Diaphragm-assisted impact amplitude and localization measurement system with FBG sensors

Abstract

This paper presents the development, numerical and experimental analyses of a fiber Bragg grating (FBG) based sensor for force amplitude and localization (in 2D plane) detection. The sensor system is based on a diaphragm-embedded FBG, where the spectral features, namely wavelength shift, optical power and full width at half maximum (FWHM) are analyzed as a function of the force application parameters (amplitude and position). The diaphragm results in a higher spatial range for the sensor as its larger dimensions (when compared with the optical fiber) enable the strain transmission to the optical fiber even when the force is not directly applied to the fiber. In order to verify the proposed approach, finite element method is applied on the strain analysis in the optical fiber when the diaphragm is subjected to forces at different positions. Then, the FBG reflected spectra are simulated considering the strain distribution obtained at each condition, where there are variations not only in the Bragg wavelength, but also in the FWHM and optical power as a function of the force amplitude and position. The experimental analysis confirms the results numerically obtained and shows the possibility of simultaneously measuring force amplitude and position (x and y components) using a single FBG. Results show the feasibility of the method, where root mean squared errors of 0.47 N (in 10 N range), 0.48 mm (in 10 mm range) and 0.33 mm (in 6 mm range) are found for the force, horizontal (x-) and vertical (y-) components estimations, respectively. Thus, the proposed approach shows relative errors below 5% and is an interesting approach for sub-millimeter resolution force and impact detection, which can also be used in multiplexed systems with the advantage of higher spectral efficiency, since a single FBG can provide multiple measurements that are commonly made employing a higher number of sensors.