Hydrophone for pipeline monitoring and manufacturing method

Abstract

The invention discloses a hydrophone for pipeline monitoring and a manufacturing method, a sound transmission shell is embedded in a middle mounting area of a main shell, the sound transmission shell is of a cylindrical structure, and a sensitive element is arranged in the sound transmission shell; a rear end cover is arranged at the end part of the main shell; an integrally-formed annular limiting convex edge is arranged at the end, close to the main shell, of the sound transmission shell, a limiting clamping groove is formed in the position, corresponding to the limiting convex edge, of the inner wall of the main shell, and a sealing ring and a sealing ring pressing ring are sequentially assembled in the limiting clamping groove; a first cavity is arranged in the sound transmission shell, an annular gap is formed between the outer wall of the sensitive element and the inner wall of the first cavity, and the annular gap is used for encapsulating the impedance matching layer; positioning convex edges are uniformly arranged on the edges of the first end cover and the second end cover in the circumferential direction, and the outer diameter of the positioning convex edges is matched with the inner diameter of the first cavity; the end face of the rear end cover is provided with three through holes. The central through hole is used for the penetration of an external cable. And the other two through holes are glue injection holes.

Description

Technical Field

[0001] This invention relates to the field of underwater acoustic transducers, and more particularly to a hydrophone for pipeline monitoring and its manufacturing method. Background Technology

[0002] Water pipelines are vital infrastructure for modern industry and daily life. However, frequent leaks due to aging, corrosion, and external stress not only cause significant economic losses and resource waste but also lead to ground subsidence and environmental pollution. Hydrophone detection technology, as a pipeline leak detection technique, offers advantages such as precise location, wide monitoring range, and continuous monitoring. Its method primarily involves processing the acoustic signals collected by a hydrophone within the pipeline to determine whether a leak has occurred and pinpoint its location.

[0003] Piezoelectric tube hydrophones can receive leakage signals from pipes in a horizontal, omnidirectional manner, making them one of the preferred solutions for pipe leak detection. Due to the need for real-time monitoring, hydrophones must be installed on pipes for extended periods, and the pipe environment places extremely stringent requirements on their materials: hydrophones must not only be immersed in corrosive liquids for long periods but also withstand multiple effects such as fluid erosion, pressure pulsation, and installation stress. Traditional piezoelectric tube hydrophones primarily use vulcanized rubber or polyurethane as the sound-transmitting material for the sensing head. Vulcanized rubber, when immersed in water for extended periods, releases harmful substances, and its vulcanization process is complex, making it unsuitable for pipe inspection applications. Polyurethane, on the other hand, is prone to aging and hydrolysis due to prolonged water immersion, leading to leaks and damage, resulting in poor durability.

[0004] Furthermore, during construction and installation, the connection between the hydrophone housing and the piezoelectric ceramic is prone to breakage due to external force and twisting, resulting in a high damage rate (e.g. Figure 1 (As shown). Due to the above-mentioned drawbacks, traditional piezoelectric tube hydrophones require frequent replacement when used for pipeline inspection, which not only leads to high maintenance costs, but also poses safety hazards due to the blind spots created during maintenance. Summary of the Invention

[0005] This invention provides a hydrophone for pipeline monitoring and its manufacturing method. The invention uses PEEK as the fabrication material and, through standardized assembly processes, encapsulates the core functional component, a piezoelectric ceramic tube, within a PEEK housing, thereby forming a highly integrated and compact structure. This effectively solves the problem of short lifespan in hydrophones. See the description below for details: A first aspect is a hydrophone for pipeline monitoring, the hydrophone comprising: a main housing, a sound-permeable housing, a rear end cover, a sensitive element, a grounding washer, a sealing ring, a circuit board, and an external cable. A sound-permeable shell is embedded in the middle mounting area of ​​the main housing. The sound-permeable shell has a cylindrical structure and a sensitive element is installed inside the sound-permeable shell. The end of the main housing is provided with a rear end cover. The rear end cover, the main housing and the grounding gasket together form a closed metal electromagnetic shielding layer. The sound-permeable shell has an integrally formed annular limiting protrusion at one end near the main shell. A limiting groove is opened on the inner wall of the main shell at the position corresponding to the limiting protrusion. A sealing ring and a sealing ring pressure ring are sequentially assembled in the limiting groove. The acoustically transparent housing contains a first chamber. A circular gap is formed between the outer wall of the sensitive element and the inner wall of the first chamber. The circular gap is used to encapsulate the impedance matching layer. The impedance matching layer is made of a mixture of epoxy resin and alumina. The edges of the first end cap and the second end cap are uniformly provided with positioning protrusions. The outer diameter of the positioning protrusions is adapted to the inner diameter of the first chamber. At least two anti-rotation grooves are evenly distributed circumferentially on the end face of the limiting protrusion; three through holes are provided on the end face of the rear end cover: the central through hole is used to pass through the external cable; the other two through holes are glue injection holes.

[0006] The sensitive element is a PZT-5 cylindrical piezoelectric ceramic, and its two ends are sealed by a first end cap and a second end cap. The sealing process uses epoxy structural adhesive.

[0007] The first end cap has a through hole in its central area for wires soldered inside the sensitive element to pass through and be led out; the gap between the wires and the through hole is sealed and filled with adhesive.

