基于铝—聚酰亚胺薄膜的光纤麦克风及其应用研究

发布时间：2018-06-28 00:42

本文选题：低相干干涉 + 光纤麦克风　；参考：《安徽大学》2017年硕士论文

【摘要】：随着光纤传感技术的进步与发展,相比于电学麦克风,光纤麦克风在微纳信号探测、光声光谱测量等领域具有更广的应用前景。其中,干涉型光纤麦克风因其具有结构轻巧、灵敏度高、抗电磁干扰等优点,吸引了诸多研究人员的关注。在外腔干涉结构的光纤麦克风系统中,薄膜的性能及其制备工艺非常重要,对薄膜振动幅值的定量测量可直接反映其灵敏度的大小。本文对基于高灵敏度薄膜的光纤传感探头进行了研究,结合可实现物理量绝对测量的低相干光纤微分干涉仪,对薄膜探头的灵敏度进行了高精度测量,并将其应用于光声光谱气体浓度定量标定及气体泄漏声信号特征谱分析中。首先,我们采用MEMS等离子体硅刻蚀方法制备大尺寸(直径3.1mm)的铝-聚酰亚胺复合薄膜。该制备方法可在一定程度上释放膜内应力,提高薄膜表面平整度;通过稀释聚酰胺酸浓度,使膜的厚度低于500nm。复合薄膜的铝层在刻蚀过程中可保护聚酰亚胺不被破坏,同时提高膜整体的光反射率;聚酰亚胺的弹性性能好,且其具有的高强度特性可保证复合薄膜整体的结构强度。其次,对基于铝-聚酰亚胺薄膜探头进行了实验测量。由于低相干微分干涉测量可实现非接触式绝对幅值的振动测量,我们将其与铝-聚酰亚胺薄膜探头组合成低相干微分干涉光纤麦克风系统。该系统可以实现对膜振动幅值绝对位移量的测量,由此直接得出薄膜探头的声压灵敏度。实验结果表明:系统的线性响应度良好;在频率响应上,系统在1KHz至5KHz频率段声压灵敏度保持稳定,平均为120nm/Pa,其最小可探测声压为53uPa;铝-聚酰亚胺薄膜的结构稳定性好,其性能在四个月时间内保持不变;具有良好的温度稳定性,温度的上升对其灵敏度产生微弱的负影响,影响幅度最大为9.3%。最后,基于铝-聚酰亚胺膜的光纤麦克风,我们分别开展了光纤光声光谱测量和气体泄漏检测的应用研究。本文对光纤光声光谱测量系统进行了模块化设计,包括可调谐激发光模块,开放式微腔光声池和低相干微分干涉麦克风模块,并对每个模块进行实验验证,之后对整个系统进行实验。实验结果表明:开放式微腔光声池的谐振频率为3KHz,可产生最大光声信号为2.3mPa;相比传统电学麦克风(BK2192),在脉冲频率6KHz和7KHz上的信号强度分别高出10.2dB和9.9dB。在气体泄漏检测方面,通过拾取气体泄漏的四极子声场信号,分辨气体泄漏的特征频谱来判断气罐泄漏的相关信息。实验表明,随着气罐内压及泄漏孔尺寸的改变,气体泄漏特征谱只出现整体的起伏变化没有发生频谱上的变化。该研究为气体泄漏检测方法提供了新的检测手段。
[Abstract]:With the progress and development of optical fiber sensing technology, compared with electric microphone, fiber optic microphone has a wider application prospect in micro-nano signal detection, photoacoustic spectrum measurement and other fields. Among them, interferometric fiber-optic microphone has attracted many researchers' attention because of its advantages of light structure, high sensitivity, anti-electromagnetic interference and so on. In the optical fiber microphone system with external cavity interference structure, the performance of the film and its fabrication process are very important. The quantitative measurement of the vibration amplitude of the film can directly reflect the sensitivity of the film. In this paper, the optical fiber sensor based on high sensitivity thin film is studied, and the sensitivity of the thin film probe is measured with high precision combined with the low coherent fiber differential interferometer, which can realize the absolute measurement of physical quantity. It is applied to the quantitative calibration of the photoacoustic spectrum gas concentration and the analysis of the characteristic spectrum of the gas leakage acoustic signal. Firstly, large size (diameter 3.1mm) aluminum polyimide composite films were fabricated by MEMS plasma silicon etching. The prepared method can release the stress in the film to a certain extent and improve the surface smoothness of the film, and the thickness of the film is lower than 500 nm by diluting the concentration of polyamide acid. The aluminum layer of the composite film can protect the polyimide from destruction and improve the overall photoreflectivity of the film. The elastic property of the polyimide is good and its high strength characteristic can guarantee the structural strength of the composite film as a whole. Secondly, the aluminum-polyimide film probe was measured experimentally. Because the non-contact absolute amplitude can be measured by low coherence differential interferometry, we combine it with aluminum polyimide film probe to form a low coherent differential interference optical fiber microphone system. The system can measure the absolute displacement of the film vibration amplitude and obtain the sound pressure sensitivity of the film probe directly. The experimental results show that the linear responsivity of the system is good, the sound pressure sensitivity of the system is stable in the frequency range from 1kHz to 5KHz, the average sound pressure is 120 nm / Pa, and the minimum detectable sound pressure is 53uPa.The structure stability of the aluminum-polyimide film is good. Its performance remains unchanged in four months, and has good temperature stability. The temperature rise has a weak negative effect on its sensitivity, and the maximum effect is 9.3%. Finally, based on the aluminum-polyimide film optical fiber microphone, we developed the optical fiber photoacoustic spectrum measurement and gas leakage detection. In this paper, the modularization design of optical fiber optoacoustic spectrum measurement system is carried out, including tunable excited light module, open microcavity photoacoustic cell and low coherent differential interference microphone module, and each module is verified by experiments. Then the whole system is tested. The experimental results show that the resonant frequency of the open microcavity photoacoustic cell is 3 KHz, and the maximum photoacoustic signal is 2.3 MPA. Compared with the traditional electric microphone (BK2192), the signal intensity at the pulse frequency of 6 kHz and 7 kHz is 10.2dB and 9.9 dB higher than that at the pulse frequency of 6kHz and 7kHz, respectively. In the aspect of gas leakage detection, the relevant information of gas tank leakage is judged by picking up the quadrupole sound field signal of gas leakage and distinguishing the characteristic spectrum of gas leakage. The experimental results show that with the change of the internal pressure of the gas tank and the size of the leak hole, the characteristic spectrum of the gas leakage only changes in the whole fluctuation and does not change in the spectrum. This study provides a new method for gas leakage detection.
【学位授予单位】：安徽大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN253

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