A thermal flexible flow sensor and its preparation method

Abstract

The present invention discloses a thermal flexible flow sensor and a preparation method thereof, comprising a flexible substrate, a conductive circuit, a sensitive layer and a thermal insulation device, wherein the conductive circuit and the sensitive layer are both located on one surface of the flexible substrate, the sensitive layer is a metal material or a semiconductor material, and the thermal insulation device is covered on the flexible substrate surface to reduce the influence of the outside world on the conductive circuit and the sensitive layer. Compared with the prior art, the laser integration technology based on the device of the present invention is suitable for processing a variety of materials, and materials can be selected as the sensitive layer and conductive circuit of the device in a targeted manner, and the required pattern can be accurately processed to obtain the best performance and structure. In addition, the device of the present invention not only combines the detection principle of hot wire and thermal temperature difference to greatly broaden the measurement range, but can also be flexibly attached to complex curved surfaces to measure the direction of flow velocity, thereby broadening the scope of use of the flow sensor.

Description

Technical Field

[0001] The present invention belongs to the field of flexible sensor technology and fluid measurement, and relates to a thermal flexible flow sensor and a preparation method thereof. The specific principle is based on the combination of thermal temperature difference type and hot wire type. Background Art

[0002] Fluid measurement is widely used in hydraulic and pneumatic pipelines, flight status detection, and deep-sea sensing. Obtaining information such as the flow velocity, flow direction, and flow field characteristics of the fluid is beneficial for flow management of pipeline systems and for determining the delivery status. It can also assist in determining whether the wing is stalled, and thus whether the flight is safe. Furthermore, in deep-sea conditions where visual measurement is not possible, sensing the flow state of the surrounding seawater through flow sensors also provides an auxiliary means for deep-sea self-perception. Traditional flow sensors are mostly pipe-type, making them difficult to install or unable to adapt to complex curved surface installation conditions. They are often installed with rigid connections, which alter the original surface of the device. Therefore, flexible flow sensors are of great significance in the field of fluid detection.

[0003] There are many different principles of flow sensors, such as piezoresistive, acoustic Doppler, and thermoelectric. However, existing cantilever-type piezoresistive flow sensors produce deflection under the hydrodynamic force of the fluid, and their resistance will change due to the piezoresistive effect. Its main disadvantages are: (1) the presence of the cantilever reduces the convenience of sensor installation; (2) a single cantilever cannot detect the direction of the flow velocity; (3) the presence of the cantilever interferes with the distribution of the original flow field, that is, the load effect is obvious. The acoustic Doppler type is accompanied by many problems such as complex signal collection and processing and susceptibility to temperature influence. Thermal structures are mostly based on thermocouples, namely the Seebeck effect, which uses the influence of the flow field on the thermal field to create a temperature difference between the upstream and downstream, and then outputs the signal based on the thermoelectric effect. This method often uses MEMS technology, which is complex to process and has a small range.

[0004] Compared with the MEMS technology based on thermocouples, the laser integration technology based on the flexible thermal flow sensor has the advantages of high energy density, easy and precise control of the spot diameter, direction and position, easy to obtain the sensor sensitive layer and main structure, and a wider processing environment. Laser integration technology refers to the interaction between laser and matter to adjust the laser processing mode such as power, speed, wavelength, pulse period and other parameters to achieve additive manufacturing or subtractive manufacturing. Laser integration technology can be combined with a variety of processing methods, such as the combination with electroless deposition technology. First, the metal seed layer is processed by laser, and then the structure designed by chemical plating laser is used to prepare complex two-dimensional metal micro-nano patterns. Compared with chemical vapor deposition (CVD), laser integration technology can be used to adjust the laser processing mode such as power, speed, wavelength, pulse period and other parameters to achieve additive manufacturing or subtractive manufacturing. Deposition, CVD), first of all, the material is targeted by laser processing as the sensitive layer and basic structure of the sensor to obtain the best performance and structural three-dimensional structure for heat treatment, and then a nano-metal film of a certain thickness is deposited on the three-dimensional structure by CVD; combined with transfer technology, laser transfer technology does not require lithography and etching to prepare metal microstructure devices on a variety of material substrates; in addition, laser can also be combined with interface cladding transfer, patterned deposition and other technologies to process sensors. At the same time, laser integration technology can be applied to various metal or non-metal materials.

[0005] It can be seen that through laser integration technology, we can widely and specifically select materials as the sensitive layer and basic structure of the sensor to obtain the best performance and structure. Based on this, the present invention provides a thermal flexible flow sensor. Summary of the Invention

[0006] The purpose of the invention is to address the deficiencies of the existing technology and provide a flexible flow sensor prepared by laser integrated direct writing processing, which has a more convenient processing method and a wider measurement range.

