This paper presents machine learning classification on simulated data of permeable conducting spheres in air and seawater
irradiated by low frequency electromagnetic pulses. Classification accuracy greater than 90% was achieved. The simulated data
were generated using an analytical model of a magnetic dipole in air and seawater placed 1.5 – 3.5 m above the center of the sphere
in 50 cm increments. The spheres had radii of 40 cm and 50 cm and were of permeable materials, such as steel, and non-permeable
materials, such as aluminum. A series RL circuit was analytically modeled as the transmitter coil, and an RLC circuit as the receiver
coil. Additive white Gaussian noise was added to the simulated data to test the robustness of the machine learning algorithms to
noise. Multiple machine learning algorithms were used for classification including a perceptron and multiclass logistic regression,
which are linear models, and a neural network, 1D convolutional neural network (CNN), and 2D CNN, which are nonlinear models.
Feature maps are plotted for the CNNs and provide explainability of the salient parts of the time signature and spectrogram data
used for classification. The pulses investigated, which expand the literature, include a two-sided decaying exponential, Heaviside
step-off, triangular, Gaussian, rectangular, modulated Gaussian, raised cosine, and rectangular down-chirp. Propagation effects,
including dispersion and frequency dependent attenuation, are encapsulated by the analytical model, which was verified using
finite element modeling. The results in this paper show that machine learning methods are a viable alternative to inversion of
electromagnetic induction (EMI) data for metallic sphere classification, with the advantage of real-time classification without the
use of a physics-based model. The nonlinear machine learning algorithms used in this work were able to accurately classify metallic
spheres in seawater even with significant pulse distortion caused by dispersion and frequency dependent attenuation. This paper
presents the first effort towards the use of machine learning to classify metallic objects in seawater based on EMI sensing.