A high-temperature thin-film strain sensor

Abstract

The present invention belongs to the field of strain sensor technology, specifically relating to a high-temperature thin-film strain sensor comprising a substrate and a strain-sensitive grid. The strain-sensitive grid comprises an indium tin oxide layer and a platinum layer, the indium tin oxide layer deposited on the substrate, and the platinum layer deposited on the indium tin oxide layer. The indium tin oxide layer contains 50% by mass of indium oxide and 50% by mass of tin oxide. The high-temperature thin-film strain sensor provided by the present invention can be used at temperatures ranging from room temperature to 500°C and exhibits extremely high sensitivity at temperatures of 500°C. Unlike conventional metal foil strain gauges, which are several microns thick, the high-temperature thin-film strain grid is 500 nm thick, effectively transmitting the strain of the object being measured at high temperatures.

Description

Technical Field

[0001] The present invention belongs to the technical field of strain sensors, and in particular relates to a high-temperature thin-film strain sensor, and more particularly to a thin-film stress and strain sensor with high sensitivity and fast response at high temperatures. Background Art

[0002] The continuous development of the aerospace industry has led to increasingly complex operating environments that pose significant challenges to the performance of aerospace engines. Many flight components must operate under high temperatures, high pressures, and intense vibrations. Accurately sensing the operating conditions of various aircraft components and maintaining their proper operation relies on sensors designed to operate under these extreme conditions. High temperatures in spacecraft generate a range of thermal stresses in many components, and real-time monitoring of these stresses is crucial to ensuring flight safety.

[0003] Resistance strain gauges are based on the resistance strain effect, detecting changes in resistance to measure the strain of the object being measured. During measurement, the resistance strain gauge is in direct contact with the object being measured, accurately transmitting the strain. Common resistance strain gauges can be categorized as wire, foil, thin film, and thick film, depending on the sensitive grid fabrication process. Thin film strain gauges are fabricated using methods such as laser pulse deposition, vacuum evaporation, and magnetron sputtering. Aerospace engine components face complex environments of high temperature, high pressure, and strong vibration during operation, necessitating real-time monitoring of the thermal stresses experienced by the components. Temperature changes alter the resistance of the strain gauge and cause thermal expansion between the strain gauge and the object being measured, affecting the true strain measurement. Current commercial high-temperature strain gauges have a low operating temperature (less than 200°C) and a low sensitivity (approximately 2°C). Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a high-temperature thin-film strain sensor with high sensitivity and fast response at high temperatures, and extremely high sensitivity under 500°C insulation conditions. The high-temperature thin-film strain sensor of the present invention is less invasive to the test environment, and the preparation material is resistant to high temperatures, which effectively solves the above problems.

[0005] The present invention is specifically achieved through the following technical solutions.

[0006] A high-temperature thin-film strain sensor comprises a substrate on which a strain-sensitive grid is deposited. The strain-sensitive grid is made of a composite thin film consisting of an indium tin oxide layer and a platinum layer. The indium tin oxide layer is deposited on the substrate, and the platinum layer is deposited on the indium tin oxide layer.

[0007] The strain sensitive grid includes a plurality of vertical grids, the plurality of vertical grids are deposited in parallel on the substrate, a horizontal grid is connected between two adjacent vertical grids, the horizontal grid is deposited on the substrate, the vertical grids and the horizontal grids form a continuous S-shaped structure, the two ends of the continuous S-shaped structure are respectively connected to one end of a transition grid, and the other ends of the two transition grids are respectively connected to an electrode;

[0008] The horizontal gate, vertical gate, transition gate and electrode are all composite thin films composed of an indium tin oxide layer and a platinum layer. The indium tin oxide layer is deposited on the substrate, and the platinum layer is deposited on the indium tin oxide layer.

[0009] ITO (indium tin oxide) and platinum have excellent heat resistance. Composite high-temperature thin-film strain sensors made of ITO and Pt have a high gauge factor (GF), exceeding 10 under laboratory conditions. Furthermore, ITO has a negative temperature coefficient, while Pt has a positive temperature coefficient. The positive and negative temperature coefficients of the laminated film offset each other, making the resistance relatively stable over temperature, reducing the impact of thermal output on strain sensitivity factor measurements.

