Orthogonal series thin film thermocouple two-dimensional flow velocity and flow direction sensor and measuring method

Abstract

This invention discloses a two-dimensional flow velocity and direction sensor and measurement method using orthogonal series-connected thin-film thermocouples, belonging to the technical field of thermal fluid parameter detection and thin-film sensor. The sensor includes a substrate, an S-shaped thin-film heater located in the central region of the substrate, and four sets of series-connected thin-film thermocouples. The four sets of series-connected thin-film thermocouples are arranged along two mutually perpendicular measurement directions, with two sets of series-connected thin-film thermocouples on either side of the heater in each measurement direction and equidistantly symmetrical. When the fluid flows through the heater, it causes a thermal field shift, and corresponding temperature difference signals are obtained in the two measurement directions. Based on the correspondence between the temperature difference signal and the flow velocity, two positive and negative alternating velocity components are obtained. The magnitude and direction of the fluid flow are obtained through velocity vector synthesis. This invention can achieve simultaneous two-dimensional flow velocity and direction measurement in a planar thin-film structure.

Description

Technical Field

[0001] This invention belongs to the field of thermal fluid parameter detection and thin-film sensor technology, specifically relating to a two-dimensional flow velocity and direction sensor and measurement method of orthogonal series thin-film thermocouples. Background Technology

[0002] Thermal flow meters are a type of sensing device that detects flow velocity based on the heat transfer between a fluid and a heat source. They typically create a localized temperature field in the fluid being measured using a heating element, and detect the flow state by utilizing the convective heat transfer changes caused by fluid movement. In particular, differential temperature thermal flow meters place a temperature detection unit near the heating element. When fluid flows through the heated area, fluid convection causes a shift in the original temperature field. By detecting the temperature difference across the heating element, a flow velocity-related response signal can be obtained. This type of sensor has no moving mechanical parts, has a small structural size, and is suitable for detecting minute flow rates and measuring miniaturized fluid parameters.

[0003] Existing thermal flow sensors with temperature difference typically have heating elements and temperature sensing elements arranged according to a predetermined flow direction. Their output signal mainly reflects the velocity component in the sensor's sensitive direction. When the flow direction of the fluid being measured is not fixed, or when there is lateral flow, swirling flow, or other multi-directional motion in the flow field, the temperature difference signal obtained from a single measurement direction cannot fully describe the fluid's motion state in a two-dimensional plane, making it difficult to simultaneously determine the fluid's velocity and flow direction.

[0004] To acquire flow information in multiple directions, existing solutions can add temperature detection units in different directions or set up multiple independent measurement modules to detect the flow velocity response in different directions, and then combine the measurement results from all directions to determine the fluid motion state. However, when using multiple independent measurement units, the distance between each measurement unit and the heat source, the relative position, and the local thermal field in which they are located are prone to differences, making it difficult to maintain consistent geometric and thermal conditions in different measurement directions. At the same time, the measurement units may also be affected by the thermal conductivity of the substrate and the mutual influence of adjacent thermal fields, causing additional deviations between measurement signals in different directions. As the number of measurement units increases, it also brings problems such as increased sensor size, structural complexity, and accumulation of multi-channel errors.

[0005] Furthermore, two-dimensional thermal sensing requires identifying thermal field changes caused by fluid disturbances in different directions, while the temperature difference signals corresponding to such thermal field changes are typically small. The output amplitude of a single temperature sensing element is limited, and under conditions of minute temperature differences, the signal differences corresponding to flow velocity changes are not easily fully reflected. Simply increasing the number of sensing units to improve directional detection capability would further increase thermal coupling between devices. Therefore, two-dimensional flow velocity measurement not only requires a reasonable distribution of temperature sensing units in multiple directions, but also needs to consider the heat distribution in the heat source region, structural consistency in different measurement directions, and the ability to detect weak temperature difference signals.

[0006] Meanwhile, the thermal conductivity of the substrate itself is also a significant factor affecting the measurement performance of thin-film thermal sensors. When the heat generated by the heater diffuses to the surrounding area through the substrate, the temperature detection units at different locations may experience additional temperature changes due to non-fluid convection, weakening the directional thermal field shift characteristics generated by fluid flow. Therefore, within a planar structure of finite size, how to concentrate heat in the sensitive area, reduce thermal coupling between different functional components, and maintain the same thermal and geometric conditions in both measurement directions are key issues that need to be addressed in two-dimensional thin-film thermal flow velocity and direction detection.

[0007] Therefore, existing technologies still require a compact two-dimensional thin-film thermal flow sensor that establishes two mutually orthogonal and structurally consistent temperature difference detection directions on the same substrate. This would reduce substrate heat conduction and thermal interference between temperature measurement units, while improving signal identification capability under small temperature difference conditions. The temperature difference signals obtained from the two directions can stably characterize the corresponding flow velocity components, thereby achieving synchronous measurement of flow velocity magnitude and flow direction in a two-dimensional plane. Summary of the Invention

[0008] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing an orthogonal series thin-film thermocouple two-dimensional flow velocity and direction sensor and measurement method. In a planar thin-film integrated structure, two orthogonal differential temperature measurement channels with consistent structure are constructed using a single central heat source, and the weak temperature difference signal generated by fluid disturbance is enhanced to stably acquire two orthogonal alternating velocity components in a two-dimensional plane. This invention solves the technical problems of existing thermal flow sensors in two-dimensional flow measurement, such as difficulty in maintaining consistent geometric and thermal conditions of measurement channels in different directions, weakening of directional thermal response due to substrate heat conduction and thermal coupling between temperature measurement units, and insufficient identification capability of weak temperature difference signals, which limit the stability of two-dimensional flow velocity component measurement and the accuracy of flow direction identification.

