Sensor, preparation method thereof, and integrated strain temperature sensing measurement system

Abstract

The present invention discloses a sensor that integrates strain and temperature measurement. The sensor comprises a strain sensing unit, connecting leads, a flexible substrate, and a covering layer. The strain sensing unit and connecting leads are attached to the flexible substrate, and the covering layer seals the strain sensing unit and connecting leads. The connecting leads are connected to the strain sensing unit and include a first lead, a second lead, and a third lead. The second lead and the third lead are connected to the same output pin of the strain sensing unit. The sensor's first, second, and third leads form a three-wire measurement system, eliminating errors caused by line resistance and line strain due to excessively long leads. This allows for both temperature measurement and, using the measured temperature, compensation for temperature errors during strain measurement, further improving the sensor's measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of strain-temperature sensing measurement, and in particular to a sensor and a preparation method thereof, and an integrated strain-temperature sensing measurement system. Background Art

[0002] Strain and temperature are crucial factors in the health monitoring of mechanical systems, aviation, and other fields. For example, during mechanical operation, mechanical components are subjected to stress, generating strain. Strain can monitor load, and excessive strain can lead to structural fracture. Furthermore, mechanical systems are affected by external temperature during operation. Temperature fluctuations not only affect the performance of the mechanical system, but uncontrolled temperature can also have irreversible consequences. Furthermore, the measurement parameters of strain sensors change with temperature. Designing sensors that can measure both strain and temperature and adjust strain based on temperature is crucial.

[0003] To monitor the health of mechanical, aerospace, and other systems, sensors must possess high reliability, small size, and low mass, while ensuring accurate measurement. However, current strain and temperature sensors are mostly fabricated on inflexible substrates. These sensors cannot fully conform to the curved surfaces of mechanical systems, leading to measurement errors. Furthermore, current sensors primarily measure a single parameter independently, rather than combining both. This leads to mutual influence between the two measurements, reducing accuracy. Furthermore, the simultaneous deployment of both sensors results in excessive and cluttered wire leads, which takes up space. While optical fiber-based sensors for simultaneous temperature and strain measurement are available, optical fiber's poor mechanical strength and bending flexibility, unlike metal, make them less suitable for the described operating conditions. Furthermore, traditional strain sensors are susceptible to lead resistance and temperature when applied to mechanical system structural testing, requiring further improvement in measurement accuracy.

[0004] In summary, the research on thin-film strain-temperature sensor measurement systems with flexible substrates, small size, and high integration will have dual value in scientific research and practical application in the field of structural health monitoring such as mechanical systems. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned background technology and provide a sensor and its preparation method and an integrated strain and temperature sensing measurement system. The integrated strain and temperature sensing measurement system of the present invention can not only sense strain and temperature, but also compensate for the lead resistance and temperature drift of strain, thereby achieving high-precision strain measurement and temperature measurement.

[0006] In order to achieve the above technical effects, the present invention adopts the following technical solutions:

[0007] A sensor integrating strain and temperature measurement, comprising a strain sensing unit, connecting leads, a flexible substrate, and a covering layer. The strain sensing unit and the connecting leads are both attached to the flexible substrate, and the covering layer is sealed over the strain sensing unit and the connecting leads. The connecting leads are connected to the strain sensing unit and include a first lead, a second lead, and a third lead. The second lead and the third lead are connected to the same output terminal of the strain sensing unit.

[0008] In the sensor of the present invention, the first lead, the second lead and the third lead are combined to form a three-wire measurement system, which can eliminate the errors caused by the line resistance and line strain due to the excessive length of the leads. Among them, the second lead and the third lead can form a thermocouple, which can measure the temperature on the one hand and use the measured temperature to compensate for the temperature error during the strain measurement on the other hand, thereby further improving the measurement accuracy of the sensor.

[0009] Furthermore, the second lead and the strain sensing unit are made of constantan, the first lead and the third lead are made of copper, the flexible substrate is made of polyimide, and the covering layer is made of polyparaxylene, so that the sensor has good flexibility and bendability and can be attached to a curved component for measurement.

[0010] At the same time, the present invention also discloses a thin-film integrated strain and temperature sensing measurement system, including the above-mentioned sensor and a measurement compensation circuit; the measurement compensation circuit includes a three-wire strain measurement circuit and a thermocouple measurement circuit; the three-wire strain measurement circuit is used to measure strain; the thermocouple measurement circuit is used to measure temperature; the connecting lead is connected to the three-wire strain measurement circuit; in actual measurement, the temperature value measured by the thermocouple measurement circuit is fed back to the three-wire strain measurement circuit for temperature compensation, thereby improving the strain measurement accuracy of the sensing measurement system; the thin-film integrated strain and temperature sensing measurement system of the present invention integrates two signal measurement functions in one sensor, and the measurement method is not a simple repeated superposition, but fully utilizes the designed sensor structure characteristics to achieve perception measurement of temperature and strain; in addition, the measurement signals are complementary, further improving the sensor measurement accuracy.

