Thermal gas flow sensor, flow measurement method and system

Abstract

This application provides a thermal gas flow sensor, flow measurement method, and system, relating to the field of surface acoustic wave (SAW) applications. The system includes: a straight gas passage pipe, a heating element, an insulating element, and a SAW resonator. The straight gas passage pipe is used to transmit the gas to be measured. The diameter of the straight gas passage pipe must satisfy the constraint that the gas flow is laminar. The insulating element is attached to the lower outer wall of the straight gas passage pipe and includes an insulating shell and two insulating materials. The insulating materials are enclosed within the insulating shell. The heating element is attached to the lower outer wall of the straight gas passage pipe and is held between the two insulating materials. The SAW resonator is attached to the outer wall of the straight gas passage pipe and is used to sense the frequency changes upstream and downstream as the gas is transmitted through the straight gas passage pipe, thereby detecting changes in the gas flow rate within the straight gas passage pipe. This application enables rapid and accurate measurement of gas flow rate at low gas flow rates using a high-performance SAW resonator as the measuring element.

Description

Technical Field

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

[0002] With the development of semiconductor technology, increasingly higher demands are being placed on the measurement and control of fluids. Traditional resistive thermal gas flow sensors suffer from low accuracy, slow response, and temperature drift in the high-end semiconductor field. As one of the cutting-edge core technologies in the semiconductor field, surface acoustic wave (SAW) measurement technology features high output signal frequency, fast response, low pressure loss, corrosion resistance, and a wide operating pressure range, enabling high-precision and fast-response flow measurement.

[0003] To achieve high-precision and fast-response flow measurement, engineers proposed a thermal gas flow sensor based on SAW technology. Using MEMS technology, a sensor was designed that eliminates the need for a heater structure and flow test channel. While the SAW-based thermal gas flow sensor offers advantages such as low cost and high sensitivity, it suffers from drawbacks including complex structural design and insufficient accuracy.

[0004] This section is intended to provide background or context for the embodiments of the invention set forth in the claims. The description herein is not an admission that it is prior art simply because it is included in this section. Summary of the Invention

[0005] To address the problems in the prior art, this application provides a thermal gas flow sensor, flow measurement method, and system that can quickly and accurately measure gas flow rate at low gas flow rates using a high-performance surface acoustic wave resonator as the measuring element.

[0006] To solve the above-mentioned technical problems, this application provides the following technical solution:

[0007] In a first aspect, this application provides a thermal gas flow sensor, comprising: a gas passage straight pipe, a heating element, a heat insulation element, and a surface acoustic wave resonator;

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

[0009] The heat insulation element is attached to the lower outer wall of the gas passage straight pipe and includes a heat insulation shell and two pieces of heat insulation material; the heat insulation material is wrapped inside the heat insulation shell;

[0010] The heating element is attached to the lower outer wall of the gas passage straight pipe and is held between two pieces of insulation material;

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

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

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

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

[0015] Furthermore, the thickness of the piezoelectric thin 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 gas passage straight tube is circular in shape; the material of the gas passage straight tube is stainless steel, iron, or aluminum; the specification of the gas passage straight tube is capillary; the inner diameter of the capillary is 0.1 mm to 1 mm, and the outer diameter is 0.1 mm to 1 mm.

[0017] Furthermore, the heating element includes a heater and a temperature sensor; the heater is disposed below the outer wall of the straight gas passage pipe; the temperature sensor is disposed 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 pipe of the gas passage is 2mm to 12mm.

[0019] Furthermore, the temperature at the heat source of the heater is controlled between 80°C and 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 and downstream surface acoustic wave resonators are symmetrically distributed with respect to the heater.

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

[0023] Secondly, this application provides a thermal gas flow measurement system, comprising:

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

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

[0026] A heating controller is used to control the heating of the thermal gas flow sensor;

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

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

[0029] The gas to be tested 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 rate based on the resonant frequency.

[0030] Thirdly, this application provides a thermal gas flow rate measurement method, applied to the aforementioned thermal gas flow rate measurement system, comprising:

[0031] A heating controller is used to control the heating of the thermal gas flow sensor so that the thermal gas flow sensor is heated and stabilized at a preset temperature value.

[0032] A mass flow controller is used to control the gas source to output room temperature gas at 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] Using the network analyzer, the difference between the upstream and downstream resonant frequencies is quantitatively analyzed using partial least squares regression, and a linear regression curve between the set flow rate and the difference between the upstream and downstream resonant frequencies is established.