[0009] The present invention adopts the following technical solution: A two-dimensional flow velocity and direction sensor with orthogonal series thin-film thermocouples includes a substrate, a heater disposed on the surface of the substrate, and a temperature detection unit; the heater is disposed in the central region of the substrate, and the effective heating area of ​​the heater adopts an S-shaped wire structure; The temperature detection unit includes four sets of series-connected thin-film thermocouples, each set of which is composed of multiple thin-film thermocouple units connected in series. The four sets of series-connected thin-film thermocouples are arranged with the heater as the center, respectively along a first measurement direction and a second measurement direction that are perpendicular to each other. The two sets of series-connected thin-film thermocouples in each measurement direction are located on both sides of the heater and are arranged symmetrically with respect to the heater. The distance between the four sets of series-connected thin-film thermocouples and the center of the heater is the same. Two sets of series-connected thin-film thermocouples in each measurement direction detect the temperature response at the corresponding location caused by fluid flow, so as to obtain a temperature difference signal characterizing the thermal field shift in the corresponding measurement direction.

[0010] Furthermore, the substrate is made of a material with electrical insulation properties and low thermal conductivity, and the substrate is an alumina substrate or a polyimide substrate.

[0011] Furthermore, the heater is made of a metal material with electrothermal conversion performance and resistance temperature characteristics, wherein the metal material is platinum or tungsten.

[0012] Furthermore, each set of the series-connected thin-film thermocouples includes multiple thin-film thermocouple units connected in series, with adjacent thin-film thermocouple units being alternately connected by positive and negative electrodes, and the thermoelectric potentials generated by each thin-film thermocouple unit being superimposed in the same output circuit.

[0013] Furthermore, the thin-film thermocouple unit includes a copper positive electrode and a constantan negative electrode, and the copper positive electrode and the constantan negative electrode are connected to form a thermocouple junction.

[0014] Furthermore, both the heater and the series-connected thin-film thermocouple adopt a thin-film structure and are formed on the surface of the substrate by magnetron sputtering.

[0015] Furthermore, the heater is a platinum thin-film heater, and the series-connected thin-film thermocouple includes a copper thin-film positive electrode and a constantan thin-film negative electrode.

[0016] Furthermore, the sensor pattern on the substrate surface is covered by a silicon carbide protective layer, which covers the heater and the series-connected thin-film thermocouple.

[0017] Another technical solution of the present invention is a method for measuring two-dimensional flow velocity and direction using orthogonal series thin-film thermocouples, comprising the following steps: A two-dimensional flow velocity and direction sensor is used. The two-dimensional flow velocity and direction sensor includes a substrate, a heater disposed in the central region of the substrate, and four sets of series-connected thin-film thermocouples. The effective heating area of ​​the heater adopts an S-shaped wire structure. The four sets of series-connected thin-film thermocouples are arranged with the heater as the center and along a first measurement direction and a second measurement direction that are perpendicular to each other. Two sets of series-connected thin-film thermocouples in each measurement direction are located on both sides of the heater and are arranged symmetrically with respect to the heater. The distance between the four sets of series-connected thin-film thermocouples and the center of the heater is the same. When the heater is powered on, a temperature field is formed in the central region of the substrate; The output signals of the series-connected thin-film thermocouples located on both sides of the heater in the first and second measurement directions are acquired respectively. The temperature difference signal characterizing the thermal field shift in the measurement direction is obtained based on the output signals of the two sets of series-connected thin-film thermocouples in the same measurement direction. Based on the pre-established correspondence between temperature difference signal and flow velocity, the first velocity component of the fluid under test in the first measurement direction and the second velocity component in the second measurement direction are determined respectively. The first velocity component and the second velocity component are combined by velocity vector synthesis to obtain the velocity magnitude and flow direction of the fluid under test in a two-dimensional plane.

[0018] Furthermore, before the two-dimensional flow velocity and direction measurement, the series-connected thin-film thermocouple is calibrated to establish a first calibration relationship between the output thermoelectric potential of the series-connected thin-film thermocouple and the temperature difference between its hot and cold junctions, and to establish a second calibration relationship between the temperature difference signal in each measurement direction and the corresponding flow velocity component. During measurement, the output thermoelectric potential of each series-connected thin-film thermocouple is converted into a corresponding temperature response according to the first calibration relationship. The temperature difference signal in the measurement direction is obtained based on the temperature response of the two sets of series-connected thin-film thermocouples located on both sides of the heater in the same measurement direction. The corresponding flow rate component is determined according to the second calibration relationship.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects: A two-dimensional flow velocity and direction sensor using orthogonal series-connected thin-film thermocouples employs a central S-shaped heater in conjunction with four sets of series-connected thin-film thermocouples, forming a structurally consistent differential temperature measurement channel in two mutually perpendicular directions. The S-shaped heating structure extends the effective heating path within a limited area, concentrating heat in the sensitive region. The four thermocouples are equidistant and symmetrically arranged from the center of the heater, providing a unified geometric measurement reference in both directions. The series-connected thermocouples amplify the electrical signal corresponding to weak temperature changes. The thermal field shift generated after the fluid passes through the sensitive region can be projected onto the two orthogonal directions, providing two-dimensional thermal response information for simultaneously acquiring flow velocity and direction.

