阅读说明：本技术 一种多浓度区间光纤氢气传感器 (Multi-concentration interval optical fiber hydrogen sensor ) 是由 方佳豪 沈常宇 张崇 于 2019-11-06 设计创作，主要内容包括：本发明公开了一种多浓度区间光纤氢气传感器,由光源,测试气室,传感器,氢气发生源,氮气发生源,流量计,光谱仪构成。将单模光纤错位熔接形成马赫曾德干涉结构后,利用飞秒加工技术,在结构输入端写入FBG,镀钯银复合膜后,将所制成的光纤作为传感器的氢敏元件,由于Pd在与氢气反应后,会发生膨胀导致应力发生改变,从而改变光纤的光学参数,观测透射光谱的变化,即可监测实时氢气浓度变化。由于利用FBG与M-Z的级联,可以弥补单个结构对于多个区间的线性度不好问题,实现多浓度区间的监测。(The invention discloses a multi-concentration interval optical fiber hydrogen sensor which comprises a light source, a test gas chamber, a sensor, a hydrogen generation source, a nitrogen generation source, a flowmeter and a spectrometer. After a single-mode optical fiber is welded in a staggered mode to form a Mach-Zehnder interference structure, FBGs are written into the input end of the structure by utilizing a femtosecond processing technology, a palladium-silver composite film is plated, the manufactured optical fiber is used as a hydrogen sensitive element of a sensor, and stress changes due to the fact that Pd expands after reacting with hydrogen, so that optical parameters of the optical fiber are changed, changes of a transmission spectrum are observed, and real-time hydrogen concentration changes can be monitored. Due to the fact that the cascade connection of the FBG and the M-Z is utilized, the problem that the linearity of a single structure to a plurality of intervals is poor can be solved, and monitoring of the plurality of concentration intervals is achieved.)

1. A multi-concentration interval optical fiber hydrogen sensor is composed of a light source (1), a test gas chamber (2), a sensor (3), a hydrogen generating source (4), a nitrogen generating source (5), a flowmeter (6) and a spectrometer (7); the method is characterized in that a sensor (3) is formed by cascading an FBG structure (9) plated with a palladium-silver alloy nano film (8) and an M-Z structure (10) formed by a single-mode optical fiber, the sensor (3) is placed in a test gas chamber (2), a nitrogen generating source (5) and a hydrogen generating source (4) are controlled by a computer to generate hydrogen with different concentrations, the gas concentration change in the test gas chamber (2) is observed in real time through a flowmeter (6), the change of the sensor (3) is checked through a spectrometer (7), the current hydrogen concentration value can be detected through measuring the change of a spectrum in real time, the characteristic wave band 1325nm of M-Z is used for observing hydrogen with high concentration (more than 4%), the drift of the characteristic peak (1550nm) of the FBG is observed for hydrogen with low concentration (less than 4%), the cascade part of the FBG and the M-Z on the sensor (3) needs to be preprocessed before film coating, cleaning the medical absorbent cotton by using absolute ethyl alcohol through ultrasonic cleaning, putting the medical absorbent cotton into a clamp, and respectively using a volume ratio of 20mm to 5mm as 4: 1, performing hydrogen-sensitive film deposition on the palladium and silver substrate by adopting direct-current magnetron sputtering, and sputtering for about 50 seconds under the sputtering voltage of 800V and the sputtering current of 0.54A; forming the palladium-silver alloy nano-film (8).

Technical Field

The invention belongs to the field of hydrogen sensing, and particularly relates to a multi-concentration interval optical fiber hydrogen sensor.

Background

At present, the world faces serious problems of energy source deficiency, global warming and the like. The traditional non-renewable energy is vigorously developed at present, and faces the problem of exhaustion, and the traditional non-renewable energy causes pollution such as carbon emission, sulfur emission and the like, and aggravates global warming and environmental deterioration. As a renewable energy source, the hydrogen has the advantages of large reserve, zero pollution and zero emission, and is worthy of development. However, there is a technical problem of hydrogen storage, and at the same time, when the concentration of hydrogen in the air reaches 4.65%, explosion will occur when exposed to fire, so it is necessary to develop a hydrogen sensor capable of real-time and rapid detection.