[0008] Secondly, a method for manufacturing a hydrophone, the method comprising: The steps for mixing and preparing alumina-filled epoxy resin; the steps for mounting sensitive elements and potting impedance matching layers; the steps for assembling circuit boards and mounting acoustically transparent housings; the steps for mounting the rear cover; and the steps for overall potting and curing. The mixing and preparation steps of the alumina-filled epoxy adhesive include: Pretreatment: Select alumina powder with a particle size of 50~100μm, dry it in an oven at 120℃ for 2h to remove the moisture adsorbed on the powder surface; select bisphenol A type epoxy resin and aliphatic amine curing agent as matrix materials, weigh epoxy resin and alumina powder at a volume ratio of 4:1, and add γ-(2,3-epoxypropoxy)propyltrimethoxysilane coupling agent at 1%~2% of the mass of epoxy resin; Mixing process: First, pour the epoxy resin into a high-speed mixing tank, heat it to 60℃ and stir at 500 rpm for 10 min. Then, slowly add the pretreated alumina powder, increase the speed to 1200 rpm and continue stirring for 30 min to ensure that the alumina powder is uniformly dispersed in the epoxy matrix. Next, add the coupling agent and stir at 60℃ and 800 rpm for 15 min to achieve full compatibility between the inorganic and organic phases. Pre-degassing treatment: The mixed adhesive is transferred to a vacuum degassing tank and kept at a vacuum of -0.095MPa and a temperature of 60℃ for 20 minutes to remove air bubbles generated during the mixing process, thus obtaining the potting compound used as the impedance matching layer.

[0009] The steps for mounting the sensitive element and potting the impedance matching layer are as follows: Component pretreatment: Wipe the sensitive element, the first end cap, the second end cap, and the inner wall of the first cavity of the acoustic housing with anhydrous ethanol; Solder the wires on the sensitive element firmly, and pass the wires leading out from the inside of the sensitive element through the through hole of the first end cap. Fill and seal the gap between the wires and the through hole with quick-drying adhesive. Attach the first end cap and the second end cap to the two ends of the sensitive element respectively, and apply cyanoacrylate quick-drying adhesive along the edge of the end cap and the sensitive element to seal it. The sensitive element is placed at the bottom of the first chamber, and the convex edge of the end cap fits with the inner wall of the first chamber to ensure that the sensitive element is coaxially distributed with the first chamber. Impedance matching layer potting: The pre-degassed alumina-epoxy potting compound is slowly injected into the annular gap along the inner wall of the first chamber. The potting speed is controlled at 0.2~0.5 kg / min to avoid impacting sensitive components or generating new air bubbles. After the gap is completely filled, the sound-permeable shell is placed into a vacuum degassing tank and degassed for 15 minutes under a vacuum of -0.095 MPa to completely remove residual air bubbles in the gap. Curing process: Place the sound-permeable shell that has been filled in an oven and process it according to the step curing process: keep it at 25℃ for 2 hours → keep it at 60℃ for 4 hours → keep it at 100℃ for 1 hour. After curing, let it cool naturally to room temperature to form a stable impedance matching layer.

[0010] The assembly of the circuit board and the installation of the acoustically transparent housing are as follows: After the impedance matching layer has fully cured, the pre-welded circuit board is placed vertically in the upper part of the first chamber. The circuit board is reliably electrically connected to the lead wires of the sensitive element. The position of the circuit board is adjusted so that it does not interfere with the inner wall of the first chamber. Low-viscosity epoxy resin was injected into the first chamber to ensure that the adhesive completely filled the gap between the circuit board and the inner wall of the first chamber, and then allowed to cure at room temperature for 4 hours. Clean the inner wall of the main housing and the limiting groove, and then insert the sealing ring and the sealing ring pressure ring in sequence in the limiting groove; Insert the internally assembled acoustic housing into one end of the main housing, so that the limiting protrusion of the acoustic housing is engaged with the sealing ring pressure ring, and there is no axial loosening of the acoustic housing after engagement.

[0011] The installation steps for the rear end cover are as follows: Insert the nickel-plated carbon steel grounding washer into the end of the main housing so that it fits against the end face of the limiting protrusion. Pass the external cable through the center hole of the rear cover, strip 5-10mm of the outer sheath from the end of the cable, and connect the wire to the circuit board. Solder the grounding wire on the conductor to the grounding washer. The soldering point must be firm and free of defects to ensure that the grounding washer, the rear cover, and the main housing form a closed electromagnetic shielding layer. Pre-tighten the rear end cover to the end of the main housing via threaded connection. Use a double pin wrench to insert into the glue injection hole of the rear end cover and apply a preset torque to tighten the rear end cover, so that the grounding washer is axially compressed, providing a continuous axial pre-tightening force to the sound-permeable housing. After tightening, check the fit between the rear end cover and the main housing.

[0012] The overall potting and curing process includes: Clean the glue injection hole on the rear cover, place the hydrophone vertically, so that one of the glue injection holes is used as the glue inlet and the other is used as the vent. Inject low-viscosity epoxy resin into the dispensing port at a dispensing speed of 0.5~1.0 kg / min. Observe the vent. When there is a continuous flow of resin from the vent and no bubbles, stop dispensing. After potting, the hydrophone was placed back into the vacuum degassing tank and degassed for 10 minutes under a vacuum of -0.095 MPa to remove air bubbles generated during the potting process. Place the hydrophone in an oven and cure it according to the process of 25℃×4h→60℃×6h. After curing, allow it to cool naturally to room temperature.

