Title : Small size and high sensitive GFRP mandrel based fiber optic hydrophone array
Fiber optic systems are used for marine acoustic detection systems, geophysics, oil and gas exploration and military applications. Due to their size, low noise level, high sensitivity, and low cost; fiber-optic interferometric acoustic hydrophones has many advantages with respect to conventional hydrophones based on piezoelectric ceramics. There are many fiber optic techniques for sensing acoustic pressure like . Because of its high sensitivity at low frequencies, mandrel based Mach-Zehnder interferometer system has been preferred in this study. In a typical fiber optic Mach-Zehnder interferometer system, light is split by a fiber optic coupler into sensing and reference arm. The sensing arm is wrapped around a pressure sensitive mandrel. A full-detailed design has been done and fiber optic hydrophones developed. Hydrophones are mandrel type, consisting of a fiber coiled inner reference cylinder and an outer sensor cylinder (mandrel). Hydrophone performance varies with different parameters of sensor mandrel such as Poissons’s Ratio, Young Modulus and dimensions. Glass Fiber Reinforced Polymer (GFRP) has been chosen because of its strength, durability and sensitivity. Another advantage of fiber optic systems is that it is easy to increase the number of hydrophones in a single line. Some of the most recent techniques are frequency division multiplexing (FDM), wavelength division multiplexing (WDM) and time division multiplexing (TDM). Due to its simplicity, time division multiplexing method (TDM) has been implemented for the designed hydrophone array. To decrease environmental effects and prevent phase fading, PGC (Phase Generated Carrier) method has been applied for the demodulation of the acoustic signal. As a result of these decisions, high sensitive (> -160 dB re rad/µPa), low noise (<50 dB µPa/Hz1/2) fiber optic underwater acoustic four element hydrophone array system has been developed at low frequencies (<5 kHz).