A PT symmetric thermal piezoresistive MEMS wind speed and direction sensor

Abstract

The application discloses a PT-symmetry thermal piezoresistive MEMS wind speed and direction sensor, which comprises four groups of PT-symmetry MEMS resonators with thermal piezoresistive feedback and arranged in quadrature; the PT-symmetry MEMS resonator comprises two cantilever beam resonators which are completely identical in structure, a coupling spring beam connected to the two resonators, and a constant current source connected to one of the resonators; each cantilever beam resonator comprises two anchor areas, a wide beam connected to the anchor areas, a narrow beam with piezoresistive effect, a warped thin plate structure, and external electrodes located on both sides of the thin plate structure. The wind speed and direction signals are converted into stiffness changes of the resonator array through mechanical action by the warped thin plate structure, the stiffness changes make the PT-symmetry MEMS system deviate from the EP point, thereby causing frequency splitting of the system. Since the frequency splitting amount of the PT-symmetry system is proportional to the square root of the disturbance amount, the wind speed and direction sensor can detect a tiny wind speed signal, has very high sensitivity, and has the advantages of simple process, high integration and the like.

Description

Technical Field

[0001] This invention is a PT-symmetric thermopiezoresistive MEMS wind speed and direction sensor, belonging to the field of sensor technology. Background Technology

[0002] Accurate measurement of wind speed and direction is of great significance in 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 of miniaturization, low cost, and high integration. However, existing MEMS wind speed and direction sensors still face the technical challenge of insufficient sensitivity in responding to minute changes in wind speed. Therefore, developing a new type of sensor that can overcome the limitations of existing MEMS wind speed and direction sensor technology, especially in improving measurement accuracy and sensitivity, remains a pressing technical challenge in the field of wind speed and direction measurement. Summary of the Invention

[0003] Technical Problem: To address the aforementioned problems, this invention provides a parity-time (PT) symmetric thermo-piezoresistive micro-electromechanical system (MEMS) wind speed and direction sensor. This sensor comprises four orthogonally distributed PT-symmetric MEMS resonators with thermo-piezoresistive feedback. Each PT-symmetric MEMS resonator includes two identical cantilever beam resonators, 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 resonators are initially located at an exception point (EP). The warped portion of the thin-plate structure is subjected to wind pressure, causing a change in the stiffness of the two resonators, causing the PT-symmetric system to deviate from the EP point, resulting in frequency splitting. Under different wind speeds and directions, the four orthogonally distributed resonators are subjected to different wind pressure distributions, causing each resonator to produce frequency splitting to varying degrees. The wind speed information corresponding to each resonator can be vector-synthesized to obtain wind speed and direction information. The PT-symmetric thermopiezoresistive MEMS wind speed and direction sensor can achieve accurate measurement of wind direction and weak wind speed in all directions, and has the advantages of high sensitivity and 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 the other side of the beam is connected to a warped thin plate structure. External electrodes on both sides of the thin plate structure are used to read signals. 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. The changing 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 the gain in the PT-symmetric system. 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, deviating the PT-symmetric system 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 stiffness change 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: The present invention discloses a PT-symmetric thermopiezoresistive MEMS wind speed and direction sensor. This sensor uses thermopiezoresistive feedback to form a PT-symmetric system with coupled cantilever beam resonators biased at point EP. The warped portion of the cantilever beam thin plate structure is subjected to wind pressure, causing a change in the stiffness of the two resonators, which in turn causes the PT-symmetric system to deviate from point EP, resulting in frequency splitting and thus obtaining the corresponding wind speed information. Four sets of orthogonally distributed resonators are subjected to different wind pressure distributions, causing each set of resonators to produce different degrees of frequency splitting. The wind speed information corresponding to each set of resonators can be vector-synthesized to obtain wind speed and direction information. Since the frequency splitting is proportional to the square root of the disturbance signal, this sensor can detect minute wind speed signals, has very high sensitivity, and is entirely based on MEMS technology, offering advantages such as simple fabrication and high integration. Attached Figure Description

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

[0009] Figure 2 This is a top view of a PT-symmetric resonator structure with thermal piezoelectric feedback.

[0010] Figure 3 This is a cross-sectional view of a PT symmetrical resonator structure with thermo-piezoresistive feedback.

