[4B6] Magnetic induction tomography and radio-frequency atomic magnetometer

P Bevington
National Physical Laboratory, UK

Magnetic induction tomography (MIT) is a widely used method for defect detection and material identification that measures the inductive coupling between an excitation magnetic field and electrically conductive and/or magnetically permeable objects. This method typically uses pick-up coil sensors to detect eddy currents (ECs). These sensors have a sensitivity strongly related to the sensor volume and excitation frequency. A wide spectrum of other sensor systems has been proposed to improve detection, such as superconducting quantum interference device (SQUID) sensors that have extreme sensitivities (fT/Hz^1/2) and semiconductor magnetic resist sensors that can have small measurement volumes (<1 mm3).

The authors propose the use of radio-frequency atomic magnetometers, sensors with a highly tuneable low-frequency range (<kHz to MHz), sensitivities comparable with SQUIDs but without the need for cryogenics and flexible sensor architecture that be miniaturised with favourable SWaP characteristics. The National Physical Laboratory (NPL) has 20+ years’ experience in the development and optimisation of these sensors and has recently demonstrated the advantage of these systems for MIT with a portfolio of papers and patents. The NPL system has a demonstrated sensitivity of 50fT/Hz^1/2 in an industrially relevant environment and <1 mm spatial imaging resolution at a sensor-to-sample distance of tens of cm and has been used to detect defect thinning, size and depth in addition to material identification. Similar sensor systems have had commercial success in DC field sensing and NPL is involved in several projects to develop commercial sensors aimed at non-destructive testing (NDT) applications.

[4B6] Magnetic induction tomography and radio-frequency atomic magnetometer

P Bevington National Physical Laboratory, UK

P Bevington
National Physical Laboratory, UK