Airflow switching device and airflow detection method

Abstract

The invention provides an airflow switching device and an airflow detection method, an MEMS chip is integrated in a packaging body, when airflow flows through a piezoelectric film in the MEMS chip, vibration of the film is caused, and an initial electric signal is generated based on the direct piezoelectric effect of the piezoelectric film. And the signal processing circuit is electrically connected with the MEMS chip, processes the initial electric signal and outputs a switch control signal. Since the piezoelectric film converts vibration generated under the action of the airflow into the initial electric signal without external power supply, and the initial electric signal is essentially extremely weak electric energy, the operation power consumption of the airflow switching device is greatly reduced. And no movable mechanical structure is arranged in the airflow switching device, so that the impact resistance and the vibration resistance of the airflow switching device are improved, and the reliability of the device is further improved.

Description

Technical Field

[0001] This invention relates to the technical field of airflow detection, and more particularly to an airflow switching device and an airflow detection method. Background Technology

[0002] An airflow switch is a device used to detect the state of gas flow (flowing / stationary) and convert it into an electrical switching signal. Traditional airflow switches are mainly based on mechanical (such as baffle type), thermal (using thermistor temperature difference), or differential pressure principles. These traditional technologies have some inherent drawbacks: (1) Mechanical airflow switches have moving parts, are prone to wear, have a short lifespan, slow response speed, and are not sensitive to small airflows; (2) Thermal airflow switches require heating elements, consume more power, and are easily affected by ambient temperature, which may cause drift. (3) Differential pressure airflow switches usually require two pressure taps, have a complex structure, and are inconvenient to install. Summary of the Invention

[0003] To solve the above-mentioned technical problems, the present invention provides an airflow switching device and an airflow detection method, so as to realize an airflow switch with simple structure, high sensitivity, fast response, extremely low power consumption and high reliability.

[0004] According to a first aspect of the present invention, an airflow switching device is provided, comprising: The MEMS chip includes a substrate and a piezoelectric thin film on the substrate. The substrate has an opening structure that penetrates the substrate. There is a cavity between the substrate and the piezoelectric thin film. The cavity and the opening structure are connected. The piezoelectric thin film is used to convert mechanical vibrations generated by airflow into an initial electrical signal. The package includes an airflow channel, the MEMS chip is located within the airflow channel, and external airflow flows through the MEMS chip via the airflow channel. A signal processing circuit is electrically connected to the MEMS chip. The signal processing circuit is used to output a digital switch control signal based on the initial electrical signal. The digital switch control signal indicates whether there is airflow through the MEMS chip.

[0005] Optionally, the MEMS chip further includes: A support layer is located between the substrate and the piezoelectric film to support the piezoelectric film and create the cavity between the substrate and the piezoelectric film.

[0006] Optionally, one end of the piezoelectric film is fixed to the surface of the support layer, and the other end of the piezoelectric film is suspended; or One end of the piezoelectric film is fixed to the surface of the support layer located on one side of the cavity, and the other end of the piezoelectric film is fixed to the surface of the support layer located on the other side of the cavity.

[0007] Optionally, the MEMS chip further includes a bottom electrode and a top electrode, wherein the bottom electrode is located on the surface of the substrate and in contact with the substrate, and the top electrode is located on the surface of the piezoelectric thin film and in contact with the piezoelectric thin film.

[0008] Optionally, the package further includes an airflow guiding structure located within the airflow channel and at the air inlet end of the airflow channel. The airflow guiding structure is used to convert external airflow into vortex airflow and guide it to the opening structure of the substrate in the MEMS chip.

[0009] Optionally, the package further includes: a guide vane located at the outlet end within the airflow channel, the guide vane being used to guide the vortex airflow to the outside of the airflow channel.

[0010] Optionally, the signal processing circuit includes a preamplifier, a bandpass filter, a rectifier, a low-pass filter, and a threshold comparator; The preamplifier is used to initially amplify the initial electrical signal and output an amplified signal; The bandpass filter filters the amplified signal and outputs a filtered signal; The rectifier converts the filtered signal into a pulse signal; The low-pass filter smooths the pulse signal and outputs a DC voltage signal. The threshold comparator compares the DC voltage signal with the threshold voltage and outputs the digital switch control signal based on the comparison result.

[0011] Optionally, the threshold comparator compares the DC voltage signal with a first threshold voltage and a second threshold voltage, respectively; If the DC voltage signal is greater than the first threshold voltage, the threshold comparator outputs a high-level digital switch control signal; If the DC voltage signal is less than the second threshold voltage, the threshold comparator outputs a low-level digital switch control signal, and the first threshold voltage is greater than the second threshold voltage.

