Vibration interference resistant optical wall shear stress microsensor and measuring system thereof

Abstract

The invention provides an anti-vibration interference optical wall shear stress microsensor and a measuring system thereof, and belongs to the technical field of MEMS sensors. Comprising an MEMS chip module, a four-quadrant vibration sensitive film and a dynamic anti-interference shear stress correction module, the four-quadrant vibration sensitive film and the dynamic anti-interference shear stress correction module are installed on the MEMS chip module, and the four-quadrant vibration sensitive film is arranged on the lower surface of a floating element of the MEMS chip module in a quaternary orthogonal circumferential array mode and located on the periphery of a movable grating film on the lower surface of the floating element; the dynamic anti-interference shear stress correction module projects a vibration vector of a four-quadrant vibration sensitive film to a sensitive axis direction of the shear stress microsensor, extracts a vibration interference component along a shear stress measurement direction, and compensates a vibration coupling error in a shear stress signal in real time in combination with a low-pass filtering algorithm. And completing anti-interference calculation of the shear stress. The problems of limitation and vibration interference of traditional single parameter detection are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of MEMS sensors, and in particular relates to an optical wall shear stress microsensor resistant to vibration interference and a measurement system thereof. Background Art

[0002] In fluid dynamics measurements, wall shear stress detection is susceptible to interference from structural vibrations, leading to signal distortion. This is particularly true in high-temperature, highly dynamic, and complex flow environments. Mechanical vibrations, through the inherent resonant modes of the floating element-elastic beam structure, overlap with the external excitation frequency band, generating a resonance effect that severely degrades sensor reliability and measurement accuracy in extreme environments. Optical MEMS (micro-electromechanical systems) sensors, with their advantages of non-contact measurement, high sensitivity, and resistance to electromagnetic interference, are becoming the mainstream measurement method in complex environments.

[0003] However, existing technologies face multiple challenges in practical applications: First, severe vibrations exist in typical working environments such as aircraft engines and high-speed wind tunnels. The sensor's floating elements are disturbed by mechanical vibrations, which can cause distortion of the shear stress measurement signal. Existing sensors lack the ability to detect vibration synchronously, making it difficult to achieve in-situ data correction; second, the pressure gradient in complex boundary layer flows can cause unexpected warping of the floating elements, and current technology can only infer shear stress through single-degree-of-freedom displacement, resulting in accumulated measurement model errors; in addition, in order to achieve miniaturized sensor layout to obtain spatial resolution, traditional solutions require a separate light source and multiple photodetectors for each sensing unit, which not only significantly increases the system volume and power consumption, but also limits the feasibility of high-density integration due to optical path crosstalk problems.

[0004] Therefore, it is necessary to develop an optical wall shear stress microsensor and its measurement system that are resistant to vibration interference, detect the normal motion trajectory of the floating element, realize in-situ real-time measurement of shear stress and vibration, correct the shear stress measurement results, and provide a miniaturized sensor measurement system. Summary of the Invention

[0005] Technical issues to be solved:

[0006] To overcome the shortcomings of existing technologies, the present invention provides a vibration-resistant optical wall shear stress microsensor and its measurement system. By integrating a shear stress grating structure with a four-element orthogonal vibration-sensitive membrane into the same sensor, this sensor enables simultaneous measurement of shear stress and vibration. The four-element orthogonal vibration-sensitive membrane and the axisymmetric grating work together to effectively decouple shear stress and vibration signals, providing high-precision data support for fluid-structure interaction analysis. This invention addresses the limitations of traditional single-parameter detection and the problem of vibration interference.

[0007] The technical solution of the present invention is: an optical wall shear stress microsensor with resistance to vibration interference, comprising a MEMS chip module, a four-quadrant vibration-sensitive membrane mounted on the MEMS chip module, and a dynamic anti-interference shear stress correction module. The four-quadrant vibration-sensitive membrane is arranged in a four-element orthogonal circumferential array on the lower surface of a floating element of the MEMS chip module and is located outside a movable grating film on the lower surface of the floating element. The floating element drives the movable grating film and the four-quadrant vibration-sensitive membrane to displace under the action of shear stress or vibration. The reflected light signal is transmitted to a photodetector via an optical switch and a fiber coupler, which outputs decoupled shear stress and vibration parameters.

[0008] The dynamic anti-interference shear stress correction module projects the vibration vector of the four-quadrant vibration sensitive membrane onto the sensitive axis direction of the shear stress microsensor, extracts the vibration interference component along the shear stress measurement direction, and combines the low-pass filtering algorithm to compensate for the vibration coupling error in the shear stress signal in real time to complete the anti-interference calculation of the shear stress.

[0009] A further technical solution of the present invention is: the MEMS chip module includes a base layer with an I-shaped cavity and a sensitive structure layer placed thereon, and a fixed grating film is provided on the bottom surface of the I-shaped cavity; a floating element is provided on the sensitive structure layer at a position opposite to the I-shaped cavity, and the floating element is connected to a fixed anchor point on the sensitive structure layer through circumferentially distributed elastic beams, and a movable grating film is provided on its lower surface, opposite to the fixed grating film.

[0010] A further technical solution of the present invention is that the fixed grating film and the movable grating film are respectively arranged at the center of the upper surface of the base layer and the center of the lower surface of the floating element along the axisymmetric center line.

