Thermal type gas flow sensor and flow measuring method and system

Abstract

The invention provides a thermal gas flow sensor and a flow measurement method and system, and relates to the field of surface acoustic wave application, and the thermal gas flow sensor comprises a gas passage straight pipe, a heating element, a heat insulation element and a surface acoustic wave resonator; wherein the gas passage straight pipe is used for transmitting detected gas; setting of the diameter of the gas passage straight pipe needs to meet the constraint condition that the gas flow state is laminar flow; the heat insulation element is attached to the outer lower wall of the gas channel straight pipe and comprises a heat insulation shell and two heat insulation materials. The heat insulation material is wrapped by the heat insulation shell; the heating element is attached to the outer lower wall of the gas passage straight pipe and clamped by the two heat insulation materials. The surface acoustic wave resonator is attached to the outer wall of the gas passage straight pipe and used for sensing the upstream and downstream frequency change when the detected gas is transmitted in the gas passage straight pipe so as to detect the change of the gas flow in the gas passage straight pipe. According to the invention, the high-performance surface acoustic wave resonator can be used as a measuring element, and the flow of the gas can be rapidly and accurately measured under the condition of low gas flow.

Description

Technical Field

[0001] The present application relates to the field of surface acoustic wave applications, and specifically to a thermal gas flow sensor, a flow measurement method and a system. Background Art

[0002] With the development of semiconductor technology, higher and higher requirements are put forward for the measurement and control of fluids. Traditional thermal gas flow sensors based on resistance have problems such as low accuracy, slow response and temperature drift in the field of high-end semiconductors. As one of the cutting-edge core technologies in the semiconductor field, the measurement technology based on surface acoustic wave (SAW) has the characteristics of high output signal frequency, fast response, small pressure loss, corrosion resistance, and wide working pressure range, which can achieve high-precision and fast response measurement of flow.

[0003] In order to achieve high-precision and fast-response flow measurement, technicians proposed a thermal gas flow sensor based on SAW technology, and designed a sensor without a heater structure and flow test channel based on MEMS technology. Gas thermal flow sensors based on SAW technology have the advantages of low cost and high sensitivity, but have disadvantages such as complex structural design and insufficient accuracy.

[0004] This section is intended to provide a background or context to the embodiments of the invention recited in the claims. No description herein is admitted to be prior art by inclusion in this section. Summary of the invention

[0005] In response to the problems in the prior art, the present application provides a thermal gas flow sensor, a flow measurement method and a system, which can use a high-performance surface acoustic wave resonator as a measuring element to quickly and accurately measure the gas flow at low gas flow rates.

[0006] In order to solve the above technical problems, this application provides the following technical solutions:

[0007] In a first aspect, the present application provides a thermal gas flow sensor, comprising: a gas passage straight tube, a heating element, an insulating element and a surface acoustic wave resonator;

[0008] The straight pipe of the gas passage is used to transmit the gas to be measured; the setting of the diameter of the straight pipe of the gas passage must meet the constraint condition that the gas flow state is laminar flow;

[0009] The heat insulating element is applied to the outer lower wall of the gas passage straight pipe, and comprises a heat insulating shell and two pieces of heat insulating materials; the heat insulating material is wrapped in the heat insulating shell;

[0010] The heating element is applied to the outer lower wall of the gas passage straight tube and is clamped by two pieces of heat insulating material;

[0011] The surface acoustic wave resonator is applied to the outer wall of the gas passage straight tube and is used to sense the frequency changes of the measured gas upstream and downstream when it is transmitted in the gas passage straight tube, so as to detect the changes of gas flow in the gas passage straight tube.

[0012] Furthermore, the surface acoustic wave resonator includes a supporting substrate layer, a piezoelectric film layer and an electrode layer.

[0013] Furthermore, the material of the supporting substrate layer includes silicon and sapphire; the material of the piezoelectric film layer includes lithium niobate, gallium nitride and aluminum nitride; and the material of the electrode layer includes aluminum, gold, platinum and nickel.

[0014] Furthermore, the electrode layer includes an IDT and a reflection grating symmetrically arranged on both sides of the IDT.