[0020] Furthermore, a substrate with low thermal conductivity and electrical insulation properties is employed. The low thermal conductivity substrate reduces lateral heat diffusion along the substrate, weakening thermal coupling between the heater and different temperature sensing units via the substrate, thus maintaining high discernibility of local thermal field changes caused by fluid convection; the electrical insulation properties reduce the possibility of electrical interference between the heater and thermocouple electrodes. Both alumina and polyimide are suitable for carrying thin-film devices, meeting the structural requirements of planar sensor integration.

[0021] Furthermore, platinum or tungsten can be used as the heating element material. These metals possess relatively stable electrothermal conversion characteristics, and when energized, they can continuously generate a heat source in the central sensitive area. The convective heat transfer changes generated when the fluid passes through the heating area have a stable heat input basis. Using a platinum thin-film heater, its structure can be formed by magnetron sputtering, maintaining the same thin-film processing system as the peripheral thin-film thermocouple, reducing integration difficulties caused by different device manufacturing methods.

[0022] Furthermore, multiple thin-film thermocouple units are connected in series, with alternating positive and negative terminals, allowing the thermoelectric potential generated by each thermocouple to accumulate within the same circuit. Compared to a single thermocouple, this results in a higher amplitude output signal under the same temperature difference, and a stronger ability to detect smaller thermal field changes. The thermoelectric potential of the series-connected thin-film thermocouple maintains a good linear relationship with the temperature difference, with a fitting coefficient of determination of 0.9977 and a measured sensitivity of 44.56 μV / K, providing practical testing data for temperature difference detection.

[0023] Furthermore, copper and constantan are used to construct a thin-film thermocouple material combination. After the two materials form a thermocouple junction, the temperature difference between the hot junction and the cold junction can be converted into a thermoelectric potential output. In the embodiment, copper and constantan targets are used to form positive and negative electrodes by magnetron sputtering, respectively, which can directly form a planar thin-film thermocouple array and integrate it with the central heater on the same substrate, reducing the assembly space and positional errors caused by independent temperature sensing elements.

[0024] Furthermore, both the heater and the series-connected thin-film thermocouple are fabricated as thin-film structures and formed on the substrate surface using magnetron sputtering. The heating element and temperature sensing element can be patterned and fabricated in the same plane, making it easier to maintain consistency in the position, spacing, and relative orientation of each element, suitable for constructing a four-directionally symmetrical two-dimensional measurement structure. The thin-film structure itself has a small heat capacity, enabling a faster response to changes in flow field temperature, while reducing the increase in structural size caused by assembling independent devices.

[0025] Furthermore, a platinum thin-film heater and a copper / constantan thin-film thermocouple are employed. Platinum performs the central electrothermal conversion function, while copper and constantan perform the temperature difference-thermoelectric potential conversion function. Each functional layer is integrated into the substrate in the form of a metal thin film. This material combination corresponds to the actual fabrication process, allowing the heating and temperature sensing functions to be fabricated according to a predetermined two-dimensional pattern, avoiding the use of bulky discrete temperature sensors and maintaining a compact overall sensor structure.

[0026] Furthermore, a silicon carbide protective layer is applied over the sensor pattern formed by the heater and the series-connected thin-film thermocouples. This protective layer isolates the platinum, copper, and constantan thin films from the external environment, reducing the risk of oxidation failure of the metal films while preserving the internal heating and thermoelectric conversion structures. In this embodiment, the silicon carbide layer is formed using magnetron sputtering, a process that can be integrated with the aforementioned thin-film device fabrication process, maintaining the thin-film nature and integration of the entire sensitive structure.

[0027] A two-dimensional flow velocity and direction measurement method employing orthogonal series-connected thin-film thermocouples as a two-dimensional flow velocity and direction sensor is proposed. This method acquires temperature difference signals in two mutually orthogonal directions, and uses a pre-established correlation between temperature difference and flow velocity to obtain the flow velocity components in both directions. The two flow velocity components are then vector-synthesized. This measurement method decomposes any two-dimensional flow into two fixed orthogonal directions, avoiding reliance on a single sensitive direction to determine the fluid motion state. Experimental results show that the calculated angle matches the actual angle well within the range of 0° to 90°, with a maximum measurement error of 5.21° and an average resolution of 1.5°, verifying the feasibility of the two-dimensional flow direction measurement scheme.

[0028] In summary, this invention employs a central S-shaped thin-film heater and orthogonally arranged series-connected thin-film thermocouples to form two differential temperature measurement directions in the same plane, enabling simultaneous acquisition of two-dimensional flow velocity components. The series-connected thermocouples enhance the output of weak temperature differences, and the integrated thin-film structure is small in size, has a fast response, and can simultaneously measure both flow velocity magnitude and flow direction.

