An eddy current sensor can be used as a device for detecting anomalous objects, such as shovels and jacks, lying on a railway line. Such an object is called a target in this paper, which investigates the dependence of the basic characteristics of an eddy current sensor on the area of the target. The following conclusions are derived. First, the dependence of the inductance, ΔLβ, on the target/coil area, β, can be approximated by an exponential function in some coils with different radius. Second, when lift-off/coil radius γ= 1 the change in the inductance, ΔLβ/L0, is 1%, where L0 is the coil inductance without the target.