[0015] Furthermore, the thickness of the piezoelectric film layer is 0.1 μm to 5 μm; the thickness of the interdigital transducer electrode is 80 nm to 200 nm.

[0016] Furthermore, the shape of the gas passage straight tube is a round tube; the material of the gas passage straight tube is stainless steel, iron or aluminum; the specification of the gas passage straight tube is a capillary tube; the inner diameter of the capillary tube is 0.1mm to 1mm, and the outer diameter is 0.1mm to 1mm.

[0017] Furthermore, the heating element includes a heater and a temperature sensor; the heater is arranged below the outer wall of the gas passage straight tube; and the temperature sensor is arranged on the side of the outer wall of the heater.

[0018] Furthermore, the width of the contact surface between the heat source of the heater and the straight tube of the gas passage is 2 mm to 12 mm.

[0019] Furthermore, the temperature at the heat source of the heater is controlled at 80° C. to 150° C.; the heating method is constant power heating or constant temperature heating.

[0020] Furthermore, the surface acoustic wave resonator includes an upstream surface acoustic wave resonator and a downstream surface acoustic wave resonator.

[0021] Furthermore, the upstream surface acoustic wave resonator and the downstream surface acoustic wave resonator are symmetrically distributed with the heater as the center.

[0022] Furthermore, the upstream surface acoustic wave resonator and the downstream surface acoustic wave resonator are both 1 mm to 8 mm away from the center point of the heater.

[0023] In a second aspect, the present application provides a thermal gas flow measurement system, comprising:

[0024] Gas source, used to provide the gas to be tested;

[0025] The thermal gas flow sensor is used to sense the resonant frequency of the gas to be measured when it flows through;

[0026] A heating controller, used for controlling the thermal gas flow sensor to heat;

[0027] A mass flow controller respectively connected to the gas source and the thermal gas flow sensor;

[0028] and a network vector analyzer electrically connected to the thermal gas flow sensor;

[0029] The gas to be measured flows out from the gas source, passes through the mass flow controller and then flows into the thermal gas flow sensor, so that the network vector analyzer determines the gas flow according to the resonant frequency.

[0030] In a third aspect, the present application provides a thermal gas flow measurement method, which is applied to the thermal gas flow measurement system, comprising:

[0031] Using a heating controller to control the thermal gas flow sensor to heat, so that the thermal gas flow sensor is heated up and stabilized at a preset temperature value;

[0032] A mass flow controller is used to control the gas source to output the gas to be tested at room temperature with different set flow rates, and a network analyzer is used to record the resonant frequencies of the upstream and downstream surface acoustic wave resonators in the thermal gas flow sensor at different set flow rates;

[0033] By means of the network analyzer, a partial least squares regression method is used to quantitatively analyze the difference between the upstream and downstream resonant frequencies, and a linear regression curve is established between the set flow rate and the difference between the upstream and downstream resonant frequencies;

[0034] The mass flow controller is used to control the gas source to output the unknown flow of the gas to be tested at room temperature, and the linear regression curve is used to determine the flow of the unknown flow of the gas to be tested at room temperature.

[0035] In response to the problems in the prior art, the thermal gas flow sensor, flow measurement method and system provided by this application can use a high-performance surface acoustic wave resonator as a measuring element to construct a gas flow measurement structure based on surface acoustic wave technology (Surface Acoustic Wave, referred to as SAW). It subverts the traditional measurement method from the perspective of the key temperature measurement method and the entire gas flow measurement structure, and has the advantages of high sensitivity, simple structural design and high measurement accuracy. Since the cost of surface acoustic wave gas flow sensors is relatively low after mass production, the subsequent circuit part can directly read and measure the readings, thus filling the gap in the application of surface acoustic wave technology in gas flow measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0037] Figure 1 This is a structural diagram of the high-performance SAW resonator implemented by the present invention.

[0038] Figure 2 It is a schematic diagram of the core structure of the SAW-based thermal gas flow sensor of the present invention.

[0039] Figure 3 Schematic diagram of a gas flow measurement system in an embodiment of the present invention.

[0040] Figure 4 1 is a diagram of gas flow measurement parameters in an embodiment of the present invention.