[0012] Optionally, the material of the piezoelectric film includes at least lead zirconate titanate, potassium sodium niobate, sodium bismuth titanate, or polyvinylidene fluoride and its copolymers.

[0013] According to a second aspect of the present invention, an airflow detection method is provided, wherein the airflow switching device provided in the first aspect of the present invention is fixed in the area to be detected, and the airflow to be measured flows through the airflow channel through the MEMS chip; The MEMS chip outputs an initial electrical signal based on the flowing airflow; The signal processing circuit outputs a digital switch control signal based on the initial electrical signal, in order to determine whether there is airflow in the area to be detected.

[0014] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: In the airflow switching device provided by this invention, a package fixes and protects the MEMS chip and guides external airflow to the MEMS chip. Since a cavity is formed between the piezoelectric thin film located on the substrate of the MEMS chip and the substrate, and this cavity is released by an opening structure penetrating the substrate, when external airflow flows through the opening structure past the piezoelectric thin film, the piezoelectric thin film vibrates under the action of the airflow and generates an initial electrical signal due to the positive piezoelectric effect. Since the signal processing circuit is electrically connected to the MEMS chip, the signal processing circuit can process the initial electrical signal and output a switching control signal.

[0015] Because piezoelectric films can rapidly convert weak mechanical vibrations into electrical signals based on the piezoelectric effect, they achieve a fast response sensitive to low-speed airflow. Furthermore, since piezoelectric films can convert vibrations generated by airflow into initial electrical signals without external power supply, and these initial signals are essentially extremely weak electrical energy, the operating power consumption of the airflow switching device is significantly reduced. Additionally, because the airflow switching device contains no moving mechanical structures, its shock and vibration resistance is improved, thereby enhancing its reliability.

[0016] In summary, the airflow switching device provided by this invention achieves a fast response to low-speed airflow, greatly reduces operating power consumption, and features a simple structure and high reliability. Attached Figure Description

[0017] 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.

[0018] Figure 1 A schematic diagram of the module structure of the airflow switching device provided for an embodiment of the present invention; Figure 2A schematic cross-sectional structure of a MEMS chip provided for an embodiment of the present invention. Figure 1 ; Figure 3 A schematic cross-sectional structure of a MEMS chip provided for an embodiment of the present invention. Figure 2 ; Figure 4 This is a schematic diagram of the module structure of a signal processing circuit provided in an embodiment of the present invention.

[0019] 10-MEMS chip; 11-Substrate; 12-Piezoelectric thin film; 13-Cavity; 14-Open structure; 15 - Support layer; 16-Top electrode; 17- Bottom electrode; 20-Package; 21-Airflow channel; 22-Airflow guiding structure; 23-Guide vanes; 30 - Signal processing circuit; 31 - Preamplifier; 32-Bandpass filter; 33-Rectifier; 34-Low-pass filter; 35-Threshold comparator; v1 - Initial electrical signal; v2 - Digital switch control signal. Detailed Implementation

[0020] As described in the background section, these traditional technologies have some inherent drawbacks: (1) Mechanical airflow switches have moving parts, are prone to wear, have a short lifespan, slow response speed, and are not sensitive to small airflows; (2) Thermal airflow switches require heating elements, consume more power, and are easily affected by ambient temperature, which may cause drift. (3) Differential pressure airflow switches usually require two pressure taps, have a complex structure, and are inconvenient to install.

[0021] In view of this, the present invention provides a novel airflow switching device that integrates a MEMS chip within a package. When airflow passes through a piezoelectric thin film in the MEMS chip, it causes the film to vibrate, generating an initial electrical signal based on the positive piezoelectric effect of the thin film. A signal processing circuit electrically connected to the MEMS chip processes the initial electrical signal and outputs a switching control signal.

[0022] Because the piezoelectric film converts the vibrations generated by the airflow into an initial electrical signal without the need for external power supply, and because the initial electrical signal is essentially a very weak electrical energy, the operating power consumption of the airflow switching device is greatly reduced. Furthermore, since the airflow switching device has no moving mechanical structure, its shock and vibration resistance is improved, thereby enhancing the device's reliability.

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0025] The technical solution of the present invention will be described in detail below with reference to specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0026] Please refer to Figure 1 The airflow switching device provided in this embodiment may include a MEMS chip 10, a package 20, and a signal processing circuit 30.

[0027] Since the airflow switch device provided in this embodiment has no moving mechanical structure, its shock resistance and vibration resistance can be improved, thereby improving the reliability of the device.