[0011] Furthermore, the three-wire strain measurement circuit includes a Wheatstone bridge, an operational amplifier circuit, and a low-pass filter circuit. The main function of the three-wire strain measurement circuit of the present invention is to eliminate the effects of excessive wire length and temperature changes on wire resistance. The Wheatstone bridge is connected to the three leads of the sensor's connecting leads, so that the bridge output remains balanced in the initial state. In the working state, the lead resistance is eliminated, and even if the temperature changes and the resistance changes, it will not affect the output. The voltage signal output by the Wheatstone bridge is connected to the operational amplifier circuit. The operational amplifier circuit is a proportional amplifier circuit that can amplify the voltage connected to the circuit. The voltage signal output by the operational amplifier circuit is input into the low-pass filter circuit to filter out noise in the signal and improve measurement accuracy. Among them, the Wheatstone bridge, operational amplifier circuit, and low-pass filter circuit are all existing relatively mature and commonly used circuit designs. The specific connection method of connecting the three-wire leads to the Wheatstone bridge so that even if the temperature changes and the resistance changes, it will not affect the output is also existing technology and will not be repeated here.

[0012] Furthermore, in the technical solution of the present invention, the thermocouple measurement circuit needs to comprehensively consider the measured cold and hot end temperatures, especially the influence of cold end temperature interference, and needs to compensate for it. Therefore, this solution adopts a measurement method based on an analog circuit; the thermocouple measurement circuit includes a temperature compensation circuit and a low-pass filter circuit, and the voltage signal output by the temperature compensation circuit is input to the low-pass filter circuit; measurement interference is eliminated; among them, the temperature compensation circuit and the low-pass filter circuit are existing relatively mature and commonly used circuit designs, and will not be repeated here.

[0013] Furthermore, the temperature compensation circuit includes a temperature sensor chip and a voltage divider resistor, which is connected to the output end of the temperature sensor chip; specifically, the voltage divider resistor can be realized by a sliding rheostat, which can realize the voltage dividing function and adjust the voltage divided into the thermocouple circuit according to the sensitivity of the thermocouple, thereby offsetting the change in the thermocouple output voltage value caused by the change in the cold end temperature and compensating for the cold end temperature; the specific design of compensating for the cold end temperature by realizing the temperature compensation circuit by the temperature sensor chip and the voltage divider resistor is a commonly used design in the prior art and will not be repeated here.

[0014] At the same time, the present invention also discloses a method for preparing the above-mentioned sensor, comprising the following steps:

[0015] A. Clean the silicon wafer and dry it for later use;

[0016] B. Prepare a sacrificial layer on the silicon wafer using a spin coating and heating process;

[0017] C. using a spin coating method to prepare a flexible base layer using a polyimide material on the sacrificial layer and performing a pre-baking curing and imidization treatment;

[0018] D. preparing a photolithographic copper pattern or a photolithographic constantan pattern on the flexible substrate by spin coating, ultraviolet exposure, heat reversal, ultraviolet exposure, development, and metal sputtering to form a metal sensing layer; wherein the photolithographic copper pattern constitutes the first lead and the third lead respectively; and the photolithographic constantan pattern constitutes the second lead and the strain sensing unit respectively;

[0019] E. Depositing parylene on the metal sensing layer to form a covering layer, and using TRT transfer to peel off the silicon wafer to obtain a sensor; the finished sensor will evenly fracture the sacrificial layer between the silicon wafer and the flexible substrate layer without destroying the integrity of the flexible substrate layer or causing cracks in the metal sensing layer, ultimately obtaining a complete thin-film sensor.

[0020] Furthermore, the sacrificial layer in step B is made of polymethyl methacrylate.

[0021] Furthermore, in the step D, metal chromium is used as an adhesion layer to adhere the metal sensing layer to the flexible base layer.