[0029] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the following description of the relative embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the structure of the orthogonal series thin-film thermocouple two-dimensional flow velocity and direction sensor of the present invention; Figure 2 This is a schematic diagram illustrating the principle of flow velocity measurement in a single measurement direction according to the present invention; Figure 3 This is a schematic diagram illustrating the principle of two-dimensional planar flow velocity and direction measurement in this invention. Figure 4 This is a schematic diagram of the structure of the series-connected thin-film thermocouple of the present invention; Figure 5 This is a graph showing the relationship between the thermoelectric potential and temperature difference calibration of the series-connected thin-film thermocouple of the present invention; Figure 6 This is a graph showing the relationship between the temperature difference response and flow rate of the series-connected thin-film thermocouple of the present invention. Figure 7 This is a diagram showing the flow direction measurement results of the present invention.

[0032] Among them: 1. Series-connected thin-film thermocouple; 2. Heater; 3. Substrate. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "one side," "one end," and "one side," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0035] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0036] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0037] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0038] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0039] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0040] This invention provides a two-dimensional flow velocity and direction sensor and measurement method using orthogonal series-connected thin-film thermocouples. On the same plane of a low thermal conductivity insulating substrate, an S-shaped thin-film heater is placed in the central region, and four sets of series-connected thin-film thermocouples are equidistantly and symmetrically arranged around it along two mutually orthogonal measurement directions. The S-shaped heater extends the effective heating path within a limited area, concentrating heat in the sensitive area. The equidistant and symmetrical structure ensures consistent geometric reference for the two-axis measurement channels. The series-connected thin-film thermocouples enhance the output amplitude of small temperature differences through the superposition of multiple thermocouple thermoelectric potentials. The corresponding flow velocity components are determined by the differential thermal responses in the two orthogonal directions, and then velocity vector synthesis is performed, thereby achieving simultaneous detection of flow velocity magnitude and flow direction in a planar thin-film structure. Experiments show a thermocouple sensitivity of 44.56 μV / K and a linear fitting R0. 2 The value is 0.9977, the maximum flow direction error is 5.21° within the range of 0° to 90°, and the average resolution is 1.5°.

[0041] Please see Figure 1This invention discloses a two-dimensional flow velocity and direction sensor using orthogonal series-connected thin-film thermocouples, comprising a series-connected thin-film thermocouple 1, a heater 2, and a substrate 3. Both the heater 2 and the series-connected thin-film thermocouple 1 are disposed on the surface of the substrate 3, with the heater 2 located in the central region of the substrate 3. Its effective heating area employs an S-shaped conductor structure. The S-shaped conductor forms a relatively long current transmission path within a limited area, enabling the heater 2 to form a concentrated and relatively stable temperature field at the center of the substrate 3 after being energized. The heater 2 can be made of a metallic material with good electrothermal conversion performance and resistance-temperature characteristics, such as platinum or tungsten; in this embodiment, platinum is preferably used to form the thin-film heater.

[0042] The temperature detection unit includes four sets of series-connected thin-film thermocouples 1, arranged in a cross shape around the heater 2. Two sets are located in the first measurement direction, and the other two sets are located in the second measurement direction, which is perpendicular to the first measurement direction. Two sets of series-connected thin-film thermocouples 1 in each measurement direction are respectively positioned on both sides of the heater 2 and arranged symmetrically with respect to the heater 2; the distance between the four sets of series-connected thin-film thermocouples 1 and the center of the heater 2 is the same. Thus, the first and second measurement directions have a consistent geometric arrangement, forming differential temperature measurement channels in the two orthogonal directions. When fluid flows through the sensing area, the flow disturbs the central temperature field. The two sets of series-connected thin-film thermocouples 1 in each measurement direction detect the temperature response at the corresponding position and obtain a temperature difference signal characterizing the thermal field shift in that direction based on the temperature responses on both sides.

[0043] The substrate 3 is made of a material with electrical insulation properties and low thermal conductivity, such as alumina or polyimide. The low thermal conductivity of the substrate reduces the diffusion of heat generated by the heater 2 along the substrate 3 to the periphery, weakening the thermal coupling between different series-connected thin-film thermocouples 1 and between the series-connected thin-film thermocouples 1 and the heater 2 via the substrate. This ensures that the detected temperature change primarily reflects the thermal field disturbance caused by fluid convection. Both the heater 2 and the series-connected thin-film thermocouples 1 can be formed on the surface of the substrate 3 using thin-film technology. In this embodiment, magnetron sputtering is used for fabrication. The position, size, and spacing of each functional element can be determined based on the thermal field simulation results of the sensing area.

[0044] Specifically, the series-connected thin-film thermocouple 1 can be constructed using a combination of copper and constantan, with copper forming the positive electrode and constantan forming the negative electrode; the heater 2 can be formed using a platinum thin film. After completing the pattern fabrication of the heater 2 and the series-connected thin-film thermocouple 1, a silicon carbide protective layer can be formed on the surface of the sensor pattern to isolate the platinum, copper, and constantan thin films from the external environment, reducing the impact of metal thin film oxidation failure.

[0045] Please see Figure 2 , Figure 2This illustrates the principle of flow velocity measurement in a single measurement direction according to the present invention. Taking the first measurement direction as an example, two sets of series-connected thin-film thermocouples 1 are respectively arranged on both sides of the heater 2, and maintain the same distance from the center of the heater 2. When the fluid to be measured is in a static state, the heater 2 is energized to generate heat, and the temperature field formed therein is basically symmetrically distributed with the heating area as the center. The temperature responses detected by the series-connected thin-film thermocouples 1 on both sides are similar.