[0007] The purpose of the present invention can be achieved by adopting the following technical solutions:

[0008] A thermal flexible flow sensor includes a flexible substrate, a conductive circuit, a sensitive layer and a thermal insulation device. The flexible substrate is in the form of a film, which can be a film or fabric. The conductive circuit and sensitive layer are both on one side of the flexible substrate, and the other side of the flexible substrate is the measuring surface. The flexible substrate can be made of PI, PPS or PDMS materials. The sensitive layer can be made of metal material or semiconductor material. The thermal insulation device is covered on the non-measuring surface of the flexible substrate to reduce the impact of external temperature on the conductive circuit and sensitive layer. The sensitive layer includes a heat source and several pairs of temperature sensors. Each pair of temperature sensors is symmetrically distributed with the heat source as the center. Each heat source and temperature sensor are connected to the conductive circuit at both ends through electrode connection areas.

[0009] Another object of the present invention is to provide a method for preparing a thermal flexible flow sensor, the steps comprising:

[0010] Step 1: Design the conductive circuit and select appropriate processing methods for different materials to fix the conductive circuit on the flexible substrate;

[0011] Step 2: Using laser integration technology on a flexible substrate, the laser adjusts parameters to precisely process a sensitive layer with a specified pattern for different materials;

[0012] Step 3: Hand-apply conductive silver paste to modify the contact area between the conductive circuit and the sensitive layer in step 2 to ensure good contact between the two;

[0013] Step 4: Prepare a thermal insulation device cover on the sample obtained in step 3 using PDMS material.

[0014] Furthermore, the conductive circuit designed in step 1 is fixed on the flexible substrate. The conductive circuit can be obtained by printing a silver circuit on the flexible substrate using a screen printing plate, or by laser processing and sintering a metal material on the flexible substrate. The conductive circuit includes an electrode contact area and a circuit lead-out area.

[0015] Furthermore, the conductive circuit can be obtained by printing a silver circuit on the flexible substrate using a screen printing plate. According to a specific embodiment of the present invention, the specific steps may be:

[0016] (1) Fix the circuit printing screen horizontally on the screen printing table, and slightly pad one end with tin foil to ensure a certain pressing space;

[0017] (2) Place the PET on the screen printing table to prevent the silver paste from crossing the border and printing onto the metal table;

[0018] (3) Place the flexible substrate to be printed between the PET and the circuit printing stencil, and press the foot switch to start the air pump to adsorb the substrate;

[0019] (4) Stir the GC-SP360-A conductive silver paste until it becomes fluid, and use a medicine spoon to apply a sufficient amount of silver paste to the printing area of ​​the circuit printing screen;

[0020] (5) Maintaining a certain and similar force with both hands, quickly press the silver paste to cover the printed pattern of the circuit printing screen;

[0021] (6) After printing is completed, remove the flexible substrate, turn off the air pump, use Hieclean cleaning agent to clean the remaining silver paste on the circuit printing screen, and use an electric hot air drying oven to dry the printed circuit.

[0022] Furthermore, the method of laser processing and sintering metal materials can be used to obtain a conductive circuit on a flexible substrate. The method of laser processing and sintering metal materials is to sinter an oxide precursor ink of a conductive metal such as copper or nickel onto a flexible substrate using laser integration technology to obtain a conductive metal element. The specific steps are as follows:

[0023] (1) obtaining a metal precursor ink by adopting a formula and a mass fraction ratio;

[0024] (2) uniformly covering the surface of the flexible substrate with the metal precursor ink by a spin coating process to obtain a uniform precursor ink coating;

[0025] (3) Through laser integration technology, the precursor ink coating is sintered onto the flexible substrate according to the designed circuit pattern by utilizing the photothermal effect and photochemical reaction of the laser.

[0026] Furthermore, in step 2, a sensitive layer of a specified pattern is precisely processed on the flexible substrate using laser integration technology by a laser, and the sensitive layer is a metal material or a semiconductor material obtained by processing using laser integration technology.

[0027] Furthermore, the sensitive layer is prepared by laser integration technology, and the semiconductor material can be graphene or carbon nanotubes. According to a specific embodiment of the present invention, the specific preparation steps of the semiconductor material being graphene are as follows:

[0028] S1. Place the flexible substrate with the conductive circuit on the infrared laser platform and align it with the pre-processed pattern to ensure that the electrode connection area of ​​the sensitive layer obtained after laser carbonization corresponds to the electrode contact area of ​​the conductive circuit;

[0029] S2. Select appropriate processing power and speed laser processing parameters, use laser integration technology to laser modify the flexible substrate, form a conductive carbon material, and complete the preparation of the sensitive layer.

