Miniature photoacoustic probe and monitoring system for in-situ monitoring of dissolved gas in oil

Abstract

This invention relates to a miniature photoacoustic probe and monitoring system for in-situ monitoring of dissolved gases in oil. The miniature photoacoustic probe includes a pump fiber, a pump fiber ferrule, a probe fiber, an acoustic transducer film, and an oil-gas separation membrane. The pump fiber ferrule has an inner hole, and the light-emitting end of the pump fiber is positioned at a predetermined distance from the first side of the acoustic transducer film, forming a gas photoacoustic cavity in the local space between the inner hole and the ferrule. The pump fiber ferrule also has a gas guiding channel for introducing the gas to be measured, separated by the oil-gas separation membrane, into the gas photoacoustic cavity. The end face of the probe fiber and the second side of the acoustic transducer film form a Photonic Optical Interference Cavity (FP). The pump light excites the gas to be measured within the gas photoacoustic cavity, generating photoacoustic pressure. The acoustic transducer film vibrates under pressure, causing changes in the FP optical interference cavity. This probe can shorten the gas diffusion path and the sound pressure transmission path, improve the response speed, and facilitate in-situ miniaturized gas detection.

Description

Technical Field

[0001] This invention belongs to the field of gas detection technology, specifically relating to a miniature photoacoustic probe and monitoring system for in-situ monitoring of dissolved gases in oil. Background Technology

[0002] During operation, oil-filled electrical equipment such as transformers, converter transformers, and high-voltage shunt reactors release characteristic gases such as hydrogen, methane, acetylene, ethylene, and carbon monoxide into the insulating oil. The types, concentrations, and growth trends of these characteristic gases can reflect latent fault conditions such as overheating, partial discharge, and arc discharge within the equipment. Therefore, continuous online monitoring of dissolved gases in the oil is an important technical means for condition assessment and fault early warning of oil-filled electrical equipment.

[0003] To achieve in-situ detection of dissolved gases in oil, existing technologies attempt to combine oil-gas separation membranes with fiber optic photoacoustic sensors. This allows small dissolved gas molecules to pass through the membrane into a gas chamber, where a pressure wave is generated using the photoacoustic effect, and membrane deformation is detected via a fiber optic Fabry-Perot interferometer. While this approach reduces reliance on external degassing devices, the gas detection space is typically still a relatively independent gas chamber. The gas to be detected needs to diffuse into this chamber first, and the chamber volume and diffusion path affect gas exchange efficiency, thus limiting response speed.

[0004] Furthermore, in the aforementioned structure, photoacoustic excitation typically occurs within a large gas cavity or chamber, and the photoacoustic pressure wave needs to propagate within the gas cavity before acting on the acoustic diaphragm. Due to the spatial distance between the sound source region and the pressure-bearing region of the diaphragm, the photoacoustic pressure transmission path is relatively long, and the efficiency of the pressure wave acting on the diaphragm is easily affected by the cavity structure, gas distribution, and propagation loss. Simply reducing the size of the gas cavity to improve the response speed is limited by fiber optic coupling, gas entry channels, diaphragm installation space, and the arrangement of the oil-gas separation structure, making it difficult to simultaneously achieve sensing sensitivity, response speed, and probe miniaturization.

[0005] Therefore, there is an urgent need for a miniature photoacoustic probe for in-situ monitoring of dissolved gases in oil, which can improve the detection response accuracy and speed, and reduce the overall size of the probe. Summary of the Invention

[0006] One of the objectives of this invention is to solve at least one or more of the aforementioned problems in the prior art. In other words, one of the objectives of this invention is to provide a miniature photoacoustic probe and monitoring system for in-situ monitoring of dissolved gases in oil that meets one or more of the aforementioned requirements.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a miniature photoacoustic probe for in-situ monitoring of dissolved gases in oil, comprising a pump fiber, a pump fiber ferrule, a probe fiber, an acoustic transducer film, and an oil-gas separation membrane: The acoustically sensitive transducer film is disposed between the pump fiber and the probe fiber, with a first side facing the pump fiber and a second side facing the probe fiber. The pump fiber ferrule has an inner hole for the pump fiber to pass through. The light-emitting end of the pump fiber is set at a predetermined distance from the first side of the acoustic transducer film. The inner hole forms a gas photoacoustic cavity in the local space between the light-emitting end and the acoustic transducer film, and the first side of the acoustic transducer film constitutes one side cavity wall of the gas photoacoustic cavity. The pump fiber ferrule is also provided with a gas guiding channel. One end of the gas guiding channel is connected to the gas photoacoustic cavity, and the other end is connected to the inner gas space of the oil-gas separation membrane, so as to introduce the gas to be tested separated by the oil-gas separation membrane into the gas photoacoustic cavity. An FP optical interference cavity is formed between the end face of the probe fiber and the second side of the acoustic transducer film; The pump fiber is used to input pump light into the gas photoacoustic cavity so that the pump light output from the pump fiber excites the gas under test to generate photoacoustic pressure. The probe fiber is used to detect the changes in the FP optical interference cavity caused by the vibration of the acoustic transducer film driven by the photoacoustic pressure.

