Threat detection and discrimination using multiple frequency spectra

A system comprising:

• a magnetic field transmitter configured to generate a first magnetic field including a first frequency component, a second frequency component, and a third frequency component;
• a plurality of magnetic field receivers including magnetic sensors, the plurality of magnetic field receivers configured to sample a combination of the first magnetic field and a second magnetic field resulting from interaction of the first magnetic field and an object;
• and
• at least one data processor configured to at least:
• receive data characterizing the samples obtained by the plurality of magnetic field receivers;
• determine, using the received data, a polarizability index of the object, the polarizability index characterizing a magnetic polarizability property of the object, wherein the polarizability index includes:
• a first polarizability index component determined based at least on the first frequency component,
• a second polarizability index component determined based at least on the second frequency component, and
• a third polarizability index component determined based at least on the third frequency component;
• classify, using the determined polarizability index, the object as threat or non-threat;
• and
• provide the classification.