Photoacoustic cavity for gas detection

Abstract

This invention relates to the field of photoacoustic cavity technology, specifically a photoacoustic cavity for gas detection. The rectangular cavity structure of this invention is simple, easy to manufacture and install, and provides a regular space for internal components. The gas inlet facilitates the introduction of the gas to be tested, ensuring smooth detection. The filter tube guides light into the cavity, performing preliminary screening and filtering of the light to ensure that the light entering the cavity meets the detection requirements, improving detection accuracy. The detection end effectively captures the pressure wave generated by the photoacoustic effect, providing crucial data for gas detection. Through a specific noise reduction calculation formula, the noise reduction amount can be accurately calculated, thereby precisely measuring and controlling the noise reduction performance of the photoacoustic cavity. This helps optimize the working effect of the photoacoustic cavity in complex environments, reduces external noise interference, and improves detection reliability.

Description

Technical Field

[0001] This invention relates to the field of photoacoustic cavity technology, specifically a photoacoustic cavity for gas detection. Background Technology

[0002] Photoacoustic detection technology, as a novel gas detection technology, boasts advantages such as high sensitivity and high selectivity. The photoacoustic cavity, developed from photoacoustic detection technology, performs exceptionally well in detecting the concentration of various gases.

[0003] Patent CN112986153B discloses a real-time formaldehyde gas concentration detection system and method based on photoacoustic spectroscopy. The system includes: an infrared light source, a chopper, a photoacoustic cell, a filter, an acoustic signal acquisition unit, and an acoustic signal processing unit. The acoustic signal acquisition unit is placed inside the photoacoustic cell, and the acoustic signal acquisition unit and the acoustic signal processing unit are connected. A calcium fluoride lens is provided on the side of the photoacoustic cell facing the infrared light source. The acoustic signal acquisition unit is used to acquire the periodic pressure fluctuation signal generated after the gas absorbs the laser, and convert the pressure fluctuation signal into an electrical signal. The acoustic signal processing unit is used to process the electrical signal, compare the processed electrical signal with a pre-generated formaldehyde gas concentration standard curve, and obtain the formaldehyde gas concentration of the gas to be measured.

[0004] The drawback of the mechanical chopper modulation in the aforementioned prior art is that the rotation of the chopper during operation introduces interference, affecting the measurement. Simultaneously, the photoacoustic cavity in the prior art generates noise during gas concentration detection. Conventional noise reduction methods involve adjusting the structure of the photoacoustic cavity; however, while the adjustment process aims to minimize noise, it is difficult to accurately calculate the noise reduction amount, leading to poor adjustment results. Consequently, the generation of the photoacoustic effect and the detection effect are unsatisfactory, affecting the accuracy and reliability of gas detection. Therefore, a solution is urgently needed. Summary of the Invention

[0005] To avoid and overcome the technical problems existing in the prior art, the present invention provides a photoacoustic cavity for gas detection. The present invention can calculate the noise reduction of the photoacoustic cavity with relatively high accuracy.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A photoacoustic cavity for gas detection includes a cavity body, an inlet for introducing the gas to be tested, a filter tube for guiding light into the cavity, and a detection end for detecting pressure waves generated by the photoacoustic effect; the noise reduction of the photoacoustic cavity is [missing information]. :

[0008] ;

[0009] In the formula, Represents the logarithmic function with base 10; This represents the area ratio between the cross-sectional area of ​​the cavity and the cross-sectional area of ​​the filter tube. Represents the sine function; Indicates wave number; This indicates the length of the photoacoustic cavity.

[0010] As a further aspect of the present invention: the detection end includes a connection channel fixedly installed on the cavity and communicating with the cavity, a microphone is installed in the connection channel, and the other end of the connection channel is connected to a detector for detecting and analyzing the electrical signal converted by the microphone.

[0011] As a further embodiment of the present invention: there are two filter tubes, which are arranged symmetrically on both sides of the cavity with the axis of the connecting channel as the axis of symmetry.

[0012] As a further embodiment of the present invention: a light source is installed at the input end of the filter tube, the light source includes an infrared laser, a laser controller is connected to the output end of the infrared laser, a filter is connected to the output end of the laser controller, and the output end of the filter is connected to the filter tube.

[0013] As a further aspect of the present invention, the axis of the connecting channel coincides with the axis of symmetry along the length of the cavity.

[0014] As a further aspect of the present invention, the length of the connecting channel is 20 centimeters.

[0015] As a further embodiment of the present invention, the cavity is rectangular.

[0016] As a further embodiment of the present invention: an air source is connected to the air intake end.

