An optical fiber flow velocity sensor based on the cursor effect and its measurement method

Abstract

The present invention discloses an optical fiber flow velocity sensor based on the Vernier effect and a measurement method thereof, comprising: an artificial cilia cantilever beam, an elastic support structure, and an optical fiber strain sensing module; one end of the artificial cilia cantilever beam is inserted into the elastic support structure, and the other end is exposed to the fluid. There are multiple relatively arranged optical fiber strain sensing modules inside the elastic support structure, and the outside of the elastic support structure is wrapped with a packaging shell; the exposed end of the artificial cilia cantilever beam deforms under the flow field, and at the same time drives the lower end to deform, so that the cavity length of the optical fiber resonator in the optical fiber strain sensing module changes. The spectra of the relatively arranged optical fiber resonators can be superimposed to generate a superimposed spectrum with a Vernier envelope. The sensor of the present invention not only has the ability to resist interference and seawater corrosion, but also can greatly increase the sensitivity of measuring the flow velocity and direction of the fluid by using the Vernier enhancement effect.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber sensors, and particularly to an optical fiber flow velocity sensor based on the Vernier effect and a measurement method thereof. Background Art

[0002] Traditional water flow sensors can be divided into gear mechanical tachometers, hot wire sensors, electromagnetic current meters, Doppler laser velocimeters, acoustic velocimeters, particle image velocimeters, etc. Most of these sensing devices are large in size and high in cost, require complex equipment and installation environments, or need additional auxiliary devices to measure the fluid direction. On the one hand, they cannot meet the increasing requirements of digital, intelligent, and arrayed ocean detection network construction. On the other hand, it is difficult to be conveniently integrated into exploration or operation equipment for real-time sensing.

[0003] Inspired by the structure of hair cells, researchers have successfully developed various artificial hair cell water flow sensors using microelectromechanical systems. However, for such sensor devices that need to be immersed in seawater for a long time, microelectromechanical sensors still need to overcome problems such as device damage or instability caused by the strong conductivity of seawater, or limited service life caused by strong corrosion. Currently, there have been some studies on using optical fiber sensors for water flow sensing in the prior art, but most of them are mechanical sensing systems with optical fibers as cantilever beams, or heat conduction sensing systems based on the principle of heat exchange, and do not have the ability to sense the water flow direction. Summary of the Invention

[0004] The present invention provides an optical fiber flow velocity sensor based on the Vernier effect and a measurement method thereof to overcome the problems of low sensitivity, weak corrosion resistance, and inability to sense the water flow direction of traditional optical fiber sensors.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] An optical fiber flow velocity sensor based on the Vernier effect, comprising: an artificial cilia cantilever beam, an elastic support structure, an optical fiber strain sensing module, and a packaging shell;

[0007] One end of the artificial cilia cantilever beam is inserted into the elastic support structure, and the other end is exposed to the fluid. There are multiple oppositely arranged optical fiber strain sensing modules inside the elastic support structure, and the optical fiber strain sensing modules are horizontally arranged. The elastic support structure is externally wrapped with the packaging shell;

[0008] The optical fiber strain sensing module includes: a packaging capillary, a first single-mode optical fiber, a second single-mode optical fiber, a hard fixing glue, and an elastic fixing glue;

[0009] One end of the encapsulated capillary is provided with an elastic fixing glue, and the elastic fixing glue is in interference fit with the lower part of the artificial cilia cantilever beam; the other end is provided with the hard fixing glue, and the hard fixing glue abuts against the encapsulation shell;

[0010] A through hole is arranged inside the encapsulated capillary, and the second single-mode optical fiber is connected with the elastic fixing glue and arranged in the through hole; one end of the first single-mode optical fiber passes through the hard fixing glue and is inserted into the through hole inside the encapsulated capillary, and the other end is outside the encapsulated capillary. A fiber optic resonator is formed between the first single-mode optical fiber and the second single-mode optical fiber.

[0011] Further, there are four fiber optic strain sensing modules, and the interval angle between any two fiber optic strain sensing modules is 90 degrees. Two fiber optic strain sensing modules on the same straight line form a group of fiber optic strain sensing devices.

[0012] Further, the cavity length range of the fiber optic resonator is 20 to 500 μm.

[0013] Further, the encapsulation shell is of a cylindrical structure, the elastic support structure is of a cylindrical structure with a blind hole in the middle, and the inner diameter of the blind hole matches the outer diameter of the artificial cilia cantilever beam.

