A fiber optic sensor for high frequency vibration detection

Abstract

The application provides a fiber sensor for high-frequency vibration detection, comprising a sensor diaphragm which is a deflected-hole fiber sensor diaphragm or a deflected-slot fiber sensor diaphragm, and a single-mode optical fiber, a light source, a circulator, an amplifier and a collection card connected in sequence; the deflected-hole fiber sensor diaphragm and the deflected-slot fiber sensor diaphragm are formed by presetting a plurality of holes or arc-shaped slots on the diaphragm which are not overlapped with the geometric center of the diaphragm and are symmetrically distributed, then the plurality of holes or arc-shaped slots are collectively deflected relative to the geometric center of the diaphragm, so that the holes or arc-shaped slots on the diaphragm finally present an asymmetric structure. The sensor device has the characteristics of high sensitivity, strong anti-interference ability and convenient production, and greatly increases the range of frequency domain response compared with the sensor made of the traditional diaphragm.

Description

Technical Field

[0001] This invention belongs to the field of sensor technology, and in particular relates to an optical fiber sensor for high-frequency vibration detection. Background Technology

[0002] Today, with the deepening of national economic development and urbanization, most economically developed regions have adopted the method of laying power transmission lines underground by constructing cable tunnels. This compact and clearly categorized layout makes it easier for power workers to maintain and replace internal cables, not only making city roads more aesthetically pleasing but also saving valuable urban land.

[0003] Besides power tunnels, urban underground space plays a vital role in critical sectors such as water supply, drainage, gas, and communications. As urban buildings become increasingly dense, the available space for underground pipelines dwindles, inevitably leading to overlaps and adjacent structures during construction. In addition to various pipeline facilities, large-scale urban buildings like subways and underground infrastructure also intersect with cable tunnels. Their construction affects soil structure, significantly altering the stress conditions of the tunnel structure, potentially resulting in discrepancies from the initial construction conditions. While the planning of these facilities takes many factors into account, human error during construction and prolonged road loads pose potential dangers to cable tunnels. If such dangers occur, they can cause significant damage to the entire city's power supply system.

[0004] Therefore, measuring changes in tunnel structure is particularly important. Traditional measurement methods are mature and have been used for a long time, but each has its limitations due to its underlying principles. For example, the total station deformation detection method can only measure monitoring points periodically, and these monitoring points can only be discrete. Furthermore, because cable tunnels are relatively small and the lines are not necessarily straight and horizontal, with multiple cables running along both sides of narrow passages, the operating length of a single automatic total station is very limited, making it unsuitable for cable tunnels. The hydrostatic level and electromagnetic sensor detection methods are both large and complex systems. If used to detect structural changes in cable tunnels, the project would be massive and maintenance costs relatively high. To achieve the required accuracy, very advanced versions might need to be purchased, making it less economical. Other older detection methods, while small, easy to install, and low-cost, mostly suffer from short lifespans, susceptibility to environmental factors, electromagnetic interference, and difficulty in achieving the required accuracy, making them unsuitable for the safety inspection of such important facilities as cable tunnels.

[0005] Following electromagnetic-based sensor technologies, fiber optic sensor technologies are gaining a foothold in the market due to their numerous unique advantages. These sensors use optical fibers as the signal propagation path, utilizing the properties of light reflection, refraction, and diffraction to acquire external signals, thus combining sensing and transmission. Their advantages include the fiber's resistance to corrosion and electromagnetic interference, high signal propagation speed, high accuracy and sensitivity, slow attenuation, and the ability to achieve remote real-time detection. There are some examples of using fiber optic sensing technology for tunnel safety inspection in China, but these mainly target low-frequency vibrations or stress deformation. Summary of the Invention

[0006] To address the shortcomings of current high-frequency vibration detection methods for unknown types and characteristics, this invention proposes an optical fiber sensor for high-frequency vibration detection, comprising a sensor diaphragm and a single-mode optical fiber, a light source, a circulator, an amplifier, and a data acquisition card connected in sequence. The sensor diaphragm is characterized by being either an offset aperture type optical fiber sensor diaphragm or an offset slot type optical fiber sensor diaphragm.

