The Novel Structure Hydrophone Based on a Fiber Bragg Grating

• Main Authors: WANG, TENG-LUNG, 王登隆
• Other Authors: LIU, WEN-FUNG
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/wgd4kp

碩士 === 逢甲大學 === 電機工程學系 === 107 === This thesis proposes a novel structure based on a fiber Bragg grating hydrophone. The sensor is based on the Bragg fiber grating by using the Spherical cap’s principle to design the structure of the sensor. The architecture is mainly composed of two circular areas in which one side is use for receiving sound source and the other side is the sensing end with the fiber grating. Because the receiving area becomes larger than the sensing area, and the sensing end will receive the lager sound pressure for increasing the sensitivity of the sensor. The operating principle is that the receiving end receives the sound wave from the sound source. The sound wave passes through the medium to the other end with a sensing element. The sensing element is mainly composed of a silicon thin film to coat a Bragg fiber grating. When the acoustic wave pushes the thin film to cause the fiber Bragg grating wavelength shift. The grating wavelength will be shifted to the longer wavelength side. Therefore, the reflected wavelength will leave away from the matching grating to cause the light power change which is converted to the voltage signal by using a photodetector. The result displays on the oscilloscope. This research investigates the acoustic frequency response by changing matching position, the internal pressure, the elastic coefficient of the thin film, the thickness of the thin film. The results show that the receiving surface area, the internal pressure, the elastic coefficient of the thin film, number of the pulse all will affect the sensing result. This novel hydrophone has a good response for sensing sound wave.