[0014] Further, the materials of the artificial cilia cantilever beam and the encapsulation shell are PLA polylactic acid; the materials of the elastic support structure and the elastic fixing glue are soft ultraviolet curable resins, and the chemical component is acrylate; the material of the hard fixing glue is a hard ultraviolet curable resin; the material of the encapsulated capillary is glass.

[0015] Further, a measurement method of a fiber optic flow velocity sensor based on the Vernier effect includes the following steps:

[0016] Connect the sensor to a light source and fixedly place it in the flow field to be measured. Calibrate the two fiber optic strain sensing modules on the same straight line as the x-axis, and the other two fiber optic strain sensing modules as the y-axis;

[0017] Connect the two fiber optic strain sensing modules on the x-axis and the two fiber optic strain sensing modules on the y-axis in parallel through a fiber optic coupler and connect them to the light source and the spectrometer at the same time, and then connect the spectrometer to the processor;

[0018] The flow field to be measured causes the lower end of the artificial cilia cantilever beam to deform, so that the cavity length of the fiber optic resonator of one fiber optic strain sensing module on the x-axis increases / decreases, the cavity length of the fiber optic resonator of the other fiber optic strain sensing module on the x-axis decreases / increases, the cavity length of the fiber optic resonator of one fiber optic strain sensing module on the y-axis increases / decreases, and the cavity length of the fiber optic resonator of the other fiber optic strain sensing module on the y-axis decreases / increases;

[0019] The growing / shortening fiber optic resonator on the x-axis generates a modulation signal with Vernier enhancement effect under the action of a light source, and the growing / shortening fiber optic resonator on the y-axis also generates a modulation signal with Vernier enhancement effect under the action of the light source;

[0020] The modulation signal is input into a spectrometer with light wave as the carrier, and the spectrometer demodulates the modulation signal and outputs a Vernier spectrum with a Vernier envelope to a processor;

[0021] The processor processes the data of the Vernier spectrum with the Vernier envelope to obtain information on the flow velocity and direction on the plane of the flow field to be measured.

[0022] Further, the processor processes the data of the Vernier spectrum with the Vernier envelope to obtain information on the flow velocity and direction on the plane of the flow field to be measured, including the following steps:

[0023] Compare the demodulated Vernier spectrum with the static field spectrum to determine the spectral drift amount;

[0024] Substitute the spectral drift amount into the corresponding relationship between the spectral drift amount and the flow velocity to obtain the flow velocities of the flow field in the x-axis and y-axis directions;

[0025] Establish a rectangular coordinate system based on the flow velocities of the flow field in the x-axis and y-axis directions, and perform rectangular vector superposition to finally reconstruct the information on the flow velocity and direction on the plane of the flow field to be measured.

[0026] Further, the static field spectrum and the corresponding relationship are obtained through sensor calibration operations. The sensor calibration operations include the following steps before the sensor is placed in the flow field to be measured:

[0027] Connect the sensor to the light source and fixedly place it in the flow field to be measured and determine the initial position. Calibrate two fiber optic strain sensing modules on the same straight line as the x-axis, and the other two fiber optic strain sensing modules as the y-axis;

[0028] Parallelly connect the two fiber optic strain sensing modules on the x-axis and the two fiber optic strain sensing modules on the y-axis through a fiber optic coupler and connect them to the light source and the spectrometer at the same time, and then connect the spectrometer to the processor;

[0029] The two fiber optic strain sensing modules on the x-axis and the two fiber optic strain sensing modules on the y-axis respectively generate modulation signals, and are demodulated by the spectrometer to obtain the static field spectrum;

[0030] Push the sensor forward and backward at a constant speed along the x-axis and y-axis respectively from the initial position at different propulsion speeds to demodulate multiple groups of Vernier spectra in different directions;

[0031] Compare the multi - group cursor spectra in different directions with the stationary - field spectrum to determine the multi - group spectral drift amounts and the corresponding sensor propulsion speeds;

[0032] In a stationary fluid flow field, the sensor propulsion speed is equal to the fluid flow speed relative to the sensor. Thus, the corresponding relational expressions between the spectral drift amounts and the flow speeds in the x - axis and y - axis directions can be established respectively.