[0017] As a further aspect of the present invention, a corresponding gas valve is installed between the air inlet and the air source.

[0018] As a further aspect of the present invention, a corresponding flow control device is also installed between the air inlet and the air source.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. The rectangular cavity structure of this invention is simple, easy to manufacture and install, and provides a regular space for internal components. The gas inlet facilitates the introduction of the gas to be tested, ensuring smooth detection. The filter tube guides light into the cavity, performing preliminary screening and filtering of the light to ensure that the light entering the cavity meets the detection requirements, thus improving detection accuracy. The detection end can effectively capture the pressure wave generated by the photoacoustic effect, providing crucial data for gas detection. Through a specific noise reduction calculation formula, the noise reduction amount can be accurately calculated, thereby precisely measuring and controlling the noise reduction performance of the photoacoustic cavity. This helps optimize the working effect of the photoacoustic cavity in complex environments, reduces external noise interference, and improves detection reliability.

[0021] 2. The connection channel in this invention achieves an effective connection between the cavity and the detector, ensuring that the pressure wave can be smoothly transmitted to the microphone. The microphone converts the pressure wave into an electrical signal, facilitating subsequent detection and analysis. The detector processes the electrical signal, enabling precise analysis of information such as the gas composition and concentration. This structural design makes the detection process more coherent and efficient, improving detection sensitivity and accuracy, and allowing for rapid and accurate acquisition of gas detection results.

[0022] 3. The two filter tubes in this invention are symmetrically arranged, which can guide light into the cavity from different angles, increasing the incident range and intensity of the light, allowing the light to fully interact with the gas to be tested, enhancing the photoacoustic effect, and thus improving the sensitivity and accuracy of detection. The symmetrical structure also ensures the balance of the cavity in terms of stress and optical performance, reducing detection errors caused by uneven light distribution, and improving the overall stability and reliability of the photoacoustic cavity.

[0023] 4. Infrared lasers emit light of specific wavelengths, suitable for exciting the photoacoustic effect of gases, thus improving the specificity of detection. The laser controller can precisely adjust the laser's output parameters, such as intensity and frequency, to meet the needs of different gas detections, enhancing the flexibility and adaptability of the detection process. The filter further filters the laser light, removing stray light and other interference signals, ensuring the purity of the light entering the filter tube, improving the accuracy and reliability of the detection, and making the detection results more credible.

[0024] 5. The coincident axis design ensures a smoother propagation path for pressure waves within the cavity and connecting channels, reducing pressure wave reflection and loss, improving the microphone's efficiency in receiving pressure waves, and thus enhancing detection accuracy and sensitivity. Simultaneously, it contributes to the overall structural compactness and stability, facilitating installation and maintenance, and reducing the manufacturing and operating costs of the photoacoustic cavity.

[0025] 6. Determining the length of the connection channel to be 20 cm optimizes the propagation characteristics of the pressure wave. An appropriate length ensures that the pressure wave maintains sufficient intensity and stability during propagation, enabling the microphone to accurately receive the pressure wave signal. This avoids signal attenuation or distortion caused by a channel that is too long or too short, thereby improving detection accuracy and reliability and providing a stable and reliable signal transmission path for gas detection. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the present invention.

[0027] In the diagram: 1. Sealing joint; 2. Connecting channel; 3. Air inlet; 4. Filter tube; 5. Cavity. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] I. Photoacoustic Cavity Structure

[0030] like Figure 1 As shown, this photoacoustic cavity includes a cuboid cavity 5, on which an air inlet 3, a filter tube 4, and a detection end are arranged.

[0031] Inlet 3: Used to introduce the gas to be tested, allowing it to enter the photoacoustic cavity and participate in the photoacoustic effect. Inlet 3 can be equipped with a suitable gas valve and flow control device to precisely control the inflow rate and volume of the gas to be tested.

[0032] Filter tubes 4: Two tubes are arranged symmetrically on both sides of cavity 5 with the axis of connection channel 2 as the axis of symmetry. A light source, including an infrared laser, is installed at the input end of filter tube 4. The output end of the infrared laser is connected to a laser controller, and the output end of the laser controller is connected to a filter. The output end of the filter is connected to filter tube 4. This structural design helps ensure that light enters cavity 5 uniformly, allowing the light to interact fully and uniformly with the gas to be measured within cavity 5. A special optical coating can be applied inside filter tube 4 to reduce light loss during propagation.