[0013] The beneficial effects of the technical solution provided by this invention are: 1. The sensitive head encapsulation structure of the present invention uses polyetheretherketone (PEEK) material, which has excellent corrosion resistance, aging resistance and hydrolysis resistance compared with traditional vulcanized rubber and polyurethane. It can withstand corrosive fluids, scouring and pressure pulsation in pipelines for a long time, avoiding water leakage and damage to the hydrophone. At the same time, it eliminates the problem of harmful substances being released from vulcanized rubber, and does not require a complicated vulcanization process. It is suitable for the harsh environment of pipeline inspection and reduces the maintenance cost caused by frequent replacement. 2. This invention achieves efficient acoustic impedance transition between the sound-transparent shell (PEEK) and the sensitive element (PZT piezoelectric ceramic) by precisely designing a mixed impedance matching layer of epoxy resin and alumina (volume ratio 4:1), thereby increasing the sound transmission coefficient by more than 80% compared to the single epoxy resin solution. 3. The sound-permeable shell of the present invention achieves axial positioning and circumferential anti-rotation through the locking fit between the limiting protrusion and the sealing ring pressure ring, and the interlocking structure between the anti-rotation groove and the potting compound, so as to avoid the connection parts being twisted and damaged during installation or use; a rubber sealing ring is set between the main shell and the sound-permeable shell to prevent the intrusion of external fluids and ensure long-term sealing reliability. 4. The grounding gasket of the present invention, together with the main housing and the rear end cover, forms a closed metal electromagnetic shielding layer, which effectively blocks external electromagnetic interference and improves the signal-to-noise ratio. 5. The injection hole of the rear end cap of the present invention has the functions of assembly tightening and potting venting. With the help of a double pin wrench, the rear end cap can be pre-tightened and fixed quickly. During potting, the double hole design ensures that the glue is full and free of air bubbles. The positioning protrusion of the sensitive element end cap not only ensures that the element and the chamber are coaxially distributed, but also provides a flow channel for the potting glue to avoid assembly interference. 6. This invention encapsulates the piezoelectric ceramic tube in a PEEK shell through a standardized assembly process, forming a highly integrated and compact structure. The material selection (such as PEEK, fluororubber, nickel-plated carbon steel, etc.) and structural design (sealing, anti-rotation positioning, electromagnetic shielding) are adapted to complex working conditions such as internal pipeline corrosion and high pressure. It can receive pipeline leakage signals horizontally and omnidirectionally, meeting the requirements of accurate positioning, wide monitoring range, and strong continuity in pipeline leakage detection. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of a case of damage to an existing hydrophone structure; Figure 2 This is a schematic diagram of the structural appearance of a hydrophone for pipeline monitoring according to an embodiment of the present invention; Figure 3 This is a cross-sectional view of a hydrophone for pipeline monitoring according to an embodiment of the present invention; Figure 4 This is an exploded view of the structure of a hydrophone for pipeline monitoring according to an embodiment of the present invention; Figure 5 A hydrophone for pipeline monitoring in an embodiment of the present invention operates at 20Hz. Simulated sensitivity curve at 20kHz.

[0015] The attached diagram lists the components represented by each number as follows: 1: Main housing; 2: Sound-permeable housing; 3: Rear end cover; 4: Sensitive element; 5: Grounding washer; 6: Sealing ring; 7: Circuit board; 8: External cable; The main housing 1 includes: 101: limiting groove; 102: connecting thread; the sound-permeable housing 2 includes: first chamber 201; 202: limiting protrusion; 203: anti-rotation groove; the rear end cover 3 includes: injection hole 301; second chamber 302; the sensitive element 4 includes: first end cover 401; second end cover 402; through hole 403; annular gap 404; positioning protrusion 405; the sealing ring 6 includes: sealing ring pressure ring 601. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below.

[0017] Based on the above reliability analysis of traditional piezoelectric tubular hydrophones, this invention provides a design concept: using polyetheretherketone (PEEK) as the encapsulation material for the sensing head. Traditional vulcanized rubber and polyurethane have relatively weak rigidity and are prone to deformation and damage when subjected to pressure pulsations within the pipe, making it difficult to stably support the internal structure of the sensing head. In contrast, PEEK possesses excellent mechanical strength and rigidity, firmly encapsulating the core components of the sensing head and preventing structural deformation due to external forces or pressure fluctuations, thus ensuring the structural stability of the hydrophone.

[0018] In terms of weather resistance and durability, compared to traditional vulcanized rubber and polyurethane, PEEK can withstand complex working conditions for a long time, is less prone to performance degradation due to environmental corrosion, and can maintain the integrity of the encapsulation structure for a long time, significantly extending the service life of the hydrophone. It also avoids the safety hazards of vulcanized rubber leaching harmful substances during long-term immersion in water, and eliminates the need for complex vulcanization processes, resulting in superior adaptability and practicality. This invention embodiment uses standardized assembly procedures to encapsulate the piezoelectric ceramic tube in a PEEK shell, forming an integrated structure, resulting in a hydrophone with high sensitivity and long service life.

