Dual-resonant-cavity coupling type photoacoustic gas sensor capable of telemetering

Abstract

The invention provides a double-resonant-cavity coupling type photoacoustic gas sensor capable of telemetering. Comprising an optical fiber collimator, a left metal shell, a right metal shell, a buffer chamber, a left resonant cavity, a cantilever-beam-based optical fiber sonic sensor, a right resonant cavity, an excitation light beam, a single-mode optical fiber and an air hole. Due to the fact that the excitation optical fiber and the detection optical fiber are located on one side of the photoacoustic cell, the problem that a traditional H-type photoacoustic cell cannot achieve long-distance in-situ measurement of trace gas is solved. According to the scheme, the resonant frequencies of the photoacoustic cell and the cantilever beam type optical fiber acoustic wave sensor are designed at high frequencies and are matched with each other, so that the signal-to-noise ratio of the system can be greatly improved; and the double-resonant-cavity coupling type photoacoustic gas sensor capable of telemetering is good in stability, simple in structure, low in sensitivity, good in signal-to-noise ratio, low in detection limit and capable of being detachably mounted. The invention provides a new thought for the resonant long-distance telemetering type photoacoustic sensor, and has a huge application prospect in the field of photoacoustic spectroscopy.

Description

Technical Field

[0001] The invention belongs to the technical field of photoacoustic spectroscopy and trace gas detection, and relates to a remotely measurable dual-resonance cavity coupled photoacoustic gas sensor. Background Art

[0002] Trace gas detection plays an important role in atmospheric environmental monitoring, disease prevention, aerospace, mine safety and other fields. Laser-based photoacoustic spectroscopy is widely used in trace gas measurement due to its high sensitivity, strong gas selectivity and fast response speed. Recently, due to its small size, non-resonant photoacoustic cells can realize long-distance telemetry of trace gases, making non-resonant photoacoustic cells not only convenient to carry, but also able to quickly monitor changes in trace gas concentrations in real time. However, the noise of non-resonant photoacoustic cells is large, so the gas detection limit is poor. For traditional resonant photoacoustic cells, due to the presence of a buffer chamber, the noise is very low and the gas detection limit is very good. However, the traditional resonant photoacoustic cell must be matched with an acoustic wave sensor and an excitation light source, which results in a large volume of the entire photoacoustic spectroscopy system, making it difficult to achieve high-sensitivity long-distance in-situ detection in places with limited space. Especially for the traditional H-type photoacoustic cell, such as the document X. Mao, P. Zheng, X. Wang, S. Yuan, Breath methane detection based on all-optical photoacoustic spectrometer, Sens. Actuators B 239 (2017) 1257-1260, the largest photoacoustic signal is in the center of the resonant cavity. If a higher sensitivity is required, a small hole must be opened in the center of the resonator so that the photoacoustic signal can be transmitted to the position of the acoustic sensor, and the acoustic sensor is placed in the center of the resonant cavity of the H-type photoacoustic cell. In fact, opening a small hole in the center of the resonant cavity will cause a certain loss of photoacoustic signal. In addition, the excitation fiber and the detection fiber of the traditional H-type photoacoustic cell cannot be placed on the same side, which makes the traditional H-type photoacoustic cell not only increase the probability of fiber damage, but also difficult to achieve long-distance in-situ detection of trace gases.

[0003] In summary, designing a photoacoustic spectroscopic gas sensor that is small in size, highly sensitive, and can perform high-sensitivity and long-distance real-time in-situ monitoring of trace gases has important application value. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a remotely detectable dual-resonant cavity coupled photoacoustic gas sensor. The gas sensor has a small overall volume and can perform high-sensitivity and real-time in-situ monitoring of trace gases at a long distance, providing a new idea for resonant long-distance remote sensing photoacoustic sensors and having great application prospects in the field of photoacoustic spectroscopy.

[0005] The technical solution of the present invention:

[0006] A remotely measurable dual-resonance cavity coupled photoacoustic gas sensor, the main structure of which includes a left metal shell and a right metal shell, between which a cantilever beam-based optical fiber acoustic wave sensor is arranged;

[0007] Inside the left metal shell, a buffer chamber and a left resonant cavity are arranged from left to right;

[0008] Inside the right metal shell, a buffer chamber and a right resonant cavity are arranged from left to right;

[0009] The cantilever-based fiber optic acoustic wave sensor is located at the end of the left resonant cavity, and a small hole is opened to transmit the excitation light and ensure that the gases in the two resonant cavities are connected;

[0010] The optical fiber collimator extends from the left metal shell into the buffer chamber, and the excitation light beam it emits enters the right resonant cavity through the small hole on the cantilever beam optical fiber acoustic wave sensor; the buffer chamber inside the metal shell on the left side of the buffer chamber is provided with air holes for gas exchange; the gas to be measured diffuses into the entire cavity through the air holes, and the excitation light is emitted into the buffer chamber, the left resonant cavity and the right resonant cavity through the optical fiber collimator and the small hole, and generates a photoacoustic effect with the gas to be measured, thereby causing the vibration of the cantilever beam optical fiber acoustic wave sensor, and the single-mode optical fiber located inside the cavity causes the vibration change of the cantilever beam to be obtained, thereby inferring the concentration of the gas to be measured.

