Military applications of Fiber Bragg Gratings

Abstract

Fiber Bragg gratings (FBGs) are widely used in sensing technologies due to their compact size, distributed sensing capability, immunity to electromagnetic interference, and ability to measure various physical parameters. These advantages of FBG have paved a way for the development of numerous applications in measuring and monitoring physical, chemical, and biological parameters, even in harsh industrial environments. This thesis explores novel military applications of FBG. At first, an effort to develop a hydrophone to listen and interpret underwater sounds and signals using FBG technology is discussed in detail. An innovative method for the measurement of pressure with very high sensitivity was developed by inscribing FBG in side-hole packaging fabricated by using a polymer RTV-3145 which paves maximization of pressure around the FBG portion so that sensor become more sensitive to ambient acoustic variations. Before fabricating the sensor head, simulation investigations, using COMSOL software, have been carried out. Studies to understand the effect of different parameters of the side-hole package, in rendering the maximum pressure amplification on the FBG were investigated. The role of various in fostering the pressure on FBG were studied. By the novel side-hole sensor packaging, a pressure sensitivity which is 1000 times better than the bare FBG sensitivity was achieved. Besides, temperature effect was found to be negligible because of the insulation due to polymer side-hole packaging. It is anticipated that the sensors sensitivity can be further enhanced by encapsulating etched FBG inside the side-hole packaging. Later, it was observed that the Young’s modulus of optic fiber forbids the pressure sensitivity of the side-hole packaging. This problem was addressed by a simple yet an effective way of improving the aggregate hydro-acoustic sensitivity of a bare FBG sensor through clad-etching of the FBG followed by a side-hole polymer packaging. The proposed underwater acoustic sensor system is characterized and validated with a standard PZT based hydrophone under various experimental conditions. In addition to underwater acoustic sensing, the thesis highlights the application of FBGs in estimating the recoil force on UAVs during gun firing. The research introduces a recoil mitigation system designed to stabilize the UAV and enable quick back-to-back firing The results show a remarkable reduction in rearward impulse during firing, facilitating rapid re-aiming for continuous firing scenarios.