Hemispherical photoacoustic cell and gas detection method

Abstract

The invention relates to the technical field of optical spectrums, and particularly provides a hemispherical photoacoustic cell and a gas detection method.The hemispherical photoacoustic cell comprises a cell body, a base and a lamp panel, the cell body is provided with a resonant cavity, a resonant cavity and gas holes, the resonant cavity is a hemispherical groove body, the resonant cavity is of a through hole structure, and the gas holes are communicated with the resonant cavity. The resonant cavity is communicated with the resonant cavity through a communicating hole, the resonant frequency of the resonant cavity is the same as that of the resonant cavity, and the air hole penetrates through the pool body and is communicated with the resonant cavity; the base is fixedly connected with the tank body, and the base is located at the opening part of the resonant cavity to block the resonant cavity; the lamp panel is fixedly connected to the base, the lamp panel is located at the opening of the pool body, and a light-emitting assembly is arranged on the lamp panel to generate light with preset wavelength, frequency and light intensity; the microphone is used for picking up a photoacoustic signal in the resonant cavity; according to the invention, the cost of gas measurement by the photoacoustic technology can be effectively reduced.

Description

Technical Field

[0001] The invention relates to the technical field of optical spectroscopy, and in particular to a hemispherical photoacoustic cell and a gas detection method. Background Art

[0002] Photoacoustic absorption spectroscopy is internationally recognized as one of the most promising laser spectroscopy technologies. This spectroscopy technology uses the fact that the pollutant to be tested absorbs the incident light energy and becomes heated, causing thermal expansion of the surrounding air, thereby generating thermal waves. The periodic thermal waves, i.e., sound wave signals, are detected by a microphone. The concentration of the pollutant is inverted by analyzing the sound signal. It has the advantages of simple structure, low cost, and good stability.

[0003] The photoacoustic resonance cavity widely used at present is a cylindrical structure. The resonance mode widely used in the cylindrical acoustic resonance cavity is the first-order longitudinal resonance effect. The cylindrical acoustic resonance cavity has high requirements on the quality of the light source spot. Its light source generally adopts a laser. The use of laser increases the application cost of the photoacoustic spectroscopy technology. At the same time, the incident mode of the light source of the cylindrical acoustic resonance cavity also limits the photoacoustic spectroscopy technology to realize the simultaneous detection of multiple gases. Therefore, the present invention discloses a hemispherical photoacoustic cell and a gas detection method. Summary of the invention

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

[0005] To achieve the above object, the present invention provides the following technical solutions: A hemispherical photoacoustic cell, comprising: A pool body, wherein a resonant cavity, a resonant cavity and an air hole are arranged on the pool body, wherein the resonant cavity is a hemispherical groove body, wherein the resonant cavity is a through-hole structure, wherein the resonant cavity is connected with the resonant cavity through a connecting hole, wherein the resonant cavity and the resonant cavity have the same resonant frequency, and wherein the air hole penetrates the pool body and is connected with the resonant cavity; A base, the base is fixedly connected to the cell body, and the base is located at the mouth of the resonant cavity to block the resonant cavity; A light board, the light board is fixedly connected to the base, the light board is located at the mouth of the pool body, and a light-emitting component is arranged on the light board to generate light of preset wavelength, frequency and light intensity; A microphone is used to pick up the photoacoustic signal in the resonance cavity.

[0006] Furthermore, buffer cavities are provided at both ends of the resonance cavity, the length of the buffer cavity is half of the length of the resonance cavity, and the radius of the buffer cavity is more than three times the radius of the resonance cavity.

[0007] Furthermore, the resonance cavity is located on a side of the pool body away from the opening of the resonance cavity, and the axis of the resonance cavity is parallel to the surface where the opening of the resonance cavity is located.

[0008] Furthermore, there are multiple resonance cavities, which are cross-arranged, and the angles between adjacent resonance cavities are the same, and the microphone is located at the intersection of the multiple resonance cavities.

[0009] Furthermore, the air hole passes through the resonant cavity, so that the air hole forms two air channels.

[0010] Furthermore, the photoacoustic cell further comprises: A sealing gasket is used to seal the pool body and the base.

[0011] Furthermore, the light-emitting components are provided in plurality, and the plurality of light-emitting components are distributed circumferentially around the axis of the resonant cavity.

[0012] The present invention also discloses a gas detection method, which is implemented based on the above-mentioned hemispherical photoacoustic cell, and the method comprises the following steps: The gas to be measured is introduced into the resonant cavity, and after the gas to be measured fills the resonant cavity and the resonant cavity, both ends of the resonant cavity are sealed, and the microphone is connected to a signal processing device; Using an electrical signal to modulate the light-emitting component, 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 near the resonance frequency of the resonant cavity; The signal processing device is started to demodulate the photoacoustic signal collected by the microphone to realize the detection light board of the gas to be detected.