[0010] In a preferred embodiment of the present invention, the indium tin oxide layer contains 50% indium oxide by mass and 50% tin oxide by mass. ITO is a mixture of indium (III) oxide (In2O3) and tin (IV) oxide (SnO2), typically with a mass ratio of 90% In2O3 and 10% SnO2. The ITO used in the present invention has a mass ratio of 5:5 indium oxide to tin oxide, enabling extremely high sensitivity even at temperatures of 500°C.

[0011] In a preferred embodiment of the present invention, the indium tin oxide layer is 450nm thick, and the platinum layer is 50nm thick. Unlike conventional metal foil strain gauges, which are several microns thick, the high-temperature thin-film strain gauge in this invention is 500nm thick, effectively transmitting the strain of the measured object at high temperatures.

[0012] In a preferred embodiment of the present invention, the length of the continuous S-shaped structure is 6.3 mm, the width is 2.4 mm, the width of the vertical grid is 0.15 mm, and the distance between two adjacent vertical grids is 0.3 mm.

[0013] In a preferred embodiment of the present invention, the indium tin oxide layer and the platinum layer are deposited by magnetron sputtering.

[0014] In a preferred embodiment of the present invention, the substrate is an aluminum oxide sheet with a thickness of 0.5 mm, a length of 25 mm and a width of 17 mm.

[0015] In a preferred embodiment of the present invention, the strain sensor has a temperature resistance of 500°C.

[0016] In a preferred embodiment of the present invention, it is fixed to the surface of the component to be tested by high temperature glue.

[0017] In a preferred embodiment of the present invention, the electrodes are coated with conductive silver paste and connected to platinum wires for measuring resistance changes.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention provides a thin film strain sensor for use in a high-temperature environment. A strain-sensitive grid is deposited on a substrate. The material of the strain-sensitive grid is a composite thin film consisting of an indium tin oxide layer and a platinum layer. The indium tin oxide layer is deposited on the substrate, and the platinum layer is deposited on the indium tin oxide layer. The indium tin oxide layer contains 50% by mass of indium oxide and 50% by mass of tin oxide. The sensor has a high strain sensitivity coefficient at 500°C.

[0020] The strain-sensitive grid is deposited on a substrate and mounted on a high-temperature resistant, constant-strength cantilever beam. The substrate transmits the cantilever beam strain to the strain-sensitive grid, which then converts the strain into a change in the device's resistance. Strain sensitivity reflects the sensitivity of the strain-to-resistance signal conversion. Typical commercial metal foil strain gauges have a sensitivity of approximately 2 and a temperature resistance of up to 200°C. The high-temperature thin-film strain sensor of the present invention can be used at temperatures ranging from room temperature to 500°C. It exhibits extremely high sensitivity at 500°C and a short response time at room temperature. Unlike conventional metal foil strain gauges, which are several microns thick, the high-temperature thin-film strain grid is 500nm thick, effectively transmitting the strain of the measured object at high temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of cantilever beam strain test, where 1 is the cantilever beam; 2 is the substrate; 3 is the strain sensitive grid; 4 is the horizontal grid; 5 is the vertical grid; 6 is the transition grid; and 7 is the electrode.

[0022] Figure 2 The resistance change of the strain gauge in Example 1 under alternating stress at 500°C.

[0023] Figure 3 This is the relationship between the relative change of the strain gauge resistance and the strain in Example 1.

[0024] Figure 4 This is the response time test of Example 1.

[0025] Figure 5 This is a response time test of a step signal in Example 1.

[0026] Figure 6 The resistance change of the strain gauge under alternating stress at 500°C in comparative example 1.