[0030] When the semiconductor material is carbon nanotubes, the preparation thereof can be as follows: the carbon nanotubes are first deposited on a conductive metal by chemical deposition (CVD) or the like, and then a stable carbon nanotube-metal connection is formed by laser in a specified pattern, thereby processing a carbon nanotube sensitive layer.

[0031] Furthermore, the sensitive layer is prepared using laser integration technology. The preparation method for the metal material can refer to the aforementioned method for laser processing and sintering metal materials to form a conductive circuit. Using laser integration technology, a metal precursor ink coating is sintered onto a flexible substrate according to the designed sensitive layer pattern to form a metallic sensitive layer. When both the conductive circuit and the sensitive layer are made of metallic materials, laser processing can be used to directly produce the entire pattern in one go, and the subsequent step 3 can be omitted. When laser processing is used to prepare a semiconductor material sensitive layer, a high-power infrared laser with a strong thermal effect is often used. When the sensitive layer is made of metallic material, a low-power ultraviolet laser or continuous green laser with precise processing is often used.

[0032] Furthermore, in step 3, conductive silver paste is applied by hand to modify the contact area between the conductive circuit and the sensitive layer area in step 2 so that the two are in good contact. Specifically, the electrode contact area of ​​the conductive circuit is in contact with the electrode connection area corresponding to the sensitive layer, and the contact area is modified with conductive silver paste to ensure good contact between the conductive circuit and the sensitive layer.

[0033] Furthermore, according to a specific embodiment of the present invention, step 4 of preparing a thermal insulation device using PDMS material is specifically as follows:

[0034] (1) Design the size diagram of the PDMS air cavity. The PDMS air cavity is in the shape of a circular lid because the PDMS is solidified and demolded under the acrylic plate mold. Design the mold pattern;

[0035] (2) cutting the acrylic sheets, aligning them, and splicing them together using acrylic adhesive to obtain a mold;

[0036] (3) Introducing the well-proportioned PDMS (prepolymer: curing agent mass ratio 15:1);

[0037] (4) Place in a 75°C environment to cure for about 50 minutes;

[0038] (5) After curing, place the PDMS in a FUJIWARA vacuum chamber to remove bubbles from the PDMS for 30 minutes.

[0039] The beneficial technical effects of the present invention are:

[0040] 1. The present invention combines the detection principles of hot wire and thermal temperature difference. The hot wire measurement range is as wide as 25m / s, and the thermal temperature difference can measure the flow velocity direction.

[0041] 2. Using PI, PPS or PDMS materials as flexible substrates, it can adapt to different installation surfaces, and the film-like structure can be installed in pipes or other complex environments without damage.

[0042] 3. The sensor of the present invention is a thin film structure, and its thickness is less than 100 microns except for the thermal insulation device (the thickness of the thermal insulation device in the present invention is about 2 mm, of which the air cavity is about 1.5 mm high. The device is generally tightly covered on the surface of the sensor and has little effect on the flow field. If the flow field has high requirements on thickness, the thermal insulation device can be omitted). The existing columnar piezoresistive flow sensors are mostly mm-level or even cm-level. Compared with the existing columnar piezoresistive flow sensors, the interference to the original flow field is smaller. At the same time, compared with the acoustic flow sensor, the thin film structure makes the signal less likely to be blocked during transmission and has low noise; and compared with the optical flow sensor, the cost is low, and extremely expensive and sophisticated equipment is not required, and the scope of application is wide.

[0043] 4. The conductive circuit and sensitive layer of the present invention can be prepared by laser integration technology. Laser integration technology is applicable to metal and non-metal materials, making the preparation process of the present invention more convenient and able to more accurately prepare the conductive circuit and sensitive layer of the corresponding pattern, making the detection results of the device more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 1 is a schematic structural diagram of an embodiment of the thermal flexible flow sensor of the present invention, wherein a is a schematic structural diagram of the sensor, b is a structural diagram of the sensor, and c is a structural diagram of the thermal insulation device;

[0045] Figure 2 This is a measurement experiment diagram of the thermal flexible flow sensor of the present invention;

[0046] Figure 3 This is a diagram showing the processing results of the metal sensitive layer in the thermal flexible flow sensor of the present invention;

[0047] Figure 4 The conductive circuit and sensitive layer of the thermal flexible flow sensor of the present invention are prepared on the PI fabric;

[0048] Figure 5 This is a calibration diagram of the thermal performance of the semiconductor sensitive layer of the thermal flexible flow sensor of the present invention;

