A novel capacitive infrasound sensor and method of infrasound detection

Abstract

The embodiment of the application provides a novel capacitive infrasound sensor and an infrasound detection method, and belongs to the technical field of pipeline leakage detection. The novel capacitive infrasound sensor is characterized in that the novel capacitive infrasound sensor comprises: a detection cavity, which is connected with a pipeline to be detected through an acoustic sampling channel and is used for sensing infrasonic pressure pulsation caused by pipeline leakage; a reference cavity, which is connected with an external environment through a micropore array to form a pressure relief path with a preset time constant and is used for providing a stable reference pressure in a low frequency band; a capacitive sensing unit located between the detection cavity and the reference cavity, which is used for converting a differential pressure change between the detection cavity and the reference cavity into an electric signal; and a chopping demodulation circuit connected with the capacitive sensing unit, which is used for inhibiting low-frequency noise and DC drift in a demodulation process and obtaining a stable infrasound signal output. The scheme of the application realizes high-fidelity introduction of an infrasound signal for pipeline leakage detection while ensuring safety and reliability.

Description

Technical Field

[0001] This invention relates to the field of pipeline leak detection technology, specifically to a novel capacitive infrasound sensor and an infrasound detection method. Background Technology

[0002] Leaks in pipelines transporting oil, natural gas, and chemical media not only waste energy but can also lead to serious safety accidents and environmental pollution. Therefore, early and accurate leak detection in pipelines has always been a crucial issue in the industrial sector. In existing technologies, leak detection methods based on acoustic and infrasound signals have attracted widespread attention due to their ability to capture low-frequency pulsating signals generated by leaks. However, these methods still face several challenges in practical applications. For example, while the pipeline leak detection scheme based on sound pressure changes proposed in patent application CN101832472B can identify some leak events, it is susceptible to mechanical vibration interference in environments with strong low-frequency noise. The differential pressure sensing detection structure disclosed in patent application CN115031906A suffers from zero-point drift accumulation under complex pipeline network conditions. Furthermore, the infrasound signal recognition algorithm described in patent application CN115597790A still has insufficient detection rate for minor leaks in low signal-to-noise ratio scenarios.

[0003] Existing acoustic leak detection sensors have limited performance in low signal-to-noise ratio environments. The infrasound signal amplitude generated by pipeline leaks is typically extremely low, while the operating environment is subject to low-frequency interference such as wind noise, mechanical vibration, and water hammer from pump start-up and shutdown. These background noises highly overlap with the leak signal in the frequency band, easily leading to false alarms and missed alarms. Especially in the case of minute leaks, the signal is submerged by environmental noise, and the detection rate of the sensor drops significantly, making it difficult to meet the early leak warning requirements of long-distance pipelines.

[0004] Furthermore, existing infrasound sensors lack stability during long-term operation. Most sensors rely on mechanical structures or traditional capacitor transducers to acquire signals, but under long-term monitoring conditions, temperature fluctuations, zero-point drift, and the potential accumulation of condensate within the sensing cavity can all lead to decreased sensing sensitivity or signal distortion. In addition, when operating in complex outdoor environments, sensors are susceptible to moisture, corrosion, and electromagnetic interference, resulting in insufficient reliability of detection results and increasing maintenance costs and detection risks.

[0005] In summary, existing infrasound leak detection technology for pipelines has insufficient anti-interference capability under low signal-to-noise ratio conditions, and the long-term stability and reliability of sensors are difficult to guarantee. Improvements are urgently needed to achieve continuous, stable, and accurate detection of pipeline leaks. Summary of the Invention

[0006] The purpose of this invention is to provide a novel capacitive infrasound sensor and infrasound detection method, so as to at least solve the problems of insufficient detection rate in low signal-to-noise ratio environments and poor long-term operational stability of existing pipeline leak detection.

[0007] To achieve the above objectives, the first aspect of the present invention provides a novel capacitive infrasound sensor, comprising: a detection cavity connected to the pipe under test via an acoustic sampling channel for sensing infrasound pressure pulsations caused by leakage within the pipe; a reference cavity connected to the external environment via a micropore array to form a pressure relief path with a preset time constant for providing a stable reference pressure in the low-frequency range; a capacitive sensing unit located between the detection cavity and the reference cavity for converting the differential pressure change between the detection cavity and the reference cavity into an electrical signal; and a chopper demodulation circuit connected to the capacitive sensing unit for suppressing low-frequency noise and DC drift during demodulation to obtain a stable infrasound signal output.

[0008] Optionally, the novel capacitive infrasound sensor further includes an electrostatic self-calibration unit; the electrostatic self-calibration unit is connected to the capacitive sensing unit through a driving electrode, and is used to apply an equivalent electrostatic force pulse of preset amplitude to the capacitive sensing unit during sensor operation; after receiving the equivalent electrostatic force pulse, the capacitive sensing unit generates a capacitance change signal, and the capacitance change signal is input through the chopper demodulation circuit to form a parameter sequence for zero-point correction and sensitivity correction.

[0009] Optionally, the acoustic sampling channel includes a capillary damping tube disposed at the sampling port and an explosion-proof isolation membrane installed at the end of the capillary damping tube; the capillary damping tube has preset inner diameter and length parameters to limit the frequency transmission characteristics of the acoustic channel; the explosion-proof isolation membrane is mechanically fixed to the sampling port to transmit low-frequency sound pressure signals while blocking the medium inside the pipe being tested.

[0010] Optionally, the micropore array of the reference cavity is composed of replaceable acoustic impedance ferrules; the impedance parameters of the acoustic impedance ferrules are adjusted by changing the micropore diameter and arrangement density; the acoustic impedance ferrules are connected to the reference cavity through a sealing sleeve, and the impedance parameters are used to set the pressure relief time constant of the reference cavity, so that the reference cavity maintains the response characteristics of a preset frequency band under different media and pipeline pressure conditions.

