Method for detecting weak airflow in flexible scene

Abstract

The invention discloses a method for detecting weak airflow in a flexible scene, and the method comprises the steps: enabling the surface of a detection end of an airflow sensor to be perpendicular to the direction of the weak airflow, transmitting a laser signal to the detection end through an optical fiber, detecting a reflected light signal, further obtaining the trough displacement information of the reflected light signal, and finally obtaining the size of the weak airflow. The airflow sensor detection end comprises a spiral structure coaxially arranged on the end face of the optical fiber and a flat plate structure arranged at the other end of the spiral structure and parallel to the end face of the optical fiber, and an FP resonant cavity is formed between the end face of the optical fiber and the flat plate structure. By means of the method, high-sensitivity detection can be conducted on the tiny airflow, meanwhile, detection of a flexible scene can be achieved, the overall size of the adopted sensor is small, and detection of the micro-area airflow can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of airflow detection, and in particular to a method for detecting weak airflow in a flexible scene. Background Art

[0002] Ultra-sensitive airflow sensing can avoid many dangerous accidents in production and life, and prevent serious losses of life and property safety. It has outstanding significance for the storage and transportation of dangerous gases, meteorological detection, and industrial and agricultural development.

[0003] Today, commonly used airflow sensors use traditional methods and can only detect airflow within the macroscopic scale (centimeter level). In addition, accurate sensing of extremely weak airflows faces great difficulties. On the other hand, most sensors are made of hard materials and are difficult to adapt to flexible scenarios (such as positioning detection in complex hollow pipes). Therefore, it is particularly important to develop a microscopic airflow sensor with ultra-sensitive resolution that can adapt to flexible scenarios.

[0004] Patent document with publication number CN 115524040A discloses an ultra-sensitive stress sensor structure and system based on optical fiber, including: a spiral structure coaxially arranged on the end face of the optical fiber and a flat plate structure arranged at the other end of the spiral structure and parallel to the end face of the optical fiber, and an FP resonant cavity is formed between the end face of the optical fiber and the flat plate structure. The document focuses on the structure of the stress sensor and the relationship between the spectral shift and the added weight. Summary of the invention

[0005] The present invention provides a method for detecting weak airflow in a flexible scene. The method can be used to detect tiny airflows with high sensitivity. At the same time, the method can realize the detection of flexible scenes, and the overall size of the sensor used is small, which can realize the detection of airflow in a micro area.

[0006] A method for detecting weak airflow in a flexible scene comprises: arranging the detection end surface of an airflow sensor perpendicular to the direction of the weak airflow, emitting a laser signal to the detection end of the airflow sensor through an optical fiber, detecting a reflected light signal, further acquiring trough displacement information of the reflected light signal, and finally obtaining the magnitude of the weak airflow; the airflow sensor detection end comprises a spiral structure coaxially arranged on an optical fiber end face and a flat plate structure arranged at the other end of the spiral structure and parallel to the optical fiber end face, and an FP resonant cavity is formed between the optical fiber end face and the flat plate structure.

[0007] The method of the present invention can be used to detect various weak airflow scenarios. As an implementation method, the weak airflow is caused by leakage of the pipeline side wall. In this case, the method can be used to detect whether the pipeline is leaking. At the same time, combined with the structural characteristics of the present invention itself, it has good flexibility and is suitable for pipeline detection in various complex environments.

[0008] Preferably, the pressure range of the weak airflow is 1 to 12 psi; further, the pressure range of the weak airflow is 1.5 to 11 psi.

[0009] Preferably, the distance between the detection end surface of the airflow sensor and the weak airflow outlet is 10 to 30 microns.

[0010] Preferably, the spiral structure is a cylindrical spiral structure, which is composed of a plurality of spirals with the same spiral direction, the number of spirals is 2 to 4, and the cross-sectional area of ​​each spiral is 2 to 16 μm 2 The spiral height is 60 to 100 μm, and the number of turns is 1 to 3; the flat plate structure is a disk structure with a diameter of 80 to 100 μm.