[0011] Figure 4 This is a schematic diagram of the thermo-piezoresistive feedback principle.

[0012] Figure 5 This embodiment compares the frequency splitting caused by the PT-symmetric thermoplastic MEMS wind speed and direction sensor with square root response and the traditional linear wind speed sensor under the same stiffness variation.

[0013] In the figure: a, First cantilever beam resonator; b, First cantilever beam resonator; 1a1, First narrow beam; 1b1, Second narrow beam; 1a2, First wide beam; 1b2, Second wide beam; 1a3, First thin plate structure; 1b3, Second thin plate structure; 2a1, First anchor region one; 2a2, First anchor region two; 2b1, Second anchor region one; 2b2, Second anchor region two; 3a1, First external electrode one; 3a2, First external electrode two; 3b1, Second external electrode one; 3b2, Second external electrode two; 4, Coupled spring beam; 5, Constant current source; 6, Substrate. Detailed Implementation

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

[0015] Example: The PT-symmetric thermopiezoresistive MEMS wind speed and direction sensor involved in this invention is described in [reference needed]. Figure 1It includes four sets of PT symmetrical resonators with thermo-piezoresistive feedback, distributed in orthogonal directions. The direction of the axis of symmetry of each set of PT symmetrical resonators with thermo-piezoresistive feedback is the wind speed sensitive direction.

[0016] See the structure of the PT-symmetric MEMS resonator. Figure 2 , Figure 3 The system comprises two identical cantilever beam resonators, namely a first cantilever beam resonator a and a 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 2b1 and the second anchor region 2b2, and 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 2a1 and the first anchor region 2a2, and the second cantilever beam resonator b includes the second anchor region 2b1 and the second anchor region 2b2. The first anchor region 2a1, the first anchor region 2a2, the second anchor region 2b1, and the second anchor region 2b2 are located on the substrate 6. The positive terminal of the constant current source 5 is connected to the second anchor region 2b2, and the negative terminal is connected to the second anchor region 2b1. The first wide beam 1a2 and the second wide beam 1b2 are connected to anchor areas 2a2 and 2b2, respectively. The first narrow beam 1a1 and the second narrow beam 1b1, which have a piezoresistive effect, are connected to the second anchor area 2b1 and the second anchor area 2b2. The first wide beam 1a2 and the first narrow beam 1a1 connect to a warped first thin plate 1a3, and the second wide beam 1b2 and the second narrow beam 1b1 connect to a warped second thin plate 1b3. The warped first thin plate 1a3 has a first external electrode 3a1 and a second external electrode 3a2 on both sides; the warped second thin plate 1b3 has a second external electrode 3b1 and a second external electrode 3b2 on both sides.

[0017] The thermal piezoelectric feedback principle diagram involved in this invention is shown below. Figure 4 As shown, the constant current source 5 is connected to the second anchor region 2b1 and the second anchor region 2b2, allowing a constant current to flow through the path formed by the second anchor region 2b2, the second narrow beam 1b1, the warped second thin plate 1b3, the second wide beam 1b2, and the second anchor region 2b1. The Joule heat generated by the current is concentrated at the second narrow beam 1b1. When the cantilever beam vibrates, displacement occurs 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 temperature. Since the temperature causes thermal expansion of the beam, the stress caused by the thermal expansion acts on the second narrow beam 1b1, causing a change in displacement. This feedback process can be equivalent to an effect opposite to damping, i.e., gain in a PT-symmetric system. Meanwhile, no current flows through the first cantilever beam resonator a connected to the first anchor region 2a1 and the first anchor region 2a2, and it is directly subjected to damping. The first cantilever beam resonator a and the second cantilever beam resonator b form a PT-symmetric system through the weak mechanical coupling 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 beam resonator a and connected to the first anchor region 2a1 and the first anchor region 2a2, thereby forming a path between the first anchor region 2a2, the first narrow beam 1a1, the warped first thin plate 1a3, the first wide beam 1a2 and the first anchor region 2a1.