[0027] Figure 7 This is the relationship between the relative change of the strain gauge resistance and the strain in comparative example 1. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below with reference to specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0029] The experimental methods and detection methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0030] The high-temperature thin film strain sensor provided by the present invention is deposited on a ceramic substrate and connected with a high-temperature conductive adhesive to output signals. Figure 1 As shown, a strain-sensitive grid 3 is deposited on the substrate 2 (for carrying the strain-sensitive grid and transmitting strain). The strain-sensitive grid 3 includes multiple vertical grids 5 (for detecting the magnitude of the strain). The multiple vertical grids 5 are deposited in parallel on the substrate 2. A horizontal grid 4 (for connecting) is connected between two adjacent vertical grids 5. The horizontal grid 4 is deposited on the substrate 2. The vertical grids 5 and the horizontal grid 4 form a continuous S-shaped structure. The two ends of the continuous S-shaped structure are respectively connected to one end of a transition grid 6 (for connecting the grid to the electrode). The other ends of the two transition grids 6 are respectively connected to an electrode 7 (for external lead detection of strain gauge resistance changes).

[0031] The horizontal gate, vertical gate, transition gate, and electrodes are all made of a composite thin film of ITO and Pt. A first sensitive layer of ITO (the indium tin oxide layer contains 50% indium oxide and 50% tin oxide by mass) is deposited on an alumina ceramic substrate. A second sensitive layer of Pt is then applied to the first sensitive layer. During strain testing, the entire structure is secured to a cantilever beam 1 (used to generate strain) using high-temperature adhesive. ITO and platinum exhibit excellent heat resistance, and the composite high-temperature thin-film strain sensor of ITO and Pt exhibits a high gauge factor (GF), exceeding 10 under laboratory conditions. Furthermore, ITO has a negative temperature coefficient, while Pt has a positive temperature coefficient. The positive and negative temperature coefficients of the laminated film offset each other, resulting in a relatively stable resistance with temperature changes, reducing the impact of thermal output on strain sensitivity factor measurements.

[0032] The deposition substrate of the high-temperature thin film strain sensor is a 0.5 mm alumina sheet with a length of 25 mm and a width of 17 mm.

[0033] The sensitive gate of the high-temperature thin-film strain sensor is a composite laminate of ITO (indium tin oxide) and Pt (platinum), with an overall thickness of 500nm. The ITO layer is 450nm thick, and the Pt layer is 50nm thick. This thinness allows for better transmission of strain in the object being measured at high temperatures.

[0034] The overall length of the structure consisting of the horizontal grid and the vertical grid is 6.3 mm, the width is 2.4 mm, the width of the vertical grid is 0.15 mm, and the vertical grid spacing is 0.3 mm.

[0035] Conductive silver glue is used to connect the electrodes to the platinum sheet carrying the platinum wire. The connection is established after hot pressing and air drying. The conductive silver glue has a maximum temperature resistance of 600°C and cures under room temperature and heating conditions, meeting testing conditions from room temperature to 500°C.

[0036] High-temperature glue is thinly applied to the surface of the cantilever beam with a scraper, and the strain sensor substrate is pressed and fixed to the surface of the cantilever beam through the high-temperature glue, and solidified at room temperature or heating conditions. The working length of the equal-strength cantilever beam is 540mm, the maximum width is 60mm, and the thickness is 5mm. The test area is an isosceles triangle, and the stress distribution on each cross section of the beam is uniform. The free end width of the beam is 15mm and the length is 145mm, which is convenient for dynamic load device support. The material is 65mn and the elastic modulus is 201GPa. No obvious plastic deformation occurs from room temperature to 600℃. The strain sensitive grid is deposited on the substrate and installed on the high-temperature resistant equal-strength cantilever beam. The substrate transmits the cantilever beam strain to the strain sensitive grid, and the strain sensitive grid converts the strain into a change in the device resistance. Strain sensitivity reflects the sensitivity of the strain-resistance signal conversion. The present invention has high sensitivity (GF=45) in a 500℃ environment and a short response time (τ<0.2S).

[0037] In a 500°C heat preservation environment, a cantilever beam is used to apply dynamic alternating displacement to a high-temperature thin-film strain gauge. The resistance of the strain gauge produces a regular waveform as the strain changes. The alternating displacement signal is set using a console and servo motor, and is set to a triangular wave to detect strain sensitivity. Within one cycle, the free end of the cantilever beam uniformly displaces to the maximum range and then rebounds. The average peak-to-peak value of the resistance-time relationship within one detection cycle is considered the resistance change ΔR, and the average trough value is considered the initial resistance value R0. The actual strain value ε of the strain gauge is calculated based on the displacement of the free end of the cantilever beam (see formula (1)). The strain sensitivity of the sensor is calculated using formula (2).

