Vehicle Detection Method Based On Geomagnetic Vector Signals

With the acceleration of urbanization,traffic congestion is becoming more and more serious,which not only brings huge economic loss,but also causes a series of problems such as environmental pollution problems and resource waste.In order to alleviate the increasing traffic congestion,the intelligent transportation system is introduced to further improve the traffic efficiency.As the data collector of the intelligent transportation systems which provides basic traffic data,vehicle detector is an indispensable part of the system.Compared with traditional vehicle detection technology,magnetic sensing technology has been widely concerned by its easy installation,maintenance,higher stability,higher sensitivity and scalability.However,relevant researches focus on the vehicle detection basing on the peak value of the measured magnetic signal and determining vehicle model and vehicle characteristics by using the different waveforms of magnetic induction signal.Most of them did not dig into the measured magnetic signal deeply.Therefore,the vehicle magnetic signal measured by the magnetoresistance sensor is modeled theoretically,and the position and velocity of vehicle is detected on the basis of the vehicle magnetic field model.Firstly,the principle of magnetic vehicle detection is introduced,based on the working principle of the magnetoresistance sensor and the experimental platform for geomagnetic vehicle detection is built.Then,the vehicle can be seen as a single magnetic dipole when it is far enough from the measuring point on the basic of the magnetic dipole model,the theoretical derivation of the magnetic perturbation by the vehicle is given.By inversing the obtained theoretical model,the relationship model between the position of the vehicle and the value of the magnetic induction intensity is established,and the vehicle position can be determined in real time using the magnetic induction intensity measured by a single three-axis geomagnetic sensor.Furthermore,the vehicle is regarded as a rectangular magnet.Based on the principle of magnetic field superposition,the magnetic induction intensity caused by the vehicle at the measuring point is integrated and solved.Considering the height of the vehicle is smaller than the length and width,the height direction can be ignored in the solving process.Only the length and width direction of the vehicle is integrated and the equation is simplified.Two groups of magnetic induction intensity signals measured by two magnetic sensors on one side of the road are used to determine the position and magnetic characteristic parameters of the vehicle in real time.On the basis of the position detected,the numerical relationship between the vehicle speed and the value of magnetic induction intensity can be developed by differentiate the time of the measured magnetic induction intensity signal.Finally,in order to better meet the practical application requirements,the vehicle is divided into magnetic dipole units and the more accurate theoretical model between the vehicle position and the magnetic induction intensity caused on the measuring point is established.Considering the high complexity of the established equation,it is difficult to inverse.So the database method is used to confirm the vehicle position by matching the measured magnetic induction intensity of the vehicle.