A hemispherical photoacoustic cell and a gas detection method

Abstract

This invention relates to the field of optical spectroscopy, specifically providing a hemispherical photoacoustic cell and a gas detection method. The hemispherical photoacoustic cell includes a cell body, a base, and a lamp plate. The cell body is provided with a resonant cavity, a resonant chamber, and an air vent. The resonant cavity is a hemispherical groove, and the resonant chamber has a through-hole structure. The resonant chamber is connected to the resonant chamber through a connecting hole. The resonant cavity and the resonant chamber have the same resonant frequency. The air vent penetrates the cell body and is connected to the resonant chamber. The base is fixedly connected to the cell body and is located at the opening of the resonant chamber to block it. The lamp plate is fixedly connected to the base and is located at the opening of the cell body. The lamp plate is provided with a light-emitting component to generate light with a preset wavelength, frequency, and intensity. A microphone is used to pick up the photoacoustic signal within the resonant chamber. This invention can effectively reduce the cost of photoacoustic gas measurement.

Description

Technical Field

[0001] This invention relates to the field of optical spectroscopy, and more particularly to a hemispherical photoacoustic cell and a gas detection method. Background Technology

[0002] Photoacoustic absorption spectroscopy is recognized internationally as one of the most promising laser spectroscopy technologies. This spectroscopy technology utilizes the absorption of incident light energy by the pollutant to be measured, which is heated and causes the surrounding air to expand thermally, thereby generating thermal waves. The periodic thermal waves, i.e. sound wave signals, are detected by a microphone. The concentration of pollutants can be deduced by analyzing the sound signals. It has the advantages of simple structure, low cost, and good stability.

[0003] Currently, the most widely used photoacoustic resonators are cylindrical structures. The most commonly used resonance mode in cylindrical acoustic resonators is the first-order longitudinal resonance effect. Cylindrical acoustic resonators require high-quality light source spots, typically using lasers. The use of lasers increases the application cost of photoacoustic spectroscopy. Furthermore, the incident method of the light source in a cylindrical acoustic resonator limits the simultaneous detection of multiple gases. Therefore, this invention discloses a hemispherical photoacoustic cell and a gas detection method. Summary of the Invention

[0004] The purpose of this invention is to provide a hemispherical photoacoustic cell and a gas detection method to solve the problem of high cost in current photoacoustic technology for measuring the gas to be measured.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A hemispherical photoacoustic cell, the photoacoustic cell comprising:

[0007] The pool body is provided with a resonant cavity, a resonant cavity, and an air hole. The resonant cavity is a hemispherical groove and a through-hole structure. The resonant cavity is connected to the resonant cavity through a connecting hole. The resonant cavity and the resonant cavity have the same resonant frequency. The air hole penetrates the pool body and is connected to the resonant cavity.

[0008] A base, which is fixedly connected to the pool body, is located at the opening of the resonant cavity to block the resonant cavity;

[0009] A light panel is fixedly connected to the base and located at the opening of the pool. The light panel is equipped with a light-emitting component to generate light with a preset wavelength, frequency, and intensity.

[0010] A microphone is used to pick up photoacoustic signals within the resonant cavity.

[0011] Furthermore, buffer cavities are provided at both ends of the resonant cavity. The length of the buffer cavity is half the length of the resonant cavity, and the radius of the buffer cavity is more than three times the radius of the resonant cavity.

[0012] Furthermore, the resonant cavity is located on the side of the pool body opposite to the opening of the resonant cavity, and the axis of the resonant cavity is parallel to the plane where the opening of the resonant cavity is located.

[0013] Furthermore, multiple resonant cavities are provided, and the multiple resonant cavities are arranged intersectingly. The included angle between adjacent resonant cavities is the same, and the microphone is located at the intersection of multiple resonant cavities.

[0014] Furthermore, the vent passes through the resonant cavity, thus forming two air channels.

[0015] Furthermore, the photoacoustic cell also includes:

[0016] A sealing gasket is used to seal the pool body and the base.

[0017] Furthermore, multiple light-emitting components are provided, and the multiple light-emitting components are distributed around the axis of the resonant cavity in the circumferential direction.