[0033] Advantageous effects: By changing the cavity lengths of multiple pairs of relatively arranged fiber optic resonators, the present invention forms a Vernier effect to measure the fluid flow speed and direction, solving the problem in the prior art that most mechanical sensing systems using optical fibers or thermal conductivity sensing systems based on the principle of heat exchange cannot sense and measure the water flow direction. Brief Description of the Drawings

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following - described drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0035] Figure 1 It is the overall structure diagram of the sensor of the present invention;

[0036] Figure 2 It is the top - view sectional view of the sensor of the present invention;

[0037] Figure 3 It is the front - view sectional view of the sensor of the present invention;

[0038] Figure 4 It is the schematic diagram of different states of the fiber - optic strain sensing module in the sensor of the present invention;

[0039] Figure 5 It is the schematic diagram of the working - state connection of the sensor of the present invention;

[0040] Figure 6 It is the structural diagram of the fiber - optic strain sensing module in the sensor of the present invention;

[0041] Figure 7 It is the simulation diagram of the independent spectra and the superimposed spectrum of the sensor of the present invention with the original cavity lengths of 100μm and 105μm without deformation;

[0042] Figure 8 It is the simulation diagram of the independent spectra and the superimposed spectrum of the sensor of the present invention with the cavity lengths of 95μm and 106μm after deformation;

[0043] Figure 9 It is the simulation diagram of the independent spectra and the superimposed spectrum of the sensor of the present invention with the cavity lengths of 100.1μm and 104.8μm after deformation;

[0044] Figure 10 These are the simulation diagrams of the independent spectra and the superimposed spectra of the comparison cavity lengths of 20 μm and 25 μm of the sensor of the present invention;

[0045] Figure 11 These are the simulation diagrams of the independent spectra and the superimposed spectra of the comparison cavity lengths of 1000 μm and 1005 μm of the sensor of the present invention;

[0046] Figure 12 These are the simulation diagrams of the superimposed spectra and the demodulated envelopes of the comparison cavity lengths of 20 μm and 25 μm of the sensor of the present invention;

[0047] Figure 13 These are the simulation diagrams of the superimposed spectra and the demodulated envelopes of the comparison cavity lengths of 100 μm and 105 μm of the sensor of the present invention;

[0048] In the figure: 1. Artificial cilia cantilever beam; 2. Elastic support structure; 3. Optical fiber strain sensing module; 31. Encapsulation capillary; 32. First single-mode optical fiber; 33. Second single-mode optical fiber; 34. Hard fixing glue; 35. Elastic fixing glue; 4. Encapsulation housing. Detailed implementation manners

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0050] Embodiment 1

[0051] This embodiment provides an optical fiber flow velocity sensor based on the vernier effect, including: an artificial cilia cantilever beam 1, an elastic support structure 2, an optical fiber strain sensing module 3, and an encapsulation housing 4;

[0052] One end of the artificial cilia cantilever beam 1 is inserted into the elastic support structure 2, and the other end is exposed to the fluid. There are multiple oppositely arranged optical fiber strain sensing modules 3 inside the elastic support structure 2, and the optical fiber strain sensing modules 3 are horizontally arranged. The elastic support structure 2 is externally wrapped with the encapsulation housing 4;

[0053] The optical fiber strain sensing module 3 includes: an encapsulation capillary 31, a first single-mode optical fiber 32, a second single-mode optical fiber 33, a hard fixing glue 34, and an elastic fixing glue 35;

[0054] One end of the encapsulated capillary 31 is provided with an elastic fixing glue 35, and the elastic fixing glue 35 is in interference fit with the lower part of the artificial cilia cantilever beam 1; the other end is provided with the rigid fixing glue 34, and the rigid fixing glue 34 abuts against the encapsulation shell 4;

[0055] A through hole is provided inside the encapsulated capillary 31, and the second single-mode optical fiber 33 is connected to the elastic fixing glue 35 and arranged in the through hole; one end of the first single-mode optical fiber 32 passes through the rigid fixing glue 34 and is inserted into the through hole inside the encapsulated capillary 31, and the other end is outside the encapsulated capillary 31. An optical fiber resonant cavity is formed between the first single-mode optical fiber 32 and the second single-mode optical fiber 33.

[0056] There are four optical fiber strain sensing modules 3, and the interval angle between any two optical fiber strain sensing modules 3 is 90 degrees. Two optical fiber strain sensing modules 3 on the same straight line form a group of optical fiber strain sensing devices.

[0057] The cavity length range of the optical fiber resonant cavity is 20 to 500 μm.

[0058] The encapsulation shell 4 is of a cylindrical structure, and the elastic support structure 2 is of a cylindrical structure with a blind hole in the middle. The inner diameter of the blind hole matches the outer diameter of the artificial cilia cantilever beam 1.

[0059] The materials of the artificial cilia cantilever beam 1 and the encapsulation shell 4 are PLA polylactic acid; the materials of the elastic support structure 2 and the elastic fixing glue 35 are soft ultraviolet curing resins, and the chemical composition is acrylate; the material of the rigid fixing glue 34 is a hard ultraviolet curing resin; the material of the encapsulated capillary 31 is glass.

