Surface acoustic wave thermal type gas flow velocity sensor

Abstract

The invention provides a surface acoustic wave thermal type gas flow velocity sensor, and belongs to the field of micro electro mechanical systems. The problems that a thermal MEMS sensor is large in time drift and temperature drift and is easily interfered by other physical fields are solved. The device comprises a surface acoustic wave device which is connected with a circuit board; the heating assembly is coupled with the surface acoustic wave device and provides initial temperature bias for the surface acoustic wave device; and the clamping assembly wraps the heating assembly and the surface acoustic wave device and is provided with an open part used for keeping the surface acoustic wave device in external contact with the clamping assembly, and the clamping assembly is used for keeping the heating assembly and the surface acoustic wave device in stable contact. The device is mainly used for detecting gas flow velocity.

Description

Technical Field

[0001] The invention belongs to the field of micro-electromechanical systems, and in particular relates to a surface acoustic wave thermal gas flow velocity sensor. Background Art

[0002] Gas flow rate sensors play an important role in biomedicine, meteorological environment monitoring, aerospace, industrial control systems and other fields. However, traditional flow rate sensors have shortcomings such as large size and susceptibility to ambient temperature, and their application scenarios are relatively limited. In recent years, with the development of micro-electromechanical system (MEMS) processing technology, sensors have been continuously miniaturized. MEMS thermal flow rate sensors prepared based on MEMS technology have greatly improved in performance. They have the advantages of small size, high sensitivity, fast response, and easy integration, and have been rapidly developed.

[0003] Most of the existing MEMS flow sensors are thermal MEMS flow sensors, which are mainly composed of a substrate and a hot wire / hot film thermistor, where the thermal sensitive materials are mostly metal materials such as Pt and Ni. There are two main working principles: one is the heat loss principle of the anemometer, that is, the flow rate is reflected by measuring the change in the thermal resistance of the heating element when the fluid flows through; the other is the thermal temperature difference principle of the calorimeter, that is, the fluid velocity is detected by detecting the temperature distribution around the heating resistor.

[0004] However, there are some problems with the mechanism of this type of thermal MEMS sensor: it is easily interfered by other physical fields (such as electric fields, magnetic fields, etc.); the analog signal output usually requires analog-to-digital conversion to meet subsequent processing; there is a large static drift over the measurement time, etc.

[0005] In summary, a surface acoustic wave thermal gas flow velocity sensor is proposed. Summary of the invention

[0006] In view of this, the present invention aims to propose a surface acoustic wave thermal gas flow rate sensor to solve the shortcomings of hot wire and hot film MEMS sensors that their outputs are easily interfered by other electromagnetic fields and have static drift over the measurement time.

[0007] To achieve the above object, the present invention adopts the following technical solution: a surface acoustic wave thermal gas flow rate sensor, comprising:

[0008] A surface acoustic wave device connected to a circuit board;

[0009] A heating component, coupled to the surface acoustic wave device, to provide an initial temperature bias for the surface acoustic wave device;

[0010] The clamping assembly wraps the heating assembly and the surface acoustic wave device and is provided with an opening portion for keeping the surface acoustic wave device in contact with the outside of the clamping assembly. The clamping assembly is used to keep the heating assembly and the surface acoustic wave device in stable contact.

[0011] Furthermore, the surface acoustic wave device includes interdigital electrodes, piezoelectric material, bottom electrode and substrate arranged in sequence.

[0012] Furthermore, there are two interdigital electrodes.

[0013] Furthermore, the interdigital electrodes are electrically connected to a circuit board.

[0014] Furthermore, the bottom electrode is an aluminum film, the interdigital electrodes are gold films, and the piezoelectric material and the substrate are both highly heat-sensitive materials.

[0015] Furthermore, the high heat-sensitive material is lithium niobate, zinc oxide or lead zirconate titanate.

[0016] Furthermore, the clamping assembly includes an upper clamp and a lower clamp, the upper clamp is connected to the surface acoustic wave device, and the opening portion is arranged on the upper clamp.

[0017] Furthermore, the opening portion is a rectangular opening.

[0018] Furthermore, the heating component is provided with resistance wires arranged in a serpentine shape.

[0019] Furthermore, the resonant frequency of the surface acoustic wave device is 1 MHz-1 GHz.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The overall sensor design has no suspended structure and has strong mechanical stability. The heating device is fixed by a clamp to promote thermal isolation between the heating device and the environment, thereby building a stable thermal equilibrium condition for the sensor. The surface acoustic wave propagation process is an elastic wave on the crystal surface, with no free electrons and no electron migration process involved, so it has strong anti-electromagnetic interference capability. The quasi-digital signal output is convenient for subsequent signal processing, and the static drift over time is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0023] Figure 1 This is a schematic diagram of the overall structure of a surface acoustic wave thermal gas flow velocity sensor according to the present invention;

[0024] Figure 2 It is a schematic structural diagram of a surface acoustic wave device of a surface acoustic wave thermal gas flow velocity sensor according to the present invention;

[0025] Figure 3 It is a structural schematic diagram of a heating plate of a surface acoustic wave thermal gas flow velocity sensor according to the present invention;

[0026] Figure 4 This is a flow chart of the detection principle of a surface acoustic wave thermal gas flow velocity sensor described in the present invention.

