Flexible thermoelectric flow velocity sensor for surface flow field monitoring

Abstract

The invention belongs to the technical field of integrated circuit design, and particularly relates to a flexible thermoelectric flow velocity sensor for surface flow field monitoring, which comprises a flexible substrate, and a central heating circuit and a thermopile arranged on the flexible substrate, wherein the thermopile surrounds the periphery of the heating circuit, and a thermoelectric junction close to the heating circuit and a thermoelectric junction far away from the heating circuit are formed. The structure of the central heating circuit and the surrounding thermopile is adopted, the temperature difference output voltage generated by the heating circuit and the flow field is utilized to measure the flow velocity, and the use scene of the sensor is expanded through the arrangement of the flexible substrate.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of integrated circuit design, and particularly relates to a flexible thermal electric flow rate sensor for surface flow field monitoring. BACKGROUND

[0002] Thermal flow rate sensors have become the dominant technology in the field of flow rate detection due to their simple structure, convenient measurement, and high compatibility with MEMS manufacturing technology. These sensors achieve flow rate measurement through multiple stages of signal conversion: first, converting fluid mechanics parameters into thermal parameters, and then converting thermal signals into electrical signals for output. According to the different thermal-electric signal conversion mechanisms, thermal flow rate sensors can be further classified into four categories: thermal resistance type based on resistance change principle, thermoelectric type utilizing thermoelectric effect, pyroelectric type using pyroelectric effect, and frequency analog type through frequency modulation. Compared with the other three methods, thermoelectric flow rate sensors have simpler manufacturing processes, higher flow rate measurement sensitivity, faster response speed, and minimal disturbance to the flow field. In addition, thermoelectric flow rate sensors can directly output voltage signals, simplifying the signal processing process. They do not require the resistance-voltage conversion circuit of thermal resistance type or the charge amplifier of pyroelectric type, reducing the complexity of the peripheral circuit, and reducing the power consumption and volume of signal processing in flexible systems.

[0003] Most existing thermoelectric flow rate sensors are manufactured on rigid substrates such as silicon or glass. This method has the advantages of high device integration and high sensor sensitivity, resulting in good measurement accuracy. However, the rigid substrate limits the application scenarios of the flow rate sensor. For example, in the field of aerospace, aircrafts usually adopt a shape design that conforms to aerodynamic principles. However, due to the rigidity and size limitations of the structural material, traditional flow rate sensors often cannot match the complex curvature of the aircraft surface. This mismatch not only changes the local flow field characteristics, leading to inaccurate measurement, but also can generate additional aerodynamic drag, thereby reducing the overall performance of the aircraft and even causing safety hazards. Therefore, it is necessary to manufacture thermoelectric flow rate sensors on flexible substrates to ensure measurement accuracy and good deformation adaptability.

[0004] In the application of wearable devices, the rigid substrate can directly reduce the comfort of the device in contact with the human body and increase the difficulty of deployment on the human body. Manufacturing thermoelectric flow rate sensors on flexible substrates can facilitate their integration into wearable devices for physiological signal measurement such as respiration and blood flow, and play a significant role in health monitoring. SUMMARY

[0005] Therefore, the present application provides a flexible thermoelectric flow rate sensor for surface flow field monitoring, which expands the use scenarios of the sensor through the use of a flexible substrate and also has the advantages of low power consumption and high sensitivity.

[0006] The technical solutions of the present application are as follows:

[0007] A flexible thermoelectric current velocity sensor for surface flow field monitoring comprises a flexible substrate, a central heating circuit and a thermoelectric pile arranged on the flexible substrate; wherein the thermoelectric pile is arranged around the central heating circuit and forms a hot junction (hot end) close to the central heating circuit and a cold junction (cold end) away from the central heating circuit.

[0008] Optionally, the central heating circuit is formed by winding a metal wire in a serpentine shape, and the two ends of the metal wire are current input and output ends; the thermoelectric pile is formed by winding a metal wire in a serpentine shape with two materials alternately connected, and the two ends of the metal wire are voltage signal collection ends.

[0009] Optionally, the present application further comprises a signal processing and control module, which is used to control the current input of the heating circuit on the one hand, and to collect the output voltage of the thermoelectric pile on the other hand, and to calculate the change of the output voltage before and after the fluid input, and to obtain the flow velocity of the fluid flowing through the surface of the sensor according to the pre-calibrated voltage-flow velocity curve.

[0010] Optionally, the material of the metal wire of the central heating circuit is platinum (Pt); the thermoelectric pile is formed by winding a metal wire in a serpentine shape with bismuth telluride (Bi2Te3) and silver (Ag) alternately connected.

[0011] Optionally, the central heating circuit is rectangular, and the thermoelectric pile is arranged around the central heating circuit to form a cross shape together with the central heating circuit.