[0008] In a preferred embodiment, the pump fiber, the probe fiber, the acoustic transducer film, the gas photoacoustic cavity, and the FP optical interference cavity are arranged coaxially.

[0009] As a further preferred embodiment, the miniature photoacoustic probe further includes a probe fiber ferrule, which has an inner hole for the probe fiber to pass through, and one end near the acoustic transducer film is flush with the end face of the probe fiber.

[0010] As a further preferred embodiment, the miniature photoacoustic probe also includes a sleeve with an axial through hole, and the pump fiber ferrule, the probe fiber ferrule, and the acoustic transducer film are fixed in the axial through hole.

[0011] As a further preferred embodiment, the sleeve is provided with a connecting groove that penetrates the sleeve wall, so that the inner gas space is connected to the gas guide channel through the connecting groove.

[0012] In a preferred embodiment, the oil-gas separation membrane is formed into an oil-gas separation membrane tube and is sleeved on the outside of the micro photoacoustic probe.

[0013] In a preferred embodiment, the air guide channel is widened along the axial direction of the pump fiber ferrule to increase the air intake area of ​​the air guide channel.

[0014] In a preferred embodiment, the acoustic transducer film is a chromium-silver-gold metal composite film.

[0015] On the other hand, the present invention also provides a monitoring system for in-situ monitoring of dissolved gases in oil, including a modulation module, a pump light source, a detection light source, a photoelectric detection module, a signal demodulation module, and a miniature photoacoustic probe as described in any of the above. The modulation module is connected to the pump light source and is used to modulate the pump light output by the pump light source. The pump light source is connected to the pump fiber of the micro photoacoustic probe and is used to input pump light into the gas photoacoustic cavity through the pump fiber; The detection light source is connected to the detection optical fiber of the miniature photoacoustic probe, and is used to input detection light into the FP optical interferometer cavity via the detection optical fiber; The photoelectric detection module is connected to the detection optical fiber and is used to receive the reflected light returned by the FP optical interferometer cavity and convert it into an electrical signal; The signal demodulation module is connected to the photoelectric detection module and is used to obtain the vibration information of the acoustic transducer film based on the electrical signal, and then analyze the concentration of the gas to be measured.

[0016] In a preferred embodiment, the system further includes an optical coupler and a balanced detector. The optical coupler is connected to the output of the detection light source and is used to split the output of the detection light source into a detection light and a reference light. The detection light is input to the FP optical interferometer cavity, and the reference light and the reflected light are respectively input to the two inputs of the balanced detector. The balanced detector is used to perform differential detection of the reference light and the reflected light to suppress the fluctuation noise of the detection light source.

[0017] Compared with the prior art, the miniature photoacoustic probe and monitoring system for in-situ monitoring of dissolved gases in oil provided by the present invention have the following beneficial effects: First, the present invention forms a gas photoacoustic cavity inside the pump fiber ferrule, such that the gas photoacoustic cavity is defined by the light-emitting end of the pump fiber, the inner hole wall of the pump fiber ferrule, and the first side of the acoustic transduction film as a local cavity located in the inner hole of the pump fiber ferrule, which can significantly reduce the diffusion volume of the gas to be measured after entering, and is beneficial to the response speed of the gas concentration detection.

[0018] Simultaneously, the pump light output from the pump fiber excites the gas under test within the gas photoacoustic cavity, generating photoacoustic pressure. This pressure directly acts on the acoustic transducer film and subsequently on the FP optical interference cavity, causing a change in cavity length. The detection fiber detects this change in cavity length from the opposite side of the corresponding region. These relative regions ensure that the pump excitation path, the pressure-bearing position of the film, and the FP optical detection path are structurally corresponding. Compared to structures where photoacoustic excitation occurs in a larger gas cavity and the pressure wave then propagates to the diaphragm, this invention reduces the propagation distance and loss of the photoacoustic pressure within the cavity and facilitates the rapid conversion of the film's micro-vibrations caused by the photoacoustic pressure into a change in the cavity length of the FP optical interference cavity, thereby improving the vibration response intensity and detection sensitivity of the acoustic transducer film. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of a miniature photoacoustic probe for in-situ monitoring of dissolved gases in oil according to an embodiment of the present invention; Figure 2 This is a cross-sectional view of a miniature photoacoustic probe for in-situ monitoring of dissolved gases in oil, according to an embodiment of the present invention. Figure 3 This is an architecture diagram of the monitoring system for in-situ monitoring of dissolved gases in oil according to the present invention; Figure reference numerals: - Pump fiber - 1, Gas photoacoustic cavity - 101, Gas guide channel - 102, Pump fiber ferrule - 2, Probe fiber - 3, Probe fiber ferrule - 4, Acoustic transducer film - 5, FP optical interference cavity - 6, Oil-gas separation membrane tube - 7, Sleeve - 8. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0021] The following description provides examples and does not limit the scope, applicability, or examples set forth in the claims. Changes may be made to the function and arrangement of the described elements without departing from the scope of this application. Various processes or components may be appropriately omitted, substituted, or added to the examples. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Furthermore, features described with respect to some examples may be combined into other examples.

