Wireless passive temperature sensor

Abstract

The invention relates to a wireless passive temperature sensor, which comprises a temperature-sensitive layer; a first inductance coil, a second inductance coil and a magnetic film. The first inductance coil is fixedly arranged on one side of the temperature-sensitive layer, the second inductance coil is fixedly arranged on the other side of the temperature-sensitive layer, and the first inductance coil and the second inductance coil are both spirally arranged with the direction perpendicular to the temperature-sensitive layer as the center. The spiral directions of the first inductance coil and the second inductance coil are opposite; the magnetic thin film is located on the side, away from the temperature-sensitive layer, of the second inductance coil, and the magnetic thin film fixedly abuts against the second inductance coil; or, the magnetic thin film is located on the side, away from the temperature-sensitive layer, of the first inductance coil, and the magnetic thin film fixedly abuts against the first inductance coil; and the magnetic film and the temperature-sensitive layer are arranged at an interval. The sensor has the excellent performance of high sensitivity, high accuracy and the like.

Description

Technical Field

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

[0002] In industrial environments, aerospace, transportation and other fields, real-time monitoring of the operation of each component is particularly important for the normal operation of the overall system. Most traditional sensors are powered by power or wired testing, but the installation of power supplies in harsh environments such as high temperature and confined spaces requires high operating skills, and external power supplies in precision components will affect other electronic components. LC wireless passive sensors can achieve testing in closed and confined environments, breaking through the shortcomings of sensors requiring power or signal reception requiring leads, and can achieve non-contact measurement.

[0003] The LC temperature sensors currently under study are only inductively sensitive or capacitively sensitive, that is, there is only one sensitive unit for temperature measurement, resulting in poor sensitivity and response time of this type of sensor. In addition, when using LC wireless passive sensors on metal mechanical parts such as bearings and wind turbine blades, the electromagnetic signal cannot be coupled between the external reading antenna and the sensor inductor coil due to the characteristics of metal reflection of electromagnetic waves, resulting in the inability of this type of sensor to perform parameter detection and wireless transmission on metal parts. Secondly, when this type of sensor is attached to the bent test piece, the sensor structure will be stretched or compressed, causing the initial resonant frequency of the sensor to drift when it is bent, resulting in problems such as excessive temperature detection errors or even errors. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a wireless passive temperature sensor, which has high sensitivity, can detect and wirelessly transmit the temperature of metal, and suppress the initial resonant frequency drift problem caused by the bending sensor, so that the sensor detects the temperature error of the bent test piece, etc., and has good applicability.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A wireless passive temperature sensor comprises: a temperature-sensitive layer; a first inductance coil and a second inductance coil, wherein the first inductance coil is fixedly arranged on one side of the temperature-sensitive layer, and the second inductance coil is fixedly arranged on the other side of the temperature-sensitive layer, and the first inductance coil and the second inductance coil are both spirally arranged with the direction perpendicular to the temperature-sensitive layer as the center, and the spiral directions of the first inductance coil and the second inductance coil are opposite; a magnetic film, located on the side of the second inductance coil away from the temperature-sensitive layer, and the magnetic film is fixedly abutted against the second inductance coil; or, the magnetic film is located on the side of the first inductance coil away from the temperature-sensitive layer, and the magnetic film is fixedly abutted against the first inductance coil; the magnetic film is spaced apart from the temperature-sensitive layer.

[0006] Preferably, along a direction perpendicular to the temperature-sensitive layer, the first inductor coil and the second inductor coil at least partially overlap.

[0007] Preferably, the magnetic film is attached to a flat test piece, the temperature-sensitive layer includes a first surface and a second surface arranged in parallel, the first inductance coil is in a planar spiral shape and is fixedly arranged on the first surface, and the second inductance coil is in a planar spiral shape and is fixedly arranged on the second surface; along the direction perpendicular to the temperature-sensitive layer, the distance between the first inductance coil and the second inductance coil is equal everywhere.

[0008] Preferably, along a direction perpendicular to the temperature-sensitive layer, a distance between the first inductor coil and the second inductor coil is 0.1-0.3 mm.

[0009] Preferably, the number of turns of the first inductor coil and the second inductor coil is 8 to 10, and the line spacing of the first inductor coil is equal everywhere, and the line spacing of the second inductor coil is equal everywhere.

[0010] Preferably, the magnetic film is attached to the arc-shaped test piece, the temperature-sensitive layer includes a first surface and a second surface both of which are arc-shaped, and one of the first surface and the second surface is located radially outside the other; the first inductance coil is fixedly arranged on the first surface, and the second inductance coil is fixedly arranged on the second surface.

[0011] Preferably, the first surface is located radially outside the second surface, and the line spacing of the first inductor coil is greater than the line spacing of the second inductor coil; or, the second surface is located radially outside the first surface, and the line spacing of the second inductor coil is greater than the line spacing of the first inductor coil.

[0012] Preferably, the outer diameter of the first inductor coil and the second inductor coil is 14.1-21.2 mm, the inner diameter is 9.3-15.7 mm, the line width of the first inductor coil and the second inductor coil is 0.3-0.5 mm; the thickness of the magnetic film is 0.25-0.35 mm.