[0022] Furthermore, the step D is specifically as follows: performing the following processes on the flexible substrate layer in sequence: spin coating photoresist, drying, ultraviolet exposure, heating inversion, ultraviolet exposure, and development followed by sputtering, and first sputtering metal chromium, then sputtering copper or constantan, and using acetone for degumming to form a photolithographic copper pattern or a photolithographic constantan pattern.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The thin-film integrated strain temperature sensing measurement system of the present invention consists of a sensor that integrates strain and temperature measurement and a measurement compensation circuit. The sensor can not only sense strain signals, but also measure temperature signals. The measurement compensation circuit adopts a three-wire measurement scheme, which can completely eliminate the influence of the line resistance of the long lead connecting the strain area of the sensor. In addition, the temperature signal measured by the thermocouple can be used to temperature compensate the strain measurement results, thereby further improving the strain measurement accuracy of the sensor. At the same time, the sensor of the present invention is made on a flexible substrate, has good flexible bending performance, can be attached to curved surface components for measurement, and has a small strain sensitive area. Therefore, it is very suitable for application in the field of health monitoring of structures with small installation space, long measurement lines, and large temperature effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic diagram of the sensor of the present invention.

[0026] Figure 2 It is along Figure 1 Cross-sectional view in the AA direction.

[0027] Figure 3 It is a schematic diagram of a three-wire strain measurement circuit in a measurement compensation circuit in an embodiment of the present invention.

[0028] Figure 4 Schematic diagram of a thermocouple measurement circuit in a measurement compensation circuit in an embodiment of the present invention.

[0029] Figure 5 This is a schematic diagram of the temperature compensation principle of the strain unit of the thin film integrated strain temperature sensing measurement system of the present invention.

[0030] Reference numerals: 1 - strain sensing unit, 2 - first lead, 3 - second lead, 4 - third lead, 5 - covering layer, 6 - flexible substrate. DETAILED DESCRIPTION

[0031] The present invention will be further described and illustrated below in conjunction with the embodiments of the present invention.

[0032] Example:

[0033] Example 1:

[0034] like Figure 1 and Figure 2 As shown, a sensor that integrates strain and temperature measurement includes a strain sensing unit 1, connecting leads, a flexible substrate 6 and a covering layer 5. The strain sensing unit 1 and the connecting leads are neatly attached to the flexible substrate 6, and the covering layer 5 seals and covers the strain sensing unit 1 and the connecting leads to provide them with sealing protection. The connecting leads are connected to the strain sensing unit 1 and include a first lead 2, a second lead 3 and a third lead 4, wherein the second lead 3 and the third lead 4 are connected to the same output end of the strain sensing unit 1.

[0035] Specifically, in this embodiment, the second lead 3 and the strain sensing unit 1 are made of constantan, the first lead 2 and the third lead 4 are made of copper, the flexible substrate 6 is made of polyimide, and the covering layer 5 is made of polyparaxylene, so that the sensor has good flexibility and bendability and can be attached to a curved component for measurement.

[0036] In the sensor of this embodiment, the first lead 2, the second lead 3 and the third lead 4 are combined to form a three-wire measurement, which can eliminate the errors caused by the line resistance and line strain caused by the excessive length of the leads. Among them, the second lead 3 and the third lead 4 form a thermocouple, which on the one hand measures the temperature, and on the other hand uses the measured temperature to compensate for the temperature error during strain measurement, thereby further improving the measurement accuracy of the sensor.

[0037] When making a sensor, the connecting leads of the sensor are divided into wiring terminals and pad terminals, such as Figure 1The thinner left end of each connecting lead is the wiring terminal, and the thicker right end is the pad end. When making the sensor, only the wiring end of the connecting lead is attached to the flexible substrate 6 and sealed by the covering layer 5, and the pad end of the connecting lead is exposed to facilitate subsequent corresponding cable connection.

[0038] Example 2

[0039] A thin-film integrated strain and temperature sensing and measurement system comprises the sensor of Example 1 and a measurement compensation circuit; the measurement compensation circuit comprises a three-wire strain measurement circuit and a thermocouple measurement circuit; the three-wire strain measurement circuit is used to measure strain; the thermocouple measurement circuit is used to measure temperature; connecting leads are connected to the three-wire strain measurement circuit; during actual measurement, the temperature value measured by the thermocouple measurement circuit is fed back to the three-wire strain measurement circuit for temperature compensation, thereby improving the strain measurement accuracy of the sensing and measurement system. The thin-film integrated strain and temperature sensing and measurement system of the present invention integrates two signal measurement functions in a single sensor. The measurement method does not rely on simple repeated superposition, but rather fully utilizes the structural characteristics of the designed sensor to achieve sensory measurement of both temperature and strain. In addition, the measurement signals complement each other, further improving the measurement accuracy of the sensor.