[0022] This application provides a miniature photoacoustic probe for in-situ monitoring of dissolved gases in oil, as shown in the schematic diagram below. Figure 1 and Figure 2As shown, it includes a pump fiber 1, a pump fiber ferrule 2, a probe fiber 3, an acoustic transducer film 5, and an oil-gas separation membrane. The acoustic transducer film 5 is disposed between the pump fiber 1 and the probe fiber 3, with its first side facing the pump fiber 1 and its second side facing the probe fiber 3.

[0023] The pump fiber ferrule 2 has an inner hole for the pump fiber 1 to pass through. The inner hole extends along the axial direction of the pump fiber ferrule 2, and the pump fiber 1 is embedded in the inner hole. An acoustic transducer 5 covers the end face of the pump fiber ferrule 2 facing the acoustic transducer 5. The light-emitting end of the pump fiber 1 facing the acoustic transducer 5 is located in the inner hole and is set at a predetermined distance from the first side of the acoustic transducer 5, so that a gas photoacoustic cavity 101 is formed in the local space inside the inner hole from the light-emitting end of the pump fiber 1 to the acoustic transducer 5. The light-emitting end of the pump fiber 1 constitutes the left cavity wall of the gas photoacoustic cavity 101, which is used to input pump light into the gas photoacoustic cavity 101. At the same time, the first side of the acoustic transducer 5 constitutes the right cavity wall of the gas photoacoustic cavity 101.

[0024] The dimensions of the gas photoacoustic cavity 101 can be determined by the distance between the light-emitting end of the pump fiber 1 and the acoustic transducer film 5, and the diameter of the inner hole of the pump fiber ferrule 2. The diameter of the inner hole of the pump fiber ferrule 2 is used to constrain the diameter of the gas photoacoustic cavity 101, so that the pump light interacts with the gas to be measured in a smaller volume. The first side of the acoustic transducer film 5 directly bears the photoacoustic pressure generated in the gas photoacoustic cavity 101 as the cavity wall.

[0025] As a feasible example, the predetermined spacing between the light-emitting end of the pump fiber 1 and the acoustic transducer film 5 is 200 μm. This predetermined spacing defines the axial length of the gas photoacoustic cavity 101 and, together with the inner diameter of the pump fiber ferrule 2, determines the volume of the gas photoacoustic cavity 101.

[0026] The region where the center of the acoustic transducer film 5 is opposite to the inner hole of the pump fiber ferrule 2 forms a thin-film acoustic region. At this time, the first side of the acoustic transducer film 5 serves as the cavity wall of the gas photoacoustic cavity 101 and bears the sound pressure to sense the photoacoustic pressure in the gas photoacoustic cavity 101. This photoacoustic pressure can directly act on the acoustic transducer film 5, causing the acoustic transducer film 5 to vibrate slightly. The vibration amplitude of the acoustic transducer film 5 is related to the absorption response of the gas to be measured to the pump light in the gas photoacoustic cavity 101.

[0027] In the above structure of this application, the gas photoacoustic cavity 101 is formed in the local inner hole space of the pump fiber ferrule 2, which can reduce the volume of the independent photoacoustic cell structure and make the photoacoustic excitation position and the pressure position of the acoustic transducer 5 directly correspond inside the probe.

[0028] The pump fiber ferrule 2 is provided with a gas guide channel 102. One end of the gas guide channel 102 is connected to the gas photoacoustic cavity 101, and the other end is connected to the inner gas space of the oil-gas separation membrane. This allows the gas to be tested separated by the oil-gas separation membrane to enter the gas photoacoustic cavity 101 through the gas guide channel 102, and allows the gas photoacoustic cavity 101 to exchange gases with the inner gas space of the oil-gas separation membrane through the gas guide channel 102.

[0029] As a feasible example, the gas guiding channel 102 is a vertical through hole that penetrates the pump fiber ferrule 2 radially. One end of the channel is opened on the outside of the pump fiber ferrule 2, and the other end is connected to the inner hole of the pump fiber ferrule 2. The connection point with the inner hole is located on the wall of the gas photoacoustic cavity 101, so that the gas to be tested can directly enter the gas photoacoustic cavity 101 from the gas guiding channel 102.

