PT symmetrical hot-resistance MEMS wind speed and direction sensor

Abstract

The invention discloses a PT symmetrical hot-pressing resistance MEMS wind speed and wind direction sensor. The sensor comprises four groups of PT symmetrical MEMS resonators which are orthogonally distributed and have hot-pressing resistance feedback; the PT symmetrical MEMS resonator comprises two cantilever beam resonators with completely same structures, a coupling spring beam connected with the two resonators, and a constant current source connected with one resonator, each cantilever resonator comprises two anchor areas, a wide beam connected with the anchor areas, a narrow beam with a piezoresistive effect, a warped thin plate structure and external electrodes located on the two sides of the thin plate structure. Wind speed and wind direction signals are converted into rigidity change of the resonator array through mechanical action by means of a warped thin plate structure, and the rigidity change enables the PT symmetrical MEMS system to deviate from an EP point, so that system frequency splitting is caused. As the frequency splitting quantity of the PT symmetric system is in direct proportion to the square root of the disturbance quantity, the wind speed and direction sensor can detect tiny wind speed signals, and has the advantages of very high sensitivity, simple process, high integration level and the like.

Description

Technical Field

[0001] The invention relates to a PT-symmetrical thermal piezoresistive MEMS wind speed and direction sensor, belonging to the technical field of sensors. Background Art

[0002] Accurate measurement of wind speed and direction is of great significance in fields such as meteorological monitoring, aerospace, intelligent transportation, environmental monitoring, and wind energy utilization. In recent years, with the development of microelectronics and MEMS technologies, MEMS wind speed and direction sensors have become a research hotspot in the field of wind speed and direction measurement due to their advantages such as miniaturization, low cost, and high integration. However, existing MEMS wind speed and direction sensors still face the technical challenge of insufficient sensitivity to small changes in wind speed. Therefore, developing a new sensor that can overcome the technical limitations of existing MEMS wind speed and direction sensors, especially in terms of improving measurement accuracy and sensitivity, remains a technical challenge that needs to be urgently addressed in the field of wind speed and direction measurement. Summary of the Invention

[0003] Technical Problem: To address the above-mentioned problems, the present invention provides a parity-time (PT) symmetric thermo-piezoresistive micro-electronic mechanical system (MEMS) wind speed and direction sensor, which includes four orthogonally distributed PT-symmetric MEMS resonators with thermo-piezoresistive feedback. The PT-symmetric MEMS resonators include two cantilever beam resonators with identical structures, a coupling spring beam connecting the two resonators, and a constant current source connected to one of the resonators. Each cantilever beam resonator includes two anchor regions, a wide beam connected to the anchor regions and a narrow beam with a piezoresistive effect, a warped thin plate structure, and external electrodes located on both sides of the thin plate structure. The thermo-piezoresistive feedback causes the coupled resonators to form a PT-symmetric system. The PT-symmetric resonator is initially located at an exceptional point (EP). The warped portion of the thin plate structure is subjected to wind pressure, causing the stiffness of the two resonators to change, causing the PT-symmetric system to deviate from the EP point, resulting in eigenfrequency splitting. At different wind speeds and directions, the four orthogonally distributed resonators are subjected to varying wind pressure distributions, causing varying degrees of frequency splitting in each resonator group. The wind speed information corresponding to each resonator group is then vector-synthesized to yield wind speed and direction information. This PT-symmetrical thermal piezoresistive MEMS wind speed and direction sensor accurately measures both omnidirectional wind direction and weak wind speeds, offering high sensitivity and a simple manufacturing process.

[0004] Technical solution: To achieve the above object, the present invention provides a technical solution for a PT-symmetric thermopiezoresistive MEMS wind speed and direction sensor. The wind speed and direction sensor includes four groups of PT-symmetric MEMS resonators with thermopiezoresistive feedback for obtaining wind speed signals in orthogonal directions, so as to obtain the wind direction result through vector synthesis. Each group of PT-symmetric MEMS resonators includes two cantilever beam resonators with exactly the same structure, a coupling spring beam connecting the two resonators, and a constant current source connected to one of the resonators. Each cantilever beam resonator includes two anchor regions fixed to the substrate, a wide beam and a narrow beam with piezoresistive effect respectively connected to the two anchor regions, and a warped thin plate structure is connected to the other side of the beam. External electrodes are provided on both sides of the thin plate structure for signal reading. Since the structures of the two cantilever beam resonators are exactly the same, their inherent parameters such as effective mass and stiffness are also the same. Among them, for the resonator connected to the constant current source, due to the piezoresistive effect of its narrow beam, the displacement caused by the oscillation of the resonator will cause the resistance of the narrow beam to change. Since the size of the narrow beam is much smaller than that of the wide beam, it has a higher resistance. Under the action of the constant current source, the Joule heat generated by the current flowing through the resonator is concentrated at the narrow beam. And the change in resistance caused by the oscillating displacement causes the Joule heat power to change. Due to the heat conduction and heat diffusion of the object, the temperature changes, and the change in temperature causes thermal expansion, generating a changing stress. According to Hooke's law, the stress will cause the displacement of the narrow beam to change, forming a thermopiezoresistive feedback. This feedback process can be equivalent to an action opposite to damping, that is, as a gain in the PT-symmetric system. And the cantilever beam resonator not connected to the constant current source is directly affected by damping. The two resonators form a PT-symmetric system through the mechanical weak coupling of a coupling spring beam. In the initial state, the PT-symmetric system is biased at the EP point. The warped part of the thin plate structure of the cantilever beam is affected by the wind pressure, causing the stiffness of the two resonators to change, making the PT-symmetric system deviate from the EP point, resulting in the splitting of the eigenfrequency. The expression of the angular frequency splitting amount is as follows:

