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Abstract. Exact solutions for the electromagnetic response of a transmit-receive coil pair situated above two parallel plates separated by a gap, were developed using the recently published general model of Desjardins et al. that accounts for all electromagnetic interactions between the voltage-driven probe and the conducting samples. This model was then compared to the well-known model developed by Dodd and Deeds, which assumes a constant amplitude sinusoidal current and an open-circuit pick-up coil. Both models were compared with experimental results that measured the gap -materials simulated the electromagnetic properties of a Zr 2.5% Nb pressure tube and Zr-2 calandria tube, respectively, as found in the fuel channels of CANDU ® reactors. It was observed that while the Dodd and Deeds' model as applied to this work achieved a good shape agreement with experimental data for excitation frequencies at 2 kHz, at the higher frequency of 16 kHz good agreement was not achieved. In contrast, the model of Desjardin's et al., adapted for a transmitreceive probe configuration above two infinite flat plates, achieved an excellent shape agreement at both frequencies.

The capability of magnetic induction to transmit signals in attenuating environments has recently gained significant research interest. The wave aspect—magnetoinductive (MI) waves—has been proposed for numerous applications in RF-challenging environments, such as underground/underwater wireless networks, body area networks, and in-vivo medical diagnosis and treatment applications, to name but a few, where conventional electromagnetic waves have a number of limitations, most notably losses. To date, the effects of eddy currents inside the dissipative medium have not been characterised analytically. Here we propose a comprehensive circuit model of coupled resonators in a homogeneous dissipative medium, that takes into account all the electromagnetic effects of eddy currents, and, thereby, derive a general dispersion equation for the MI waves. We also report laboratory experiments to confirm our findings. Our work will serve as a fundamental model for design and analysis of every system employing MI waves or more generally, magnetically-coupled circuits in attenuating media.

A validated analytical model of a transmit–receive coil pair situated above two parallel plates, separated by an air gap, was used as the basis for an inversion algorithm (IA) to extract probe liftoff, second layer plate resistivity, and plate-to-plate gap from multi-frequency eddy current data. The IA was tested over a large range of first layer wall thickness (3.80–4.64 mm), second layer plate resistivity (1.7–174 µΩ cm), second layer wall thickness (1.20–4.85 mm), probe liftoff (2.8–7.9 mm), and plate-to-plate gap (0–13.3 mm). At nominal liftoff (2.8 mm), the IA achieved a gap measurement accuracy of ±0.7 mm and was able to return good estimates of the second layer resistivity within ±1 μΩ cm for low resistivity samples, but with decreasing accuracy for higher resistivities. When the gap was fixed, the IA was able to measure changes in probe liftoff (relative to nominal) to an accuracy of ±0.2 mm. The reported accuracy and a demonstration for the ability to accurately estimate parameters outside of the calibration range provide confidence in the potential utility of the algorithm.