[0049] Figure 6 This is a heat source calibration diagram of the semiconductor sensitive layer of the thermal flexible flow sensor of the present invention;

[0050] Figure 7 This is a thermal temperature difference performance measurement diagram of the thermal flexible flow sensor of the present invention under different heat source powers;

[0051] Figure 8 This is a thermal temperature difference performance measurement diagram of the thermal flexible flow sensor of the present invention at different distances between the heat source and the temperature sensor;

[0052] Figure 9This is a thermal temperature difference measurement diagram of the thermal flexible flow sensor of the present invention under different flow rates under the condition of fixed heat source voltage;

[0053] Figure 10 This is a hot-wire measurement diagram of the thermal flexible flow sensor of the present invention at different flow rates under a fixed heat source voltage condition;

[0054] Figure 11 1 is a diagram showing the thermal temperature difference and hot wire simulation results of the thermal flexible flow sensor of the present invention, wherein a is the simulation result of the thermal temperature difference method and b is the simulation result of the hot wire method;

[0055] In the figure: 1. Flexible substrate; 2. Conductive circuit; 3. Sensitive layer; 4. Thermal insulation device. DETAILED DESCRIPTION

[0056] The following embodiments of the technical solution of the present invention are described in detail. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and are therefore only used as examples and are not intended to limit the scope of protection of the present invention.

[0057] The thermal flexible flow sensor of the present invention combines the detection principles of thermal temperature difference and hot wire, and utilizes the interaction between flow field and thermal field to measure flow velocity.

[0058] The principle of thermal temperature difference is that, in a zero-flow state, the heat generated by the intermediate heat source is theoretically transferred symmetrically. When fluid flows, while maintaining the power of the heat source constant, the fluid will carry some heat downstream, disrupting the original symmetrical thermal field and causing a temperature difference between upstream and downstream. When the flow rate reverses, the thermal field shifts in the opposite direction, and the temperature sensor also changes in the opposite direction. The direction of flow velocity can be determined by the voltage change trend (or the voltage sign after eliminating zero drift) of the Wheatstone bridge or voltage divider circuit. Because the fluid also cools the thermal field, a saturated flow rate will occur. When the sensor is not saturated, the greater the flow rate, the greater the sensor voltage output.

[0059] The hot wire principle is to pass a fixed voltage / current through a heating resistor (hot wire). The hot wire reaches a certain stable temperature due to the Joule heating effect, and the fluid passing through it reaches a convective heat transfer equilibrium. The greater the flow rate, the lower the hot wire temperature, but a single hot wire cannot measure the direction of the flow rate.

[0060] The method of the present invention can obtain a thermally stable and linear thermal resistor with a small thermal sensitivity coefficient (characteristic value of about -0.05%) (such as Figure 5) sensitive layer state. When the flow rate changes, the maximum temperature change of the heat source is equal to the difference between the flexible substrate's temperature limit and room temperature, approximately 200°C. At this time, the heat source's resistance change rate is approximately 0.1%, and its power change is not significant. Therefore, the heat source can be considered both as a constant-power heat source for the upstream and downstream temperature sensors in the thermal temperature difference measurement method and as the hot wire resistance in the hot wire measurement method. Therefore, the two measurement methods can be used in conjunction.

[0061] A thermal flexible flow sensor, such as Figure 1 As shown, it includes a flexible substrate 1, a conductive circuit 2, a sensitive layer 3 and a thermal insulation device 4. The flexible substrate 1 is in a film shape. The conductive circuit 2 and the sensitive layer 3 are both on one side of the flexible substrate 1. The other side of the flexible substrate 1 is a measuring surface. The flexible substrate 1 can be made of materials such as PI, PPS or PDMS. As long as the flexible substrate contains rich aromatic and imide repeating units, it can be modified by laser integration to form a conductive carbon material.

[0062] The sensitive layer can be made of metal or semiconductor material. The thermal insulation device 4 can be covered on the flexible substrate 1 to reduce the influence of the external temperature on the conductive circuit 2 and the sensitive layer 3. Figure 1 ), the sensitive layer 3 includes six electrode connection areas, two temperature sensors and a heat source, the heat source is in a broken line shape, the two temperature sensors are symmetrically distributed on both sides of the heat source with the heat source as the center, when the fluid flows through, a temperature difference appears between the two symmetrical temperature sensors, and the detected voltage will also change, thereby realizing the detection result by utilizing the thermal temperature difference detection principle, since the heat source has resistance and can generate heat after being energized, the temperature sensor and the heat source are made in one piece, and the two are in the same place, so the temperature and fluctuation changes detected by the temperature sensor are obtained by the change in the output voltage, and the results of the two detection principles can be output at the same time, thereby realizing the combination of the hot wire detection principle and the thermal temperature difference detection principle, so that the flow detection combines the advantages of the two detection principles, so that the detection range is larger, the sensitivity is higher, and the direction of flow field flow can be determined, and at the same time, the sensitive layer is thin and is on a thin film-like flexible substrate, so that the flow sensor of the present invention is small in size and can be applied to narrower and more complex spaces.