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

[0035] To address the problems in existing technologies, this application provides a thermal gas flow sensor, flow measurement method, and system that utilizes a high-performance surface acoustic wave (SAW) resonator as the measuring element to construct a gas flow measurement structure based on SAW technology. This approach revolutionizes traditional measurement methods by addressing key temperature measurement techniques and the overall gas flow measurement structure, offering advantages such as high sensitivity, simple structural design, and high measurement accuracy. Furthermore, the low cost of mass-produced SAW gas flow sensors allows for direct reading and measurement in subsequent circuitry, thus filling a gap in the application of SAW technology for gas flow measurement. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. 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.

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

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

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

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

[0041] Figure 5 This is a flowchart of the gas flow measurement method in an embodiment of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Here, the illustrative 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 enable rapid and accurate measurement of gas flow rate at low gas flow rates using a high-performance surface acoustic wave resonator as the measuring element, this application provides a thermal gas flow sensor, including: a gas passage straight pipe, a heating element, a heat insulation element, and a surface acoustic wave resonator.

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

[0045] The insulation element is applied to the lower outer wall of the straight pipe in the gas passage, and includes an insulation shell and two pieces of insulation material; the insulation material is wrapped inside the insulation shell;

[0046] The heating element is attached to the lower outer wall of the straight gas passage pipe and is held between two pieces of insulation material;

[0047] Two surface acoustic wave resonators are attached to the outer wall of the gas passage straight pipe to sense the frequency changes of the measured gas upstream and downstream as it travels through the gas passage straight pipe, so as to detect the changes in gas flow rate in the gas passage straight pipe.

[0048] Understandably, see Figure 2 This invention provides a thermal gas flow sensor based on surface acoustic wave (SAW), comprising: a gas passage straight pipe 1, a heater 2, a temperature sensor 3, an insulating shell 4, insulating material 5, an upstream SAW resonator 6, and a downstream SAW resonator 7. The gas passage straight pipe 1 is used to transmit the gas to be measured (also called the gas to be tested), with an inlet on the left and an outlet on the right. The gas passage straight pipe is made of stainless steel. The inner diameter of the gas passage straight pipe must satisfy the constraint that the gas flow is laminar. The heating element includes the heater 2 and the temperature sensor 3, located below the gas passage straight pipe and between the upstream SAW resonator 6 and the downstream SAW resonator 7. The heater operates under constant temperature heating, controlled by an external controller, with the temperature controlled between 100-150℃. The insulating element includes the insulating shell 4 and the internal insulating material 5, thereby reducing heat transfer from the heating element to non-heat source locations and ensuring measurement accuracy. The upstream SAW resonator 6 and the downstream SAW resonator 7 are located on the outer wall of the straight pipe of the gas passage, respectively, and are used to sense the frequency change of the gas flowing through the upstream and downstream, thereby sensing the temperature change of the upstream and downstream, and thus detecting the change of gas flow in the gas pipeline.

[0049] The surface acoustic wave (SAW) resonator comprises a supporting substrate, a piezoelectric thin film layer, and an electrode layer. The supporting substrate is made of silicon or sapphire; the piezoelectric thin film layer is made of lithium niobate, gallium nitride, or aluminum nitride; and the electrode layer is made of aluminum, gold, platinum, or nickel. The electrode layer includes interdigital transducers and symmetrically arranged reflective gratings on both sides of the interdigital transducers. The thickness of the piezoelectric thin film layer is 0.1 μm to 5 μm; the thickness of the interdigital transducer electrodes is 80 nm to 200 nm. The gas passage straight tube is cylindrical; the gas passage straight tube is made of stainless steel, iron, or aluminum; the gas passage straight tube is capillary-shaped; the inner diameter of the capillary is 0.1 mm to 1 mm, and the outer diameter is 0.1 mm to 1 mm. The heating element includes a heater and a temperature sensor; the heater is located below the outer wall of the gas passage straight tube; the temperature sensor is located to 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 2 mm to 12 mm. The temperature at the heater's heat source is controlled between 80℃ and 150℃; the heating method is constant power heating or constant temperature heating. The surface acoustic wave (SAW) resonator includes an upstream SAW resonator and a downstream SAW resonator. The upstream and downstream SAW resonators are symmetrically distributed around the heater. Both the upstream and downstream SAW resonators are located 1mm to 8mm from the center point of the heater.

