Photoacoustic sensor and detection system for simultaneous detection of multiple gases

Abstract

The present invention discloses a photoacoustic sensor and detection system for simultaneous detection of multiple gases, and relates to the field of optical fiber sensing and trace gas detection. The photoacoustic sensor includes a detection optical fiber, three excitation optical fibers, a cylindrical metal shell, a non-resonance cavity arranged inside the cylindrical metal shell, and a cantilever beam microphone connected to the top of the cylindrical metal shell; the through hole at the center of the circle at the bottom of the cylindrical metal shell is placed with a detection optical fiber, and each through hole arranged at the bottom of the cylindrical metal shell in a circular array form is placed with an excitation optical fiber; a rectangular pit is provided on the cantilever beam microphone; the three sides of the bottom surface of the rectangular pit are all gaps to form a cantilever beam, and the bottom surface of the rectangular pit faces the non-resonance cavity; the size of the cylindrical metal shell and the non-resonance cavity is at the millimeter level. The present invention can realize high-sensitivity detection of multiple gases at the same time, and has miniaturization.

Description

Technical Field

[0001] The invention relates to the field of optical fiber sensing and trace gas detection, and in particular to a photoacoustic sensor and a detection system for simultaneously detecting multiple gases. Background Art

[0002] Trace gas detection plays an important role in atmospheric environment detection, industrial process control and life sciences. With the development of laser technology, photoacoustic spectroscopy has become a gas detection method with high sensitivity, fast response time and strong selectivity, and is widely used in trace gas detection. Photoacoustic spectroscopy is a spectral calorimetric technology that directly measures the heat energy generated by the gas due to the absorption of light energy. It is a background-free absorption spectroscopy technology. The basic principle can be summarized as follows: when the periodically modulated light source covers the absorption spectrum of the gas molecules to be measured, the gas molecules transition from the ground state to the excited state, and then return to the ground state through a radiationless transition and release heat, causing the air around the gas molecules to expand periodically to generate sound waves. Since the size of the sound wave is proportional to the concentration of the gas to be measured, the concentration information of the gas to be measured can be obtained by detecting the size of the photoacoustic signal through a photoacoustic sensor.

[0003] At present, trace gas detection systems based on photoacoustic spectroscopy technology can be divided into two categories according to different working models, namely resonant photoacoustic systems and non-resonant photoacoustic systems. The resonant photoacoustic cell is characterized by high sensitivity, but the overall volume is large. The non-resonant photoacoustic cell has low sensitivity, but its overall volume is small and suitable for trace gas detection in a small space. However, there are few studies on the measurement of multiple gases by non-resonant photoacoustic cells. Usually, the measurement of multiple gases requires the simultaneous use of multiple lasers and multiple microphones to achieve the function of multiple gas detection, so multiple lasers need to be connected in parallel; during the experiment, a laser is first turned on, and after the measurement of one gas is completed, the laser is turned off, and then the corresponding laser of the next gas is turned on, which increases the complexity of the system and increases the time to measure the gas. Therefore, there is an urgent need for a small-volume, high-sensitivity photoacoustic system for simultaneous measurement of multiple gases. Summary of the invention

[0004] The purpose of the present invention is to provide a photoacoustic sensor and a detection system for detecting multiple gases simultaneously, which can realize high-sensitivity detection of multiple gases simultaneously and has miniaturization.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] In a first aspect, the present invention provides a photoacoustic sensor for simultaneous detection of multiple gases, comprising: a plurality of single-mode optical fibers, a cylindrical metal shell, a non-resonant cavity disposed inside the cylindrical metal shell, and a cantilever beam microphone connected to the top of the cylindrical metal shell;

[0007] The plurality of single-mode optical fibers include one detection optical fiber and three excitation optical fibers;

[0008] Four through holes are provided at the bottom of the cylindrical metal shell; wherein one through hole is located at the center of the bottom of the cylindrical metal shell, and the other three through holes are arranged in a circular array on the bottom of the cylindrical metal shell, and the through hole located at the center is provided with the detection optical fiber, and each through hole arranged in the circular array is provided with the excitation optical fiber;

[0009] The cantilever beam microphone is provided with a rectangular parallelepiped pit; three sides of the bottom surface of the rectangular parallelepiped pit are all gaps to form a cantilever beam, and the bottom surface of the rectangular parallelepiped pit faces the non-resonance cavity;

[0010] The sizes of the cylindrical metal shell and the non-resonant cavity are in the millimeter level.