[0063] Example 1:

[0064] A method for preparing a thermal flexible flow sensor, comprising the following steps:

[0065] Step 1: Design a conductive circuit and fix it on a flexible substrate 1. The conductive circuit can be obtained by laser processing and sintering metal materials on the flexible substrate. The conductive circuit includes six electrode contact areas and a circuit lead-out area. The circuit lead-out area is connected to an FPC adapter board with a corresponding number of pins and a circuit with a data acquisition function pre-built on a breadboard. The circuit transmits the collected voltage signal to a computer terminal, completing the sensor signal transmission;

[0066] The method of laser processing and sintering metal materials can be used to obtain a conductive circuit on a flexible substrate. The method of laser processing and sintering metal materials is to sinter oxide precursor ink of conductive metals such as copper and nickel onto a flexible substrate using laser integration technology to obtain a conductive metal element. Cu is selected as the material for the conductive circuit. The specific preparation steps are as follows:

[0067] (1) A CuO metal precursor ink was prepared by adopting a formula and mass fraction ratio (polyvinyl pyrrolidone 25%, ethylene glycol 15%, copper oxide nanowires 60%), combined with heating, stirring and ultrasonic dispersion;

[0068] (2) uniformly coating the CuO metal precursor ink on the surface of the flexible substrate by a spin coating process to obtain a uniform CuO precursor ink coating;

[0069] (3) Through laser integration technology, the CuO precursor ink coating is sintered into metal Cu according to the designed circuit pattern on the flexible substrate using the photothermal reduction effect of the laser, thus obtaining a conductive circuit.

[0070] Step 2: Using laser integration technology, a laser is used to precisely process a sensitive layer of a specified pattern on a flexible substrate. The sensitive layer is a metal material or a semiconductor material processed using laser integration technology.

[0071] When the sensitive layer is made of semiconductor material, the flexible substrate can be directly carbonized in one step. For example, the flexible substrate is a PI film, and the preparation of the sensitive layer is as follows:

[0072] S1. Place the flexible substrate 1 with the conductive circuit obtained in step 1 on a VLS6.75-SYS infrared laser platform and align the pre-processed pattern to ensure that the electrode connection area of ​​the sensitive layer obtained after carbonization corresponds to the electrode contact area of ​​the conductive circuit;

[0073] S2. Select appropriate processing power and speed laser processing parameters (adjust to 18% power and 20% speed in the software interface supporting the laser; the power can also be fine-tuned to 20%), use laser integration technology to laser modify the flexible substrate 1 to form a conductive carbon material, and complete the preparation of the sensitive layer.

[0074] Step 3: Hand-apply conductive silver paste to modify the contact area between the conductive circuit and the carbonized area in step 2: the six electrode contact areas of the conductive circuit correspond to and contact the six electrode connection areas of the sensitive layer, and the contact areas are hand-applied with conductive silver paste to ensure better contact between the conductive circuit and the sensitive layer.

[0075] Step 4: Prepare a thermal insulation device using PDMS material. The specific steps are as follows:

[0076] (1) Design the dimensions of the PDMS air cavity, which is in the shape of a circular lid. The PDMS is solidified and molded under an acrylic plate mold, and the mold pattern is designed;

[0077] (2) cutting acrylic sheets according to the mold pattern designed in (1), aligning them, and splicing them together using acrylic adhesive to obtain a mold;

[0078] (3) Introducing PDMS liquid with a prepolymer: curing agent mass ratio of 15:1;

[0079] (4) Place in a 75°C environment to cure for about 50 minutes;

[0080] (5) After curing, place the PDMS in a FUJIWARA vacuum chamber to remove bubbles from the PDMS for 30 min;

[0081] (6) After taking it out, the PDMS air cavity is obtained.

[0082] Calibrate the sensor.

[0083] The experimental conditions of the voltage output test of the present invention are as follows Figure 2 As shown, a thermal flexible flow sensor was connected to a voltage divider circuit with the non-carbonized area facing upward and placed in a piping system. Calibration and measurement experiments were performed using an OUTSTANDING 2×1100-50L pump and an MF5712 commercial flow meter. The airflow was kept as horizontal as possible with the sensor to prevent structural changes that could cause sudden changes in resistance. The air pump was turned on and the valve opening was gradually increased to observe how the output voltage changed with flow rate.