Palladium metal is a metal with excellent hydrogen storage capacity, is a common hydrogen sensitive material, is often used for manufacturing a sensor, and pure palladium has the problems of hydrogen absorption alpha-beta phase change, hydrogen embrittlement and the like.

Disclosure of Invention

The method aims at the problems that the existing optical fiber hydrogen sensor is only suitable for a certain concentration interval, and the detection result of a spectrometer is very inaccurate and the linearity is greatly reduced after the concentration exceeds the range. The invention adopts a structure of cascade connection of FBG and M-Z to solve the problem of narrow concentration interval. The change of the hydrogen concentration of more than 4% can be monitored through the change of the M-Z characteristic wave band, and the change of the hydrogen concentration of less than 4% can be detected by detecting the FBG characteristic wave band. Therefore, the wide detection of each concentration interval can be completed by using one sensor.

The invention is realized by the following technical scheme: a multi-concentration interval optical fiber hydrogen sensor is composed of a light source (1), a test gas chamber (2), a sensor (3), a hydrogen generating source (4), a nitrogen generating source (5), a flowmeter (6) and a spectrometer (7); the sensor is characterized in that the sensor (3) is formed by cascading an FBG structure (9) plated with a palladium-silver alloy nano film (8) and an M-Z structure (10) formed by single-mode optical fibers. The input end of the sensor (2) is connected with the light source (1), the output end of the sensor is connected with the spectrometer (7), the sensor (3) is placed in the test air chamber (2), the nitrogen generating source (5) and the hydrogen generating source (4) are controlled by the computer to generate hydrogen with different concentrations, the gas concentration change in the test air chamber (2) is observed in real time through the flowmeter (6), the change of the sensor (3) is checked by utilizing the spectrometer (7), and the current hydrogen concentration value can be detected by measuring the change of the spectrum in real time. The characteristic wave band 1325nm of M-Z is used for observing high-concentration (more than 4%) hydrogen, and the drift of the characteristic peak (1550nm) of the FBG is observed for low-concentration (less than 4%) hydrogen.

The palladium-silver alloy nano film (8) on the sensor (3) needs to pretreat the optical fiber before film coating, is cleaned by absolute ethyl alcohol and then cleaned by medical absorbent cotton and then placed in a clamp, and the volume ratio of the widths of the palladium-silver alloy nano film to the widths of the palladium-silver alloy nano film (8) is 4: 1, performing hydrogen-sensitive film deposition on the palladium and silver substrate by adopting direct-current magnetron sputtering, and sputtering for about 50 seconds under the sputtering voltage of 800V and the sputtering current of 0.54A; forming the palladium-silver alloy nano-film (8).

The working principle of the invention is as follows: when light from the light source (1) is input to the sensor (3) through the optical fiber, a specific spectrum is generated due to the FBG and the M-Z structure. The palladium-silver alloy nano film (8) on the sensor (3) is a material which is easy to combine with hydrogen, and palladium and hydrogen can be combined

The reaction produces metal hydrides that cause changes in the refractive index and stress and other parameters of the fiber surface, and thus a corresponding change in the spectrum. The interference principle of M-Z structure can be written as

ΔnL＝2(n_{Coating film}-n_{Fiber core})d+(n_{Cavity body}-n_{Fiber core})(L-2d)

Wherein d is the thickness of the coating film. When the hydrogen concentration is changed, the refractive index and the thickness of the coating film are changed, so that the light intensity of transmitted light is influenced, and the change of the transmission spectrum at 1325nm can be observed so as to detect the change of high-concentration hydrogen. At low hydrogen concentrations, the spectral variation of the M-Z structure is extremely small, so the center wavelength (1550nm) of the FBG is chosen as the observation band. The center wavelength of an FBG can be expressed as

λ_B＝2n_effΛ

Wherein n is_effThe effective refractive index of the fiber core, and lambda is the period of the grating, and the wavelength offset expression is as follows because the coating film can change the surface stress after the hydrogen absorption reaction

Δλ_B＝λ_B(1-p_e)ε

p_eIs the material elastic-optical coefficient, epsilon is the surface tensile stress, and surface tension in the low concentration rangeThe change of the stress and the change of the hydrogen concentration have better linearity, so the change of the hydrogen concentration can be detected by observing the offset of the central wavelength of the FBG.