[0005]

[0006] where k is the stiffness of the resonator when not disturbed, k c is the stiffness of the coupling spring beam, ω0 is the natural frequency of the resonator, all of which are known parameters; Δk is the change in stiffness caused by the wind speed. For weak wind speeds, Δk << k. Compared with the frequency splitting amount Δω = ω0Δk / 2k of the traditional wind speed sensor, there is an order-of-magnitude improvement in the frequency splitting amount Δω.

[0007] Beneficial effects: For the PT-symmetric thermopiezoresistive MEMS wind speed and direction sensor of the present invention, the wind speed and direction sensor forms a PT-symmetric system through thermopiezoresistive feedback and biases it at the EP point. The warped part of the cantilever beam thin plate structure is affected by the wind pressure, causing changes in the stiffness of the two resonators, deviating the PT-symmetric system from the EP point, resulting in the splitting of the eigenfrequency, and thus obtaining the corresponding wind speed information. The four groups of orthogonally distributed resonators are subjected to different wind pressure distributions, causing different degrees of frequency splitting in each group of resonators. The wind speed and direction information can be obtained through vector synthesis of the wind speed information corresponding to each group of resonators. Since the amount of frequency splitting is proportional to the square root of the perturbation signal, this sensor can detect tiny wind speed signals, has very high sensitivity, and is completely based on the MEMS process, with the advantages of simple process and high integration. Description of the Drawings

[0008] Figure 1 It is a schematic structural diagram of the PT-symmetric thermopiezoresistive MEMS wind speed and direction sensor.

[0009] Figure 2 It is a top view of the PT-symmetric resonator structure with thermopiezoresistive feedback.

[0010] Figure 3 It is a cross-sectional view of the PT-symmetric resonator structure with thermopiezoresistive feedback.

[0011] Figure 4 It is a schematic diagram of the principle of thermopiezoresistive feedback.

[0012] Figure 5 It is a comparison of the amount of frequency splitting caused by the PT-symmetric thermopiezoresistive MEMS wind speed and direction sensor with square root response and the traditional linear wind speed sensor under the same stiffness change in this embodiment.

[0013] In the figure: a, the first cantilever beam resonator, b, the first cantilever beam resonator, 1a1, the first narrow beam, 1b1, the second narrow beam, 1a2, the first wide beam, 1b2, the second wide beam, 1a3, the first thin plate structure, 1b3, the second thin plate structure, 2a1, the first anchor area one, 2a2, the first anchor area two, 2b1, the second anchor area one, 2b2, the second anchor area two, 3a1, the first external electrode one, 3a2, the first external electrode two, 3b1, the second external electrode one, 3b2, the second external electrode two, 4, the coupling spring beam, 5, the constant current source, 6, the substrate; Detailed Embodiment

[0014] To deepen the understanding and recognition of the present invention, the present invention will be further described below with reference to the accompanying drawings.

[0015] Embodiment: For the PT-symmetric thermopiezoresistive MEMS wind speed and direction sensor involved in the present invention, refer to Figure 1, including four groups of PT - symmetric resonators with thermopiezoresistive feedback, distributed in orthogonal directions. The direction of the symmetry axis where each group of PT - symmetric resonators with thermopiezoresistive feedback is located is the wind - speed sensitive direction.