[0019] To address the problems of existing piezoelectric cylindrical hydrophones, such as the release of harmful substances from the encapsulation materials (vulcanized rubber, polyurethane), easy aging and hydrolysis, and easy breakage at the connection between the shell and the piezoelectric ceramic, resulting in short lifespan, high maintenance costs, and safety risks due to detection blind spots, this invention provides an improved piezoelectric cylindrical hydrophone. The core improvement lies in using polyetheretherketone (PEEK) as the encapsulation material for the sensitive head and directly encapsulating the piezoelectric ceramic tube into an integrated structure through machining. The technical solution of this invention will be described in detail below with reference to specific embodiments.

[0020] Example 1 To achieve the aforementioned objectives, and addressing the problems of short lifespan, insufficient sealing reliability, and weak anti-interference capability of existing piezoelectric circular tube hydrophones in pipeline inspection scenarios, this invention combines... Figures 2 to 4 As shown in the embodiment of the present invention, a hydrophone for pipeline monitoring is disclosed. The hydrophone mainly includes: a main housing 1, a sound-transparent housing 2, a rear end cover 3, a sensitive element 4, a grounding washer 5, a sealing ring 6, a circuit board 7, and an external cable 8, etc. The components work together to form an integrated detection structure.

[0021] The sensitive element 4 is preferably a radially polarized PZT-5 cylindrical piezoelectric ceramic, suitable for high voltage sensitivity requirements. It is housed in a specially designed first chamber 201 inside the acoustically transparent housing 2. Through acoustic coupling with the acoustically transparent housing 2, it achieves accurate capture and detection of underwater sound waves such as leakage signals in the pipeline, ensuring high efficiency of sound-to-electric conversion. The acoustically transparent housing 2 has a cylindrical structure and is embedded in the middle installation area of ​​the main housing 1. Its material is polyetheretherketone (PEEK). Compared with traditional vulcanized rubber, polyurethane and other encapsulation materials, PEEK not only has excellent acoustic transmission performance (acoustic impedance of about 3.5M ayl, which can achieve efficient sound wave penetration without significant propagation loss), but also has outstanding mechanical strength, corrosion resistance, anti-aging and anti-hydrolysis performance. It can withstand the scouring of corrosive fluids, pressure pulsation and installation stress in the pipeline for a long time, effectively solving the problem of leakage damage caused by material aging and hydrolysis in traditional hydrophones.

[0022] The acoustic receiving end of the acoustic housing 2 is exposed outside the main housing 1, and its end face is flat and smooth without any additional obstruction structure, so as to minimize the incident resistance of sound waves and ensure effective reception of underwater acoustic signals. The rear end cover 3 is detachably assembled to the end of the main housing 1 by means of threaded connection. Both are made of metal structure, preferably 304 or 316 stainless steel (which has excellent corrosion resistance, mechanical strength and conductive shielding performance). The rear end cover 3, the main housing 1 and the grounding washer 5 together form a closed metal electromagnetic shielding layer, which can effectively block external electromagnetic interference signals from entering the internal cavity of the hydrophone and avoid interfering with the acoustic signal detection accuracy of the sensitive element 4. At the same time, the stainless steel material can be used in humid and corrosive environments of pipelines, extending the overall service life of the hydrophone. In addition, the assembly of the rear end cover 3 can also provide axial pre-tightening support for the acoustic housing 2, further improving the stability of the overall structure.

[0023] Combination Figure 3 , Figure 4 As shown in the diagram, the sensing element 4 is a cylindrical structure located at the bottom region of the first chamber 201 at the end of the acoustically transparent housing 2. The sensing element 4 is preferably a PZT-5 cylindrical piezoelectric ceramic, with its two ends sealed by a first end cap 401 and a second end cap 402. The sealing process uses epoxy structural adhesive to achieve an airtight seal between the internal chamber of the sensing element 4 and the external environment. A through-hole 403 is provided in the central region of the first end cap 401 for a wire (not shown) welded inside the sensing element 4 to pass through and exit. The gap between the wire and the through-hole 403 is sealed with adhesive to ensure overall airtightness. The first end cap 401 and the second end cap 402 are made of rigid polyurethane, and their core function is to suppress sound wave reflection at the end of the sensing element, absorb stray vibration modes, provide mechanical support for the piezoelectric ceramic tube, and improve sensitivity.

[0024] A circular gap 404 is formed between the outer wall of the sensitive element 4 and the inner wall of the first chamber 201. This circular gap 404 is used to pot the impedance matching layer. The impedance matching layer is made of a mixture of epoxy resin and alumina, with a volume mixing ratio preferably selected as 4:1. Furthermore, the edges of the first end cap 401 and the second end cap 402 are uniformly provided with positioning protrusions 405, the outer diameter of which matches the inner diameter of the first chamber 201. The functions of the positioning protrusions 405 include: firstly, providing radial support for the sensitive element 4, ensuring that the sensitive element 4 and the first chamber 201 remain coaxially aligned, thus guaranteeing the consistency of the hydrophone's acoustic performance in all directions; secondly, during installation, the potting mixture can flow smoothly through the gaps between the positioning protrusions 405, preventing the mixture from failing to fully fill the circular gap 404.

[0025] Alumina (Al) is used in hydrophones O The epoxy resin is used as an acoustic transition layer between the PEEK (acoustic-permeable shell 2) and the piezoelectric ceramic (sensitive element 4). To achieve good acoustic impedance matching, the alumina filling ratio must be rationally designed. Assuming the PEEK acoustic impedance: ZPEEK≈3.5MRayl and the PZT acoustic impedance: ZPZT≈32MRayl, then the ideal transition layer impedance (geometric mean) is: MRayl is the unit of acoustic impedance.

