Non-destructive structural imaging of steelwork with atomic magnetometers

Abstract

We demonstrate imaging of ferromagnetic carbon steel samples and we detect the thinning of their profile with a sensitivity of 0.1 mm using a Cs radio-frequency atomic magnetometer. Images are obtained at room temperature, in magnetically unscreened environments. By using a dedicated arrangement of the setup and active compensation of background fields, the magnetic disturbance created by the samples' magnetization is compensated. Proof-of-concept demonstrations of non-destructive structural evaluation in the presence of concealing conductive barriers are also provided. Relevant impact for steelwork inspection and health and usage monitoring without disruption of operation is envisaged, with direct benefit for industry, from welding in construction, to pipelines inspection and corrosion under insulation in the energy sector.

Enhanced material defect imaging with a radio-frequency atomic magnetometer

“…Alternatives involve the implementation of magnetic sensors such as giant magnetoresistance (GMR) magnetometers, [6][7][8] superconducting quantum interference devices (SQUIDs), 9,10 and radio-frequency magnetometers. [11][12][13][14]18 The magnetic field sensors directly monitor the response of the medium, the so-called secondary magnetic field (b). The secondary field is produced by the primary magnetic field through eddy currents excited in electrically conductive samples, or magnetisation induced in samples with a magnetic permeability, 18 and contains signatures of the inhomogeneities/structural defects within the sample.…”

“…[11][12][13][14]18 The magnetic field sensors directly monitor the response of the medium, the so-called secondary magnetic field (b). The secondary field is produced by the primary magnetic field through eddy currents excited in electrically conductive samples, or magnetisation induced in samples with a magnetic permeability, 18 and contains signatures of the inhomogeneities/structural defects within the sample.…”

Imaging of material defects with a radio-frequency atomic magnetometer

“…In most of the measurements, the frequency of the primary field has been scanned across the rf resonance, i.e. the whole resonance profile has been recorded, for each point of the image [15]. We also tested an alternative mode of data acquisition, which significantly decreases the image acquisition time.…”

“…In this mode, the modulation of the B frequency has been replaced with low-frequency modulation (1 Hz-20 Hz) of the amplitude of B bias . Since the amplitude of the bias field is stabilised with the fluxgate magnetometer [15], a small planar coil placed on top of the fluxgate magnetometer is used to modulate B bias . As a result of this, the output of the fluxgate contains an oscillatory component in the relevant direction.…”

A cold atom radio-frequency magnetometer

“…This surpasses the sensitivities of cold magnetometers reported thus far in non-degenerate, non-squeezed gases. Our results pave the way to robust DC and AC magnetometry at the sub-mm scale, with potential for quick application in emerging fields such as high-resolution electromagnetic induction imaging 19,20 and characterization of surfaces and materials 25,34 .…”