[0040] The main function of the three-wire strain measurement circuit of the present invention is to eliminate the effects of excessive wire length and temperature changes on wire resistance. Specifically, the three-wire strain measurement circuit of this embodiment includes a Wheatstone bridge, an operational amplifier circuit, and a low-pass filter circuit. The Wheatstone bridge is connected to the three leads of the sensor's connecting leads, which can keep the bridge output balanced in the initial state. In the working state, the lead resistance is eliminated, and even if the temperature changes and causes the resistance to change, it will not affect the output. The voltage signal output by the Wheatstone bridge is connected to the operational amplifier circuit. The operational amplifier circuit is a proportional amplifier circuit that can amplify the voltage connected to the circuit. The voltage signal after amplification by the operational amplifier circuit is input into the low-pass filter circuit to filter out noise in the signal and improve measurement accuracy.

[0041] Specifically, such as Figure 3 As shown, the Wheatstone bridge circuit in this embodiment specifically includes fixed resistors R1 and R2, line resistors RL1 and RL2, a sensor RS, and a sliding rheostat RV2. The operational amplifier circuit includes fixed resistor R3, a sliding rheostat RV3, and an operational amplifier U1. This operational amplifier circuit is a proportional amplifier circuit, and the amplification factor is controlled by adjusting the value of the sliding rheostat RV3. The low-pass filter circuit specifically includes fixed resistors R4 and R5, a sliding rheostat RV4, an operational amplifier U2, and a capacitor C1. The main function of this filter circuit is to filter out noise in the signal and improve measurement accuracy.

[0042] Specifically, in the technical solution of this embodiment, the thermocouple measurement circuit needs to comprehensively consider the measured cold and hot end temperatures, especially the cold end temperature interference effect, and needs to compensate for it. Therefore, this solution adopts a measurement method based on an analog circuit; the thermocouple measurement circuit includes a temperature compensation circuit and a low-pass filter circuit. Specifically, Figure 4 As shown in FIG, in this embodiment, the temperature compensation circuit is implemented by the temperature sensor chip LM35 and the voltage divider resistor, wherein the voltage divider resistor is implemented by the sliding rheostat RV6, which can realize the voltage divider function and adjust the voltage divided into the thermocouple circuit according to the sensitivity of the thermocouple, thereby offsetting the change in the thermocouple output voltage value caused by the change in the cold end temperature and compensating for the cold end temperature. The voltage signal output by the temperature compensation circuit is input into the low-pass filter circuit to eliminate measurement interference, such as Figure 4 The low-pass filter circuit of the embodiment shown has the same structure as that of the three-wire strain measurement circuit, and specifically includes a resistor R7, a fixed resistor R8, a sliding rheostat RV5, an operational amplifier U3 and a capacitor C2.

[0043] like Figure 5 The figure shows the principle of temperature compensation of the strain unit of the thin film integrated strain temperature sensor measurement system of this embodiment. In the thin film integrated strain temperature sensor measurement system of this embodiment, the output signal of the strain sensing unit 1 includes the voltage difference ΔV caused by the strain. ε and the voltage difference ΔV caused by the ambient temperature T , where the voltage difference signal caused by the ambient temperature is a useless interference signal that will reduce the measurement accuracy, so it needs to be filtered out. Specifically, the calculation formula for the voltage difference caused by the ambient temperature is as follows: ΔV T =IR0(1+αΔT); where I is the input current; R0 is the initial resistance value of the strain measurement unit; α is the resistance temperature coefficient of the sensitive gate material of the strain measurement unit; and ΔT is the temperature change value.

[0044] The signal measured by the thermocouple measurement circuit can be converted into an initial temperature difference digital signal through A / D conversion, thereby obtaining the temperature difference ΔT. The temperature difference measured by the thermocouple measurement circuit is fed back into the above temperature difference signal calculation formula to calculate the voltage difference ΔV caused by the ambient temperature. T Then, the voltage difference ΔV caused by the calculated ambient temperature is subtracted from the pressure difference value of the output signal of the strain sensing unit 1 of the sensor. T The voltage difference ΔV caused by strain can be obtained ε , thereby removing the influence of temperature on strain measurement.

[0045] Example 3

[0046] Meanwhile, a method for preparing a sensor according to an embodiment 1 includes the following steps:

[0047] Step 1. Clean the silicon wafer. Prepare a clean silicon wafer and use acetone for ultrasonic cleaning at 80W for 5 minutes, then use alcohol for ultrasonic cleaning at 80W for 2 minutes, and finally use deionized water for ultrasonic cleaning at 40W for 3 minutes, and dry it for later use.

[0048] Step 2. Prepare a sacrificial layer; use PMMA (polymethyl methacrylate) as a sacrificial layer and spin-coat it on the silicon wafer. The specific spin-coating parameters are first a speed of 500 rpm for 10 seconds, then a speed of 3000 rpm for 30 seconds, and finally heating at 180°C for 5 minutes (to evaporate the solvent), finally forming a thin PMMA sacrificial layer.