[0041] Figure 5 It is a flow chart of the gas flow measurement method in an embodiment of the present invention. DETAILED DESCRIPTION

[0042] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0043] In one embodiment, see Figure 2 , in order to use a high-performance surface acoustic wave resonator as a measuring element to quickly and accurately measure the flow rate of a gas at a low gas flow rate, the present application provides a thermal gas flow sensor, including: a gas passage straight tube, a heating element, an insulating element and a surface acoustic wave resonator;

[0044] The straight pipe of the gas passage is used to transmit the gas to be measured; the setting of the diameter of the straight pipe of the gas passage must meet the constraint condition that the gas flow state is laminar flow;

[0045] The heat insulating element is applied to the outer lower wall of the gas passage straight pipe, and includes a heat insulating shell and two pieces of heat insulating materials; the heat insulating materials are wrapped in the heat insulating shell;

[0046] The heating element is applied to the outer lower wall of the gas passage straight pipe and is clamped by two pieces of heat insulating materials;

[0047] Two surface acoustic wave resonators are applied to the outer wall of the gas passage straight pipe and are used to sense the frequency changes of the gas under test upstream and downstream when it is transmitted in the gas passage straight pipe, so as to detect the changes of gas flow in the gas passage straight pipe.

[0048] Understandably, see Figure 2 The thermal gas flow sensor based on surface acoustic wave (SAW) provided by the present invention includes: a gas passage straight tube 1, a heater 2, a temperature sensor 3, an insulating shell 4, an insulating material 5, an upstream SAW resonator 6 and a downstream SAW resonator 7. Among them, the gas passage straight tube 1 is used to transmit the gas to be measured (also called the gas to be measured), with the left side as the air inlet and the right side as the air outlet. The gas passage straight tube is a stainless steel straight tube. Among them, the inner diameter of the gas passage straight tube must meet the constraint condition that the flow state of the gas is laminar flow. The heating element includes: a heater 2 and a temperature sensor 3, which are arranged below the gas passage straight tube and between the upstream SAW resonator 6 and the downstream SAW resonator 7. The working mode of the heater is constant temperature heating, which is controlled by an external controller and the temperature is controlled at 100-150°C. The insulating element includes: an insulating shell 4 and an internal insulating material 5, so as to reduce the transfer of heat from the heating element to the non-heat source position and ensure the measurement accuracy. The upstream SAW resonator 6 and the downstream SAW resonator 7 are located on the outer wall of the gas passage straight tube, respectively arranged upstream and downstream, and are used to sense the frequency changes of the gas flowing upstream and downstream, and then sense the temperature changes of the upstream and downstream, so as to detect the changes in the gas flow in the gas pipeline.

[0049] The surface acoustic wave resonator includes: a supporting substrate layer, a piezoelectric film layer and an electrode layer. The material of the supporting substrate layer includes silicon and sapphire; the material of the piezoelectric film layer includes lithium niobate, gallium nitride and aluminum nitride; the material of the electrode layer includes aluminum, gold, platinum and nickel. The electrode layer includes an interdigital transducer and a reflective grating symmetrically arranged on both sides of the interdigital transducer. The thickness of the piezoelectric film layer is 0.1μm to 5μm; the thickness of the interdigital transducer electrode is 80nm to 200nm. The shape of the gas passage straight tube is a round tube; the material of the gas passage straight tube is stainless steel, iron or aluminum; the specification of the gas passage straight tube is a capillary tube; the inner diameter of the capillary tube is 0.1mm to 1mm, and the outer diameter is 0.1mm to 1mm. The heating element includes a heater and a temperature sensor; the heater is arranged below the outer wall of the gas passage straight tube; the temperature sensor is arranged on the side of the outer wall of the heater. The width of the contact surface between the heat source of the heater and the gas passage straight tube is 2mm to 12mm. The temperature at the heat source of the heater is controlled at 80°C to 150°C; the heating method is constant power heating or constant temperature heating. The surface acoustic wave resonator includes an upstream surface acoustic wave resonator and a downstream surface acoustic wave resonator. The upstream surface acoustic wave resonator and the downstream surface acoustic wave resonator are symmetrically distributed with the heater as the center. The upstream surface acoustic wave resonator and the downstream surface acoustic wave resonator are both 1mm to 8mm away from the center point of the heater.