[0011] Preferably, the outer diameter of the cylindrical spiral structure is 80-100 μm.

[0012] Preferably, the cross-section of each spiral is circular, rectangular, elliptical, or any shape in between.

[0013] Preferably, each spiral structure has a rectangular cross section with a size of 3μm*3.5μm, a spiral height of 80-90μm, and a number of turns of 1-3; the flat plate structure is a disc structure with a diameter of 80-90μm and a thickness of 1-3μm (preferably 2μm); the overall size of the probe is less than 100μm. As a further preference, when multiple spirals are provided, the multiple spirals are evenly arranged around the center of the optical fiber end face.

[0014] As an experimental case, the cross section of the 3D spiral structure (single spiral) is rectangular, with a size of 3μm*3.5μm and a spiral height of 80μm. The diameter of the disk structure is 90μm and the thickness is 2μm. The overall size of the probe is less than 100μm, which can detect micro-area airflow.

[0015] Preferably, the airflow sensor further comprises:

[0016] A tunable laser provides an optical signal;

[0017] An optical power meter receives reflected optical signals;

[0018] Optical fiber connectors (such as optical fiber circulators and related optical fibers) are used to achieve corresponding connections between the tunable laser, the optical power meter and the sensor detection end.

[0019] When working, the tunable laser provides a laser signal, which passes through the optical fiber and the optical fiber connector to reach the sensor detection end, and then reflects at the end face of the optical fiber and the bottom surface of the flat structure. The two reflected lights are transmitted in the opposite direction and interfere with each other, which are received by the optical power meter. The height of the spiral determines the height of the FP resonant cavity. When the flat structure is subjected to the force of a small airflow, the spiral expands and contracts, and the height of the FP resonant cavity changes accordingly, which in turn affects the trough position of the reflected light.

[0020] In some cases, the airflow sensor further includes a computer, which receives the reflected light signal of the optical power meter and obtains the corresponding trough displacement information according to the signal, thereby obtaining the corresponding airflow size information.

[0021] The present invention also provides a trace gas sensing verification case using a glass needle to inject gas as an example. It includes:

[0022] A glass needle provides a channel for air flow injection;

[0023] Fluid dispenser, precise control of micro airflow.

[0024] During verification, the sensor detection end is set to face the airflow direction of the glass needle outlet. The known airflow is controlled by the fluid dispensing machine, and the quantitative relationship between the airflow pressure and the trough displacement can be established.

[0025] The present invention provides a method for detecting micro airflow using an optical fiber-based FP cavity airflow sensing system, which has the following characteristics and advantages compared with the prior art:

[0026] The sensors used in the above method can simultaneously possess the following capabilities required for extreme environments: extremely high sensitivity to detect extremely weak airflows; flexibility to be compatible with complex detection pipelines; and high spatial resolution to accurately locate gas leaks. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the structure of the detection end of an optical fiber-based airflow sensor used in the present invention.

[0028] Figure 2 This is a device diagram of the airflow sensor used in the present invention.

[0029] Figure 3 This is a diagram of the airflow sensor verification system used in the present invention.

[0030] Figure 4 The interference spectrum of the optical fiber airflow sensor provided by the present invention and the spectrum drift diagram of the trough position before and after applying airflows of different magnitudes.

[0031] Figure 5 Comparison chart of CFD simulation and experimental results. DETAILED DESCRIPTION

[0032] For ease of understanding, the present invention is further described below in conjunction with the accompanying drawings. Note that the following description is only a preferred embodiment of the present invention, which is only used to help understand the present invention and should not be considered as limiting the scope of the present invention.

[0033] The present invention provides a method for detecting weak airflow in a flexible scene, which comprises: arranging the detection end surface of an airflow sensor perpendicular to the direction of the weak airflow, emitting a laser signal to the detection end through an optical fiber, detecting a reflected light signal, further acquiring trough displacement information of the reflected light signal, and finally obtaining the magnitude of the weak airflow; the airflow sensor detection end comprises a spiral structure coaxially arranged on an optical fiber end face and a flat plate structure arranged at the other end of the spiral structure and parallel to the optical fiber end face, and an FP resonant cavity is formed between the optical fiber end face and the flat plate structure.

