Abstract:

A push--pull fiber-optic acoustic accelerometer using Mach--Zehnder interferometry to detect surface strains in a centrally clamped, peripherally free disk will be described. The measured sensitivity is approximately 20 rad/g below the resonance of 10 kHz. A total of 36 m of optical fiber wound in a pancake spiral was used for each interferometer leg. The disk is housed in a cylindrical case that allows the device to be near neutrally buoyant in water, thus acting as an acoustic motion sensor. The interferometer was interrogated with a Nd:YAG laser at 1310 nm and a 3x3 fiber coupler. Considering a total disk mass of 19.6 gm, the fractional phase change per unit force is 4.0x10[sup -6] N[sup -1]. Based on an electro-optic noise floor of 5 (mu)rad/Hz[sup 1/2], the minimum detectable signal is 0.25x10[sup -6]g/Hz[sup 1/2]. [Work supported by the University of Massachusetts, Dartmouth.]