[0013] Preferably, when performing single gas measurement, a light board having a single model of light emitting component is used.

[0014] Preferably, when performing multi-gas measurements, a light panel having light emitting components of various models is used.

[0015] In summary, the present invention has the following beneficial effects compared with the prior art: The hemispherical photoacoustic cell disclosed in the present invention reduces the requirements on the quality of the light source spot, so that the light emitting component can produce the photoacoustic effect by using an LED light source, thereby eliminating the use of a laser and effectively reducing the cost of measuring gas using the photoacoustic technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the structure of the hemispherical photoacoustic cell disclosed in Example 1 of the present invention.

[0017] Figure 2 This is a front view of the hemispherical photoacoustic cell disclosed in Example 1 of the present invention.

[0018] Figure 3 for Figure 2 Sectional view of AA.

[0019] Figure 4 for Figure 2 Cross-sectional view of BB.

[0020] Figure 5 This is a schematic diagram of the connection between the base and the lamp board in the hemispherical photoacoustic cell disclosed in Example 1 of the present invention.

[0021] Figure 6 This is the frequency response curve of the hemispherical photoacoustic cell at the top position disclosed in Example 1 of the present invention.

[0022] Figure 7 This is a diagram showing the working principle of the resonant cavity and the resonance cavity in the hemispherical photoacoustic cell disclosed in Example 1 of the present invention.

[0023] Reference numerals: 10. Pool body; 11. Resonant cavity; 12. Resonant cavity; 13. Buffer cavity; 14. Connecting hole; 15. Air hole; 16. Pickup hole; 20. Base; 21. Mounting hole; 22. Mounting slot; 30. Light board; 31. Light-emitting component; 40. Microphone; 50. Air hole interface; 60. Sealing gasket. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Example

[0025] like Figures 1 to 3As shown, a hemispherical photoacoustic cell is provided in accordance with an embodiment of the present invention. The hemispherical photoacoustic cell comprises a cell body 10, a base 20 and a lamp board 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 slot body. The resonant cavity 12 is a through hole structure whose axis is parallel to the surface where the notch 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 frequencies of the resonant cavity 11 and the resonant cavity 12 are the same. The air hole 15 runs through the cell body 10 and The pool body 10 is connected to the resonant cavity 11, and a sound pickup hole 16 connected to the resonant cavity 12 is further provided on the pool body 10. A microphone 40 is fixedly connected in the sound 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 the base 20 is located at the mouth of the resonant cavity 11 to block the resonant cavity 11. The lamp board 30 is fixedly connected to the base 20, and the lamp board 30 is located at the mouth of the pool body 10. A light-emitting component 31 is provided on the lamp board 30 to generate light of preset wavelength, frequency and light intensity.

[0026] In this embodiment, if Figure 3 As shown, when measuring gas, the gas to be measured is introduced into the resonant cavity 11 through the air hole 15. After the gas to be measured fills the resonant cavity 12 and the resonant cavity 11, the two ends of the resonant cavity 12 are blocked, and the microphone 40 is installed in the pickup hole 16. The microphone 40 is connected to a signal processing device, such as a phase-locked amplifier, a data acquisition card, an industrial computer, etc. The light board 30 is connected to a control device, and the control device controls the light board 30 to emit light, and the light generates a photoacoustic effect with the gas to be measured in the resonant cavity 11. The resonant The cavity 12 resonates with the resonant cavity 11 and amplifies the photoacoustic signal. The 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 on the quality of the light source spot, thereby reducing the requirements on the light source, so that the light-emitting component 31 can use an LED light source to produce a photoacoustic effect, thereby eliminating the use of a laser.

[0027] The hemispherical photoacoustic cell disclosed in the embodiment of the present invention is provided with a hemispherical resonant cavity 11 and a resonant cavity 12 connected to the resonant cavity 11. When measuring gas, a light-emitting component 31 is used to generate light of a specific wavelength. Due to the arrangement of the light-emitting component 31 and the shape of the resonant cavity 11, the hemispherical photoacoustic cell disclosed in the present invention reduces the requirements on the quality of the light source spot, so that the light-emitting component 31 can produce a photoacoustic effect by using an LED light source, thereby eliminating the use of a laser, and effectively reducing the cost of measuring gas by photoacoustic technology.

[0028] Specifically, in this embodiment, Figures 1 to 3 As shown, the pool body 10 is a square block structure, the resonance cavity 11 is a hemispherical groove opened on one of the surfaces of the pool body 10, the resonance cavity 12 and the air hole 15 are both through-hole structures opened on the pool body 10, and the air hole 15 passes through the resonance cavity 11, so that the air hole 15 forms two airways, one of which is used for air intake and the other is used for exhaust.

