CN110346302B

CN110346302B - Diaphragm resonance type gas sensor based on poly-chloro-p-xylene and detection system

Info

Publication number: CN110346302B
Application number: CN201910657619.2A
Authority: CN
Inventors: 宫振峰; 陈烨伟; 高田力; 于清旭
Original assignee: Dalian University of Technology
Current assignee: Dalian University of Technology
Priority date: 2019-07-20
Filing date: 2019-07-20
Publication date: 2021-08-10
Anticipated expiration: 2039-07-20
Also published as: CN110346302A

Abstract

The invention belongs to the technical field of optical fiber sensing and trace gas detection, and discloses a diaphragm resonance type gas sensor and a detection system based on poly-chloro-p-xylene. The gas sensor adopts the structure of an F-P interferometer, and an F-P cavity of the F-P interferometer is also a non-resonant photoacoustic cell of a photoacoustic system. The Parylene-C has the characteristics of low Young modulus and high elongation at break, and the Parylene-C film prepared by the vacuum vapor polymerization deposition method has the characteristics of high deposition property and high deposition uniformity, so that the Parylene-C film prepared by the vacuum vapor polymerization deposition method can have the characteristics of large radius and thin thickness at the same time. The natural resonant frequency of the F-P interferometer is proportional to the thickness of the membrane and inversely proportional to the square of the radius of the membrane, and can therefore be as low as a few tens of hertz. The invention provides a new technical means for high-sensitivity remote gas telemetering in a narrow space.

Description

Diaphragm resonance type gas sensor based on poly-chloro-p-xylene and detection system

Technical Field

The invention belongs to the technical field of optical fiber sensing and trace gas detection, and relates to a diaphragm resonance type gas sensor and a detection system based on poly-chloro-p-xylene.

Background

Trace gas detection has wide application requirements in the fields of atmospheric environment detection, industrial process control and life science. With the development of laser technology, spectroscopic technology has become a gas detection method with the advantages of high sensitivity, fast response time, strong selectivity and the like. The photoacoustic spectrometry detection technology is a spectral calorimetric technology for directly measuring the heat energy generated by a substance due to the absorption of light energy. In the closed photoacoustic cell, gas molecules are excited to a high-energy state by absorbing light with specific wavelength, the high-energy state molecules collide with each other to enable part of the excited molecules to return to a ground state through radiationless transition, the absorbed light energy is converted into heat energy, and the gas in the cavity is heated and expanded to generate sound waves. The gas concentration is measured by converting the acoustic wave signal into an electric signal through a microphone, such as a microphone, a fiber optic acoustic wave sensor, a quartz tuning fork and the like.

Because the generation field of the acoustic wave is positioned in the closed photoacoustic cell, and the traditional photoacoustic cell is matched with the microphone and the excitation light source, the whole photoacoustic spectroscopy system has larger volume and is difficult to realize remote measurement. A miniaturized photoacoustic spectrometry gas detection system is designed according to Cao Y, Jin W, Ho H L, et al, miniature fiber-tip photoacoustic spectrometer for trace gas detection [ J ]. Optics letters,2013,38(4): 434-436. the F-P cavity of a fiber Fabry-Perot (F-P) acoustic wave sensor is used as a non-resonant photoacoustic cell of the photoacoustic system, a photoacoustic excitation light source and a fiber F-P acoustic wave sensor detection light source are coupled into a fiber, and the characteristics of long transmission distance and telemetability of the fiber acoustic wave sensor are utilized to realize miniaturization and long distance telemetering of the photoacoustic spectrometry gas detection system. Since the magnitude of photoacoustic signal in non-resonant photoacoustic system is approximately inversely proportional to the modulation frequency, in order to increase the magnitude of photoacoustic signal, the modulation frequency of the excitation light source in the system is set to 200Hz, but the resonant frequency of the sensitive diaphragm of the F-P acoustic wave sensor in the system is much larger than the modulation frequency of the excitation light source, resulting in the low sensitivity of the fiber-optic F-P acoustic wave sensor at the modulation frequency, and the gas detection sensitivity of the system is different from that of the conventional photoacoustic spectroscopy system by several orders of magnitude. In conclusion, the miniaturized photoacoustic spectrometry gas sensor which can realize remote measurement and has high sensitivity has important application value.

Disclosure of Invention

The invention aims to provide a diaphragm resonance type small gas sensor and a detection system based on poly-p-xylene monochloride, aims to solve the problem that the long-distance telemetering and high-sensitivity detection of the traditional photoacoustic spectroscopy gas detection system cannot be realized simultaneously, and expands a larger space for the application of photoacoustic spectroscopy detection technology in the field of long-distance telemetering of trace gas.