[0027] In the figure: upper fixture 1-1; lower fixture 1-2; heating component 2; resistance wire 2-1; surface acoustic wave device 3; circuit board 4; substrate 5; bottom electrode 6; piezoelectric material 7; interdigital electrode one 8-1; interdigital electrode two 8-2. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely explain the technical solutions in the embodiments of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict, and the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0029] It should be noted that the descriptions of the present invention regarding directions such as "left", "right", "left side", "right side", "upper", "lower", "top", and "bottom" are all defined based on the relationship between the orientations or positions shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the structure must be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention. In the description of the present invention, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0030] In the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0031] Referring to the accompanying drawings, this embodiment is described, providing a surface acoustic wave thermal gas flow rate sensor, comprising:

[0032] A surface acoustic wave device 3 is connected to a circuit board 4;

[0033] A heating component 2, one side of which is in contact with the surface acoustic wave device 3 to provide an initial temperature bias for the surface acoustic wave device 3, and the other side of which is in contact with the circuit board 4; the steady-state temperature of the surface acoustic wave device 3 is changed by the heating component 2 to apply a temperature bias; and the anti-interference electromagnetic capability is enhanced.

[0034] The clamping assembly 1 wraps the heating assembly 2, the surface acoustic wave device 3 and the circuit board 4, and is provided with an opening for keeping the surface acoustic wave device 3 in contact with the outside world. The clamping assembly 1 is used to keep the heating assembly 2 and the surface acoustic wave device 3 in stable contact. The gas flows over the surface of the surface acoustic wave device 3, takes away the heat, and changes the steady-state temperature of the surface acoustic wave device; the resonant frequency of the surface acoustic wave device is affected by temperature, and the proportional coefficient of the two in the linear segment is the temperature coefficient of frequency, i.e., TCF.

[0035] The TCF calculation formula is:

[0036]

[0037] Where: T is the temperature of the surface acoustic wave device 3 after the temperature bias is applied, T0 is the initial temperature of the surface acoustic wave device 3, and f T is the resonance frequency of the surface acoustic wave device 3 when the temperature is T, and f0 is the resonance frequency of the surface acoustic wave device 3 at the initial temperature.

[0038] Since the gas flow rate corresponds to the steady-state temperature of the sensor system when the ambient temperature is constant, the gas flow rate can be indirectly measured by measuring the resonant frequency. The sensor needs to be calibrated before use, and the TCF and the mapping relationship between the gas flow rate and the resonant frequency of the surface acoustic wave sensor under fixed heating unit power at various ambient temperatures are recorded as a table or fitting function. In practical applications, first keep the heating unit turned off, measure the resonant frequency of the surface acoustic wave sensor, substitute it into the TCF calculation formula, and measure the ambient temperature; then turn on the heating unit, measure the resonant frequency of the surface acoustic wave sensor, and calculate the corresponding gas flow rate by looking up the table or fitting function.

[0039] In this embodiment, the surface acoustic wave device 3 is provided with interdigital electrodes, piezoelectric material 7, bottom electrode 6 and substrate 5 from top to bottom. The surface acoustic wave device 3 is formed by stacking the substrate 5, bottom electrode 6, piezoelectric material 7 and interdigital electrodes layer by layer. The initial resonance frequency of the surface acoustic wave device 3 is jointly determined by parameters such as the period of the interdigital electrodes, the material of the piezoelectric layer, the thickness of the piezoelectric layer and the ambient temperature. The substrate 5 is rectangular.

[0040] In this embodiment, two interdigital electrodes are provided. The interdigital electrodes include interdigital electrode 1 8-1 and interdigital electrode 2 8-2, and the interdigital electrode 1 8-1 and interdigital electrode 2 8-2 are both arranged on the side of the piezoelectric material 7 away from the bottom electrode 6, and the interdigital electrode 1 8-1 and interdigital electrode 2 8-2 are connected to the circuit board 4. The interdigital electrode 1 8-1 and the interdigital electrode 2 8-2 are plated on the surface of the piezoelectric material 7 by magnetron sputtering.

[0041] In this embodiment, the interdigital electrodes are connected to the circuit board 4 via gold wires, which facilitates wiring and lead-out.

[0042] In this embodiment, the bottom electrode 6 is an aluminum film, the interdigital electrodes are gold films, and the piezoelectric material 7 is selected from zinc oxide, lithium niobate, and lead zirconate titanate, so that the absolute value of TCF of the surface acoustic wave sensor is greater than 100ppm / K, which is convenient for improving the temperature measurement sensitivity. The aluminum film and the gold film are prepared by an electron beam evaporation coating machine.

[0043] In this embodiment, the highly heat-sensitive material is lithium niobate, zinc oxide or lead zirconate titanate, which can be prepared by magnetron sputtering or bonding method.