[0011] Optionally, the chopper demodulation circuit includes a capacitor bridge, a chopper switch, and a lock-in amplifier; the capacitor bridge consists of a differential measurement circuit formed by the capacitor-sensitive unit and a reference capacitor; the chopper switch periodically switches the polarity of the input signal at a preset frequency; the lock-in amplifier extracts amplitude information under the condition of being synchronized with the preset frequency, thereby forming a stable low-frequency electrical signal output.

[0012] Optionally, the acoustic sampling channel is provided with a condensation drainage structure; the condensation drainage structure includes a drainage chamber located at the bottom of the acoustic channel and a one-way liquid guide valve communicating with the drainage chamber; the drainage chamber is connected to the side wall of the acoustic sampling channel through a pipeline, and the one-way liquid guide valve opens when the liquid inside the channel accumulates to a preset liquid level, so as to drain the liquid to the external environment.

[0013] Optionally, the novel capacitive infrasound sensor further includes a main body housing made of metal or composite material; the surface of the main body housing is sequentially covered with a waterproof layer and an anti-corrosion coating, the waterproof layer is formed by polymer coating to form a continuous coverage, and the anti-corrosion coating is formed by spraying epoxy resin material; the main body housing is integrally sealed and fixed with the detection cavity and the reference cavity.

[0014] Optionally, the inner wall of the sensor housing is provided with a metal shielding layer; the metal shielding layer is connected to an external grounding circuit through a grounding lead, and the grounding lead is fixed to the cable sheath grounding wire via a dedicated terminal; the shielding layer covers the capacitive sensing unit and the chopper demodulation circuit inside, so as to reduce the influence of external electromagnetic interference on the circuit signal.

[0015] A second aspect of the present invention provides an infrasound detection method based on the novel capacitive infrasound sensor described above. The method includes: acquiring structural parameters and operating condition parameters of the pipeline under test, and using these parameters as reference inputs; introducing a leakage pulsation signal from the pipeline into the sensor's detection chamber via an acoustic sampling channel, forming a differential pressure with the reference chamber, the differential pressure response being stored corresponding to the structural parameters and operating condition parameters; using a capacitive sensing unit disposed between the detection chamber and the reference chamber to convert the differential pressure change into an electrical signal, and comparing the electrical signal with the reference input to generate a corrected detection signal; performing chopping and demodulation processing on the corrected detection signal in a chopper demodulation circuit to suppress low-frequency noise and DC drift, and outputting an infrasound detection signal sequence associated with the structural parameters and operating condition parameters; forming a feature sequence based on the infrasound detection signal sequence and the reference input, the feature sequence serving as input data for leak determination and location analysis.

[0016] Optionally, the method further includes: during sensor operation, applying an equivalent electrostatic force pulse of preset amplitude to the driving electrode of the capacitance sensing unit through an electrostatic self-calibration unit, causing the capacitance sensing unit to generate a corresponding capacitance change signal; inputting the capacitance change signal to the chopper demodulation circuit to generate a calibration sequence; the calibration sequence is used to correct the zero-point offset and sensitivity drift of the capacitance sensing unit when detecting differential pressure signals.

[0017] Through the above technical solution, this invention sets up a detection cavity and a reference cavity in the sensor structure, and uses a micro-pore array to form a pressure relief path with a preset time constant. This allows the infrasound pulsations of pipeline leakage sensed by the detection cavity to form a differential pressure with a stable low-frequency reference signal, which is then converted into an electrical signal by a capacitive sensing unit. Combined with a chopper demodulation circuit to process the output signal, the influence of low-frequency noise and DC drift is effectively reduced, thereby obtaining a stable and usable infrasound detection signal. The overall structure achieves reliable sensing and signal conversion of weak infrasound leakage in complex pipeline environments, providing accurate input for subsequent leakage analysis.

[0018] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings:

[0020] Figure 1 This is a schematic diagram of the system structure of a novel capacitive infrasound sensor provided in one embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of the physical structure of a novel capacitive infrasound sensor provided in one embodiment of the present invention;

[0022] Figure 3 This is a flowchart of the steps of an infrasound detection method provided in one embodiment of the present invention.

[0023] Explanation of reference numerals in the attached figures

[0024] 10 - Reference cavity; 20 - Detection cavity; 30 - Acoustic sampling channel. Detailed Implementation

[0025] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0026] like Figure 1As shown, this invention provides a novel capacitive infrasound sensor, comprising: a detection cavity 20 connected to the pipe under test via an acoustic sampling channel 30, used to sense infrasound pressure pulsations caused by leakage within the pipe; a reference cavity 10 connected to the external environment via a micropore array to form a pressure relief path with a preset time constant, used to provide a stable reference pressure in the low-frequency range; a capacitive sensing unit located between the detection cavity 20 and the reference cavity 10, used to convert the differential pressure change between the detection cavity 20 and the reference cavity 10 into an electrical signal; and a chopper demodulation circuit connected to the capacitive sensing unit, used to suppress low-frequency noise and DC drift during demodulation to obtain a stable infrasound signal output.

