Development of a simple distributed optical fibre sensor for weigh-in-motion applications

<h2>Abstract</h2> This paper describes the development of a novel intensity-modulated weigh-in-motion (WIM) sensor. The sensor mainly consists of a long fibre coil, which is fabricated with a uniform number of turns per unit length. This uniformity allows a moving vehicle to be weighed at any point along the sensor. Results are reported here from two experiments: a laboratory experiment, and a field experiment. The laboratory experiment was carried out using a model vehicle and WIM sensor with one long fibre coil, whereas the field experiment was performed using an actual vehicle, and the WIM sensor consisted of three long fibre coils, thus allowing the sensor to provide a wide surface sensor area that matched the tire contact (tire print) area. The proposed sensor was fabricated by embedding the coil into a mechanical support made of hard rubber. It was found that the behaviour of the sensor was easily understood using a spring-like model obeying Hooke's law. The decreasing light intensity transmitted through the fibre coil is proportional to the vehicle load and speed. At any speed, the total dynamic load can be represented as the sum of the change in light transmittance resulting from the front and back axles.