[0011] The left metal shell is connected to the right metal shell through threads;

[0012] The cantilever beam-based optical fiber acoustic wave sensor is located between the left resonant cavity and the right resonant cavity, which changes the boundary conditions of the two resonant cavities, thereby making the sound pressure at the end of the right resonant cavity the maximum, and the sound pressure at the end of the left resonant cavity is less than the sound pressure at the end of the right resonant cavity.

[0013] The radius and length of the buffer chamber are 2.5 mm and 5 mm, respectively.

[0014] The radius and length of the left resonant cavity and the right resonant cavity are 0.85 mm and 11 mm respectively. Therefore, the volume and resonant frequency of the designed photoacoustic sensor are 246 cubic millimeters and 15400 Hz respectively.

[0015] The length, width and thickness of the cantilever beam are 0.6 mm, 0.3 mm and 4 μm, and the resonant frequency based on this size is 15390 Hz, which can match the resonant frequency of the designed photoacoustic sensor to achieve a double resonance effect.

[0016] The internal cavity of the cantilever beam optical fiber acoustic wave sensor is the entire photoacoustic pool, which will greatly improve the sensitivity of the cantilever beam acoustic wave sensor.

[0017] The diameter of the single-mode optical fiber is 0.125 microns, which size will not weaken the size of the photoacoustic signal formed in the resonant photoacoustic cell. In addition, the length of the single-mode optical fiber used is 3 kilometers.

[0018] The distance between the end of the single-mode optical fiber and the cantilever beam is controlled to be about 0.5 mm.

[0019] The left resonant cavity and the right resonant cavity are connected by threads, so the photoacoustic cell is detachable.

[0020] Beneficial effects of the present invention: The present invention provides a remotely detectable dual-resonance cavity coupled photoacoustic gas sensor. Since the excitation optical fiber and the detection optical fiber are located on one side of the photoacoustic cell, this solution solves the problem that the traditional H-type photoacoustic cell cannot realize remote in-situ measurement of trace gases. The internal cavity of the cantilever beam fiber optic acoustic wave sensor is the entire photoacoustic cell, which will greatly improve the sensitivity of the cantilever beam acoustic wave sensor, and thus improve the detection sensitivity of gas detection. This solution designs the resonant frequencies of the photoacoustic cell and the cantilever beam fiber optic acoustic wave sensor to be high frequency and match each other, which can greatly improve the signal-to-noise ratio of the system. The remotely detectable dual-resonance cavity coupled photoacoustic gas sensor has good stability, simple structure, low sensitivity, good signal-to-noise ratio, low detection limit, and detachable installation. The present invention provides a new idea for a resonant long-distance telemetry photoacoustic sensor, and has great application prospects in the field of photoacoustic spectroscopy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The invention relates to a double-resonance cavity coupled photoacoustic gas sensor capable of remote measurement.

[0022] In the figure: 1 optical fiber collimator; 2 left metal shell; 3 buffer chamber; 4 left resonant cavity; 5 cantilever beam-based optical fiber acoustic wave sensor; 6 right metal shell; 7 right resonant cavity; 8 single-mode optical fiber; 9 excitation beam; 10 air hole. DETAILED DESCRIPTION

[0023] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0024] Figure 1 Schematic diagram of a dual-resonance cavity coupled photoacoustic gas sensor capable of remote measurement according to the present invention. Figure 1As shown, the telemetric dual-resonance cavity coupled photoacoustic gas sensor provided by the embodiment of the present invention comprises a fiber collimator 1, a left metal shell 2, a buffer chamber 3, a left resonant cavity 4, a cantilever beam fiber acoustic wave sensor 5, a right metal shell 6, a right resonant cavity 7, a single-mode optical fiber 8, an excitation light beam 9, and an air hole 10. The buffer chamber 3 and the left resonant cavity 4 are arranged inside the left metal shell 2. The buffer chamber 3 and the right resonant cavity 7 are arranged inside the right metal shell 6, and the left and right metal shells are connected by threads; the cantilever beam fiber acoustic wave sensor 5 is located at the end 4 of the left resonant cavity, and there is a small hole on one side that can transmit the excitation light and ensure that the gases in the two resonant cavities are connected; the excitation light beam 9 emitted by the fiber collimator 1 enters the right resonant cavity 7 through a small hole on one side of the cantilever beam microphone; the air hole is used for gas exchange. The gas to be measured diffuses into the entire cavity through the air hole 10, and the excitation light 9 is emitted into the buffer chamber 3, the left resonant cavity 4 and the right resonant cavity 7 through the collimator 1 and the small hole, and generates a photoacoustic effect with the gas to be measured, thereby causing the cantilever beam type optical fiber acoustic wave sensor 5 to vibrate. The single-mode optical fiber 8 located inside the photoacoustic cavity feeds back the vibration change of the cantilever beam to the computer, thereby calculating the concentration of the gas to be measured.