[0026] The acoustic impedance of mixed materials is estimated using the Rule of Mixtures, specifically: (1) in: Given the volume fraction of alumina, the acoustic impedance of alumina (Zfiller) = 39.5 MRayl, the acoustic impedance of epoxy resin (Zmatrix) = 3.105 MRayl, and Zcomp = 10.6, calculate... : (2) Calculations show that when using 20.6% alumina by volume (corresponding to an approximately 4:1 volume ratio of epoxy resin to alumina), the acoustic impedance of this composite material is 10.6 MRayl. Using this composite material as an impedance matching layer, compared to using epoxy resin alone, can increase the sound transmission coefficient by over 80% (for specific calculations, refer to relevant formulas in the field of sound projection technology). Using a PEEK shell with an impedance matching layer of epoxy resin and alumina can achieve high sensitivity. Figure 5 As can be seen, within the frequency range of 20Hz to 20kHz, the sensitivity is -198dB and the frequency response flatness is ±2dB.

[0027] After the sensitive element 4 is positioned, the end cap is sealed, and the impedance matching layer is potted and cured, the circuit board 7 with the pre-welded electrical components is fixed in the upper accommodating area of ​​the first chamber 201 in a vertical arrangement to ensure a reliable electrical connection between the circuit board 7 and the lead wires of the sensitive element 4. Subsequently, the area is potted with low-viscosity epoxy resin. The potting operation must ensure that the epoxy resin completely fills the gap between the circuit board 7 and the inner wall of the first chamber 201 to simultaneously improve the structural stability and electrical insulation performance of the circuit board 7. The sound-permeable shell 2 has an annular limiting protrusion 202 formed by an integral molding process at one end near the main shell 1. A limiting groove 101 is opened on the inner wall of the main shell 1 at a position corresponding to the limiting protrusion 202. A sealing ring 6 and a sealing ring pressure ring 601 are sequentially assembled in the limiting groove 101.

[0028] The sealing ring 601 is made of 304 stainless steel (which has both mechanical strength and corrosion resistance). Its end face fits against the end face of the limiting protrusion 202 and the bottom end face of the rear cover 3. When the rear cover 3 is fastened to the end of the main housing 1 by a threaded connection, the limiting protrusion 202 and the bottom end face of the rear cover 3 will simultaneously apply an axial preload to the sealing ring 601, so that the sealing ring 601 can evenly transmit the preload to the sealing ring 6. The sealing ring 6 is preferably made of fluororubber O-ring, which has excellent resistance to seawater corrosion, high and low temperature resistance (applicable temperature range -40℃~200℃) and elastic recovery performance, and can be used in complex media environments such as pipelines and deep sea where hydrophones are used. The sealing ring 6 is interference-fitted with the outer wall of the sound-permeable housing 2, and its sealing compression is strictly controlled within 15%~20%. This compression range can ensure that the sealing ring forms a tight sealing contact surface with the outer wall of the sound-permeable housing and the inner wall of the limiting groove, and can also avoid the formation of sealing gaps.

[0029] After the limiting protrusion 202 and the sealing ring 601 are engaged, they form an axial stop structure, which can effectively limit the downward displacement of the sound-permeable shell 2 along the axial direction of the main shell 1, ensuring the axial positioning accuracy of the sound-permeable shell 2 during operation. At least two anti-rotation grooves 203 are also uniformly provided circumferentially on the end face of the limiting protrusion 202. In this embodiment of the invention, four grooves are used. After the sound-permeable shell 2 and the internal cavity of the hydrophone are encapsulated and cured with epoxy resin, the cured encapsulant will completely fill the cavity of the anti-rotation groove 203, forming a circumferential limiting structure with the anti-rotation groove 203. At this time, if a circumferential torque is applied to try to rotate the sound-permeable shell 2, the interlocking structure can provide sufficient anti-torsional resistance, thereby completely restricting the circumferential rotational freedom of the sound-permeable shell 2. The main shell 1 is also provided with a connecting thread 103 for installing the hydrophone on a fluid pipeline.

[0030] The rear end cover 3 is threadedly assembled to the other end of the main housing 1. During assembly, the grounding washer 5 is axially pressed between the rear end cover 3 and the limiting protrusion 202 of the acoustic housing 2, thereby providing continuous axial pre-tightening support to the acoustic housing 2, further ensuring the axial positioning accuracy and structural stability of the acoustic housing 2 within the main housing 1. The grounding washer 5 is made of nickel-plated carbon steel (which has excellent conductivity, mechanical strength, and corrosion resistance). Its functions include: firstly, serving as a grounding connector for welding and leading out the grounding wire (not shown in the figure); secondly, forming a closed metal electromagnetic shielding layer together with the rear end cover 3 and the main housing 1. Through the electromagnetic shielding effectiveness of the shielding layer, it effectively blocks external electromagnetic interference signals from entering the hydrophone, improving the signal-to-noise ratio. Three through holes are provided on the end face of the rear cover 3: the central through hole is used to pass through the external cable 8; the other two through holes are injection holes 301 (the two are symmetrically distributed) and have dual functions: firstly, the assembly operation function. During the threaded connection assembly of the rear cover 3 and the main housing 1, a double pin wrench is used to insert into the injection hole 301 and apply a tightening torque to the rear cover 3 through the injection hole 301 to ensure that the threaded connection between the rear cover 3 and the main housing 1 reaches the preset pre-tightening force; secondly, the potting auxiliary function. During the potting operation of the internal cavity of the hydrophone, the potting glue is injected from one of the injection holes 301, and the other injection hole 301 serves as an exhaust channel to expel air from the cavity, ensuring that the potting glue can completely fill the internal gap and avoid affecting the structural stability or sealing performance due to residual air bubbles.

