π相移光纤光栅水听器的超声波传感指向特性  

Ultrasonic sensing directivity of π-phase-shifted fiber Bragg grating hydrophone

作　　者：安秉文 陈家熠 李斐然 李子琪 吴先梅[1,2] An Bing-Wen;Chen Jia-Yi;Li Fei-Ran;Li Zi-Qi;Wu Xian-Mei(State Key Laboratory of Acoustics,Institute of Acoustics,Chinese Academy of Sciences,Beijing 100190,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院声学研究所,声场声信息国家重点实验室,北京100190 [2]中国科学院大学,北京100049

出　　处：《物理学报》2023年第6期155-165,共11页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11674351)资助的课题.

摘　　要：π相移光纤光栅因具有较短的有效光栅传感长度,近年来成为了超声传感领域的研究热点.本研究旨在探究π相移光纤光栅作为水听器应用时对超声波的指向性特性.选取π相移光纤光栅作为超声传感单元,先基于分层介质的声传播理论计算出水中超声波入射时光纤纤芯的应变,再运用基于光学耦合模方程的传递矩阵法计算反射光谱得到光波长偏移.将角度-频率空间分为三个区域,计算了声波频率在1-10 MHz时不同角度下的应变结果和光波长偏移响应特性,并开展了实验研究.结果表明,理论和实验结果具有较高的一致性,π相移光纤光栅在超声波垂直光纤入射时响应最大,随声波入射方向与光纤法向间夹角的增加,π相移光纤光栅的声响应先急剧下降,后在水中直达声波和光纤中导波叠加时出现极大值.此外,π相移光纤光栅的声响应随声波频率增加而降低.本研究对π相移光纤光栅在超声传感中的实际应用具有重要意义.ππ15◦15◦π-phase-shifted fiber Bragg grating with a short effective sensing length becomes one of research hotspots in ultrasonic sensing,because light undergoes strong localization centered at its phase shift position.To investigate the directional sensing characteristics of-phase-shifted fiber Bragg grating as hydrophone,the theory of sound propagation in layered media is used to calculate the strain of fiber core,then the transfer matrix method based on the coupled-mode theory in optics is used to calculate the shift of central wavelength in optical reflection spectrum.Results of strain and wavelength shift under obliquely incident ultrasonic from 1-10 MHz are divided into A area,B area,and C area,and analyzed by numerical calculation and simulation calculation.Axial strain and elasto-optical strain change the grating period and effective refractive index by the mechanical effect and elasto-optical effect,respectively,thereby resulting in wavelength shift.In A area(frequency below 5 MHz,incident angle below 15°),the axial strain nearly equals zero,thus elasto-optical effect plays a predominant role in wavelength shift.The maximal response occurs at vertical incidence,and then obviously declines with angle increasing.The maximum is essentially unchanged with grating length.In B area and C area(angle above 15°),both mechanical effect and elasto-optical effect contribute to wavelength shift.In B area(frequency below 5 MHz),the amplitude of strain is the largest in three areas.A peak of wavelength shift appears at the same angle of the peak of strain,where exists the interference of the guided wave in fiber with the direct ultrasonic wave form water.The peak amplitude of wavelength shift decreases with grating length increasing.In C area(frequency below 5 MHz),the amplitude of strain is larger than in A area,but the wavelength shift is smaller,which is correlated to its higher axial wave number.Comparing the results in three areas,it is clear that the wavelength shift is larger at lower frequency and at ve

关 键 词：π相移光纤光栅 超声传感 指向性 

分 类 号：TP212[自动化与计算机技术—检测技术与自动化装置] TB565.1[自动化与计算机技术—控制科学与工程]