Sensitization structure based on distributed optical fiber sound wave sensing system

Abstract

The invention relates to a sensitization structure based on a distributed optical fiber sound wave sensing system, and belongs to the field of weak signal monitoring by distributed optical fiber sound wave sensing. Comprising a first aluminum base, a second aluminum base, a first silica gel paramorphic cylinder, a second silica gel paramorphic cylinder, an inertia mass block, a single-mode optical fiber and an aluminum shell. The two ends of the inertia mass block in the aluminum shell are tightly connected with the first silica gel paramorphic cylinder and the second silica gel paramorphic cylinder respectively to form a simple harmonic oscillator. Wherein a single-mode optical fiber is uniformly wound outside one of the silica gel variable cylinders, a prestress of 5N is applied to the single-mode optical fiber, and the single-mode optical fiber is led out from the side surface of the aluminum shell and is connected into an external light path. Compared with a traditional DAS system structure, the system is high in sensitivity, large in frequency response range, resistant to electromagnetic interference, high in environmental adaptability, simple in structure, fireproof and explosion-proof, suitable for signal monitoring in the complex environment of a railway track, and capable of recording vibration signals with a high signal-to-noise ratio. And meanwhile, the sensitization structure is protected by the aluminum shell, so that monitoring tasks under complex and severe conditions can be competent, and the application prospect is wide.

Description

Technical Field

[0001] The present invention relates to the field of weak signal monitoring by distributed optical fiber acoustic wave sensing, and in particular to a sensitivity enhancement structure based on a distributed optical fiber acoustic wave sensing system (DAS). Background Art

[0002] Railway tracks are important infrastructure for railway transportation, and their safety is directly related to the safety and efficiency of train operation. With the increasing busyness of railway transportation, the load on the tracks is increasing. Coupled with the influence of the natural environment and factors such as material aging, the problem of track damage is becoming increasingly prominent. Therefore, the extraction and identification of damage signals on railway tracks is of great significance to ensure the safety of railway transportation. With the development of distributed fiber optic sensing technology, distributed fiber optic acoustic wave sensing technology has been introduced into the field of rail transportation safety, providing technical support for railway track damage detection. By laying long-distance sensing optical fibers, vibration event monitoring along long distances of optical fibers can be achieved, and accurate disturbance positioning and signal identification can be achieved at the same time. However, the Young's modulus of the optical fiber itself is large, and the sensitivity is low when directly detecting vibration signals. Compared with conventional detectors and seismographs, the signal-to-noise ratio is low. Summary of the invention

[0003] The purpose of the present invention is to provide a sensitivity enhancement structure based on a distributed optical fiber acoustic wave sensing system, which solves the problem of low signal-to-noise ratio of signals collected by traditional DAS systems. Compared with the traditional DAS system structure, the sensitivity enhancement structure of the present invention has high sensitivity, large frequency response range, anti-electromagnetic interference, strong environmental adaptability, simple structure, fireproof and explosion-proof, and is suitable for signal monitoring in complex railway track environments, and can record vibration signals with a high signal-to-noise ratio.

[0004] The above-mentioned object of the present invention is achieved by the following technical solutions: The sensitivity enhancement structure based on the distributed optical fiber acoustic wave sensing system includes an aluminum base 15, an aluminum base 2 18, a silicone compliant column 16, a silicone compliant column 2 17, an inertial mass block 13, a single-mode optical fiber 12 and an aluminum shell 14. The two ends of the inertial mass block 13 inside the aluminum shell 14 are tightly connected to the silicone compliant column 16 and the silicone compliant column 2 17 to form a simple harmonic oscillator; a single-mode optical fiber 12 with a length of 20 meters is uniformly wound on the outside of one of the silicone compliant columns, and a prestress of 5N is applied to the single-mode optical fiber 12 wound on the silicone compliant column during winding, and the single-mode optical fiber 12 is led out from the side of the aluminum shell 14 and connected to the external optical path; the single-mode optical fiber is not wound on the outside of the other silicone compliant column, which only constitutes the overall structure of the system.

