A carbon monoxide detection system based on photoacoustic spectroscopy

Abstract

The present invention relates to the technical field of carbon monoxide detection, and particularly relates to a carbon monoxide detection system based on photoacoustic spectroscopy technology, which includes a light source, an optical fiber, a gas chamber, a first micro-resonator, a second micro-resonator, and a tuning fork. The light source generates mid-infrared band laser, and the mid-infrared band laser is coupled into the optical fiber. The optical fiber penetrates through the gas chamber, and an optical fiber taper region is provided in the middle of the optical fiber. The optical fiber taper region is arranged inside the gas chamber. The first micro-resonator and the second micro-resonator are respectively arranged on both sides of the optical fiber taper region, and the tuning fork is arranged on the side of the optical fiber taper region. An air inlet and an air outlet are provided on the wall of the gas chamber, and metal oxide particles are arranged outside the optical fiber taper region. In the present invention, metal oxide particles are arranged in the optical fiber taper region, so that more light in the optical fiber can be coupled out of the optical fiber, enhancing the absorption of the mid-infrared band laser by the gas, thereby improving the sensitivity of gas detection, and having good application prospects in the field of gas detection by photoacoustic spectroscopy technology.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon monoxide detection, and particularly to a carbon monoxide detection system based on photoacoustic spectroscopy technology. Background Art

[0002] Carbon monoxide is a major air pollutant, which plays an important role in atmospheric chemistry. It can directly affect the formation of tropospheric ozone and indirectly affect global warming. The carbon monoxide emitted into the atmosphere mainly comes from the incomplete combustion of natural gas and other carbon-containing fuels used for energy generation, petrochemical refining, and motor vehicle use. In addition, carbon monoxide is prone to endanger personal safety. Therefore, it is necessary to monitor the carbon monoxide concentration in real time during industrial combustion emissions.

[0003] Common non-optical gas detection technologies include gas chromatography technology, mass spectrometry technology, chemiluminescence analysis technology, electrochemistry technology, etc. Optical gas detection technology not only has the characteristics of high sensitivity, high selectivity, and long-term stability of some other detection technologies, but also has the unique advantages of long life and fast response, and is suitable for real-time online detection. The main optical gas detection technologies include non-dispersive infrared technology, tunable diode laser spectroscopy technology, cavity enhanced spectroscopy, and photoacoustic spectroscopy technology. Among them, the photoacoustic spectroscopy technology has the highest sensing sensitivity.

[0004] Photoacoustic spectroscopy gas detection technology is an indirect absorption spectroscopy technology that measures gas concentration using the photoacoustic effect and is an important branch of molecular spectroscopy. Since the fundamental vibration bands of many molecules are located in the mid-infrared spectral region, which is the strongest spectral absorption band of gas molecules, in this region, the absorption line intensities of many target gases are much greater than those of other surrounding gases. Due to this advantage, the method of detecting gas concentration by infrared spectral absorption has been adopted by more and more researchers at home and abroad. Among them, the theoretical mechanism of photoacoustic spectroscopy gas detection technology can be described as follows: When the gas to be measured in the photoacoustic cell is irradiated by light, the gas molecules are excited to a high-energy state after absorbing light radiation of a specific wavelength. During the non-radiative transition of the gas molecules from the high-energy state to the low-energy state, the temperature and pressure of the gas change. If the intensity or wavelength of the incident light is modulated, the gas temperature in the photoacoustic cell will show a temperature change with the same modulation frequency, which will further lead to a change in pressure. When the modulation frequency is within the audio frequency range, a sound signal is generated. The change in the sound signal reflects the change in the concentration of the absorber. By measuring the photoacoustic signal, the concentration and components of the gas to be measured can be spectroscopically analyzed.

[0005] In the existing photoacoustic spectroscopy gas detection technology, to avoid noise caused by direct laser irradiation on the tuning fork, a fiber optic coupling system is used instead of the spatial optical path. The directly tapered fiber is applied to pass through the centers of the two arms of the tuning fork, and the evanescent field is used to convert the laser energy into sound waves generated after gas absorption, and then the sound waves are transmitted to the position of the tuning fork. In this process, the gas absorbs less energy of the evanescent field, resulting in low sensitivity of gas detection. Summary of the Invention

[0006] To solve the above problems, the present invention provides a carbon monoxide detection system based on photoacoustic spectroscopy technology, including a light source, an optical fiber, a gas chamber, a first micro-resonator, a second micro-resonator, and a tuning fork. The light source generates a laser in the mid-infrared band, and the mid-infrared band laser is coupled into the optical fiber. The optical fiber penetrates through the gas chamber, and a fiber optic taper region is provided in the middle of the optical fiber. The fiber optic taper region is arranged inside the gas chamber. The first micro-resonator and the second micro-resonator are respectively arranged on both sides of the fiber optic taper region, and the tuning fork is arranged on the side of the fiber optic taper region. An air inlet and an air outlet are provided on the wall of the gas chamber, and metal oxide particles are provided outside the fiber optic taper region.

