An Improved Impact Source Locating System Using FBG Rosette Array

Abstract

For structures vulnerable to foreign object impact damages, it would be desirable to detect and locate any occurrence of such impacts. This can be achieved by monitoring the stress waves generated by an impact together with certain source localization algorithms. Being small, electromagnetic influence immune and durable, Fiber Bragg grating (FBG) sensors are advantageous for this task. One drawback of FBGs for this purpose is their uneven directional sensitivity, which limits its localization ability to within 50° on either side of the fiber axis. Beyond this range, the signal is too weak and masked by noises and the location errors increase abruptly. Two approaches have been tested on a 0.8 m × 0.8 m × 6 mm plate for possible improvement on the system accuracy: firstly, an interrogation scheme with stronger light source intensity and steeper edge filter is employed to enhance the signal-to-noise ratio and system sensitivity; secondly, rosettes with two orthogonal FBGs are cascaded together to replace single FBGs to alleviate the directional sensitivity problem. It was found that a four-fold increase in signal to noise ratio contributed by stronger light source does improve the location accuracy, but only marginally. For the rosette approach, the relative positions of the Bragg wavelength of the FBGs and the light source spectrum are crucial to accuracy. Three different wavelength configurations have been tested and the reasons for their success or failure are discussed. It was shown that with an optimal wavelength configuration, the rosette array can virtually extend the good location accuracy to all over the plate.

Optical Fiber Sensors for Ultrasonic Structural Health Monitoring: A Review

“…Chen et al [148] presented that the key limitation of FBG sensors for impact localization stems from their directional sensitivity. They show the limited effectiveness of a single FBG sensor for impact localization.…”

Amplifying Lamb Wave Detection for Fiber Bragg Grating with a Phononic Crystal GRIN Lens Waveguide

“…In addition, FBG sensors have strong directional sensitivity with respect to ultrasonic wave detection; therefore, they can filter out signals not directly from the actuator, for example, unwanted reflections from boundaries [ 5 ]. Similarly, directional sensors can be arranged in a rosette or phased array configuration to identify the location of impact or acoustic emission sources [ 6 , 7 , 8 ].…”

Low-Velocity Impact Localization on a Honeycomb Sandwich Panel Using a Balanced Projective Dictionary Pair Learning Classifier

“…Under visual observation, the damage caused by low-velocity impacts is usually not obvious, which makes damage detection difficult [ 8 ]. However, by arranging a sensor network on the structure to measure the response signal caused by an impact, the impact can be localized via a positioning algorithm, which is very important for structural health monitoring [ 9 , 10 ]. Fiber Bragg grating (FBG) sensors can be conveniently arranged on various material structures, have the advantages of anti-electromagnetic interference and integrated sensing and communication functions, and are very suitable for constructing a sensor network for impact positioning [ 11 ].…”