The Usage of Frequency Swept Signals for Metal Detection

The usage of frequency swept signals for an eddy current metal detector is described in this paper. The main task for researchers is to minimize false alarms which account for up to 99.9% of the total alarms. Better discrimination should be performed to distinguish between mine and scrap metals. Firstly, a short theoretical background is presented. Secondly, experimental data measured by the search head of the metal detector ATMID is presented. The detector was excited with frequency swept sine signals from 1 kHz to 45 kHz. Synchronous demodulation was used for signal processing. Various spheres from different materials and sizes placed in the open air were used as the test targets. A grenade, without explosives, was also presented for comparison. Amplitude and phase graphs or polar graphs are presented to differentiate between the different objects. On the basis of these polar graphs, better identification and discrimination between the different buried objects (i.e., Anti-Personnel mines) should be undertaken.