Investigations Of Element And Test Technology Of Fiber-Optic Gradient Hydrophone

With the needs for anti-submarine reconnaissance and ocean exploitation, and based on rapid development of optical fiber sensing technique, the fiber-optic hydrophone and the vector hydrophone become two main tendencies of hydrophone design due to its superior performances. The fiber- optic hydrophone has many advantages such as high sensitivity, wide bandwidth and easy to multiplex. The vector hydrophone can get more information about underwater acoustic field. It is very significant to design the fiber optic vector hydrophone with combining these advantages of two kinds of hydrophones together. Because the fiber optic vector hydrophone is a very complex system which includes optics, acoustics, mechanics and electrics, there is much difficulty in research on it and a little report of it. It is still at the stage of research in laboratories.A kind of fiber-optic gradient hydrophone which is based on Michelson interferometer and the composite structure of variable cylinder and diaphragm is designed. The theoretical mechanics model of pressure sensitivity is proposed for fiber-optic gradient hydrophone, the mathematical expression of its pressure sensitivity is obtained, its vector building principle is analyzed, and the "8" directivity response is also tested.The sensor's design parameters are discussed, and simulation results on the relationship between these design parameters and sensor's pressure sensitivity are carried out. The influence of sensor's two ends'sensitivities inconsistency on its pressure sensitivity is analyzed and simulated. Three different fiber-optic gradient hydrophones are made according to analyses on design parameters and simulations, test experiments on the sensor's pressure sensitivity and its directivity response are carried out in the first class underwater acoustic measurement station of national defence. The test results validate the theoretical model and the simulation.The dynamic frequency response of the fiber-optic gradient hydrophone is analyzed by the elastic dynamics model, the mathematical expression of its resonant frequency is obtained, the influence of elastic modulus and mechanical sizes of the variable cylinder on sensor's resonant frequency is analyzed and simulated. Two different fiber-optic gradient hydrophones are made according to analyses on dynamic frequency response and simulations, test experiments on the sensor's resonant frequency are also carried out. The test results validate the elastic dynamics model and the simulation.There is some characteristic in vibration fluid column method calibration for fiber-optic gradient hydrophone, The influence of sensor's two ends'sensitivities inconsistency on its vibration fluid column method calibration is analyzed and simulated, the mathematical expression of this influence is obtained. Test experiments are carried out according to simulation, and the test results validate the theoretical analysis and simulation.