[0005] The aluminum base 15 and the aluminum base 2 18 are made of aluminum and are respectively composed of three cylinders. The three cylinders are coaxial and have decreasing diameters. The diameters of the three cylinders of the aluminum base 15 are cylinder A1, cylinder B1, and cylinder C1 from small to large, and the diameters of the three cylinders of the aluminum base 2 18 are cylinder A2, cylinder B2, and cylinder C2 from small to large, and the diameter relationship is A1=A2, B1=B2, and C1=C2. The entire surface of the aluminum base is anodized to show the original color of aluminum.

[0006] The material of the inertial mass block 13 is brass, and the surface is treated with anti-corrosion oxidation. The inertial mass block is an axisymmetric structure, and the whole is composed of five cylinders, which are cylinder D1, cylinder E1, cylinder F, cylinder E2, and cylinder D2 from top to bottom, respectively. Cylinder D1 has the same diameter as cylinder D2, and cylinder E1 has the same diameter as cylinder E2. The diameter relationship between them is F>D1=D2>E1=E2.

[0007] The silicone compliant cylinder 16 and the silicone compliant cylinder 2 17 are in the shape of cylinders, with a portion of their two ends extending outward to form cylinders. The larger cylinder of the silicone compliant cylinder 16 is cylinder M1, and the smaller cylinder is cylinder N1. The larger cylinder of the silicone compliant cylinder 2 17 is cylinder M2, and the smaller cylinder is cylinder N2. The cylinder N1 of the silicone compliant cylinder 16 tightly covers the cylinder C1 in the aluminum base 15, and the cylinder M1 tightly covers the inertial brass mass block cylinder D1; the cylinder N2 of the silicone compliant cylinder 2 17 tightly covers the cylinder C2 in the aluminum base 2 18, and the cylinder M2 tightly covers the inertial brass mass block cylinder D2.

[0008] The aluminum shell 14 is a cylinder, and its inner diameter is the same as the diameter of the cylinder A1 of the aluminum base 15. The aluminum shell fits tightly with the aluminum base 15 and the aluminum base 2 18, ensuring the stability of the overall structure.

[0009] Another object of the present invention is to provide a method for monitoring the intrusion of foreign objects in urban rail using a sensitivity enhancement structure based on a distributed optical fiber acoustic wave sensing system. When measuring, the sensitivity enhancement structure 7 is connected to the end of the sensing optical fiber 6 of the DAS system, and the sensing optical fiber 6 is fixed at the location to be monitored. The back Rayleigh scattered light collected at the incident port is sent to the weak optical coherent receiving module 9 for reception, the optical signal is amplified and converted into an electrical signal, and then the electrical signal is collected, and finally analyzed and processed by the host computer 11. The host computer 11 uses a digital orthogonal demodulation algorithm to demodulate the phase data of the back Rayleigh scattered light, and the demodulated phase data can be used to restore the vibration information.

