In order to resolve the disturbance of external perturbation in Weight-In-Motion (WIM) measurement by traditional methods, a novel pressure sensor for WIM of vehicles based on fiber ring-down spectroscopy is proposed here. A micro-bending sensing head is designed and its working principle is discussed in this paper. The fiber loop ring-down (FLRD) system reveals that the sensing forces applied to the sensing head can be obtained by measuring the ring-down time. Meanwhile, the velocity of vehicles is measured by analyzing two ring-down spectrums in this scheme. Experiment results show that the precision of velocity of vehicles is good and the sensor has a linear response to the applied force.
A fiber-optic sensing scheme of measuring pressure is described here. The high reflective mirror in a laser cavity is replaced by a Sagnac loop in this scheme. The method combining the Sagnac effect with fiber loop ringdown technology fully embodies the advantages of both. The working principle is discussed in detail, and the whole sensing performance is demonstrated by applying sensing force to the sensor area. The sensing force can be obtained by measuring the ringdown time. The pressure measurement range of this device is 40 to 350 N. The detection sensitivity 0.4 ns/N can be realized in this system. The experimental curve reveals a close relationship between the sensing strain and the ringdown time.
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