[0011] A further technical solution of the present invention is: the vibration vector solution process of the four-quadrant vibration sensitive membrane is as follows:

[0012] The X-axis vibration component Vx is calculated by the signal difference of the vibration sensitive film in the positive and negative directions of the X-axis, and the Y-axis vibration component Vy is calculated by the signal difference of the vibration sensitive film in the positive and negative directions of the Y-axis;

[0013] The normal Z-axis vibration component Vz is calculated by averaging the four signals of the four-quadrant vibration sensitive membrane;

[0014] Calculate the three-dimensional composite vibration amplitude and three-dimensional vibration direction angle based on the X, Y, and Z axis vibration components Vx, Vy, and Vz;

[0015] The vibration vector is normalized to generate a unit direction vector, which is used to represent the main direction of the vibration.

[0016] A further technical solution of the present invention is: the specific steps of the anti-interference calculation of the shear stress are as follows:

[0017] The original shear stress signal is obtained by the difference of the two grating signals;

[0018] Calculate the three-dimensional vibration direction vector based on the X, Y, and Z axis vibration components Vx, Vy, and Vz;

[0019] Based on the three-dimensional vibration direction vector and the three-dimensional synthetic vibration amplitude, the projection component of the vibration direction vector on the shear stress sensitive axis is calculated;

[0020] Perform low-pass filtering on the projection component to suppress high-frequency noise;

[0021] The original shear stress signal is adjusted by filtering the vibration interference signal to dynamically correct the shear stress signal. The expression is as follows:

[0022] S corrected =S raw -α×v proj_filtered

[0023] Where S corrected represents the compensated shear stress signal, S raw represents the original shear stress signal, α represents the compensation coefficient, which controls the influence of vibration interference, and v proj_filtered Represents the vibration interference signal after filtering.

[0024] A further technical solution of the present invention is: the calculation formula of the projection component of the vibration direction vector on the shear stress sensitive axis is as follows:

[0025] v proj =V·S×V norm

[0026] Where, v proj Represents the vibration interference component obtained by projection, V norm represents the three-dimensional composite vibration amplitude, S represents the shear stress sensitive axis, V=(V x , V y , V z ) represents the three-dimensional vibration direction vector.

[0027] A further technical solution of the present invention is: the fixed grating film, the movable grating film and the vibration sensitive film are all chromium film layers and platinum film layers from bottom to top, and a dielectric multilayer film with alternating low and high refractive indices is plated on the surface of the platinum film layer to improve the reflectivity of the metal film and enhance the sensitivity of the sensor.

[0028] A further technical solution of the present invention is that the area of the I-shaped cavity is larger than the area of the floating element and the depth is 10-20 μm, so as to realize the XY axial displacement and normal vibration of the floating element.

[0029] A vibration-resistant optical wall shear stress microsensor measurement system, comprising:

[0030] Light source, including an LED light source for shear stress measurement and a laser light source for vibration measurement;

[0031] Optical switches, including a 1×2 optical switch for shear stress measurement and a 1×4 optical switch for vibration measurement;

[0032] Fiber optic couplers, including a 1×2 coupler for shear stress measurement and a 1×4 coupler for vibration measurement;

[0033] A photodetector, used to convert the reflected light signal into an electrical signal;

[0034] Data collector, used to synchronously collect and demodulate shear stress and vibration parameters;

[0035] The optical switch selects the shear stress or vibration measurement channel through split-time optical multiplexing technology. The reflected light signal is aggregated by the optical fiber coupler and transmitted to the photodetector to form an electrical signal carrying displacement information. The real-time suppression of vibration interference is achieved through four-quadrant directional solution and dynamic compensation.

[0036] A further technical solution of the present invention is: the time-sharing optical path multiplexing technology switches the measurement channels within a microsecond time window through a high-speed optical switch, so that the shear stress and vibration signals are collected in a time-sharing manner on the same photodetector, and the crosstalk between channels is eliminated through the phase-locked amplification technology.

[0037] Beneficial effects

[0038] The beneficial effects of the present invention are as follows: the present invention combines shear stress and vibration into the same microsensor through an optical measurement method, breaking through the limitations of traditional single parameter detection and realizing the fusion measurement of wall shear stress and vibration signals. The vibration sensitive membrane is arranged in a four-element orthogonal circumferential array and works synergistically with the grating film structure to improve the sensor's adaptability to complex working conditions, effectively solve the problem of shear stress measurement distortion caused by vibration interference, and can realize in-situ data correction, providing more comprehensive data support for fluid-solid coupling analysis, and improving the system's reliability and measurement accuracy in extreme environments. The specific advantages are analyzed as follows:

[0039] 1. This invention integrates a vibration-sensitive membrane arranged in a four-element orthogonal circumferential array with a grating film structure into a single sensor, achieving simultaneous detection of shear stress and three-dimensional vibration signals. The vibration-sensitive membrane calculates the vibration direction vector (X / Y / Z axis components and the resulting vector) based on differential signals, while the grating film captures shear stress displacement through light intensity modulation. These two work together to overcome the limitations of traditional single-parameter detection and provide comprehensive data support for fluid-structure interaction analysis.

[0040] 2. The present invention introduces a dynamic anti-interference shear stress correction module, which uses the vibration direction vector to project onto the shear stress sensitive axis and combines it with a low-pass filtering algorithm to separate and compensate for vibration coupling errors in real time, significantly improving the measurement accuracy and stability in complex vibration environments.