[0019] The PT-symmetric system is biased at point EP. The warping of the cantilever beam, caused by wind pressure on the first thin plate structure 1a3 and the second thin plate structure 1b3, leads to changes in the stiffness of the two resonators, causing the PT-symmetric system to deviate from point EP. This results in the splitting of the system's angular frequency, with the following angular frequency splitting amounts:

[0020]

[0021] The stiffness change Δk can be obtained from the frequency splitting amount Δω. Then, based on the calibration relationship between stiffness and 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 3a1, the first external electrode 3a2, the second external electrode 3b1, and the second external electrode 3b2, thereby creating a voltage difference between the first thin plate 1a3 and the second thin plate structure 1b3, forming a capacitor transducer structure.

[0023] As an optional readout method, the changing current signal can be directly read from the second anchor area 2b2 connected to the positive terminal of DC source 5 to obtain the corresponding vibration signal containing frequency information.

[0024] The criteria for distinguishing whether something belongs to this structure are as follows:

[0025] (a) A MEMS cantilever beam resonator with PT symmetry is used;

[0026] (b) Gain is provided for the PT-symmetric system by a narrow beam with thermal piezoelectric effect;

[0027] (c) Wind direction is obtained by vector synthesis of four orthogonally distributed wind speed sensors.

[0028] A structure that meets the above three conditions should be considered as a wind speed and direction sensor.

[0029] The above description is only a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. Any equivalent modifications or changes made by those skilled in the art based on the content disclosed in the present invention should be included within the scope of protection set forth 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 sets of orthogonally distributed PT symmetrical resonators with thermo-piezoresistive feedback; each set includes two cantilever beam resonators with identical structures, namely the first cantilever beam resonator (a) and the second cantilever beam resonator (b), a coupling spring beam (4) connecting the two resonators, a constant current source (5) forming a circuit with the second cantilever beam resonator (b), and a substrate (6) supporting the resonators. 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) and the first narrow beam (1a1) with piezoresistive effect are connected. A narrow beam (1a1) is connected, the first anchor area two (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 area one (2b1) is connected to the second narrow beam (1b1), the second anchor area two (2b2) ​​is connected to the second wide beam (1b2), 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 area one (2b1) and the second anchor area two (2b2), and the coupling spring beam (4) is connected to the warped first thin plate structure (1a3) and the second thin plate structure (1b3); Thermo-piezoresistive feedback enables the coupled cantilever beam resonators to form a PT-symmetric system. The PT-symmetric MEMS resonator is initially located at point EP. The warped parts of the first thin plate structure (1a3) and the second thin plate structure (1b3) are subjected to wind pressure, causing changes in the stiffness of the first cantilever beam resonator (a) and the second cantilever beam resonator (b), causing the PT-symmetric system to deviate from point EP, resulting in the splitting of the intrinsic frequencies, thereby realizing the measurement of wind speed. Under different wind speeds and directions, the four sets of orthogonally distributed resonators are subjected to different wind pressure distributions, causing each set of resonators to produce frequency splitting to different degrees. The wind speed information corresponding to each set of resonators can be obtained by vector synthesis to obtain wind speed and wind direction information. The expression for the frequency splitting quantity is as follows: where k is the stiffness of the resonator when it is not perturbed, k c is the stiffness of the coupled spring beam, ω0 is the natural frequency of the resonator, and both are known parameters; Δk is the change in stiffness caused by the wind speed. For a weak wind speed, Δk << k, and it shows an obvious change in the frequency splitting amount Δω; A constant current source 5 connects the second anchor region 1 (2b1) and the second anchor region 2 (2b2), allowing a constant current to flow through the path formed by the second anchor region 2 (2b2), the second narrow beam (1b1), the warped second thin plate structure (1b3), the second wide beam (1b2), and the second anchor region 1 (2b1). The Joule heat generated by the current is concentrated in the second narrow beam (1b1). When the first cantilever beam resonator (a) and the second cantilever beam resonator (b) vibrate, displacement occurs 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. The temperature on the two narrow beams (1b1) changes. Since the temperature causes the beam to expand thermally, the stress caused by the thermal expansion acts on the second narrow beam (1b1) in turn, causing the displacement to change. This feedback process is equivalent to an action opposite to damping, namely the gain in the PT symmetric system. No current flows through the first cantilever beam resonator (a) connected to the first anchor region one (2a1) and the first anchor region two (2a2), and it is directly subjected to damping. The first cantilever beam resonator (a) and the second cantilever beam resonator (b) form a PT symmetric system through the weak mechanical coupling of a coupling spring beam (4).

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