[0060] Specifically, such as Figure 1 、 Figure 2 、 Figure 3As shown in the figure, the artificial cilia cantilever beam 1 is a long strip-shaped elastic structure. Its upper half is exposed to the flow field and deforms under the action of the shear stress of the flow field. At the same time, the lower half buried in the elastic support structure 2 will also deform driven by the deformation of the upper half. The lower half contacts the fiber optic strain sensing module 3, and the outermost layer of the elastic support structure 2 is wrapped with a packaging shell 4. The main body of the fiber optic strain sensing module 3 is a packaged capillary 31. One end of the packaged capillary 31 is sealed with an elastic fixing glue 35, and the other end is provided with a hard fixing glue 34. The hard fixing glue 34 is provided with a round hole, so that a part of the first single-mode optical fiber 32 is inserted into the packaged capillary 31 through the round hole. At the end sealed with the elastic fixing glue 35 inside the tube, there is a second single-mode optical fiber 33. And the part of the artificial cilia cantilever beam 1 buried in the elastic support structure 2 contacts the elastic fixing glue 35 of the fiber optic strain sensing module 3. When the elastic fixing glue 35 deforms, it will drive the second single-mode optical fiber 33 to displace relative to the packaging shell 4, while the first single-mode optical fiber 32 is fixed relative to the packaging shell 4. As Figure 4 shown, the cavity length of the fiber optic resonator formed between the first single-mode optical fiber 32 and the second single-mode optical fiber 33 changes.

[0061] Specifically, there are four fiber optic strain sensing modules 3, as Figure 6 shown, which are arranged horizontally in a cross shape in the elastic support structure 2, that is, the included angle between every two adjacent fiber optic strain sensing modules 3 is 90 degrees. Every two relatively arranged fiber optic strain sensing modules 3 form a group of fiber optic strain sensing devices. In a group of fiber optic strain sensing devices, when the lower end of the artificial cilia cantilever beam 1 deforms, it will compress the cavity length of the fiber optic resonator in one of the fiber optic strain sensing modules 3. At the same time, the cavity length of the fiber optic resonator in the relatively arranged fiber optic strain sensing module 3 will be stretched. When the peak drift directions of the spectra of the two resonators are opposite, a vernier enhancement effect will be generated. At the same time, the two groups of fiber optic strain sensing devices are connected in parallel through a fiber optic coupler, and the flow direction of the fluid on the plane can be measured more accurately.

[0062] In this embodiment, the materials of the artificial cilia cantilever beam 1 and the encapsulation housing 4 are PLA (polylactic acid), a biodegradable polymer material formed by the polycondensation of lactic acid monomers. It has good seawater corrosion resistance, does not pollute the environment, and has a simple manufacturing method. It can be fabricated by 3D printing. The materials of the elastic support structure 2 and the elastic fixing glue 35 are a single-component soft ultraviolet-curing resin, whose chemical composition is acrylate. It can be cured when irradiated with ultraviolet light at a wavelength of 365 nm. After curing, it still has a certain degree of softness and can cooperate with the artificial cilia cantilever beam 1 to undergo extremely small deformations, enabling the sensor to be in a good and precise working state. The material of the hard fixing glue 34 is a hard ultraviolet-curing resin, a highly rigid epoxy resin that hardly deforms. The hard fixing glue 34 is provided on the inner wall of the encapsulation housing 4 to ensure that the first single-mode optical fiber 32 does not displace relative to the encapsulation housing 4. The combined use of the hard fixing glue 34 and the elastic fixing glue 35 can keep the sensor in a stable working state and make the measurement results more accurate.

[0063] Embodiment 2

[0064] This embodiment provides a measurement method for an optical fiber flow velocity sensor based on the Vernier effect, including the following steps:

[0065] Connect the sensor to a light source and fixedly place it in the flow field to be measured. Calibrate two fiber optic strain sensing modules 3 on the same straight line as the x-axis, and the other two fiber optic strain sensing modules 3 as the y-axis.

[0066] Connect the two fiber optic strain sensing modules 3 on the x-axis and the two fiber optic strain sensing modules 3 on the y-axis in parallel through a fiber optic coupler and connect them to the light source and the spectrometer at the same time. Then connect the spectrometer to the processor.