[0084] Thermal temperature difference measurement results are as follows Figure 9 As shown in the figure, when the flow velocity increases, the upstream and downstream thermal temperature difference first increases and then decreases. The flow velocity corresponding to the maximum point is called the saturated flow velocity. The figure shows that the saturated flow velocity is about 1.2m / s. The thermal temperature difference formula is sensitive to small flow velocities. Due to the large experimental range, in order to more clearly display the small flow velocity data points, the local 0-5m / s interval is magnified and displayed. After calculation, the sensitivity of the thermal temperature difference formula at the origin is about 108K / (m / s).

[0085] Hot wire measurement results are as follows Figure 10As shown in the figure, when the flow velocity increases, the hot wire temperature gradually decreases, and the decreasing speed gradually decreases, and finally stabilizes at 25m / s. By zooming in on the local 0-5m / s, it can be seen that the linearity of the hot wire measurement in this range is good. After calculation, the sensitivity of the hot wire is about 29K / (m / s).

[0086] The above results are obtained by converting the measured voltage data and the thermal sensitivity coefficient. The sensitivity is defined as the slope at 0m / s.

[0087] The results show that the sensor can measure the size of the flow velocity. The thermal temperature difference type can measure the direction of the flow velocity due to its structural characteristics and is sensitive to small flow velocities (0-1m / s). The hot wire type can expand the measurement range to 25m / s.

[0088] Pre-calibration experiment of the sensor:

[0089] The thermal calibration experiment of the carbonized semiconductor was carried out using the ESPEC sh262 temperature and humidity bellows and the HIOKI U8552 voltage sampler. The experimental method of this part is to place the sensor in the bellows, connect it to the voltage divider measurement circuit with alligator clips, and then transmit the data to the HIOKI software on the computer via a USB data cable. The bellows operation is set to 20-60℃, while keeping the humidity constant and reducing other variables. The experiment is repeated several times to obtain the measurement results of the sensor sensitive layer resistance with temperature. The repeated stability experiment is to set the bellows to operate at 20-80℃ for 30 cycles and observe the measurement results; the results are as follows Figure 5 As shown, it shows that it has good linear thermal sensitivity and good repeatability under the above-mentioned appropriate processing conditions.

[0090] The temperature-power performance of carbonized semiconductors as heat sources was observed using a FLIR thermal imager. The experimental method for this part was as follows: a fixed thermal imager was used to observe the center point of the sensor's heat source, the heat source supply voltage was continuously adjusted, and the relationship between the temperature detected by the thermal imager and the supply voltage was observed. After the experiment, the supply voltage was converted into power; the following was obtained: Figure 6 The results show that under the above-mentioned appropriate processing conditions, the temperature and power have a good linear correlation within a certain power range.

[0091] Investigate the effect of heat source power on thermal temperature difference, the results are as follows Figure 7 As shown, the saturation flow rate increases with the increase of display power, and the sensitivity increases. Since the PI substrate will fail at about 400°C, the heat source power will be limited and cannot be too large.

[0092] The distance between the heat source and the temperature sensor is also a major factor affecting the sensor's measurement performance. By setting the distance between the temperature sensor and the heat source to 0.3mm, 0.5mm, and 1.0mm, the temperature sensor's sensing performance was measured respectively. The results are as follows: Figure 8As shown, sensitivity decreases monotonically with increasing distance, while smaller spacing increases the temperature sensor's sensitivity (no significant change occurs when the spacing is less than 500 μm). The saturated flow velocity at each spacing ranges from approximately 0.7 to 1.2 m / s, indicating that the sensor's sensitivity decreases with increasing spacing, while the saturated flow velocity changes slightly. Furthermore, the data demonstrates that thermal temperature differences are sensitive to small flow rates. In this example, the distance between the temperature sensor and the heat source is 0.3 mm.

[0093] Figure 8 In the figure, the amplitudes of the two curves for 0.3mm spin-coated PDMS are smaller than those measured for 0.3mm, indicating that the spin coating of PDMS affects sensor sensitivity. Furthermore, the upside and downside curves for 0.3mm spin-coated PDMS are measured with the sensor facing up and down, respectively. Other parameters (such as the airflow direction) remain constant, equivalent to the sensor being stationary. Airflow is incident from the left and right directions, respectively. The opposite voltage signs of the two curves indicate opposite thermal offset directions, indicating that the sensor can distinguish the direction of airflow.