[0012] Optionally, the distance from the hot end of the thermoelectric pile to the central heating circuit is 25 um, and the length of the thermoelectric leg is 2000 um.

[0013] Optionally, the line width of the central heating circuit and the thermoelectric pile is 50 um, and the spacing is also 50 um.

[0014] Optionally, the thermoelectric pile is a gear or a ring.

[0015] Optionally, the material of the central heating circuit and the thermoelectric pile electrode is silver, and the material of the flexible substrate is PI, PDMS, paper or PVDF.

[0016] Optionally, a 5 um thick protective layer is spin-coated on the surface of the central heating circuit and the thermoelectric pile.

[0017] Beneficial effects:

[0018] Firstly, the application adopts the structure of central heating circuit and surrounding thermoelectric pile, uses the temperature difference output voltage generated by the heating circuit and flow field to measure the flow rate, and expands the use scene of the sensor through the setting of the flexible substrate.

[0019] Secondly, in order to obtain a suitable output voltage, the optimal structure and size are finally determined through multi-parameter comprehensive optimization, and the flexible thermoelectric flow rate sensor is successfully prepared through photolithography, magnetron sputtering, thermal evaporation and other methods. The simulation and experimental data show that the application realizes good linearity at low flow rate, has high measurement sensitivity, and can still maintain the original performance in the case of bending. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0021] Figure 1 The functional layer of the flexible thermoelectric flow rate sensor;

[0022] Figure 2 The functional layer size schematic diagram;

[0023] Figure 3 The overall structure of the flexible thermoelectric flow rate sensor;

[0024] Figure 4 The layered schematic diagram of the flexible thermoelectric flow rate sensor;

[0025] Figure 5 The simulation modeling diagram;

[0026] Figure 6 The temperature distribution diagram of the sensor when the flow rate is 0;

[0027] Figure 7 The sensor output voltage when the flow rate is 0;

[0028] Figure 8 The temperature distribution when the flow rate v=0.1m / s;

[0029] Figure 9 The cross-sectional diagram comparison of the temperature distribution with and without flow field;

[0030] Figure 10 The output voltage-flow rate response curve diagram;

[0031] Figure 11 The gear-shaped thermoelectric pile schematic diagram;

[0032] Figure 12 The physical map of the prepared sensor is shown. DETAILED DESCRIPTION

[0033] The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0034] It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict; and all other embodiments obtained by those skilled in the art based on the embodiments in the present disclosure without creative labor are within the scope of protection of the present disclosure.

[0035] It should be noted that various aspects of the embodiments described below are within the scope of the appended claims. It should be apparent that the aspects described herein can be embodied in a wide variety of forms and that any specific structure and / or function described herein is merely illustrative. Based on the teachings herein one skilled in the art should appreciate that an aspect described herein can be implemented independently of any other aspects and that an aspect can be implemented both as any number of software, firmware, and / or hardware structures. For example, an aspect can be implemented as a single structure on an integrated circuit or a structure implemented in multiple structures such as software coupled with a proper general purpose digital computer. An aspect can also be implemented as multiple structures (e.g., combined into a single structure for ease of use). An aspect can be implemented as a general structure (e.g., independent of the programming language or other specifics of a software written to carry out operations) or as a specific structure (e.g., written in C++). An aspect can be implemented as a proper virtual component (e.g., component that is not tied to a physical entity in any manner, where the virtual component can be accessed by multiple users and can be provided in different physical structures to different users).

[0036] As shown in Figure 1 The flexible thermoelectric flow sensor for surface flow field monitoring in the embodiments of the present application comprises a flexible substrate, and a center heating circuit and a thermoelectric pile arranged on the flexible substrate; wherein the thermoelectric pile is surrounded around the heating circuit and forms a thermoelectric junction (hot end) close to the heating circuit and a thermoelectric junction (cold end) away from the heating circuit.

[0037] The sensor in the embodiments utilizes two mechanisms of thermoelectric effect and thermal convection principle, establishes a temperature field through a heating resistor, and converts a temperature difference signal into a measurable voltage output by the thermoelectric pile through the temperature gradient change caused by fluid flow, so as to realize the measurement of flow rate. Meanwhile, the center heating circuit and the thermoelectric pile are arranged on the flexible substrate in the embodiments, which expands the application scenarios of the sensor.

