Calculation Errors of the Electric Field Induced in a Human Body Under Quasi-Static Approximation Conditions

Abstract

We analytically compute the internal electric fields in a spherical model and numerically calculate the fields in the head of a realistic human model exposed to the incident magnetic fields only or to both the incident electric and magnetic fields. We then investigate the effects of ignoring the electric fields incident on a biological object that is exposed to electromagnetic fields (EMFs) from an IF source, such as an induction hob or a wireless power transmission system, in which the magnetic fields are generally dominant. The induced electric fields inside a lossy dielectric sphere exposed to a plane wave are computed using rigorous formulas and quasi-static approximation (QSA) formulas. The highest frequency to which a QSA is valid and the difference made by ignoring the incident electric fields by varying the ratio of incident electric field intensity to incident magnetic field intensity (field impedance, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> ) are investigated through this computation. We also estimate the internal electric fields and specific absorption rates in the head of a Japanese adult male model exposed to EMFs or to magnetic fields only at 1 and 10 MHz with the finite-difference time-domain method, a full-wave analysis that takes both electric and magnetic fields into consideration, and the impedance method, a QSA calculation that takes only the magnetic fields into consideration. The <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> ratio must be lower than 17 Ω to ignore the electric fields incident on the sphere with errors of less than 5% from 10 Hz to 10 MHz. The difference made by ignoring the incident electric fields in the realistic head model is a little larger than that in the sphere model. The results suggest that we should carefully consider <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> to exactly evaluate the dosimetry.