embodiment of the present invention;

[0039] Figure 8 is a schematic diagram of the capacitance-frequency variation corresponding to the sensor encoded with 0001 provided by an embodiment of the present invention;

[0040] Figure 9 is a schematic diagram of the capacitance-frequency variation corresponding to the sensor encoded with 0010 provided by an embodiment of the present invention;

[0041] Figure 10 is a schematic diagram of the capacitance-frequency variation corresponding to the sensor encoded with 0011 provided by an embodiment of the present invention;

[0042] Figure 11 It is a schematic diagram of the capacitance-frequency change corresponding to the sensor encoding 0100 provided by an embodiment of the present invention;

[0043] Figure 12 It is a schematic diagram of the capacitance-frequency change corresponding to the sensor encoding 0101 provided by an embodiment of the present invention;

[0044] Figure 13 It is a schematic diagram of the capacitance-frequency change corresponding to the sensor encoding 0110 provided by an embodiment of the present invention;

[0045] Figure 14 It is a schematic diagram of the capacitance-frequency change corresponding to the sensor encoding 0111 provided by an embodiment of the present invention;

[0046] Figure 15 It is a schematic diagram of the capacitance-frequency change corresponding to the sensor encoding 1000 provided by an embodiment of the present invention;

[0047] Figure 16 It is a schematic diagram of the capacitance-frequency change corresponding to the sensor encoding 1001 provided by an embodiment of the present invention;

[0048] Figure 17 It is a schematic diagram of the capacitance-frequency change corresponding to the sensor encoding 1010 provided by an embodiment of the present invention;

[0049] Figure 18 It is a schematic diagram of the capacitance-frequency change corresponding to the sensor encoding 1011 provided by an embodiment of the present invention;

[0050] Figure 19 It is a schematic diagram of the capacitance-frequency change corresponding to the sensor encoding 1100 provided by an embodiment of the present invention;

[0051] Figure 20 It is a schematic diagram of the capacitance-frequency change corresponding to the sensor encoding 1101 provided by an embodiment of the present invention;

[0052] Figure 21 It is a schematic diagram of the capacitance-frequency change corresponding to the sensor encoding 1110 provided by an embodiment of the present invention;

[0053] In the figure: 1. Power divider; 2. Quarter-wavelength open-circuit line; 3. Combiner; 4. First split-ring resonator; 5. Second split-ring resonator; 6. Third split-ring resonator; 7. Fourth split-ring resonator; 8. Varactor diode; 9. Dielectric substrate; 10. Metal floor. Detailed implementation manners

[0054] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0055] Embodiment 1: High-precision ambient temperature detection sensor

[0056] 1) Functional description

[0057] This temperature sensor is used to monitor the temperature changes in indoor or industrial environments in real time and output the temperature value in the form of digital coding, and is suitable for scenarios that require high-precision temperature control.

[0058] 2) Structural design

[0059] Power splitter 1 and combiner 3: Made of high-precision metal copper material with a thickness of 1 ounce (0.035 mm) to ensure high stability of signal distribution and combination.

[0060] Resonant rings 4 - 7: Slightly different in length and width, designed for temperature signal adjustment in different frequency bands. The varactor diode 8 realizes the digital coding output of temperature signals by adjusting the resonant frequency of the resonant ring.

[0061] Dielectric substrate 9: Rogers RT / duroid 5880(tm) is selected, with a dielectric constant of 2.2, a thickness of 0.254 mm, and a loss tangent of 0.0009 to ensure low-loss signal transmission.

[0062] 3) Usage scenarios

[0063] In industrial workshops, monitor the ambient temperature changes in real time and adjust the temperature through the control system.

[0064] Used for temperature control management of precision instruments in laboratories.

[0065] 4) Working principle

[0066] The power splitter 1 evenly distributes the input signal to the two branches of the quarter-wavelength open circuit line 2. The signal is transmitted to the resonant rings 4 - 7, and the fine-tuning of the frequency is realized through the regulation of the varactor diode. Finally, the signal is output through the combiner 3 and converted into the form of digital coding to reflect the current temperature.

[0067] Embodiment 2: Vehicle-mounted temperature sensor

[0068] 1) Functional description

[0069] This temperature sensor is used to detect the temperature changes in the engine compartment or inside the vehicle in a vehicle-mounted environment and transmit the digital signal to the vehicle central control system, and is suitable for temperature monitoring and adjustment of intelligent vehicles.