[0028] Please refer to Figure 2 The MEMS chip 10 may include a substrate 11 and a piezoelectric thin film 12 located on the substrate 11.

[0029] In this embodiment, the substrate 11 has an opening structure 14 that penetrates the substrate 11, and there is a cavity 13 between the substrate 11 and the piezoelectric film 12. The cavity 13 and the opening structure 14 are connected, and the piezoelectric film 12 converts the mechanical vibration generated by the airflow into an initial electrical signal v1.

[0030] Specifically, the substrate 11 can be made of silicon.

[0031] Specifically, the material of the piezoelectric film 12 includes at least lead zirconate titanate, potassium sodium niobate, sodium bismuth titanate, or polyvinylidene fluoride and its copolymers. Of course, the piezoelectric film 12 can also be made of other materials with high piezoelectric coefficients, which are not limited here.

[0032] Please continue to refer to this. Figure 2 In this embodiment, the MEMS chip 10 may further include a support layer 15, which is located between the substrate 11 and the piezoelectric film 12 to support the piezoelectric film 12 and create the cavity 13 between the substrate 11 and the piezoelectric film 12.

[0033] In one embodiment, one end of the piezoelectric film 12 is fixed to the surface of the support layer 15, and the other end of the piezoelectric film 12 is suspended to form a cantilever beam structure.

[0034] Please refer to Figure 3 Of course, in other embodiments, one end of the piezoelectric film 12 is fixed to the surface of the support layer 15 located on one side of the cavity 13, and the other end of the piezoelectric film 12 is fixed to the surface of the support layer 15 located on the other side of the cavity 13. The piezoelectric film 12 has through holes to form a bridge structure. Compared with a cantilever beam structure, the bridge structure has a higher resonant frequency and higher mechanical strength.

[0035] Specifically, the material of the support layer 15 may include silicon nitride or other materials with high mechanical strength, such as silicon carbide, aluminum oxide or titanium alloy, etc., without limitation.

[0036] Please continue to refer to this. Figure 2 In this embodiment, the MEMS chip 10 may further include a bottom electrode 17 and a top electrode 16. The bottom electrode 17 is located on the surface of the substrate 11, and the top electrode 16 is located on the surface of the piezoelectric film 12. The bottom electrode 17 and the top electrode 16 are used to output the initial electrical signal v1 to the outside.

[0037] Specifically, the material of the bottom electrode 17 may include a Pt / Ti composite electrode, which is based on titanium and has a platinum layer deposited on its surface by electroplating or sputtering.

[0038] Specifically, the material of the top electrode 16 may include iridium dioxide.

[0039] The following is Figure 2 Taking the structure of the MEMS chip 10 shown as an example, the working principle of the MEMS chip 10 will be explained: When external airflow flows through the opening structure 14 of the substrate 11 and passes through the piezoelectric film 12, it causes the piezoelectric film 12 to vibrate periodically. According to the positive piezoelectric effect of the piezoelectric film 12, the piezoelectric film 12 converts the energy of the mechanical vibration caused by the airflow into a corresponding initial electrical signal v1. The initial electrical signal v1 is essentially a sinusoidal AC voltage signal, and the amplitude of the initial electrical signal v1 is proportional to the intensity of the airflow. Therefore, the stronger the airflow, the stronger the amplitude of the initial electrical signal v1.

[0040] Since this embodiment selects a material with a high piezoelectric coefficient as the piezoelectric film 12, it can efficiently convert weak mechanical vibrations into an initial electrical signal v1, thereby improving the sensitivity and response speed of low-speed airflow detection.

[0041] Meanwhile, since the piezoelectric film 12 converts mechanical vibration into an initial electrical signal v1 without external power supply, passive airflow detection is achieved, reducing the device's operating power consumption. Furthermore, because the initial electrical signal v1 is very weak, the power consumption of subsequent circuits processing the initial electrical signal v1 is greatly reduced, further lowering the device's operating power consumption.

[0042] Please continue to refer to this. Figure 1 The package 20 may include an airflow channel 21, the MEMS chip is located in the airflow channel 21, and external airflow flows through the airflow channel 21 and through the MEMS chip 10.

[0043] Please continue to refer to this. Figure 1 and Figure 2 The package 20 is further provided with an airflow guiding structure 22, which is located inside the airflow channel 21 and at the air inlet end of the airflow channel 21. The airflow guiding structure 22 is used to convert the external airflow into a vortex airflow and guide it to the opening structure 14 of the substrate 11 in the MEMS chip 10.