[0013] Preferably, the material of the magnetic film is ferrite, the material of the temperature-sensitive layer is polyimide, the magnetic permeability of the magnetic film and the dielectric constant of the temperature-sensitive layer change with temperature, and the changing trends of the magnetic permeability of the magnetic film and the dielectric constant of the temperature-sensitive layer are the same.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: first, the magnetic film can be attached to the metal part to be tested, and the magnetic film can shield the reflection effect of the metal on the electromagnetic wave, so that the sensor of the present application can detect the temperature of the metal part and transmit it wirelessly. Secondly, the magnetic permeability of the magnetic film changes with the temperature, causing the change of the total inductance value (L) in the LC resonant circuit, and adding a sensitive unit with a temperature detection function to the inductor; in addition, the temperature change will affect the dielectric constant of the temperature sensitive layer, thereby causing the change of the total capacitance value (C) in the LC resonant circuit, and adding a sensitive unit with a temperature detection function to the capacitor; therefore, the sensor of the present application has two sensitive units, namely inductance and capacitance, which significantly improves the performance of the sensor sensitivity and response time; at the same time, since the spiral directions of the first inductor coil and the second inductor coil are opposite, according to Lenz's law, the mutual induction between the first inductor coil and the second inductor coil is enhanced, which improves the influence of the magnetic permeability on the total inductance value, so the temperature change can cause a significant change in the total inductance value, thereby further improving the performance of the wireless passive temperature sensor such as sensitivity and response time. In addition, the spiral directions of the first inductor coil and the second inductor coil are opposite, and the combination of the temperature-sensitive layer and the magnetic film can suppress the initial frequency drift of the sensor caused by the test piece attached to different curvature radii to a certain extent, thereby improving the temperature detection accuracy of the curved test piece. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 An exploded diagram of a wireless passive temperature sensor provided by an embodiment of the present invention; Figure 2 A cross-sectional view of a wireless passive temperature sensor provided by an embodiment of the present invention; Figure 3 A cross-sectional view of a wireless passive temperature sensor after bending provided by an embodiment of the present invention; Figure 4 The initial resonant frequency test of different sensors under bending provided by the embodiments of the present invention; Figure 5The variation trend of total inductance and capacitance values ​​in different sensor bending frequency tests provided by the embodiment of the present invention; Figure 6 The sensor performance test is performed using different structural parameters provided by the embodiment of the present invention; Figure 7 The sensor performance is tested using different magnetic film parameters provided in the embodiments of the present invention.

[0016] 1. First inductor; 2. Temperature-sensitive layer; 21. First surface; 22. Second surface; 3. Second inductor; 4. Magnetic film. DETAILED DESCRIPTION

[0017] The present invention will be described in more detail below in conjunction with the accompanying drawings. It should be noted that the description of the present invention with reference to the accompanying drawings is only illustrative and not restrictive. The various embodiments can be combined with each other to form other embodiments not shown in the following description.

[0018] See also Figures 1 to 3 The wireless passive temperature sensor includes a first inductor coil 1, a temperature-sensitive layer 2, a second inductor coil 3, and a magnetic film 4.

[0019] The first inductor 1 is fixedly disposed on one side of the temperature-sensitive layer 2. Specifically, the first inductor 1 can be printed on one side of the temperature-sensitive layer 2 by a dispensing process, and the first inductor 1 is arranged in a spiral. The second inductor 3 is fixedly disposed on the other side of the temperature-sensitive layer 2. Specifically, the second inductor 3 can be printed on the other side of the temperature-sensitive layer 2 by a dispensing process, and the second inductor 3 is arranged in a spiral. In order to enhance the total inductance value of the sensor, the spiral directions of the first inductor 1 and the second inductor 3 are opposite.

[0020] It should be clear that according to Lenz's law, since the spiral directions of the first inductor 1 and the second inductor 3 are opposite, the changing directions of the magnetic field are also opposite, and the mutual induction effect between the first inductor 1 and the second inductor 3 will be enhanced, and the total inductance value (L) is the inductance value of the first inductor 1 (L top ) and the inductance value of the second inductor 3 (L bot ), so the first inductor 1 and the second inductor 3 can amplify the influence of the magnetic permeability of the magnetic film 4 on the total inductance (L). When the temperature changes, the first inductor 1, the second inductor 3 and the magnetic film 4 will produce a synergistic effect, which will enhance the change in the total inductance of the sensor, further increase the change in the resonant frequency caused by the temperature, and ultimately improve the sensitivity and resolution of the wireless passive temperature sensor.

[0021] The magnetic film 4 may be located on the side of the second inductor 3 away from the temperature-sensitive layer 2, and the magnetic film 4 is fixedly abutted against the second inductor 3; or, the magnetic film 4 may also be located on the side of the first inductor 1 away from the temperature-sensitive layer 2, and the magnetic film 4 is fixedly abutted against the first inductor 1. Taking the example that the magnetic film 4 is located on the side of the second inductor 3 away from the temperature-sensitive layer 2, the magnetic film 4 may be bonded to the second inductor 3 by glue or the like. In addition, in order to detect the object to be measured, the side of the magnetic film 4 away from the second inductor 3 may also be coated with glue or other adhesives. It should be noted that when the magnetic film 4 is attached to the object to be measured by glue or other adhesives, the magnetic film 4 directly contacts the object to be measured, and the remaining structures do not directly contact the object to be measured.