[0041] 3. This invention uses split-wave optical multiplexing technology to time-share the shear stress and vibration measurement channels via a high-speed optical switch, allowing the two types of signals to share the same photodetector, significantly reducing the number of light sources and detectors. This eliminates the redundant architecture of traditional multi-channel sensors, which require independent configuration of light sources and photodetectors, and successfully achieves miniaturized, low-power system integration. It can simultaneously extract the dynamic characteristics of shear stress and vibration, solving problems such as optical crosstalk during simultaneous multi-parameter measurement. This provides an efficient and compact solution for real-time, in-situ detection in aerospace and other fields, with significant economic benefits and engineering application value.

[0042] 4. Based on the differential signals of a four-element orthogonal vibration-sensitive membrane, this invention calculates the three-dimensional vibration direction angles (pitch and yaw) and the unit direction vector, accurately characterizing the spatial directivity of the vibration. For example, by calculating the X / Y axis components by differentially calculating the membrane signals in the positive and negative directions of the X / Y axis, and combining the average values to extract the normal component, this allows for precise identification of the vibration direction and localization of the interference source.

[0043] 5. The grating film and vibration sensitive film of the present invention adopt a chromium / platinum multilayer film structure, for example, the surface is plated with an Al2O3 / ZrO2 alternating dielectric film, which greatly improves the reflectivity.

[0044] 6. Through compact integration and real-time in-situ correction capabilities, this invention provides an efficient, low-cost solution for aerospace, fluid dynamics, and other fields. For example, deploying a sensor array on the surface of an aircraft engine blade can monitor aerodynamic shear stress and structural vibration in real time, optimizing design and extending component life. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a top view of the sensitive structure layer in an embodiment of the present invention;

[0046] Figure 2 A bottom view of the sensitive structure layer in an embodiment of the present invention;

[0047] Figure 3 This is a schematic diagram of the XY axis direction of the sensitive structure layer in an embodiment of the present invention;

[0048] Figure 4 2 is a cross-sectional view of an optical wall shear stress microsensor resistant to vibration interference according to an embodiment of the present invention;

[0049] Figure 5 is a top view of the base layer in an embodiment of the present invention;

[0050] Figure 6 Schematic diagram of the shear stress measurement portion of the vibration-resistant optical wall shear stress microsensor measurement system according to an embodiment of the present invention;

[0051] Figure 7 Schematic diagram of the vibration measurement portion of the vibration-interference-resistant optical wall shear stress microsensor measurement system according to an embodiment of the present invention;

[0052] Explanation of the accompanying symbols: 1. Elastic beam; 2. Floating element; 3. Etching area; 4. Fixed anchor point; 5. Vibration sensitive membrane; 6. Movable grating film; 7. Sensitive structure layer; 8. Base layer; 9. Fixed grating film; 10. Cavity. DETAILED DESCRIPTION

[0053] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0054] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0055] Traditional solutions require a separate light source and multiple photodetectors for each sensing unit, which not only significantly increases system volume and power consumption but also limits the feasibility of high-density integration due to optical crosstalk. The present invention provides an optical wall shear stress microsensor that is resistant to vibration interference, comprising a MEMS chip module, a four-quadrant vibration-sensitive membrane mounted on the MEMS chip module, and a dynamic anti-interference shear stress correction module. The four-quadrant vibration-sensitive membrane is arranged in a four-element orthogonal circumferential array on the lower surface of a floating element of the MEMS chip module and is located outside a movable grating film on the lower surface of the floating element. Under the action of shear stress or vibration, the floating element drives the movable grating film and the four-quadrant vibration-sensitive membrane to displace. The reflected light signal is transmitted to the photodetector via an optical switch and a fiber coupler, which outputs decoupled shear stress and vibration parameters.

[0056] The dynamic anti-interference shear stress correction module projects the vibration vector of the four-quadrant vibration sensitive membrane onto the sensitive axis direction of the shear stress microsensor, extracts the vibration interference component along the shear stress measurement direction, and combines the low-pass filtering algorithm to compensate for the vibration coupling error in the shear stress signal in real time to complete the anti-interference calculation of the shear stress.

[0057] Specifically, the MEMS chip module includes a base layer with an I-shaped cavity and a sensitive structure layer placed thereon, wherein a fixed grating film is provided on the bottom surface of the I-shaped cavity; a floating element is provided on the sensitive structure layer at a position opposite to the I-shaped cavity, and the floating element is connected to a fixed anchor point on the sensitive structure layer through circumferentially distributed elastic beams, and a movable grating film is provided on its lower surface, opposite to the fixed grating film.

[0058] Specifically, the fixed grating film and the movable grating film are respectively arranged at the center of the upper surface of the base layer and the center of the lower surface of the floating element along the axisymmetric center line.

[0059] Specifically, the vibration vector solution process of the four-quadrant vibration sensitive membrane is as follows:

[0060] The X-axis vibration component Vx is calculated by the signal difference of the vibration sensitive film in the positive and negative directions of the X-axis, and the Y-axis vibration component Vy is calculated by the signal difference of the vibration sensitive film in the positive and negative directions of the Y-axis;

[0061] The normal Z-axis vibration component Vz is calculated by averaging the four signals of the four-quadrant vibration sensitive membrane;

[0062] Calculate the three-dimensional composite vibration amplitude and three-dimensional vibration direction angle based on the X, Y, and Z axis vibration components Vx, Vy, and Vz;

[0063] The vibration vector is normalized to generate a unit direction vector, which is used to represent the main direction of the vibration.

