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一个核心问题。该提案旨在研究在此背景下基于原子磁力计的成像和断层扫描的潜力，以及在水下金属物体的情况下提供原理证明。磁感应断层扫描（MIT）是一种非接触式技术，可以对导电物体进行成像。它依赖于感兴趣的对象中的振荡磁场产生的涡电流以及对这些涡电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。MIT允许检测隐藏在地下/水下的导电物体，因为土壤/水的电导率很低。物体可以被检测到的深度取决于驱动磁场的频率，以及传感器的灵敏度。虽然非常低的频率，赫兹的数量级，允许穿透深度为几公里，thesensitivity的传统线圈为基础的探测器是非常低的，在这样的频率。最近由UCL团队展示的用于MIT系统的原子磁力计的使用提供了一种有效的解决方案，因为原子磁力计在低频下非常敏感，并且比基于线圈的相同线圈的传感器精确地高出7个数量级。此外，在UCL开发的技术适用于在无屏蔽的环境中使用，并且不需要任何校准，因为原子磁力计的响应通过基本物理常数与磁场相关联。

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.