[0018] This invention also discloses a gas detection method based on the aforementioned hemispherical photoacoustic cell, the method comprising the following steps:

[0019] The gas to be tested is introduced into the resonant cavity. After the gas to be tested fills the resonant cavity and the resonant cavity, the two ends of the resonant cavity are sealed. The microphone is connected to the signal processing device.

[0020] The light-emitting component is modulated by an electrical signal, so that the light-emitting component generates pulsed light with a preset light intensity and frequency, and the modulation frequency of the light generated by the light-emitting component is located near the resonant frequency of the resonant cavity;

[0021] The signal processing device is activated to demodulate the photoacoustic signal collected by the microphone, thereby realizing the detection lamp board for the gas to be tested.

[0022] Preferably, when performing single gas measurements, a lamp board with a single type of light-emitting component is used.

[0023] Preferably, when performing multi-gas measurements, a lamp board with various types of light-emitting components is used.

[0024] In summary, the present invention has the following advantages compared with the prior art:

[0025] The hemispherical photoacoustic cell disclosed in this invention reduces the requirements for the quality of the light spot of the light source, so that the light-emitting component can generate the photoacoustic effect using an LED light source, thereby eliminating the need for a laser and effectively reducing the cost of photoacoustic technology for gas measurement. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the hemispherical photoacoustic cell disclosed in Embodiment 1 of the present invention.

[0027] Figure 2 This is a front view of the hemispherical photoacoustic cell disclosed in Embodiment 1 of the present invention.

[0028] Figure 3 for Figure 2 Sectional view of AA.

[0029] Figure 4 for Figure 2 A cross-sectional view of BB.

[0030] Figure 5 This is a schematic diagram showing the connection between the base and the lamp plate in the hemispherical photoacoustic cell disclosed in Embodiment 1 of the present invention.

[0031] Figure 6 This is the frequency response curve of the hemispherical photoacoustic cell at the top position as disclosed in Embodiment 1 of the present invention.

[0032] Figure 7 This is a schematic diagram illustrating the working principle of the resonant cavity and resonant chamber in the hemispherical photoacoustic cell disclosed in Embodiment 1 of the present invention.

[0033] Figure label:

[0034] 10. Pool body; 11. Resonant cavity; 12. Resonant cavity; 13. Buffer cavity; 14. Connecting hole; 15. Air vent; 16. Sound pickup hole; 20. Base; 21. Mounting hole; 22. Mounting groove; 30. Lamp board; 31. Light-emitting component; 40. Microphone; 50. Air vent interface; 60. Sealing gasket. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Example

[0036] like Figures 1 to 3As shown, a hemispherical photoacoustic cell is provided according to an embodiment of the present invention. The hemispherical photoacoustic cell includes a cell body 10, a base 20, and a lamp plate 30. The cell body 10 is provided with a resonant cavity 11, a resonant cavity 12, and an air hole 15. The resonant cavity 11 is a hemispherical groove, and the resonant cavity 12 is a through-hole structure with its axis parallel to the surface where the groove of the resonant cavity 11 is located. The resonant cavity 12 is connected to the resonant cavity 11 through a connecting hole 14. The resonant cavities 11 and 12 have the same resonant frequency. The air hole 15 penetrates the cell body 10 and... The pool body 10 is connected to the resonant cavity 11 and is also provided with a pickup hole 16 that is connected to the resonant cavity 12. A microphone 40 is fixedly connected in the pickup hole 16 to pick up the photoacoustic signal in the resonant cavity 12. The base 20 is fixedly connected to the pool body 10 and is located at the opening of the resonant cavity 11 to block the resonant cavity 11. The lamp board 30 is fixedly connected to the base 20 and is located at the opening of the pool body 10. The lamp board 30 is provided with a light-emitting component 31 to generate light with a preset wavelength, frequency and intensity.

