Capacitive sensor for vehicle obstacle detection, especially for pedestrian detection

Every year, some of the accidents occur at low speed because of drivers’ blind areas. The probes cannot be assembled on the whole body of vehicle due to cost. In this paper, we present and demonstrate a simple, low-cost obstacle detection system based on capacitive sensors. These sensors are manufactured by conventional printed circuit board. We deduce the sensing principle of the capacitive sensor using mirror image method. A interdigitated sensor with 26 fingers, which dimensions are 30 cm × 10 cm × 0.2 cm, is designed. To read the sensor, we propose a measuring system which includes a wave generator, a C/V converter, a multiplier, some LPFs and amplifiers. It offers a DC-voltage output with low linearity error (0.2%). The experimental results show that human-body and conductor can be easily detected by the sensor compared with wood and wall, and that also verify the validity of the derivation of sensing principle. By testing different persons, the results denote that the measuring system enable detect a child at a distance up to 60 cm that guaranteed the protection system can be valid activated. The last experimental results demonstrate that the more accurate position can be obtain by the linear weighted summation of sensor positions weighted. The proposed detection system also can be used for parking assistance.