[0027] In this embodiment of the invention, a novel capacitive infrasound sensor is proposed. This sensor is specifically optimized for handling low-frequency infrasound signals generated by pipe leaks. Specifically, a detection chamber 20 is arranged in the lower structure of the sensor. This detection chamber 20 is directly connected to the pipe being measured via an acoustic sampling channel 30. The geometry and damping characteristics of the acoustic sampling channel 30 are preset to effectively introduce infrasound pressure pulsations caused by internal pipe leaks into the detection chamber 20. Outside the detection chamber 20, a reference chamber 10 is also provided. The reference chamber 10 is not directly open to the external environment but is maintained in communication through a micropore array. The pore size and arrangement density of the micropore array determine the decompression time constant of the reference chamber 10, thus enabling the construction of a smooth and stable reference pressure environment in the low-frequency range. A differential pressure condition is formed between the detection chamber 20 and the reference chamber 10, and the dynamic changes in the differential pressure are converted by a capacitive sensing element arranged between them. The capacitive sensing unit typically employs a parallel electrode structure, with the gap size and initial capacitance value strictly set to ensure that differential pressure changes are linearly mapped to capacitance changes, which are then converted into an electrical signal output through a circuit interface. Considering the extremely low amplitude of infrasound signals and their susceptibility to environmental noise interference, the weak signal output from the capacitive sensing unit directly enters the chopper demodulation circuit. The chopper demodulation circuit uses an alternating switching method to suppress 1 / f noise and DC drift, and achieves steady-state readout of the low-frequency signal through lock-in amplification. After this series of processing steps, a stable electrical signal corresponding to the height of the infrasound pulsations from the pipeline leak is finally obtained. Overall, the sensor design achieves a continuous closed loop from acoustic acquisition and differential pressure conversion to circuit demodulation, enabling operators to accurately acquire the infrasound characteristic signals of pipeline leaks in complex operating environments, ensuring a reliable data foundation for subsequent detection and analysis.

[0028] like Figure 2This diagram illustrates the specific structure of a novel capacitive infrasound sensor. The sensor is an integrated cylindrical housing with a standard threaded interface for mechanical fixation and acoustic sealing with the sampling port of the tested pipeline. The upper part is a relatively large cylindrical cavity, serving as a reference cavity 10, which maintains limited communication with the outside world through a micropore array, allowing the internal pressure to change slowly in the low-frequency range, forming a stable reference. The middle section houses the detection cavity 20, which is connected to the pipeline via an acoustic sampling channel 30 to receive infrasound pulsations generated by pipeline leakage. A capacitive sensing element is arranged between the detection cavity 20 and the reference cavity 10, shown in the diagram as a stack of parallel electrodes. The gap between these electrodes changes capacitance with differential pressure, converting the acoustic signal into an electrical signal. The lower threaded area is the sampling connection and sealing fixation part, screwed into the pipeline sidewall via a standard thread to maintain stable acoustic coupling during operation. The overall structural design allows the reference cavity 10, the detection cavity 20, and the capacitive sensing unit to be stacked sequentially in space to form a three-dimensional differential pressure pickup unit, which facilitates subsequent integration with circuit modules to achieve signal demodulation and output.

[0029] Preferably, the novel capacitive infrasound sensor further includes an electrostatic self-calibration unit; the electrostatic self-calibration unit is connected to the capacitive sensing unit through a driving electrode, and is used to apply an equivalent electrostatic force pulse of a preset amplitude to the capacitive sensing unit during sensor operation; after receiving the equivalent electrostatic force pulse, the capacitive sensing unit generates a capacitance change signal, and the capacitance change signal is input through the chopper demodulation circuit to form a parameter sequence for zero-point correction and sensitivity correction.

[0030] In this embodiment of the invention, the novel capacitive infrasound sensor further includes an electrostatic self-calibration unit. This electrostatic self-calibration unit is connected to the capacitive sensing unit via a driving electrode and can apply an equivalent electrostatic force pulse of a preset amplitude to the capacitive sensing unit during sensor operation. Specifically, the electrostatic self-calibration unit utilizes the electrical connection between the capacitive sensing unit and the driving electrode to periodically apply an equivalent electrostatic force pulse of a preset amplitude to the capacitive sensing unit during sensor operation. These pulses induce changes in capacitance through the capacitive structure of the capacitive sensing unit, thereby generating an electrical signal. Since the capacitance change of the capacitive sensing unit is closely related to changes in voltage and electric field, by applying known electrostatic force pulses, the amplitude of the capacitance change can be controlled very precisely, thereby effectively correcting the drift phenomenon that may occur in the capacitive sensing unit during actual operation.

[0031] After the capacitance change signal is generated by the capacitance-sensitive unit, it is further processed by a chopper demodulation circuit. The function of the chopper demodulation circuit is to suppress low-frequency noise and DC drift by changing the frequency characteristics of the electrical signal, ensuring that the weak signal received from the capacitance-sensitive unit can be accurately extracted. Through chopper demodulation, the capacitance change signal can be converted into a high-frequency signal that is easy to process and analyze, reducing interference from environmental noise and making the signal more stable and clear. The chopper demodulation circuit inputs this signal to the sensor's readout link, forming a calibrated infrasound signal output.

[0032] During this process, the equivalent electrostatic force pulse applied by the electrostatic self-calibration unit, through periodic calibration of the capacitance-sensitive unit, can eliminate zero-point drift and sensitivity changes caused by temperature fluctuations, long-term use, and other factors. This significantly improves the detection accuracy of the capacitance-sensitive unit, ensuring the stability and accuracy of the sensor during long-term operation.

[0033] This calibration method generates a complete parameter sequence, which is used for subsequent zero-point calibration and sensitivity correction. With prolonged sensor operation, the electrostatic self-calibration unit ensures the sensor remains in optimal working condition, maintaining high-quality signal output even under complex operating conditions. This technical solution significantly improves the long-term reliability and accuracy of the sensor, enabling it to operate stably in various harsh environments and greatly enhancing the sensitivity and reliability of pipeline leak detection.

