I want to make a vehicle detection prototype. I find there are multiple choices of sensors that can be used to detect a vehicle, such as acoustic, ultrasonic, infrared, magnetic inductive sensor.
I am only familiar with infrared sensors, which are low cost, can be a good choice of detection of approaching objects, whereas the acoustic and ultrasonic are much more expensive.
However an infrared sensor is not a complete solution. In order to find whether the approaching object is either a vehicle or any other objects, I suppose I need either a magnetic or an inductive sensor. I learned that scalar magnetometers are suitable for the vehicle detection, because it measure the total strength of the magnetic field to which they are subjected. However then I learned that magnetic sensors can be also divided into DC and AC sensors.
in wiki, it says "AC" if they measure fields that vary relatively rapidly in time, and "DC" if they measure fields that vary only slowly (quasi-static) or are static. AC magnetometers find use in electromagnetic systems (such as magnetotellurics), and DC magnetometers are used for detecting mineralisation and corresponding geological structures.
Can anybody explain the difference between DC and AC based magnetometers? Currently my idea is to use a magnetometer with an infrared sensor. What do you think of this approach? My evaluation criteria is performance first, then power consumption, and cost last.