[0022] In a direction perpendicular to the temperature-sensitive layer 2, the first inductor 1 and the second inductor 3 at least partially overlap. At this time, the effect of the change in magnetic permeability of the magnetic film 4 on the inductance value of the first inductor 1 and the second inductor 3 can be enhanced, further improving the change in the resonant frequency caused by temperature, and ultimately improving the sensitivity and resolution of the wireless passive temperature sensor.

[0023] It should be clear that when the temperature of the test piece changes, the dielectric constant of the temperature-sensitive layer 2 changes, thereby changing the total parasitic capacitance value of the first inductor 1 and the second inductor 3. At the same time, the temperature change will also change the magnetic permeability of the magnetic film 4. Combined with the double-layer inductor structure formed by the first inductor 1 and the second inductor 3, the change of the total inductance value in the LC resonant circuit is enhanced, and the total inductance value and the total parasitic capacitance value change in the same direction at the same time, further enhancing the resonant frequency of the present application when detecting temperature changes. Significant changes occur, and then the external device realizes wireless passive detection of temperature by measuring the resonant frequency.

[0024] In addition, the sensor designed with a magnetic film 4 and a double-layer inductor structure can achieve high-sensitivity, passive wireless detection and low-power temperature detection on the metal surface, solving problems in many aspects such as materials, reliability, repeatability and production costs, thereby providing support and guarantee for the industrial application of passive wireless temperature sensors.

[0025] In order to simplify the structure of the wireless passive temperature sensor and reduce the difficulty of the manufacturing process of the wireless passive temperature sensor, the double-layer inductor structure composed of the first inductor coil 1 and the second inductor coil 3 can form an LC resonant circuit with its own parasitic capacitance. The double-layer inductor structure can realize energy exchange with the external alternating electromagnetic field through electromagnetic induction, and can introduce energy into the LC resonant circuit through mutual inductance coupling with external devices, thereby eliminating the need for the LC resonant circuit to have its own power supply, thereby achieving the effect of passive sensing. Secondly, in the process of realizing wireless energy transmission through electromagnetic induction, the external electromagnetic field can load a specific signal and couple with the sensor to transmit the electromagnetic wave signal back, thereby realizing wireless signal transmission between the LC resonant circuit and the outside world.

[0026] The double-layer inductor structure formed by the first inductor coil 1 and the second inductor coil 3 does not need to be electrically connected. Through the mutual inductance effect, the inductance values ​​of the first inductor coil 1 and the second inductor coil 3 can be superimposed on each other, forming an increase in the total inductance value of the double-layer inductor structure. The increase in the total inductance value helps to improve the quality factor (Q) value of the circuit. The circuit with a high quality factor can work more effectively within a specific frequency range, thereby improving performance stability. At the same time, the parasitic capacitance formed by the double-layer inductor structure, the temperature-sensitive layer 2, and the magnetic film 4 can be used as the capacitance part in the LC resonant circuit, simplifying the structure of the wireless passive temperature sensor, which not only helps to reduce the volume and manufacturing process of the wireless passive temperature sensor, but also reduces the manufacturing cost.

[0027] In order to enhance the performance of the sensor, especially the improvement of the wireless coupling distance of the sensor, the structural parameters of the sensor are simulated. The relevant conclusions are as follows and the results are shown in Figure 6 .

[0028] It should be noted that Figure 6 The test results of coupling distance optimization of the structural parameters of the first inductor coil 1 and the second inductor coil 3 of the sensor of this application are shown. In each test, only one structural parameter of the first inductor coil 1 and the second inductor coil 3 is changed at the same time, and the other parameters remain unchanged, among which (a) only the inner diameter is changed; (b) only the outer diameter is changed; (c) only the line width is changed, and (d) only the number of turns is changed. The conclusions are as follows: (1) The outer diameter of the first inductor 1 and the second inductor 3 is preferably 14.1-21.2 mm, and the inner diameter is preferably 9.3-15.7 mm. The outer diameter within this range can improve the induction range of the first inductor 1 and the second inductor 3, and the inner diameter within this range helps to increase the coupling efficiency between the first inductor 1 and the second inductor 2.

[0029] (2) The line width of the first inductor coil 1 and the second inductor coil 3 is preferably 0.3-0.5 mm. The wider the line width, the higher the coupling efficiency. However, considering the size of the overall wireless passive temperature sensor, the line width should not be too large. Selecting a line width of 0.3-0.5 mm can ensure both sensor performance and volume for the first inductor coil 1 and the second inductor coil 3.

[0030] (3) The optimal number of turns of the first inductor 1 and the second inductor 3 is 8 to 10. When the number of turns is too small, the intensity of the induced electromagnetic field is too low, which is not conducive to the coupling between the first inductor 1 and the second inductor 3. When the number of turns is too large, the resistance will increase, resulting in increased energy loss, and the coupling distance cannot be effectively increased.

[0031] In general, the double-layer inductor structure formed by the first inductor coil 1 and the second inductor coil 3 has the following functions: (1) Signal transmission: The double-layer inductor structure can realize wireless signal transmission by exchanging energy with the external alternating electromagnetic field through electromagnetic induction.