[0025] Experimental Example 1:

[0026] The traditional H-type resonant photoacoustic gas sensor can refer to the literature X. Mao, P. Zheng, X. Wang, S. Yuan, Breath methane detection based on all-optical photoacoustic spectrometer, Sens. Actuators B 239 (2017) 1257-1260, in which the volume of the photoacoustic cavity reaches 205 cubic centimeters, the response time is very long, and it requires artificial gas collection, which makes it impossible to achieve long-distance telemetry of trace gases. In addition, a small hole needs to be opened in the center of the resonant cavity of the H-type photoacoustic cell to transmit the photoacoustic signal to the acoustic wave sensor position, but this will cause a certain loss of the photoacoustic signal.

[0027] Experimental Example 2:

[0028] The newly proposed remotely detectable dual-resonance cavity coupled photoacoustic gas sensor has a photoacoustic cavity volume of only 246 cubic millimeters, which is nearly 3 orders of magnitude lower than that of the reference. Therefore, the response time is about 40 seconds, which is sufficient to measure diffused gases. The sensor proposed in this patent does not require artificial gas sampling, and there is no need to open a hole in the center of the resonant cavity, which can achieve high-sensitivity long-distance remote sensing of leaked gases.

[0029] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A remotely detectable dual-resonance cavity coupled photoacoustic gas sensor, characterized in that: The main structure of the remotely detectable dual-resonance cavity coupled photoacoustic gas sensor includes a left metal shell and a right metal shell, between which a cantilever beam-based optical fiber acoustic wave sensor is arranged; Inside the left metal shell, a buffer chamber and a left resonant cavity are arranged from left to right; Inside the right metal shell, a buffer chamber and a right resonant cavity are arranged from left to right; The cantilever-based fiber optic acoustic wave sensor is located at the end of the left resonant cavity, and a small hole is opened to transmit the excitation light and ensure that the gases in the two resonant cavities are connected; The optical fiber collimator extends from the left metal shell into the buffer chamber, and the excitation light beam it emits enters the right resonant cavity through the small hole on the cantilever beam optical fiber acoustic wave sensor; the buffer chamber inside the metal shell on the left side of the buffer chamber is provided with air holes for gas exchange; the gas to be measured diffuses into the entire cavity through the air holes, and the excitation light is emitted into the buffer chamber, the left resonant cavity and the right resonant cavity through the optical fiber collimator and the small hole, and generates a photoacoustic effect with the gas to be measured, thereby causing the vibration of the cantilever beam optical fiber acoustic wave sensor, and the single-mode optical fiber located inside the cavity causes the vibration change of the cantilever beam to be obtained, thereby inferring the concentration of the gas to be measured.

2. The remotely detectable dual-resonance cavity coupled photoacoustic gas sensor according to claim 1, characterized in that: The left metal shell and the right metal shell are connected through threads.

3. The remotely detectable dual-resonance cavity coupled photoacoustic gas sensor according to claim 1, characterized in that: The radius and length of the buffer chamber are 2.5 mm and 5 mm, respectively.

4. The remotely detectable dual-resonance cavity coupled photoacoustic gas sensor according to claim 1, characterized in that: The radius and length of the left resonant cavity and the right resonant cavity are both 0.85 mm and 11 mm.

5. The remotely detectable dual-resonance cavity coupled photoacoustic gas sensor according to claim 1, characterized in that: The length, width and thickness of the cantilever beam are 0.6 mm, 0.3 mm and 4 μm.

6. The remotely detectable dual-resonance cavity coupled photoacoustic gas sensor according to claim 1, characterized in that: The diameter of single-mode optical fiber is 0.125 microns.

7. The remotely detectable dual-resonance cavity coupled photoacoustic gas sensor according to claim 1, characterized in that: The distance between the end of the single-mode optical fiber and the cantilever beam is controlled at 0.5 mm.

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