[0007] Preferably, by pre-setting multiple holes or arc-shaped grooves that do not overlap with the geometric center of the diaphragm and are symmetrically distributed, and then shifting the multiple holes or arc-shaped grooves relative to the geometric center of the diaphragm as a whole, the holes or arc-shaped grooves on the diaphragm will eventually present an asymmetrical structure to form the offset hole type fiber optic sensor diaphragm and the offset groove type fiber optic sensor diaphragm.

[0008] Preferably, the number of holes on the offset hole type fiber optic sensor diaphragm is 2-6, and the number of arc grooves on the offset slot type fiber optic sensor diaphragm is 2-4.

[0009] Preferably, the material of the offset aperture type fiber optic sensor diaphragm is non-metallic, while the material of the offset slot type fiber optic sensor diaphragm is metallic.

[0010] Preferably, the hole is a round hole or a square hole.

[0011] Preferably, the aperture of the offset aperture fiber optic sensor diaphragm is 100 μm and the center-to-center distance is 400 μm; the width of the arc groove on the offset slot fiber optic sensor diaphragm is 50 μm.

[0012] Preferably, the geometric center of the hole on the offset hole type fiber optic sensor diaphragm and the geometric center of the arc groove on the offset groove type fiber optic sensor diaphragm are kept at a certain distance from the edge of the diaphragm to ensure that the diaphragm is fixed on the capillary.

[0013] Preferably, the offset of the hole on the diaphragm of the offset hole type fiber optic sensor and the arcuate groove on the diaphragm of the offset groove type fiber optic sensor is 30µm relative to the geometric center of the diaphragm.

[0014] Preferably, the detection characteristic frequency range of the offset aperture sensor diaphragm is 10615Hz to 97409Hz, and the detection characteristic frequency range of the offset slot sensor diaphragm is 10361Hz to 97669Hz.

[0015] Preferably, during testing, when the facility or location has high requirements for the strength of the outer wall, the sensor device can be attached tightly to the inner wall; if the facility or location has low requirements for the strength of the outer wall and no strict requirements for structural integrity, the sensor device can be buried in the inner wall.

[0016] Preferably, the sensor diaphragm is arranged parallel to the axis of the facility or site being monitored.

[0017] Preferably, the sensor is used to detect high-frequency vibrations in cable tunnels or other tunnels.

[0018] The beneficial effects of this invention are as follows: The sensor device of this invention features high sensitivity, strong anti-interference capability, and ease of manufacturing, significantly increasing the frequency domain response range compared to sensors made with traditional diaphragms. The sensor of this invention is easy to install in the field and can be used as a point sensor, conveniently installed in various tunnels such as cable tunnels and cable wells, or other locations requiring vibration monitoring for online detection of high-frequency vibrations. The sensor device of this invention can sensitively measure high-frequency signals. Because it uses optical measurement, it avoids strong electromagnetic interference at the equipment operating site, enabling online monitoring of facilities and locations equipped with high-voltage electrical equipment. Attached Figure Description

[0019] Figure 1 This is a structural diagram of the offset aperture type fiber optic sensor diaphragm of the present invention;

[0020] Figure 2 This is a structural diagram of the offset slot type fiber optic sensor diaphragm of the present invention;

[0021] Figure 3 This is a cross-sectional view showing the bare optical fiber, capillary tube, and the cut sensor diaphragm of the present invention connected together.

[0022] Figures 4(a)-4(c) Figure 4(a) shows the number of characteristic frequencies of the sensor diaphragm of the present invention and the displacement at the center of the characteristic frequency of the ordinary EFPI fiber optic sensor; Figure 4(b) shows the number of characteristic frequencies of the offset aperture fiber optic sensor of the present invention and the displacement at the center of the characteristic frequency; Figure 4(c) shows the number of characteristic frequencies of the offset slot fiber optic sensor of the present invention and the displacement at the center of the characteristic frequency.

[0023] Figure 5 The diagram shows the working principle of the two types of diaphragm fiber optic sensors of the present invention;

[0024] Figure 6 This is a schematic diagram of the installation position of the fiber optic sensor for high-frequency vibration detection in cable tunnels or other tunnels, based on the diaphragm sensor of the present invention. Detailed Implementation

[0025] The implementation plan is described in detail below with reference to the accompanying drawings.