[0034] The airflow sensor used in the present invention is an airflow sensor based on the FP cavity of optical fiber, and the structural schematic diagram of the detection end thereof is shown in FIG. Figure 1 As shown, the detection end of the sensor includes a single-mode optical fiber (including an optical fiber core 101 and an optical fiber cladding 102) and a micro 3D structure arranged on the optical fiber end face (corresponding to the optical fiber core 101). The micro 3D structure includes a micro 3D spiral structure 103 and a top flat plate structure 104. The flat plate structure is aligned with the center of the optical fiber end face and is parallel to the optical fiber end face. The micro 3D spiral structure is used to connect the optical fiber end face and the flat plate structure.

[0035] As an experimental case, during the design, the cross-section of the 3D spiral structure (i.e., the cross-section of a single spiral) is rectangular, the cross-sectional size (w*t) is 3μm*3.5μm (other circular or elliptical cross-sectional structures or structures between circular and elliptical shapes can also be used), and the spiral height is H=90μm. The flat plate structure is a disc structure with a diameter of 90μm and a thickness of 2μm. The size of the overall structure is less than 100μm and can be used as a micro-area probe. The spiral is a cylindrical spiral structure, consisting of three single spirals with the same spiral rotation direction, and the three single spirals are evenly distributed around the center of the optical fiber. The number of turns of the spiral (i.e., the number of circles of spiral rotation on the central axial projection plane) is approximately 1, and the outer diameter of the spiral rotation is 90μm. The spiral axial direction is elastic and can be extended and retracted under the action of external force.

[0036] Figure 2 The figure is a schematic diagram of the structure of the airflow sensor based on the optical fiber FP cavity used in the present invention. The airflow sensor comprises: a tunable laser, an optical fiber circulator, an optical power meter and Figure 1 The specific functions and structures of the optical fiber-based FP cavity sensor can be found in the existing literature (CN 115524040A).

[0037] Figure 3 This is a device diagram of a micro airflow sensing gas injection system based on optical fiber used to verify the airflow detection method of the present invention. At the same time, the device can be used to construct the early data relationship of the sensor. Specifically, before the sensor is used, it can be used Figure 3 The device shown detects known airflow, establishes the relationship between airflow pressure and the displacement of the trough of reflected light, and stores the information in a computer. During actual detection, the pressure information of the airflow can be quickly obtained by detecting the displacement of the trough of reflected light.

[0038] The above-mentioned device includes: a fluid dispensing machine (HP3cc, EFD Inc.), a gas injection needle;

[0039] As an example, to ensure the accuracy of the signal, the outlet direction of the gas injection needle and the sensor surface (ie, the top flat plate structure 104) need to be placed vertically.

[0040] As an example, the distance between the gas injection needle and the sensing surface is 20 microns and the radius of the needle is 1 micron.

[0041] Figure 4 The interference spectrum of the optical fiber airflow sensor provided by the present invention and the change diagram of the trough position under different airflow pressures. From the results, it can be seen that before and after the airflow injection (the airflow pressure is 3psi, 6psi, 9psi and 12psi respectively), the spectrum produces a blue shift of 0.6nm, 1.6nm, 4.1nm and 9.6nm respectively. After the air pressure returns to the initial value, the trough position of the interference spectrum can also be restored at the same time, indicating the excellent repeatability of the sensor.

[0042] As an example, considering the signal range of optical sensing, the force sensing range is 30nN, and the applied airflow force needs to be below the range, that is, the application scenario of the airflow sensor is extremely weak airflow detection.

[0043] like Figure 5 As shown in the figure, the airflow force corresponding to the spectral drift in the experiment is consistent with the CFD fluid mechanics simulation, which verifies the high accuracy and reliability of the sensor.