[0031] Furthermore, the rear cover 3 has a second chamber 302 for containing potting compound inside; after the hydrophone completes the overall potting operation, the potting compound will completely fill and solidify in the second chamber 302, forming a fully enclosed structure for the external cable 8 passing through the chamber.

[0032] Example 2 This invention provides a method for manufacturing a hydrophone for pipeline monitoring. The manufacturing method is described in detail below with reference to the structural design of the hydrophone in Embodiment 1. The method includes the following steps: S1: Preparation of alumina-filled epoxy resin mixture; Pretreatment: Select alumina (Al₂O₃) with a particle size of 50~100μm. O The powder was placed in a 120℃ oven and dried for 2 hours to remove the moisture adsorbed on the powder surface. Bisphenol A type epoxy resin and aliphatic amine curing agent were selected as matrix materials. Epoxy resin and alumina powder were weighed at a volume ratio of 4:1. γ-(2,3-epoxypropoxy)propyltrimethoxysilane coupling agent was added at 1%~2% of the mass of epoxy resin.

[0033] Mixing operation: First, pour the epoxy resin into a high-speed mixing tank, heat it to 60℃ and stir at 500r / min for 10min. Then, slowly add the pretreated alumina powder, increase the speed to 1200r / min and continue stirring for 30min to ensure that the alumina powder is uniformly dispersed in the epoxy matrix. Then, add the coupling agent and stir at 60℃ and 800r / min for 15min to achieve full compatibility between the inorganic and organic phases.

[0034] Pre-degassing treatment: The mixed adhesive is transferred to a vacuum degassing tank and kept at a vacuum of -0.095MPa and a temperature of 60℃ for 20 minutes to remove air bubbles generated during the mixing process, thus obtaining the potting compound used as the impedance matching layer.

[0035] S2: Mounting of sensitive components and potting of impedance matching layer; Component pretreatment: Wipe the sensitive element 4 (PZT-5 round tube piezoelectric ceramic), the first end cap 401, the second end cap 402 and the inner wall of the first chamber 201 of the sound-permeable housing 2 with anhydrous ethanol to remove surface oil and impurities, and then let it dry for later use.

[0036] Sensitive element end cap (first end cap 401 and second end cap 402) assembly: The wires on the sensitive element 4 are soldered firmly, and the wires leading out from the inside of the sensitive element 4 are passed through the through hole 403 of the first end cap 401. The gap between the wires and the through hole is filled and sealed with quick-drying adhesive. The first end cap 401 and the second end cap 402 are respectively attached to the two end faces of the sensitive element 4. Cyanoacrylate quick-drying adhesive is applied along the edge of the end cap (first end cap 401 and second end cap 402) and the sensitive element to seal it, ensuring that the internal cavity of the sensitive element is isolated from the outside.

[0037] Positioning and installation: The sensitive element 4, with the end caps (first end cap 401 and second end cap 402) assembled, is placed at the bottom of the first chamber 201. The sensitive element 4 is coaxially distributed with the first chamber 201 by the cooperation between the protruding edge 405 of the end cap edge and the inner wall of the first chamber 201.

[0038] Impedance matching layer potting: The pre-degassed alumina-epoxy potting compound is slowly injected into the annular gap 404 along the inner wall of the first chamber 201. The potting speed is controlled at 0.2~0.5 kg / min to avoid impacting sensitive components or generating new air bubbles. After the gap is completely filled, the sound-permeable shell 2 is placed into a vacuum degassing tank and degassed for 15 minutes under a vacuum of -0.095 MPa to completely remove residual air bubbles in the gap.

[0039] Curing process: Place the sound-permeable shell 2 that has been filled into an oven and process it according to the step curing process: keep it at 25℃ for 2 hours → keep it at 60℃ for 4 hours → keep it at 100℃ for 1 hour. After curing, let it cool naturally to room temperature to form a stable impedance matching layer.

[0040] S3: Assembly of circuit board 7 and installation of the acoustically transparent housing; Fixing the circuit board 7: After the impedance matching layer has been completely cured, the pre-soldered circuit board 7 is placed vertically in the upper area of ​​the first chamber 201 to ensure that the circuit board 7 is reliably electrically connected to the lead wire of the sensitive element 4. The position of the circuit board 7 is adjusted so that it does not interfere with the inner wall of the first chamber 201.

[0041] Encapsulation of circuit board 7: Low-viscosity epoxy resin is injected into the first chamber 201 to ensure that the adhesive completely fills the gap between circuit board 7 and the inner wall of the first chamber 201. Then, it is left to stand and cure at room temperature for 4 hours to improve the structural stability and electrical insulation performance of circuit board 7.

