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

Imaging large objects hidden underground and underwater is a central problem in defence and security. This proposal aims
to investigate the potential for imaging and tomography based on atomic magnetometers in this context, as well as to
provide 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 on
the generation of eddy currents by an oscillating magnetic field in the object of interest and on the detection of the magnetic
field produced by those eddy currents. Position resolved measurements allow then the reconstruction of the image of the
object 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 the
sensitivity of the sensors. While very low frequency, of the order of Hz, allows penetration depths of a few kilometres, the
sensitivity of conventional coil-based detectors is very low at such frequencies. The use of atomic magnetometers for MIT
systems, as recently demonstrated by the UCL team, provides an effective solution, as atomic magnetometers are very
sensitive at low frequency, and precisely up to 7 orders of magnitude more sensitive than a coil based sensor of the same
volume. In addition, the technique developed at UCL is suitable for use in an unscreened environment and does not require
any calibration because the atomic magnetometer response is linked to the magnetic field by fundamental physical
constants.

The proposed research aims to develop novel instrumentation, based on atomic magnetometers, dedicated to imaging for
defence and security applications. We thus expect impact on the economy both in the short and in the long term.
Immediate Impact: There is already a market for imaging systems for defence and security applications. The proposed
feasibility study will determine specific scenarios where imaging systems based on atomic magnetometers find application.
Additionally, we will provide proof-of-principle of the possibility to perform imaging of objects hidden under deep water.
Thales UK is best placed to translate the results of the feasibility study into products for the security and defence sectors,
with immediate impact on the economy.
Long-term Vision: In the long-term ultra-low frequency magnetic imaging has potential application beyond the defence and
security sector. A significant impact is expected in the oil and mining sector, as deep underground magnetic imaging may
offer superior performances with respect to current acoustic techniques. The instrumentation proposed here will also
constitute a useful technique for environmental and infrastructure related applications. For infrastructure applications, there
is interest in the use of ground penetrating technologies for geological surveying of construction sites. For the
environmental applications, hydrogeological surveying might be a strong candidate, as fresh water becomes a scarce resource in areas affected by climate change, for example.
Thales UK has existing interests in aerospace, ground transportation and space where this technology may find
applications. In addition, they are well placed to develop new business lines to address new opportunities.