[0032] (2) Temperature sensitive unit: The magnetic permeability of the magnetic film 4 changes with temperature, causing the total inductance value (L) in the LC resonant circuit to change, thereby adding a sensitive unit with temperature detection function to the inductor; at the same time, since the spiral directions of the first inductor coil 1 and the second inductor coil 3 are opposite, the double-layer inductor structure and the magnetic film produce a synergistic effect. According to Lenz's law, the mutual induction between the first inductor coil 1 and the second inductor coil 3 is enhanced, which increases the influence of the magnetic permeability on the total inductance value. Therefore, when the temperature changes, the total inductance value can change significantly, thereby further improving the sensitivity and response time of the wireless passive temperature sensor.

[0033] (3) Enhanced sensor performance: The double-layer inductor structure has the characteristics of high inductance and low resistance, which enhances the quality factor of the wireless passive temperature sensor. At the same time, since the spiral directions of the first inductor coil 1 and the second inductor coil 3 are opposite, the direction of change of the magnetic field is also opposite. The mutual induction effect between the first inductor coil 1 and the second inductor coil 3 will be enhanced. The total inductance value (L) is the inductance value of the first inductor coil 1 (L top ) and the inductance value of the second inductor 3 (L bot ) are superimposed on each other, so the double-layer inductor structure can amplify the effect of magnetic permeability on the inductance value, enhance the significant change in the resonant frequency of the present application when detecting temperature changes, thereby enhancing the sensitivity and response time of the wireless passive temperature sensor.

[0034] The first inductor 1 and the second inductor 3 can be planar spiral metal coils. The planar spiral inductor is a spiral inductor wound on a plane. Compared with the weakly coupled spiral inductor, the mutual inductance coefficient of the planar spiral inductor is relatively high, and a larger mutual inductance effect can be achieved in a relatively small size. At the same time, its structure is more compact than the traditional wire-wound inductor, easy to integrate, and convenient to manufacture, and is suitable for use in places with limited size and weight. In addition, the planar spiral metal coil has good thermal stability, and the performance parameters can be flexibly adjusted by optimizing the number of turns, line width, line spacing and other parameters of the metal coil.

[0035] It should be noted that the line spacing refers to the horizontal distance between two adjacent wires in the first inductor 1 or the second inductor 3 ; the line width refers to the width of the wire in the first inductor 1 or the second inductor 3 .

[0036] In order to enhance the sensitivity of the wireless passive temperature sensor, the material of the metal coil may be silver. Silver has a high electrical conductivity, which can effectively reduce the impedance of the LC resonant circuit, improve the quality factor, and improve the sensitivity of the wireless passive temperature sensor.

[0037] In order to enhance the corrosion resistance of the wireless passive temperature sensor, the surface of the first inductor 1 and the second inductor 3 is coated with a JPL-ring water-soluble anti-discoloration agent to prevent oxidation of silver and silver plating. The anti-discoloration agent can form an extremely thin nano protective film on the silver surface to prevent sulfide or other materials from reacting with it. The temperature-sensitive layer 2 can provide good adhesion to the formed nano protective film and form a good combination, so that the first inductor 1 and the second inductor 3 have excellent corrosion resistance and wear resistance, extend the service life of the wireless passive temperature sensor, and also enable the wireless passive temperature sensor to adapt to different application scenarios.

[0038] In order to improve the sensitivity and anti-interference ability of the wireless passive temperature sensor, the temperature-sensitive layer 2 uses polyimide (PI) material. Polyimide is a polymer compound formed by polymerization of monomers containing polyimide groups. Its chemical structure contains repeated imide units. This special structure gives polyimide excellent performance and is a high-performance engineering film. Polyimide has high tensile strength and modulus, excellent tensile and tear resistance, and good chemical corrosion resistance. It can resist the erosion of many chemicals, including strong acids and strong alkalis. Polyimide has excellent wear resistance and friction resistance, and shows good surface smoothness and wear resistance. It is suitable for applications that require long-term use and high-load conditions. The dielectric constant change of polyimide decreases with increasing temperature. The use of polyimide can improve the sensitivity and anti-interference ability of wireless passive temperature sensors. The temperature-sensitive layer 2 is made of polyimide with a thickness of 0.1 to 0.3 mm, because this thickness range ensures that its temperature-sensitive performance is fully exerted without taking up too much space or increasing the weight of the wireless passive temperature sensor. Therefore, the wireless passive temperature sensor is compact and lightweight, which meets the pursuit of miniaturization and lightweight sensors in modern applications.

[0039] The dielectric constant of the temperature-sensitive layer 2 changes with the change of temperature. After the dielectric constant of the temperature-sensitive layer 2 changes, the capacitance of the temperature-sensitive layer 2 also changes. Since the change trend of the dielectric constant of the temperature-sensitive layer 2 is the same as the change trend of the magnetic permeability of the magnetic film 4, the temperature-sensitive layer 2 can be used as a temperature-sensitive unit, and the first inductor 1 and the second inductor 3 are used as another temperature-sensitive unit. The combination of the two makes the wireless passive temperature sensor have better sensitivity.

[0040] In general, the use of polyimide material in the temperature-sensitive layer 2 has the following effects: (1) Synergistic effect of inductance and capacitance: Since the magnetic permeability of the magnetic film 4 decreases with increasing temperature, in order to ensure that the changing trends of the inductance and capacitance are consistent, the dielectric constant of the temperature-sensitive layer 2 should decrease with increasing temperature.