[0038] The structure composition, preparation method, working process and simulation test of the sensor are described in detail as follows:

[0039] Structure composition: the main structure (i.e. functional layer) of the flexible thermoelectric flow sensor is as shown in Figure 1As shown, the device consists of a flexible substrate, a central serpentine heating circuit, and a surrounding thermopile. The flexible substrate can be made of polyimide (PI), polypropylene (PDMS), paper, or polyvinyl chloride (PVDF). The heating circuit is made of platinum (Pt), deposited on a polyimide (PI) substrate using magnetron sputtering. Platinum is chosen for its exceptional high-temperature resistance and stability. Heating resistors made from it can operate stably at temperatures around 800°C for nearly 10,000 hours. The thermopile is made of bismuth telluride (Bi2Te3) and silver (Ag). These two materials alternate around the heating circuit to form a serpentine thermopile circuit, forming a thermoelectric junction (hot end) close to the heating circuit and a thermoelectric junction (cold end) further away from the circuit. Bi2Te3 is currently one of the best performing thermoelectric materials near room temperature, with a ZT value (a key measure of thermoelectric efficiency) of 0.8–1.2, far exceeding that of other thermoelectric materials such as PbTe and SiGe. This enables it to efficiently generate voltage signals even at low temperature gradients. The role of silver is to use its low resistivity (1.59×10 -8 Ω·m) to reduce the internal resistance of the thermopile. The device's electrodes are also made of silver, so choosing silver as another material for the thermopile allows for the simultaneous fabrication of electrodes and functional layers, simplifying the process.

[0040] At the same time, the sensor of this embodiment also includes a signal processing and control module, which is used on the one hand to control the current input of the heating circuit, and on the other hand to collect the output voltage of the thermopile, and calculate the change in the output voltage before and after the fluid input, and obtain the flow rate flowing through the sensor surface based on a pre-calibrated voltage-flow rate curve.

[0041] Figure 2 It is a schematic diagram of the functional layer dimensions. In order to obtain a suitable output voltage, after comprehensive optimization of multiple parameters, the optimal structure and dimensions are finally determined. The central heating circuit is rectangular, and the thermopile surrounds the central heating circuit and forms a cross shape with the heating circuit. The distance from the hot end of the thermopile to the heating circuit is 25um, and the length of the thermoelectric leg is 2000um. This design ensures that the hot end fully receives the heat of the heating circuit and maintains a temperature difference of about 15K between the hot end and the cold end. The line width of the heating circuit and the thermopile are both 50um, and the spacing is also 50um. The compact design allows the device to be 0.25cm 2 31 pairs of thermoelectric junctions are integrated on an area of ​​​​1000 square meters. High-density thermoelectric junctions can output a larger voltage under a certain temperature difference, improving the sensitivity and range of the device. The thermopile in this embodiment can also be gear or ring-shaped, such as Figure 11 shown.

[0042] Preparation method: Figure 3 This is the overall structure diagram of the flexible thermal current velocity sensor. Figure 4Figure 1 is a layered schematic diagram of the sensor. First, the sensor is fabricated on a 5um thick PI substrate. Through photolithography, magnetron sputtering, thermal evaporation, lift-off and other processes, a patterned thermocouple circuit and a platinum heating circuit are prepared on the PI substrate, and the thickness of the prepared thin film is 300nm. Finally, a 5um thick PI protective layer is spin-coated on the device. The excellent thermal insulation performance and moderate elastic modulus of PI can not only protect the device from damage, but also reduce heat loss and improve measurement accuracy.

[0043] Workflow: The main mechanisms are the thermoelectric effect and the principle of thermal convection. The core is to establish a temperature field by heating the resistance, and to convert the temperature difference signal into a measurable voltage output by the thermocouple. The specific working process is as follows:

[0044] 1. The heating resistance establishes the initial temperature field. The platinum heating resistance is located in the center of the sensor. After a constant current is passed, the Joule heat is generated, forming a high-temperature area (hot end) centered on the heating area, and conducting heat to the surrounding area, establishing a stable radial temperature gradient field.

[0045] 2. Fluid flow disturbs the temperature field distribution. When the fluid (gas or liquid) flows through the surface of the sensor, the forced convection of the fluid will accelerate the heat loss of the hot end, causing the temperature of the hot end to drop, while the temperature of the cold end far from the heating area is more affected by the ambient temperature. The higher the flow rate (v) of the fluid, the greater the convection heat transfer coefficient (h), and the smaller the temperature difference (ΔT) between the hot end and the cold end.

[0046] 3. The thermocouple responds to the temperature difference and outputs voltage. Bi2Te3 is a thermoelectric material with a high Seebeck coefficient (S≈100μV / K), and Ag electrodes with low resistivity and low Seebeck coefficient form a loop. When there is a temperature difference (ΔT), the Seebeck effect drives the directional migration of charge carriers, generating a thermoelectric potential (Vout=N·S·ΔT), where N is the number of thermoelectric junctions. When the flow rate increases, the heat dissipation of the hot end increases, ΔT decreases, resulting in a decrease in output voltage Vout; conversely, when the flow rate decreases, ΔT increases, Vout increases. By calibrating the Vout-v curve, the flow rate can be inverted.

[0047] Simulation test: COMSOL Multiphysics is used to simulate the output voltage-flow rate response under the action of thermoelectric effect and thermal convection principle.

