Simultaneous measurement of dynamic displacement and strain in a single fiber using coarse wavelength-division multiplexing and fiber Bragg-grating filter-based sensing system.

Displacement and strain, two of the most important physical quantities in experimental solid mechanics, are seldomly measured simultaneously in a single experimental configuration. In order to provide and improve corresponding sensing techniques, an experimental setup system for simultaneous measurement of dynamic displacement and strain on a flexible cantilever beam using two fiber Bragg gratings (FBGs) in a single fiber is proposed. To realize high-speed multiplexing and demodulation, a configuration incorporating a coarse wavelength-division multiplexing (CWDM) technique and an FBG transmission filter is implemented. The cantilever beam is subjected to steel-ball impact from which the dynamic multipoint displacement/strain sensing performances of the CWDM and FBG filter-based sensing system are demonstrated. Experimental results in temporal and frequency domain are compared with those obtained by the finite element method (FEM) predictions based on identification of the impact-loading history. A noncontact Fotonic displacement sensor and a polyvinylidene-fluoride film (PVDF) strain sensor are also used for comparison. With transient and resonant frequency simulations conducted by the FEM, loading effects of the sensing system are examined. The results obtained in this study indicate that the proposed CWDM and FBG filter-based sensing system is capable of performing simultaneous multipoint displacement/strain measurements in a single fiber with large bandwidth, high sensitivity, and low intensity loss.