[0034] Preferably, the acoustic sampling channel 30 includes a capillary damping tube disposed at the sampling port and an explosion-proof isolation membrane installed at the end of the capillary damping tube; the capillary damping tube has preset inner diameter and length parameters to limit the frequency transmission characteristics of the acoustic channel; the explosion-proof isolation membrane is mechanically sealed at the sampling port to transmit low-frequency sound pressure signals while blocking the medium inside the pipe being tested.

[0035] In this embodiment of the invention, the acoustic sampling channel 30 includes a capillary damping tube disposed at the sampling port and an explosion-proof isolation membrane installed at the end of the capillary damping tube. The acoustic sampling channel 30 is designed to ensure effective acquisition of infrasound signals from the tested pipeline and to avoid contamination or leakage of the internal medium of the pipeline affecting the detection accuracy of the sensor. The function of the capillary damping tube is to limit the frequency transmission characteristics of the acoustic channel through its preset inner diameter and length. Specifically, the inner diameter and length of the capillary damping tube are matched with the frequency range of infrasound generated by leakage in the pipeline, ensuring that only low-frequency infrasound signals within a specific frequency range can smoothly pass through the channel into the detection chamber 20. The inner diameter, length, and damping characteristics of the capillary damping tube are precisely designed to effectively control the frequency range of the acoustic signal, thereby improving the sensor's response sensitivity to minute leakage signals and avoiding interference from high-frequency noise signals.

[0036] The explosion-proof isolation diaphragm is mechanically sealed at the sampling port, serving two main functions: First, it effectively isolates the medium inside the tested pipe, preventing liquids or gases from directly entering the acoustic sampling channel 30, thus protecting the sensor from corrosive substances or high-pressure fluids. Second, the design of the explosion-proof isolation diaphragm allows low-frequency sound pressure signals to be transmitted through the diaphragm, enabling infrasound pulsations generated by leaks in the pipe to enter the detection chamber 20 without obstruction. This design greatly improves the stability and service life of the sensor, avoiding potential equipment failures under extreme environments such as high pressure and high temperature.

[0037] Furthermore, the material and thickness of the explosion-proof diaphragm are designed with full consideration of environmental factors such as the pressure and temperature of the gas or liquid inside the pipeline. This ensures both the mechanical strength of the diaphragm and the quality of acoustic signal transmission. The diaphragm is typically made of a material with good elasticity, enabling it to withstand the instantaneous impact pressure of the fluid inside the pipeline while maintaining sufficient sensitivity to detect low-frequency infrasound waves generated by leaks.

[0038] By combining a capillary damping tube and an explosion-proof isolation diaphragm into an integrated acoustic sampling channel 30, this invention can effectively control the quality of leakage signal acquisition from the tested pipeline while ensuring the stability of the sensor in harsh environments. This design has significant advantages in the field of pipeline leak detection, enabling stable operation in complex industrial environments and maintaining high detection accuracy even after prolonged use. Especially under low signal-to-noise ratio conditions, it can effectively improve the detection sensitivity of minute leaks.

[0039] In summary, the present invention, through its carefully designed acoustic sampling channel 30, ensures that the infrasound signal collected from inside the pipeline is not affected by the external environment, while also protecting the core components of the sensor from harsh working conditions, thereby improving the reliability and accuracy of the equipment. It is particularly suitable for pipeline leak detection applications with long-term and high stability requirements.

[0040] Preferably, the micropore array of the reference cavity 10 is composed of replaceable acoustic impedance ferrules; the impedance parameters of the acoustic impedance ferrules are adjusted by changing the micropore diameter and arrangement density; the acoustic impedance ferrules are connected to the reference cavity 10 through a sealing sleeve, and the impedance parameters are used to set the pressure relief time constant of the reference cavity 10, so that the reference cavity 10 maintains the response characteristics of a preset frequency band under different media and pipeline pressure conditions.

[0041] In this embodiment of the invention, the micropore array of the reference cavity 10 is composed of replaceable acoustic impedance ferrules. These ferrules employ a multi-micropore structure, and the acoustic impedance characteristics can be precisely adjusted by parametrically controlling the diameter, number, and arrangement density of the micropores. Specifically, the diameter of the micropores determines the channel width for the sound pressure signal to travel between the reference cavity 10 and the external environment. A smaller diameter results in a more pronounced viscosity effect of gas molecules within the channel, leading to higher acoustic impedance. Conversely, the arrangement density of the micropores affects the overall permeability of the channel; a denser arrangement reduces the equivalent impedance, making the low-frequency pressure relief path smoother. By adjusting these two parameters in combination, the pressure relief time constant of the reference cavity 10 can be flexibly set.

[0042] To ensure adaptability under different operating conditions, the acoustic impedance ferrule is designed to be replaceable, with a sealing sleeve on its outer periphery and an airtight connection to the wall of the reference cavity 10 via a sealing ring. This allows for quick replacement of ferrules with different impedance characteristics when the type of pipeline medium or operating pressure changes, ensuring the reference cavity 10 maintains a stable response within the target frequency band. For example, in high-pressure gas pipeline conditions, ferrules with smaller orifice diameters and more sparser spacing can be used to increase impedance and extend the pressure relief time constant, preventing interference from rapid external pressure fluctuations to the reference cavity 10. In low-pressure or liquid pipeline scenarios, ferrules with larger diameters and higher density can be used to reduce impedance and shorten the pressure relief time constant, thereby ensuring rapid establishment of the low-frequency reference pressure.

[0043] This method of setting the frequency band characteristics of the reference cavity through an acoustic impedance ferrule enables the sensor to maintain a preset frequency response under complex and variable media conditions. This not only improves the identification accuracy of infrasound from pipeline leaks but also enhances the sensor's applicability and long-term stability.