[0050] Understandably, see Figure 1 The thermal gas flow sensor provided in the present application has a surface acoustic wave gas sensing device which is a surface acoustic wave single-port resonator, and its basic unit includes: a piezoelectric film layer and a supporting substrate layer 8, an IDT electrode 10, a left reflection grating 9 and a right reflection grating 11.

[0051] The period of the metal IDT electrode 10 can determine the wavelength λ, and the IDT electrode 10 includes upper and lower electrodes and a bus bar, thereby forming a transmission channel for surface acoustic waves. The width of the metal IDT finger is in the range of 0.3-1μm, and the number of upper and lower forked electrode pairs is 150-250 pairs. The metal IDT electrode 10 mainly includes: an adhesion layer and a metal electrode layer. Among them, the adhesion layer adopts metals such as Ti and Cr, and the metal electrode adopts metals such as Au, Al, and Pt. The thickness of the adhesion layer is 5-10nm, and the thickness of the metal electrode is 100-150nm, and both need to be kept in a reasonable range. Preferably, the adhesion layer is 10nm and the metal layer is 100nm.

[0052] A reflection grating of the same shape as the IDT electrode 10 is also provided on the piezoelectric substrate. The reflection grating can be short-circuited or open-circuited and is symmetrically distributed on both sides of the IDT to form an elastic wave resonator. The preparation process and parameters of the reflection grating are the same as those of the IDT electrode, and the number of pairs of the reflection grating is in the range of 50-200 pairs.

[0053] In one embodiment, see Figure 3, the present application provides a thermal gas flow measurement system, comprising:

[0054] Gas source, used to provide the gas to be tested;

[0055] The thermal gas flow sensor is used to sense the resonant frequency of the gas to be measured when it flows through;

[0056] A heating controller, used for controlling the thermal gas flow sensor to heat;

[0057] A mass flow controller respectively connected to the gas source and the thermal gas flow sensor;

[0058] and a network vector analyzer electrically connected to the thermal gas flow sensor;

[0059] The gas to be measured flows out from the gas source, passes through the mass flow controller and then flows into the thermal gas flow sensor, so that the network vector analyzer determines the gas flow according to the resonant frequency.

[0060] It is understandable that, based on the above, see Figure 3 , the embodiment of the present application has built a gas flow measurement system based on SAW. In this embodiment, a nitrogen bottle 13 is used as a gas source, and the required nitrogen is outputted through a valve 14 (the valve can be multiple). Subsequently, a mass flow controller 15 (Mass Flow Controller, referred to as MFC) is used, and a laptop computer 17 is used to read and control the gas flow through the host computer software of the mass flow controller 15. After the nitrogen in the nitrogen bottle 13 enters the mass flow controller 15, it is connected to the upstream side (air inlet) of the gas path channel of the thermal gas flow sensor provided by the present application, and the gas path channel outlet is connected to a hose to directly discharge the gas into the fume hood. The two ends of the cross-digital transducers of the upstream SAW resonator 6 and the downstream SAW resonator 7 are respectively connected to the two ports of the network vector analyzer 19 through PCB, leads and coaxial cables 16. Then, turn on the heating controller 18 switch, heat to the specified temperature, and keep the temperature stable. Finally, the vector network analyzer 19 is used to observe the S parameters of the two-port SAW resonators, and the corresponding relationship with the flow rate is obtained through the change of the resonant frequency. Subsequently, the system can be used to measure the flow rate of the gas to be measured. The specific method is described below. The performance of the thermal gas flow sensor provided in this application can also be analyzed.