[0064] Specifically, the anti-interference calculation steps of the shear stress are as follows:

[0065] The original shear stress signal is obtained by the difference of the two grating signals;

[0066] Calculate the three-dimensional vibration direction vector based on the X, Y, and Z axis vibration components Vx, Vy, and Vz;

[0067] Based on the three-dimensional vibration direction vector and the three-dimensional synthetic vibration amplitude, the projection component of the vibration direction vector on the shear stress sensitive axis is calculated;

[0068] Perform low-pass filtering on the projection component to suppress high-frequency noise;

[0069] The original shear stress signal is adjusted by filtering the vibration interference signal to dynamically correct the shear stress signal. The expression is as follows:

[0070] S corrected =S raw -α×v proj_filtered

[0071] Where S corrected represents the compensated shear stress signal, S raw represents the original shear stress signal, α represents the compensation coefficient, which controls the influence of vibration interference, and v proj_filtered Represents the vibration interference signal after filtering.

[0072] Specifically, the calculation formula for the projection component of the vibration direction vector on the shear stress sensitive axis is as follows:

[0073] v proj =V·S×V norm

[0074] Where, v proj Represents the vibration interference component obtained by projection, V norm represents the three-dimensional composite vibration amplitude, S represents the shear stress sensitive axis, V=(V x , V y , V z ) represents the three-dimensional vibration direction vector.

[0075] Specifically, the fixed grating film, movable grating film and vibration sensitive film are all composed of chromium film layers and platinum film layers from bottom to top, and a dielectric multilayer film with alternating low and high refractive indices is plated on the surface of the platinum film layer to improve the reflectivity of the metal film and enhance the sensitivity of the sensor.

[0076] Specifically, the area of the I-shaped cavity is larger than the area of the floating element, and the depth is 10-20 μm, so as to achieve XY axial displacement and normal vibration of the floating element.

[0077] The present invention provides a vibration-resistant optical wall shear stress microsensor measurement system, comprising:

[0078] Light source, including an LED light source for shear stress measurement and a laser light source for vibration measurement;

[0079] Optical switches, including a 1×2 optical switch for shear stress measurement and a 1×4 optical switch for vibration measurement;

[0080] Fiber optic couplers, including a 1×2 coupler for shear stress measurement and a 1×4 coupler for vibration measurement;

[0081] A photodetector, used to convert the reflected light signal into an electrical signal;

[0082] Data collector, used to synchronously collect and demodulate shear stress and vibration parameters;

[0083] The optical switch selects the shear stress or vibration measurement channel through split-time optical multiplexing technology, and the reflected light signal is aggregated by the optical fiber coupler and transmitted to the photodetector, and the real-time suppression of vibration interference is achieved through four-quadrant directionality solution and dynamic compensation.

[0084] Specifically, the time-sharing optical multiplexing technology switches the measurement channels within a microsecond time window through a high-speed optical switch, so that the shear stress and vibration signals are collected on the same photodetector in a time-sharing manner, and the crosstalk between channels is eliminated through the phase-locked amplification technology.

[0085] The working principle of the sensor of the present invention using the above technical solution is as follows:

[0086] The optical wall shear stress microsensor operates based on the principle of light intensity modulation. A floating element acts as the primary flow interface and provides a surface for the fluid wall shear stress to act on. Two incoherent light beams are injected into the device through an optical fiber, reflected by two sets of gratings, and then returned to the optical fiber. As the floating element deflects along the flow direction, the overlap area of one set of gratings decreases, reducing the reflected light intensity, while the overlap area of the other set of gratings increases, increasing the reflected light intensity. The differential change in the light intensity of the two sets of gratings is analyzed through photoelectric signal processing to characterize the shear stress value.

[0087] Optical vibration microsensors operate based on the principle of optical leverage. When the sensor is operating, light from a laser light source, emitted from an optical fiber, is reflected by a vibration-sensitive membrane. As the fluid vibrates against the wall, the membrane undergoes normal displacement. The reflection path of the light beam on the membrane changes accordingly, and the reflected light is recollected by the optical fiber. The displacement of the membrane causes a linear change in the radial distance of the reflected light from the axis, resulting in a linear change in the light intensity. The sensor accurately measures the vibration value by detecting this change in light intensity.

[0088] The above technical solution is further described below with reference to the accompanying drawings:

[0089] In one embodiment, reference Figure 4 As shown in the figure, this embodiment of a vibration-resistant optical wall shear stress microsensor includes a base layer 8, a fixed grating film 9, a movable grating film 6, a vibration-sensitive film 5, and a sensitive structural layer 7, arranged sequentially along the optical path. An optical signal is transmitted via the base layer 8 to the sensitive structural layer 7, where it is reflected by the fixed grating film 9 and the movable grating film 6, carrying the displacement. The reflected optical signal is then transmitted to a photodetector via an optical switch and a fiber coupler. The photodetector converts the optical signal into an electrical signal, thereby obtaining displacement information used to calculate shear stress and vibration.

[0090] Reference Figure 1As shown, the floating element 2 has a square structure, and its edges are connected to the fixed anchor points 4 through four groups of symmetrically distributed folded elastic beams 1, which can drive the movable grating film 6 and the vibration sensitive film 5 installed on the lower surface of the floating element 2 to generate displacement and vibration.

[0091] Optionally, when the wall shear stress acts along the fluid flow direction, the floating element 2 generates a lateral translation parallel to the wall along the fluid flow direction through the bending deformation of the elastic beam 1 .