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

[0051] The period of the metal IDT electrode 10 can be determined by the wavelength λ. The IDT electrode 10 includes upper and lower electrodes and a busbar, thus forming a transmission channel for surface acoustic waves. The width of the metal IDT finger bar is in the range of 0.3-1 μm, and the number of upper and lower interdigitated electrode pairs is 150-250 pairs. The metal IDT electrode 10 mainly includes an adhesion layer and a metal electrode layer. The adhesion layer uses metals such as Ti and Cr, and the metal electrode uses metals such as Au, Al, and Pt. The thickness of the adhesion layer is 5-10 nm, and the thickness of the metal electrode is 100-150 nm; both need to be kept within a reasonable range. Preferably, the adhesion layer is 10 nm thick, and the metal layer is 100 nm thick.

[0052] A reflective grating with the same shape as the IDT electrode 10 is also disposed on the piezoelectric substrate. The reflective grating can be in a short-circuit or open-circuit state and is symmetrically distributed on both sides of the IDT to form an elastic wave resonator. The above-mentioned reflective grating is the same as the IDT electrode in terms of fabrication process and parameters, and the number of reflective grating pairs is in the range of 50-200 pairs.

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

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

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

[0056] A heating controller is used to control the heating of the thermal gas flow sensor;

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

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

[0059] The gas to be tested 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 rate based on the resonant frequency.

[0060] Understandably, based on the above, see [link / reference] Figure 3 This application embodiment constructs a gas flow measurement system based on SAW (Self-Driving Flow) technology. In this embodiment, a nitrogen cylinder 13 is used as the gas source, and the required nitrogen output is controlled by valves 14 (multiple valves are possible). Subsequently, a mass flow controller 15 (MFC) is used, and a laptop computer 17 is used to read and control the gas flow through the host computer software built into the mass flow controller 15. After the nitrogen in the nitrogen cylinder 13 enters the mass flow controller 15, it is connected to the upstream side (inlet) of the gas path channel of the thermal gas flow sensor provided in this application. The outlet of the gas path channel is connected to a flexible hose to directly discharge the gas into the fume hood. The two ends of the interdigital transducers of the upstream SAW resonator 6 and the downstream SAW resonator 7 are connected to the two ports of the network vector analyzer 19 through a PCB, leads, and coaxial cable 16, respectively. Then, the heating controller 18 is turned on to heat to the specified temperature and maintain a stable temperature. Finally, the S-parameters of the two port SAW resonators are observed using the vector network analyzer 19, and the correspondence between the resonant frequency and 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 no nitrogen flows through, the temperature of the gas passage straight pipe 1 rises because heater 2 is attached to the bottom of the gas passage straight pipe 1. At this time, since the gas flow test structure is symmetrical about the heat source, the temperature distribution on the outer wall of the gas passage straight pipe is symmetrical from left to right, with the highest temperature at the center of the heat source. The heating method of the heat source is controlled by feedback from temperature sensor 3 and external heating controller 18 to maintain a constant temperature. When the valve is opened to allow gas to flow, the room temperature gas absorbs heat from the upstream pipe wall, causing its temperature to rise. The upstream pipe also cools down as heat is carried away. When the gas flows through the heat source to the downstream pipe, the downstream pipe wall cools up due to the heat from the gas. At this time, the upstream high-performance SAW resonator 6 and the downstream high-performance SAW resonator 7 sense the temperature change, and their resonant frequencies also change. Because the SAW resonator has a negative temperature coefficient, when gas is introduced, the upstream SAW resonant frequency increases due to the decrease in temperature, while the downstream SAW resonant frequency decreases due to the initial increase followed by a decrease in temperature, eventually stabilizing. Because SAW resonators have high frequencies and fast responses, they are also beneficial for achieving high-precision and rapid detection of low-flow-rate gases.

[0062] In one embodiment, see Figure 5 This application provides a thermal gas flow rate measurement method, applied to the aforementioned thermal gas flow rate measurement system, comprising:

[0063] S101: The heating controller is used to control the heating of the thermal gas flow sensor so that the thermal gas flow sensor is heated and stabilized at a preset temperature value.

[0064] S102: The mass flow controller controls the gas source to output room temperature gas to be tested at different set flow rates, and the network analyzer records the resonant frequencies of the upstream and downstream surface acoustic wave resonators in the thermal gas flow sensor at different set flow rates.

[0065] S103: Using the network analyzer, the difference between the upstream and downstream resonant frequencies is quantitatively analyzed using the partial least squares regression method, and a linear regression curve between the set flow rate and the difference between the upstream and downstream resonant frequencies is established.

[0066] S104: The mass flow controller is used to control the gas source to output a room temperature gas of unknown flow rate, and the linear regression curve is used to determine the flow rate of the room temperature gas of unknown flow rate.