[0030] An oil-gas separation membrane is disposed on the outside of the pump fiber ferrule 2. The oil-gas separation membrane is used to separate the external oil phase environment from the gas exchange space inside the probe. Specifically, the gas space inside the oil-gas separation membrane is connected to the gas guide channel 102 on the pump fiber ferrule 2. The gas guide channel 102 is then connected to the gas photoacoustic cavity 101, so that the gas to be tested dissolved in the oil can pass through the oil-gas separation membrane and enter the gas photoacoustic cavity 101, while the liquid is isolated in the external environment of the membrane and cannot enter the gas photoacoustic cavity 101.

[0031] The oil-gas separation membrane can cover the outer opening of the gas guide channel 102. In a more specific embodiment, the oil-gas separation membrane can be in the form of a membrane tube.

[0032] Specifically, the oil-gas separation membrane forms an oil-gas separation membrane tube 7, which is sleeved on the outside of the micro photoacoustic probe and at least covers the gas sensing area including the gas photoacoustic cavity 101, the outer end of the gas guiding channel 102, and the adjacent insert structure.

[0033] Both ends of the oil-gas separation membrane tube 7 can be fixed to a supporting structure. For example, both ends can be sealed and fixed to the insert, thereby forming an inner gas space between the inner wall of the oil-gas separation membrane tube 7 and the outer circumferential surface of the insert on which it is fitted.

[0034] The membrane tube design facilitates the formation of a complete and continuous oil-gas separation zone along the probe axis of this application, thereby enabling the probe to be directly and easily placed into the oil.

[0035] Therefore, when the probe is in the in-situ monitoring state in the oil, the gas to be tested in the external oil phase first passes through the oil-gas separation membrane and enters its inner gas space; the gas to be tested that enters the inner gas space then enters the gas photoacoustic cavity 101 through the gas guide channel 102 on the pump fiber ferrule 2 and is excited by the pump light.

[0036] In the above embodiment, since the gas photoacoustic cavity 101 is formed by a local space in the inner hole, its volume can realize a nano-level micro gas detection space. After the gas to be tested enters the gas space inside the oil-gas separation membrane tube 7, it does not need to diffuse to fill the large-volume gas chamber. Instead, it enters the gas photoacoustic cavity 101 through the gas guide channel 102. In just a short time, under the action of the pump light output from the pump fiber 1, a photoacoustic pressure corresponding to the gas concentration can be generated.

[0037] For example, in some specific examples, the inner diameter of the pump fiber ferrule 2 is 127 μm, the distance between the light-emitting end of the pump fiber 1 and the acoustic transducer film 5 is 200 μm, and the volume of the gas photoacoustic cavity 101 is 2.5 nL.

[0038] Meanwhile, in the embodiment where the oil-gas separation membrane is in the form of a membrane tube, the oil-gas separation membrane tube 7 is sleeved on the outside of the micro photoacoustic probe, forming a continuous gas permeation area along the probe axis. This increases the effective contact area between the oil phase and the oil-gas separation membrane, allowing the analyte gas dissolved in the oil to diffuse from the entire circumferential surface of the membrane tube into its inner gas space. This larger membrane diffusion area, combined with the nanoliter gas photoacoustic cavity 101, further shortens the time required for the analyte gas to enter the gas photoacoustic cavity 101, improving the probe's response speed to changes in the concentration of dissolved gas in the oil.

[0039] On the other side of the acoustic transducer film 5, the probe fiber 3 and the acoustic transducer film 5 form an FP optical interference cavity 6. The end face of the probe fiber 3 faces the second side of the acoustic transducer film 5, and a gap is maintained between the end face of the probe fiber 3 and the second side of the acoustic transducer film 5, which forms the cavity length of the FP optical interference cavity 6. The end face of the probe fiber 3 and the second side of the acoustic transducer film 5 serve as two reflection interfaces in the FP optical interference cavity 6, respectively. After the probe light enters the FP optical interference cavity 6 through the probe fiber 3, interference reflection is formed between the end face of the probe fiber 3 and the acoustic transducer film 5.

[0040] When the photoacoustic pressure within the gas photoacoustic cavity 101 drives the acoustic transducer 5 to vibrate, the position of the second side of the acoustic transducer 5 relative to the end face of the probe fiber 3 changes, and the cavity length of the FP optical interference cavity 6 changes accordingly. The reflected light returning to the probe fiber 3 undergoes a phase change, thereby generating an interference signal. Thus, the photoacoustic pressure experienced by the acoustic transducer 5 on the pump fiber 1 side is converted into a change in the interference signal that can be read on the probe fiber 3 side.

[0041] In some specific embodiments, the pump fiber 1, the probe fiber 3, the acoustic transducer film 5, the gas photoacoustic cavity 101, and the FP optical interference cavity 6 are coaxially arranged. This arrangement helps to improve the alignment between the pump excitation position, the film vibration region, and the interference detection position, thereby improving the accuracy and stability of the detection.

[0042] In existing atmospheric cavity structures, the gas to be tested needs to diffuse within a larger cavity and reach a relatively stable concentration distribution. The photoacoustic pressure response generated by pump light excitation also needs to form a stable coupling with the diaphragm within the larger cavity before accurate detection results can be obtained. For example, if a contrast structure with a larger gas cavity is used, it takes approximately 1.5 hours for the gas to be tested to diffuse into the gas cavity and form a stable, detectable response.