[0044] Preferably, the chopper demodulation circuit includes a capacitor bridge, a chopper switch, and a lock-in amplifier; the capacitor bridge consists of a differential measurement circuit formed by the capacitor-sensitive unit and a reference capacitor; the chopper switch periodically switches the polarity of the input signal at a preset frequency; and the lock-in amplifier extracts amplitude information under the condition of being synchronized with the preset frequency, thereby forming a stable low-frequency electrical signal output.

[0045] In this embodiment of the invention, the chopper demodulation circuit comprises three parts: a capacitor bridge, a chopper switch, and a lock-in amplifier. Each part performs a different function and works in sequence within the overall signal chain to extract and output the infrasound signal. The capacitor bridge consists of a capacitor-sensitive unit and a reference capacitor forming a differential measurement circuit. Its function is to convert the differential pressure change between the detection cavity 20 and the reference cavity 10 into a change in differential capacitance. Since the capacitance value of the capacitor-sensitive unit changes dynamically with the differential pressure, while the reference capacitor remains stable, the two form an unbalanced state in the bridge circuit, thereby outputting an AC signal corresponding to the differential pressure. In this way, even pressure disturbances with extremely small amplitudes can be reflected through differential amplification of the bridge circuit, enhancing the usability of subsequent processing.

[0046] Chopper switches are designed to suppress low-frequency noise and DC drift. They operate by periodically switching the polarity of the input signal at a preset frequency, essentially shifting the low-frequency signal to a higher frequency range. Common structures consist of alternating MOSFETs or analog switches, with the turn-on timing controlled by a reference clock, causing the signal polarity to flip within each clock cycle. This modulates the useful signal, originally located in the DC or low-frequency range, to a higher frequency, effectively avoiding common 1 / f noise interference in circuits and preventing DC drift from superimposing on the effective signal.

[0047] The lock-in amplifier (LPA) is responsible for demodulating and extracting amplitude information. Under strict synchronization with a preset frequency, the LPA performs coherent detection on the chopper-modulated signal. It uses a reference signal as a phase reference to extract components with the same frequency and phase, while filtering out unrelated frequencies and noise. The final output is an electrical signal with stable amplitude and a frequency restored to the low-frequency range, which can clearly reflect the amplitude of infrasound pressure pulsations caused by leakage.

[0048] Through this three-stage coordinated design of capacitor bridge, chopper switch, and lock-in amplifier, the entire circuit can ensure both high sensitivity of differential measurement and maintain a high signal-to-noise ratio under complex noise backgrounds. Its technical advantages are reflected in the fact that even in environments with low signal-to-noise ratios and long-term operation, the electrical signal output by the sensor remains stable and reliable, providing a solid foundation for subsequent pipeline leak detection.

[0049] Preferably, the acoustic sampling channel 30 is provided with a condensation drainage structure; the condensation drainage structure includes a drainage chamber located at the bottom of the acoustic channel and a one-way liquid guide valve communicating with the drainage chamber; the drainage chamber is connected to the side wall of the acoustic sampling channel 30 through a pipeline, and the one-way liquid guide valve opens when the liquid inside the channel accumulates to a preset liquid level, so as to drain the liquid to the external environment.

[0050] In this embodiment of the invention, the acoustic sampling channel 30 is equipped with a condensation drainage structure to address the problem of liquid accumulation inside the channel due to condensation during long-term operation. The specific design of this condensation drainage structure is as follows: a drainage chamber is reserved at the bottom of the acoustic channel. This drainage chamber serves as a liquid collection area, and its volume and shape are pre-set so that when condensate is generated in the channel or external media seeps in, it can preferentially flow into the drainage chamber without directly submerging the sampling acoustic path. The drainage chamber is connected to the side wall of the acoustic sampling channel 30 via a pipe. The diameter and height of the pipe are reasonably selected to ensure that the transmission of acoustic signals is not affected during gas flow and that liquid is smoothly introduced into the drainage chamber when it is present.

[0051] A one-way guide valve is installed at the outlet of the drainage chamber. This valve is a small mechanical structure, typically using a resilient valve plate or a spring-loaded ball valve. It automatically opens when the liquid level inside the channel reaches a preset level. The preset level is determined by the geometry of the drainage chamber and the valve opening pressure. When the liquid level exceeds the threshold, the internal hydraulic pressure overcomes the valve's elastic force, opening the valve and promptly draining the accumulated liquid to the external environment. After drainage, the one-way guide valve closes again when the liquid level drops and the pressure inside the chamber decreases, preventing external gas or impurities from flowing back into the acoustic channel.

[0052] Through this structural design, the acoustic sampling channel 30 can automatically drain condensate and seepage fluid without affecting acoustic signal transmission. The drainage process does not rely on external operation and does not interfere with the sensor's real-time monitoring function, ensuring that the acoustic sampling channel 30 remains dry and unobstructed at all times. This not only improves the sensor's operational stability in humid and high-temperature environments but also avoids acoustic path blockage or signal attenuation problems caused by liquid accumulation. Overall, this condensate drainage structure provides the necessary guarantee for the long-term reliable operation of the sensor, ensuring accurate acquisition of infrasound signals generated by pipeline leaks even under complex operating conditions.

[0053] Preferably, the novel capacitive infrasound sensor further includes a main body housing made of metal or composite material; the surface of the main body housing is sequentially covered with a waterproof layer and an anti-corrosion coating, the waterproof layer is formed by polymer coating to form a continuous coverage, and the anti-corrosion coating is formed by spraying epoxy resin material, and the main body housing is integrally sealed and fixed with the detection cavity 20 and the reference cavity 10.