[0044] In this embodiment, the clamping assembly 1 includes an upper clamp 1-1 and a lower clamp 1-2, wherein the upper clamp 1-1 contacts the surface acoustic wave device 3, the opening portion is arranged on the upper clamp 1-1, and the lower clamp 1-2 contacts the circuit board 4. The upper clamp 1-1 and the lower clamp 1-2 provide a stable contact force between the surface acoustic wave device 3 and the heating assembly 2, thereby ensuring that steady-state temperature fluctuations are reduced.

[0045] In this embodiment, the opening is a rectangular opening. The rectangular opening matches the shape of the surface acoustic wave device 3, which is conducive to the surface acoustic wave device 3 being fully in contact with the airflow, taking away the heat of the surface acoustic wave device 3, changing the temperature of the surface acoustic wave device 3, that is, changing the resonant frequency of the surface acoustic wave device 3.

[0046] In this embodiment, the heating component 2 is provided with a resistance wire 2-1, and the resistance wire is serpentine. The serpentine setting of the resistance wire 2-1 is conducive to full contact with the surface acoustic wave device 3, so that the surface acoustic wave device 3 is heated evenly and the measurement accuracy is improved. The resistance wire 2-1 is powered by an external DC power supply and can provide an initial temperature bias for the surface acoustic wave device 3.

[0047] In this embodiment, the resonant frequency of the surface acoustic wave device 3 is 1 MHz-1 GHz.

[0048] The upper clamp 1-1 and the lower clamp 1-2 are used to clamp the heating component 2, the surface acoustic wave device 3 and the circuit board 4. The upper clamp 1-1 and the lower clamp 1-2 provide stable contact force for the surface acoustic wave device 3 and the heating component 2 to construct a stable thermal balance system. The steady-state temperature of the surface acoustic wave device 3 is changed by the heating component 2, and the temperature bias is applied. The gas flows through the surface of the surface acoustic wave device 3, takes away the heat, and changes the steady-state temperature of the surface acoustic wave device 3; the resonant frequency of the surface acoustic wave device 3 is affected by temperature, and the proportional coefficient of the linear segment is the frequency temperature coefficient TCF; the surface acoustic wave device 3 and the circuit board 4 are connected by gold wires, and connected to the vector network analyzer using an SMA (SubMiniature version A) adapter to measure the resonant frequency of the surface acoustic wave device 3. The measurement results of the vector network analyzer are read by the host computer and further converted into gas flow rate.

[0049] The TCF calculation formula is:

[0050]

[0051] Where: T is the temperature of the surface acoustic wave device 3 after the temperature bias is applied, T0 is the initial temperature of the surface acoustic wave device 3, and f T is the resonance frequency of the surface acoustic wave device 3 when the temperature is T, and f0 is the resonance frequency of the surface acoustic wave device 3 at the initial temperature.

[0052] The embodiments of the present invention disclosed above are only used to help illustrate the present invention. The embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. According to the content of this specification, many modifications and changes can be made. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well.

Claims

1. A surface acoustic wave thermal gas flow rate sensor, characterized in that: include: A surface acoustic wave device (3) connected to a circuit board (4); A heating component (2) coupled to the surface acoustic wave device (3) to provide an initial temperature bias for the surface acoustic wave device (3); A clamping component (1) wraps the heating component (2) and the surface acoustic wave device (3) and is provided with an opening portion for maintaining the surface acoustic wave device (3) in contact with the outside of the clamping component (1); the clamping component (1) is used to maintain the heating component (2) and the surface acoustic wave device (3) in stable contact.

2. A surface acoustic wave thermal gas flow velocity sensor according to claim 1, characterized in that: The surface acoustic wave device (3) comprises interdigital electrodes, a piezoelectric material (7), a bottom electrode (6) and a substrate (5) which are arranged in sequence.

3. A surface acoustic wave thermal gas flow velocity sensor according to claim 2, characterized in that: There are two interdigital electrodes.

4. A surface acoustic wave thermal gas flow velocity sensor according to claim 2 or 3, characterized in that: The interdigital electrodes are electrically connected to the circuit board (4).

5. The surface acoustic wave thermal gas flow velocity sensor according to claim 2, characterized in that: The bottom electrode (6) is an aluminum film, the interdigitated electrodes are gold films, and the piezoelectric material (7) and the substrate (5) are both highly heat-sensitive materials.

6. A surface acoustic wave thermal gas flow velocity sensor according to claim 5, characterized in that: The high heat-sensitive material is lithium niobate, zinc oxide or lead zirconate titanate.

7. A surface acoustic wave thermal gas flow rate sensor according to claim 1, 2, 3, 5 or 6, characterized in that: The clamping assembly (1) comprises an upper clamp (1-1) and a lower clamp (1-2); the upper clamp (1-1) is connected to the surface acoustic wave device (3); and the opening is arranged on the upper clamp (1-1).

8. The surface acoustic wave thermal gas flow velocity sensor according to claim 7, characterized in that: The opening portion is a rectangular opening.

9. The surface acoustic wave thermal gas flow velocity sensor according to claim 1, characterized in that: The heating component (2) is provided with resistance wires (2-1) arranged in a serpentine shape.

10. The surface acoustic wave thermal gas flow velocity sensor according to claim 1, characterized in that: The resonant frequency of the surface acoustic wave device (3) is 1 MHz-1 GHz.

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