[0038]

[0039]

[0040] It should be noted that f is the displacement difference of the free end of the cantilever under pressure, and h is the thickness of the cantilever, which is 5 mm. l is the working length of the cantilever, which is 540 mm. β is the transfer coefficient of the cantilever surface strain transmitted to the strain-sensitive grid through the high-temperature adhesive and the substrate. It was experimentally verified to be 20%. A trapezoidal wave displacement signal was input into the console, the rise time was set to 0.02 s, and the upper and lower limit times of the cantilever were both set to 5 s. The relationship between the strain sensor resistance and time was recorded. The time difference between the resistance jump from the lower limit to the upper limit was defined as the response time τ. Compared with room-temperature strain gauges, high-temperature resistance strain gauges have a wider operating temperature range and higher operating temperature. At higher ambient temperatures, the strain grid material faces the risk of oxidation, introducing unstable factors and causing measurement errors. The present invention selects high-temperature resistant metal oxide materials ITO (indium tin oxide) and Pt (platinum) as strain-sensitive grid materials, which are prepared on an alumina substrate by a lamination method. By controlling the mass fraction of indium oxide and tin oxide, ITO with different components was obtained, and the strain sensitivity of composite thin film strain gauges with different ITO and Pt components was compared.

[0041] The composite thin film strain gauges of TO and Pt with different components are prepared. The specific preparation method is as follows:

[0042] Example 1

[0043] A strain-sensitive grid is deposited on the substrate, comprising a plurality of longitudinal grids deposited in parallel on the substrate, with a transverse grid connected between two adjacent longitudinal grids. The transverse grid is deposited on the substrate, and the longitudinal and transverse grids form a continuous S-shaped structure. The two ends of the continuous S-shaped structure are respectively connected to one end of a transition grid, and the other ends of the two transition grids are respectively connected to electrodes. The alumina substrate is a 0.5 mm alumina sheet with a length of 25 mm and a width of 17 mm.

[0044] The horizontal gate, vertical gate, transition gate, and electrode are all composite thin films composed of an indium tin oxide layer and a platinum layer. The indium tin oxide layer is deposited on the substrate, and the platinum layer is deposited on the indium tin oxide layer. ITO is deposited using magnetron sputtering with a DC sputtering power of 60W and a sputtering time of 2 hours. Pt is deposited on top of the ITO using magnetron sputtering with a DC sputtering power of 20W and a sputtering time of 10 minutes. The indium tin oxide layer contains 50% by mass of indium oxide and 50% by mass of tin oxide. The ITO film layer has a thickness of 450nm, the Pt film layer has a thickness of 50nm, and the overall thickness is 500nm.

[0045] Comparative Example 1

[0046] Compared with Example 1, a comparative example is provided, in which the ITO and Pt laminated film with a ratio of indium oxide to tin oxide of 9:1 is changed, comprising the following steps:

[0047] A strain-sensitive grid is deposited on the substrate, comprising a plurality of longitudinal grids deposited in parallel on the substrate, with a transverse grid connected between two adjacent longitudinal grids. The transverse grid is deposited on the substrate, and the longitudinal and transverse grids form a continuous S-shaped structure. The two ends of the continuous S-shaped structure are respectively connected to one end of a transition grid, and the other ends of the two transition grids are respectively connected to electrodes. The alumina substrate is a 0.5 mm alumina sheet with a length of 25 mm and a width of 17 mm.

[0048] The horizontal gate, vertical gate, transition gate, and electrode are all composite thin films composed of an indium tin oxide layer and a platinum layer. The indium tin oxide layer is deposited on the substrate, and the platinum layer is deposited on the indium tin oxide layer. ITO is deposited using magnetron sputtering with a DC sputtering power of 60W and a sputtering time of 2 hours. Pt is deposited on top of the ITO using magnetron sputtering with a DC sputtering power of 20W and a sputtering time of 10 minutes. The indium tin oxide layer contains 90% by mass of indium oxide and 10% by mass of tin oxide. The ITO film layer has a thickness of 450nm, the Pt film layer has a thickness of 50nm, and the overall thickness is 500nm.