[0033] The detection end includes a connecting channel 2 fixedly mounted on and connected to the cavity 5. A microphone is installed inside the connecting channel 2, and the other end of the connecting channel 2 is connected to a detector for detecting and analyzing the electrical signals converted by the microphone. The axis of the connecting channel 2 coincides with the axis of the cavity 5 along its length, and the length of the connecting channel 2 is 20 cm. This design allows the pressure waves generated by the photoacoustic effect to propagate to the microphone more directly and efficiently, reducing losses and interference during pressure wave propagation. The inner wall of the connecting channel 2 can be smoothed to reduce frictional losses during pressure wave propagation.

[0034] II. Noise Reduction Amount of Optical Acoustic Cavity

[0035] The noise reduction of the photoacoustic cavity satisfies formula (1), which involves parameters such as a logarithmic function with base 10, the area ratio between the cross-sectional area of ​​cavity 5 and the cross-sectional area of ​​filter tube 4, and a sine function. These parameters reflect the influence of the structural characteristics of the photoacoustic cavity on the noise reduction effect. A reasonable structural design can effectively reduce background noise.

[0036] (1);

[0037] In the formula, Represents the logarithmic function with base 10; This represents the area ratio between the cross-sectional area of ​​the cavity and the cross-sectional area of ​​the filter tube. Represents the sine function; Indicates wave number; This indicates the length of the photoacoustic cavity.

[0038] Area ratio in this implementation The value is 49. The value is 1.5 π The corresponding maximum noise reduction is 11.22dB.

[0039] III. Photoacoustic Cavity Usage Process

[0040] 1. Preparation

[0041] Equipment Inspection and Debugging: Check the installation of each component of the photoacoustic cavity, ensuring that the air inlet 3, filter tube 4, and connecting channel 2 are tightly connected without any looseness or leakage. Check that the sealing joint 1 is installed correctly and ensure the sealing of the upper surface of the connecting channel 2.

[0042] Inspect the infrared laser to ensure it can output continuous laser light normally. Check the laser controller's parameter settings, such as temperature control range and current adjustment accuracy, to ensure stable operation. Inspect the filter to ensure it can effectively filter out unwanted wavelength components.

[0043] Check the microphone's performance to ensure it can sensitively detect pressure fluctuations and accurately convert them into electrical signals. Adjust the detector and amplifier, setting appropriate amplification and detection range to ensure accurate processing and analysis of the electrical signals.

[0044] 2. Gas preparation

[0045] Prepare the gas to be tested according to the testing requirements. Ensure that the purity and stability of the gas meet the testing requirements. For some special gases, pretreatment may be necessary, such as removing impurities and adjusting humidity.

[0046] Connect the gas delivery pipeline and connect inlet 3 to the gas source. During the connection process, pay attention to the sealing of the pipeline to avoid gas leakage.

[0047] 3. Light source modulation

[0048] Using an infrared laser as the working light source, wavelength modulation is employed to transform the continuous laser beam with constant output power into a time-varying beam. The specific operation is as follows:

[0049] 1) Set laser controller parameters

[0050] Turn on the laser controller and set appropriate temperature and current based on the characteristics of the infrared laser and the detection requirements. The temperature setting must consider the laser's operational stability and the wavelength stability of the output laser light; it is generally precisely adjusted through the temperature control module inside the laser controller. The current setting directly affects the laser's output power and needs to be optimized and adjusted based on experiments or practical experience to ensure a stable DC light intensity output from the laser.

[0051] 2) Superimposed modulation signal

[0052] Turn on the signal generator and set it to output a sine wave signal. The frequency and amplitude of the sine wave need to be selected based on the characteristics of the photoacoustic cavity and the absorption characteristics of the target gas. Generally, the frequency selection should take into account the resonant frequency of the photoacoustic effect to improve the intensity of the photoacoustic signal.

[0053] The sine wave output from the signal generator is input to the external input terminal of the laser controller. Inside the laser controller, the DC light intensity signal and the sine wave signal are superimposed to generate a light intensity whose wavelength varies sinusoidally. This modulation method allows the window of the photoacoustic cavity to have almost the same light absorption coefficient within the wavelength modulation range, and the window material absorbs heat almost inconsistently, effectively reducing background noise.

[0054] 4. Photoacoustic effect

[0055] 1) Gas introduction

[0056] Open the gas valve at inlet 3 and adjust the inflow rate and velocity of the gas to be tested using the flow control device. Generally, the flow rate should be set to ensure that the gas to be tested can fully fill the photoacoustic cavity, while avoiding excessively high flow rates that could lead to uneven gas distribution within the cavity. During the gas introduction process, the pressure changes within the photoacoustic cavity can be observed to ensure that the pressure remains stable within a suitable range.