The technical scheme of the invention is as follows:

a diaphragm resonance type gas sensor based on poly-chloro-P-xylene comprises a single mode fiber 1, an F-P cavity 2, a poly-chloro-P-xylene (Parylene-C) membrane 3, a vent hole 4 and a shell 5; the diaphragm resonance type gas sensor adopts the structure of an F-P interferometer, and an F-P cavity 2 of the F-P interferometer is also a non-resonance photoacoustic cell of a photoacoustic system; the Parylene-C has lower Young's modulus and larger elongation at break, and the Parylene-C film 3 prepared by the vacuum vapor polymerization deposition method has the characteristics of strong coating property and good deposition uniformity, so that the Parylene-C film 3 prepared by the vacuum vapor polymerization deposition method can have the characteristics of large radius and thin thickness at the same time. Whereas the natural resonant frequency of the F-P interferometer is proportional to the thickness of the membrane and inversely proportional to the square of the membrane radius, the resonant frequency of F-P interferometers based on Parylene-C films 3 can be as low as a few tens of hertz. After the gas to be measured is filled in the F-P cavity 2 through the vent hole 4, the modulation frequency of the excitation laser 7 is set at the resonance frequency of the F-P interferometer, at the moment, the optical fiber gas sensor works in a resonance mode state, the generated photoacoustic signal can reach the maximum value, and the diaphragm resonance type photoacoustic gas sensing system is realized.

A gas detection system based on the gas sensor. Coupling a detection laser 6 and an excitation laser 7 into an optical fiber through a 1 x 2 optical fiber coupler 8, wherein the central wavelength of one laser is superposed with the absorption spectral line of the gas to be detected to serve as the excitation laser 7 of the photoacoustic signal; the other laser is used as a detection laser 6 of the fiber F-P interferometer. When laser light emitted from the excitation laser 7 is coupled from an optical fiber into the F-P cavity 2 of the gas sensor 10 through the circulator 9, an acoustic wave signal is generated in the F-P cavity 2 due to the photoacoustic effect, causing periodic vibration of the Parylene-C film 3. The laser emitted by the detection laser 6 is respectively reflected on the end face of the optical fiber 1 and the surface of the Parylene-C film 3, two beams of reflected light are interfered, the interfered light is emitted from the other port of the circulator 9 and received by the photoelectric detector 12 through the tunable band-pass filter 11, and the tunable band-pass filter 11 is used for filtering the reflected light of the excitation laser 7 and preventing the reflected light from interfering with detection signals. The photodetector 12 converts the detected optical signal into an electrical signal, and performs second harmonic demodulation through the phase-locked amplification module 13. The sawtooth wave signal generated by the industrial personal computer 14 and the sine signal generated by the phase-locked amplification module 13 are superposed through the adder 15, and the photoacoustic excitation laser 7 is driven together. The industrial personal computer 14 realizes the stability of the working point by adjusting the wavelength of the detection laser 6 of the F-P interferometer.

The diameter of the sensitive diaphragm Parylene-C film 3 of the optical fiber F-P acoustic wave sensor is 9mm, the thickness is 800nm, and the resonant frequency of the gas sensor 10 is about 30 Hz.

The modulation frequency of the excitation laser 7 is set to 30Hz, and the gas sensor 10 works in a resonance state, so that a diaphragm resonance type gas sensor is realized.

The invention has the advantages that: the method is characterized in that a Parylene-C material is used as a sensitive membrane of the F-P interferometer, and the resonance frequency of the Parylene-C membrane is matched with the modulation frequency of an excitation light source by controlling the coating thickness of the Parylene-C membrane, so that the resonance enhancement amplification of photoacoustic signals is realized. The F-P cavity of the F-P interferometer is used as a micro non-resonant photoacoustic cell, so that the volume of the sensor is reduced, and meanwhile, the laser emitted by the excitation laser and the detection laser is coupled into one optical fiber, so that the structure of the system is simplified. The invention provides a new technical means for high-sensitivity remote gas telemetering in a narrow space.

Drawings

FIG. 1 is a schematic diagram of a Parylene-C based diaphragm resonant gas sensor.

Fig. 2 is a schematic diagram of a detection system based on the diaphragm resonant gas sensor.

FIG. 3 is a frequency response spectrum of a Parylene-C based diaphragm resonant gas sensor.

In the figure: 1, a single mode optical fiber; a 2F-P cavity; 3Parylene-C film; 4, ventilating holes; 5, a shell; 6, detecting a laser; 7 exciting the laser; 81 × 2 couplers; 9 a circulator; 10 a gas sensor; 11 a tunable band-pass filter; 12 a photodetector; 13 a phase-locked amplification module; 14 industrial personal computers; 15 an adder.

Detailed Description

The following further describes a specific embodiment of the present invention with reference to the drawings and technical solutions.

The invention provides a diaphragm resonance type gas sensor based on Parylene-C shown in figure 1, which comprises a single mode optical fiber 1, an F-P cavity 2, a Parylene-C membrane 3, a vent hole 4 and a shell 5. The F-P cavity 2 is not only the cavity of the F-P interferometer, but also a micro non-resonant photoacoustic cell for generating photoacoustic signals. The gas to be measured enters the F-P cavity 2 through the vent hole 4, and the periodic vibration of the Parylene-C film 3 is caused by a photoacoustic signal generated by the photoacoustic effect of the gas. The diameter of the Parylene-C film 3 is 9mm and the thickness is 800nm, at which the resonance frequency of the F-P interferometer is about 30 Hz.