[0061] When there is no nitrogen passing through, since the heater 2 is attached to the bottom of the gas passage straight tube 1, the temperature of the gas passage straight tube 1 will rise. At this time, since the gas flow test structure is symmetrical with the heat source as the center point, the temperature distribution of the outer wall of the gas passage straight tube is symmetrical on both sides, and the temperature at the center point of the heat source is the highest. The heat source heating mode is feedback-controlled to be constant temperature heating through the temperature sensor 3 and the external heating controller 18. When the valve 16 is opened for ventilation, the room temperature gas absorbs the heat from the upstream pipe wall and the temperature rises, and the upstream pipe also takes away the heat and the temperature decreases. When the gas flows to the downstream pipe through the heat source, the temperature of the downstream pipe wall increases due to the heat brought by the gas. At this time, the upstream high-performance SAW resonator 6 and the downstream high-performance SAW resonator 7 will feel the temperature change, and the resonant frequency will also change. Since the SAW resonator has a negative temperature coefficient, when the gas is passed in, the upstream SAW resonant frequency increases due to the temperature decrease, while the downstream SAW resonant frequency decreases due to the temperature first increasing and then decreasing, and finally tends to be stable. Since the SAW resonator has high frequency and fast response, it is also conducive to the high-precision and rapid detection of low-flow gas.

[0062] In one embodiment, see Figure 5 The present application provides a thermal gas flow measurement method, which is applied to the thermal gas flow measurement system, comprising:

[0063] S101: Using a heating controller to control the thermal gas flow sensor to heat, so that the thermal gas flow sensor is heated up and stabilized at a preset temperature value;

[0064] S102: using a mass flow controller to control the gas source to output the gas to be tested at room temperature with different set flow rates, and recording the resonant frequencies of the upstream and downstream surface acoustic wave resonators in the thermal gas flow sensor at different set flow rates through a network analyzer;

[0065] S103: using the network analyzer, using a partial least squares regression method to quantitatively analyze the difference between the upstream and downstream resonant frequencies, and establishing a linear regression curve between the set flow rate and the difference between the upstream and downstream resonant frequencies;

[0066] S104: Using the mass flow controller to control the gas source to output the unknown flow of the gas to be tested at room temperature, and using the linear regression curve to determine the flow of the unknown flow of the gas to be tested at room temperature.

[0067] It can be understood that the thermal gas flow measurement method can be divided into two stages: the first stage is to calibrate the "thermal gas flow sensor" provided in this application (in this process, a linear regression equation can be obtained); the second stage is to measure the flow of the gas to be measured.

[0068] The specific steps include:

[0069] S1: Build a SAW-based gas flow measurement system, including: nitrogen bottle 13, mass flow controller 15, laptop 17 (can run host computer software), heating controller 18, thermal gas flow sensor 12, coaxial line 16 and vector network analyzer 19, as well as some necessary accessories such as hoses. Among them, the mass flow controller 15 selects a flow detection range of 0-300sccm.

[0070] S2 The above measurement system can be placed in a laboratory environment, all equipment is powered on, the vector network analyzer 19 is calibrated, the laptop 17 is turned on to connect the mass flow controller 15, and a zeroing operation is performed. The heater in the thermal gas flow sensor 12 is heated to a fixed 120°C by an external heating controller 18. The gas pressure of the nitrogen bottle 13 is controlled by a valve 16 within the working pressure specified by the mass flow controller 15;

[0071] S3 After the temperature displayed by the heating controller 18 is stable at 120°C, the test data is recorded, and the initial data is the resonant frequency at 0 sccm. The resonant frequencies of the two SAW devices are observed and recorded by analyzing the S parameters of the two ports through the network;

[0072] S4 controls the output of room temperature nitrogen with set flow rates of 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70 sccm through the host computer software 17, and records the resonant frequencies of the upstream and downstream SAW resonators at each gas flow rate in turn through the network vector analyzer 19. After preprocessing the collected upstream and downstream resonant frequency data (for example, removing bad pixel data, etc.), the difference between the upstream and downstream resonant frequencies at different set gas flow rates is quantitatively analyzed using the partial least squares regression method to establish a linear regression curve between the gas flow rate and the frequency difference (which can correspond to the temperature difference). The relationship between the above frequency difference and the temperature difference can be converted by p = 57.9kHz / ℃, where p is the resonant frequency change of the SAW device per unit degree Celsius, 57.9kHz.