[0046] When the fluid under test flows through the heater 2 along the first measurement direction, fluid convection carries some of the heat near the heater 2 downstream, causing the original symmetrical temperature field to shift along the flow direction. Two sets of series-connected thin-film thermocouples 1, located upstream and downstream of the heater 2, detect the temperature changes at their respective locations, forming a first temperature difference signal characterizing the shift of the thermal field in the first measurement direction. When the flow velocity changes, the degree to which the fluid carries away and transports heat changes accordingly, and the degree of thermal field shift and the difference between the temperature responses on both sides change accordingly. Therefore, the correspondence between the temperature difference signal and the flow velocity can be established in advance through calibration, and the first velocity component of the fluid under test in the first measurement direction can be determined based on the measured first temperature difference signal. The second velocity component is obtained in the second measurement direction using the same measurement principle.

[0047] Please see Figure 3 , Figure 3 The principle of two-dimensional planar flow velocity and direction measurement of the present invention is illustrated. Four sets of series-connected thin-film thermocouples 1 are arranged around the heater 2 along two mutually perpendicular measurement directions, wherein the first measurement direction can be defined as the x-direction and the second measurement direction can be defined as the y-direction. The series-connected thin-film thermocouples 1 in both directions are equidistant and symmetrically arranged with respect to the heater 2.

[0048] When a fluid flows through the sensing area in any direction within a two-dimensional plane, the thermal field shift caused by fluid convection can generate corresponding temperature responses in the x and y directions, respectively. The output signals of the series-connected thin-film thermocouples 1 on both sides of the x-direction are acquired, and a first temperature difference signal is obtained based on the temperature responses on both sides. The flow velocity component in the x-direction is determined using a pre-established correspondence between the temperature difference signal and the flow velocity. A second temperature difference signal in the y-direction is acquired in the same manner, and the flow velocity component in the y-direction is determined.

[0049] After obtaining two mutually orthogonal velocity components, they are combined into a velocity vector. The magnitude of the combined velocity vector corresponds to the actual velocity of the fluid under test in the two-dimensional plane, and the angle between the combined velocity vector and the predetermined coordinate axis corresponds to the flow direction of the fluid under test. Thus, the same sensor can simultaneously obtain velocity components in two directions using two orthogonal differential temperature measurement channels, and further determine the velocity magnitude and flow direction. This measurement principle is consistent with the "temperature difference signal—velocity component—vector synthesis" processing chain defined in claim 9.

[0050] Please see Figure 4 , Figure 4 The structure of the series-connected thin-film thermocouple 1 of the present invention is shown. Each series-connected thin-film thermocouple 1 is composed of multiple thin-film thermocouple units connected in series. This embodiment takes three thin-film thermocouple units connected in series as an example. The thin-film thermocouple units use two different thermoelectric materials to form the positive and negative electrodes. Adjacent thin-film thermocouple units are connected in series in an alternating manner of positive and negative electrodes. The thermoelectric potentials generated by each thin-film thermocouple unit are superimposed in the same output circuit.

[0051] In this embodiment, the thin-film thermocouple unit is constructed of copper and constantan, with copper forming the positive electrode and constantan forming the negative electrode. Each thermocouple unit generates a corresponding thermoelectric potential when there is a temperature difference between the hot and cold junctions. When multiple thermocouple units are connected in series, the total output thermoelectric potential is the cumulative result of the thermoelectric potentials of each thermocouple unit. Therefore, under the same temperature difference conditions, the series-connected thin-film thermocouple 1 can obtain a higher output signal amplitude than a single thermocouple, and has a more obvious electrical signal response to small temperature changes caused by fluid disturbances.

[0052] Before performing actual measurements on the series-connected thin-film thermocouple 1, a calibration relationship between its output thermoelectric potential and temperature difference can be established. In this example, the thermoelectric potential was measured within the range of 0~100℃, and the obtained thermoelectric potential and temperature difference showed a good linear relationship, with a linear fitting determination coefficient R0. 2 The temperature difference sensing sensitivity of the series-connected thin-film thermocouple is 44.56 μV / K, which is 0.9977. During the measurement process, the temperature response at the corresponding position can be obtained from the output thermoelectric potential of the series-connected thin-film thermocouple 1, and the temperature difference signal in that direction can be obtained from the temperature response of the two sets of series-connected thin-film thermocouples 1 on both sides of the heater 2 in the same measurement direction.

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0054] Example This embodiment provides a two-dimensional flow velocity and direction sensor with orthogonal series-connected thin-film thermocouples and its measurement process. The sensor includes series-connected thin-film thermocouples 1, a heater 2, and a substrate 3. The heater 2 is disposed in the central region of the substrate 3, and four sets of series-connected thin-film thermocouples 1 are arranged around the heater 2 along two mutually perpendicular measurement directions. Two sets of series-connected thin-film thermocouples 1 in each measurement direction are located on either side of the heater 2 and maintain the same distance from the center of the heater 2, thereby forming two mutually orthogonal differential temperature measurement channels on the surface of the substrate 3. The effective heating area of ​​the heater 2 adopts an S-shaped wire structure, and each set of series-connected thin-film thermocouples 1 is composed of multiple thin-film thermocouple units connected in series.