[0011] Optionally, the cantilever microphone is formed by engraving on a silicon dioxide wafer using MEMS technology; two long sides and one short side of the bottom surface of the rectangular pit are gaps, and the short side is close to the center of the bottom surface of the rectangular pit.

[0012] Optionally, under the first target size, the resonance frequency of the cantilever beam is 7690 Hz; the first target size is that the length of the cantilever beam is 0.8 mm, the width of the cantilever beam is 0.4 mm, and the thickness of the cantilever beam is 3.5 um.

[0013] Optionally, under the first target size and the second target size, the sensitivity of the cantilever beam at the first-order resonant frequency reaches 14000nm / Pa; the second target size is that the length of the non-resonant cavity is 4mm and the diameter of the non-resonant cavity is 3.2mm.

[0014] Optionally, the length of the cylindrical metal shell is 6 mm, and the diameter of the cylindrical metal shell is 3.6 mm.

[0015] Optionally, the diameters of the four through holes are all 0.3 mm;

[0016] Each of the single-mode optical fibers includes a core, a cladding, and a coating layer, and the diameters of the cladding and the coating layer are 0.25 mm and 0.9 mm, respectively.

[0017] Optionally, the through hole for placing the detection optical fiber is concentric with the non-resonant cavity, and the three through holes for placing the excitation optical fibers are distributed in a ring array at a position 0.6 mm away from the inner wall of the non-resonant cavity.

[0018] Optionally, the distance between one detection optical fiber and the cantilever microphone is within 300 nm, and the distance between three excitation optical fibers and the cantilever microphone is between 3.2 mm and 3.8 mm.

[0019] In a second aspect, the present invention provides a detection system, comprising: three near-infrared lasers, an optical fiber circulator, a high-speed spectrometer, a wide-spectrum light source, a computer, and the photoacoustic sensor for simultaneous detection of multiple gases as described in the first aspect; the computer is internally provided with multiple virtual lock-in amplifiers based on LabVIEW;

[0020] A variety of gases enter the photoacoustic sensor through the gap of the cantilever microphone, and each of the near-infrared lasers emits an excitation light source into the photoacoustic sensor through an excitation optical fiber to generate a photoacoustic effect, causing the cantilever beam to vibrate periodically; the detection light emitted by the wide-spectrum light source passes through the optical fiber circulator and the detection optical fiber in turn and is incident on the non-resonant cavity in the photoacoustic sensor, and the interference light reflected by different gases enters the high-speed spectrometer 15 through the optical fiber circulator 14, and the interference light is demodulated by the white light interferometric demodulation algorithm in the high-speed spectrometer to obtain a demodulated photoacoustic signal; the demodulated photoacoustic signal is processed by multiple virtual lock-in amplifiers based on LabVIEW to obtain the intensity of the photoacoustic signals of the various gases.

[0021] Optionally, the sampling frequency of the high-speed spectrometer is 32 kHz.

[0022] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0023] The present invention provides a photoacoustic sensor and detection system for simultaneous detection of multiple gases. Due to the unique design of the cantilever beam and its use in combination with a non-resonant cavity, the cantilever beam has ultra-high sensitivity, which makes up for the defect of low sensitivity of the non-resonant photoacoustic cell. The operating frequencies of multiple gas detections are all at high frequencies, so that the overall noise level is low, and thus the detection limit is low. Since the volume of the photoacoustic sensor reaches the cubic millimeter level, the volume of the non-resonant cavity is small, and thus the response speed of multiple gas detection is extremely fast. In addition, the detection optical fiber and the excitation optical fiber are both located on one side, providing a new solution for high-sensitivity measurement of multiple gases at a long distance and at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0025] Figure 1 This is a schematic diagram of the structure of the photoacoustic sensor for detecting multiple gases simultaneously according to the present invention;

[0026] Figure 2 It is a structural schematic diagram of the cantilever beam microphone of the present invention;

[0027] Figure 3 It is a schematic diagram of the structure of the single-mode optical fiber of the present invention;

[0028] Figure 4 It is a schematic diagram of the structure of the detection system of the photoacoustic sensor for simultaneous detection of multiple gases according to the present invention.