[0029] As a preferred implementation in this embodiment, buffer cavities 13 are further provided at both ends of the resonance cavity 12, the length of the buffer cavity 13 is half the length of the resonance cavity 12, and the radius of the buffer cavity 13 is more than three times the radius of the resonance 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 piece). For example, in this embodiment, the length of the resonance cavity 12 is 22 mm, and the inner diameter of the resonance cavity 12 is 2 mm. Then, the length of the buffer cavity 13 at one end of the resonance cavity 12 is 11 mm, and the radius of the buffer cavity 13 is 6.5 mm.

[0030] As a preferred implementation in this embodiment, Figure 3 and Figure 4 As shown, the resonant cavity 12 is located on the side of the cell body 10 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. Figure 7 As shown, after the photoacoustic signal in the resonant cavity 11 is reflected and superimposed inside, the sound pressure amplitude at the top is the strongest. The resonant cavity 12 is located at the top of the resonant cavity 11, and the connecting hole 14 is connected to the top area of ​​the resonant cavity 11. The sound pressure amplitude in the resonant cavity 11 is the strongest and is transmitted to the resonant cavity 12 through the connecting hole 14 and is amplified twice in the resonant cavity 12, so that a clearer photoacoustic signal can be formed.

[0031] Preferably, Figure 4As shown, the resonant cavity 12 is provided with a plurality of them. In the present embodiment, the resonant cavity 12 is provided with two of them. The plurality of resonant cavities 12 are cross-arranged, and the axis of the resonant cavity 12 is parallel to the plane where the mouth of the resonant cavity 11 is located, and the angles between adjacent resonant cavities 12 are the same. For example, in the present embodiment, the two resonant cavities 12 are arranged vertically. The connecting holes 14 are provided with a plurality of them. For example, in the present embodiment, each of the resonant cavities 12 is provided with 5 connecting holes 14.

[0032] According to acoustic theory, the resonance modes of a spherical photoacoustic cell can be divided into radial, θ-angular and φ-angular modes. The amplitude of the sound signal generated in the resonant cavity 11 needs to be maximum at the top of the hemispherical shape, such as Figure 6 The frequency response curve of the resonance cavity 11 at the top is shown. The resonance cavity 11 has a higher resonance frequency near the frequency of 7200 Hz (taking the diameter of the resonance cavity 11 in this example as 30 mm of the lamp board). Therefore, the resonance cavity 12 also needs to form a sound resonance effect near 7200 Hz.

[0033] The resonant cavity 12 adopts the first-order longitudinal vibration mode, and its resonant frequency Calculated by formula (1): ;Formula (1) Wherein, L is the length of the resonance cavity 12, is the correction coefficient, ΔL=16R / 3π, R is the radius of the resonance cavity 12; c is the speed of sound in air at a standard atmospheric pressure and 15°C, which is approximately 340 m / s.

[0034] like Figure 7 As shown, the photoacoustic signal at the top of the resonance cavity 11 reaches a maximum value when the modulation frequency reaches about 7200 Hz. When the sound frequency is 7200 Hz, the sound pressure mode of the resonance cavity 12 is a resonance mode with a wave crest in the middle and wave nodes at both ends. The strongest points of the sound pressure amplitudes of the resonance cavities 11 and 12 overlap each other, forming a secondary amplification of the sound signal.

[0035] In this embodiment, the sound pickup hole 16 is connected to the intersections of the plurality of resonance cavities 12 .

[0036] In this embodiment, the pool body 10 and the base 20 are fixed by bolts 70. 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 inner side of the mounting groove 22. The bolt 70 passes through the base 20 and is fastened to the end of the pool body 10 through a threaded connection; Preferably, a sealing gasket 60 is further provided between the pool body 10 and the base 20 for sealing the pool body 10 and the base 20 , thereby preventing air leakage from a gap between the pool body 10 and the base 20 .

[0037] In this embodiment, a mounting hole 21 is further provided on the base 20, and the mounting hole 21 is a countersunk hole. The lamp board 30 is sealed and connected 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 a sealing ring is provided between the lamp board 30 and the mounting hole 21, so that the lamp board 30 and the mounting hole 21 are sealed. 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.

[0038] As a preferred implementation in this embodiment, the light emitting components 31 are provided in plurality, and the plurality of 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; Preferably, the multiple light-emitting components 31 can be lamp beads of the same model or different models, that is, the parameters of the multiple light-emitting components 31 can be consistent or inconsistent, so as to realize the measurement of 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 optical power modulation of the four light-emitting components 31 is 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 of the light-emitting components 31 is used to measure a gas, and the optical power modulation of the light-emitting components 31 is at different frequencies, but each modulation frequency is within the resonant frequency bandwidth of the hemispherical photoacoustic cell, thus realizing the use of the hemispherical photoacoustic cell for multiple gas detection.