[0092] Optionally, under external vibration excitation, the floating element 2 may move up and down perpendicular to the wall surface, and the amplitude of the movement is directly related to the vibration acceleration.

[0093] Optionally, the cross-sectional shape of the elastic beam 1 can be an I-shape, an L-shape, etc., to reduce the equivalent stiffness in the direction of shear stress, so that a small external force can drive a significant displacement; while maintaining a high stiffness in the non-sensitive direction to suppress interference coupling.

[0094] Optionally, fixed anchor points 4 are symmetrically arranged at the four corners of the floating element 2 to construct an orthogonal constraint system, with two diagonal fixed anchor points mainly controlling lateral motion constraints and the other two diagonal fixed anchor points taking on normal limitations.

[0095] Optionally, the etched area 3 provides a movement space for the floating element 2 and the elastic beam 1 to act along the fluid flow direction, and the width of the etched area 3 should be greater than the maximum theoretical displacement value of the floating element 2 .

[0096] In one embodiment, reference Figure 2 As shown, the vibration sensitive film 5 is arranged on the lower surface of the floating element 2 in a four-element orthogonal circumferential array, forming a four-quadrant symmetrical measurement structure for synchronously detecting the lateral and normal vibration response signals; the movable grating film 6 is arranged at the center of the lower surface of the floating element 2 along the axial symmetry center line.

[0097] Optionally, the vibration sensitive film 5 and the movable grating film 6 are sequentially formed of a chromium film layer and a platinum film layer from bottom to top, the thickness of the chromium film layer is 20-50 nm, and the thickness of the platinum film layer is 300-500 nm.

[0098] Optionally, in order to enhance the reflectivity of the vibration sensitive film 5 and the movable grating film 6, a dielectric multilayer film with alternating low and high refractive indices can be plated on the surface of the metal film layer, in the order of low refractive medium layer / high refractive medium layer / low refractive medium layer / high refractive medium layer, and the thickness of each layer is λ / 4.

[0099] Optionally, the low-refractive dielectric layer of the dielectric multilayer film is Al2O3, and the high-refractive dielectric layer is ZrO2, which is 120nmAl2O3 / 100nmZrO2 / 120nmAl2O3 / 100nmZrO2 in sequence.

[0100] Optionally, the area of the vibration sensitive film 5 and the movable grating film 6 should be larger than the projection area of the optical fiber end face to ensure complete reception and reflection of the optical signal.

[0101] Optionally, the regional edges of the vibration sensitive film 5 and the movable grating film 6 should be more than 500 μm away from the regional edges of the floating element 2 to ensure the integrity of the vibration sensitive film 5 and the movable grating film 6 .

[0102] In one embodiment, reference Figure 4 As shown, the sensitive structural layer 7 serves as the core sensing unit, synchronously converting wall shear stress and vibration into optical signal changes. The movable grating film 6 and vibration-sensitive membrane 5 achieve dual-parameter decoupled measurement, ensuring high-precision detection and system stability. The base layer 8, the structural foundation of the sensor, performs both mechanical support and optical transmission. As the optical signal transmission medium, its highly transparent surface enables efficient transmission of incident light, ensuring long-term reliable operation of the measurement system.

[0103] Optionally, the thickness of the sensitive structure layer 7 should be 100-150 nm, and the thickness of the base layer 8 should be 250-300 nm.

[0104] Optionally, the material of the sensitive structural layer 7 may be a semiconductor material such as silicon, silicon carbide, or sapphire, and the base layer 8 should be a transparent material such as quartz or sapphire.

[0105] Optionally, the wafer is connected to the sensitive structure layer 7 and the base layer 8 by metal hot pressing bonding or laser welding technology, and the thickness of the wafer after connection is 350-450um.

[0106] In one embodiment, reference Figure 5 As shown, an I-shaped cavity 10 is provided on the upper surface of the base layer 8, and a fixed grating film 9 is provided on the upper surface of the cavity.

[0107] Optionally, the area of the cavity 10 should be larger than that of the floating element 2 to ensure that the floating element 2 acts along the direction of fluid flow.

[0108] Optionally, the depth of the cavity 10 should be 10-20 μm to ensure that the floating element 2 can move up and down perpendicular to the wall.

[0109] Optionally, the fixed grating film 9 is arranged at the center of the upper surface of the cavity 10 along the axisymmetric center line to ensure that it overlaps with a partial area of the movable grating 6 .

[0110] Optionally, the fixed grating film 9 is composed of a chromium film layer and a platinum film layer from bottom to top, the thickness of the chromium film layer is 20-50 nm, and the thickness of the platinum film layer is 300-500 nm.

[0111] In one embodiment, reference Figure 3 As shown, in this embodiment, to achieve directional resolution of signals from four-quadrant vibration-sensitive membranes, the vibration direction is identified through vector decomposition and normalization, based on the principle of vector synthesis. This algorithm takes the light intensity change signals from four orthogonally distributed vibration-sensitive membranes as input and calculates the transverse (X-axis) and longitudinal (Y-axis) vibration components. Specifically, by differentially calculating the signals from the upper and lower membranes and the left and right membranes, the vibration components in the X- and Y-axis directions are extracted. The common-mode normal (Z-axis) component is then calculated by combining the average of the four membrane signals, thereby constructing a composite vibration vector in three-dimensional space.