[0070] 2) Structural Design

[0071] Power divider 1 and combiner 3: Made of copper metal with a thickness of 1 ounce (0.035 mm) to ensure signal stability in the in-vehicle vibration environment.

[0072] Resonant rings 4 - 7: The length and width are specially designed according to the high-temperature environment in the engine compartment, supporting a higher frequency band range.

[0073] Varactor diode 8: Enhances the high-temperature resistance ability to ensure stable operation in high-temperature environments.

[0074] Metal floor 10: Made of copper metal with a thickness of 1 ounce, playing a good electromagnetic shielding role.

[0075] 3) Usage Scenarios

[0076] It is used in the temperature control system inside intelligent vehicles to adjust the air conditioner or engine cooling system through real-time temperature monitoring.

[0077] In new energy vehicles, it monitors the temperature changes of the battery pack to avoid failures caused by overheating.

[0078] 4) Working Principle

[0079] After the input signal is distributed by the power divider 1, it enters the resonant rings 4 - 7 through the quarter-wavelength open-circuit line 2. Temperature changes will affect the resonant frequency of the resonant rings, and the varactor diode adjusts the signal response. The output signal is digitally encoded by the combiner 3 and then transmitted to the vehicle control system to achieve real-time monitoring.

[0080] These two embodiments demonstrate the specific applications of the temperature sensor in different environments, meeting various requirements through precise design, and enhancing the practicality and reliability of the device.

[0081] Such as Figure 1As shown in the figure, a temperature sensor with digital encoding function includes seven parts: a power divider 1, a quarter-wavelength open-circuit line 2, a combiner 3, a first split-ring resonator 4, a second split-ring resonator 5, a third split-ring resonator 6, and a fourth split-ring resonator 7, four varactor diodes 8, a dielectric substrate 9, and a metal ground plane 10. The power divider 1, the quarter-wavelength open-circuit line 2, and the combiner 3 are directly connected to form a structure similar to a cross. The first split-ring resonator 4, the second split-ring resonator 5, the third split-ring resonator 6, and the fourth split-ring resonator 7 are respectively located at the four directions of the cross-shaped structure. The four varactor diodes 8 are located at the openings of the first split-ring resonator 4, the second split-ring resonator 5, the third split-ring resonator 6, and the fourth split-ring resonator 7. The power divider 1, the quarter-wavelength open-circuit line 2, the combiner 3, the first split-ring resonator 4, the second split-ring resonator 5, the third split-ring resonator 6, the fourth split-ring resonator 7, and the four varactor diodes 8 are located on one side of the dielectric substrate 9, and the metal ground plane 10 is located on the other side of the dielectric substrate 9.

[0082] The power divider 1, the quarter-wavelength open-circuit line 2, and the combiner 3 are made of copper with a thickness of 1 ounce, that is, 0.035 mm. The power divider 1 and the combiner 3 are symmetrically distributed with respect to the quarter-wavelength open-circuit line 2.

[0083] The first split-ring resonator 4, the second split-ring resonator 5, the third split-ring resonator 6, and the fourth split-ring resonator 7 are made of copper with a thickness of 1 ounce, that is, 0.035 mm. The gap distances between the first split-ring resonator 4, the second split-ring resonator 5, the third split-ring resonator 6, the fourth split-ring resonator 7 and the power divider 1, the quarter-wavelength open-circuit line 2, and the combiner 3 are the same. The lengths and widths of the first split-ring resonator 4, the second split-ring resonator 5, the third split-ring resonator 6, and the fourth split-ring resonator 7 are slightly different.

[0084] The four varactor diodes 8 have exactly the same model size and are respectively located at the openings of the first split-ring resonator 4, the second split-ring resonator 5, the third split-ring resonator 6, and the fourth split-ring resonator 7 and are connected to the rings.

[0085] The dielectric substrate 9 is selected as Rogers RT / duroid 5880(tm) with a dielectric constant of 2.2, a substrate thickness of 0.254 mm, and a loss tangent of 0.0009.

[0086] The metal ground plane 10 is made of copper with a thickness of 1 ounce, that is, 0.035 mm.