[0037] In this embodiment, as Figure 3 As shown, during gas measurement, the gas to be measured is introduced into the resonant cavity 11 through the gas port 15. After the gas to be measured fills the resonant cavity 12 and the resonant cavity 11, both ends of the resonant cavity 12 are blocked. The microphone 40 is installed in the pickup port 16 and connected to a signal processing device, such as a lock-in amplifier, data acquisition card, or industrial control computer. The lamp board 30 is connected to a control device, which controls the lamp board 30 to emit light. The light interacts with the gas to be measured in the resonant cavity 11 to produce a photoacoustic effect. Cavity 12 resonates with the resonant cavity 11 and amplifies the photoacoustic signal. Microphone 40 collects the photoacoustic signal in the resonant cavity 12 and sends it to the signal processing device. The signal processing device processes the photoacoustic signal to complete the photoacoustic measurement of the gas to be measured. The light-emitting component 31 is located at the bottom of the resonant cavity 11. The resonant cavity 11 is hemispherical. This structure reduces the requirements for the quality of the light spot of the light source, thereby reducing the requirements for the light source. The light-emitting component 31 can generate the photoacoustic effect using an LED light source, thereby eliminating the need for a laser.

[0038] The hemispherical photoacoustic cell disclosed in this invention, by setting a hemispherical resonant cavity 11 and a resonant cavity 12 connected to the resonant cavity 11, uses a light-emitting component 31 to generate light of a specific wavelength when measuring gas. Due to the arrangement of the light-emitting component 31 and the shape of the resonant cavity 11, the hemispherical photoacoustic cell disclosed in this invention reduces the requirements for the quality of the light spot of the light source, so that the light-emitting component 31 can generate the photoacoustic effect using an LED light source, thereby eliminating the need for a laser and effectively reducing the cost of photoacoustic technology for gas measurement.

[0039] Specifically, in this embodiment, such as Figures 1 to 3 As shown, the pool body 10 is a square block structure, the resonant cavity 11 is a hemispherical groove opened on one side of the pool body 10, the resonant cavity 12 and the air hole 15 are both through holes opened on the pool body 10, the air hole 15 passes through the resonant cavity 11, so that the air hole 15 forms two air channels, one air channel is used for air intake and the other air channel is used for air exhaust.

[0040] In a preferred embodiment of this invention, buffer cavities 13 are provided at both ends of the resonant cavity 12. The length of the buffer cavity 13 is half the length of the resonant cavity 12, and the radius of the buffer cavity 13 is more than three times the radius of the resonant cavity 12. When measuring the gas to be measured, the buffer cavity 13 is blocked by a plug structure (such as a calcium fluoride window). In this embodiment, the length of the resonant cavity 12 is 22 mm, and the inner diameter of the resonant cavity 12 is 2 mm. Therefore, the length of the buffer cavity 13 located at one end of the resonant cavity 12 is 11 mm, and the radius of the buffer cavity 13 is 6.5 mm.

[0041] As a preferred embodiment of this example, Figure 3 and Figure 4 As shown, the resonant cavity 12 is located on the side of the pool body 10 facing away from the opening of the resonant cavity 11, that is, the resonant cavity 12 is located at the top of the resonant cavity 11, as shown. Figure 7 As shown, the photoacoustic signal in the resonant cavity 11 is reflected and superimposed inside, and the sound pressure amplitude at its top is the strongest. The resonant cavity 12 is located at the top of the resonant cavity 11. The connecting hole 14 connects to the top region of the resonant cavity 11. The strongest sound pressure amplitude in the resonant cavity 11 is transmitted to the resonant cavity 12 through the connecting hole 14 and amplified twice in the resonant cavity 12, which can form a clearer photoacoustic signal.

[0042] Preferred, such as Figure 4As shown, multiple resonant cavities 12 are provided. In this embodiment, two resonant cavities 12 are provided. The multiple resonant cavities 12 are arranged intersectingly, and the axis of the resonant cavity 12 is parallel to the plane where the opening of the resonant cavity 11 is located. The included angle between adjacent resonant cavities 12 is the same. In this embodiment, the two resonant cavities 12 are arranged perpendicularly. Multiple connecting holes 14 are provided. In this embodiment, each resonant cavity 12 is provided with 5 connecting holes 14.

[0043] According to acoustic theory, the resonant modes of a spherical photoacoustic cell can be divided into radial, θ-angular, and φ-angular modes. The amplitude of the sound signal generated within the resonant cavity 11 needs to reach its maximum at the top of the hemispherical shape. Figure 6 The frequency response curve of the resonant cavity 11 shown at the top shows that the resonant cavity 11 has a high resonant frequency near 7200Hz (taking the diameter of the resonant cavity 11 in this example as 30mm for the lamp board). Therefore, the resonant cavity 12 also needs to form a sound resonance effect near 7200Hz.