[0016] The structure of the PT - symmetric MEMS resonator is shown in Figure 2 、 Figure 3 , including two cantilever beam resonators with exactly the same structure, namely the first cantilever beam resonator a and the second cantilever beam resonator b, a coupling spring beam 4 connecting the two resonators, and a constant - current source 5 connected to the second cantilever beam resonator b. The constant - current source 5 is connected to the second anchor region one 2b1 and the second anchor region two 2b2. The coupling spring beam 4 is connected to the warped first thin - plate structure 1a3 and the second thin - plate structure 1b3. The first cantilever beam resonator a includes the first anchor region one 2a1 and the first anchor region two 2a2. The second cantilever beam resonator b includes the second anchor region one 2b1 and the second anchor region two 2b2. The first anchor region one 2a1, the first anchor region two 2a2, the second anchor region one 2b1, and the second anchor region two 2b2 are on the substrate 6. The positive pole of the constant - current source 5 is connected to the second anchor region two 2b2, and the negative pole is connected to the second anchor region one 2b1. The first wide beam 1a2 and the second wide beam 1b2 are connected to the anchor regions 2a2 and 2b2, and the first narrow beam 1a1 and the second narrow beam 1b1 with piezoresistive effect are connected to the second anchor region one 2b1 and the second anchor region two 2b2. The first wide beam 1a2 and the first narrow beam 1a1 are connected to the warped first thin - plate 1a3, and the second wide beam 1b2 and the second narrow beam 1b1 are connected to the warped second thin - plate 1b3. On both sides of the warped first thin - plate 1a3, there are the first external electrode one 3a1 and the first external electrode two 3a2; on both sides of the warped second thin - plate 1b3, there are the second external electrode one 3b1 and the second external electrode two 3b2.

[0017] The schematic diagram of the thermopiezoresistive feedback involved in the present invention is as shown in Figure 4 . The constant - current source 5 is connected to the second anchor region one 2b1 and the second anchor region two 2b2, so that a constant current flows through the path formed by the second anchor region two 2b2, the second narrow beam 1b1, the warped second thin - plate 1b3, the second wide beam 1b2, and the second anchor region one 2b1. The Joule heat generated by the current will concentrate at the second narrow beam 1b1. When the cantilever beam vibrates, a displacement is generated on the second narrow beam 1b1. Due to the piezoresistive effect, the resistance of the second narrow beam 1b1 changes, causing a change in Joule heat, and thus a change in the temperature on the second narrow beam 1b1. Since the temperature can cause thermal expansion of the beam, the stress caused by the thermal expansion acts on the second narrow beam 1b1 in turn, causing a change in displacement. This feedback process can be equivalent to an action opposite to damping, that is, the gain in the PT - symmetric system. And there is no current flowing through the first cantilever beam resonator a connected to the first anchor region one 2a1 and the first anchor region two 2a2, which is directly affected by the damping. The first cantilever beam resonator a and the second cantilever beam resonator b form a PT - symmetric system through the mechanical weak - coupling action of a coupling spring beam 4.

[0018] It should be noted that the above is only one embodiment of the present invention. The constant current source 5 can also be added to the first cantilever resonator a and connected to the first anchor region 1 2a1 and the second anchor region 2 2a2, so as to form a path formed by the second anchor region 2 2a2, the first narrow beam 1a1, the warped first thin plate 1a3, the first wide beam 1a2 and the first anchor region 1 2a1.

[0019] The PT - symmetric system is biased at the EP point. The warped first thin plate structure 1a3 and the second thin plate structure 1b3 of the cantilever beam are affected by the wind pressure, causing the stiffness change of the two resonators, deviating the PT - symmetric system from the EP point, resulting in the splitting of the eigen - frequencies of the system. The angular frequency splitting amount is as follows:

[0020]

[0021] According to the frequency splitting amount Δω, the stiffness change Δk can be obtained. Then, according to the calibration relationship between the stiffness and the wind pressure and the wind speed corresponding to the wind pressure, the wind speed to be measured can be obtained.

[0022] The vibration signal containing frequency information can be read out by applying a DC bias voltage to any one of the first external electrode 1 3a1, the first external electrode 2 3a2, the second external electrode 1 3b1, and the second external electrode 2 3b2, forming a voltage difference between the warped first thin plate 1a3 and the second thin plate structure 1b3, and forming a capacitive transducer structure.

[0023] As an optional read - out method, the changing current signal can be directly read on the second anchor region 2 2b2 connected to the positive pole of the DC source 5 to obtain the corresponding vibration signal containing frequency information.

[0024] The criteria for distinguishing whether it is this structure are as follows:

[0025] (a) Adopt a PT - symmetric MEMS cantilever resonator;

[0026] (b) The narrow beam with piezoresistive effect provides gain for the PT - symmetric system;

[0027] (c) Obtain the wind direction through the vector synthesis of four groups of wind speed sensors distributed orthogonally.

[0028] The structure that meets the above three conditions should be regarded as the wind speed and wind direction sensor of this structure.

[0029] The above - mentioned is only the preferred embodiment of the present invention. The protection scope of the present invention is not limited to the above - mentioned embodiment. Any equivalent modification or change made by those of ordinary skill in the art according to the disclosure of the present invention should be included in the protection scope recorded in the claims.