[0055] In this embodiment, the substrate 3 is a polyimide (PI) substrate. PI material has electrical insulation properties and low thermal conductivity, which can reduce the heat generated by the heater 2 from being transferred to the periphery along the substrate 3, and reduce the thermal coupling between different thin-film thermocouples through the substrate. Besides PI substrates, materials such as alumina can also be used as substrates, provided that the electrical insulation and low thermal conductivity requirements are met.

[0056] First, the positive electrode of the series-connected thin-film thermocouple 1 was prepared using magnetron sputtering. In this embodiment, copper (Cu) was used as the positive electrode material, and sputtering was performed using a copper target. The sputtering power was 100 W, the sputtering time was 60 min, the argon flow rate was 45 sccm, and the vacuum degree was 5 × 10⁻⁶. -5 Torr, with a substrate temperature of 60 °C. After sputtering, a copper positive electrode with a thickness of approximately 2 μm was obtained.

[0057] Subsequently, the negative electrode of the series-connected thin-film thermocouple 1 was fabricated using magnetron sputtering. In this embodiment, constantan (CuNi) was used as the negative electrode material, and sputtering was performed using a constantan target at a sputtering power of 80 W, a sputtering time of 60 min, an argon flow rate of 45 sccm, and a vacuum degree of 5 × 10⁻⁶. -5 Torr, with a substrate temperature of 60 ℃. The prepared constantan negative electrode has a thickness of approximately 2 μm. The copper positive electrode and the constantan negative electrode are connected to form a thin-film thermocouple unit. Multiple thin-film thermocouple units are connected in series in an alternating manner with positive and negative electrodes, so that the thermoelectric potential generated by each thin-film thermocouple unit can be accumulated in the same output circuit.

[0058] After the fabrication of the series-connected thin-film thermocouple 1, the heater 2 was fabricated in the central region of the substrate 3 using magnetron sputtering. In this embodiment, platinum (Pt) was used as the heating material, and sputtering was performed using a platinum target. The sputtering power was 150 W, the sputtering time was 180 min, the argon flow rate was 45 sccm, and the vacuum degree was 5 × 10⁻⁶. -5Torr forms a platinum thin-film heater 2 with a thickness of approximately 4 μm. The effective heating area of ​​the heater 2 is fabricated as an S-shaped conductor structure, which forms a long current transmission path within a limited central area, concentrating the heat generated by energization in the sensing area and providing a common heat source for the surrounding series-connected thin-film thermocouples 1.

[0059] A silicon carbide protective layer is further sputtered onto the overall sensor pattern formed by the heater 2 and the series-connected thin-film thermocouple 1. In this embodiment, a silicon carbide (SiC) target is used for magnetron sputtering at a sputtering power of 200 W, a sputtering time of 120 min, an argon flow rate of 45 sccm, and a vacuum level of 5 × 10⁻⁶. -5 Torr was used to prepare a silicon carbide protective layer with a thickness of approximately 2 μm. This protective layer covered platinum, copper, and constantan films to reduce oxidation failure of these metal materials during use. After the film structure was prepared, conductive silver paste was used to connect leads to the positive and negative electrodes of the series-connected thin-film thermocouple 1 and the two ends of the heater 2, forming corresponding electrical connection terminals.

[0060] After the sensor was fabricated, the series-connected thin-film thermocouple 1 was calibrated to establish the correspondence between its output thermoelectric potential and temperature difference. The calibration results are shown in [reference needed]. Figure 5 This embodiment measured the thermoelectric potential output of a series-connected thin-film thermocouple within a temperature difference range of 0~100 ℃. Experimental results show that the thermoelectric potential exhibits a good linear relationship with the temperature difference, and linear fitting yields the following: Y = -80.5 + 44.56△T Where Y represents the output thermoelectric potential of the series-connected thin-film thermocouple, and ΔT represents the temperature difference response parameter between the hot and cold junctions of the series-connected thin-film thermocouple. The linear fit R0 2 The value is 0.9977. Based on the fitting results, the temperature difference sensing sensitivity of the series-connected thin-film thermocouple 1 is 44.56 μV / K. This calibration relationship can convert the thermoelectric potential signal obtained in the actual measurement process into the corresponding temperature response, providing a basis for subsequent differential temperature measurement in two orthogonal directions.

[0061] Please see Figure 6 The flow rate measurement performance of the sensor in this embodiment was tested. During the test, the fluid to be measured flowed through the heater 2 along a predetermined measurement direction, and the series-connected thin-film thermocouples 1 on both sides of the heater 2 along the measurement direction detected the temperature response at the corresponding positions. When the fluid flows through the central heating area, the fluid convection carries some heat downstream, causing a shift in the original temperature field, thereby creating a temperature difference between the upstream and downstream measurement positions of the heater 2.

[0062] In this embodiment, as the flow rate gradually increases from 0 m / s to 10 m / s, the temperature difference between the hot and cold junctions of the series-connected thin-film thermocouple increases from approximately 15.3 °C to approximately 16.5 °C. Experimental results show that this temperature difference exhibits a monotonically linear change with increasing flow rate. Linear fitting of the experimental data yields: △T = 15.32 + 0.1078V Where V represents the flow velocity of the fluid to be measured, and ΔT represents the temperature difference response parameter between the hot and cold junctions of the series-connected thin-film thermocouple.