[0029] In the figure: 1. Cylindrical metal shell; 2. Non-resonant cavity; 3. Cantilever microphone; 4. Detection optical fiber; 5. Excitation optical fiber; 6. Through hole; 7. Silica wafer; 8. Cantilever beam; 9. Fiber core; 10. Cladding; 11. Coating; 12. Photoacoustic sensor; 13. Near-infrared laser; 14. Fiber circulator; 15. High-speed spectrometer; 16. Broad-spectrum light source; 17. Computer; 18. Virtual phase-locked amplifier based on LabVIEW. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] The purpose of the present invention is to provide a photoacoustic sensor and detection system for the simultaneous detection of multiple gases. Since the overall volume of the photoacoustic sensor is at the cubic millimeter level and it can achieve high-sensitivity detection of multiple gases simultaneously, it provides a new idea for miniaturized non-resonant photoacoustic sensors for the simultaneous detection of multiple gases, and has great application prospects in the field of photoacoustic spectroscopy.

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Embodiment 1

[0034] Figure 1 Schematic diagram of the structure of the photoacoustic sensor for simultaneous detection of multiple gases according to the present invention. Figure 1As shown, a miniaturized, highly sensitive photoacoustic sensor for simultaneous detection of multiple gases provided by an embodiment of the present invention includes multiple single-mode optical fibers, a cylindrical metal shell 1, a non-resonant cavity 2 arranged inside the cylindrical metal shell 1, and a cantilever microphone 3 connected to the top of the cylindrical metal shell 1.

[0035] The multiple single-mode optical fibers include a detection optical fiber 4 and three excitation optical fibers 5; four through holes 6 are opened at the bottom of the cylindrical metal shell 1; wherein one through hole is located at the center of the bottom of the cylindrical metal shell 1, and the other three through holes are arranged in the form of a circular array on the bottom of the cylindrical metal shell 1, and the through hole located at the center of the circle is placed with the detection optical fiber 4, and each of the through holes arranged in the form of a circular array is placed with the excitation optical fiber 5.

[0036] The cantilever beam microphone 3 is provided with a rectangular parallelepiped pit; three sides of the bottom surface of the rectangular parallelepiped pit are gaps to form a cantilever beam 8, and the bottom surface of the rectangular parallelepiped pit faces the non-resonance cavity 2.

[0037] The sizes of the cylindrical metal shell 1 and the non-resonant cavity 2 are in the millimeter level.

[0038] Furthermore, the cantilever beam microphone 3 described in the embodiment of the present invention is formed by engraving on the silicon dioxide wafer 7 using MEMS technology, that is, the cantilever beam 8 is formed by engraving on the silicon dioxide wafer 7 using MEMS technology. The two long sides and one short side of the bottom surface of the rectangular pit are both gaps, and the short side is close to the center of the bottom surface of the rectangular pit, that is, the other short side is connected to the silicon dioxide wafer 7. The specific structural diagram is as shown in FIG. Figure 2 shown.

[0039] The top of the cylindrical metal shell 1 and the cantilever beam microphone 3 are fixedly connected by gluing.

[0040] Furthermore, the length of the cylindrical metal shell 1 described in the embodiment of the present invention is 6 mm, and the diameter of the cylindrical metal shell 1 is 3.6 mm.

[0041] The length of the non-resonant cavity 2 is 4 mm, and the diameter of the non-resonant cavity 2 is 3.2 mm.

[0042] The length of the cantilever beam 8 is 0.8 mm, the width of the cantilever beam 8 is 0.4 mm, and the thickness of the cantilever beam 8 is 3.5 um. The resonance frequency of the cantilever beam 8 at this size is 7690 Hz.

[0043] The size of the non-resonant cavity 2 is simulated and analyzed and matches the size of the cantilever beam 8. Only when the cantilever beam 8 is combined with the non-resonant cavity 2 of this size can the sensitivity of the cantilever beam 8 at the first-order resonance frequency reach 14000nm / Pa.

[0044] In summary: at the first target size, the resonance frequency of the cantilever beam 8 is 7690 Hz; the first target size is that the length of the cantilever beam 8 is 0.8 mm, the width of the cantilever beam 8 is 0.4 mm, and the thickness of the cantilever beam is 3.5 um.