[0049] Step 3. Spin-coat the PI (polyimide) substrate. Specifically, in this embodiment, the spin-coating parameters of PI are a rotation speed of 500 rpm for 15 seconds, then a rotation speed of 1500 rpm for 45 seconds and an acceleration of 500 r / s. A layer of low viscosity 1000-2000 cp is spin-coated, and then a layer of high viscosity 5000-6000 cp is spin-coated. The substrate is pre-baked at 90°C and then kept at 220°C for 1 hour to imidize the polyimide.

[0050] Step 4. Photolithography of the copper pattern, spin coating of AZ5214 photoresist, parameters are 1000 rpm for 10 seconds, 2000 rpm for 12 seconds, and 3000 rpm for 15 seconds, followed by pre-baking at 90°C for 60 seconds, UV exposure for 7.5 seconds, heating at 110°C for 60 seconds, reversing, UV exposure for 15 seconds, and sputtering after development. First, sputtering of metal chromium, sputtering parameters are 0.6 Pa, 70 W, 3 minutes, and then sputtering of copper, sputtering parameters are 0.8 Pa, 70 W, 25 minutes, and finally degumming with acetone;

[0051] Step 5. Photolithography constantan pattern, spin coating AZ5214 photoresist, parameters are 1000 rpm 10s, 2000 rpm, 12s; 3000 rpm 15s, then pre-bake at 90°C for 60s, UV exposure for 7.5s, heating at 110°C for 60s, reverse, UV exposure for 15s, and after development, sputter constantan, sputtering parameters are 0.8Pa, 70W, 25min, and finally debonding with acetone.

[0052] After steps 4 and 5, the metal sensing layer of the sensor is fabricated. The photolithographic copper pattern forms the first lead 2 and the third lead 4, respectively; the photolithographic constantan pattern forms the second lead 3 and the strain sensing unit 1, respectively. It should be noted that this embodiment uses the example of photolithography of the copper pattern followed by the constantan pattern. In practice, the photolithography of the constantan pattern can also be performed first and then the copper pattern.

[0053] Step 6. Deposit polyparaxylene as a covering layer 5 and use TRT tape to attach it to the sensor surface, separate the finished sensor sheet from the silicon wafer substrate, and then place the TRT tape on a hot plate and heat it at 130°C for 1 minute to inactivate the TRT tape layer and separate it from the sensor to obtain a complete sensor.

[0054] It will be understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present invention, and the present invention is not limited thereto. Those skilled in the art will appreciate that various modifications and improvements can be made without departing from the spirit and substance of the present invention, and such modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A thin film integrated strain temperature sensing measurement system, characterized in that: The invention comprises a sensor and a measurement compensation circuit; the sensor integrates strain and temperature measurement, and includes a strain sensing unit, a connecting lead, a flexible substrate and a covering layer; the strain sensing unit and the connecting lead are both attached to the flexible substrate, and the covering layer is sealed and covered on the strain sensing unit and the connecting lead; the connecting lead is connected to the strain sensing unit, and the connecting lead includes a first lead, a second lead and a third lead, wherein the second lead and the third lead are connected to the same output pin of the strain sensing unit; the second lead and the strain sensing unit are made of constantan, the first lead and the third lead are made of copper, the flexible substrate is made of polyimide, and the covering layer is made of polyparaxylene; the measurement compensation circuit includes a three-wire strain measurement circuit and a thermocouple measurement circuit; the three-wire strain measurement circuit is used to measure strain; the thermocouple measurement circuit is used to measure temperature; the three leads of the connecting lead are connected to the three-wire strain measurement circuit; The first, second, and third leads form a three-wire measurement system, eliminating errors caused by line resistance and line strain due to excessive lead lengths. The second and third leads form a thermocouple, which measures temperature and uses the measured temperature to compensate for temperature errors in strain measurements. The three-wire strain measurement circuit includes a Wheatstone bridge, an operational amplifier circuit, and a low-pass filter circuit. The Wheatstone bridge is connected to three leads of the sensor connection lead. The voltage signal output by the Wheatstone bridge is connected to the operational amplifier circuit, which is a proportional amplifier circuit. The voltage signal output by the operational amplifier circuit is input into the low-pass filter circuit to filter out noise in the signal. The thermocouple measurement circuit includes a temperature compensation circuit and a low-pass filter circuit, and the voltage signal output by the temperature compensation circuit is input to the low-pass filter circuit; The temperature compensation circuit includes a temperature sensing chip and a voltage dividing resistor, and the voltage dividing resistor is connected to the output end of the temperature sensing chip.

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