Transcranial magnetic stimulation (TMS) uses transient magnetic field to activate brain regions by inducing an electric field across and an electric current through neurons. Functional magnetic resonance imaging (fMRI) allows the measurement of brain activity making it a potentially useful tool in combination with TMS to analyze the sites of stimulation within the brain. TMS typically utilizes a high current pulse up to 8 kA at approximately 2.5 kHz to induce an electric field inside the brain sufficient for neural stimulation. Lorentz forces are created on the TMS coil and are increased in the presence of a high external magnetic field from the MRI magnet. This study implements a realistic coil model developed from X-ray images of a commercial figure-of-eight TMS coil. The Lorentz forces and stress profile inside the current carrying material of this realistically modeled coil are presented. Results show that the maximum Lorentz force density is significantly larger than previously calculated, by a factor of more than 3.

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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.

Purpose -The purpose of this paper is to present a novel electromagnetic non-destructive evaluation technique, so called Lorentz force eddy current testing (LET). This method can be applied for the detection and reconstruction of defects lying deep inside a non-magnetic conducting material. Design/methodology/approach -In this paper the technique is described in general as well as its experimental realization. Besides that, numerical simulations are performed and compared to experimental data. Using the output data of measurements and simulations, an inverse calculation is performed in order to reconstruct the geometry of a defect by means of sophisticated optimization algorithms. Findings -The results show that measurement data and numerical simulations are in a good agreement. The applied inverse calculation methods allow to reconstruct the dimensions of the defect in a suitable accuracy. Originality/value -LET overcomes the frequency dependent skin-depth of traditional eddy current testing due to the use of permanent magnets and low to moderate magnetic Reynolds numbers (0.1-1). This facilitates the possibility to detect subsurface defects in conductive materials.