[0112] Specifically, the azimuth angle of the composite vibration vector in the horizontal plane, as well as the unit direction vector, are calculated to accurately characterize the main direction and amplitude of the vibration. This approach not only effectively identifies the spatial direction of vibration but also provides core data support for vibration direction calculation, thereby decoupling and compensating for vibration interference signals, thereby improving the accuracy and robustness of shear stress measurements, especially in complex flow and high vibration environments.

[0113] The core idea of this algorithm is to use four orthogonally distributed vibration-sensitive membranes to construct a two-dimensional differential model. By differential operations on the upper and lower and left and right membrane signals, the transverse and longitudinal vibration components are extracted; at the same time, the normal common-mode vibration component is obtained by calculating the average value of the four membrane signals. In essence, the algorithm converts the local normal vibration response into a global three-dimensional vibration vector solution problem, and uses the projection relationship of the vibration direction on each sensitive membrane to derive the spatial directionality of the vibration. Ultimately, the algorithm can calculate the direction angle and unit direction vector of the vibration vector in the horizontal plane, providing a mathematical basis for subsequent vibration direction identification, shear stress decoupling compensation, and flow disturbance analysis. The specific calculation process is as follows:

[0114] Step 1: Calculate the X-axis component of vibration (Vx)

[0115] The vibration component in the X-axis direction is obtained by taking the difference between the left and right direction signals. The expression is as follows:

[0116]

[0117] Where V x- Indicates the signal of the vibration sensitive film in the negative direction of the x-axis, V x- The signal representing the vibration of the sensitive membrane in the positive x-axis direction; the difference between the positive and negative x-axis signals represents the intensity of the vibration in the x-axis direction. The differential method is used because the membrane on the positive and negative x-axis sides is symmetrical, and the difference reflects the vibration in the x-direction.

[0118] Step 2: Calculate the Y-axis component of vibration (Vy)

[0119] The vibration component in the Y-axis direction is obtained by taking the difference between the up and down direction signals. The expression is as follows:

[0120]

[0121] Where V y+ Indicates the signal (voltage change) of the sensitive film vibrating in the positive direction of the y-axis, V y- The difference between the positive and negative y-axis signals represents the vibration intensity along the Y-axis. Similarly, differential calculations can reveal the symmetrical vibration characteristics of the upper and lower diaphragms.

[0122] Step 3: Calculate the normal vibration component (Vz)

[0123] Calculate the average value of the four signals to obtain the common mode vibration component in the normal direction (Z axis). The expression is as follows:

[0124]

[0125] The normal vibration component represents the vibration perpendicular to the four diaphragm planes and is usually caused by an external vibration source in the environment. A comprehensive normal signal can be obtained by calculating the average value thereof.

[0126] Step 4: Calculate the three-dimensional composite vibration amplitude (V norm )

[0127] The three-dimensional composite vibration amplitude is calculated based on the vibration components in the X, Y, and Z directions. The expression is as follows:

[0128]

[0129] The composite vibration amplitude represents the total intensity of the vibration, integrating the vibration information in all directions.

[0130] Step 5: Calculate the three-dimensional vibration angles: pitch and yaw

[0131] Pitch angle: The angle of the vibration direction relative to the Z axis

[0132] The pitch angle is usually defined as the angle between the vibration vector and the Z axis, which can be calculated using the following formula:

[0133]

[0134] Yaw angle (yaw): the angle of vibration direction in the XY plane

[0135] The yaw angle is calculated on the XY plane and represents the rotation angle of the vibration direction relative to the X axis. The formula is:

[0136] θ yaw=arctan2(V y , V x )

[0137] Step 6: Calculate the unit direction vector

[0138] The purpose is to normalize the vibration vector so that the length of the vector is 1, which can only represent the direction information without being affected by the vibration amplitude.

[0139]

[0140] Where,

[0141] Based on the signals of four orthogonally distributed vibration-sensitive membranes, the direction vector and amplitude of the vibration in three-dimensional space are calculated in real time to obtain complete vibration vector information. By projecting the vibration vector in the direction of the sensitive axis of the shear stress sensor, the vibration interference component along the shear stress measurement direction is extracted and used as an interference term for subsequent compensation. The method steps are as follows: First, the two grating output signals of the shear stress sensor are differentiated to obtain the original shear stress signal containing the vibration disturbance. Subsequently, the algorithm solves the effective projection of the vibration interference on the shear stress measurement axis based on the dot product relationship between the vibration direction vector and the shear stress direction unit vector obtained by the above solution, and establishes a corresponding compensation model. By deducting the projection component from the original shear stress signal, directional suppression and real-time compensation of the vibration interference are achieved, thereby obtaining a high-precision shear stress output.

[0142] In order to further improve the robustness and signal stability of the compensation results, a first-order or second-order low-pass filter is introduced into the algorithm to filter the vibration projection component and suppress the measurement fluctuations caused by high-frequency noise and system oscillation.

[0143] In summary, this algorithm effectively separates vibration interference from shear stress signals by integrating vector decoupling and signal filtering, starting from the signal source. Its clear structure and high computational efficiency allow it to adapt to multi-directional vibration scenarios and any configuration of shear stress-sensitive axes. It is suitable for real-time processing tasks on embedded platforms and is an ideal compensation mechanism for complex vibration-shear stress coupling environments. The specific calculation process is as follows:

[0144] Step 1: Calculation of the original shear stress signal:

[0145] The original shear stress signal is obtained from the grating signal of the sensor. The original shear stress value S is obtained by the difference between the two grating signals. raw :

[0146] S raw =V1-V2

[0147] Where V1 and V2 are the output voltages of the two grating sensors. This signal contains both shear stress and vibration interference.