[0073] In one embodiment, the experimental results of step S4 are shown in Figure 4 The linear regression equation for the temperature difference in the range of 0-10sccm is finally selected as: y = -20.543x-45.806, and the square of the correlation coefficient R 2=99.7%, where y is the difference between the downstream resonant frequency and the upstream resonant frequency (which can be referred to as the frequency difference), in kHz, and x is the gas flow rate, in SCCM. This equation is generated in the aforementioned first stage. When actually measuring the gas flow rate (the aforementioned second stage), it is necessary to reverse the y and x in the above formula, that is, use x as the ordinate and y as the abscissa. Therefore, the formula used in the measurement is s=-0.0486f-2.2178, where s is the value of the gas flow rate during actual measurement, and f is the difference between the downstream resonant frequency and the upstream resonant frequency (which can be referred to as the frequency difference). For example, when the difference between the downstream resonant frequency and the upstream resonant frequency is -70kHz, the formula (f=-70) is substituted to obtain a flow rate of 1.18SCCM at this time. Multiple experiments have shown that the gas flow sensor provided in this application has good linearity in the range of 0-10sccm, thereby verifying the accuracy and effectiveness of the measurement method provided in this application.

[0074] It should be noted that the above steps S1-S4 can be understood as the first stage of calibration of the "thermal gas flow sensor" provided by the present application. Next, the second stage can be carried out: the mass flow controller is used to control the gas source to output the unknown flow of the room temperature gas to be tested, and the flow rate of the room temperature gas to be tested with the unknown flow rate is determined using the linear regression curve obtained above. Specifically, the above linear regression equation has been established, so when the resonant frequencies of the upstream and downstream surface acoustic wave resonators are measured using the thermal gas flow sensor, the gas flow rate can be mapped.

[0075] From the above description, it can be seen that the thermal gas flow sensor, flow measurement method and system provided by the present application can use a high-performance surface acoustic wave resonator as a measuring element to construct a gas flow measurement structure based on surface acoustic wave technology (Surface AcousticWave, referred to as SAW). It subverts the traditional measurement method from the perspective of the key temperature measurement method and the entire gas flow measurement structure, and has the advantages of high sensitivity, simple structural design and high measurement accuracy. Since the cost of surface acoustic wave gas flow sensors is relatively low after mass production, the subsequent circuit part can directly read and measure the readings, thus filling the gap in the application of surface acoustic wave technology in gas flow measurement.

[0076] Because the surface acoustic wave device has a good temperature-frequency coefficient, a high resonant frequency and a Q value, the sensitivity and response speed of the sensor are improved, so that the sensor can quickly and accurately measure various gases at low gas flow rates. At room temperature, the detection limit can reach less than 5SCCM, and it has good linearity in the range of 0-10SCCM, and the response time is about 1-3S.

[0077] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the embodiment of the device implementation method, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0078] The above is a description of a specific embodiment of the specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the embodiments and still achieve the desired results. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0079] Although the present specification embodiment provides the method operation steps as described in the embodiment or flow chart, more or less operation steps may be included based on conventional or non-creative means. The order of steps listed in the embodiment is only one way in the order of execution of many steps, and does not represent a unique execution order. The term "include", "comprise" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, product or equipment including a series of elements not only includes those elements, but also includes other elements not clearly listed, or also includes elements inherent to such process, method, product or equipment. In the absence of more restrictions, it is not excluded that there are other identical or equivalent elements in the process, method, product or equipment including the elements.

[0080] Each embodiment in this specification is described in a progressive manner, and the same and similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. In the description of this specification, the description of the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of this specification. In this specification, the schematic representation of the above terms does not necessarily target the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, in the absence of contradiction, a person skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0081] The above is only an example of the embodiment of the present specification and is not intended to limit the embodiment of the present specification. For those skilled in the art, the embodiment of the present specification may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the embodiment of the present specification shall be included in the scope of the claims of the embodiment of the present specification.

Claims

1. A thermal gas flow sensor, characterized in that: include: Gas passage straight pipe, heating element, insulation element and surface acoustic wave resonator; The straight pipe of the gas passage is used to transmit the gas to be measured; the setting of the diameter of the straight pipe of the gas passage must meet the constraint condition that the gas flow state is laminar flow; The heat insulating element is applied to the outer lower wall of the gas passage straight pipe, and comprises a heat insulating shell and two pieces of heat insulating materials; the heat insulating material is wrapped in the heat insulating shell; The heating element is applied to the outer lower wall of the gas passage straight tube and is clamped by two pieces of heat insulating material; The surface acoustic wave resonator is applied to the outer wall of the gas passage straight tube and is used to sense the frequency changes of the measured gas upstream and downstream when it is transmitted in the gas passage straight tube, so as to detect the changes of gas flow in the gas passage straight tube.

