Electromagnetic-induction vehicle sensor detecting the gradient of magnetic flux

A stable and highly reliable electromagnetic-induction-type vehicle sensor that takes appearance, installation, and maintenance into consideration is developed. It utilizes the electromagnetic coupling of two kinds of ferrite coils. This sensor detects the magnetic field generated by one ferrite coil with the other ferrite coil, and detects the presence of a vehicle from the minute change in the magnetic field generated when the vehicle enters. The installation of the ferrite coils is fairly simple, and this application as other types of sensors can also be considered. The basic principles, configuration of the equipment, and results of experiments on the highly sensitive directional synthesizing system which can sense the minute change in the magnetic field caused by an entering vehicle, and automatically maximize its sensitivity, are discussed. In practical tests, vehicles were satisfactorily detected even when the transmitting and receiving units were installed in the road 3.5 m apart. When installed at the roadside at intervals of one meter, a detection distance of 2.0 m was obtained. These experiments confirmed the ease of installation and the high sensitivity of this sensor