Mladen Zec

Lorentz force sigmometry: A contactless method for electrical conductivity measurements

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. We conduct a series of experiments which demonstrate that the measured Lorentz forces are in excellent agreement with the numerical predictions. Applying this technique to an aluminum sample with a known electrical conductivity of rAl ¼ 20:4MS=m and to a copper sample with rCu ¼ 57:92MS=m we obtain rAl ¼ 21:59MS=m and rCu ¼ 60:08MS=m, respectively. This demonstrates that LoFoS is a convenient and accurate technique that may find application in process control and thermo-physical property measurements for solid and liquid conductors. V C 2012 American Institute of Physics.

Finite Element Analysis of Nondestructive Testing Eddy Current Problems With Moving Parts

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.

Fast Technique for Lorentz Force Calculations in Non-Destructive Testing Applications

The primary aim of this paper is to present new 2-D/3-D numerical technique providing fast calculations of Lorentz forces acting on a permanent magnet moving relatively to a solid electrically conducting object. This specific field configuration represents a typical problem arising in novel non-destructive testing and evaluation technique known as the Lorentz force eddy-current testing (LET). The proposed technique, referred to as the weak reaction approach (WRA) is based on several model simplifications, which, in the limits of low magnetic Reynolds numbers, allow considerable reduction of the simulation time while maintaining the accuracy of the solution. For evaluation of the computational requirements and verification of the obtained results, the well-established sliding mesh technique is used. Finally, the presented WRA is applied to various parametric studies in form of defect imaging, which can throw light on possible reconstruction and localization of defects by solving an inverse LET problem.

Application of Lorentz force eddy current testing and eddy current testing on moving nonmagnetic conductors

Lorentz force eddy current testing is a novel nondestructive testing technique which can be applied preferably to the identification of internal defects in non-ferromagnetic moving conductors. This paper describes the comparison of this new technique with well-known eddy current testing. Measurements and numerical simulations have been done for both techniques for artificial subsurface defects in a test specimen made of Aluminum alloy moving with constant velocity.