To perform active Structural Health Monitoring (SHM) Guided Waves (GW) have received great interest as they can inspect large areas with a few sensors and are sensitive to barely-visible structural damages. Fiber Bragg Grating (FBG) sensors offer several advantages, but their use has been limited for the GW sensing due to its limited sensitivity. FBG sensors in the edge-filtering configuration have overcome this issue with sensitivity and there is a renewed interest in their use. The sensitivity of the FBG sensors can be further improved through the use of the remote bonding. One of the challenges with the effective and repetitive measurements with the FBG sensors is uncertainty in the bond quality. This is especially important due to the small area of contact of the fiber with the structure. A solution to this is the use of a D-shaped optical fiber which will increase the area in contact. This paper experimentally investigates the coupling of the wave from the structure into the D-shaped fiber. 4 different geometries of optical fiber are studied and the coupling and the propagation amplitudes are investigated using 3D laser Doppler vibrometery measurements.
This paper presents a new flow-coating method to fabricate adhesively bonded optical fiber coupler for acoustic signals. The goal is to decrease losses as acoustic signals representing Lamb waves are transferred from one fiber to another. The flow-coating method significantly improves the geometry of the adhesive in the coupler. As a result, the losses to the acoustic signal energy are significantly reduced in the coupler.
The efficacy of using Fiber-Bragg Grating (FBG) sensors for the purpose of sensing and characterizing dynamic deployment of bistable composite tape springs is investigated in this paper. Ultra-thin composite structures such as tape springs have seen increased popularity in spacecraft structures due to enabling the precise deployment of flexible solar arrays, sails, reflectors, and antennas. These composite members can elastically transition from either the coiled or folded state to the deployed extended state while possessing superior stiffness, thermal properties, mass efficiency, and compactness when compared to their metal counterparts. Bistability is leveraged to influence more controllable self-deployment and energy efficient stowage, while reducing or eliminating the need for mechanical restraints or motorized deployment. However, a need exists to monitor both the deployment dynamics and overall structural health of the deployed member. Fiber optic sensors such as FBGs have the capability to sense pressure, temperature, and mechanical strain. Due to their relative thinness, low mass, and flexibility, fiber optics may be integrated into these deployable composite structures without significantly interfering with bistability, packaging, or deployability. This paper experimentally demonstrates dynamic strain sensing of deploying bistable composite tape springs via the integration of fiber optics containing FBG sensors. Free deployment from both coiled and folded stowed configurations are characterized.
When using fiber Bragg grating (FBG) sensors in structural health monitoring (SHM) applications, one of the drawbacks is that the sensor location is fixed once it is installed and it is difficult to extend an already existing system. The use of an acoustic coupler to transfer fiber guided traveling waves from one fiber to another could resolve this issue as the system could be modified for extension. In this study, we investigate the coupling of optical fiber guided waves between two different types of fibers through an acoustic coupler. Specifically, input waves are launched into an input fiber and coupled to an output fiber through the acoustic coupler. The input waves are measured using a high-resolution 3D laser Doppler Vibrometer (LDV) and the output waves from the output fiber are measured using an FBG. We demonstrate that the wave coupling between two fibers varies with the cross-sectional area of the input fiber.
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