Ultra-Low Frequency Magnetic Induction Tomography with Atomic Magnetometers for Security and Defence applications

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Imaging large objects hidden underground and underwater is a central problem in defence and security. This proposal aimsto investigate the potential for imaging and tomography based on atomic magnetometers in this context, as well as toprovide a proof-of-principle in the case of metallic objects underwater.Magnetic Induction Tomography (MIT) is a non-contact technique which allows imaging of conductive objects. It relies onthe generation of eddy currents by an oscillating magnetic field in the object of interest and on the detection of the magneticfield produced by those eddy currents. Position resolved measurements allow then the reconstruction of the image of theobject under the form of a conductivity map.MIT allows the detection of conductive objects hidden underground/underwater, given the low conductivity of the soil/water.The depth at which objects can be detected depends on the frequency of the driving magnetic field, as well as on thesensitivity of the sensors. While very low frequency, of the order of Hz, allows penetration depths of a few kilometres, thesensitivity of conventional coil-based detectors is very low at such frequencies. The use of atomic magnetometers for MITsystems, as recently demonstrated by the UCL team, provides an effective solution, as atomic magnetometers are verysensitive at low frequency, and precisely up to 7 orders of magnitude more sensitive than a coil based sensor of the samevolume. In addition, the technique developed at UCL is suitable for use in an unscreened environment and does not requireany calibration because the atomic magnetometer response is linked to the magnetic field by fundamental physicalconstants.