Personnel inspection with threat detection and discrimination

A system comprising:

• a magnetic field transmitter configured to generate a first magnetic field, the first magnetic field including at least two frequency components, the first frequency component between 100 Hz and 1000 Hz and the second frequency component between 5 Hz and 100 Hz;
• 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, the polarizability index including a first polarizability index component determined based at least on the first frequency component and a second polarizability index component determined based at least on the second frequency component;
• classify, using the polarizability index, the object as threat or non-threat, the classifying including determining a first property of the object based at least on the first polarizability index component associated with the first frequency component and determining at least one material property of the object based at least on the second polarizability index component associated with the second frequency component;
• and
• provide the classification.