[0007] Through the coupling between the metal oxide particles and the fiber optic taper region in the present invention, more light in the fiber optic taper region overflows from the optical fiber; a strong light field is formed near the metal oxide particles, and the metal oxide particles also form strong radiation, all of which enhance the absorption of the mid-infrared band laser by the gas, making the gas generate a stronger sound signal, and improving the sensitivity and accuracy of gas detection.

[0008] Furthermore, the tuning fork is a quartz tuning fork. In terms of the sound transmission device, the traditional acoustic conduction device is a miniature microphone, and the general design has a flat resonance frequency (from several hundred to two thousand hertz), which is not suitable for separating weak gas signals and external environmental noise. The resonance frequency of the quartz tuning fork is high, up to several thousand to one hundred thousand hertz, is very sensitive to weak sound signals, and is much higher than the frequency of environmental noise at the same time.

[0009] Furthermore, the fiber optic taper region passes through the space between the two prongs of the tuning fork to enhance the effect of the gas on the tuning fork.

[0010] Furthermore, the optical fiber is a single-mode optical fiber.

[0011] Furthermore, the optical fiber is a mid-infrared optical fiber.

[0012] Furthermore, both the first micro-resonator and the second micro-resonator are capillary tubes. The first micro-resonator and the second micro-resonator are sleeved on the optical fiber to enhance the phonon vibration excited by the gas in the capillary tubes, effectively improving the signal of the gas detection system.

[0013] Furthermore, on the side closer to the fiber taper region, the side wall of the capillary is thick; on the side farther from the fiber taper region, the side wall of the capillary is thin. Since the cross-sectional area of the capillary is large on the side of the fiber taper region, the effect of the gas on the capillary is enhanced, and a stronger sound field can be concentrated between the two capillaries, thereby enhancing the effect of the sound field on the tuning fork.

[0014] Furthermore, the material of the metal oxide particles is titanium dioxide, zinc oxide, tin oxide, indium oxide or ITO.

[0015] Furthermore, the metal oxide particles are spherical.

[0016] Advantages of the present invention:

[0017] (1) By arranging metal oxide particles in the fiber taper region of the present invention, light in the optical fiber can be more coupled out of the optical fiber, enhancing the absorption of mid-infrared band laser by the gas, thereby improving the sensitivity of gas detection.

[0018] (2) By using a quartz tuning fork to measure the sound field generated by the gas in the present invention, the influence of external environmental noise is avoided, and the accuracy of the system for detecting gas is improved.

[0019] (3) By using capillaries with different side wall thicknesses in the present invention, the effect of the gas on the capillaries is enhanced, and a stronger sound field can be concentrated between the two capillaries, thereby causing a larger amplitude vibration of the tuning fork and improving the sensitivity of the system for detecting gas.

[0020] Combining the above effects, the present invention has good application prospects in the detection of carbon monoxide by photoacoustic spectroscopy technology.

[0021] The following will further describe the present invention in detail with reference to the accompanying drawings. Description of the Drawings

[0022] Figure 1 is a schematic diagram of a carbon monoxide detection system based on photoacoustic spectroscopy technology.

[0023] Figure 2 is a schematic diagram of the fiber taper region and the metal oxide particles.

[0024] Figure 3 is a schematic diagram of the fiber taper region, the first micro-resonator and the second micro-resonator.