2. The thermal gas flow sensor according to claim 1, characterized in that: The surface acoustic wave resonator comprises a supporting substrate layer, a piezoelectric film layer and an electrode layer.

3. The thermal gas flow sensor according to claim 2, characterized in that: The material of the supporting substrate layer includes silicon and sapphire; the material of the piezoelectric film layer includes lithium niobate, gallium nitride and aluminum nitride; the material of the electrode layer includes aluminum, gold, platinum and nickel.

4. The thermal gas flow sensor according to claim 2, characterized in that: The electrode layer includes an IDT and a reflection grating symmetrically arranged on both sides of the IDT.

5. The thermal gas flow sensor according to claim 4, characterized in that: The thickness of the piezoelectric film layer is 0.1 μm to 5 μm; the thickness of the interdigital transducer electrode is 80 nm to 200 nm.

6. The thermal gas flow sensor according to claim 1, characterized in that: The shape of the gas passage straight tube is a round tube; the material of the gas passage straight tube is stainless steel, iron or aluminum; the specification of the gas passage straight tube is a capillary tube; the inner diameter of the capillary tube is 0.1mm to 1mm, and the outer diameter is 0.1mm to 1mm.

7. The thermal gas flow sensor according to claim 1, characterized in that: The heating element includes a heater and a temperature sensor; the heater is arranged below the outer wall of the gas passage straight tube; and the temperature sensor is arranged on the side of the outer wall of the heater.

8. The thermal gas flow sensor according to claim 7, characterized in that: The width of the contact surface between the heat source of the heater and the straight tube of the gas passage is 2 mm to 12 mm.

9. The thermal gas flow sensor according to claim 7, characterized in that: The temperature at the heat source of the heater is controlled at 80°C to 150°C; the heating method is constant power heating or constant temperature heating.

10. The thermal gas flow sensor according to claim 9, characterized in that: The surface acoustic wave resonator includes an upstream surface acoustic wave resonator and a downstream surface acoustic wave resonator.

11. The thermal gas flow sensor according to claim 10, characterized in that: The upstream surface acoustic wave resonator and the downstream surface acoustic wave resonator are symmetrically distributed with the heater as the center.

12. The thermal gas flow sensor according to claim 11, characterized in that: The upstream surface acoustic wave resonator and the downstream surface acoustic wave resonator are both 1 mm to 8 mm away from the center point of the heater.

13. A thermal gas flow measurement system, characterized in that: include: Gas source, used to provide the gas to be tested; The thermal gas flow sensor according to any one of claims 1 to 12, used to sense the resonant frequency of the gas to be measured when it flows through; A heating controller, used for controlling the thermal gas flow sensor to heat; A mass flow controller respectively connected to the gas source and the thermal gas flow sensor; and a network vector analyzer electrically connected to the thermal gas flow sensor; The gas to be measured flows out from the gas source, passes through the mass flow controller and then flows into the thermal gas flow sensor, so that the network vector analyzer determines the gas flow according to the resonant frequency.

14. A thermal gas flow measurement method, applied to the thermal gas flow measurement system according to claim 13, characterized in that: include: Using a heating controller to control the thermal gas flow sensor to heat, so that the thermal gas flow sensor is heated up and stabilized at a preset temperature value; A mass flow controller is used to control the gas source to output the gas to be tested at room temperature with different set flow rates, and a network analyzer is used to record the resonant frequencies of the upstream and downstream surface acoustic wave resonators in the thermal gas flow sensor at different set flow rates; By means of the network analyzer, a partial least squares regression method is used to quantitatively analyze the difference between the upstream and downstream resonant frequencies, and a linear regression curve is established between the set flow rate and the difference between the upstream and downstream resonant frequencies; The mass flow controller is used to control the gas source to output the unknown flow of the gas to be tested at room temperature, and the linear regression curve is used to determine the flow of the unknown flow of the gas to be tested at room temperature.

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