[0041] (2) Protecting the circuit and extending the life of the wireless passive temperature sensor: Polyimide has excellent chemical stability, and the inductor in the LC circuit in the present application is a double-layer inductor structure, and there is no physical connection between the first inductor coil 1 and the second inductor coil 3. If the first inductor coil 1 is used for a long time, it may be worn out. The second inductor coil 3 is located between the temperature-sensitive layer 2 and the magnetic film 4. Even if the first inductor coil 1 cannot be used after long-term wear, the second inductor coil 3 can still be used normally. Therefore, the wireless passive temperature sensor will only reduce some performance and will not affect normal use, which greatly extends the service life of the wireless passive temperature sensor.

[0042] In order to further improve the sensitivity of the wireless passive temperature sensor, and in order to realize the temperature measurement of the metal to be detected or in the metal environment, the magnetic film 4 is made of ferrite material. Ferrite is a special magnetic wave absorbing material, and its magnetic property enhances the magnetic induction intensity of the inductor coil. When the temperature changes, the magnetic permeability of the ferrite will change. Since the magnetic permeability of the ferrite will change due to the influence of temperature, the magnetic flux of the first inductor coil 1 and the second inductor coil 3 will change significantly, thereby changing the change of the inductance value. Therefore, the magnetic film can add the function of a sensitive unit to the first inductor coil 1 and the second inductor coil 3, that is, the first inductor coil 1 and the second inductor coil 3 can become a temperature sensitive unit, thereby increasing the sensitivity of the wireless passive temperature sensor.

[0043] At the same time, ferrite materials have high magnetic permeability and hysteresis loss. When electromagnetic waves pass through ferrite, the magnetic moment inside the ferrite will oscillate with the change of electromagnetic waves, causing current to be generated inside the ferrite. This current will cause a magnetic field to be generated inside the ferrite, thereby re-radiating part of the electromagnetic waves to avoid signal shielding in a metal environment. This greatly enhances the reliability and application scope of wireless passive temperature sensors, allowing wireless passive temperature sensors to perform temperature detection on metal test pieces or in a metal environment.

[0044] In order to enhance the performance of the sensor, especially to achieve wireless signal transmission on metal objects to be tested, the parameters of the magnetic film 4 are simulated, and the relevant conclusions are as follows: Figure 7 .

[0045] It should be noted that Figure 7 The test results of the parameters of the magnetic film 4 in the sensor of this application on the signal transmission are shown in Figure 1. In each test, only one structural parameter of the magnetic film 4 is changed, and the other parameters remain unchanged, including (a) thickness and (b) magnetic rate. The conclusions are as follows: (1) The thickness of the magnetic film 4 is preferably 0.25-0.35 mm. If the thickness is too small, the reflective characteristics of the metal cannot be shielded, and the signal quality cannot reach the best. If the thickness is too large, the performance of the wireless passive temperature sensor will be improved less, and the induced current will produce eddy current effect on the surface of the magnetic film 4, which will reduce the signal quality.

[0046] (2) The magnetic permeability of the magnetic film 4 is preferably 160-180 H / m. If it is too small, the reflection characteristics of the metal cannot be shielded and the signal quality cannot reach the best. If it is too large, the performance of the wireless passive temperature sensor will be improved little and the cost performance is low.

[0047] In general, the use of ferrite material in the magnetic film 4 has the following effects: (1) Expanding the application scope of sensors: Ferrite materials can shield and isolate the electromagnetic wave signals caused by metals, enabling wireless passive temperature sensors to measure the temperature of metal test pieces or in metal environments.

[0048] (2) Improving sensor performance: When the temperature changes, the magnetic permeability of the ferrite material will change, and the magnetic flux of the first inductor 1 and the second inductor 3 will also change. The double-layer inductor structure formed by the first inductor 1 and the second inductor 3 can achieve a synergistic effect, and the first inductor 1 and the second inductor 3 are added with the function of a sensitive unit, so that the number of sensitive units of the wireless passive temperature sensor is increased to two, thereby improving the sensitivity and response time of the wireless passive temperature sensor.

[0049] (3) Protection circuit: Under high humidity, condensation of water droplets will cause inductor short circuit, which seriously affects the robustness of the wireless passive temperature sensor. The magnetic film 4 attached to one side of the second inductor coil 3 can avoid condensation of water droplets, protect the circuit and extend the service life of the sensor.

[0050] From the composition structure of the above sensor, it can be seen that the synergistic effect of the magnetic film 4 on the sensitive unit is reflected in the following two aspects: (1) The magnetic permeability of the magnetic film 4 will affect the change of the inductance value. The present application has a first inductor 1 and a second inductor 3. The magnetic permeability will change the first inductor 1 and the second inductor 3 at the same time, thereby greatly improving the change of the total inductance value.

[0051] (2) Temperature changes the magnetic permeability of the magnetic film 4 and the dielectric constant of the temperature-sensitive layer 2, which in turn changes the total inductance and the total capacitance. The change trends of the total inductance and the total capacitance are simultaneous and in the same direction.

[0052] From the composition structure of the above sensor, it can be seen that the suppression effect of the magnetic film 4 and the temperature-sensitive layer 2 on the initial resonance frequency of the sensor during bending is reflected in the following two aspects: (1) When bent, the inductance value (L top ), the parasitic capacitance value (C1) of the first inductor 1 and the temperature-sensitive layer 2 and the inductance value (L bot ), the parasitic capacitance value (C3) of the second inductor 3 and the temperature-sensitive layer 2 has an opposite change trend, which suppresses the change range of the total inductance value and the total capacitance value.