[0094] Example 2:

[0095] As another embodiment of the present invention, in step 1, a silver circuit is printed on a flexible substrate using a screen printing plate to obtain a conductive circuit. The specific steps are:

[0096] (1) Fix the circuit printing screen horizontally on the screen printing table, and slightly pad one end with tin foil to ensure a certain pressing space;

[0097] (2) Place the PET on the screen printing table to prevent the silver paste from crossing the border and printing onto the metal table;

[0098] (3) Place the flexible substrate to be printed between the PET and the circuit printing stencil, and press the foot switch to start the air pump to adsorb the substrate;

[0099] (4) Stir the GC-SP360-A conductive silver paste until it becomes fluid, and use a medicine spoon to apply a sufficient amount of silver paste to the printing area of ​​the circuit printing screen;

[0100] (5) Maintaining a certain and similar force with both hands, quickly press the silver paste to cover the printed pattern of the circuit printing screen;

[0101] (6) After printing is completed, remove the flexible substrate, turn off the air pump, use Hieclean cleaning agent to clean the remaining silver paste on the circuit printing screen, and use an electric hot air drying oven to dry the printed circuit.

[0102] The remaining steps of this embodiment are the same as those of embodiment 1.

[0103] Example 3:

[0104] As another embodiment of the present invention, when the sensitive layer in step 2 is made of metal material, taking metal Cu as an example, the preparation method of the metal material used for the sensitive layer can also be a method of laser processing and sintering the metal material, and the specific steps are as follows:

[0105] (1) A CuO metal precursor ink was prepared by adopting a formula and mass fraction ratio (polyvinyl pyrrolidone 25%, ethylene glycol 15%, copper oxide nanowires 60%), combined with heating, stirring and ultrasonic dispersion;

[0106] (2) The CuO metal precursor ink is evenly covered on the surface of the flexible substrate by a spin coating process to obtain a uniform CuO precursor ink coating (such as Figure 3 shown);

[0107] (3) Through laser integration technology, the CuO precursor ink coating is sintered into metal Cu according to the designed sensitive layer pattern on the flexible substrate using the photothermal reduction effect of the laser, thus obtaining the sensitive layer.

[0108] The remaining steps of this embodiment are the same as those of embodiment 1.

[0109] Example 4:

[0110] As another embodiment of the present invention, PI fabric can be selected as a flexible substrate, and steps 1 and 2 can also be processed by hot pressing to obtain a conductive circuit. The flexible substrate 1 can be carbonized by laser integration technology to obtain a sensitive layer of semiconductor material. The conductive fabric can be attached to the PI fabric using nickel-plated tape, and a conductive circuit and a sensitive layer can be prepared on the PI fabric. Figure 4 The specific steps are as follows:

[0111] Step 1: After attaching nickel-plated tape to the PI fabric, the PI fabric is placed on the VLS6.75-SYS infrared laser platform. The conductive fabric is cut according to the designed conductive circuit pattern, and the excess conductive fabric is manually removed to obtain a conductive circuit.

[0112] Step 2: Use a hot press to press the conductive circuit and the PI fabric tightly, so that the conductive circuit is fully attached to the PI fabric and stably connected;

[0113] Step 3: Place the hot-pressed PI fabric with the conductive circuit in the VLS6.75-SYS infrared laser platform, and carbonize the PI fabric according to the sensitive layer pattern to obtain the sensitive layer of the semiconductor material;

[0114] Step 4: Hand-apply silver paste to modify the connection area between the conductive circuit and the sensitive layer to ensure sufficient connection.

[0115] The remaining steps of this embodiment are the same as those of embodiment 1.

[0116] In Examples 1 and 3, in Steps 1 and 2 of the method for preparing the thermal flexible flow sensor, regarding the method for preparing the laser-processed sintered metal material used for the conductive circuit and the sensitive layer, the ratio of different metal materials is as follows:

[0117] (1) Cu: The formula and mass fraction ratio are: polyvinyl pyrrolidone 25%, ethylene glycol 15%, copper oxide nanowires 60%), and CuO metal precursor ink is prepared by heating, stirring and ultrasonic dispersion;

[0118] (2) Ni: The formula and mass fraction ratio are 9.05wt% PVP, 0.65wt% CTAB, 24.42wt% n-pentanol, 41.69wt% NiO NP, 7.44wt% gum arabic powder, and 16.75wt% glycerol, and a NiO metal precursor ink is prepared by heating, stirring, and ultrasonic dispersion.

[0119] (3) Cu-Ni: The formula and mass fraction ratio are 13.0 wt% PVP, 27.0 wt% ethylene glycol, 37.0 wt% CuONW, and 23.0 wt% NiO NP. The CuO-NiO metal precursor ink is prepared by heating, stirring, and ultrasonic dispersion.

