Modelling and design of broadband low-crossing FBG-integrated three-dimensional geophones

• Aiming at the problems of existing 3D FBG geophones , a 3D FBG sensing model based on one inertial body is established and analyzed. • By designing the package layout of the FBG, it is achieved that each direction is sensitive while minimizing the influence of cross-directional factors. • An FBG three-dimensional accelerometer combining an elastomer and an inertial body has been produced through a very simple and low-cost packaging process. A three-dimensional fiber Bragg grating (FBG) geophone with single inertial mass is presented and experimentally demonstrated. The design, fabrication and optimization of the FBG geophone are analyzed. A theoretical model of the one-body 3D geophone based on FBG is established, and the mechanical structure is designed to optimize the geophone’s structural parameters and improved consistency of sensitivity across the three spindles. Meanwhile, the distribution of FBG is skillfully utilized to improve the sensitivity in all directions while reducing crosstalk. The experimental results show that the bandwidths of the sensor in the X, Y and Z directions are from 20 Hz to 500 Hz, and the flat range sensitivities in the X, Y and Z directions are from 30.87 to 63.52 pm/G, 32.2 to 70 pm/G, and 31.22 to 64.7 pm/G, respectively, which indicate that the parameters of this type of sensor in the three directions have good consistency and are in accordance with the design concept. The random error of the 3D geophone is also analyzed by Allan variance method. Such geophones have potential theoretical significance and practical applications in the fields of seismic exploration, geology and structural health and safety monitoring.