[0087] The power splitter 1 is used to evenly distribute the input signal to the two branches of the quarter - wavelength open - circuit line 2. After the signal is transmitted along the branch path, through the structure of the quarter - wavelength open - circuit line 2, two symmetric output paths of the signal are formed in the propagation direction. The signals of these two output paths finally converge at the combiner 3 to form a feedback signal or the final output signal. The symmetric structure between the power splitter 1 and the combiner 3 ensures the phase stability of the signal during transmission, guaranteeing the working efficiency of the resonant ring and the accuracy of the overall sensor.

[0088] The first split - ring resonator 4, the second split - ring resonator 5, the third split - ring resonator 6, and the fourth split - ring resonator 7 are respectively arranged in the four directions of the cross - shaped structure. Each resonator determines its own resonant frequency through its specific geometric dimensions (length and width). Since the lengths and widths of the four resonators are slightly different, they generate different resonant frequencies in a specific signal frequency band. These differences in resonant frequencies provide the multi - frequency characteristics for the sensor, which are used for subsequent digital coding functions.

[0089] A varactor diode 8 is connected to the opening of each resonator. These diodes are used to dynamically adjust the capacitance value of the resonator. As the external temperature changes, the capacitance value of the varactor diode changes accordingly, thereby affecting the equivalent resonant frequency of the resonator. The temperature change introduces a frequency shift in the resonator through the non - linear characteristics of the varactor diode, enabling each resonator to respond to the resonant changes under different temperature conditions, providing a basis for subsequent digital coding.

[0090] The dielectric substrate 9 uses a low - loss high - frequency material Rogers RT / duroid 5880, with a dielectric constant of 2.2 and a loss tangent of 0.0009, ensuring the low - attenuation characteristics of the signal in the high - frequency band. The metal floor 10 serves as a shielding layer, reducing the interference between the resonator and the external environment, while providing good electromagnetic isolation, enhancing the stability of signal transmission and the anti - interference ability of the detector.

[0091] The digital coding function of the temperature sensor is realized by recording the resonant frequency characteristics of the four resonators. When the temperature changes, the resonant frequency of each resonator shifts, forming a spectral characteristic corresponding to the temperature. By analyzing the combination of the frequency characteristics of the four resonators, a specific temperature range can be mapped to a unique digital code. This characteristic of the multi - frequency composite spectrum improves the resolution and measurement accuracy of the sensor.

[0092] When the temperature changes, the capacitance value of the varactor diode 8 changes with the temperature, resulting in a change in the resonance frequency of each resonant ring. The power divider 1 distributes the input signal to the resonant rings, and the frequency response of the resonant rings after temperature regulation is aggregated into a composite signal by the combiner 3 for output. Finally, the output signal undergoes demodulation and digital processing to generate corresponding digital codes, thereby achieving the high sensitivity and accuracy of the temperature sensor. The entire sensor has a compact structure, high precision, and can effectively meet the temperature monitoring requirements in complex environments.

[0093] The technology of the present invention aims at a temperature sensor with digital coding function, and the specific implementation of its function can be divided into three parts: capacitance-frequency change based on the group delay spike generated by the electromagnetically induced transparency effect, temperature-capacitance change based on the temperature drift characteristics of the SMV1405-079LF varactor diode, and digital coding function based on whether the split-ring resonator is loaded with a varactor diode.

[0094] 1. Capacitance-frequency change based on the group delay spike generated by the electromagnetically induced transparency effect

[0095] The basic working principle of the electromagnetically induced transparency effect can be explained by a three-level atomic system. As Figure 2 shown, when a probe light beam is incident on the first energy level, the probe light beam will be absorbed by the atoms at the first energy level, causing a transition between energy levels and unable to continue propagating. When another induced light beam with the same or similar frequency is incident on the second energy level at the same time, the atoms no longer absorb the probe light beam, and the probe light directly passes through the energy level system, generating a transmission passband spectrum, and the electromagnetically induced transparency effect is obtained. The passband generated by this effect is a relatively narrow passband window. Utilizing the change of this narrow band to achieve the sensing function has the characteristic of high precision.

