An electromagnetic induction system, suitable for 2D imaging of metallic samples of different electrical conductivities,
has been developed. The system is based on a parallel LCR circuit comprising a ferrite-cored coil (7.8 mm x 9.5 mm,
L=680 μH at 1 KHz), a variable resistor and capacitor. The working principle of the system is based on eddy current
induction inside a metallic sample when this is introduced into the AC magnetic field created by the coil. The inductance
of the LCR circuit is modified due to the presence of the sample, to an extent that depends on its conductivity. Such
modification is known to increase when the system is operated at its resonant frequency. Characterizing different metals
based on their values of conductivity is therefore possible by utilizing a suitable system operated at resonance. Both
imaging and material characterization were demonstrated by means of the proposed electromagnetic induction technique.
Furthermore, the choice of using a system with an adjustable resonant frequency made it possible to select resonances
that allow magnetic-field penetration through conductive screens. Investigations on the possibility of imaging concealed
metals by penetrating such shields have been carried out. A penetration depth of δ~3 mm through aluminium (Al) was
achieved. This allowed concealed metallic samples- having conductivities ranging from 0.54 to 59.77 MSm-1 and hidden
behind 1.5-mm-thick Al shields- to be imaged. Our results demonstrate that the presence of the concealed metallic
objects can be revealed. The technique was thus shown to be a promising detection tool for security applications.
A new electromagnetic induction imaging system is presented which is capable of imaging metallic samples of different conductivities. The system is based on a parallel LCR circuit made up of a cylindrical ferrite-cored coil and a capacitor bank. An AC current is applied to the coil, thus generating an AC magnetic field. This field is modified when a conductive sample is placed within the magnetic field, as a consequence of eddy current induction inside the sample. The electrical properties of the LCR circuit, including the coil inductance, are modified due to the presence of this metallic sample. Position-resolved measurements of these modifications should then allow imaging of conductive objects as well as enable their characterization. A proof-of-principle system is presented in this paper. Two imaging techniques based on Q-factor and resonant frequency measurements are presented. Both techniques produced conductivity maps of 14 metallic objects with different geometries and values of conductivity ranging from 0.54х106 to 59.77х106 S/m. Experimental results highlighted a higher sensitivity for the Q-factor technique compared to the resonant frequency one; the respective measurements were found to vary within the following ranges: ΔQ=[-11,-2]%, Δf=[-0.3,0.7]%. The analysis of the images, conducted using a Canny edge detection algorithm, demonstrated the suitability of the Q-factor technique for accurate edge detection of both magnetic and non-magnetic metallic samples.