Inductive Imaging of the Concealed Defects with Radio-Frequency Atomic Magnetometers

Abstract

We explore the capabilities of the radio-frequency atomic magnetometers in the non-destructive detection of concealed defects. We present results from the systematic magnetic inductive measurement of various defect types in an electrically conductive object at different rf field frequencies (0.4–12 kHz) that indicate the presence of an optimum operational frequency of the sensor. The optimum in the frequency dependence of the amplitude/phase contrast for defects under a 0.5–1.5 mm conductive barrier was observed within the 1–2 kHz frequency range. The experiments are performed in the self-compensated configuration that automatically removes the background signal created by the rf field producing object response.

Identification of object composition with Magnetic Inductive Tomography

“…We have previously shown that for conductive objects an optimum value within a 1-2 kHz frequency range can be identified, which maximises the amplitude and contrast of features (defect, edge signatures) observed in the inductive images [7]. Similar behaviour was seen in magnetically permeable objects, but where the optimum values were shifted to a higher frequency range [21].…”

“…MIT provides a portfolio of measurements addressing a wide range of contemporary challenges in applied physics. In the area of non-destructive testing (NDT), inductive measurements enable detection of defects either covered by insulation or concealed within the object structure [3][4][5][6][7]. Immediate applications of the technology lie in the energy sector where corrosion under insulation is responsible for a significant fraction of the losses in the transport and storage of oil and gas.…”

“…The use of an rf atomic magnetometer as the sensor in MIT brings superior sensitivity [9][10][11][12] as well as a range of functionalities such as the ability to obtain vector measurements [13,14], high bandwidth in self-oscillating mode [15,16], and tunability over a wide frequency range without compromise of performance [17,18]. Measurement of the object response with an rf atomic magnetometer relies on monitoring the change in the amplitude and phase of the rf resonance recorded with the magnetometer while scanning across the material, Fig.…”

Two-photon electromagnetic induction imaging with an atomic magnetometer

“…The simplicity in tuning the two-photon resonance effectively bypasses the need to adjust transverse field/gradient field setpoints that would normally be required in bias field tuning. 18 Reinforcing this is an analysis of the SNR of the two configurations in Fig. 4.…”

Electromagnetic Induction Imaging: Signal Detection Based on Tuned-Dressed Optical Magnetometry

“…In 2001, Griffiths [1] proposed an imaging technique based on inferring one or more of the three passive electromagnetic properties (conductivity σ, permittivity and permeability µ) to produce images on the basis of the response to a position dependent oscillating magnetic field. Several denominations are used to identify this kind of methodologies, among which electromagnetic induction imaging (EII) [2], electro-magnetic tomograhy (EMT) [3], magnetic induction tomography (MIT) [4,5], and also mutual inductance tomography (same acronym) [6], the latter three stressing the potential of the technique to provide 3D mapping. A review on the subject was recently authored by Ma and Soleimani [7].…”