We present the logical expressions (LE) approach that allows fast computation of three-dimensional eddy current problems, including parts in motion. The approach applies time-dependent logical expressions to describe moving parts of the model on a fixed computational grid. The study is motivated by a novel nondestructive testing technique called Lorentz force eddy current testing (LET), which enables the detection of defects lying deep inside a conducting material. Depending on the definition of the frame of reference, we present two different implementations of the LE approach referred to as 1) moving magnet approach, and 2) moving defect approach. In order to demonstrate the advantages of the LE approach, we compare its results with the sliding mesh technique. The validation of the obtained results with experiments is also presented.Index Terms-Eddy current testing, finite element method (FEM), logical expressions, Lorentz force, nondestructive testing.

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The problem of determining defects in structures using eddy current methods was investigated. The goal of this work is to demonstrate that the forces generated by the eddy currents and acting back on the magnet system can be used to detect defects in the object. Numerical simulations and experimental investigations have been performed. This novel technique has been found to be sensitive enough to detect even deep defects in an Aluminium bar moving relative to the field-generating magnet system

Interaction of a small permanent magnet with a liquid metal duct flow Journal of Applied Physics 112, 124914 (2012) The present communication reports a new technique for the contactless measurement of the specific electrical conductivity of a solid body or an electrically conducting fluid. We term the technique "Lorentz force sigmometry" where the neologism "sigmometry" is derived from the Greek letter sigma, often used to denote the electrical conductivity. Lorentz force sigmometry (LoFoS) is based on similar principles as the traditional eddy current testing but allows a larger penetration depth and is less sensitive to variations in the distance between the sensor and the sample. We formulate the theory of LoFoS and compute the calibration function which is necessary for determining the unknown electrical conductivity from measurements of the Lorentz force.