[0148] Step 2: Calculate the three-dimensional vibration direction vector based on the X, Y, and Z axis vibration components Vx, Vy, and Vz;

[0149] Three-dimensional vibration direction vector V=(V x , V y , V z );

[0150] Step 3: Projection of Vibration Interference

[0151] Based on the known vibration direction, the projection of the vibration direction vector on the shear stress sensitive axis is further calculated. Assuming that the shear stress sensitive axis is S, the component of the vibration interference can be obtained by calculating the dot product of the vibration direction vector and the shear stress direction:

[0152] v proj =V·S×V norm

[0153] Where, v proj is the vibration interference component obtained by projection, V norm is the amplitude of the vibration direction vector.

[0154] Step 4: Filtering of vibration interference

[0155] To suppress high-frequency noise and stabilize the compensation results, the algorithm introduces a low-pass filter to filter the vibration interference signal. By designing a low-pass filter (such as a Butterworth filter), interference components with frequencies above the preset cutoff frequency are removed, improving the stability of the compensation results.

[0156] Step 5: Vibration Compensation

[0157] The vibration interference signal after filtering will be used to adjust the original shear stress signal. The specific compensation method is:

[0158] S corrected =S raw -α×v proj_filtered

[0159] Where S correcte represents the compensated shear stress signal, S raw represents the original shear stress signal, α represents the compensation coefficient, which controls the influence of vibration interference, and v proj_filtered Represents the vibration interference signal after filtering.

[0160] In one embodiment, reference Figure 6As shown, the light source of the shear stress measurement part should be an LED light source. The light signal is transmitted to the movable grating film 6 and the fixed grating film 9 of the microsensor through the corresponding channel selected by the optical switch. The reflected light is transmitted to the photodetector through the optical fiber coupler to form an electrical signal carrying displacement information, which is collected and demodulated by the data collector to obtain the shear stress.

[0161] Optionally, the LED light source can generate a stable multi-mode optical signal with a wavelength of 850 nm, and the optical signal is transmitted using a multi-mode optical fiber.

[0162] Optionally, the optical switch of the shear stress measurement part is a 1×2 optical switch, and the optical fiber coupler of the shear stress measurement part is a 1×4 optical fiber coupler.

[0163] In one embodiment, reference Figure 7 As shown, the light source of the vibration measurement part should be a laser light source. The optical signal is transmitted to the vibration sensitive membrane 5 of the microsensor through the corresponding channel selected by the optical switch. The reflected light is transmitted to the photodetector through the optical fiber coupler to form an electrical signal carrying displacement information, which is collected and demodulated by the data collector to obtain the vibration information.

[0164] Optionally, the laser light source can generate a stable optical signal with a single-mode wavelength of 1550 nm, and the optical signal is transmitted using a single-mode optical fiber.

[0165] Optionally, the optical switch of the vibration measurement part is a 1×4 optical switch, and the optical fiber coupler of the shear stress measurement part is a 1×4 optical fiber coupler.

[0166] Optionally, the shear stress measurement section and the vibration measurement section can be integrated into the same measurement system to ensure miniaturized and low-power system integration.

[0167] Alternatively, split-wave optical multiplexing (SOD) technology achieves multifunctional detection using a single optical path through time division. The system utilizes a high-speed optical switch to switch measurement channels at different times, staggering the transmission of optical signals for shear stress or vibration measurement. For example, the optical switch connects the LED light source to one set of gratings during the first half of the cycle and to another set of gratings during the second half. This allows the two types of signals to share the same set of photodetectors without interfering with each other. This technology overcomes the limitation of traditional multi-sensor independent optical paths, enabling compact integration while ensuring measurement synchronization.

[0168] According to the present invention, an optical wall shear stress microsensor and its measurement system that are resistant to vibration interference, on the one hand, combines shear stress and vibration onto the same microsensor through an optical measurement method, breaking through the limitations of traditional single parameter detection and realizing the fusion measurement of wall shear stress and vibration signals. The vibration sensitive membrane is arranged in a four-element orthogonal circumferential array and works in synergy with the grating film structure, which improves the adaptability of the sensor to complex working conditions, effectively solves the problem of shear stress measurement distortion caused by vibration interference, can realize in-situ correction of data, provides more comprehensive data support for fluid-solid coupling analysis, and improves the reliability and measurement accuracy of the system in extreme environments. On the other hand, the measurement system solves the redundant architecture of traditional multi-channel sensors that require independent configuration of light sources and photodetectors through highly integrated optical path design and time-sharing multiplexing technology, and successfully realizes miniaturized and low-power system integration. The dynamic characteristics of shear stress and vibration can be extracted simultaneously, solving problems such as optical path crosstalk in multi-parameter synchronous measurement, providing an efficient and compact solution for real-time, in-situ detection in aerospace and other fields, with significant economic benefits and engineering application value.