[0067] The flow field to be measured causes the lower end of the artificial cilia cantilever beam 1 to deform, increasing / decreasing the cavity length of the fiber optic resonator of one fiber optic strain sensing module 3 on the x-axis, decreasing / increasing the cavity length of the fiber optic resonator of the other fiber optic strain sensing module 3 on the x-axis, increasing / decreasing the cavity length of the fiber optic resonator of one fiber optic strain sensing module 3 on the y-axis, and decreasing / increasing the cavity length of the fiber optic resonator of the other fiber optic strain sensing module 3 on the y-axis.

[0068] The increasing / decreasing fiber optic resonator on the x-axis generates a modulation signal with a Vernier enhancement effect under the action of the light source, and the increasing / decreasing fiber optic resonator on the y-axis also generates a modulation signal with a Vernier enhancement effect under the action of the light source.

[0069] The modulation signal is input into the spectrometer with light waves as the carrier. The spectrometer demodulates the modulation signal and outputs a Vernier spectrum with a Vernier envelope to the processor.

[0070] The processor processes the cursor spectrum with the cursor envelope to obtain information on the flow velocity and direction on the plane of the flow field to be measured.

[0071] The steps for the processor to process the cursor spectrum with the cursor envelope to obtain information on the flow velocity and direction on the plane of the flow field to be measured are as follows:

[0072] Compare the demodulated cursor spectrum with the static field spectrum to determine the spectral drift amount;

[0073] Substitute the spectral drift amount into the corresponding relationship between the spectral drift amount and the flow velocity to obtain the flow velocities of the flow field in the x-axis and y-axis directions;

[0074] Establish a rectangular coordinate system based on the flow velocities of the flow field in the x-axis and y-axis directions, and perform rectangular vector superposition to finally reconstruct the information on the flow velocity and direction on the plane of the flow field to be measured.

[0075] Specifically, place the sensor in the flow field to be measured for on-site measurement. Before measurement, first calibrate the two groups of fiber optic strain sensing devices as the x-axis and y-axis. Since the two groups of fiber optic strain sensing devices are arranged perpendicular to each other, any one of them can be arbitrarily selected and calibrated as the x-axis, and the other group is the y-axis; connect the two groups of fiber optic strain sensing devices in parallel through a fiber optic coupler, and connect a light source so that the optical write resonant cavity can generate a modulation signal. After parallel connection, connect a spectrometer to demodulate the signal, and then connect a processor for signal processing; the water flow of the flow field to be measured generates shear stress on the upper end of the artificial cilia cantilever beam 1, and at the same time, the lower end of the artificial cilia cantilever beam 1 will deform in the opposite direction along with the upper end. When the lower end of the artificial cilia cantilever beam 1 deforms, it will drive the displacement of the four second single-mode optical fibers 33 in contact with it, causing the cavity lengths of the four fiber optic resonators to change. The specific change situation is as follows: for the two fiber optic resonators in the x-axis direction, one is compressed and the other is stretched, and for the two fiber optic resonators in the y-axis direction, one is also compressed and the other is stretched, and the two compressed resonators are adjacent, and the two stretched resonators are adjacent, but the compression amount and the stretching amount in the same direction are not necessarily the same, which is specifically related to the water flow direction; at this time, under the action of the light source, the two fiber optic resonators in the same direction will generate a modulation signal, and since the cavity lengths of the two fiber optic resonators change in the opposite direction, the modulation signal will have an enhanced cursor effect; the modulation signal will be input into the spectrometer for demodulation with light waves as the carrier, and the output cursor spectrum with the cursor envelope will be input into the processor for data processing; compare the demodulated cursor spectrum with the static field spectrum measured in the static flow field to determine the spectral drift amount, and then substitute the spectral drift amount into the corresponding relationship obtained during sensor calibration to obtain the flow velocity components in the x-axis and y-axis directions. Based on the flow velocity components, establish a rectangular coordinate system and perform rectangular vector superposition to reconstruct the information on the flow velocity and direction on the plane of the flow field to be measured.

[0076] The static field spectrum and the corresponding relational expressions are obtained from the sensor calibration operation, which, before the sensor is placed in the flow field to be measured, includes the following steps:

[0077] Connect the sensor to the light source and fixedly place it in the flow field to be measured, and determine the initial position. Calibrate two fiber optic strain sensing modules 3 on the same straight line as the x-axis, and the other two fiber optic strain sensing modules 3 as the y-axis;

[0078] Parallelly connect the two fiber optic strain sensing modules 3 on the x-axis and the two fiber optic strain sensing modules 3 on the y-axis through a fiber optic coupler, and simultaneously connect them to the light source and the spectrometer, and then connect the spectrometer to the processor;

