On the Use of Conformal Models and Methods in Dosimetry for Non-Uniform Field Exposure

Dragan Poljak, Mario Cvetković, Oriano Bottauscio, Akimasa Hirata, Ilkka Laakso, Esra Neufeld, Sylvain Reboux, Craig Warren, Antonis Giannopolous, and Fumie Costen, IEEE Transactions on Electromagnetic Compatibility, online 18 July, 2017, doi: 10.1109/TEMC.2017.2723459

Numerical artifacts affect the reliability of computational dosimetry of human exposure to low-frequency electromagnetic fields. In the guidelines of the International Commission of Non-Ionizing Radiation Protection, a reduction factor of 3 was considered sufficient to account for numerical uncertainties associated with determination of limitting values for human exposure. However, the rationale for this value is insecure. The IEEE International Committee on Electromagnetic Safety has published a research agenda to resolve numerical uncertainties in low-frequency dosimetry. For this purpose, intercomparison of results computed by different research groups using a variety of methods is important. In previous intercomparison studies for low-frequency (LF) exposures, only a few computational methods were used, and the computational scenario was limited to a uniform magnetic field exposure. In this study, we present the application of various numerical techniques, including several finite-element method (FEM) schemes, method of moments (MoM), and boundary-element method (BEM) variants, and, finally, a hybrid FEM/BEM approach. As a computational example, the electric field induced in the brain by the coil used in transcranial magnetic stimulation is investigated. Intercomparison of the computational results is presented qualitatively. Some remarks regarding the effectiveness and limitations of the application of the various computational methods are provided.

The scientific and technical impact of the study can be summarized as:

  • Intercomparison of several commputational methods applied to conformal models in LF dosimetry, including nonuniform exposure, is reviewed and presented
  • The MoM, FEM, BEM, and hybrid FEM/BEM approaches were implemented to investigate the transcranial magnetic stimulation setup for a sphere and simplified homogeneous isotropic brain geometry
  • Differences attributable to the implementation of methods for nonuniform exposure are addressed
  • For future work, precise source information and the specific evaluation trajectories for the planes and setups investigated could be included for more quantitative comparison of the variations introduced by the different approximation methods 
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