2007 年 48 巻 6 号 p. 1208-1214
In order to overcome some problems of conventional parallel-type acoustic emission (AE) monitoring system, we developed a new Michelson-type laser interferometer with feedback circuit. We first compared the performance of the developed system with those by the Mach-Zender interferometer previously developed. Average signal to noise ratio (S/N) of the system to the F(1.1) mode cylinder wave is measured as 14.3 dB and comparable to that (14.7 dB) of the Mach-Zender interferometer. Sensitivity of the system to the cylinder waves was found to be significantly improved by multi-winding of the sensing fiber on the pipe. We then measured the attenuation of longitudinal and flexural mode cylinder waves via a pipe wrapped by adhesive tape for corrosion protection. The attenuation of the F(1,1) mode wave by the adhesive tape was measured as 10 dB/m and slightly lower than that (12 dB/m) of the L(0,1)-mode wave. Leakages of water through a hole or medical paper tape were successfully monitored by the highly sensitive system.
