The application of new magnetic sensors for traffic surveillance

Magnetic sensors are used for magnetic field sensing. There are a variety of magnetic sensors and they are classified by their detecting theory, such as search coil, fluxgate, Hall effect, Anisotropic Magnetoresistance (AMR), Giant Magnetoresistance (GMR), Magnetic Tunnel Junctions (MTJ), Tunnel Magnetoresistance (TMR), Giant Magnetoimpedance (GMI), magnetodiode magnetotransistor and magnetooptic, etc. Here we mainly compare the performance of the Hall effect, AMR, GMR and TMR sensors. The application of traffic surveillance based on magnetic sensors has been receiving increasing attention due to the multifunctionality, installability, maintainability, economy, robustness and wireless capabilities of magnetic sensors. The paper presents recent magnetic research about traffic flow detection, vehicle classification, and vehicle speed detection using magnetic sensors. Most of this research is based on the AMR sensor. Although TMR sensors have better performance than AMR sensors, traffic surveillance based on TMR sensors has not been the focus of researchers. The paper proposes a hardware architecture for a wireless traffic surveillance system based on a TMR magnetic sensor and gives a noninvasive traffic detection experiment on city road.