Double Mach–Zehnder acoustic emission interferometer for detection of damage in structures

Abstract

The work described in this article pertains to the development of a modified Mach–Zehnder double interferometer for multi-source detection of high frequency acoustic emission signals. The proposed modified double interferometer is capable of detecting acoustic emissions with central frequencies within the MHz spectral range applicable for detection of microcracks in welded and bolted joints of steel structures such as in bridges. The location detection accuracy of the modified double interferometer is 2 meters, which is markedly more precise than the existing Mach–Zehnder interferometers at 20 meters. In compare to phase shifted FBGs, the proposed modified interferometer is capable of detecting higher frequency acoustic emission signals. Proof of concept experiments were conducted on an arch steel bridge in the laboratory, in which high frequency acoustic emissions simulating damage were created by breakage of pencil leads and detected by the modified double interferometer.