[0045] Under the first target size and the second target size, the sensitivity of the cantilever beam 8 at the first-order resonance frequency reaches 14000nm / Pa; the second target size is that the length of the non-resonant cavity 2 is 4mm, and the diameter of the non-resonant cavity 2 is 3.2mm.

[0046] Furthermore, if Figure 3 As shown, each of the single-mode optical fibers described in the embodiment of the present invention comprises a core 9, a cladding 10 and a coating layer 11, and the diameters of the cladding 10 and the coating layer 11 are 0.25 mm and 0.9 mm, respectively.

[0047] The bottom of the cylindrical metal shell 1 described in the embodiment of the present invention is provided with four through holes 6 with a diameter of 0.3 mm. The diameter of the through holes described in the embodiment of the present invention matches the diameter of the cladding 10, and the cavity is sealed by gluing.

[0048] The distance between one detection optical fiber 4 and the cantilever microphone 3 is within 300 nm, and the distance between three excitation optical fibers 5 and the cantilever microphone is between 3.2 mm and 3.8 mm.

[0049] The through hole for placing the detection optical fiber 4 is concentric with the non-resonant cavity 2, and the three through holes for placing the excitation optical fibers 5 are distributed in a circular array at a distance of 0.6 mm from the inner wall of the non-resonant cavity 2. The purpose of this is to ensure that the laser light source does not hit the inner wall of the non-resonant cavity and that the photoacoustic signal reaches the maximum at this position.

[0050] Embodiment 2

[0051] like Figure 4 As shown, an embodiment of the present invention provides a detection system, including: three near-infrared lasers 13, an optical fiber circulator 14, a high-speed spectrometer 15, a wide-spectrum light source 16, a computer 17, and the photoacoustic sensor 12 for simultaneous detection of multiple gases as described in Example 1; the computer 17 is internally provided with multiple virtual phase-locked amplifiers 18 based on LabVIEW.

[0052] The operating frequencies corresponding to various gases are set to 7390Hz, 7520Hz, and 7680Hz respectively.

[0053] A variety of gases enter the photoacoustic sensor 12 through the gap of the cantilever microphone 3, and each of the near-infrared lasers 13 injects the excitation light source into the photoacoustic sensor 12 through an excitation optical fiber 5 to generate a photoacoustic effect, causing the cantilever beam 8 to vibrate periodically; the detection light emitted by the wide-spectrum light source 16 passes through the optical fiber circulator 14 and the detection optical fiber 4 in turn and enters the non-resonant cavity 2 in the photoacoustic sensor 12, and the interference light reflected by different gases enters the high-speed spectrometer 15 through the optical fiber circulator 14, and the interference light is demodulated by the white light interference demodulation algorithm in the high-speed spectrometer 15 to obtain a demodulated photoacoustic signal; then, the demodulated photoacoustic signal is processed by a plurality of virtual phase-locked amplifiers 18 based on LabVIEW inside the computer 17, and the intensity of the photoacoustic signal of the various gases is obtained. Since the intensity of the photoacoustic signal is proportional to the gas concentration, the gas concentration at this time can be obtained.

[0054] The present invention provides a photoacoustic sensor and detection system for simultaneous detection of multiple gases. The photoacoustic sensor includes a cylindrical metal shell, a non-resonant cavity, a cantilever microphone, and multiple single-mode optical fibers. The cylindrical metal shell and the cantilever microphone have the same outer diameter of 3.6 mm, and the cantilever microphone is fixed to the top of the cylindrical metal shell. Four circular holes with a diameter of 0.3 mm are provided at the bottom of the cylindrical metal shell for matching the fiber core. The multiple gases to be tested enter and exit the non-resonant cavity through the gap between the cantilever beam and the silica. The present invention can achieve high-sensitivity and long-distance detection of multiple gases at the same time by using a non-resonant cavity and a detection optical fiber, three excitation optical fibers and combining a cantilever microphone. The miniaturized high-sensitivity photoacoustic sensor for simultaneous detection of multiple gases has many characteristics such as simple structure, small size, short response time, low detection limit, low cost, etc., and provides a highly competitive technical solution for high-sensitivity remote leakage monitoring of multiple gases.