[0025] In the figure: 1, light source; 2, optical fiber; 3, gas chamber; 4, first micro-resonator; 5, second micro-resonator; 6, tuning fork; 7, air inlet; 8, air outlet; 9, metal oxide particles; 21, fiber taper region. Specific Embodiments

[0026] To make the objectives, technical solutions and advantages of the present application more clear and understandable, the following provides a further detailed description of the present application with reference to the accompanying drawings and by way of examples. The present invention provides a carbon monoxide detection system based on photoacoustic spectroscopy. As Figure 1 shown, it includes a light source 1, an optical fiber 2, a gas chamber 3, a first microresonator 4, a second microresonator 5, and a tuning fork 6. The light source 1 generates a mid-infrared band laser, and the mid-infrared band laser is coupled into the optical fiber 2. Specifically, the light source 1 is a 2.3-micron near mid-infrared band distributed feedback laser with a power of 1.8 mW. The wavelength of the laser, 2.3 microns, exactly targets the absorption line of carbon monoxide at 4297.70 cm -1 . The optical fiber 2 is a single-mode optical fiber and is a mid-infrared optical fiber. Specifically, in the present invention, the optical fiber 2 is a germanium-doped silica core optical fiber. At a wavelength of 2.3 microns, the optical fiber 2 has a small loss, less than 0.25 dB / m. As Figure 1 shown, the optical fiber 2 penetrates through the gas chamber 3. The optical fiber 2 enters from the left side of the gas chamber 3 and exits from the right side of the gas chamber 3. The contact between the optical fiber 2 and the gas chamber 3 is sealed. A fiber taper region 21 is provided in the middle of the optical fiber 2, and the fiber taper region 21 is provided inside the gas chamber 3. The first microresonator 4 and the second microresonator 5 are respectively provided on both sides of the fiber taper region 21. Specifically, as Figure 1 shown, both the first microresonator 4 and the second microresonator 5 are capillary tubes. The first microresonator 4 and the second microresonator 5 are sleeved on the optical fiber 2 to enhance the phonon vibration excited by the gas inside the capillary tubes, thereby effectively improving the signal of the gas detection system. The length of the capillary tube is 3-5 mm and the inner diameter is 0.6 mm. The tuning fork 6 is provided on the side of the fiber taper region 21. Figure 1 The two rectangular blocks in Figure 1 represent the two columns of the tuning fork 6. Specifically, the fiber taper region 21 passes through the space between the two prongs of the tuning fork 6 to enhance the effect of gas vibration on the tuning fork. In practical applications, the fiber taper region 21 is in the middle of the two columns of the tuning fork and does not contact the tuning fork 6, so that the tuning fork 6 can receive stronger sound waves. As Figure 2 shown, an air inlet 7 and an air outlet 8 are provided on the wall of the gas chamber 3 for pumping out the gas to be measured. As Figure 2 shown, metal oxide particles 9 are provided outside the fiber taper region 21. The material of the metal oxide particles 9 is titanium dioxide, zinc oxide, tin oxide, indium oxide or ITO. The shape of the metal oxide particles 9 can be spherical or block-shaped. The surface plasmon resonance wavelength of the metal oxide particles 9 is in the infrared band, covering a wavelength of 2.3 microns. Due to the presence of the metal oxide particles 9, the infrared band laser in the fiber taper region 21 can more easily enter the space where the carbon monoxide gas is located.

[0027] Through the coupling between the metal oxide particles 9 and the optical fiber taper region 21, more light in the optical fiber taper region 21 overflows from the optical fiber 2 and enters the space where the carbon monoxide gas is located; a strong light field is formed near the metal oxide particles 9, and the metal oxide particles 9 also form strong radiation. These phenomena enhance the absorption of the mid-infrared band laser by the gas, causing the gas to generate a stronger acoustic signal, thereby improving the sensitivity and accuracy of gas detection.

[0028] In practical applications, fixing frames are provided on the outer sides (i.e., the sides far from the optical fiber taper region 21) of the first micro-resonator 4 and the second micro-resonator 5 to fix the optical fiber 2. The two fixing frames are fixedly connected to the side wall of the gas chamber 3 through a support frame. Similarly, the tuning fork 6 is also fixed or stably arranged on the side wall of the gas chamber 3 through a support frame.

[0029] During application, the vibration signal of the tuning fork is converted into an electrical signal by a piezoelectric conversion device fixed on the tuning fork 6. After passing through a pre-amplification circuit, the electrical signal enters the signal acquisition and processing system.

[0030] During application, on the Figure 1 right side of [], outside the gas chamber 3, the optical fiber 2 is connected to an optical power meter to monitor the operating state of the optical path.

[0031] Preferably, the tuning fork 6 is a quartz tuning fork. In terms of the sound transmission device, the traditional acoustic conduction device is a miniature microphone, and the general design has a flat resonance frequency (from several hundred to two thousand hertz), which is not suitable for separating weak gas signals and external environmental noise. The resonance frequency of the quartz tuning fork is high, up to several thousand to one hundred thousand hertz, is very sensitive to weak acoustic signals, and is much higher than the frequency of environmental noise.