[0120] like Figure 11 As shown in FIG, based on the simulation results of COMSOL 5.6, the experimental results of thermal temperature difference and hot wire are consistent with the theoretical simulation trend, which proves that the sensitive layer can measure the flow velocity in the form of thermal temperature difference and hot wire respectively.

[0121] In summary, according to Examples 1-4, the laser integration technology used in the present invention can be produced on metal materials and semiconductor materials, which is different from the mature traditional MEMS processing technology, making it more convenient to produce the sensor, and the conductive circuit, temperature sensor and heat source can be prepared at the same time. In addition, the present invention combines the thermal temperature difference detection principle and the hot wire detection principle into a sensitive layer, and fixes it on a flexible substrate of a film or fabric structural steel to ensure that thermal temperature difference and hot wire detection results can be obtained in a small space. Secondly, the two types of data can be combined for analysis, the thermal temperature difference analyzes the perception and direction perception of small flow rates, and the hot wire analyzes large flow rates, with better linearity.

[0122] Preliminary experiments have proved that the sensitive layer of the sensor obtained using laser integration technology not only has good linear thermal sensitivity, but also has good linear correlation between temperature and power. The detection results of the thermal temperature difference and hot wire detection principle output by the sensor at the same time confirm with theoretical simulation that the sensor can detect the direction and size of flow velocity.

[0123] The above is only a further embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes based on the technical solutions and concepts of the present invention within the scope disclosed by the present invention, which fall within the scope of protection of the present invention.

Claims

1. A thermal flexible flow sensor, characterized in that: The measuring range is 0-25 m / s, and the flow velocity direction can be measured. The sensor comprises a flexible substrate (1), a conductive circuit (2), a sensitive layer (3), and a heat insulating device (4). The flexible substrate (1) is in the form of a thin film. The conductive circuit (2) and the sensitive layer (3) are both located on one side of the flexible substrate (1). The other side of the flexible substrate (1) is a measuring surface. The sensitive layer is made of a metal material or a semiconductor material. The heat insulating device (4) is covered on the non-measuring surface of the flexible substrate (1) to reduce the influence of the external temperature on the conductive circuit (2) and the sensitive layer (3). The sensitive layer comprises a heat source obtained by processing using laser integration technology. and several pairs of temperature sensors, which are symmetrically distributed around a heat source, with both ends of the heat source and both ends of each temperature sensor respectively connected to a conductive circuit through an electrode connection area, and a spacing between the temperature sensor and the heat source of 300 to 500 μm; when the sensitive layer is a semiconductor material, an infrared laser is used to perform laser integration modification on a flexible substrate, and the flexible substrate is PI; when the sensitive layer is a metal material, an ultraviolet laser or a continuous green laser is used to perform laser integration processing on a metal precursor ink coated on the flexible substrate, and the metal precursor ink is composed of 25% polyvinyl pyrrolidone, 15% ethylene glycol, and 60% copper oxide nanowires by mass.

2. The thermal flexible flow sensor according to claim 1, characterized in that: The heat source in the sensitive layer is in a broken line shape.

3. A method for preparing the thermal flexible flow sensor according to any one of claims 1 to 2, characterized in that: The preparation steps are: Step 1: Design a conductive circuit and fix it on a flexible substrate; Step 2: Using laser integration technology, a laser is used to precisely process a sensitive layer with a specified pattern on a flexible substrate; Step 3: Hand-apply conductive silver paste to modify the contact area between the conductive circuit and the sensitive layer obtained in step 2 to ensure good contact between the two; Step 4: Prepare a thermal insulation device cover on the sample obtained in step 3 using PDMS material.

4. The method for preparing the thermal flexible flow sensor according to claim 3, characterized in that: The conductive circuit described in step 1 is designed and fixed on the flexible substrate. The conductive circuit can be obtained by printing a silver circuit on the flexible substrate using a screen printing plate, or by laser processing and sintering a metal material on the flexible substrate. The conductive circuit includes an electrode contact area and a circuit lead-out area.

5. The method for preparing the thermal flexible flow sensor according to claim 4, characterized in that: The method of laser processing sintered metal materials can be used to obtain a conductive circuit on a flexible substrate. The specific steps of the laser processing sintered metal materials are as follows: (1) preparing a metal precursor ink; the metal precursor ink is composed of 25% polyvinyl pyrrolidone, 15% ethylene glycol, and 60% copper oxide nanowires by mass percentage; (2) uniformly covering the surface of the flexible substrate with the metal precursor ink by a spin coating process to obtain a uniform precursor ink coating; (3) Through laser integration technology, the photothermal effect and photochemical reaction of the laser are used to sinter the precursor ink coating on the flexible substrate according to the designed pattern to obtain a conductive circuit of the metal material.

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