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

对隐藏在地下和水下的大型物体进行成像是国防和安全领域的核心问题。这一提议旨在研究基于原子磁强计的成像和层析成像的潜力，并在金属物体在水下的情况下提供原理证明。磁感应层析成像(MIT)是一种非接触式技术，可以对导电物体进行成像。它依赖于由感兴趣物体中的振荡磁场产生的涡流，以及对这些涡流产生的磁场的检测。位置分辨测量允许以电导率图的形式重建物体的图像。由于土壤/水的低电导率，MIT允许探测隐藏在地下/水下的导电物体。探测物体的深度取决于驱动磁场的频率以及传感器的灵敏度。虽然频率很低，大约为赫兹，允许穿透深度为几公里，但传统的基于线圈的探测器在这样的频率下灵敏度非常低。伦敦大学学院的团队最近证明，在MIT系统中使用原子磁强计是一种有效的解决方案，因为原子磁强计在低频下非常灵敏，比基于线圈的同类传感器的灵敏度高出7个数量级。此外，伦敦大学学院开发的这项技术适合在未经筛选的环境中使用，不需要任何校准，因为原子磁强计的响应通过基本物理常数与磁场联系在一起。

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.