[0048] 1. Simulation when the flow rate is 0

[0049] Figure 5is the modeling diagram of the sensor and the external flow field, the sensor adopts the structure and size described above, a flow field area is added above the sensor, one end is set as a gas inlet, and the other end is an outlet, the speed of the inflowing gas can be set as any value, and the output voltage response under different flow speeds is studied. Figure 6 and Figure 7 respectively are the temperature distribution diagram and the output voltage of the heating circuit on the device when the flow speed is 0. The results show that when the flow speed is 0, the temperature distribution generated by the central heating circuit is uniformly diffused to the four directions, and a temperature difference of about 10K can be generated at the hot end and the cold end of the thermoelectric pile. The theoretical output voltage value calculated based on the results is 31mV, Figure 7 The simulation results of show that the output voltage is 36mV, which is close to the theoretical value, indicating that the simulation modeling is consistent with the actual situation. In addition, the voltage applied to the heating circuit is only 1.2V, and the current is 6mA, and the power consumed by the sensor is 7.2mW, so the flexible thermoelectric flow speed sensor has the advantage of low power consumption.

[0050] 2. Simulation under different flow speeds

[0051] The flow speed of 0.1m / s-1m / s is parameterized and simulated. Figure 8 is the temperature distribution when the flow speed is 0.1m / s. It can be seen that the addition of a flow field of 0.1m / s makes the overall temperature drop by about 30℃. Due to the limitation of the size of the simulation memory, the simulation of smaller flow speeds is not accurate, but it can be inferred that the thermoelectric flow speed sensor designed in the application can measure the flow speed of millimeter level. The airflow not only reduces the temperature of the device, but also causes the asymmetric distribution of the temperature, as shown in Figure 9 . Figure 8 The temperature difference between the left and right hot ends and cold ends of the thermoelectric pile in is 8K and 5K respectively, which is lower than that when the flow speed is 0, and the temperature difference at the inlet end decreases more, which is consistent with the theory. Figure 10 is the output voltage response curve of the device in the flow speed range of 0.1m / s-1m / s. It can be seen that in this interval, the linearity of the curve is good, and it has excellent sensitivity, as shown in Figure 12 .

[0052] In summary, the above is only a preferred embodiment of the application, and is not used to limit the protection scope of the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A flexible thermal current velocity sensor for surface flow field monitoring, characterized in that: include: A flexible substrate, and a central heating circuit and a thermopile arranged on the flexible substrate; wherein the thermopile surrounds the heating circuit to form a thermoelectric junction close to the heating circuit and a thermoelectric junction far away from the heating circuit.

2. The flexible thermal current velocity sensor for surface flow field monitoring according to claim 1, characterized in that: The central heating circuit is formed by serpentine winding of metal wire, and the two ends of the metal wire are heating current input and output ends; the thermopile is formed by serpentine winding of metal wire connected alternately with two materials, and the two ends of the metal wire are voltage signal acquisition ends.

3. The flexible thermal current velocity sensor for surface flow field monitoring according to claim 1 or 2, characterized in that: It also includes a signal processing and control module, which is used to control the current input of the heating circuit on the one hand, and to collect the output voltage of the thermopile on the other hand, and calculate the change in the output voltage before and after the fluid input, and obtain the flow rate flowing through the sensor surface based on the pre-calibrated voltage-flow rate curve.

4. The flexible thermal current velocity sensor for surface flow field monitoring according to claim 2, characterized in that: The material of the central heating circuit metal wire is platinum; the thermopile is formed by serpentine winding of metal wires alternately connected with bismuth telluride and silver.

5. The flexible thermal current velocity sensor for surface flow field monitoring according to claim 2, characterized in that: The central heating circuit is rectangular, and the thermopile surrounds the central heating circuit and forms a cross shape together with the heating circuit.

6. The flexible thermal current velocity sensor for surface flow field monitoring according to claim 5, characterized in that: The distance between the hot end of the thermopile and the heating circuit is 25 μm, and the length of the thermoelectric leg is 2000 μm.

7. The flexible thermal current velocity sensor for surface flow field monitoring according to claim 5, characterized in that: The line width of the heating circuit and the thermopile is 50 μm, and the spacing is also 50 μm.

8. The flexible thermal current velocity sensor for surface flow field monitoring according to claim 2, characterized in that: The thermopile is in the shape of a gear or a ring.

9. The flexible thermal current velocity sensor for surface flow field monitoring according to claim 1, characterized in that: The central heating circuit and the thermopile electrodes are made of silver, and the flexible substrate is made of PI, PDMS, paper or PVDF.

10. The flexible thermal current velocity sensor for surface flow field monitoring according to claim 1, characterized in that: A 5 μm thick protective layer is spin-coated on the surface of the central heating circuit and the thermopile.

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