[0096] There are mainly three ways to achieve the electromagnetically induced transparency effect: bright mode directly coupled with an external electric field + dark mode coupled with the bright mode, bright mode coupled with an external electric field + quasi-dark mode weakly coupled with the external electric field, and Fano effect generated by an asymmetric structure. The present invention utilizes the form of bright mode + quasi-dark mode, and generates four similar frequencies through a power divider, a combiner, and four split-ring resonators with slightly different sizes. The simulation results of the transmission coefficient generated by the electromagnetically induced transparency effect are as Figure 3 shown. In order to obtain a better sensing effect, we adopt a group delay with a higher Q value. The group delay is consistent with the trend of the transmission coefficient but has a higher spike, as Figure 4 shown.

[0097] The above simulation results are obtained by substituting the equivalent model of the SMV1405-079LF varactor diode into HFSS for simulation, and its equivalent circuit is as Figure 5As shown, the resistance value is 0.3 ohm, the initial capacitance value is 1.84 pF, and the inductance value is 0.7 nH. At this time, the reverse bias voltage applied across the varactor diode is 1 V, and the temperature is 25 °C.

[0098] When the capacitance value of the SMV1405-079LF varactor diode changes from 1.78 pF to 1.90 pF with a step of 0.02 pF, the frequency corresponding to the group delay peak shifts towards the lower frequency, and it basically shows a linear relationship, as Figure 6 shown. We obtained the capacitance-frequency variation of the group delay peak generated based on the electromagnetically induced transparency effect, laying a microwave theoretical foundation for subsequent work.

[0099] 2. Temperature-Capacitance Variation Based on the Temperature Drift Characteristic of the SMV1405-079LF Varactor Diode

[0100] According to the curve graph of the temperature drift characteristic in the product manual of the SMV1405-079LF varactor diode, as Figure 7 shown, when the reverse bias voltage is 1 V, when the temperature changes from -40 °C to 25 °C, the percentage change in capacitance changes from 96% to 100%, that is, from 1.7664 pF to 1.84 pF; when the temperature changes from 25 °C to 85 °C, the percentage change in capacitance changes from 100% to 102%, that is, from 1.84 pF to 1.8768 pF. It is worth noting that both sections of the line are in a direct proportional relationship, which is convenient for meeting the requirements of temperature sensing in the present invention. Combining the capacitance-frequency variation relationship in the previous part, the present invention finally selects the temperature measurement range of -10 °C - 85 °C, and at this time the capacitance change range is 1.8 pF - 1.88 pF.

[0101] 3. Digital Coding Function Based on Whether the Split Ring Resonator Loads a Varactor Diode

[0102] The most basic temperature sensor designed in the present invention loads varactor diodes at four split ring resonators, thus generating four group delay peaks. The four group delay peaks are respectively in four frequency bands of 850 - 875 MHz, 875 - 900 MHz, 900 - 925 MHz, and 925 - 950 MHz. We stipulate that the state code when there is a group delay peak in the frequency band is 1, and the peaks from the lower frequency to the higher frequency respectively correspond to the high and low bits of the digital coding. Then the digital coding corresponding to the four split ring resonators is 1111. Because the sizes of the four split ring resonators are slightly different, four group delay peaks of different frequencies are generated. Therefore, we can respectively control the group delay peaks in the four frequency bands. When a varactor diode is loaded, a group delay peak will be generated in the frequency band, and the state is 1 at this time; when a varactor diode is not loaded, that is, when the opening of the split ring resonator is closed, no group delay peak is generated in the frequency band, and the state is 0 at this time. Obviously, the present invention has 15 (2 4-1 kind of digital coding state can be used, which are 1111, 1110, 1101, 1100, 1011, 1010, 1001, 1000, 0111, 0110, 0101, 0100, 0011, 0010, 0001 respectively. For the last digital coding state 0000, due to the absence of group delay spikes, temperature sensing cannot be achieved. The 15 kinds of digital coding states of the present invention can respectively detect the temperature changes at 15 points, and the bandwidth occupied by a single sensor is only 6.67 MHz, saving spectral resources to a great extent. Figure 6 shows the capacitance-frequency change of the sensor corresponding to the code 1111. The following gives Figures 8 to 21 , showing the group delay capacitance-frequency changes of the remaining 14 states:

[0103] The temperature sensors with 15 kinds of digital coding can basically work normally within the working temperature range. Placing 15 sensors at 15 points can achieve the identification of the identities of 15 positions and temperature monitoring. Compared with the existing temperature sensors, the advantages are huge. Through calculation, the sensitivity of the digital coding temperature sensor of the present invention is 0.114 MHz / °C within the range of -10°C to 25°C, and 0.073 MHz / °C within the range of 25°C to 85°C, realizing high-precision temperature sensing of more points to be measured within a limited bandwidth.

