Practical 3-D Mapping of the Interior of Non-Magnetic and Non-Metallic Everyday Materials with Fast and Non-Contact Magnetostatic Susceptibility Tomography

Magnetostatic Susceptibility Tomography (MST) aims to map the weak magnetizability (diamagnetic or paramagnetic) inside practically non-magnetic and non- or poorly conducting objects: plastics, minerals, wood, glasses, food or living beings, or liquid flows like oil and water. For the first time, fast and contactless 3-D MST mapping without contrast agents is presented here in practice. MST offers a non-invasive, linear and safe methodology with non-contact 3-D data acquisition in less than a second. MST is also not subject to the special conditions of nuclear magnetic resonance. Challenging are the weak magnetic signals in the pico- to nanotesla range, requiring control of noise, electromagnetic, and mechanical interference. Furthermore, the spatial resolution is limited because the signal carrying magnetic fields are inherently diffuse: as with many electromagnetic “soft field” methods, an ill-posed inverse problem occurs. This practical work, based on recent preliminary results on the topic, presents an improved and enlarged setup with more independent measurements and increased signal-to-noise ratio. The 6-channel system records subtle field deformations caused by rapidly passing objects. From the multiple signals, a Landweber inversion reconstructs a 3-D map of the inhomogeneous susceptibility inside the object. The results confirm for the first time the practical capability of 3-D MST for fast and internal examination of almost non-magnetic everyday objects. MST could be promising for quality control, material sorting, and biomedical diagnostics, where rapid, harmless and non-contact material differentiation is required.