[0043] When using the miniature photoacoustic probe of the above embodiment, since the oil-gas separation membrane tube 7 provides a large gas permeation area, the gas photoacoustic cavity 101 is a nano-level small volume cavity, and the pressure area of ​​the acoustic transducer 5 is coaxially corresponding with the FP optical detection area, the gas to be tested can quickly form a stable photoacoustic detection signal after entering the gas photoacoustic cavity 101, and the response time can be shortened to about 5 minutes.

[0044] In some specific implementations, the probe fiber 3 can be disposed within the probe fiber ferrule 4.

[0045] Specifically, the probe fiber ferrule 4 is used to support and position the probe fiber 3, and has an inner hole along its axial direction for the probe fiber 3 to pass through, and the probe fiber 3 extends along the inner hole.

[0046] The end of the probe fiber ferrule 4 closest to the acoustic transducer film 5 is flush with the end face of the probe fiber 3. Therefore, the probe fiber ferrule 4 and the probe fiber 3 together form the FP optical interference cavity 6 relative to the acoustic transducer film 5. At this time, the distance between the end face of the probe fiber 3 and the acoustic transducer film 5 is no longer determined solely by the flexible optical fiber, but can be limited by the end face position of the probe fiber ferrule 4, which is conducive to forming a stable FP optical interference cavity 6 shape.

[0047] In some embodiments, the miniature photoacoustic probe further includes a sleeve 8. An axial through hole is formed in the sleeve 8, and the pump fiber ferrule 2, the acoustic transducer 5, and the probe fiber ferrule 4 are sequentially inserted and fixed along the axial through hole of the sleeve 8.

[0048] As an example, the pump fiber ferrule 2 is fixed to the left side of the sleeve 8 to maintain the relative position between the light-emitting end of the pump fiber 1 and the first side of the acoustic transducer film 5; the probe fiber ferrule 4 is fixed to the right side of the sleeve 8 to maintain the relative position between the end face of the probe fiber 3 and the second side of the acoustic transducer film 5; the acoustic transducer film 5 is located between the pump fiber ferrule 2 and the probe fiber ferrule 4, and is held in a predetermined position by fixing it to the sleeve 8.

[0049] Through the axial through-hole of the sleeve 8, the pump fiber ferrule 2 and the probe fiber ferrule 4 can be subject to common radial restraint, thereby enabling the pump fiber 1, the gas photoacoustic cavity 101, the acoustic transducer 5, the FP optical interference cavity 6, and the probe fiber 3 to be arranged more precisely and stably along the same axis.

[0050] After being fixed by the sleeve 8, the length of the gas photoacoustic cavity 101 between the light-emitting end of the pump fiber 1 and the acoustic transducer film 5, the length of the FP cavity between the end face of the probe fiber 3 and the acoustic transducer film 5, and the positional relationship of the acoustic transducer film 5 between the two cavities are all easier to maintain and stabilize.

[0051] Meanwhile, the casing 8 can also provide external support for the oil-gas separation membrane or the oil-gas separation membrane tube 7. For example, the end of the oil-gas separation membrane tube 7 can be sealed and fixed to the outer wall of the casing 8, so that a closed gas space is isolated inside the oil-gas separation membrane tube 7.

[0052] In some embodiments, a connecting groove may also be provided on the sleeve 8. The connecting groove penetrates the wall of the sleeve 8, so that when the sleeve 8 is located between the pump fiber ferrule 2 and the oil-gas separation membrane, the gas space inside the oil-gas separation membrane can be connected to the gas guide channel 102 through the connecting groove.

[0053] As a feasible example, the connecting groove on the sleeve 8 is opened at a position corresponding to the gas guiding channel 102, and the gas to be tested in the gas space inside the oil-gas separation membrane enters the gas photoacoustic cavity 101 in sequence through the connecting groove and the gas guiding channel 102.

[0054] In some further embodiments, the gas guide channel 102 disposed on the pump fiber ferrule 2 may have an increased inner diameter or be widened along the axial direction of the pump fiber ferrule 2 to increase the communication area between the gas guide channel 102 and the gas space inside the oil-gas separation membrane, thereby improving the gas exchange efficiency between the outside of the pump fiber ferrule 2 and the gas photoacoustic cavity 101.

[0055] In some embodiments, the sleeve 8 is made of ceramic and its inner diameter is 5 nm larger than the outer diameter of the pump fiber ferrule 2 to facilitate gas diffusion into the gas guide channel 102.

[0056] In some embodiments, the acoustic transducer film 5 can be a chromium-silver-gold metal composite film. This application also provides a feasible example for preparing the acoustic transducer film 5.

