13 May 2015 Imaging by electromagnetic induction with resonant circuits
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Abstract
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.
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Roberta Guilizzoni, Roberta Guilizzoni, Joseph C. Watson, Joseph C. Watson, Paul Bartlett, Paul Bartlett, Ferruccio Renzoni, Ferruccio Renzoni, } "Imaging by electromagnetic induction with resonant circuits", Proc. SPIE 9481, Image Sensing Technologies: Materials, Devices, Systems, and Applications II, 94810Q (13 May 2015); doi: 10.1117/12.2183180; https://doi.org/10.1117/12.2183180
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