High-Spatial-Resolution Strain and Vibration Dual-Parameter Sensor Based on Ultra-Short FBG

Abstract

A method for simultaneous measurement of static strain and dynamic vibration with high spatial resolution based on millimeter sized ultra-short fiber Bragg grating (FBG) is proposed and experimented in this paper. Dual-parameter can be measured on the single unit of cascaded FBGs, which interrogate with optical coherence tomography method by a designed wavelength swept light source. In experiments, the sensing units were precisely located with mm degrees by inverse FFT of coherent signals and the phase difference calculation. And also the strain and vibration could be simultaneously measured in time and frequency domain: demodulating strain with low frequency component’s phase shift of coherent signals by extracting envelope and interpolation; demodulating vibration by finding peak positions of sidebands in FFT spectrum. Spatial resolution of positioning can reach 0.77 mm. Sensitivity of strain measurement reaches 0.811 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{\times} 10^{-3} rad/\mu \varepsilon $</tex-math></inline-formula> under a wavelength sweep rate of 0.2 nm/ms, and forces of several milli newtons can be perceived. The measurement accuracy of kHz vibration frequency is over 98%. Moreover, by comparing simultaneous and respective measurement of dual-parameter, it can be seen that there is almost no crosstalk affectting the results. The results shows great application potential in the field of mechanical sensing, especially in bionic tactile sensing for its simultaneous dynamic and static measurement with accurate positioning performance.