[0063] Based on the above fitting relationship, the flow velocity component in the corresponding measurement direction can be deduced from the measured temperature difference signal. This experiment established the calibration relationship between the temperature difference at the upstream and downstream temperature measurement locations and the flow velocity, and verified the feasibility of using differential thermal response for flow velocity measurement.

[0064] In the actual two-dimensional flow velocity measurement process, the first and second measurement directions employ the same measurement method. First, the output signals of the series-connected thin-film thermocouples 1 located on both sides of the heater 2 in the first measurement direction are acquired. Based on the thermocouple calibration relationship, the temperature response at the corresponding position is obtained, and the first temperature difference signal is derived from the temperature responses on both sides. Then, the flow velocity component in the first measurement direction is determined based on the correspondence between the temperature difference signal and the flow velocity. The second temperature difference signal in the second measurement direction is obtained in the same manner, and the flow velocity component in the second measurement direction is further determined. Since the two measurement directions are perpendicular to each other, the two flow velocity components jointly characterize the velocity state of the fluid under test in the two-dimensional plane. This process is similar to... Figure 3 The two-dimensional flow velocity decomposition and synthesis principles shown correspond to each other.

[0065] Please see Figure 7 The flow direction measurement performance of the sensor in this embodiment is verified. The velocity components in the x and y directions are calculated based on the temperature difference signals obtained from two orthogonal measurement directions, and then velocity vectors are synthesized from the two velocity components. The magnitude of the synthesized velocity vector is taken as the actual flow velocity of the fluid under test, and the angle between the synthesized velocity vector and the x-direction is taken as the flow direction of the fluid under test.

[0066] The flow direction calculated based on sensor measurements was compared with the actual set angle. Experimental results show that within the test range of 0° to 90° in the flow velocity direction, the calculated flow direction has good consistency with the actual flow direction, with a maximum measurement error of 5.21° and an average resolution of 1.5°. The experimental results indicate that the flow direction measurement error mainly originates from the measurement error of the thin-film thermocouple. The above experiments verify the feasibility of determining the two-dimensional flow direction using flow velocity components in two orthogonal directions.

[0067] In this embodiment, four sets of series-connected thin-film thermocouples 1 are arranged equidistantly and symmetrically around a single central heater 2, forming two mutually orthogonal differential temperature measurement channels on the same substrate 3 surface. The use of the same central heat source and consistent geometric arrangement in both directions reduces spatial positional differences between different measurement directions when using multiple independent heat sources or discrete measurement modules. The low thermal conductivity PI substrate reduces thermal coupling caused by lateral heat diffusion through the substrate, the S-shaped heater 2 forms a concentrated heat source within a limited area, and the series-connected thin-film thermocouples 1 increase the output signal amplitude through the accumulation of thermoelectric potential from multiple thermocouple units. The above structure collectively addresses three issues in two-dimensional measurement: measurement channel consistency, substrate thermal coupling, and identification of weak temperature difference signals.

[0068] Meanwhile, both the heater 2 and the series-connected thin-film thermocouple 1 adopt a thin-film structure and are formed on the surface of the substrate 3 using magnetron sputtering, allowing the heating structure and the temperature measuring structure to be integrated in the same plane according to a predetermined positional relationship. During measurement, the thermal field shift caused by the fluid is converted into a temperature difference signal in two orthogonal directions, and then two positive alternating velocity components are obtained according to the calibration relationship. The velocity magnitude and flow direction of the fluid under test are obtained through velocity vector synthesis, realizing the synchronous measurement of velocity and flow direction in a two-dimensional plane.

[0069] In summary, this invention provides a two-dimensional flow velocity and direction sensor and measurement method using orthogonal series-connected thin-film thermocouples. An S-shaped thin-film heater is positioned at the center of a substrate, and four sets of series-connected thin-film thermocouples are arranged around the heater along two mutually perpendicular directions. The two sets of opposing thermocouples maintain the same distance from the heater, forming two structurally consistent differential temperature measurement directions within the same plane. The S-shaped heating structure increases the effective heating path within a limited area, maintaining a relatively concentrated heat distribution in the sensitive area. The series-connected thin-film thermocouples superimpose the thermoelectric potentials generated by multiple thermocouple units, improving the output signal corresponding to weak temperature changes. Both the heater and thermocouples are fabricated using thin-film technology, resulting in a compact overall structure suitable for miniaturized integration. The temperature difference signals in the two orthogonal directions correspond to two flow velocity components, which can be vector-synthesized to obtain the flow velocity magnitude and flow direction. In the experiment, the sensitivity of the series-connected thin-film thermocouple reached 44.56 μV / K, and the coefficient of determination for fitting the thermoelectric potential and temperature difference was 0.9977. The maximum error of the flow direction measurement was 5.21°, and the average resolution was 1.5°. This structure has good temperature difference detection and two-dimensional flow direction recognition capabilities.