[0042] Pre-treatment of main housing 1: Clean the inner wall of main housing 1 and limit groove 101, and embed sealing ring 6 and sealing ring pressure ring 601 in sequence in limit groove 101 to ensure that sealing ring 6 is installed in place without twisting.

[0043] Assembly of the sound-permeable housing 2: Insert the sound-permeable housing 2, which has been internally assembled, into one end of the main housing 1, so that the limiting protrusion 202 of the sound-permeable housing 2 is engaged with the sealing ring pressure ring 601. After engagement, the sound-permeable housing 2 has no axial looseness and can rotate slightly in the circumferential direction without jamming.

[0044] S4: Installation of rear cover 3; Assembly of grounding washer 5: Insert the nickel-plated carbon steel grounding washer 5 into the end of the main housing 1 so that it fits against the end face of the limiting protrusion 202.

[0045] Cable installation: Pass the external cable 8 through the center through hole of the rear cover 3, strip 5-10mm of the outer sheath from the end of the cable, and reliably connect the wire to the circuit board 7.

[0046] Grounding treatment: Solder the grounding wire on the conductor to the grounding washer 5. The soldering point must be firm and free of defects to ensure that the grounding washer 5, the rear cover 3, and the main housing 1 form a closed electromagnetic shielding layer.

[0047] Fastening of the rear cover 3: The rear cover 3 is pre-tightened to the end of the main housing 1 through the threaded connection. A double pin wrench is inserted into the glue injection hole 301 of the rear cover 3, and a preset torque is applied to tighten the rear cover 3, so that the grounding washer 5 is axially compressed, providing a continuous axial pre-tightening force to the sound-permeable housing 2. After tightening, check the fit between the rear cover 3 and the main housing 1 to ensure that there is no looseness.

[0048] S5: Overall potting and curing.

[0049] Preparation for potting: Clean the glue injection hole 301 of the rear cover 3 to ensure that the hole is unobstructed; place the hydrophone vertically, so that one of the glue injection holes is used as the glue injection port and the other is used as the vent.

[0050] Overall potting: Inject low-viscosity epoxy resin into the potting port, controlling the injection speed at 0.5~1.0 kg / min. Observe the vent. When there is continuous resin flowing out of the vent and no bubbles, it indicates that the internal cavity has been completely filled, and stop the injection.

[0051] Three-stage degassing: The potted hydrophone is placed back into the vacuum degassing tank and degassed for 10 minutes under a vacuum of -0.095MPa to remove air bubbles generated during the potting process.

[0052] Final curing: Place the hydrophone in an oven and cure it according to the process of 25℃×4h→60℃×6h. After curing, allow it to cool naturally to room temperature to complete the production of the entire hydrophone.

[0053] Unless otherwise specified, the model numbers of the various devices in this embodiment of the invention are not limited, and any device that can perform the above functions is acceptable.

[0054] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of a preferred embodiment, and the sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A hydrophone for pipeline monitoring, characterized in that, The hydrophone comprises a main shell, a sound-transmitting shell, a rear end cover, a sensitive element, a grounding gasket, a sealing ring, a circuit board and an external cable, The sound-transmitting shell is embedded in the middle mounting area of the main shell and has a cylindrical structure, and the sound-transmitting shell is provided with the sensitive element; The end of the main shell is provided with the rear end cover, and the rear end cover, the main shell and the grounding gasket jointly form a closed metal electromagnetic shielding layer; The sound-transmitting shell is provided with an integrally-formed annular limiting protruding edge at one end close to the main shell, a limiting clamping groove is formed on the inner wall of the main shell at a position corresponding to the limiting protruding edge, and the limiting clamping groove is sequentially fitted with the sealing ring and a sealing ring pressing ring; The sound-transmitting shell is internally provided with a first chamber, and an annular gap is formed between the outer wall of the sensitive element and the inner wall of the first chamber, which is used for pouring and sealing an impedance matching layer; the impedance matching layer is made of a mixed material of epoxy resin and aluminum oxide; the edges of the first end cover and the second end cover are uniformly provided with positioning protruding edges, and the outer diameter of the positioning protruding edges is matched with the inner diameter of the first chamber; At least two anti-rotation grooves are uniformly formed on the end face of the limiting protruding edge; and the end face of the rear end cover is provided with three through holes: a central through hole for penetrating the external cable; and the other two through holes are glue injection holes.

2. A hydrophone for pipeline monitoring according to claim 1, characterized in that, The sensitive element is a PZT-5 circular tube type piezoelectric ceramic, and the two ends are sealed by the first end cover and the second end cover, and the sealing process adopts epoxy structural adhesive.

3. A hydrophone for pipeline monitoring according to claim 1, characterized in that, A via hole is formed in the central area of the first end cover for penetrating and leading out the wire welded in the sensitive element; and the gap between the wire and the via hole is sealed and filled with adhesive.