[0104] The specific application fields or related products of the present invention.

[0105] 1. Smart agriculture: The products of the present invention can simultaneously monitor the moisture content of crop leaves and other conditions at multiple points to guide agricultural irrigation plans;

[0106] 2. Industrial production: The products of the present invention can monitor the environmental conditions of multiple production workshops and the temperatures of key components to ensure the smooth progress of the process;

[0107] 3. Healthcare: The products of the present invention can be used for inventory management to improve the tracking and management efficiency of items such as drugs and medical equipment;

[0108] 4. Smart home: The products of the present invention perform multi-point temperature measurement, which helps to automatically adjust the indoor temperature and create a comfortable living atmosphere.

[0109] There are already some examples of chip - less RFID temperature - measuring products, such as chip - less RFID temperature sensors fabricated using screen - printing technology. This kind of sensor utilizes a square single - split - ring resonator and multi - walled carbon nanotubes as temperature - sensitive materials, and measures temperature by detecting the shift of the resonance frequency. Experimental results show that this sensor has high temperature sensitivity and accuracy, and has certain application potential in wireless temperature measurement. The present invention combines chip - less RFID technology and the electromagnetically induced transparency effect for temperature measurement. The product has characteristics such as low cost, simple structure, high temperature sensitivity, and wireless temperature measurement, and has broad application prospects in various occasions that require temperature monitoring. With the continuous development of technology, the products involved in the present invention will become more and more mature and perfect, bringing more convenience and safety to people's life and work.

[0110] As described above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A temperature sensor with digital coding function, characterized in that: It includes a power divider, a quarter-wavelength open line, a combiner, a first open resonant ring, a second open resonant ring, a third open resonant ring and a fourth open resonant ring, four variable capacitance diodes, a dielectric substrate and a metal floor; The power divider, the quarter-wavelength open line and the combiner are directly connected and form a structure similar to a cross. The first open resonant ring, the second open resonant ring, the third open resonant ring and the fourth open resonant ring are respectively located at four positions of the cross structure. Four varactor diodes are located at the openings of the first open resonant ring, the second open resonant ring, the third open resonant ring and the fourth open resonant ring. The power divider, the quarter-wavelength open line, the combiner, the first open resonant ring, the second open resonant ring, the third open resonant ring and the fourth open resonant ring, and the four varactor diodes are located on one side of the dielectric substrate, and the metal floor is located on the other side of the dielectric substrate.

2. The temperature sensor with digital coding function as claimed in claim 1, characterized in that: The power divider, the quarter-wavelength open line, and the combiner are made of metal copper with a thickness of ounce, namely 0.035 mm; the power divider and the combiner are symmetrically distributed about the quarter-wavelength open line.

3. The temperature sensor with digital coding function according to claim 1, characterized in that: The first open resonant ring, the second open resonant ring, the third open resonant ring and the fourth open resonant ring are made of metal copper with a thickness of ounce, i.e., 0.035 mm; the first open resonant ring, the second open resonant ring, the third open resonant ring and the fourth open resonant ring have the same gap spacing as the power divider, the quarter-wavelength open line and the combiner; the first open resonant ring, the second open resonant ring, the third open resonant ring and the fourth open resonant ring have slightly different lengths and widths.

4. The temperature sensor with digital coding function according to claim 1, characterized in that: The four varactor diodes are exactly the same in size and are respectively located at the openings of the first open resonant ring, the second open resonant ring, the third open resonant ring and the fourth open resonant ring and connected to the rings.

5. The temperature sensor with digital coding function according to claim 1, characterized in that: The dielectric substrate is Rogers RT / duroid 5880, with a dielectric constant of 2.2, a substrate thickness of 0.254 mm, and a loss tangent of 0.0009.

6. The temperature sensor with digital coding function according to claim 1, characterized in that: The metal floor is copper with a thickness of 1 ounce, or 0.035 mm.

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