[0079] The two fiber optic strain sensing modules 3 on the x-axis and the two fiber optic strain sensing modules 3 on the y-axis respectively generate modulation signals, and are demodulated by the spectrometer to obtain the static field spectrum;

[0080] Move the sensor forward and backward at a constant speed along the x-axis and the y-axis respectively from the initial position at different advancing speeds, and demodulate multiple sets of cursor spectra in different directions;

[0081] Compare the multiple sets of cursor spectra in different directions with the static field spectrum to determine multiple sets of spectral drift amounts and the corresponding sensor advancing speeds;

[0082] In a static flow field, the sensor advancing speed is equal to the flow velocity of the fluid relative to the sensor, and the corresponding relational expressions between the spectral drift amount and the flow velocity in the x-axis and y-axis directions can be established respectively.

[0083] Specifically, before actually applying the sensor of the present invention to measure the flow velocity and direction in the flow field to be measured, the sensor needs to be calibrated. Before the calibration work, it is also necessary to label the four fiber optic strain sensing modules 3 in the sensor as the x-axis and the y-axis. Label any pair of relatively arranged fiber optic strain sensing modules 3 as the x-axis, and the other pair of relatively arranged fiber optic strain sensing modules 3 as the y-axis, and then place the sensor in the static flow field and connect the circuit, such as Figure 5As shown in the figure, two relatively arranged fiber optic strain sensing modules 3 are respectively connected in parallel and simultaneously connected to a light source and a spectrometer, and then the spectrometer is connected to a processor. Under the action of the light source, two groups of fiber optic resonant cavities in the x-axis and y-axis directions respectively generate modulation signals. The modulation signals are demodulated by the spectrometer to obtain the static field spectrum, and the position of the sensor at this time is marked as the initial position; then the sensor is respectively pushed forward and backward along the x-axis and y-axis at a constant speed. Using the same method, the demodulated spectrum with the vernier enhancement effect can be measured, and the spectrum drift amount can be determined by comparing it with the static field spectrum. Since in a static fluid field, the uniform motion speed of the sensor is the fluid flow rate when the sensor position is stationary, the spectrum drift amount and the corresponding fluid flow rate can be corresponding one by one. Subsequently, the propulsion speed of the sensor is changed, and multiple groups of drift amounts and the corresponding fluid flow rates are respectively recorded, and the corresponding relationship formulas between the spectrum drift amount and the fluid flow rate in the x-axis and y-axis directions can be respectively established.

[0084] In this embodiment, when performing the sensor calibration work, the cavity lengths of two relatively arranged resonant cavities in the x-axis and y-axis directions are respectively set to 100 μm and 105 μm, and the obtained spectral simulation diagram is as Figure 7 shown. It can be seen the vernier envelope formed by the superposition of the spectra of two FP interference cavities with different cavity lengths. This simulated spectrum is used as the static field spectrum; subsequently, the measurement of the fluid to be measured is carried out. After the sensor is placed in the fluid to be measured, in the x-axis direction, the cavity length of one of the FP interference cavities is compressed by 5 μm, and the cavity length of the other relative FP interference cavity is stretched by 1 μm. The independent spectra and the superimposed spectrum of the FP interference cavity are as Figure 8 shown. It can be seen that when the peak drift directions of two relatively interference cavities are opposite, the enhanced vernier effect will be generated; in the y-axis direction, the cavity length of one of the FP interference cavities is compressed by 0.2 μm, and the cavity length of the other relative FP interference cavity is stretched by 0.1 μm. The independent spectra and the superimposed spectrum of the FP interference cavity are as Figure 9 shown. It can be seen that when the flow rate component of the fluid to be measured in the y-axis direction is small, the wavelength drift amounts of the interference spectra of the respective interference cavities are small, while the drift amount of the superimposed spectrum of the double interference cavities is large.

[0085] Specifically, the design of the resonant cavity length range is mainly determined by whether the vernier envelope of the superimposed spectrum can be detected and demodulated, and the recognizability of the vernier envelope is mainly determined by the detectable wavelength range and wavelength resolution of the spectral analyzer configured in the system. Taking the AQ6370C model spectral analyzer produced by Yokogawa Corporation of Japan as an example, its wavelength detection range is from 600 nm to 1700 nm, and the wavelength resolution is 0.02 nm. Its detection range and detection resolution are both good, so the selection range of the designed resonant cavity is larger. The resonant cavity length can theoretically obtain the superimposed spectrum with the vernier envelope from 20 μm to 1000 μm. As Figure 10 shown is the simulation diagram of the independent spectra and the superimposed spectrum of the interference cavity with a cavity length of 20 μm and 25 μm.Figure 11 The simulation diagrams of the independent spectra and the superimposed spectra with the cavity lengths of the interference cavity being 1000μm and 1005μm are shown. It can be seen that the Vernier envelopes of the spectra obtained in the range of the cavity length of the interference cavity from 20μm to 1000μm are very obvious.