[0010] The beneficial effects of the present invention are as follows: when various vibrations generated in the outside world are transmitted to the sensitivity enhancement structure, the brass mass block will drive the silicone compliant cylinder to move along its axial direction due to inertia, and the axial movement will stretch or compress the compliant cylinder, and then the single-mode optical fiber wrapped on the compliant cylinder will also deform. When the vibration effect is the same, this deformation will be amplified compared with the optical fiber deformation of the traditional DAS; then the back Rayleigh scattered light carrying vibration information returned in the optical fiber interferes with the local oscillation light in the optical fiber coupler, and is received by the weak light coherent receiving module, and the optical signal is amplified and converted into an electrical signal, and then the electrical signal is collected by the data acquisition card, and finally received and processed by the host computer. This structure solves the problem of low signal-to-noise ratio of the traditional DAS system. In practical applications, the signal can be amplified and collected, which improves the signal-to-noise ratio of the signal; at the same time, because the sensitivity enhancement structure is protected by an aluminum shell, it can be competent for monitoring tasks under complex and harsh conditions, and has a broader application prospect in the fields of urban underground structure detection, road traffic safety detection, oil and gas resource exploration and development, perimeter security, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The drawings described herein are used to provide further understanding of the present invention and constitute a part of this application. The illustrative examples of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0012] Figure 1 It is a structural block diagram of a distributed optical fiber acoustic wave sensing system with a sensitivity enhancement structure of the present invention; Figure 2 It is a structural schematic diagram of the sensitivity enhancement structure of the distributed optical fiber acoustic wave sensing system of the present invention; Figure 3 A schematic structural diagram of an aluminum base of a distributed optical fiber acoustic wave sensing system sensitivity enhancement structure of the present invention; Figure 4 It is a structural schematic diagram of a silica gel compliant column of a sensitization structure of a distributed optical fiber acoustic wave sensing system of the present invention; Figure 5 A schematic diagram of the structure of the inertial brass mass block of the distributed optical fiber acoustic wave sensing system sensitivity enhancement structure of the present invention; Figure 6 A schematic diagram of the structure of an aluminum housing of a distributed optical fiber acoustic wave sensing system sensitivity enhancement structure of the present invention; Figure 7 A grid division diagram of the distributed optical fiber acoustic wave sensing system sensitivity enhancement structure of the present invention; Figure 8 It is a static stress analysis diagram of the sensitization structure of the distributed optical fiber acoustic wave sensing system of the present invention; Fig. 9Comparison diagram of the original noise signals collected by the traditional distributed fiber optic acoustic wave sensing system and the distributed fiber optic acoustic wave sensing system with enhanced sensitivity structure; Fig.10 This is a comparison chart of 100Hz signals collected by the traditional distributed fiber optic acoustic wave sensing system and the distributed fiber optic acoustic wave sensing system with enhanced sensitivity structure; Fig.11 The discrete Fourier transform diagram of the 100Hz signal collected by the traditional distributed fiber optic acoustic wave sensing system; Fig.12 This is a discrete Fourier transform diagram of the 100 Hz signal collected by the sensitization structure of the distributed optical fiber acoustic wave sensing system of the present invention.

[0013] In the figure: 1. narrow linewidth laser; 2. fiber coupler 1; 3. acousto-optic modulator; 4. erbium-doped fiber amplifier; 5. circulator; 6. sensing fiber; 7. sensitivity enhancement structure; 8. fiber coupler 2; 9. weak light coherent receiving module; 10. data acquisition card; 11. host computer; 12. single-mode optical fiber; 13. inertial mass block; 14. aluminum housing; 15. aluminum base 1; 16. silicone compliant cylinder 1; 17. silicone compliant cylinder 2; 18. aluminum base 2. DETAILED DESCRIPTION

[0014] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0015] See also Figure 1 As shown, the DAS system uses a narrow linewidth laser 1, and the emitted light is divided into two parts through a fiber coupler 2, of which 99% is used as signal light and 1% is used as local oscillator light. The signal light passes through an acousto-optic modulator 3 to modulate the continuous light emitted by the laser into pulsed light. Then, an erbium-doped fiber amplifier 4 is used to amplify the optical signal, and after the optical signal is amplified, it is passed through a circulator 5, and then enters the sensing optical fiber 6 through another port of the circulator 5. Then, the back-scattered Rayleigh light carrying vibration information returned in the optical fiber interferes with the local oscillator light in the fiber coupler 8, and is received by a weak light coherent receiving module 9, which amplifies the optical signal and converts it into an electrical signal. Then, the data acquisition card 10 collects the electrical signal, and finally, the host computer receives and processes it.

[0016] See also Figure 2As shown, the sensitivity enhancement structure of the distributed fiber optic acoustic wave sensing system includes an aluminum base 15, an aluminum base 2 18, a silicone compliant cylinder 16, a silicone compliant cylinder 2 17, an inertial mass block 13, a single-mode optical fiber 12 and an aluminum shell 14. The two ends of the inertial mass block 13 inside the aluminum shell 14 are tightly connected to the silicone compliant cylinder 16 and the silicone compliant cylinder 2 17 to form a simple harmonic oscillator. The single-mode optical fiber 12 is evenly wound around the outside of one of the silicone compliant cylinders, and a prestress of 5N is applied to the single-mode optical fiber 12. The single-mode optical fiber 12 is led out from the side of the aluminum shell 14 and connected to the external optical path.

