Detection of acoustic emission in structure using Sagnac-like fiber-loop interferometer

A Sagnac-like fiber-loop interferometer sensor has been proposed for the detection of micro crack induced acoustic emission in concrete structures. The use of a Sagnac-like configuration eliminates much of the undesirable noise by combining the reference and the sensing arms within the same optical fiber. The photo-elastic response of optical fiber to ultrasonic stress wave in elastic structural material and the effect of the soft fiber coating are analyzed. The sensor can be configured as a long gauge length sensor to detect the existence of acoustic emission in a large structural area, or as a point sensor with a short gauge length or a coiled long fiber length to detect acoustic wave at a particular location in a structure. Experiments were conducted and compared with the results from traditional piezoelectric transducers.