Induction loop

The inductive-loop system behaves as a tuned electrical circuit in which the loop wire and lead-in cable are the inductive elements.

However, the peripheral metal of the vehicle has an opposite effect on the inductance due to eddy currents that are produced.

Railways may use an induction loop to detect the passage of trains past a given point, as an electronic treadle.

Sampling the loop at a high frequency results in a unique signature for each vehicle allowing for classification of the body type.

An anti-submarine indicator loop was a device used to detect submarines and surface vessels using specially designed submerged cables connected to a galvanometer.

[5] Since there is no "tuning" available, as the telecoil directly picks up all audio-frequency magnetic fields, careful system design is required where more than one induction loop is used in a building; for example, adjacent movie theatres or lecture halls.