[0017] See also Figure 3 , Figure 4 , Figure 5 , Figure 6 As shown, the sensitization structural components of the distributed optical fiber acoustic wave sensor system are shown in the figure. The aluminum base 15 and the aluminum base 2 18 are made of aluminum and are respectively composed of three cylinders. The three cylinders are coaxial and have decreasing diameters. The diameters of the three cylinders of the aluminum base 15 are cylinder A1, cylinder B1, and cylinder C1 from small to large, and the diameters of the three cylinders of the aluminum base 2 18 are cylinder A2, cylinder B2, and cylinder C2 from small to large, and the diameter relationship is A1=A2, B1=B2, and C1=C2. The entire surface of the aluminum base is anodized to show the original color of aluminum.

[0018] The material of the inertial mass block 13 is brass, and the surface is treated with anti-corrosion oxidation. The inertial mass block is an axisymmetric structure, and the whole is composed of five cylinders, which are cylinder D1, cylinder E1, cylinder F, cylinder E2, and cylinder D2 from top to bottom, respectively. Cylinder D1 has the same diameter as cylinder D2, and cylinder E1 has the same diameter as cylinder E2. The diameter relationship between them is F>D1=D2>E1=E2.

[0019] The silicone compliant cylinder 16 and the silicone compliant cylinder 2 17 are in the shape of cylinders, with a portion of their two ends extending outward to form cylinders. The larger cylinder of the silicone compliant cylinder 16 is cylinder M1, and the smaller cylinder is cylinder N1. The larger cylinder of the silicone compliant cylinder 2 17 is cylinder M2, and the smaller cylinder is cylinder N2. The cylinder N1 of the silicone compliant cylinder 16 tightly covers the cylinder C1 in the aluminum base 15, and the cylinder M1 tightly covers the inertial brass mass block cylinder D1; the cylinder N2 of the silicone compliant cylinder 2 17 tightly covers the cylinder C2 in the aluminum base 2 18, and the cylinder M2 tightly covers the inertial brass mass block cylinder D2.

[0020] The aluminum shell 14 is a cylinder, and its inner diameter is the same as the diameter of the cylinder A1 of the aluminum base 15. The aluminum shell fits tightly with the aluminum base 15 and the aluminum base 2 18, ensuring the stability of the overall structure. Example

[0021] The sensitivity enhancement structure based on the distributed optical fiber acoustic wave sensing system of the present invention comprises an aluminum base 15, an aluminum base 2 18, a silicone compliant cylinder 16, a silicone compliant cylinder 2 17, an inertial mass block 13, a single-mode optical fiber 12 and an aluminum housing 14. On each side of the inertial mass block 13, there is a cylinder with a diameter of 44 mm and a height of 2 mm and a cylinder with a diameter of 40 mm and a height of 3.5 mm, plus a cylinder with a diameter of 54 mm and a height of 15 mm at the center of the inertial mass block 13, that is, a protruding ring with a height of 4 mm and a width of 2 mm is formed at both ends of the inertial mass block 13, and correspondingly, a cylinder with an outer diameter of 48 mm, an inner diameter of 44 mm and a height of 5.5 mm is respectively provided at one end of the silicone compliant cylinders 1, 2, 17, and the cylinder and the protruding ring of the inertial mass block 13 can just achieve a tight connection with the inertial mass block 13. At the other end of the silicone variable columns 1, 2 16, 17, there is a cylinder with an outer diameter of 48mm, an inner diameter of 44mm, and a height of 4.7mm; correspondingly, at one end of the aluminum base 15 and the aluminum base 2 18, there is a cylinder with a diameter of 44mm and a height of 4.7mm, thereby achieving a tight connection between the silicone variable columns 1, 2 16, 17 and the aluminum base 15 and the aluminum base 2 18. The single-mode optical fiber 12 wound on the silicone compliant cylinder 16 is wound by machine to ensure that the winding is as uniform as possible. The length of the single-mode optical fiber 12 wound on the silicone compliant cylinder 16 is 20m. A prestress of 5N is applied during winding to ensure that the structure has a better response effect. Then, the aluminum bases 1, 2 15, 18, the silicone compliant cylinders 1, 2 16, 17, the inertial mass block 13, and the single-mode optical fiber 12 are placed as a whole inside the aluminum housing 14. Bolts are used to connect four M3 threaded holes on the side of the aluminum housing 14 and four 3.2mm diameter holes on the upper and lower parts of the aluminum housing 14 to fix the entire sensor. One end of the single-mode optical fiber 12 is led out from the side of the aluminum housing 14 to connect to the external optical path. Sealant is used to seal the joints of each component.