[0055] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0056] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A photoacoustic sensor for simultaneous detection of multiple gases, characterized in that: include: A plurality of single-mode optical fibers, a cylindrical metal shell, a non-resonant cavity disposed inside the cylindrical metal shell, and a cantilever beam microphone connected to the top of the cylindrical metal shell; The plurality of single-mode optical fibers include one detection optical fiber and three excitation optical fibers; Four through holes are provided at the bottom of the cylindrical metal shell; wherein one through hole is located at the center of the bottom of the cylindrical metal shell, and the other three through holes are arranged in a circular array on the bottom of the cylindrical metal shell, and the through hole located at the center is provided with the detection optical fiber, and each through hole arranged in the circular array is provided with the excitation optical fiber; The cantilever beam microphone is provided with a rectangular parallelepiped pit; three sides of the bottom surface of the rectangular parallelepiped pit are all gaps to form a cantilever beam, and the bottom surface of the rectangular parallelepiped pit faces the non-resonance cavity; The sizes of the cylindrical metal shell and the non-resonant cavity are in the millimeter level.

2. A photoacoustic sensor for simultaneous detection of multiple gases according to claim 1, characterized in that: The cantilever beam microphone is formed by engraving on a silicon dioxide wafer using MEMS technology; the two long sides and one short side of the bottom surface of the rectangular parallelepiped pit are both gaps.

3. The photoacoustic sensor for simultaneous detection of multiple gases according to claim 1, characterized in that: At the first target size, the resonant frequency of the cantilever beam is 7690 Hz; the first target size is that the length of the cantilever beam is 0.8 mm, the width of the cantilever beam is 0.4 mm, and the thickness of the cantilever beam is 3.5 um.

4. The photoacoustic sensor for simultaneous detection of multiple gases according to claim 3, characterized in that: Under the first target size and the second target size, the sensitivity of the cantilever beam at the first-order resonant frequency reaches 14000 nm / Pa; the second target size is that the length of the non-resonant cavity is 4 mm and the diameter of the non-resonant cavity is 3.2 mm.

5. The photoacoustic sensor for simultaneous detection of multiple gases according to claim 1, characterized in that: The length of the cylindrical metal shell is 6 mm, and the diameter of the cylindrical metal shell is 3.6 mm.

6. The photoacoustic sensor for simultaneous detection of multiple gases according to claim 1, characterized in that: The diameters of the four through holes are all 0.3 mm; Each of the single-mode optical fibers includes a core, a cladding, and a coating, and the diameters of the cladding and the coating are 0.25 mm and 0.9 mm, respectively.

7. The photoacoustic sensor for simultaneous detection of multiple gases according to claim 1, characterized in that: The through hole for placing the detection optical fiber is concentric with the non-resonant cavity, and the three through holes for placing the excitation optical fibers are distributed in a ring array at a position 0.6 mm away from the bottom inner wall of the non-resonant cavity, so as to prevent the laser light source from hitting the inner wall of the non-resonant cavity and maximize the photoacoustic signal.

8. The photoacoustic sensor for simultaneous detection of multiple gases according to claim 1, characterized in that: The distance between one of the detection optical fibers and the cantilever microphone is within 300 nm, and the distance between the three excitation optical fibers and the cantilever microphone is between 3.2 mm and 3.8 mm.

9. A detection system, characterized in that: include: Three near-infrared lasers, an optical fiber circulator, a high-speed spectrometer, a broadband light source, a computer, and a photoacoustic sensor for simultaneous detection of multiple gases as described in any one of claims 1 to 8; the computer is internally provided with multiple virtual lock-in amplifiers based on LabVIEW; A variety of gases enter the photoacoustic sensor through the gap of the cantilever microphone, and each of the near-infrared lasers emits an excitation light source into the photoacoustic sensor through an excitation optical fiber to generate a photoacoustic effect, causing the cantilever beam to vibrate periodically; the detection light emitted by the wide-spectrum light source passes through the optical fiber circulator and the detection optical fiber in turn and is incident on the non-resonant cavity in the photoacoustic sensor, and the interference light reflected by different gases enters the high-speed spectrometer through the optical fiber circulator, and the interference light is demodulated by the white light interferometric demodulation algorithm in the high-speed spectrometer to obtain a demodulated photoacoustic signal; the demodulated photoacoustic signal is processed by a plurality of virtual lock-in amplifiers based on LabVIEW, and the intensity of the photoacoustic signals of the various gases is obtained.

10. The detection system according to claim 9, characterized in that: The sampling frequency of the high-speed spectrometer is 32 kHz.

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