[0053] (2) When bending, the total inductance and total capacitance change in opposite trends. According to the LC resonant frequency formula, the drift of the initial resonant frequency can be suppressed.

[0054] The working principle of the two sensitive units and the problem of suppressing the initial resonant frequency drift caused by bending in this application is as follows: (1) The first sensitive unit is the principle of parasitic capacitance;

[0055] in K(k) is the complete elliptic integral of the first kind, ε 0 and ε r are the dielectric constants of vacuum and temperature-sensitive layer 2, ε 0 The value is 8.5×10 -12 F / m, s is the line distance between the first inductor 1 and the second inductor 3, w is the line width of the first inductor 1 and the second inductor 3, d out is the maximum diameter of the first inductor 1 and the second inductor 3, n is the number of turns of the first inductor 1 and the second inductor 3. The parasitic capacitance of the first inductor 1 and the second inductor 3 will be affected by the voltage drop from the outermost circle to the inner circle. Considering the influence of the linear drop of voltage, it is selected to divide by the number of turns. n To approximate the situation where the capacitance is equal to the degradation factor, this is more similar to the total parasitic capacitance of the first inductor 1 and the second inductor 3.

[0056] When the external ambient temperature changes, the dielectric constant of the temperature-sensitive layer 2 changes due to the temperature change, which changes the parasitic capacitance value (C1) in the first inductor 1, the parasitic capacitance (C2) similar to the parallel plate structure, and the parasitic capacitance value (C3) in the second inductor 3, thereby changing the total parasitic capacitance value (C).

[0057] (2) The second sensitive unit is the principle of inductance;

[0058] μ r is the magnetic permeability of the magnetic film 4, l e is the effective magnetic path length, d is the thickness of the temperature-sensitive layer 2. When the external ambient temperature changes, the magnetic permeability of the magnetic film 4 will also change ( μ r ), the change of magnetic permeability will cause the inductance value of the first inductor 1 (L top ) and the second inductor 3 inductance value (L bot ) changes, thereby changing the total inductance value (L).

[0059] (3) The principle of suppressing the initial resonant frequency drift caused by bending.

[0060] When the first surface 21 is located radially outside the second surface 22, the first inductor 1 is equivalent to being stretched, that is, compared with the line spacing of the first inductor 1 in a planar spiral shape, the line spacing of the first inductor 1 will increase. At the same time, the second inductor 3 is equivalent to being compressed, that is, compared with the second inductor 3 in a planar spiral shape, the line spacing of the second inductor 3 will decrease. It can be seen that the line spacing of the first inductor 1 is greater than the line spacing of the second inductor 3. As the line spacing of the first inductor 1 increases, according to the above calculation formula of C1, it can be seen that the C1 value decreases. According to the above calculation formula of the first inductor 1 (L top ) calculation formula shows that as the line spacing increases, the effective magnetic circuit ( l e ) increases, which will lead to an increase in the inductance of the first inductor 1; while the line spacing of the second inductor 3 decreases. According to the above calculation formula of C3, it can be seen that as the value of C3 increases, the effective magnetic circuit ( l e ) decreases, which will cause the inductance value of the second inductor 3 (L bot ) is reduced. Therefore, when the wireless passive temperature sensor detects the DUT within a certain bending radius, the change amplitude of the total inductance value (L) and the total parasitic capacitance value (C) are significantly reduced and the trends are opposite, which can greatly reduce the initial frequency drift, thereby improving the accuracy of temperature detection.

[0061] Similarly, the second surface 22 may also be located radially outside the first surface 21 , and the effect is the same as that when the first surface 21 is located radially outside the second surface 22 , which will not be described in detail herein.

[0062] According to the resonant frequency f 0 The calculation formula is:

[0063] The resonant frequency of the wireless passive temperature sensor changes with the change of inductance and capacitance, and the inductance and capacitance change simultaneously and in the same direction, so that the resonant frequency of the wireless passive temperature sensor changes significantly, and then the wireless passive detection of temperature is realized by measuring the resonant frequency, that is, the resonant frequency of a wireless passive temperature sensor has a functional relationship with the temperature.

[0064] The above principle explains the technical approach of the present application to expand the sensitive unit of the wireless passive temperature sensor to two and suppress the initial resonant frequency drift problem caused by the bending of the sensor, which can significantly improve the performance of the sensor such as sensitivity and can suppress the initial resonant frequency drift problem caused by the bending of the sensor to a certain extent.

[0065] Beneficial effect: The wireless passive temperature sensor uses a temperature-sensitive material with good temperature-sensing properties as the temperature-sensitive layer 2. When the temperature changes, the dielectric constant of the temperature-sensitive layer 2 changes, causing the parasitic capacitance to change. At the same time, the magnetic permeability of the magnetic film 4 changes, so that the inductance and capacitance of the wireless passive temperature sensor are converted into sensitive units, and then the wireless passive temperature sensor can be quickly and accurately detected by wireless through the measurement of the resonant frequency.

