The random fiber laser (RFL) combining a 3×3 coupler phase interrogation technique is demonstrated and applied to acoustic emission (AE) detection for damage detection of buoyant materials. The random chirped grating array (RCGA) is used to provide random distributed feedback and act as an AE sensing head. The random distributed feedback inside RCGA significantly extends the effective cavity length of the RFL, thus reduces the thermal frequency noise of the RFL and improves the resolution of AE signal. A π-phase-shifted fiber Bragg grating (π-FBG) loop mirror is used as a wavelength locking to ensure a stable and narrow lasing. A high AE signal resolution of 2.6×10-7 pm/√Hz@10 kHz is achieved.
In this paper, a real-time monitoring method of buoyancy material curing process based on cascaded fiber Bragg grating (FBG) sensors is proposed. The strain change of buoyancy material curing at different heights is monitored by embedding prestressed-cascaded FBGs in the mixture of hollow glass beads and epoxy resin. Meanwhile, the cascaded reference FBGs encapsulated in a capillary glass tube is used to monitor the temperature change of buoyancy material curing process. The experimental results show that the strain and temperature change trends at different heights are different during the entire process. The proposed method is practical in monitoring of the curing process of buoyancy materials.
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