[0169] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. An optical wall shear stress microsensor resistant to vibration interference, characterized by: The system comprises a MEMS chip module, a four-quadrant vibration-sensitive membrane mounted on the MEMS chip module, and a dynamic anti-interference shear stress correction module. The four-quadrant vibration-sensitive membrane is arranged in a four-element orthogonal circumferential array on the lower surface of the floating element of the MEMS chip module and is located outside a movable grating film on the lower surface of the floating element. Under the action of shear stress or vibration, the floating element drives the movable grating film and the four-quadrant vibration-sensitive membrane to displace. The reflected light signal is transmitted to a photodetector via an optical switch and a fiber coupler, which outputs decoupled shear stress and vibration parameters. The dynamic anti-interference shear stress correction module projects the vibration vector of the four-quadrant vibration sensitive membrane onto the sensitive axis direction of the shear stress microsensor, extracts the vibration interference component along the shear stress measurement direction, and combines the low-pass filtering algorithm to compensate for the vibration coupling error in the shear stress signal in real time to complete the anti-interference calculation of the shear stress.

2. The optical wall shear stress microsensor resistant to vibration interference according to claim 1, characterized in that: The MEMS chip module includes a base layer with an I-shaped cavity and a sensitive structure layer placed thereon, wherein a fixed grating film is provided on the bottom surface of the I-shaped cavity; a floating element is provided on the sensitive structure layer at a position opposite to the I-shaped cavity, and the floating element is connected to a fixed anchor point on the sensitive structure layer through circumferentially distributed elastic beams, and a movable grating film is provided on its lower surface, opposite to the fixed grating film.

3. The optical wall shear stress microsensor resistant to vibration interference according to claim 2, characterized in that: The fixed grating film and the movable grating film are respectively arranged at the center of the upper surface of the base layer and the center of the lower surface of the floating element along the axisymmetric center line.

4. The optical wall shear stress microsensor resistant to vibration interference according to claim 3, characterized in that: The vibration vector solution process of the four-quadrant vibration sensitive membrane is as follows: The X-axis vibration component Vx is calculated by the signal difference of the vibration sensitive film in the positive and negative directions of the X-axis, and the Y-axis vibration component Vy is calculated by the signal difference of the vibration sensitive film in the positive and negative directions of the Y-axis; The normal Z-axis vibration component Vz is calculated by averaging the four signals of the four-quadrant vibration sensitive membrane; Calculate the three-dimensional composite vibration amplitude and three-dimensional vibration direction angle based on the X, Y, and Z axis vibration components Vx, Vy, and Vz; The vibration vector is normalized to generate a unit direction vector, which is used to represent the main direction of the vibration.

5. The optical wall shear stress microsensor resistant to vibration interference according to claim 4, characterized in that: The specific steps of the anti-interference calculation of the shear stress are as follows: The original shear stress signal is obtained by the difference of the two grating signals; Calculate the three-dimensional vibration direction vector based on the X, Y, and Z axis vibration components Vx, Vy, and Vz; Based on the three-dimensional vibration direction vector and the three-dimensional synthetic vibration amplitude, the projection component of the vibration direction vector on the shear stress sensitive axis is calculated; Perform low-pass filtering on the projection component to suppress high-frequency noise; The original shear stress signal is adjusted by filtering the vibration interference signal to dynamically correct the shear stress signal. The expression is as follows: S corrected =S raw -α×v proj_filtered Where S corrected represents the compensated shear stress signal, S raw represents the original shear stress signal, α represents the compensation coefficient, which controls the influence of vibration interference, and v proj_filtered Represents the vibration interference signal after filtering.

6. The optical wall shear stress microsensor resistant to vibration interference according to claim 5, characterized in that: The calculation formula for the projection component of the vibration direction vector on the shear stress sensitive axis is as follows: v proj =V·S×V norm Where, v proj Represents the vibration interference component obtained by projection, V norm represents the three-dimensional composite vibration amplitude, S represents the shear stress sensitive axis, V=(V x , V y , V z ) represents the three-dimensional vibration direction vector.

7. The optical wall shear stress microsensor resistant to vibration interference according to claim 3, characterized in that: The fixed grating film, movable grating film and vibration sensitive film are all chromium film layers and platinum film layers from bottom to top, and a dielectric multilayer film with alternating low and high refractive indices is plated on the surface of the platinum film layer to improve the reflectivity of the metal film and enhance the sensitivity of the sensor.

8. The vibration-resistant optical wall shear stress microsensor according to claim 1, characterized in that: The area of the I-shaped cavity is larger than that of the floating element, and the depth is 10-20 μm, so as to realize XY axial displacement and normal vibration of the floating element.

9. A vibration-resistant optical wall shear stress microsensor measurement system according to any one of claims 1 to 8, characterized in that include: Light source, including an LED light source for shear stress measurement and a laser light source for vibration measurement; Optical switches, including a 1×2 optical switch for shear stress measurement and a 1×4 optical switch for vibration measurement; Fiber optic couplers, including a 1×2 coupler for shear stress measurement and a 1×4 coupler for vibration measurement; A photodetector, used to convert the reflected light signal into an electrical signal; Data collector, used to synchronously collect and demodulate shear stress and vibration parameters; The optical switch selects the shear stress or vibration measurement channel through split-time optical multiplexing technology. The reflected light signal is aggregated by the optical fiber coupler and transmitted to the photodetector to form an electrical signal carrying displacement information. The real-time suppression of vibration interference is achieved through four-quadrant directional solution and dynamic compensation.

10. The vibration-resistant optical wall shear stress microsensor measurement system according to claim 9, characterized in that: The time-sharing optical multiplexing technology switches the measurement channels within a microsecond time window through a high-speed optical switch, so that the shear stress and vibration signals are collected on the same photodetector in a time-sharing manner, and the crosstalk between channels is eliminated through the phase-locked amplification technology.

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