[0049] The above-mentioned Example 1 and Comparative Example 1 were tested. During the test, they were fixed on an equal-strength cantilever beam by high-temperature glue, and the platinum sheet carrying the platinum wire was connected to the electrode with conductive silver glue. The connection was established after hot pressing and air drying. The conductive silver glue has a maximum temperature resistance of up to 600°C, and is cured under normal temperature and heating conditions, meeting the test conditions of room temperature to 500°C. The working length of the equal-strength cantilever beam is 540mm, the maximum width is 60mm, and the thickness is 5mm. The shape of the test area is an isosceles triangle, and the stress distribution on each cross section of the beam is uniform. The free end width of the beam is 15mm and the length is 145mm, which is convenient for the support of the dynamic load device. The material is 65mn and the elastic modulus is 201GPa. No obvious plastic deformation occurs from room temperature to 600°C.

[0050] In a 500°C heat preservation environment, a cantilever beam is used to apply dynamic alternating displacement to a high-temperature thin-film strain gauge. The resistance of the strain gauge produces a regular waveform as the strain changes. The alternating displacement signal is set using a console and servo motor, and is set to a triangular wave to detect strain sensitivity. Within one cycle, the free end of the cantilever beam uniformly displaces to the maximum range and then rebounds. The average peak-to-peak value of the resistance-time relationship within one detection cycle is considered the resistance change ΔR, and the average trough value is considered the initial resistance value R0. The actual strain value ε of the strain gauge is calculated based on the displacement of the free end of the cantilever beam (see formula (1)). The strain sensitivity of the sensor is calculated using formula (2).

[0051]

[0052]

[0053] Wherein, f is the displacement difference of the free end of the cantilever beam under pressure, h is the thickness of the cantilever beam, which is 5mm. l is the working length of the cantilever beam, which is 540mm. β is the transfer coefficient of the surface strain of the cantilever beam to the strain sensitive grid through the high-temperature glue and the substrate. It is verified by experiments to be 20%. Input the trapezoidal wave displacement signal into the console, set the rise time to 0.02S, set the upper limit time and the lower limit time of the cantilever beam to 5S, and record the relationship between the resistance of the strain sensor and time. The time difference when the resistance jumps from the lower limit to the upper limit is defined as the response time τ. In high-temperature strain measurement, temperature changes will cause the resistance of the strain gauge to change, and at the same time cause the strain gauge and the object to be measured to undergo thermal expansion, affecting the measurement of the true strain. In order to eliminate the false strain caused by temperature changes, the present invention performs strain testing under the condition of a constant temperature of 500°C. Keep it warm at 500°C for a period of time to improve the resistance stability of the strain gauge. Measure the resistance drift rate of the strain gauge to meet the conditions for measuring strain sensitivity.

[0054] The present invention fabricated a laminated composite thin-film strain sensor (Example 1 and Comparative Example 1) by depositing different mass fractions of ITO (indium oxide:tin oxide) and Pt on an alumina substrate. Electrodes were coated with conductive silver glue, connected to a platinum wire, and resistance changes were measured. The substrate was pressed and fixed to the center axis of a cantilever beam of constant strength using high-temperature adhesive. After curing, high-temperature strain measurements were performed. The strain sensor was placed in a high-temperature furnace and heated to a constant temperature. A servo motor controlled a pull rod to press down the free end of the cantilever beam.

[0055] The constant-strength cantilever beam is a strain-generating device. The surface strain of the cantilever beam acts on the strain-sensitive grid through high-temperature adhesive, substrate, and other media. The actual strain of the strain-sensitive grid causes a change in resistance. The surface strain of the cantilever beam and the actual strain of the strain-sensitive grid are proportional.