[0054] In the embodiments of this invention, the novel capacitive infrasound sensor further includes a main housing made of metal or composite material. This main housing, as an integral load-bearing structure, not only houses and protects the detection cavity 20, reference cavity 10, and capacitive sensing unit, but also maintains good mechanical strength and environmental adaptability during long-term use. Typically, the main housing can be made of stainless steel, aluminum alloy, or carbon fiber reinforced composite material. The former has excellent compressive strength and temperature resistance, while the latter is more advantageous in terms of weight reduction. To further improve environmental protection performance, the outer surface of the main housing is sequentially covered with a waterproof layer and an anti-corrosion coating. The waterproof layer is formed by polymer coating, such as polyurethane or fluorocarbon coatings, which can form a continuous covering film on the metal or composite material surface, ensuring that external liquids cannot penetrate the housing even in high humidity or rainy environments. Below this, an anti-corrosion coating is applied, preferably formed by spraying epoxy resin. After curing, the epoxy material forms a dense protective film that effectively resists the corrosion of acidic or alkaline gases, salt spray, or chemical media, thereby extending the sensor's lifespan.

[0055] In terms of structural fixation, the main housing is integrally sealed and fixed to the internal detection chamber 20 and reference chamber 10 through sealing threads, O-rings, or welding. This ensures that the sensor can withstand external impacts during operation while preventing performance degradation due to leakage at the housing joints. Through this multi-layered protection and sealing design, the sensor can operate stably for extended periods under complex conditions. This design not only improves the reliability of the sensor in outdoor or chemical plant applications but also protects the internal capacitive sensing unit and chopper demodulation circuit from external environmental influences, thereby achieving continuous and stable detection of infrasound signals.

[0056] Preferably, the inner wall of the sensor housing is provided with a metal shielding layer; the metal shielding layer is connected to an external grounding circuit through a grounding lead, and the grounding lead is fixed to the cable sheath grounding wire via a dedicated terminal; the shielding layer covers the capacitive sensing unit and the chopper demodulation circuit inside, so as to reduce the influence of external electromagnetic interference on the circuit signal.

[0057] In this embodiment of the invention, a metal shielding layer is provided on the inner wall of the sensor housing. This shielding layer serves as an electromagnetic shielding structure, covering the inner side of the sensor housing to form a continuous conductive envelope. The shielding layer is typically made of high-conductivity metals such as copper foil, aluminum foil, or nickel-plated steel sheets, and is fixed to the inner wall of the housing by mechanical pressing, spraying conductive paint, or adhesive film bonding. To ensure continuous shielding effect, the overlaps of the shielding layer are treated with lap welding or conductive adhesive bonding to form a complete closed conductive surface. The metal shielding layer is connected to an external grounding circuit through a grounding lead. The grounding lead is made of low-impedance copper wire or tin-plated multi-strand conductor and is protected by an insulating sheath to prevent accidental contact with the internal circuitry.

[0058] The grounding lead is fixedly connected to the grounding wire in the cable sheath via a dedicated terminal when it exits the housing. This terminal has a crimp or screw fastening structure to ensure sufficiently low contact resistance and prevent shielding failure due to loosening or oxidation during long-term operation. In this way, the shielding layer can completely enclose the capacitive sensing unit and the chopper demodulation circuit inside, forming a stable electromagnetic shielding cavity. When the sensor is running, external electromagnetic interference signals, such as the power frequency magnetic field generated by high-voltage cables, electromagnetic waves emitted by wireless communication equipment, and transient pulses from peripheral equipment, are preferentially coupled to the shielding layer and discharged to the ground through the grounding loop, thereby preventing interference energy from directly entering the internal sensitive circuit.

[0059] Through this shielding and grounding design, the sensor's core capacitive sensing element and chopper demodulation circuit are always in a low-interference electromagnetic environment, enabling the stable extraction and processing of differential capacitance change signals. Overall, this metal shielding layer significantly improves electromagnetic interference resistance, ensuring that the sensor can still output stable and reliable infrasound detection signals in complex electromagnetic environments, providing necessary signal quality assurance for pipeline leak detection.

[0060] like Figure 3 As shown, an embodiment of the present invention provides an infrasound detection method, the method comprising:

[0061] S10: Obtain the structural parameters and operating condition parameters of the pipeline under test, and use the structural parameters and operating condition parameters as reference inputs.

[0062] Specifically, the structural parameters include, but are not limited to, the pipe diameter, wall thickness, material, and layout of the pipe under test, such as the presence of elbows, tees, or welds. These parameters are obtained through design drawings, online thickness gauges, or optical ranging devices and stored as fixed input parameters in the data interface. The operating condition parameters include information such as the type of medium inside the pipe, operating pressure, flow rate, and temperature. These are typically acquired in real time by pressure sensors, temperature sensors, and flow meters and input to the processing link via a signal acquisition module. These parameters serve as reference inputs and are used in conjunction with subsequent leak signal detection data. In particular, when the medium inside the pipe differs (e.g., natural gas and crude oil), the propagation characteristics of acoustic waves differ significantly. Therefore, the introduction of operating condition parameters can provide a benchmark for the interpretation of differential pressure signals, avoiding a decrease in detection accuracy due to inconsistent medium characteristics. By presetting and continuously updating these reference inputs before the sensor operates, the accuracy of subsequent signal comparison, correction, and judgment can be guaranteed, establishing a stable data foundation for overall leak detection.

[0063] S20: The leakage pulsation signal in the pipeline is introduced into the detection chamber of the sensor through the acoustic sampling channel, and a differential pressure is formed with the reference chamber. The differential pressure response is stored in correspondence with the structural parameters and operating parameters.