[0086] Specifically, the free spectral range FSR v is calculated as follows:

[0087]

[0088]

[0089] where FSR S1或S2 is the free spectral range of two FP fiber optic interference cavities, that is, the wavelength difference between two peaks. L is the cavity length of the interference cavity, λ is the wavelength, and n is the refractive index of the interference cavity. It can be seen from formula (2) that FSR v is determined by the respective cavity lengths of the two interference cavities and their cavity length difference. The free spectral range of the Vernier envelope determines the number of Vernier envelopes within the wavelength range that can be recognized by the spectrometer, and also determines the amplification factor M of the Vernier envelope to external signals. The calculation formula of the amplification factor M is as follows:

[0090]

[0091] In addition, whether the Vernier envelope can be correctly demodulated is also an important factor to be considered when designing the resonator length. As Figure 12 shown, when the cavity lengths are 20μm and 25μm respectively, the interference peaks in the Vernier envelope of the superimposed spectrum are relatively sparse. Therefore, when judging the peak of the Vernier envelope, only a few peak points can be relied on, and there may be inaccurate peak judgment in the actual spectrum. When the cavity lengths are 100μm and 105μm respectively, as Figure 13 shown, the interference peaks in the envelope are relatively dense, and it is relatively easy and accurate to judge the envelope position and the envelope peak. Although the increase in the cavity length makes the peaks denser and the free spectral range smaller, it is still restricted by the wavelength resolution of the optical spectrum analyzer. In actual production, when the length of the interference cavity is too long, on the one hand, a large amount of light will be dissipated in the interference cavity, and the reflected light intensity will be greatly reduced, making it impossible to form distinguishable interference peaks; on the other hand, it is difficult to keep the two fiber resonant surfaces parallel to each other at a long distance in terms of production technology. Therefore, there is no standard calculation value for the length range of the resonator, but it is designed by comprehensively considering aspects such as the configuration of the optical spectrum analyzer in the detection system and the production technology. In summary, the resonator cavity length range of the present invention is designed to be between 20μm and 500μm.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An optical fiber flow velocity sensor based on the cursor effect, characterized in that, Comprising: Artificial cilia cantilever beam (1), elastic support structure (2), fiber optic strain sensing module (3), and encapsulation housing (4); One end of the artificial cilia cantilever beam (1) is inserted into the elastic support structure (2), and the other end is exposed to the fluid. There are multiple relatively arranged fiber optic strain sensing modules (3) inside the elastic support structure (2), and the fiber optic strain sensing modules (3) are horizontally arranged. The elastic support structure (2) is externally wrapped with the encapsulation housing (4); The fiber optic strain sensing module (3) includes: encapsulation capillary (31), first single-mode fiber (32), second single-mode fiber (33), hard fixing glue (34), and elastic fixing glue (35); One end of the encapsulation capillary (31) is provided with elastic fixing glue (35), and the elastic fixing glue (35) is in interference fit with the lower part of the artificial cilia cantilever beam (1); the other end is provided with the hard fixing glue (34), and the hard fixing glue (34) abuts against the encapsulation housing (4); A through hole is provided inside the encapsulation capillary (31), and the second single-mode fiber (33) is connected to the elastic fixing glue (35) and arranged in the through hole; one end of the first single-mode fiber (32) passes through the hard fixing glue (34) and is inserted into the through hole inside the encapsulation capillary (31), and the other end is outside the encapsulation capillary (31). A fiber optic resonator is formed between the first single-mode fiber (32) and the second single-mode fiber (33).

2. The fiber optic flow velocity sensor based on the cursor effect according to claim 1, wherein There are four fiber optic strain sensing modules (3), and the interval angle between any two fiber optic strain sensing modules (3) is 90 degrees. The two fiber optic strain sensing modules (3) on the same straight line are a group of fiber optic strain sensing devices.

3. The fiber optic flow velocity sensor based on the cursor effect according to claim 1, characterized in that, The cavity length range of the fiber optic resonator is 20 to 500 μm.

4. The fiber optic flow velocity sensor based on the cursor effect according to claim 1, characterized in that, The encapsulation housing (4) is a cylindrical structure, and the elastic support structure (2) is a cylindrical structure with a blind hole in the middle. The inner diameter of the blind hole matches the outer diameter of the artificial cilia cantilever beam (1).