[0057] 2) Light irradiation and photoacoustic effect excitation

[0058] The modulated light passes through filter tube 4 and illuminates the photoacoustic cavity. Since the two filter tubes 4 are symmetrically arranged on both sides of the cavity 5, the light can enter the cavity 5 uniformly and make full contact with the gas to be tested within the cavity 5. The gas molecules inside the cavity absorb the light energy and convert it into heat energy through intermolecular collisions, causing a local increase in gas temperature. Because the light intensity of the light source varies sinusoidally, the gas temperature also changes periodically, resulting in periodic pressure changes, i.e., the photoacoustic effect.

[0059] 5. Signal Detection and Processing

[0060] 1) Pressure wave detection

[0061] The pressure fluctuations generated by the photoacoustic effect propagate through the gas to connecting channel 2. Since the axis of connecting channel 2 coincides with the axis of length 5 and is 20 cm long, the pressure waves can propagate more directly and efficiently to the microphone within connecting channel 2. Upon detecting the pressure fluctuations, the microphone converts them into electrical signals.

[0062] 2) Signal transmission and amplification

[0063] The electrical signal is transmitted to the amplifier via a vacuum adapter and a seven-star adapter. The vacuum adapter ensures a sealed signal transmission, reducing external interference. The seven-star adapter accurately transmits the signal to the amplifier's input. The amplifier amplifies the electrical signal, increasing its strength for subsequent detection and analysis.

[0064] 3) Signal analysis and gas information determination

[0065] The amplified electrical signal is transmitted to the detector. The detector uses advanced signal processing algorithms to analyze the electrical signal. Because different gases have different light absorption characteristics, the resulting pressure change signals are also different. By analyzing the signal's frequency, amplitude, phase, and other characteristic parameters, information such as the type and concentration of gas inside the photoacoustic cavity can be accurately determined.

[0066] 6. Follow-up work

[0067] 1) Data recording and storage

[0068] Detailed information such as the type and concentration of the detected gases should be recorded, including the detection time, environmental conditions, and results. The data can be saved to a computer or other storage device for subsequent analysis and comparison.

[0069] 2) Equipment cleaning and maintenance

[0070] After the test is completed, close the gas valve to stop the gas introduction. Clean the photoacoustic cavity to remove any residual gas and impurities. Cleaning can be done using methods such as gas purging or vacuum suction.

[0071] Inspect and maintain key components such as light sources, microphones, and detectors, including cleaning optical elements and checking circuit connections. Regularly calibrate and maintain the equipment to ensure stable and reliable performance.

[0072] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A photoacoustic cavity for gas detection, characterized in that, The cavity includes a chamber (5), on which are arranged an air inlet (3) for introducing the gas to be tested, a filter tube (4) for guiding light into the cavity (5), and a detection end for detecting the pressure wave generated by the photoacoustic effect; and the noise reduction of the photoacoustic cavity is ; ； In the formula, It is a logarithmic function with base 10; This represents the ratio of the cross-sectional area of ​​the cavity (5) to the cross-sectional area of ​​the filter tube (4); Represents the sine function; Indicates wave number; The length of the photoacoustic cavity is indicated; the detection end includes a connecting channel (2) fixedly installed on the cavity (5) and connected to the cavity (5), a microphone is installed in the connecting channel (2), and the other end of the connecting channel (2) is connected to a detector for detecting and analyzing the electrical signal converted by the microphone; there are two filter tubes (4), which are arranged symmetrically on both sides of the cavity (5) with the axis of the connecting channel (2) as the axis of symmetry; a light source is installed at the input end of the filter tube (4), and the axis of the connecting channel (2) coincides with the axis of the length of the cavity (5).

2. The photoacoustic cavity for gas detection according to claim 1, characterized in that, The light source includes an infrared laser. The output end of the infrared laser is connected to a laser controller. The output end of the laser controller is connected to a filter. The output end of the filter is connected to the filter tube (4).

3. The photoacoustic cavity for gas detection according to claim 2, characterized in that, The length of the connecting channel (2) is 20 centimeters.

4. The photoacoustic cavity for gas detection according to claim 3, characterized in that, The cavity (5) is rectangular.

5. A photoacoustic cavity for gas detection according to claim 4, characterized in that, The air inlet (3) is connected to an air source.

6. A photoacoustic cavity for gas detection according to claim 5, characterized in that, The air inlet (3) and the air source are equipped with corresponding gas valves and flow control devices.

7. A photoacoustic cavity for gas detection according to claim 6, characterized in that, A microphone is installed in the connecting channel (2).

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