Discriminating capabilities of multifrequency EMI data

An object, made partly or wholly of metals, has a distinct combination of electrical conductivity, magnetic permeability, and geometrical shape and size. When the object is exposed to a low-frequency electromagnetic field, it produces a secondary magnetic field. By measuring the broadband spectrum of the secondary field, the authors obtain a distinct spectral signature that may uniquely identify the object. Based on the response spectrum, they attempt to "fingerprint" the object. This is the basic concept of electromagnetic induction spectroscopy (EMIS). From numerous surveys that they have conducted using our multifrequency electromagnetic sensors (GEM-2 and GEM-3), they have accumulated significant evidence that a metallic object undergoes continuous changes in response as the transmitter frequency changes. These observations made over many UXO targets suggest strongly that the EMI anomaly measured in a broad band offers an ability to both detect and identify a target. The frequency-dependent structure of the difference was also reproducible and consistent over a range of depths. These experiments have established that the GEM-3 is capable of delivering broadband EMT data with ample target-specific information content for the purpose of target classification and identification.