[0070] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A two-dimensional flow velocity and flow direction sensor of orthogonal series thin film thermocouples characterized by, It includes a substrate (3), a heater (2) disposed on the surface of the substrate (3), and a temperature detection unit; the heater (2) is disposed in the central region of the substrate (3), and the effective heating area of ​​the heater (2) adopts an S-shaped wire structure; The temperature detection unit includes four sets of series-connected thin-film thermocouples (1), each set of series-connected thin-film thermocouples (1) is composed of multiple thin-film thermocouple units connected in series; The four sets of series-connected thin-film thermocouples (1) are arranged with the heater (2) as the center, respectively along the first measurement direction and the second measurement direction that are perpendicular to each other. The two sets of series-connected thin-film thermocouples (1) in each measurement direction are located on both sides of the heater (2) and are arranged symmetrically with respect to the heater (2). The distance between the four sets of series-connected thin-film thermocouples (1) and the center of the heater (2) is the same. Two sets of series-connected thin-film thermocouples (1) in each measurement direction detect the temperature response at the corresponding position caused by fluid flow, so as to obtain the temperature difference signal characterizing the thermal field shift in the corresponding measurement direction.

2. The orthogonal-in-series thin-film thermocouple two-dimensional flow velocity and flow direction sensor according to claim 1, characterized in that, The substrate (3) is made of a material with electrical insulation properties and low thermal conductivity, and the substrate (3) is an alumina substrate or a polyimide substrate.

3. The orthogonal series-connected thin-film thermocouple two-dimensional flow velocity and direction sensor according to claim 1, characterized in that, The heater (2) is made of a metal material with electrothermal conversion performance and resistance temperature characteristics, and the metal material is platinum or tungsten.

4. The orthogonal series-connected thin-film thermocouple two-dimensional flow velocity and direction sensor according to claim 1, characterized in that, Each of the series-connected thin-film thermocouples (1) includes multiple thin-film thermocouple units connected in series. Adjacent thin-film thermocouple units are connected alternately by positive and negative electrodes, and the thermoelectric potentials generated by each thin-film thermocouple unit are superimposed in the same output circuit.

5. The orthogonal series-connected thin-film thermocouple two-dimensional flow velocity and direction sensor according to claim 4, characterized in that, The thin-film thermocouple unit includes a copper positive electrode and a constantan negative electrode, and the copper positive electrode and the constantan negative electrode are connected to form a thermocouple junction.

6. The orthogonal series-connected thin-film thermocouple two-dimensional flow velocity and direction sensor according to claim 1, characterized in that, Both the heater (2) and the series-connected thin-film thermocouple (1) adopt a thin-film structure and are formed on the surface of the substrate (3) by magnetron sputtering.

7. The orthogonal series-connected thin-film thermocouple two-dimensional flow velocity and direction sensor according to claim 6, characterized in that, The heater (2) is a platinum thin film heater, and the series-connected thin film thermocouple (1) includes a copper thin film positive electrode and a constantan thin film negative electrode.

8. The orthogonal series-connected thin-film thermocouple two-dimensional flow velocity and direction sensor according to claim 6 or 7, characterized in that, The sensor pattern on the surface of the substrate (3) is covered by a silicon carbide protective layer, which covers the heater (2) and the series-connected thin-film thermocouple (1).

9. A method for measuring two-dimensional flow velocity and direction using orthogonal series-connected thin-film thermocouples, characterized in that, Includes the following steps: A two-dimensional flow velocity and direction sensor is used. The two-dimensional flow velocity and direction sensor includes a substrate (3), a heater (2) disposed in the central region of the substrate (3), and four sets of series-connected thin film thermocouples (1). The effective heating area of ​​the heater (2) adopts an S-shaped wire structure. The four sets of series-connected thin film thermocouples (1) are arranged with the heater (2) as the center and along a first measurement direction and a second measurement direction that are perpendicular to each other. The two sets of series-connected thin film thermocouples (1) in each measurement direction are located on both sides of the heater (2) and are arranged symmetrically with respect to the heater (2). The distance between the four sets of series-connected thin film thermocouples (1) and the center of the heater (2) is the same. Power is supplied to the heater (2), forming a temperature field in the central region of the substrate (3); The output signals of the series-connected thin-film thermocouples (1) located on both sides of the heater (2) in the first measurement direction and the second measurement direction are respectively acquired. The temperature difference signal characterizing the thermal field shift in the measurement direction is obtained based on the output signals of the two sets of series-connected thin-film thermocouples (1) in the same measurement direction. Based on the pre-established correspondence between temperature difference signal and flow velocity, the first velocity component of the fluid under test in the first measurement direction and the second velocity component in the second measurement direction are determined respectively. The first velocity component and the second velocity component are combined by velocity vector synthesis to obtain the velocity magnitude and flow direction of the fluid under test in a two-dimensional plane.

10. The method for measuring two-dimensional flow velocity and direction using orthogonal series thin-film thermocouples according to claim 9, characterized in that, Before the two-dimensional flow velocity and direction measurement, the series-connected thin film thermocouple (1) is calibrated to establish a first calibration relationship between the output thermoelectric potential of the series-connected thin film thermocouple (1) and the temperature difference between its hot and cold ends, and to establish a second calibration relationship between the temperature difference signal in each measurement direction and the corresponding flow velocity component. During measurement, the output thermoelectric potential of each series-connected thin-film thermocouple (1) is converted into the corresponding temperature response according to the first calibration relationship. The temperature difference signal in the measurement direction is obtained based on the temperature response of the two sets of series-connected thin-film thermocouples (1) located on both sides of the heater (2) in the same measurement direction. The corresponding flow rate component is determined according to the second calibration relationship.

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