The invention has the beneficial effects that: the palladium-silver alloy is used for replacing simple substance palladium as a coating material, so that the hydrogen embrittlement problem and the alpha-beta phase change problem during palladium hydrogenation are effectively improved. Meanwhile, the cascade connection of the FBG and the M-Z structure is utilized, so that the effective linear detection interval is expanded, and the method is not limited to single low-concentration or high-concentration detection. The detection range of the sensor is enlarged, and the detection speed and sensitivity of the improved coating material can be improved.

Drawings

Fig. 1 is a schematic diagram of a multi-concentration-interval optical fiber hydrogen sensor testing system.

FIG. 2 is a schematic diagram of a palladium-silver alloy film coating method.

Detailed Description

As shown in figure 1, the multi-concentration interval optical fiber hydrogen sensor consists of a light source (1), a test gas chamber (2), a sensor (3), a hydrogen generating source (4), a nitrogen generating source (5), a flowmeter (6) and a spectrometer (7); the sensor is characterized in that the sensor (3) is formed by cascading an FBG structure (9) plated with a palladium-silver alloy nano film (8) and an M-Z structure (10) formed by single-mode optical fibers. The method comprises the steps of placing a sensor (3) in a test air chamber (2), controlling a nitrogen generating source (5) and a hydrogen generating source (4) to generate hydrogen with different concentrations through a computer, observing the change of the gas concentration in the test air chamber (2) in real time through a flowmeter (6), checking the change of the sensor (3) through a spectrometer (7), and measuring the change of a spectrum in real time to detect the current hydrogen concentration value. The characteristic wave band 1325nm of M-Z is used for observing high-concentration (more than 4%) hydrogen, and the drift of the characteristic peak (1550nm) of the FBG is observed for low-concentration (less than 4%) hydrogen. The FBG and the M-Z cascade part on the sensor (3) need to be pretreated before film coating, are cleaned by using medical absorbent cotton after being cleaned by absolute ethyl alcohol ultrasonic waves, are placed into a clamp, and are respectively cleaned by using a volume ratio of 20mm to 5mm, namely 4: 1, performing hydrogen-sensitive film deposition on the palladium and silver substrate by adopting direct-current magnetron sputtering, and sputtering for about 50 seconds under the sputtering voltage of 800V and the sputtering current of 0.54A; forming the palladium-silver alloy nano-film (8).

A hydrogen concentration determination method of a multi-concentration interval optical fiber hydrogen sensor comprises the following steps: after nitrogen with the concentration of 100% is introduced into the test air chamber (2) to exhaust air, the bottom of the sensor (3) is heated, and the spectrum when the current hydrogen concentration is 0 is observed as reference. After low-concentration (0-4%) hydrogen is introduced, the M-Z structure has extremely low sensitivity to the change of the concentration of the hydrogen with the concentration, so that the characteristic wave band of the FBG is selected and observed, the FBG wave band selects a Bragg wave peak at 1550nm, the sensitivity to the change of the concentration of the hydrogen is high, and a good linear interval is formed between 0.1% and 4%. And then after introducing high-concentration hydrogen (more than 5 percent), observing the FBG wave band, and finding that the change of the Bragg wave peak has no better linearity and the change of the M-Z characteristic wave band 1325nm has good linearity relative to the low-concentration hydrogen, so that the change of the high-concentration hydrogen can be detected in real time by observing the M-Z characteristic wave band.