[0044] The resonant cavity 12 adopts a first-order longitudinal vibration mode, and its resonant frequency is... Calculated using formula (1):

[0045] ;Formula (1)

[0046] In the formula, L is the length of the resonant cavity 12, which is a correction coefficient, ΔL=16R / 3π, R is the radius of the resonant cavity 12; c is the speed of sound in air at one standard atmosphere and 15℃, which is approximately 340m / s.

[0047] like Figure 7 As shown, the photoacoustic signal at the top of the resonant cavity 11 reaches its maximum value at a modulation frequency of about 7200Hz. When the sound frequency is 7200Hz, the sound pressure mode of the resonant cavity 12 is a resonance mode with antinodes in the middle and nodes at both ends. The strongest sound pressure amplitudes of the resonant cavity 11 and the resonant cavity 12 overlap, forming a secondary amplification of the sound signal.

[0048] In this embodiment, the pickup hole 16 is connected to the intersection of the plurality of resonant cavities 12.

[0049] In this embodiment, the pool body 10 and the base 20 are fixed together by bolts 70, such as... Figure 5 As shown, the base 20 is a square block, and a square mounting groove 22 is provided on the base 20. The end of the pool body 10 is embedded in the mounting groove 22. The bolt 70 passes through the base 20 and is fastened to the end of the pool body 10 by a threaded connection.

[0050] Preferably, a sealing gasket 60 is also provided between the pool body 10 and the base 20 to seal the pool body 10 and the base 20, thereby preventing air leakage from the gap between the pool body 10 and the base 20.

[0051] In this embodiment, the base 20 is also provided with a mounting hole 21, which is a countersunk hole. The lamp board 30 is sealed to the mounting hole 21. For example, the lamp board 30 is fixed to the mounting hole 21 by hot melt adhesive or screws. A sealing gasket or sealing ring is provided between the lamp board 30 and the mounting hole 21 to seal the connection between the lamp board 30 and the mounting hole 21. The mounting hole 21 is circular, the lamp board 30 is a circular circuit board, and the light-emitting component 31 is an LED lamp bead.

[0052] In a preferred embodiment of this invention, multiple light-emitting components 31 are provided, and the multiple light-emitting components 31 are distributed around the axis of the resonant cavity 11 in the circumferential direction. In this embodiment, four light-emitting components 31 are provided.

[0053] Preferably, the multiple light-emitting components 31 can be LEDs of the same model or different models. That is, the parameters of the multiple light-emitting components 31 can be the same or different, for the purpose of measuring single gas and multiple gases. When the four light-emitting components 31 are of the same model, the hemispherical photoacoustic cell is used to detect a single gas, and the light power of the four light-emitting components 31 is modulated at the same frequency, which further enhances the measurement sensitivity of a single gas. When the four light-emitting components 31 are of different models, each light-emitting component 31 is used to measure a gas. At this time, the light power of the light-emitting components 31 is modulated at different frequencies, but each modulation frequency is within the resonant frequency bandwidth of the hemispherical photoacoustic cell, thus realizing the purpose of the hemispherical photoacoustic cell for the detection of multiple gases.

[0054] As a preferred embodiment of this example, Figure 1 and Figure 3 As shown, the opening of the air hole 15 is also provided with an air hole interface 50 by means of thread or adhesive, which is used to connect the air source and the air valve. Example

[0055] As another embodiment of the present invention, this embodiment also discloses a gas detection method, which is implemented based on the hemispherical photoacoustic cell described in Embodiment 1. The detection method includes the following steps:

[0056] Step S1: The gas to be tested is introduced into the resonant cavity 11. After the gas to be tested fills the resonant cavity 11 and the resonant cavity 12, the microphone 40 is connected to the signal processing device.

[0057] Step S2: Modulate the light-emitting component 31 with an electrical signal so that the light-emitting component 31 generates pulsed light with a preset light intensity and frequency, and the modulation frequency of the light generated by the light-emitting component 31 is located near the resonant frequency of the resonant cavity 11.

[0058] Step S3: Start the signal processing device to demodulate the photoacoustic signal collected by the microphone 40 to realize the detection of the gas to be tested.