[0044] In this embodiment, the airflow guiding structure 22 is specifically used to optimize the flow state of the external airflow to convert the external airflow into vortices, thereby maximizing the vibration of the piezoelectric film 12.

[0045] Please continue to refer to this. Figure 1 and Figure 2The encapsulation body 20 is also provided with a guide vane 23, which is located at the air outlet end in the airflow channel 21. The guide vane 23 is used to guide the vortex airflow to the outside of the airflow channel 21.

[0046] As mentioned above, since the signal strength of the initial electrical signal v1 is very weak compared to that of a conventional circuit, and the initial electrical signal v1 may also contain noise, the subsequent signal processing circuit 30 is required to process the initial electrical signal v1 for airflow detection.

[0047] Please continue to refer to this. Figure 1 The signal processing circuit 30 is electrically connected to the MEMS chip 10. The signal processing circuit 30 receives an initial electrical signal v1, processes the initial electrical signal v1, and outputs a digital switch control signal v2. The digital switch control signal v2 indicates whether airflow passes through the MEMS chip 10.

[0048] Please refer to Figure 4 In this embodiment, the signal processing circuit 30 may include a preamplifier 31, a bandpass filter 32, a rectifier 33, a low-pass filter 34, and a threshold comparator 35.

[0049] Specifically, the preamplifier 31 amplifies the initial electrical signal v1 and outputs an amplified signal.

[0050] As mentioned above, the initial electrical signal v1 is extremely weak, typically in the millivolt range. The MEMS chip 10 itself can be equivalent to a voltage source connected in parallel with an inter-electrode capacitor and in series with a leakage resistor. Due to the extremely high insulation properties of the piezoelectric film 12, the leakage resistor value is typically as high as 10 ohms. 6 Ω~10 12 Ω. Since the capacitance between electrodes is typically in the picofarad range, according to the formula for calculating the source impedance of MEMS chip 10, the source impedance of MEMS chip 10 is very high, specifically in the range of 10Ω. 6 Ω~10 9 Ω.

[0051] Based on the extremely high source impedance of the MEMS chip 10, the input terminal of the preamplifier 31 is set with a very high input impedance. This not only reduces the signal loss of the initial electrical signal v1 and ensures the complete transmission of the signal, but also forms impedance matching with the source impedance of the MEMS chip 10, adapting to subsequent processing circuits. At the same time, since the initial electrical signal v1 is very weak and easily affected by electromagnetic interference and circuit thermal noise, the high input impedance of the preamplifier 31 can improve the signal-to-noise ratio and enhance signal recognition.

[0052] Specifically, the bandpass filter 32 filters the amplified signal and outputs a filtered signal. Furthermore, the bandpass filter 32 filters out extremely low-frequency components caused by temperature changes or circuit drift, as well as high-frequency electromagnetic interference and noise, to maximize the signal-to-noise ratio.

[0053] Specifically, the rectifier 33 converts the AC filtered signal into a unidirectional pulse signal to improve the operating efficiency of the subsequent circuit.

[0054] Specifically, the low-pass filter 34 smooths the pulse signal and outputs a DC voltage signal. The amplitude of the DC voltage characterizes the vibration intensity of the piezoelectric film 12 caused by the airflow.

[0055] Specifically, the threshold comparator 35 compares the DC voltage signal with the threshold voltage and outputs the digital switch control signal v2 based on the comparison result.

[0056] Furthermore, the threshold comparator 35 compares the DC voltage signal with a first threshold voltage and a second threshold voltage respectively; if the DC voltage signal is greater than the first threshold voltage, it outputs a high-level digital switch control signal v2; if the DC voltage signal is less than the second threshold voltage, it outputs a low-level digital switch control signal v2, wherein the first threshold voltage is greater than the second threshold voltage.

[0057] Since the threshold comparator 35 is equipped with two threshold voltages, and the first threshold voltage is greater than the second threshold voltage, the hysteresis characteristic of the threshold comparator 35 is used to effectively prevent the output from repeatedly changing due to small fluctuations in the signal near the threshold point, thereby ensuring the clarity and precision of the digital switch control signal v2.

[0058] In this embodiment, the threshold comparator 35 is a Schmitt trigger.

[0059] In this embodiment, the digital switch control signal v2 is output to the drive circuit to buffer and amplify its power, and the resulting drive voltage signal directly drives the subsequent load circuit, such as the MCU's I / O port, LED indicator, or relay. The drive voltage signal is a standard digital level, i.e., 0V or 3.3V.