[0039] As a preferred implementation in this embodiment, Figure 1 and Figure 3 As shown, the mouth of the air hole 15 is also provided with an air hole interface 50 by means of threads or adhesive, for connecting an air source and an air valve. Example

[0040] As another embodiment of the present invention, this embodiment further discloses a gas detection method, which is implemented based on the hemispherical photoacoustic cell described in Example 1, and the detection method comprises the following steps: Step S1, introducing the gas to be measured into the resonant cavity 11, and after the gas to be measured fills the resonant cavity 11 and the resonant cavity 12, the microphone 40 is connected to the signal processing device; Step S2: using an electrical signal to modulate the light emitting component 31, 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 near the resonance frequency of the resonant cavity 11; Step S3, start the signal processing device to demodulate the photoacoustic signal collected by the microphone 40 to detect the gas to be detected.

[0041] Specifically, in the present embodiment, the light-emitting component 31 generates light of preset frequency and intensity under the control of the electrical signal of the controller. The controller controls the voltage signal to make the light-emitting component 31 generate light of preset intensity, and controls the light-emitting component 31 to generate pulsed light of preset frequency through 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 phase-locked amplifier, a data acquisition card, an industrial computer, etc. The light energy of the light generated by the light-emitting component 31 is absorbed by the gas and converted into a sound signal, which is detected by the microphone 40. The signal processing device is used to process the photoacoustic signal collected by the microphone 40, and realize the measurement of the gas to be measured based on the data processing device in the prior art.

[0042] It should be noted that when performing multi-gas measurement, a lamp board 30 having light emitting components 31 of various models is used, and when performing single gas measurement, a lamp board 30 having light emitting components 31 of a single model is used.

[0043] It should be noted that the resonant cavity 12 can be sealed before or after the gas to be measured is filled. Even if the resonant cavity 12 contains air, the light generated by the light-emitting component 31 is difficult to enter the resonant cavity 12, and the air in the resonant cavity 12 will not affect the measurement of the gas to be measured.

[0044] The terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "the" and "the" used in the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0045] It should be understood that although the terms first, second, third, etc. may be used in the present invention to describe various information, these information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present invention, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0046] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A hemispherical photoacoustic cell, characterized in that: The photoacoustic cell comprises: A pool body, wherein a resonant cavity, a resonant cavity and an air hole are arranged on the pool body, wherein the resonant cavity is a hemispherical groove body, wherein the resonant cavity is a through-hole structure, wherein the resonant cavity is connected with the resonant cavity through a connecting hole, wherein the resonant cavity and the resonant cavity have the same resonant frequency, and wherein the air hole penetrates the pool body and is connected with the resonant cavity; A base, the base is fixedly connected to the cell body, and the base is located at the mouth of the resonant cavity to block the resonant cavity; A light board, the light board is fixedly connected to the base, the light board is located at the mouth of the pool body, and a light-emitting component is arranged on the light board to generate light of preset wavelength, frequency and light intensity; A microphone is used to pick up the photoacoustic signal in the resonance cavity.

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

3. The hemispherical photoacoustic cell according to claim 1, characterized in that: The resonance cavity is located on a side of the pool body away from the opening of the resonance cavity, and the axis of the resonance cavity is parallel to the surface where the opening of the resonance cavity is located.

4. The hemispherical photoacoustic cell according to claim 3, characterized in that: There are multiple resonance cavities, which are cross-arranged, and the angles between adjacent resonance cavities are the same. The microphone is located at the intersection of the multiple resonance cavities.

5. The hemispherical photoacoustic cell according to claim 4, characterized in that: The air hole passes through the resonant cavity so that the air hole forms two air channels.

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

7. The hemispherical photoacoustic cell according to any one of claims 1 to 5, characterized in that: There are multiple light-emitting components, and the multiple light-emitting components are distributed around the axis of the resonant cavity in the circumferential direction.

8. A gas detection method, characterized in that: Based on the hemispherical photoacoustic cell according to any one of claims 1 to 7, the method comprises the following steps: The gas to be measured is introduced into the resonant cavity, and after the gas to be measured fills the resonant cavity and the resonant cavity, the microphone is connected to the signal processing device; Using an electrical signal to modulate the light-emitting component, 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 near the resonance frequency of the resonant cavity; The signal processing device is started to demodulate the photoacoustic signal collected by the microphone to realize the detection light board of the gas to be detected.

9. The gas detection method according to claim 8, characterized in that: When performing single gas measurements, a light board with a single model of light emitting component is used.

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

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