| Popis: |
A systematic study of rock mass acoustic emission (AE) detection using distributed feedback (DFB) fiber grating lasers is presented. In this, a minimum detectable strain of 10 -12 is achieved in the experiment when using a fiber optic interferometric demodulation. The dynamic strain sensitivity of DFB fiber grating laser in different coupled modes is calibrated by a comparison with PZT AE sensor.. The acoustic emission directional characteristics of the DFB fiber grating laser are investigated by two kinds of analyzing method. In the first experiment, the relationship between the wavelength drift and the angle of a continuous acoustic emission source is determined. In the second experiment, the relationship between the percentage of wavelet packet energy and the angle of the impact response is established. Their acoustic emission directional characteristics make them suitable for determining principal strains and the direction of propagation of acoustic waves. Because of these advantages, the DFB fiber lasers will provide a practical and advanced measurement means in large civil structural health monitoring. |