[0044] Working principle of airflow sensor: The optical fiber-based FP cavity airflow sensor provided by the present invention mainly adopts the FP cavity interference principle. The light intensity reflected from the optical fiber end face and the flat plate structure is recorded as I1 and I2 respectively, so the interference signal of the two can be expressed as:

[0045]

[0046] Where n represents the ambient refractive index, L represents the cavity length of the FP cavity, and λ represents the wavelength of the incident light. Represents the initial phase. The trough position of the interference spectrum must meet the following phase conditions:

[0047]

[0048] Where m represents an integer, λ m represents the position of the m-th order trough, the above formula can be transformed into:

[0049]

[0050] When airflow is injected, the airflow force will compress the spring, thereby shortening the FP cavity length. It can be seen from the above formula that the interference trough wavelength will decrease (blue shift) as the FP cavity length decreases, and there is a correlation between the two.

[0051] The relationship between the cavity length L of the FP cavity and the airflow size can be determined through preliminary experiments, and the relationship between the reflected light trough displacement and the airflow size can be obtained by conversion of the above formula, and the relationship data can be stored in a computer or other chip with the same computing function.

[0052] During actual detection, the sensor can be connected to a computer (of course, other processing units can also be selected), the computer is used to receive the laser signal, and then the airflow size result is directly obtained through the pre-stored relationship data.

Claims

1. A method for detecting weak airflow in a flexible scene is flexible, characterized in that: include: The detection end surface of the airflow sensor is set perpendicular to the direction of the weak airflow, a laser signal is emitted to the detection end through the optical fiber, and the reflected light signal is detected to further obtain the trough displacement information of the reflected light signal, and finally the size of the weak airflow is obtained; the detection end of the airflow sensor includes a spiral structure coaxially arranged on the end face of the optical fiber and a flat plate structure arranged at the other end of the spiral structure and parallel to the end face of the optical fiber, and an FP resonant cavity is formed between the end face of the optical fiber and the flat plate structure.

2. The method for detecting weak airflow in a flexible scene according to claim 1, characterized in that: The weak airflow is caused by leakage from the side wall of the pipeline.

3. The method for detecting weak airflow in a flexible scene according to claim 1, characterized in that: The pressure range of weak air flow is 1 to 12 psi.

4. The method for detecting weak airflow in a flexible scene according to claim 2, characterized in that: The distance between the detection end surface of the airflow sensor and the air outlet is 10 to 30 microns.

5. The method for detecting weak airflow in a flexible scene according to claim 1, characterized in that: The spiral structure is a cylindrical spiral structure, and the outer diameter of the cylindrical spiral structure is 80-100 μm; the spiral structure is composed of a plurality of spirals with the same spiral direction, the number of spirals is 2-4, and the cross-sectional area of ​​each spiral is 2-16 μm 2 The spiral height is 60 to 100 μm, and the number of turns is 1 to 3; the flat plate structure is a disk structure with a diameter of 80 to 100 μm.

6. The method for detecting weak airflow in a flexible scene according to claim 1, characterized in that: The air flow sensor comprises: A tunable laser provides an optical signal; An optical power meter receives reflected optical signals; The optical fiber connector is used to realize the corresponding connection between the tunable laser, the optical power meter and the sensor detection end.

7. The method for detecting weak airflow in a flexible scene according to claim 1, characterized in that: The airflow sensor also includes a computer, which receives the reflected light signal of the optical power meter and obtains the corresponding trough displacement information according to the signal, thereby obtaining the corresponding airflow size information.

8. The method for detecting weak airflow in a flexible scene according to claim 1, characterized in that: Before detection, the relationship between the trough displacement corresponding to the airflow sensor and the airflow size is pre-built.

9. The method for detecting weak airflow in a flexible scene according to claim 8, characterized in that: The relationship between the trough displacement and the airflow size is constructed using the following device: A glass needle provides a channel for air flow injection; Fluid dispenser, connected to a glass needle, to precisely control minute amounts of airflow; During testing, the detection end of the airflow sensor is arranged facing the airflow direction of the air outlet of the glass needle.

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