[0064] Specifically, the acoustic sampling channel is coupled to the outer wall of the pipeline via a fixed interface, and a capillary damping tube and an explosion-proof isolation membrane are installed within the channel. The diameter and length of the capillary damping tube are preset to limit the frequency bandwidth of the acoustic signal, enabling efficient transmission of infrasound pulsations generated by leakage in the low-frequency range while suppressing high-frequency interference. The explosion-proof isolation membrane is fixed to the sampling port by a mechanical seal, preventing the medium inside the pipeline from seeping into the sensor while allowing sound pressure waves to pass through. The leakage pulsation signal enters the detection chamber through the acoustic sampling channel, forming a differential pressure field with the ambient pressure of the reference chamber. This differential pressure response is bound and stored with the aforementioned structural and operating parameters, for example, the differential pressure signal is archived one-to-one with specific pipe diameter, pressure, and flow velocity conditions. This allows for rapid retrieval of a differential pressure reference matching the current pipeline state during subsequent calibration and analysis, avoiding characteristic drift caused by environmental changes, thereby improving the consistency and comparability of the detection signal.

[0065] S30: Using a capacitive sensing unit disposed between the detection cavity and the reference cavity, the differential pressure change is converted into an electrical signal, and the electrical signal is compared with the reference input to generate a corrected detection signal.

[0066] Specifically, the capacitive sensing unit consists of a fixed electrode and a movable electrode, forming a capacitor gap in between. Under differential pressure, the movable electrode undergoes a slight displacement, causing a change in capacitance, the magnitude of which is proportional to the differential pressure. This capacitance change is converted into a voltage signal in real time via a bridge circuit and output to the acquisition circuit. Before entering the analysis stage, the acquired electrical signal is compared with pre-stored structural and operating parameters. For example, under known flow rate and pressure, the typical spectral characteristics of leakage pulsation are used as a reference baseline. During the comparison process, the system automatically corrects deviations caused by differences in pipe wall thickness or material, thereby generating a corrected detection signal. The correction process not only compensates for differences caused by physical structure but also considers dynamic changes in operating conditions, making the output detection signal more consistent and accurate, ensuring the reliability of subsequent demodulation and feature extraction.

[0067] S40: The corrected detection signal is chopping and demodulated within the chopper demodulation circuit to suppress low-frequency noise and DC drift, and outputs an infrasound detection signal sequence associated with the structural parameters and operating parameters.

[0068] Specifically, the chopper demodulation circuit includes a capacitor bridge, a chopper switch, and a lock-in amplifier. The corrected capacitance change signal is input as a differential input to the capacitor bridge, with a reference capacitor connected to the bridge to ensure a clean differential signal output. The chopper switch periodically switches the polarity of the input signal at a preset frequency, modulating the low-frequency differential signal onto a high-frequency carrier. The modulated signal is amplified by low noise and then input to the lock-in amplifier. The lock-in amplifier uses a reference signal with the same chopper frequency as a reference to synchronously demodulate the original signal amplitude and filter out DC drift and 1 / f noise. The demodulated result is a stable infrasound detection signal sequence, which is bound to and stored with corresponding structural and operating parameters to ensure traceability of the signal output under different pipeline environments. This allows for the retrieval of standardized data under corresponding conditions in subsequent analyses, avoiding cross-condition interference.

[0069] S50: A feature sequence is formed based on the infrasound detection signal sequence and the reference input, and the feature sequence is used as input data for leakage determination and location analysis.

[0070] Specifically, the infrasound detection signal sequence first undergoes digital filtering and feature extraction processing. Extracted features include amplitude envelope, spectral energy distribution, phase delay, and autocorrelation function. Simultaneously, structural parameters and operating conditions are incorporated into the feature construction process as reference inputs. For example, frequency response curves under different pipe diameters or amplitude normalization coefficients under different pressures are used for correction. The final generated feature sequence not only contains the original dynamic characteristics of the infrasound signal but also includes correction factors that match the pipeline's physical and operating conditions, thereby improving the universality and accuracy of the features. This feature sequence serves as input data for leak detection and location analysis, and can be further used to train a discrimination model or perform correlation analysis, helping to identify the location and severity of leak events and providing core data support for pipeline safety monitoring.

[0071] Preferably, the method further includes: during sensor operation, applying an equivalent electrostatic force pulse of preset amplitude to the driving electrode of the capacitance sensing unit through an electrostatic self-calibration unit, causing the capacitance sensing unit to generate a corresponding capacitance change signal; inputting the capacitance change signal to the chopper demodulation circuit to generate a calibration sequence; the calibration sequence is used to correct the zero-point offset and sensitivity drift of the capacitance sensing unit when detecting differential pressure signals.

[0072] In this embodiment of the invention, the electrostatic self-calibration unit maintains an electrical connection with the driving electrode of the capacitive sensing unit and applies an equivalent electrostatic force pulse with controllable amplitude within a preset calibration period. This equivalent electrostatic force pulse acts directly on the movable plate of the capacitive sensing unit through the driving electrode, causing it to generate a small displacement equivalent to the real differential pressure signal without relying on external actual pressure changes, thereby introducing a repeatable capacitance change signal onto the sensitive capacitor. This capacitance change signal is input to the chopper demodulation circuit as a reference excitation, converted into a stable electrical signal by the demodulation stage, and forms a calibration sequence in the readout link. This calibration sequence is compared with the differential pressure detection signal output by the sensor in normal operating mode to quantify the zero-point drift and sensitivity decay of the sensing unit. When a zero-point shift is detected, the reference point of the sensor is readjusted to a preset initial state through the reference output of the calibration sequence; when the capacitance response slope of the sensing unit decreases or exhibits nonlinear deviation, the sensitivity parameter is numerically compensated through the calibration sequence. This method ensures that the capacitive sensing unit maintains stable detection characteristics during long-term operation, avoiding the accumulation of measurement errors caused by temperature fluctuations, material aging, or stress release, thereby guaranteeing the accuracy and consistency of the sensor in detecting infrasound signals of pipeline leaks under complex operating conditions.