[0060] After being processed sequentially by the various functional devices in the signal processing circuit 30, the initial electrical signal v1 is converted into a clean digital switching signal, which is very suitable for reading and judging by the subsequent load circuit and for driving the subsequent load circuit.

[0061] This embodiment also provides an airflow detection method, which may include: fixing the airflow switch device provided in this embodiment in the area to be detected, and allowing the airflow to be measured to flow through the airflow channel through the MEMS chip 10.

[0062] The MEMS chip 10 outputs an initial electrical signal v1 based on the airflow passing through it.

[0063] In this embodiment, the signal processing circuit 30 outputs a digital switch control signal v2 based on the initial electrical signal v1, so as to determine whether there is airflow in the area to be detected based on the digital switch control signal v2.

[0064] In summary, the airflow switching device provided in this embodiment achieves a fast response to low-speed airflow, greatly reduces operating power consumption, and features a simple structure and high reliability.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An air flow switching device, characterized by The application relates to a MEMS chip, a package and a signal processing circuit. The MEMS chip comprises a substrate and a piezoelectric film on the substrate, the substrate has an opening structure penetrating the substrate, a cavity is formed between the substrate and the piezoelectric film, the cavity is communicated with the opening structure, and the piezoelectric film is used for converting mechanical vibration caused by airflow into an initial electric signal. The package comprises an airflow channel, the MEMS chip is located in the airflow channel, and external airflow flows through the MEMS chip through the airflow channel. The signal processing circuit is electrically connected with the MEMS chip, is used for outputting a digital switch control signal based on the initial electric signal, and the digital switch control signal represents whether airflow flows through the MEMS chip.

2. The airflow switching device of claim 1, wherein, The MEMS chip further comprises a support layer between the substrate and the piezoelectric film, which is used for supporting the piezoelectric film and forming the cavity between the substrate and the piezoelectric film. One end of the piezoelectric film is fixed on the surface of the support layer, and the other end of the piezoelectric film is suspended; or 3. The airflow switching device of claim 2, wherein, One end of the piezoelectric film is fixed on the surface of the support layer on one side of the cavity, and the other end of the piezoelectric film is fixed on the surface of the support layer on the other side of the cavity. The MEMS chip further comprises a bottom electrode and a top electrode, the bottom electrode is located on the surface of the substrate and is in contact with the substrate, and the top electrode is located on the surface of the piezoelectric film and is in contact with the piezoelectric film.

4. The airflow switching device of claim 1, wherein, The package further comprises an airflow guide structure in the airflow channel and at an air inlet end of the airflow channel, which is used for converting external airflow into vortex airflow and guiding the vortex airflow to the opening structure of the substrate in the MEMS chip. The package further comprises a flow guide vane at an air outlet end of the airflow channel, which is used for guiding the vortex airflow out of the airflow channel.

5. The airflow switching device of claim 1, wherein, The signal processing circuit comprises a preamplifier, a band-pass filter, a rectifier, a low-pass filter and a threshold comparator. The preamplifier is used for preliminarily amplifying the initial electric signal and outputting an amplified signal.

6. The airflow switching device of claim 5, wherein, The band-pass filter filters the amplified signal and outputs a filtered signal.

7. The airflow switching device of claim 1, wherein, The rectifier converts the filtered signal into a pulse signal. The low-pass filter smoothes the pulse signal and outputs a direct current voltage signal. The threshold comparator compares the direct current voltage signal with a threshold voltage and outputs the digital switch control signal according to the comparison result. The threshold comparator compares the direct current voltage signal with a first threshold voltage and a second threshold voltage respectively. If the direct current voltage signal is greater than the first threshold voltage, the threshold comparator outputs a high-level digital switch control signal. If the direct current voltage signal is less than the second threshold voltage, the threshold comparator outputs a low-level digital switch control signal, and the first threshold voltage is greater than the second threshold voltage.

8. The airflow switching device of claim 7, wherein, ​ ​ ​ 9. The airflow switching device of claim 1, wherein, The material of the piezoelectric thin film at least includes lead zirconate titanate, potassium sodium niobate, sodium bismuth titanate, or polyvinylidene fluoride and its copolymer.

10. An air flow detection method characterized by, The air flow switch device of any one of claims 1 to 9 is fixed in a region to be detected, and an air flow to be detected flows through the air flow passage of the MEMS chip; The MEMS chip outputs an initial electrical signal based on the flowing air flow; The signal processing circuit outputs a digital switch control signal based on the initial electrical signal, so as to determine whether the region to be detected has an air flow flowing therethrough based on the digital switch control signal.

Images