[0067] It is 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 which a linear regression equation can be obtained); the second stage is to measure the flow rate of the gas to be measured.

[0068] The specific steps include:

[0069] S1: Build a SAW-based gas flow measurement system, including: nitrogen cylinder 13, mass flow controller 15, laptop computer 17 (capable of running host computer software), heating controller 18, thermal gas flow sensor 12, coaxial cable 16, vector network analyzer 19, and some necessary hoses and other accessories. The mass flow controller 15 is selected with a flow detection range of 0-300 sccm.

[0070] The measurement system described above (S2) can be placed in a laboratory environment. Power on all equipment, calibrate the vector network analyzer 19, connect the laptop 17 to the mass flow controller 15, and perform a zeroing operation. 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 in the nitrogen cylinder 13 is controlled by a valve within the working pressure specified by the mass flow controller 15.

[0071] After the temperature displayed by the heating controller 18 (S3) stabilizes at 120℃, test data is recorded, with the initial data being 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 via a network.

[0072] S4, controlled by host computer software 17, outputs room-temperature nitrogen gas at set flow rates of 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, and 70 sccm. A network vector analyzer 19 sequentially records the resonant frequencies of the upstream and downstream SAW resonators at each gas flow rate. After preprocessing the collected upstream and downstream resonant frequency data (e.g., removing bad data), partial least squares regression is used to quantitatively analyze the difference between the upstream and downstream resonant frequencies under different set gas flow rates, establishing a linear regression curve between gas flow rate and frequency difference (which can correspond to temperature difference). The relationship between the frequency difference and temperature difference can be converted using p = 57.9 kHz / ℃, where p represents the change in SAW device resonant frequency of 57.9 kHz per unit degree Celsius.

[0073] In one embodiment, the experimental results of step S4 are shown below. Figure 4 As shown. The final linear regression equation for the temperature difference within the range of 0-10 sccm is: y = -20.543x - 45.806, with a correlation coefficient R². 2= 99.7%, where y is the difference between the downstream resonant frequency and the upstream resonant frequency (referred to as frequency difference), in kHz, and x is the gas flow rate, in SCCM. This equation was generated in the first stage mentioned above. In the actual measurement of gas flow rate (the second stage mentioned above), y and x in the above formula need to be reversed, i.e., x is the vertical axis and y is the horizontal axis. Therefore, the formula used for measurement is s = -0.0486f - 2.2178, where s is the actual gas flow rate value, and f is the difference between the downstream resonant frequency and the upstream resonant frequency (referred to as frequency difference). For example, when the difference between the downstream resonant frequency and the upstream resonant frequency is -70kHz, substituting into the formula (f = -70) yields a flow rate of 1.18SCCM. Multiple experiments show that the gas flow sensor provided in this application has good linearity in the range of 0-10sccm, thus verifying the accuracy and effectiveness of the measurement method provided in this application.

[0074] It should be noted that steps S1-S4 above can be understood as the first stage of calibrating the "thermal gas flow sensor" provided in this application. Next, a second stage can be performed: using a mass flow controller to control the gas source to output a room-temperature gas of unknown flow rate, and using the linear regression curve obtained above to determine the flow rate of the room-temperature gas of unknown flow rate. Specifically, the linear regression equation has been established; therefore, after measuring the resonant frequencies of the upstream and downstream surface acoustic wave resonators using the thermal gas flow sensor, the gas flow rate can be mapped to it.

[0075] As described above, the thermal gas flow sensor, flow measurement method, and system provided in this application can construct a gas flow measurement structure based on surface acoustic wave (SAW) technology by using a high-performance surface acoustic wave resonator as the measuring element. This approach revolutionizes traditional measurement methods by addressing key temperature measurement techniques and the overall gas flow measurement structure, offering advantages such as high sensitivity, simple structural design, and high measurement accuracy. Since the cost of mass-produced SAW gas flow sensors is relatively low, and subsequent circuitry allows for direct reading and measurement, this application fills a gap in the application of SAW technology for gas flow measurement.

[0076] Because this surface acoustic wave device has a good temperature-frequency coefficient, a high resonant frequency, and a high Q value, it improves the sensor's sensitivity and response speed, enabling the sensor to quickly and accurately measure various gases even at low gas flow rates. At room temperature, the detection limit can reach below 5 SCCM, and it exhibits good linearity in the 0-10 SCCM range, with a response time of approximately 1-3 seconds.

[0077] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the embodiments of the device implementation method are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0078] The foregoing has described specific embodiments of this specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than that shown in the embodiments and may still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require the specific or sequential order shown to achieve the desired result. In some embodiments, multitasking and parallel processing are possible or may be advantageous.