[0056] The control console is used in conjunction with the servo motor to input a triangular wave displacement signal to the free end of the cantilever beam, with a frequency of 1HZ and a maximum displacement difference of 60mm. During the downward pressure of the free end, the resistance of the strain sensor changes accordingly with the strain loading, and a graph is drawn showing the relationship between the relative change in resistance ΔR / R and the cantilever beam strain με. The slope of the curve is approximately the strain sensitivity of the sensitive grid under high temperature testing. Composite laminated films of ITO and Pt with different compositions are prepared, wherein the thickness of the ITO film is 450nm, the thickness of the Pt film is 50nm, and the overall thickness is 500nm. After testing, it was found that the composite film formed by ITO and Pt with a mass fraction of 5:5 showed high strain sensitivity when kept at 500℃ for a period of time. Figure 2 and Figure 3 The figure shows that when the strain increases from 0 to 200με, the overall resistance changes by 20Ω, and the calculated strain sensitivity GF is about 45.

[0057] The control console is used to cooperate with the servo motor to input a trapezoidal wave displacement signal to the free end of the cantilever beam, and the upper and lower limits of the displacement are maintained for a period of time. The time for the cantilever beam to rise from the lower limit to the upper limit is set to 0.02S, which is approximately a step signal, such as Figure 4 As shown. Record the resistance-time curve of the strain gauge when the cantilever beam reciprocates up and down, and calculate the response time. The time difference between the end of the lower limit and the beginning of the upper limit in the image is recorded as the response time τ. Take the time difference of the resistance jump when a step signal occurs. After calculation, τ < 0.2S, as shown Figure 5 shown. Figure 6 The resistance change of the strain gauge under the alternating stress at 500℃ in Comparative Example 1 is shown in Figure 2. Figure 7 The relationship between the relative change of strain gage resistance and strain in comparative example 1 is shown below: Figure 6 and Figure 7 The two graphs reflect the strain sensitivity together. Figure 3 and Figure 7 Comparison of slopes, Figure 3 The slope is greater than Figure 7 , the slope indicates sensitivity. The larger the slope, the better the sensitivity. It is expressed by calculating the conversion unit. Figure 3 The slope is around 45, for comparison Figure 7 The slope is about 16, indicating that the performance of 5:5 is better than 9:1.

[0058] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications of the present invention fall within the scope of the claims and their equivalents, such changes and modifications are intended to be included.

Claims

1. A high-temperature thin-film strain sensor, characterized in that: The invention comprises a substrate (2), a strain-sensitive gate (3) is deposited on the substrate (2), the material of the strain-sensitive gate (3) is a composite thin film consisting of an indium tin oxide layer and a platinum layer, the indium tin oxide layer is deposited on the substrate (2), and the platinum layer is deposited on the indium tin oxide layer; In the indium tin oxide layer, the mass fraction of indium oxide is 50%, and the mass fraction of tin oxide is 50%; The thickness of the indium tin oxide layer is 450 nm, and the thickness of the platinum layer is 50 nm; The strain sensitive grid (3) comprises a plurality of longitudinal grids (5), the plurality of longitudinal grids (5) being deposited in parallel on the substrate (2), a transverse grid (4) being connected between two adjacent longitudinal grids (5), the transverse grid (4) being deposited on the substrate (2), the longitudinal grids (5) and the transverse grid (4) forming a continuous S-shaped structure, the two ends of the continuous S-shaped structure being respectively connected to one end of a transition grid (6), and the other ends of the two transition grids (6) being respectively connected to an electrode (7); The horizontal grid (4), vertical grid (5), transition grid (6) and electrode (7) are all composite thin films consisting of an indium tin oxide layer and a platinum layer; Both the indium tin oxide layer and the platinum layer were deposited by magnetron sputtering; The strain sensor has a sensitivity GF=45 and a response time τ<0.2S in an environment of 500°C.

2. The high-temperature thin-film strain sensor according to claim 1, characterized in that: The length of the continuous S-shaped structure is 6.3 mm, the width is 2.4 mm, the width of the vertical grid is 0.15 mm, and the distance between two adjacent vertical grids is 0.3 mm.

3. The high-temperature thin-film strain sensor according to claim 1, wherein: The substrate (2) is an aluminum oxide sheet.

4. The high-temperature thin-film strain sensor according to claim 1, wherein: The substrate (2) is fixed on the surface of the component to be tested by means of high temperature glue.

5. The high temperature thin film strain sensor according to claim 1, characterized in that: Paint the electrodes with conductive silver glue and connect them with platinum wire.

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