[0026] This invention proposes an optical fiber sensor for high-frequency vibration detection. The sensor includes a sensor diaphragm, a single-mode optical fiber, a light source, a circulator, an amplifier, and a data acquisition card. To detect high-frequency vibration signals, this invention increases the number of characteristic frequencies of the diaphragm by modifying its structure, thereby improving the frequency domain characteristics of the sensor.

[0027] Because sensor diaphragms are made of different materials, and considering their differences in toughness, different types of shapes can be cut into the diaphragms to change the number of characteristic frequencies of the diaphragms, such as round holes, square holes, and strip grooves.

[0028] Figure 1 and Figure 2 This is a schematic diagram of the structure of two different sensor diaphragms according to embodiments of the present invention.

[0029] Because the toughness of diaphragm materials varies, the cutting process on them is greatly affected. Therefore, the structure of sensors made from diaphragm materials with different toughness will also differ. Figure 1 The diagram illustrates the structure of an offset-hole fiber optic sensor diaphragm. This diaphragm utilizes non-metallic materials with poor toughness, such as quartz and silicon boride. These materials are difficult to cut, making them suitable for perforation. In this embodiment, the diaphragm is circular with a thickness of 2 mm. First, pre-defined holes are symmetrically distributed on the diaphragm, with a diameter of 100 μm and a center-to-center distance of 400 μm. Then, the pre-defined hole positions are offset in one direction by 30 μm, resulting in a perforation count of 6. Figure 1 As shown. Regarding the dimensions of the embodiment, during simulation, as the aperture on the diaphragm gradually increases, the measurement effect improves, and remains stable after the aperture reaches 100µm. At the limit state where the apertures are about to overlap, the measurement effect begins to decline. The number of apertures also affects the measurement results; as the number of apertures gradually increases, the measurement effect gradually improves, but when the number of apertures exceeds 6, the effect of increasing the number of apertures on improving sensor performance is not significant. In this embodiment of the invention, the preferred number of perforations is 2 to 6. The apertures can also be square apertures, with a similar arrangement to circular apertures.

[0030] The geometric center of the hole formed after the hole offset is set at a certain distance from the geometric center of the complete diaphragm. At the same time, it is important to ensure that there is a certain distance between the geometric center of the hole and the edge of the diaphragm to ensure that the diaphragm is fixed on the capillary. Otherwise, the two may not be able to be fixed or even the diaphragm may be damaged. The specific distance can be set according to the size and installation requirements of the capillary, and is usually not less than 300um.

[0031] Figure 2 An offset slot type fiber optic sensor diaphragm is shown. The diaphragm uses a tough material, such as aluminum foil or thin stainless steel, which is easy to cut. Longer fan-shaped slots are cut into the diaphragm; typically 2-4 fan-shaped slots are provided, preferably 4. Figure 2 As shown. Similar to the perforation above, the geometric center of the slot is set at a certain distance from the geometric center of the complete diaphragm. Figure 2 In this embodiment, four fan-shaped grooves with a width of 50 μm are cut on the diaphragm. The distance between the geometric center of the fan-shaped groove and the geometric center of the diaphragm is 700 μm. Then, the fan-shaped grooves are offset by 30 μm relative to the geometric center of the diaphragm to form an asymmetrical structure. At the same time, it is important to ensure that a certain distance is left between the geometric center of the fan-shaped groove and the edge of the diaphragm to ensure that the diaphragm can be fixed on the capillary. This distance is usually not less than 300 μm.

[0032] After the sensor diaphragm is fabricated, the single-mode fiber is stripped to expose the bare fiber. The stripped bare fiber, capillary tube, and the cut diaphragm are then connected as follows: Figure 3 They were assembled in the same way. After adjusting the cavity length of the sensor to about 80um using software, the three parts were bonded together using solid glue to complete the fabrication of the front-end fiber optic sensor.