[0032] Preferably, as Figure 3 shown, on the side close to the optical fiber taper region 21, the side wall of the capillary is thick; on the side far from the optical fiber taper region 21, the side wall of the capillary is thin. Since the cross-sectional area of the capillary is large on the side of the optical fiber taper region 21, the effect of the gas on the capillary is enhanced, and a stronger sound field can be aggregated between the two capillaries, thereby enhancing the effect of the sound field on the tuning fork 6.

[0033] The method for preparing the optical fiber taper region 21 adopts a conventional optical fiber tapering method, and the method of heating with a hydrogen flame and heating and stretching with an alcohol lamp can be used to prepare the optical fiber taper region 21. Through stretching, the diameter of the optical fiber taper region 21 is in the range of 2 - 4 micrometers, so that the laser in the optical fiber can more easily leak out from the optical fiber taper region 21.

[0034] When installing the first micro-resonator 4 and the second micro-resonator 5, that is, when installing the two capillaries, place the two capillaries in a V-shaped groove and pass the optical fiber 2 through the two capillaries.

[0035] The method for preparing metal oxide particles 9 on the optical fiber taper region 21 is as follows: First, a dispersion of metal oxide particles 9 is prepared and deposited onto the optical fiber taper region 21 by means of spin coating, air spraying, or drop coating to form a dispersed layer of metal oxide particles.

[0036] In the present invention, it is difficult to prepare capillary tubes with different thicknesses. A method of setting a coating on the outer side of the capillary tube, that is, coating other substances, can be adopted to change the side wall thickness of the capillary tube. For example, melted glass, metal and other materials are adhered to one end of the capillary tube to make one end of the capillary tube thicker. During application, the thicker end is placed close to the optical fiber taper region 21.

[0037] In summary, the present invention provides a carbon monoxide detection system based on photoacoustic spectroscopy. By introducing metal oxide particles 9 on the optical fiber taper region 21, the light energy leaking from the optical fiber taper region 21 is increased, the absorption of mid-infrared light by carbon monoxide gas is enhanced, enabling the gas to generate a stronger acoustic signal, and improving the sensitivity and accuracy of carbon monoxide gas detection. The present invention can not only be used for detecting carbon monoxide gas, but also be of great help for detecting other gases such as formaldehyde using photoacoustic spectroscopy.

[0038] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the scope of protection of the present application.

Claims

1. A carbon monoxide detection system based on photoacoustic spectroscopy technology, characterized in that, It includes a light source, an optical fiber, a gas chamber, a first micro-resonator, a second micro-resonator, and a tuning fork. The light source generates mid-infrared band laser, and the mid-infrared band laser is coupled into the optical fiber. The optical fiber penetrates through the gas chamber. The middle part of the optical fiber is provided with an optical fiber taper region, and the optical fiber taper region is arranged inside the gas chamber. The first micro-resonator and the second micro-resonator are respectively arranged on both sides of the optical fiber taper region. The tuning fork is arranged on the side of the optical fiber taper region. The wall of the gas chamber is provided with an air inlet and an air outlet. Metal oxide particles are arranged outside the optical fiber taper region. Among them, both the first micro-resonator and the second micro-resonator are capillary tubes, and the first micro-resonator and the second micro-resonator are sleeved on the optical fiber. On the side close to the optical fiber taper region, the side wall of the capillary tube is thick; on the side far from the optical fiber taper region, the side wall of the capillary tube is thin.

2. The carbon monoxide detection system based on photoacoustic spectroscopy technology according to claim 1, characterized in that: The tuning fork is a quartz tuning fork.

3. The carbon monoxide detection system based on photoacoustic spectroscopy technology according to claim 2, characterized in that: The optical fiber taper region passes through the space between the two prongs of the tuning fork.

4. The carbon monoxide detection system based on photoacoustic spectroscopy technology according to claim 1, characterized in that: The optical fiber is a single-mode optical fiber.

5. The carbon monoxide detection system based on photoacoustic spectroscopy technology according to claim 4, characterized in that: The optical fiber is a mid-infrared optical fiber.

6. The carbon monoxide detection system based on photoacoustic spectroscopy technology according to any one of claims 1-5, characterized in that: The material of the metal oxide particles is titanium dioxide, zinc oxide, tin oxide, indium oxide or ITO.

7. The carbon monoxide detection system based on photoacoustic spectroscopy technology according to claim 6, characterized in that: The metal oxide particles are spherical.

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