title: Dielectric polarization transients in biological tissue moving in a static magnetic field.
abstract: Movement of a body in a static magnetic field gives rise to the Lorentz force that induces in the medium both electric currents and dielectric polarization. It is usually assumed that the conductivity of biological tissues is sufficiently high in order to neglect dielectric phenomenon arising from non-equilibrium of polarization charges. However, the permittivity of biological tissues is extremely high and the relaxation time of free charges is relatively low. In this study, we examined the effect of dielectric polarization on the electric field (EF) induced by human movements in a strong magnetic field (MF). Analytic equations for brain and bone equivalent spheres translating and rotating in a uniform MF were derived from Maxwell equations. Several examples were computed by using Fast Fourier Transform to examine transient dielectric effects in a time domain. The results showed that dielectric polarization transients do arise, but in the case of homogeneous medium, they are vanishingly small. In contrast, the local dielectric transients are not vanishingly small in heterogeneous medium. However, due to limited acceleration and deceleration of normal human movements, the transients are relatively small, at maximum a few dozen percent of the EF induced by the change of the magnetic flux. Taking into account the high uncertainty in numerical simulation, the dielectric transients can be neglected in the case of biological materials but not in the case of many non-biological materials of low conductivity. Bioelectromagnetics. 37:409-422, 2016. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Radiation and Nuclear Safety Authority (STUK), Helsinki, Finland.
authors.forename: Kari
authors.initials: K
authors.lastname: Jokela
authors.affiliation: Department of Electrical Engineering and Automation, Aalto University School of Electrical Engineering, Espoo, Finland.
authors.forename: Ilkka
authors.initials: I
authors.lastname: Laakso
mesh_terms: D017097:Electric Impedance; D006257:Head; D006801:Humans; D060526:Magnetic Fields; D008954:Models, Biological; D009068:Movement; D012399:Rotation
keywords: Lorentz force; SMF; analytical model; induced EF sphere; movement