[0066] A wireless passive temperature sensor in the present invention provides a method for realizing wireless passive detection based on a temperature-sensitive layer 2, a magnetic film 4, a first inductor 1, a second inductor 3 and an LC resonant circuit, and the sensitivity and anti-interference ability are greatly improved. At the same time, the wireless passive temperature sensor also has the advantages of simple structure, low power consumption, long life, easy integration, low measurement error, small size, process compatibility, etc.

[0067] In order to increase practicality, the wireless passive temperature sensor provided by the present invention can detect flat and curved test pieces.

[0068] When testing a flat object to be tested, the magnetic film 4 can be flatly attached to the object to be tested. The temperature-sensitive layer 2 includes a first surface 21 and a second surface 22, and the first surface 21 and the second surface 22 are arranged in parallel. The first inductor 1 is in a planar spiral shape and is fixedly arranged on the first surface 21, and the second inductor 3 is in a planar spiral shape and is fixedly arranged on the second surface 22.

[0069] At this time, along the direction perpendicular to the temperature-sensitive layer 2 , the distance between the first inductor 1 and the second inductor 3 is equal everywhere.

[0070] It should be clear that the direction perpendicular to the temperature-sensitive layer 2 refers to the direction perpendicular to the first surface 21 and the second surface 22 .

[0071] In the direction perpendicular to the temperature-sensitive layer 2, the distance between the first inductor 1 and the second inductor 3 is 0.1-0.3 mm, that is, the thickness of the temperature-sensitive layer 2 is 0.1-0.3 mm. It is very important that the number of turns of the first inductor 1 and the second inductor 3 is preferably 8-10 turns, and the line spacing of the first inductor 1 and the second inductor 3 is equal everywhere.

[0072] When testing a bent test piece, the wireless passive temperature sensor will also bend because the wireless passive temperature sensor needs to be attached to the test piece. Figure 3, a wireless passive temperature sensor is attached to the curved test piece, at this time, the first surface 21 and the second surface 22 are both arc-shaped, and one of the first surface 21 and the second surface 22 is located radially outside the other. The first inductor 1 is fixedly arranged on the first surface 21, and the second inductor 3 is fixedly arranged on the second surface 22, so the first inductor 1 and the second inductor 3 cannot maintain the planar spiral shape, but will bend with the temperature-sensitive layer 2.

[0073] Specifically, the principle of suppressing the initial resonance frequency drift problem caused by bending has been described above and will not be repeated here.

[0074] In order to illustrate the change of the resonant frequency of the wireless passive temperature sensor when it is bent, one embodiment and two comparative examples are provided for comparison and explanation.

[0075] Comparative Example 1: The second inductor coil 3 in the present application is removed, and other parameters and structures are the same. It is named a single-layer inductor plus ferrite LC sensor, and the resonant frequency test, total inductance value and total capacitance value test are carried out at room temperature (25°C) under different bending degrees.

[0076] Comparative Example 2: The magnetic material 4 of the present application is removed, and other parameters are the same. It is named a double-layer inductor ferrite-free LC sensor, and the resonant frequency test, total inductance value and total capacitance value test are carried out at room temperature (25°C) under different bending degrees.

[0077] Example 1: The wireless passive temperature sensor of the present application, named as a double-layer inductor plus ferrite LC sensor, was tested for resonant frequency, total inductance and total capacitance at different bending degrees at room temperature (25°C).

[0078] The inventors tested the resonant frequencies of the three types of sensors in Comparative Example 1, Comparative Example 2 and Example 1 at different bending degrees, and the simulation and experimental results are shown in Figure 4 , it can be seen that the simulation results are consistent with the experimental results. It should be noted that Figure 4 The initial resonant frequency tests of different sensors under bending include (a) single-layer inductor plus ferrite LC sensor; (b) double-layer inductor without ferrite LC sensor; (c) double-layer inductor plus ferrite LC sensor. The results show that the initial frequency of the LC sensor will drift when it is bent. However, the initial resonant frequency of the single-layer inductor plus ferrite LC sensor drifts by about 18 MHz, the initial resonant frequency of the double-layer inductor without ferrite LC sensor drifts by about 8 MHz, and the initial resonant frequency of the double-layer inductor plus ferrite LC sensor drifts by about 2 MHz in the bending test. This change shows that the wireless passive temperature sensor of the present application can significantly suppress the initial frequency drift problem in different bending states.

[0079] The inventors tested the total inductance and total capacitance of the three types of sensors in Comparative Example 1, Comparative Example 2 and Example 1 at different bending degrees, and the results are shown in Figure 5 It should be noted that Figure 5 The total inductance and total capacitance values ​​of three types of sensors under bending are tested, including: (a) single-layer inductor plus ferrite LC sensor; (b) double-layer inductor without ferrite LC sensor; (c) double-layer inductor plus ferrite LC sensor.

[0080] Simulation test results Figure 5 It shows that when the radius of curvature of the single-layer inductor plus ferrite LC sensor increases, the inductance value and parasitic capacitance value both increase, and the change trend is the same, resulting in a large drift of the initial resonant frequency, and the sensor has a significant error or even cannot work normally. When the radius of curvature of the double-layer inductor ferrite-free LC sensor increases, only the total inductance value increases, and the total capacitance value remains basically unchanged. This type of sensor has a large error. However, when the radius of curvature of the double-layer inductor plus ferrite LC sensor of the present application increases, its total inductance value gradually increases and the total capacitance value decreases. The change trends of the two are opposite, which can significantly suppress the drift problem of the initial resonant frequency.