Fig. 2 shows a schematic diagram of a detection system based on the diaphragm resonant gas sensor. Laser light emitted by a detection laser 6 of the fiber F-P interferometer and an excitation laser 7 of the photoacoustic signal passes through a 1X 2 fiber coupler 8 and a fiber circulator 9 and is incident into a miniaturized gas sensor 10. The modulation frequency of the excitation laser 7 is adjusted to be 30Hz, as the central wavelength of the excitation laser 7 is overlapped with the absorption spectral line of the gas to be detected, the gas to be detected absorbs laser light and transits to a high energy level, and then the gas to be detected releases heat in the process of radiationless transition to a ground state to expand surrounding air, so that a photoacoustic signal is generated to cause periodic vibration of the Parylene-C membrane 3, the vibration frequency is equal to the modulation frequency of the excitation laser 7, the vibration amplitude is in direct proportion to the concentration of the gas, and at the moment, the gas sensor 10 just works in a resonance state to form a diaphragm resonance type gas sensing system. Laser emitted by a detection laser 6 of the optical fiber F-P interferometer is reflected on the end face of the single-mode optical fiber 1 and the surface of the Parylene-C film 3 respectively, two beams of reflected light form interference light, the interference light enters a photoelectric detector 12 through a circulator 9 and a tunable band-pass filter 11 and is converted into an electric signal, and the tunable band-pass filter 11 is used for filtering the reflected light of the excitation laser 7 and preventing the interference on the optical fiber F-P interferometer. The phase-locked amplification module 13 performs second harmonic demodulation on the signal received by the photodetector 12, thereby realizing measurement of the gas concentration. The detection laser 6 is controlled by the industrial personal computer 14, and the stability of the working point of the F-P interferometer is realized by adjusting the wavelength of the detection laser 6. The sine signal generated by the phase-locked amplification module 13 and the sawtooth wave signal generated by the industrial personal computer 14 are superposed by the adder 15 to drive the excitation laser 7 together.

FIG. 3 shows the frequency response spectrum of a diaphragm resonant gas sensor based on Parylene-C3. The effective diameter of the Parylene-C membrane 3 is 9mm and the thickness is 800nm, the resonance frequency of the gas sensor is about 30 Hz.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The diaphragm resonance type gas sensor based on the poly-P-xylene monochloride is characterized by comprising a single mode fiber (1), an F-P cavity (2), a Parylene-C membrane (3), a vent hole (4) and a shell (5); the diaphragm resonance type gas sensor (10) adopts an F-P interferometer structure, and an F-P cavity (2) is a cavity of the F-P interferometer and is also a miniature non-resonance type photoacoustic cell and is used for generating photoacoustic signals; the F-P cavity (2) is provided with a vent hole (4); the effective diameter of the Parylene-C film (3) is 9mm, the thickness is 800nm, and the first-order resonance frequency of the gas sensor is 30 Hz; after the gas to be detected is filled in the F-P cavity (2) through the vent hole (4), the modulation frequency of the excitation laser (7) is set at 30Hz, at the moment, the gas sensor (10) works in a resonance mode state, the generated photoacoustic signal reaches a maximum value, and a diaphragm resonance type photoacoustic gas sensing system is realized.

2. A gas detection system based on a diaphragm resonance type gas sensor is characterized in that a detection laser (6) and an excitation laser (7) are coupled into an optical fiber through a 1 x 2 optical fiber coupler (8), wherein the central wavelength of the excitation laser (7) is coincident with the absorption spectrum line of the gas to be detected; when laser light emitted by an excitation laser (7) is coupled into an F-P cavity (2) of a gas sensor (10) from an optical fiber through a circulator (9), an acoustic wave signal is generated in the F-P cavity (2) due to a photoacoustic effect, and periodic vibration of a Parylene-C film (3) is caused; laser emitted by a detection laser (6) is respectively reflected on the end face of a single-mode optical fiber (1) and the surface of a Parylene-C film (3), two beams of reflected light are subjected to interference, the interference light is emitted from the other port of a circulator (9) and received by a photoelectric detector (12) through a tunable band-pass filter (11), and the tunable band-pass filter (11) is used for filtering the reflected light of an excitation laser (7) and preventing the reflected light from interfering detection signals; the photoelectric detector (12) converts the detected optical signal into an electric signal and realizes second harmonic demodulation through a phase-locked amplification module (13); a sawtooth wave signal generated by the industrial personal computer (14) and a sine signal generated by the phase-locked amplification module (13) are superposed through the adder (15) to drive the photoacoustic excitation laser (7) together; the industrial personal computer (14) realizes the stability of the working point by adjusting the wavelength of the detection laser (6).

3. The diaphragm resonance type gas sensor-based gas detection system according to claim 2, wherein the modulation frequency of the excitation laser (7) is set to 30Hz, and the gas sensor (10) is operated in a resonance state, so that the diaphragm resonance type gas sensor is realized.