[0057] Specifically, the silicon substrate wafer is ultrasonically cleaned for 5-10 minutes, acetone is used to remove organic impurities from the wafer surface, and then the wafer is immersed in an alcohol solution for 10 minutes to remove the acetone. Following this, the wafer is rinsed with deionized water and dried using a nitrogen air gun. Next, photoresist is spin-coated onto the wafer using a high-precision CNC spin coater and cured at 120°C for 15 minutes. Thin film deposition is then performed using an electron beam evaporation system, with the deposition materials in the following order and thickness: 30nm for chromium, 500nm for silver, and 50nm for gold. The total thickness of the resulting acoustic transducer film 5 is 580nm.

[0058] This application also provides a feasible example for preparing the above-mentioned micro photoacoustic probe, in which a pump fiber ferrule 2 with an outer diameter of 0.8 mm and an inner diameter of 127 μm is selected, and a through hole communicating with the inner hole is opened on its outer side as a gas channel 102. The outer diameter of the through hole is 0.1 mm and the length is 336 μm.

[0059] A 1:9 ratio of A to B adhesives in 353ND epoxy resin AB glue was used. A small amount of the prepared mixture was applied to a single-mode optical fiber and dotted evenly around the inner hole of the pump fiber ferrule 2. After dotting, a single-mode optical fiber was inserted into and removed from the hole to remove any residual adhesive, thus preventing the residual adhesive from clogging the gas channel or the fiber insertion space. Subsequently, the pump fiber ferrule 2 was placed upside down on the diced acoustic transducer film 5 wafer and transferred to a heating stage. It was heated at 80°C for 60-80 minutes to cure the AB glue. The cured pump fiber ferrule 2 and the wafer were then immersed in acetone and left to stand for 24 hours. After this time, the ferrule was removed, allowing the acoustic transducer film 5 to detach from the silicon substrate and transfer to the end face of the pump fiber ferrule 2.

[0060] After the film transfer is completed, the sample is placed in a sleeve 8 with an inner diameter of 0.9 mm and an outer diameter of 1.4 mm and an axial slot. AB glue is applied to the left end of the sleeve 8 at the connection with the outer wall of the pump fiber ferrule 2 for fixation. The dimensions of the sleeve 8 are matched with the pump fiber ferrule 2 and the probe fiber ferrule 4 to ensure that the two ferrules can be stably assembled along the axial through-hole.

[0061] After the adhesive cures, the pump fiber 1 and the sleeve 8 and their internal structure are fixed in the fixture, and the X, Y, and Z axis positions and pitch of the pump fiber 1 are controlled using a six-dimensional adjustment frame. The pump fiber 1 is fed into the inner hole of the pump fiber ferrule 2 via the Z-axis of the adjustment frame, maintaining a distance between the end face of the pump fiber 1 and the reflective surface of the acoustic transducer film 5. During adjustment, a broadband light source, circulator, and spectrometer are connected to measure the double-beam interference spectrum formed between the end face of the pump fiber 1 and the acoustic transducer film 5 in real time, and the distance between the end face of the pump fiber 1 and the acoustic transducer film 5 is calculated using the free spectral range of the interference fringes. Adjustment is stopped when this distance reaches 200 μm, and the ends of the pump fiber 1 and the pump fiber ferrule 2 are fixed with AB glue to form a stable gas photoacoustic cavity 101.

[0062] After the pump end is fixed, the probe fiber ferrule 4, with the probe fiber 3 inside, is inserted into the sleeve 8 from the right end. While adjusting the position of the probe fiber ferrule 4, a broadband light source, a circulator, and a spectrometer are connected to measure the two-beam interference spectrum formed by the end face of the probe fiber 3 and the end face of the acoustic transducer film 5 in real time, and the contrast of the interference spectrum is observed. When the contrast of the interference spectrum reaches a better state, the adjustment is stopped, and AB glue is applied to the connection between the probe fiber ferrule 4 and the right end of the sleeve 8 for fixation, so that an FP optical interference cavity 6 is formed between the end face of the probe fiber 3 and the second side of the acoustic transducer film 5.

[0063] Cut an oil-gas separation membrane tube 7 with a length of 6mm, an inner diameter of 1.5mm, and an outer diameter of 2mm. Sleeve the oil-gas separation membrane tube 7 over the above structure. Apply AB glue to the connection between its two ends and the outer wall of the sleeve 8 for sealing and fixing. After the two ends are fixed, the oil-gas separation membrane tube 7 forms the outer encapsulation of the probe around the above structure.

[0064] This application also provides a monitoring system for in-situ monitoring of dissolved gases in oil, such as... Figure 3 As shown, the monitoring system includes a modulation module, a pump light source, a detection light source, a photoelectric detection module, a signal demodulation module, and a miniature photoacoustic probe according to any of the above embodiments.

[0065] The modulation module is connected to the pump light source and is used to modulate the pump light output by the pump light source.

[0066] Specifically, the modulation module may include a signal generator that generates a modulated electrical signal that superimposes a triangular wave and a sine wave. This modulated electrical signal acts on the pump light source, causing the pump light source to output pump light with preset modulation characteristics.

