Determination of Fabry-Perot spacing in optical fiber acoustic pressure sensors

Partial discharges that take place in insulating materials influenced by intense electrical field are frequently detected by electrical and acoustic systems. In acoustic detection techniques, not only detection of partial discharges but also determination of their locations is possible. Therefore, acoustic detection is more preferable than electrical detection. In this study, requirements of optical fiber sensors used in detection of partial discharge and determination of its location are analyzed and considered in the designed Fabry-Perot interferometric sensor. Moreover, the relation of Fabry-Perot spacing of the sensor with the visibility and the optical intensity is discussed. Considering specifications of the optical fiber that will be used in the fiber, the relation between the visibility and the spacing is analyzed and it is determined that the highest value for the visibility is in the order of 100 µm. Choosing the length of the Fabry-Perot spacing in the linear region of the optical intensity is important. Accordingly, considering the variation of the optical intensity with the spacing length, a deformation value of ± 200 nm for the system having a light source of 1300 nm wavelength and ± 230 nm deformation value for the system having a light source of 1550 nm wavelength are found to be measured properly. Considering these, the sensor membrane is designed and deformation values are found using ANSYS simulation medium.