FIBEROPTIC SAGNAC INTERFEROMETER FOR NONCONTACT STRUCTURAL MONITORINGIN POWER-PLANT APPLICATIONS

The design of a noncontact fiber-optic sensor is described for the det ection of acoustic emission for structural integrity monitoring in hig h-temperature power plant applications. The sensor is based on a Sagna c interferometer and produces an output proportional to target velocit y, without the need for active phase stabilization. It is inherently i nsensitive to low-frequency perturbations of the instrument or the tar get and incorporates an environmentally insensitive downlead, which ma y be of arbitrary length. It is shown that the sensor is capable of me eting the specifications for structural integrity monitoring of high-t emperature power plant components based on acoustic emission detection and has a velocity resolution of 50 nm s(-1) Hz(-1/2). (C) 1997 Optic al Society America