Acoustic tests of embedding materials for fiber optic hydrophones

Fiber optic hydrophones, fiber laser hydrophones and planar hydrophones, have got several military applications for instance as towed array sonars for underwater surveillance or as sensors mounted on the hull of underwater vehicles. The optical fiber is embedded in a material which modifies the acoustical characteristics of the hydrophones. The purpose is to develop acoustic interfaces allowing for detection of low level signals ranging down to and below the so called Sea State Zero level. Various materials with proper characteristics were tested but also new and innovative interfaces have been investigated, some of them with promising results. Geometrical design and proper choice of materials have been studied in previous work. The focus in this work has been to determine the frequency characteristic for a number of fiber laser hydrophones and planar hydrophones.