[0079] While the embodiments in this specification provide the method operation steps as described in the embodiments or flowcharts, more or fewer operation steps may be included based on conventional or non-inventive means. The order of steps listed in the embodiments is merely one possible order of execution among many steps and does not represent the only possible order of execution. The terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, product, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, product, or apparatus. Without further limitations, the presence of other identical or equivalent elements in a process, method, product, or apparatus that includes said elements is not excluded.

[0080] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, system embodiments are basically similar to method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. In the description of this specification, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the embodiments in this specification. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0081] The above description is merely an embodiment of the present specification and is not intended to limit the embodiments of the present specification. For those skilled in the art, various modifications and variations can be made to the embodiments of the present specification. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the embodiments of the present specification should be included within the scope of the claims of the embodiments of the present specification.

Claims

1. A thermal gas flow sensor, characterized by include: Gas passage straight pipe, heating element, heat insulation element and surface acoustic wave resonator; The gas passage straight pipe is used to transport the gas to be measured; the diameter of the gas passage straight pipe must meet the constraint condition that the gas flow state is laminar; the shape of the gas passage straight pipe is a circular pipe; the material of the gas passage straight pipe is stainless steel, iron or aluminum; the specification of the gas passage straight pipe is a capillary tube; the inner diameter of the capillary tube is 0.1 mm to 1 mm, and the outer diameter is 0.1 mm to 1 mm. The heat insulation element is attached to the lower outer wall of the gas passage straight pipe and includes a heat insulation shell and two pieces of heat insulation material; the heat insulation material is wrapped inside the heat insulation shell; The heating element is attached to the lower outer wall of the gas passage straight pipe and is held between two pieces of insulation material; The surface acoustic wave resonator is attached to the outer wall of the gas passage straight pipe to sense the frequency change of the gas being measured as it travels through the gas passage straight pipe, so as to detect the change in gas flow rate in the gas passage straight pipe. The thermal gas flow sensor is a surface acoustic wave-based thermal gas flow sensor that can quickly and accurately measure the gas flow rate at low gas flow rates using a high-performance surface acoustic wave resonator as the measuring element; the surface acoustic wave resonator is a surface acoustic wave single-port resonator. The width of the contact surface between the heat source of the heater and the straight pipe of the gas passage is 2 mm to 12 mm. The surface acoustic wave resonator includes an upstream surface acoustic wave resonator and a downstream surface acoustic wave resonator; Both the upstream and downstream surface acoustic resonators are located 1 mm to 8 mm from the center point of the heater.

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

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

4. The thermal gas flow sensor according to claim 2, characterized in that, The electrode layer includes interdigital transducers and reflective grids symmetrically arranged on both sides of the interdigital transducers.

5. The thermal gas flow sensor according to claim 4, characterized in that, The thickness of the piezoelectric thin 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 heating element includes a heater and a temperature sensor; the heater is located below the outer wall of the straight gas passage pipe; the temperature sensor is located on the side of the outer wall of the heater.

7. The thermal gas flow sensor according to claim 6, characterized in that, The temperature at the heater heat source is controlled between 80℃ and 150℃; the heating method is constant power heating or constant temperature heating.

8. The thermal gas flow sensor according to claim 1, characterized in that, The upstream and downstream surface acoustic resonators are symmetrically distributed with respect to the heater.

9. 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 as described in any one of claims 1 to 8 is used to sense the resonant frequency of the gas to be measured flowing through it; A heating controller is used to control the heating of the thermal gas flow sensor; A mass flow controller that is connected to the gas source and the thermal gas flow sensor respectively; And a network vector analyzer electrically connected to the thermal gas flow sensor; The gas to be tested 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 rate based on the resonant frequency.

10. A method for measuring the flow rate of a thermal gas, applied to the thermal gas flow rate measurement system of claim 9, characterized in that, include: A heating controller is used to control the heating of the thermal gas flow sensor so that the thermal gas flow sensor is heated and stabilized at a preset temperature value. A mass flow controller is used to control the gas source to output room temperature gas at 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. Using the network analyzer, the difference between the upstream and downstream resonant frequencies is quantitatively analyzed using partial least squares regression, and a linear regression curve between the set flow rate and the difference between the upstream and downstream resonant frequencies is established. The mass flow controller is used to control the gas source to output a room temperature gas of unknown flow rate, and the linear regression curve is used to determine the flow rate of the room temperature gas of unknown flow rate.

Images