[0022] See also Figure 7 and Figure 8As shown, a finite element analysis is performed on the sensitivity enhancement structure 7 of the distributed optical fiber acoustic wave sensing system. When the sensitivity enhancement structure 7 senses external vibration, the inertial mass block therein will stretch or compress the silicone compliant cylinders one and two due to inertia, thereby amplifying the deformation of the single-mode optical fiber 12 wound around one of the silicone compliant cylinders; Soildworks is used to draw the geometric model of the sensitivity enhancement structure 7 of the distributed optical fiber acoustic wave sensing system, and then the material properties of each part of the sensitivity enhancement structure 7 of the distributed optical fiber acoustic wave sensing system are set. The material of the inertial mass block 13 is brass, the material of the silicone compliant cylinders one and two is silicone, and the material of the aluminum base one and two is aluminum. The model after meshing is as shown Figure 7 As shown. A fixed constraint is applied vertically to the upper and lower bottom surfaces of the aluminum base of the distributed fiber optic acoustic wave sensor system's enhanced sensitivity structure 7, and then a pressure is applied to the inertial mass block. The static stress analysis is as follows: Figure 8 shown.

[0023] See also Fig. 9 and Fig.10 As shown, a field experiment was conducted on the sensitivity enhancement structure 7 of the distributed optical fiber acoustic wave sensing system. By collecting the acoustic wave signal with a frequency of 100 Hz played by the audio, the signals collected by the traditional distributed optical fiber acoustic wave sensing system and the signals collected by the improved distributed optical fiber acoustic wave sensing system of the present invention were compared and analyzed. Fig. 9 , Fig.10 As shown. Fig. 9 The background noise in the traditional DAS is 0.0182 dBw, and the noise power of the improved DAS of the present invention is 0.146 dBw. Fig.10 The 100 Hz signal in the image is used to calculate the power of the traditional signal to be 2.06 dBw, and the power of the improved DAS signal to be 36.7 dBw. Finally, according to the signal-to-noise ratio calculation formula

[0024] Where SNR is the system signal-to-noise ratio, is the effective signal power, is the noise signal power. According to formula (1), the signal-to-noise ratio of the traditional DAS is 20.5 dB, and the signal-to-noise ratio of the improved DAS is 23.9 dB. The signal collected by the improved DAS of the present invention is increased by 3.4 dB.

[0025] from Fig.11 , Fig.12It can be seen that the amplitude of the effective signal at 100Hz collected by the traditional DAS is 0.236 rad, and the amplitude of the effective signal at 100Hz collected by the improved DAS of the present invention is 3.61 rad, and the amplitude of the effective signal is amplified by about 15.3 times. Through the above experiment, it can be shown that the improved DAS can amplify the signal amplitude and improve the system signal-to-noise ratio.

[0026] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made to the present invention shall be included in the protection scope of the present invention.