Claims

1. A PT-symmetric thermopiezoresistive MEMS wind speed and direction sensor, characterized in that, The wind speed and direction sensor includes four groups of PT-symmetric resonators with thermopiezoresistive feedback distributed orthogonally; each group includes two cantilever beam resonators with exactly the same structure, namely a first cantilever beam resonator (a) and a second cantilever beam resonator (b), a coupling spring beam (4) connecting the two resonators, a constant current source (5) forming a loop with the second cantilever beam resonator (b), and a substrate (6) supporting the resonators.

2. The PT-symmetric thermopiezoresistive MEMS wind speed and direction sensor according to claim 1, wherein The first cantilever beam resonator (a) includes a first anchor region 1 (2a1), a first anchor region 2 (2a2), a first wide beam (1a2), a first narrow beam (1a1) with piezoresistive effect, a warped first thin plate structure (1a3), a first external electrode 1 (3a1), and a first external electrode 2 (3a2); the second cantilever beam resonator (b) includes a second anchor region 1 (2b1), a second anchor region 2 (2b2), a second wide beam (1b2), a second narrow beam (1b1) with piezoresistive effect, a warped second thin plate structure (1b3), a second external electrode 1 (3b1), and a second external electrode 2 (3b2); wherein, the first anchor region 1 (2a1) is connected to the first narrow beam (1a1), the first anchor region 2 (2a2) is connected to the first wide beam (1a2), and the warped first thin plate structure (1a3) connects the first wide beam (1a2) and the first narrow beam (1a1); the second anchor region 1 (2b1) is connected to the second narrow beam (1b1), the second anchor region 2 (2b2) is connected to the second wide beam (1b2), and the warped second thin plate structure (1b3) connects the second wide beam (1b2) and the second narrow beam (1b1), the constant current source (5) is connected to the second anchor region 1 (2b1) and the second anchor region 2 (2b2), and the coupling spring beam (4) is connected to the warped first thin plate structure (1a3) and the second thin plate structure (1b3).

3. The PT-symmetric thermopiezoresistive MEMS wind speed and direction sensor according to claim 1, characterized in that: Thermopiezoresistive feedback makes the coupled cantilever beam resonators form a PT-symmetric system. The PT-symmetric MEMS resonator is initially located at the EP point. The warped parts of the first thin plate structure (1a3) and the second thin plate structure (1b3) are affected by the wind pressure, causing changes in the stiffness of the first cantilever beam resonator (a) and the second cantilever beam resonator (b), deviating the PT-symmetric system from the EP point and resulting in the splitting of the eigenfrequency, thereby realizing the measurement of wind speed. Under different wind speeds and directions, the four groups of orthogonally distributed resonators are subjected to different wind pressure distributions, causing different degrees of frequency splitting in each group of resonators. The wind speed and direction information can be obtained through vector synthesis of the wind speed information corresponding to each group of resonators.

4. The PT-symmetric thermopiezoresistive MEMS wind speed and direction sensor according to claim 3, characterized in that: The expression of the frequency splitting amount is as follows: where k is the stiffness of the resonator when undisturbed, and k c is the stiffness of the coupled spring beam, ω0 is the natural frequency of the resonator, and all are known parameters; Δk is the change in stiffness caused by the wind speed. For weak wind speeds, Δk << k, which shows an obvious change in the frequency splitting amount Δω.

5. A PT-symmetric thermopiezoresistive MEMS wind speed and direction sensor according to claim 2 or 3, characterized in that: The constant current source 5 is connected to the second anchor region 1 (2b1) and the second anchor region 2 (2b2), so that a constant current flows through the path formed by the second anchor region 2 (2b2), the second narrow beam (1b1), the warped second thin plate (1b3), and the second wide beam (1b2) and the anchor region (2b1). The Joule heat generated by the current will be concentrated in the second narrow beam (1b1). When the first cantilever resonator (a) and the second cantilever resonator (b) vibrate, displacement is generated on the second narrow beam (1b1). Due to the piezoresistive effect, the resistance of the second narrow beam (1b1) changes, causing a change in Joule heat and a change in the temperature on the second narrow beam (1b1). Since temperature causes thermal expansion of the beam, the stress caused by thermal expansion acts on the second narrow beam (1b1) in turn, causing a change in displacement. This feedback process is equivalent to an action opposite to damping, that is, the gain in the PT-symmetric system. There is no current flowing through the first cantilever resonator (a) connected to the first anchor region 1 (2a1) and the first anchor region 2 (2a2), and it is directly subject to the damping effect. The first cantilever resonator (a) and the second cantilever resonator (b) form a PT-symmetric system through the mechanical weak coupling of a coupling spring beam (4).

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