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Optical fibre spectrometer combined with a magnetic resonance sensor for multiple depth monitoring

Under some circumstances, it is necessary to do optical spectroscopy on a front surface while at the same time monitoring the presence of a hidden metallic layer. Here, a novel sensor system to do this based on the combination of a visible light optical fibre spectrometer with a magnetic resonance eddy current sensor is demonstrated. It is shown that the the eddy current sensor can probe a hidden metallic film placed up to 1 cm behind the dielectric front surface. The combination of two such detection principles allows one to probe layered materials at multiple depths, revealing their electromagnetic properties at different frequencies.