[0081] For example: in the same environment, there is a flat piece to be tested and a bent piece to be tested, and a wireless passive temperature sensor is provided on both the flat piece to be tested and the bent piece to be tested. The temperature of the flat piece to be tested detected by the external device is 20 ℃. After the wireless passive temperature sensor is provided on the bent piece to be tested, it will bend to a certain extent. Therefore, the temperature of the bent piece to be tested detected by the external device will have a certain error from 20 ℃. It should be noted that since the inductance of the first inductor 1 increases, but the inductance of the second inductor 3 decreases, the total inductance value changes slightly. Therefore, the temperature of the bent piece to be tested detected by the external device may be 21 ℃, and the temperature error is small. However, the existing inductance-sensitive or capacitance-sensitive sensors have only one temperature-sensitive unit. When this temperature-sensitive unit is bent, its inductance or capacitance will change significantly, so that the temperature of the bent piece to be tested detected by the external device will have a large error from 20 ℃, and the detected temperature may be 25 ℃.

[0082] It should be noted that the above examples are intended to illustrate that the wireless passive temperature sensor can reduce initial frequency drift and improve temperature detection accuracy compared to existing sensors, but it does not mean that the wireless passive temperature sensor will definitely have errors when detecting bent test pieces.

[0083] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A wireless passive temperature sensor, characterized in that: include: Thermosensitive layer (2); A first inductor (1) and a second inductor (3), wherein the first inductor (1) is fixedly arranged on one side of the temperature-sensitive layer (2), and the second inductor (3) is fixedly arranged on the other side of the temperature-sensitive layer (2), with the direction perpendicular to the temperature-sensitive layer (2) as the center, the first inductor (1) and the second inductor (3) are both arranged in a spiral, and the spiral directions of the first inductor (1) and the second inductor (3) are opposite; The magnetic film (4) is located on a side of the second inductor (3) away from the temperature-sensitive layer (2), and the magnetic film (4) is fixedly abutted against the second inductor (3); or the magnetic film (4) is located on a side of the first inductor (1) away from the temperature-sensitive layer (2), and the magnetic film (4) is fixedly abutted against the first inductor (1); the magnetic film (4) is spaced apart from the temperature-sensitive layer (2).

2. The wireless passive temperature sensor according to claim 1, characterized in that: Along a direction perpendicular to the temperature-sensitive layer (2), the first inductor coil (1) and the second inductor coil (3) at least partially overlap.

3. The wireless passive temperature sensor according to any one of claims 1 to 2, characterized in that: The magnetic film (4) is attached to a flat test piece, the temperature-sensitive layer (2) comprises a first surface (21) and a second surface (22) arranged in parallel, the first inductor coil (1) is in a planar spiral shape and is fixedly arranged on the first surface (21), and the second inductor coil (3) is in a planar spiral shape and is fixedly arranged on the second surface (22); along a direction perpendicular to the temperature-sensitive layer (2), the distance between the first inductor coil (1) and the second inductor coil (3) is equal everywhere.

4. The wireless passive temperature sensor according to claim 3, characterized in that: Along a direction perpendicular to the temperature-sensitive layer (2), the distance between the first inductor coil (1) and the second inductor coil (3) is 0.1-0.3 mm.

5. The wireless passive temperature sensor according to claim 3, characterized in that: The number of turns of the first inductor coil (1) and the second inductor coil (3) is 8 to 10, and the line spacing of the first inductor coil (1) is equal everywhere, and the line spacing of the second inductor coil (3) is equal everywhere.

6. The wireless passive temperature sensor according to any one of claims 1 to 2, characterized in that: The magnetic film (4) is attached to the arc-shaped test piece; the temperature-sensitive layer (2) comprises a first surface (21) and a second surface (22) both of which are arc-shaped, and one of the first surface (21) and the second surface (22) is located radially outside the other; the first inductor coil (1) is fixedly arranged on the first surface (21), and the second inductor coil (3) is fixedly arranged on the second surface (22).

7. The wireless passive temperature sensor according to claim 6, characterized in that: The first surface (21) is located radially outside the second surface (22), and the line spacing of the first inductor coil (1) is greater than the line spacing of the second inductor coil (3); Alternatively, the second surface (22) is located radially outside the first surface (21), and the line pitch of the second inductor coil (3) is greater than the line pitch of the first inductor coil (1).

8. The wireless passive temperature sensor according to claim 1, characterized in that: The outer diameter of the first inductor coil (1) and the second inductor coil (3) is 14.1-21.2 mm, the inner diameter is 9.3-15.7 mm, the line width of the first inductor coil (1) and the second inductor coil (3) is 0.3-0.5 mm; the thickness of the magnetic film (4) is 0.25-0.35 mm.

9. The wireless passive temperature sensor according to claim 1, characterized in that: The material of the magnetic film (4) is ferrite, the material of the temperature-sensitive layer (2) is polyimide, the magnetic permeability of the magnetic film (4) and the dielectric constant of the temperature-sensitive layer (2) change with temperature, and the magnetic permeability of the magnetic film (4) and the dielectric constant of the temperature-sensitive layer (2) have the same change trend.

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