Claims

1. A sensitivity enhancement structure based on a distributed optical fiber acoustic wave sensing system, characterized in that: The invention comprises an aluminum base 1 (15), an aluminum base 2 (18), a silicone compliant column 1 (16), a silicone compliant column 2 (17), an inertial mass block (13), a single-mode optical fiber (12) and an aluminum shell (14). The two ends of the inertial mass block (13) inside the aluminum shell (14) are respectively tightly connected to the silicone compliant column 1 (16) and the silicone compliant column 2 (17) to form a simple harmonic oscillator. The single-mode optical fiber (12) is evenly wound around the outside of one of the silicone compliant columns. Prestress is applied to the single-mode optical fiber (12) during winding. The single-mode optical fiber (12) is led out from the side of the aluminum shell (14) and connected to an external optical path.

2. The sensitivity enhancement structure based on the distributed optical fiber acoustic wave sensing system according to claim 1 is characterized in that: The aluminum base 1 (15) and the aluminum base 2 (18) are made of aluminum and are respectively composed of three cylinders. The three cylinders are coaxial and have gradually decreasing diameters. The diameters of the three cylinders of the aluminum base 1 (15) are, from small to large, cylinder A1, cylinder B1, and cylinder C1, respectively. The diameters of the three cylinders of the aluminum base 2 (18) are, from small to large, cylinder A2, cylinder B2, and cylinder C2, respectively. The diameter relationships are A1=A2, B1=B2, and C1=C2.

3. The sensitivity enhancement structure based on the distributed optical fiber acoustic wave sensing system according to claim 1 is characterized in that: The inertial mass block (13) is made of brass, and its surface is treated with corrosion-resistant oxidation. The inertial mass block is an axisymmetric structure, and is composed of five cylinders, which are cylinder D1, cylinder E1, cylinder F, cylinder E2, and cylinder D2 from top to bottom, wherein cylinder D1 has the same diameter as cylinder D2, and cylinder E1 has the same diameter as cylinder E2, and the relationship between their diameters is F>D1=D2>E1=E2.

4. The sensitivity enhancement structure based on the distributed optical fiber acoustic wave sensing system according to claim 1 is characterized in that: The silicone compliant cylinder 1 (16) and the silicone compliant cylinder 2 (17) are in the shape of cylinders, with a portion of the two ends extending outward to form a cylinder. The larger cylinder of the silicone compliant cylinder 1 (16) is cylinder M1, and the smaller cylinder is cylinder N1. The larger cylinder of the silicone compliant cylinder 2 (17) is cylinder M2, and the smaller cylinder is cylinder N2. The cylinder N1 of the silicone compliant cylinder 1 (16) tightly fits the cylinder C1 in the aluminum base 1 (15), and the cylinder M1 tightly fits the inertial brass mass block cylinder D1; the cylinder N2 of the silicone compliant cylinder 2 (17) tightly fits the cylinder C2 in the aluminum base 2 (18), and the cylinder M2 tightly fits the inertial brass mass block cylinder D2.

5. The sensitivity enhancement structure based on the distributed optical fiber acoustic wave sensing system according to claim 1 is characterized in that: The aluminum shell (14) is a cylinder, and its inner diameter is the same as the diameter of the cylinder A1 of the aluminum base 1 (15). The aluminum shell fits tightly with the aluminum base 1 (15) and the aluminum base 2 (18), thereby ensuring the stability of the entire structure.

6. A method for monitoring foreign body intrusion along urban rail lines by using the sensitivity enhancement structure based on a distributed optical fiber acoustic wave sensing system according to any one of claims 1 to 5, characterized in that: When measuring, the sensitivity enhancement structure (7) is installed at the end of the sensing optical fiber (6) of the DAS system. The sensing optical fiber (6) is fixed at the location to be monitored. The back Rayleigh scattered light collected at the incident port is sent to the weak light coherent receiving module (9) for receiving. The optical signal is amplified and converted into an electrical signal, which is then collected and finally analyzed and processed by the host computer (11). The host computer (11) uses a digital orthogonal demodulation algorithm to demodulate the phase data of the back Rayleigh scattered light, and uses the demodulated phase data to restore the vibration information.

Images