5. The fiber optic flow velocity sensor based on the cursor effect according to claim 1, characterized in that, The materials of the artificial cilia cantilever beam (1) and the encapsulation housing (4) are PLA polylactic acid; the materials of the elastic support structure (2) and the elastic fixing glue (35) are soft ultraviolet curable resins, and the chemical component is acrylate; the material of the hard fixing glue (34) is a hard ultraviolet curable resin; the material of the encapsulation capillary (31) is glass.

6. The measurement method of an optical fiber flow velocity sensor based on the cursor effect according to any one of claims 1 to 5, characterized in that Including the following steps: Connect the sensor to the light source and fixedly place it in the flow field to be measured. Calibrate the two fiber optic strain sensing modules (3) on the same straight line as the x-axis, and the other two fiber optic strain sensing modules (3) as the y-axis; Parallelly connect the two fiber optic strain sensing modules (3) on the x-axis and the two fiber optic strain sensing modules (3) on the y-axis through a fiber optic coupler and simultaneously connect them to the light source and the spectrometer, and then connect the spectrometer to the processor; The flow field to be measured causes the deformation of the lower end of the artificial cilia cantilever beam (1), resulting in the increase / decrease of the cavity length of the fiber optic resonator of an optical fiber strain sensing module (3) on the x-axis, and the decrease / increase of the cavity length of the fiber optic resonator of another optical fiber strain sensing module (3) on the x-axis. The cavity length of the fiber optic resonator of an optical fiber strain sensing module (3) on the y-axis increases / decreases, and the cavity length of the fiber optic resonator of another optical fiber strain sensing module (3) on the y-axis decreases / increases; The increasing / decreasing fiber optic resonator on the x-axis generates a modulation signal with a Vernier enhancement effect under the action of a light source, and the increasing / decreasing fiber optic resonator on the y-axis also generates a modulation signal with a Vernier enhancement effect under the action of the light source; The modulation signal is input into a spectrometer with light waves as the carrier, and the spectrometer demodulates the modulation signal and outputs a Vernier spectrum with a Vernier envelope to a processor; The processor processes the data of the Vernier spectrum with the Vernier envelope to obtain the information on the flow velocity and direction on the plane of the flow field to be measured.

7. The measurement method of an optical fiber flow velocity sensor based on the cursor effect according to claim 6, characterized in that, The steps for the processor to process the data of the Vernier spectrum with the Vernier envelope to obtain the information on the flow velocity and direction on the plane of the flow field to be measured are as follows: Compare the demodulated Vernier spectrum with the static field spectrum to determine the spectral drift amount; Substitute the spectral drift amount into the corresponding relationship between the spectral drift amount and the flow velocity to obtain the flow velocities of the flow field in the x-axis and y-axis directions; Establish a rectangular coordinate system based on the flow velocities of the flow field in the x-axis and y-axis directions, and perform rectangular vector superposition to finally reconstruct the information on the flow velocity and direction on the plane of the flow field to be measured.

8. The measuring method of an optical fiber flow velocity sensor based on the cursor effect according to claim 7, characterized in that, The static field spectrum and the corresponding relationship are obtained through the sensor calibration operation. The sensor calibration operation, before the sensor is placed in the flow field to be measured, includes the following steps: Connect the sensor to the light source and fixedly place it in the flow field to be measured and determine the initial position. Calibrate the two optical fiber strain sensing modules (3) on the same straight line as the x-axis, and the other two optical fiber strain sensing modules (3) as the y-axis; Parallelly connect the two optical fiber strain sensing modules (3) on the x-axis and the two optical fiber strain sensing modules (3) on the y-axis through an optical fiber coupler and connect them to the light source and the spectrometer at the same time, and then connect the spectrometer to the processor; The two optical fiber strain sensing modules (3) on the x-axis and the two optical fiber strain sensing modules (3) on the y-axis respectively generate modulation signals, and are demodulated by the spectrometer to obtain the static field spectrum; Move the sensor forward and backward uniformly along the x-axis and y-axis respectively from the initial position at different advancing speeds to demodulate multiple sets of Vernier spectra in different directions; Compare the multiple sets of Vernier spectra in different directions with the static field spectrum to determine multiple sets of spectral drift amounts and the corresponding sensor advancing speeds; In a static flow field, the sensor advancing speed is equal to the flow velocity of the fluid relative to the sensor, and the corresponding relationships between the spectral drift amounts and the flow velocities in the x-axis and y-axis directions can be established respectively.

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