[0073] Those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. This program is stored in a storage medium and includes several instructions to cause a microcontroller, chip, or processor to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0074] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details described above. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention. It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not further describe the various possible combinations.

[0075] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the embodiments of the present invention, they should also be regarded as the content disclosed by the embodiments of the present invention.

Claims

1. A novel capacitive infrasound sensor, characterized in that, The novel capacitive infrasound sensor includes: The detection chamber, connected to the pipe under test via an acoustic sampling channel, is used to sense infrasound pressure pulsations caused by leaks within the pipe; The acoustic sampling channel includes a capillary damping tube set at the sampling port and an explosion-proof isolation membrane installed at the end of the capillary damping tube; the capillary damping tube has preset inner diameter and length parameters to limit the frequency transmission characteristics of the acoustic channel; the explosion-proof isolation membrane is sealed at the sampling port by mechanical fixing to transmit low-frequency sound pressure signals while blocking the medium inside the pipe being tested. The reference cavity is connected to the external environment through a micropore array to form a pressure relief path with a preset time constant, which is used to provide a stable reference pressure in the low frequency band. A capacitive sensing unit located between the detection cavity and the reference cavity is used to convert the differential pressure change between the detection cavity and the reference cavity into an electrical signal. The chopper demodulation circuit connected to the capacitive sensing unit is used to suppress low-frequency noise and DC drift during demodulation to obtain a stable infrasound signal output; wherein, The chopper demodulation circuit includes a capacitor bridge, a chopper switch, and a lock-in amplifier; the capacitor bridge consists of a differential measurement circuit formed by the capacitor-sensitive unit and a reference capacitor; the chopper switch periodically switches the polarity of the input signal at a preset frequency; the lock-in amplifier extracts amplitude information under the condition of being synchronized with the preset frequency, thereby forming a stable low-frequency electrical signal output. An electrostatic self-calibration unit is provided; the electrostatic self-calibration unit is connected to the capacitance sensing unit via a driving electrode, and is used to apply an equivalent electrostatic force pulse of a preset amplitude to the capacitance sensing unit during sensor operation; after receiving the equivalent electrostatic force pulse, the capacitance sensing unit generates a capacitance change signal, which is input via the chopper demodulation circuit to form a parameter sequence for zero-point correction and sensitivity correction.

2. The novel capacitive infrasound sensor according to claim 1, characterized in that, The micropore array of the reference cavity is composed of replaceable acoustic impedance ferrules. The impedance parameters of the acoustic impedance ferrule are adjusted by changing the micropore diameter and arrangement density. The acoustic impedance ferrule is connected to the reference cavity through a sealing sleeve. The impedance parameter is called to set the pressure relief time constant of the reference cavity, so that the reference cavity maintains the response characteristics of a preset frequency band under different media and pipeline pressure conditions.

3. The novel capacitive infrasound sensor according to claim 1, characterized in that, The acoustic sampling channel is equipped with a condensation removal structure. The drainage structure includes a drainage chamber located at the bottom of the acoustic channel and a one-way liquid guiding valve communicating with the drainage chamber. The drainage chamber is connected to the side wall of the acoustic sampling channel via a pipeline. The one-way liquid guide valve opens when the liquid inside the channel accumulates to a preset level, so as to discharge the liquid to the external environment.

4. The novel capacitive infrasound sensor according to claim 1, characterized in that, The novel capacitive infrasound sensor also includes a main housing made of metal or composite materials. The surface of the main housing is sequentially covered with a waterproof layer and an anti-corrosion coating. The waterproof layer is formed by polymer coating to form a continuous coverage, and the anti-corrosion coating is formed by spraying epoxy resin material. The main housing is integrally sealed and fixed with the detection cavity and the reference cavity.

5. The novel capacitive infrasound sensor according to claim 4, characterized in that, The inner wall of the sensor housing is provided with a metal shielding layer; The metal shielding layer is connected to an external grounding circuit via a grounding lead, and the grounding lead is fixed to the cable sheath grounding wire via a dedicated terminal. The shielding layer encloses the capacitive sensing unit and the chopper demodulation circuit inside to reduce the impact of external electromagnetic interference on the circuit signal.

6. A method for detecting infrasound, characterized in that, The method is implemented based on the novel capacitive infrasound sensor according to any one of claims 1-5, and the method includes: Obtain the structural parameters and operating condition parameters of the pipeline under test, and use the structural parameters and operating condition parameters as reference inputs; The leakage pulsation signal in the pipeline is introduced into the detection chamber of the sensor through the acoustic sampling channel, and a differential pressure is formed with the reference chamber. The differential pressure response is stored in correspondence with the structural parameters and operating parameters. The differential pressure change is converted into an electrical signal by using a capacitive sensing unit located between the detection cavity and the reference cavity, and the electrical signal is compared with the reference input to generate a corrected detection signal; The corrected detection signal is chopping and demodulated within the chopper demodulation circuit to suppress low-frequency noise and DC drift, and outputs an infrasound detection signal sequence associated with the structural parameters and operating parameters. A feature sequence is formed based on the infrasound detection signal sequence and the reference input, and the feature sequence serves as input data for leak determination and location analysis.

7. The method according to claim 6, characterized in that, The method further includes: During sensor operation, an equivalent electrostatic force pulse of preset amplitude is applied to the driving electrode of the capacitance sensing unit through the electrostatic self-calibration unit, causing the capacitance sensing unit to generate a corresponding capacitance change signal. The capacitance change signal is input to the chopper demodulation circuit to generate a calibration sequence; The calibration sequence is used to correct the zero-point offset and sensitivity drift of the capacitive sensing unit when detecting differential pressure signals.

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