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.
Highlights
The non-destructive testing (NDT) toolkit covers a wide range of sensing technologies including thermal [1,2], infra-red imaging [3], and ultrasound [4]
In electrically conductive objects, the method relies on the generation of eddy currents by an oscillating magnetic field, i.e., the primary field, in the object of interest and on the detection of the magnetic field produced by those eddy currents, i.e., the secondary field
We evaluate the performance of an rf atomic magnetometer in various types of NDT
Summary
The non-destructive testing (NDT) toolkit covers a wide range of sensing technologies including thermal [1,2], infra-red imaging [3], and ultrasound [4]. The sensitivity of magnetic sensors is constant over a wide range of operating frequencies (1 kHz–1 GHz) [11] It enables operation at low frequencies, where the change in the penetration depth of the rf field is most significant. The magnetometer signal is only produced by the secondary field components orthogonal to the primary field These investigations have been carried out with electrically conductive, non-magnetic aluminium objects: (1) to investigate the how the skin depth, which is related to eddy currents and rf field frequency, impacts the measurements of defects at different depths, and (2) since the changes in the local field detected by the atomic magnetometer are negligible. The area enclosed by the dashed box shows the components that make up the rf atomic magnetometer and solid box details the geometry of the holes in the object used for the validation of concealed defect detection
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