[0033] Figures 4(a)-4(c)The characteristic frequencies of the sensor diaphragm of this invention and a conventional EFPI sensor diaphragm are shown. As shown in the figure, the conventional EFPI sensor diaphragm performs well in detecting displacement at the center of the circle with characteristic frequencies between 12670Hz and 86123Hz (although the detection performance is still relatively poor in some frequency ranges). In contrast, the offset aperture sensor diaphragm of this invention detects a characteristic frequency range of 10615Hz to 97409Hz, and the offset slot sensor diaphragm detects a characteristic frequency range of 10361Hz to 97669Hz. Furthermore, the number of offset sensor diaphragms displaying the displacement at the center of the circle is significantly increased, resulting in higher reliability of the measurement results. As shown in Figure 4(b), due to the adjusted structure of the front-end diaphragm, the offset aperture fiber optic sensor diaphragm has more characteristic frequencies and a wider frequency distribution compared to the conventional EFPI sensor diaphragm. Because the displacement at the center of the circle can occur at more frequency positions, the sensor cavity length can vary sufficiently, allowing it to be displayed on the oscilloscope software. As shown in Figure 4(c), because the diaphragm structure of the offset slot fiber optic sensor has a greater degree of variation, it is superior to the offset aperture fiber optic sensor diaphragm in terms of the number and distribution of characteristic frequencies. However, due to factors such as the delicate and complex cutting process that can easily damage non-metallic diaphragms, it is currently only applicable to diaphragms made of certain materials.

[0034] The geometric center of the holes or fan-shaped grooves formed on the sensor diaphragm of the present invention deviates from the geometric center of the complete diaphragm, so that the sensor diaphragm ultimately presents an asymmetrical structure.

[0035] The sensor of this invention utilizes the asymmetry of the sensor diaphragm to include the diaphragm displacement of second-, third-, and fourth-order non-central vibration modes, other than the first-order central vibration mode, within the sensor's affected range. This increases the frequency response range, enabling it to handle a wider variety of high-frequency signals and providing better detection capabilities for high-frequency signals previously unknown to the user.

[0036] Figure 5 This paper illustrates exemplary operation of the offset aperture type and offset slot type fiber optic sensor of the present invention. A monochromatic wavelength light source with a wavelength fixed at 1310 nm is emitted from a spectrometer. A polarization-maintaining single-mode fiber is used to connect the entire sensor. The central glass core of the fiber has a diameter of 9 μm, and the outer diameter of the cladding is 125 μm. The monochromatic wavelength light first passes through a circulator and enters the sensor at the front end. The sensor diaphragm senses the external high-frequency vibration signal and resonates with it, causing deformation that changes the cavity length. This causes a change in the reflected light from the fiber end face, thus obtaining vibration information. The reflected light passes through the circulator and is transmitted to an amplifier, where the optical signal is amplified. A photoelectric conversion module then converts the optical information flux carrying the measured signal into an electrical signal that can be measured by a computer. The electrical signal is connected to a computer via a data acquisition card, allowing the observed and detected high-frequency vibration signal to be viewed in signal processing software.

[0037] When applying the sensor of this invention to measure high-frequency vibration, the entire high-frequency vibration detection fiber optic sensor, which has been fabricated and debugged, can be installed... Figure 6 The dark-colored dot indicated by the middle arrow indicates the location of the sensor device. When the facility or location has high requirements for the strength of the outer wall, the sensor device can be attached tightly to the inner wall. If the facility or location has lower requirements for the strength of the outer wall and there are no strict requirements for structural integrity, the sensor device can be buried in the inner wall to reduce signal attenuation and improve monitoring performance. Fiber optic sensor devices are deployed (attached tightly) or buried inside the facility or location to prevent signal reflection at the facility or location-air interface from reducing signal strength and the sensitivity of the entire detection device. During detection, the sensor diaphragm is preferably parallel to the axis of the facility or location. If the diaphragm is arranged parallel to the axis of the facility or location, it can receive more vibration signals and is more sensitive to high-frequency vibration signals propagating along the facility or location.

[0038] The sensor of this invention is preferably used for detecting high-frequency vibration signals in cable tunnels or other tunnels. During detection, the sensing optical fiber is attached to the conductor being measured, and the probe is placed tangentially to the tunnel axis. It detects high-frequency vibration signals generated by known or unknown vibration sources near the sensor that propagate longitudinally along the tunnel's external medium to the sensor or laterally along the tunnel wall. Frequency components in the signal that match the characteristic frequency of the diaphragm cause the diaphragm to vibrate, resulting in a change in the sensor cavity length. The vibration signal is obtained after demodulation. Arranging the sensor diaphragm parallel to the tunnel axis improves detection performance.