[0059] Specifically, in this embodiment, the light-emitting component 31 generates light of a preset frequency and intensity under the control of the controller's electrical signal. The controller controls the light-emitting component 31 to generate light of a preset intensity by controlling the voltage signal and controls the light-emitting component 31 to generate pulsed light of a preset frequency by controlling the current signal. The wavelength of the light generated by the light-emitting component 31 is determined by its own parameters. The signal processing device includes a lock-in amplifier, a data acquisition card, and an industrial control computer. The light energy of the light generated by the light-emitting component 31 is absorbed by the gas and converted into a sound signal. The sound signal is detected by the microphone 40. The signal processing device is used to process the photoacoustic signal collected by the microphone 40 and to measure the gas to be measured based on the data processing device in the prior art.

[0060] It should be noted that when performing multi-gas measurements, a lamp board 30 with multiple types of light-emitting components 31 is used, while when performing single-gas measurements, a lamp board 30 with a single type of light-emitting component 31 is used.

[0061] It should be noted that the resonant cavity 12 can be sealed before or after the gas to be tested is filled. Even if the resonant cavity 12 contains air, the air in the resonant cavity 12 will not affect the measurement of the gas to be tested because the light generated by the light-emitting component 31 is difficult to enter the resonant cavity 12.

[0062] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular forms “a,” “the,” and “the” used in this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0063] It should be understood that although the terms first, second, third, etc., may be used in this invention to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, first information may also be referred to as second information without departing from the scope of this invention, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to a determination."

[0064] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A hemispherical photoacoustic cell, characterized in that, The photoacoustic cell includes: The pool body is provided with a resonant cavity, a resonant chamber, and an air hole. The resonant cavity is a hemispherical groove and has a through-hole structure. The resonant chamber is connected to the resonant chamber through a connecting hole. The resonant cavity and the resonant chamber have the same resonant frequency. The air hole penetrates the pool body and is connected to the resonant chamber. The resonant chamber is located on the side of the pool body away from the opening of the resonant chamber, and the axis of the resonant chamber is parallel to the plane where the opening of the resonant chamber is located. A base, which is fixedly connected to the pool body, is located at the opening of the resonant cavity to block the resonant cavity; A light panel is fixedly connected to the base and located at the opening of the pool. The light panel is provided with light-emitting components to generate light with a preset wavelength, frequency, and intensity. Multiple light-emitting components are provided and distributed around the axis of the resonant cavity in the circumferential direction. A microphone is used to pick up photoacoustic signals within the resonant cavity.

2. The hemispherical photoacoustic cell according to claim 1, characterized in that, The resonant cavity is further provided with buffer cavities at both ends. The length of the buffer cavity is half the length of the resonant cavity, and the radius of the buffer cavity is more than three times the radius of the resonant cavity.

3. The hemispherical photoacoustic cell according to claim 1, characterized in that, The resonant cavity is provided in multiple ways, and the multiple resonant cavities are arranged at intersections. The included angle between adjacent resonant cavities is the same, and the microphone is located at the intersection of multiple resonant cavities.

4. The hemispherical photoacoustic cell according to claim 3, characterized in that, The vent passes through the resonant cavity, thus forming two air channels.

5. The hemispherical photoacoustic cell according to any one of claims 1-4, characterized in that, The photoacoustic cell also includes: A sealing gasket is used to seal the pool body and the base.

6. A gas detection method, characterized in that, Based on the hemispherical photoacoustic cell described in any one of claims 1-5, the method includes the following steps: The gas to be tested is introduced into the resonant cavity. After the gas to be tested fills the resonant cavity and the resonant chamber, the microphone is connected to the signal processing device. The light-emitting component is modulated by an electrical signal, so that the light-emitting component generates pulsed light with a preset light intensity and frequency, and the modulation frequency of the light generated by the light-emitting component is located near the resonant frequency of the resonant cavity; The signal processing device is activated to demodulate the photoacoustic signal collected by the microphone, thereby realizing the detection lamp board for the gas to be tested.

7. The gas detection method according to claim 6, characterized in that, When performing single gas measurements, a lamp board with a single type of light-emitting component is used.

8. The gas detection method according to claim 6, characterized in that, When performing multi-gas measurements, a lamp board with various types of light-emitting components is used.

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