[0067] The pump source is connected to the pump fiber in the miniature photoacoustic probe, and pump light is input into the gas photoacoustic cavity through the pump fiber. The output wavelength of the pump source matches the absorption peak of the gas under test, so that the gas under test absorbs the pump light in the gas photoacoustic cavity and generates photoacoustic pressure.

[0068] The probe light source is connected to the probe fiber of the miniature photoacoustic probe, which is used to input probe light into the FP optical interference cavity via the probe fiber. The probe light forms a reflected interference signal in the FP optical interference cavity, thereby loading the cavity length change caused by the vibration of the acoustic transducer thin film into the returned reflected light.

[0069] The photoelectric detection module is connected to the detection fiber and is used to receive the reflected light returned by the FP optical interferometer and convert it into an electrical signal.

[0070] The signal demodulation module performs phase demodulation on the electrical signal output by the photoelectric detection module to obtain the photoacoustic signal amplitude corresponding to the vibration of the acoustic transducer film, and analyzes the concentration of the gas to be measured according to the calibration relationship.

[0071] In some implementations, a circulator may be provided between the probe light source, the probe fiber, and the photodetector module to separate the input probe light and the returned reflected light, inputting the probe light into the FP optical interferometer cavity and inputting the reflected light returned from the FP optical interferometer cavity into the photodetector module.

[0072] In some embodiments, the monitoring system of this application further includes an optical coupler and a balanced detector. The optical coupler is connected to the output of the detection light source and is used to split the output of the detection light source into a detection light and a reference light, wherein the detection light is input to the FP optical interferometer cavity, the reference light is input to one input of the balanced detector, and the reflected light returned from the FP optical interferometer cavity is input to the other input of the balanced detector.

[0073] The balanced detector performs dual-channel differential detection of the reference light and reflected light and converts them into electrical signals to suppress the fluctuation noise of the detection light source. Since the reference light and reflected light come from the same detection light source, the light source fluctuation component carried by both can be weakened in the differential processing, while the signal component introduced by the FP optical interferometer cavity variation in the reflected light is retained and output to the signal demodulation module.

[0074] This application also provides a feasible parameter selection example for the above system to achieve acetylene gas monitoring.

[0075] In this example, the gas to be tested is acetylene dissolved in oil. A narrow-linewidth DFB laser can be used as the pump source, and the absorption peak of acetylene at 1531.6 nm is determined as the excitation wavelength. By adjusting the operating temperature and current of the DFB laser, its center absorption wavelength can be located at 1531.6 nm. A tunable laser can be used as the probe source, with an output light center wavelength of 1550 nm. The output of the probe source is split into two paths by a split-coupler: one path serves as the probe light input to a miniature photoacoustic probe, and the other path serves as the reference light input to a balanced detector.

[0076] In this example, the modulation module generates an electrical signal by superimposing a triangular wave and a sine wave through a signal generator and applies it to the pump light source. The triangular wave has a frequency of 10mHz and an amplitude of ±1V; the sine wave has a frequency of 3.25kHz and an amplitude of 250mV.

[0077] A miniature photoacoustic probe is directly immersed in an oil sample containing dissolved acetylene gas. The acetylene in the oil sample enters the gas space inside the oil-gas separation membrane tube, and then enters the gas photoacoustic cavity through the gas guide channel. The acetylene in the gas photoacoustic cavity absorbs and modulates the pump light, generating photoacoustic pressure. The acoustically sensitive transducer film converts the photoacoustic pressure into an interference spectrum shift in the FP optical interferometer, loading the frequency and amplitude information of the photoacoustic signal into the reflected light of the probe light, which then enters the balanced detector through a circulator.

[0078] The balanced detector operates in dual-channel differential mode, performing differential and photoelectric conversion on the reflected light returned by the miniature photoacoustic probe and the reference light of the probe source, and outputting an electrical signal related to the changes in the FP optical interferometer cavity.

[0079] The signal demodulation module uses intensity demodulation or phase demodulation to demodulate the reflected harmonic signal changes of the FP optical interferometer cavity. The module can also extract the harmonic signal amplitude using lock-in amplification (LIA) technology. The reference signal for the LIA is synchronously provided by a signal generator, and its frequency is consistent with the frequency of the sinusoidal modulation wave, which is 3.25 kHz.

[0080] In addition, by testing acetylene oil samples with a certain concentration gradient, the acetylene concentration can be calibrated according to the magnitude of the second harmonic amplitude at different concentrations, and the calibration results can be used for subsequent analysis of the acetylene concentration to be tested.

[0081] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this application can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0082] The above description is merely an exemplary embodiment of this application and is not intended to limit the scope of protection of this application. That is, any equivalent changes and modifications made in accordance with the teachings of this application shall still fall within the scope of this application. Those skilled in the art will readily conceive of other embodiments of this application upon considering the disclosure of the specification and practice. The above disclosure is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary technical means in the art not described in this application. The specification and embodiments are considered exemplary only, and the scope and spirit of this application are defined by the claims.