[0039] The implementation steps for offset aperture fiber optic sensors and offset slot fiber optic sensors are as follows:

[0040] A monochromatic light source emitting a monochromatic wavelength, with the wavelength fixed at 1310 nm, is emitted by a spectrometer.

[0041] The entire system is connected by polarization-maintaining single-mode fiber with a central glass core diameter of 9µm and an outer cladding diameter of 125µm.

[0042] Monochromatic wavelength light first passes through a circulator before entering the sensor at the front end;

[0043] The sensor diaphragm senses high-frequency vibration signals from the outside world. When it resonates with these signals, it deforms, causing a change in the cavity length. This changes the reflected light from the fiber end face, thus obtaining vibration information.

[0044] The reflected light passes through a circulator and is then amplified by an amplifier. The optical signal is then converted into an electrical signal that can be measured by a computer by a photoelectric conversion module.

[0045] The electrical signal is connected to the computer via a data acquisition card, and the high-frequency vibration signal observed and detected can be viewed in the signal processing software.

[0046] The above embodiments are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A fiber optic sensor for high-frequency vibration detection, comprising a sensor diaphragm and a single-mode optical fiber, a light source, a circulator, an amplifier, and a data acquisition card connected in sequence, characterized in that: The sensor diaphragm is either an offset aperture type fiber optic sensor diaphragm or an offset slot type fiber optic sensor diaphragm. Multiple holes or arc-shaped slots, which are not overlapping with the geometric center of the diaphragm and are symmetrically distributed, are pre-set on the diaphragm. Then, the multiple holes or arc-shaped slots are offset relative to the geometric center of the diaphragm as a whole, resulting in an asymmetrical structure to form the offset aperture type fiber optic sensor diaphragm and the offset slot type fiber optic sensor diaphragm. The offset of the holes on the offset aperture type fiber optic sensor diaphragm and the arc-shaped slots on the offset slot type fiber optic sensor diaphragm relative to the geometric center of the diaphragm is 30 μm. The detection characteristic frequency range of the offset aperture type sensor diaphragm is 10615 Hz to 97409 Hz, and the detection characteristic frequency range of the offset slot type sensor diaphragm is 10361 Hz to 97669 Hz.

2. The fiber optic sensor for high-frequency vibration detection according to claim 1, characterized in that: The offset hole type fiber optic sensor diaphragm has 2-6 holes, and the offset groove type fiber optic sensor diaphragm has 2-4 arc-shaped grooves.

3. The fiber optic sensor for high-frequency vibration detection according to claim 1, characterized in that: The offset aperture type fiber optic sensor diaphragm is made of non-metallic material, while the offset slot type fiber optic sensor diaphragm is made of metallic material.

4. The fiber optic sensor for high-frequency vibration detection according to claim 1, characterized in that: The hole can be round or square.

5. The fiber optic sensor for high-frequency vibration detection according to claim 1, characterized in that: The aperture of the offset aperture fiber optic sensor diaphragm is 100 μm, and the center-to-center distance of the aperture is 400 μm; the width of the arc groove on the offset slot fiber optic sensor diaphragm is 50 μm.

6. The fiber optic sensor for high-frequency vibration detection according to claim 1, characterized in that: The geometric center of the hole on the diaphragm of the offset hole type fiber optic sensor and the geometric center of the arc groove on the diaphragm of the offset groove type fiber optic sensor are kept at a certain distance from the edge of the diaphragm to ensure that the diaphragm is fixed on the capillary.

7. The fiber optic sensor for high-frequency vibration detection according to claim 1, characterized in that: During testing, when the facility or location has high requirements for the strength of the outer wall, the sensor device can be attached tightly to the inner wall; if the facility or location has low requirements for the strength of the outer wall and no strict requirements for structural integrity, the sensor device can be buried in the inner wall.

8. The fiber optic sensor for high-frequency vibration detection according to claim 1, characterized in that: During testing, the sensor diaphragm is arranged parallel to the axis of the facility or site being tested.

9. A fiber optic sensor for high-frequency vibration detection according to any one of claims 1-8, characterized in that: The sensor is used to detect high-frequency vibrations in cable tunnels or other tunnels.

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