4. A method of manufacturing a hydrophone, characterized by, The method comprises: a mixing preparation step of aluminum oxide filled epoxy glue, a mounting and impedance matching layer pouring step of the sensitive element, an assembly and sound-transmitting shell mounting step of the circuit board, a rear end cover mounting step, and an overall pouring and curing step; The mixing preparation step of the aluminum oxide filled epoxy glue comprises: pretreatment: selecting aluminum oxide powder with a particle size of 50-100 μm, drying in a 120℃ oven for 2h to remove water adsorbed on the surface of the powder; selecting bisphenol A type epoxy resin and aliphatic amine curing agent as the base material, weighing the epoxy resin and aluminum oxide powder in a volume ratio of 4:1, and adding γ-(2,3 epoxypropoxy) propyl trimethoxysilane coupling agent in an amount of 1%-2% of the mass of the epoxy resin; mixing operation: first pour the epoxy resin into a high-speed stirring tank, heat to 60℃ and stir at a speed of 500r / min for 10min, then slowly add the pretreated aluminum oxide powder, increase the stirring speed to 1200r / min, and continue stirring for 30min to ensure uniform dispersion of the aluminum oxide powder in the epoxy matrix; then add the coupling agent, keep the temperature at 60℃ and the stirring speed at 800r / min for 15min to achieve full compatibility of the inorganic and organic phases; pre-degassing treatment: transfer the mixed glue liquid to a vacuum degassing tank, and degas at a vacuum degree of-0.095MPa and a temperature of 60℃ for 20min to preliminarily remove the bubbles generated in the mixing process, thereby obtaining the pouring glue used as the impedance matching layer.

5. The method of claim 4, wherein the step of forming the hydrophone comprises the step of: The mounting and impedance matching layer pouring step of the sensitive element comprises: Component pretreatment: wipe the sensitive element, the first end cover, the second end cover and the inner wall of the first chamber of the sound-transmitting shell with anhydrous ethanol; Weld the lead wire on the sensitive element firmly, and pass the lead wire led out from the inside of the sensitive element through the via hole of the first end cover. Fill and seal the gap between the lead wire and the via hole with quick-drying glue. Attach the first end cover and the second end cover to the two end faces of the sensitive element respectively, and point coating seal along the attached edge of the end cover and the sensitive element with cyanoacrylate quick-drying glue. Put the sensitive element into the bottom of the first chamber, and ensure the coaxial distribution of the sensitive element and the first chamber through the cooperation of the convex edge of the end cover edge and the inner wall of the first chamber. Impedance matching layer pouring: slowly pour the pre-degassed alumina-epoxy pouring sealant along the inner wall of the first chamber into the annular gap, and the pouring speed is controlled at 0.2-0.5 kg / min to avoid impacting the sensitive element or generating new bubbles. After pouring until the gap is completely filled, put the sound-transmitting shell into a vacuum degassing tank, and perform secondary degassing at-0.095 MPa vacuum degree for 15 min to completely discharge the residual bubbles in the gap. Curing treatment: place the sound-transmitting shell with completed pouring into an oven, and perform step curing process: 25℃ for 2 h→60℃ for 4 h→100℃ for 1 h. After curing, naturally cool to room temperature to form a stable impedance matching layer.

6. The method of claim 4, wherein the step of forming the hydrophone comprises: The assembly of the circuit board and the installation of the sound-transmitting shell are as follows: After the impedance matching layer is completely cured, vertically place the pre-welded circuit board in the upper area of the first chamber, and reliably electrically connect the circuit board and the lead wire led out from the sensitive element. Adjust the position of the circuit board to make it have no interference with the inner wall of the first chamber. Pour low-viscosity epoxy resin into the first chamber to ensure that the glue completely fills the gap between the circuit board and the inner wall of the first chamber, and then stand still for 4 h at room temperature for curing. Clean the inner wall and the limiting clamping groove of the main shell, and sequentially embed the sealing ring and the sealing ring pressing ring in the limiting clamping groove. Insert the sound-transmitting shell with completed internal assembly into one end of the main shell, so that the limiting convex edge of the sound-transmitting shell is correspondingly clamped with the sealing ring pressing ring. After clamping, the axial direction of the sound-transmitting shell is not loose.

7. The method of claim 4, wherein the step of forming the hydrophone comprises the step of: The installation steps of the rear end cover are as follows: Put the nickel-plated carbon steel grounding gasket into the end of the main shell, so that it is attached to the end face of the limiting convex edge. Pass the external cable through the center through hole of the rear end cover, strip off the outer sheath of the cable end by 5-10 mm, and connect the lead wire with the circuit board. Weld the grounding wire on the lead wire to the grounding gasket. The welding point needs to be firm and without virtual welding, to ensure that the grounding gasket forms a closed electromagnetic shielding layer with the rear end cover and the main shell. Pre-tighten the rear end cover to the end of the main shell through threaded connection, use a double-pin wrench to clamp the glue injection hole of the rear end cover, and tighten the rear end cover by applying a preset torque to axially extrude the grounding gasket and provide continuous axial pre-tightening force to the sound-transmitting shell. After tightening, check the fit of the rear end cover and the main shell.

8. The method of claim 4, wherein the step of forming the hydrophone comprises the step of: The overall pouring and curing are as follows: Clean the glue injection hole of the rear end cover, and vertically place the hydrophone so that one of the glue injection holes serves as a glue pouring port and the other serves as an exhaust port. Pour low-viscosity epoxy resin into the glue pouring port at a pouring speed of 0.5-1.0 kg / min, and observe the exhaust port. When there is continuous glue flow and no bubbles from the exhaust port, stop pouring. The filled hydrophone was put into the vacuum degassing tank again, and was degassed at a vacuum degree of-0.095 MPa for 10 min to remove the bubbles generated in the filling process; The hydrophone was placed in an oven, and was cured according to a process of 25℃×4h→60℃×6h, and was naturally cooled to room temperature after curing.

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