Claims

1. A miniature photoacoustic probe for in-situ monitoring of dissolved gases in oil, comprising a pump fiber, a pump fiber ferrule, a probe fiber, an acoustic transducer film, and an oil-gas separation membrane, characterized in that: The acoustically sensitive transducer film is disposed between the pump fiber and the probe fiber, with a first side facing the pump fiber and a second side facing the probe fiber. The pump fiber ferrule has an inner hole for the pump fiber to pass through. The light-emitting end of the pump fiber is set at a predetermined distance from the first side of the acoustic transducer film. The inner hole forms a gas photoacoustic cavity in the local space between the light-emitting end and the acoustic transducer film, and the first side of the acoustic transducer film constitutes one side cavity wall of the gas photoacoustic cavity. The pump fiber ferrule is also provided with a gas guiding channel. One end of the gas guiding channel is connected to the gas photoacoustic cavity, and the other end is connected to the inner gas space of the oil-gas separation membrane, so as to introduce the gas to be tested separated by the oil-gas separation membrane into the gas photoacoustic cavity. An FP optical interference cavity is formed between the end face of the probe fiber and the second side of the acoustic transducer film; The pump fiber is used to input pump light into the gas photoacoustic cavity so that the pump light output from the pump fiber excites the gas under test to generate photoacoustic pressure. The probe fiber is used to detect the changes in the FP optical interference cavity caused by the vibration of the acoustic transducer film driven by the photoacoustic pressure.

2. The miniature photoacoustic probe for in-situ monitoring of dissolved gases in oil according to claim 1, characterized in that, The pump fiber, the probe fiber, the acoustic transducer film, the gas photoacoustic cavity, and the FP optical interference cavity are arranged coaxially.

3. The miniature photoacoustic probe for in-situ monitoring of dissolved gases in oil according to claim 1 or 2, characterized in that, The miniature photoacoustic probe also includes a probe fiber ferrule, which has an inner hole for the probe fiber to pass through, and one end of the probe fiber ferrule near the acoustic transducer film is flush with the end face of the probe fiber.

4. The miniature photoacoustic probe for in-situ monitoring of dissolved gases in oil according to claim 3, characterized in that, The micro photoacoustic probe also includes a sleeve with an axial through hole, and the pump fiber ferrule, the probe fiber ferrule, and the acoustic transducer film are fixed in the axial through hole.

5. The miniature photoacoustic probe for in-situ monitoring of dissolved gases in oil according to claim 4, characterized in that, The sleeve is provided with a connecting groove that penetrates the sleeve wall, so that the inner gas space is connected to the gas guide channel through the connecting groove.

6. The miniature photoacoustic probe for in-situ monitoring of dissolved gases in oil according to claim 1, characterized in that, The oil-gas separation membrane forms an oil-gas separation membrane tube, which is sleeved on the outside of the micro photoacoustic probe.

7. The miniature photoacoustic probe for in-situ monitoring of dissolved gases in oil according to claim 1, characterized in that, The air guide channel is widened along the axial direction of the pump fiber ferrule to increase the air intake area of ​​the air guide channel.

8. The miniature photoacoustic probe for in-situ monitoring of dissolved gases in oil according to claim 1, characterized in that, The acoustically sensitive transducer film is a chromium-silver-gold metal composite film.

9. A monitoring system for in-situ monitoring of dissolved gases in oil, comprising a modulation module, a pump light source, a detection light source, a photoelectric detection module, and a signal demodulation module, characterized in that, It also includes the micro photoacoustic probe as described in any one of claims 1 to 8; The modulation module is connected to the pump light source and is used to modulate the pump light output by the pump light source. The pump light source is connected to the pump fiber of the micro photoacoustic probe and is used to input pump light into the gas photoacoustic cavity through the pump fiber; The detection light source is connected to the detection optical fiber of the miniature photoacoustic probe, and is used to input detection light into the FP optical interferometer cavity via the detection optical fiber; The photoelectric detection module is connected to the detection optical fiber and is used to receive the reflected light returned by the FP optical interferometer cavity and convert it into an electrical signal; The signal demodulation module is connected to the photoelectric detection module and is used to obtain the vibration information of the acoustic transducer film based on the electrical signal, and then analyze the concentration of the gas to be measured.

10. The monitoring system for in-situ monitoring of dissolved gases in oil according to claim 9, characterized in that, The system also includes an optical coupler and a balanced detector. The optical coupler is connected to the output of the detection light source and is used to split the output of the detection light source into a detection light and a reference light. The detection light is input to the FP optical interferometer cavity, and the reference light and the reflected light are respectively input to the two inputs of the balanced detector. The balanced detector is used to perform differential detection of the reference light and the reflected light to suppress the fluctuation noise of the detection light source.

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