Andreas Barchanski

Impact of the displacement current on low-frequency electromagnetic fields computed using high-resolution anatomy models

We present a comparison of simulated low-frequency electromagnetic fields in the human body, calculated by means of the electro-quasistatic formulation. The geometrical data in these simulations were provided by an anatomically realistic, high-resolution human body model, while the dielectric properties of the various body tissues were modelled by the parametric Cole-Cole equation. The model was examined under two different excitation sources and various spatial resolutions in a frequency range from 10 Hz to 1 MHz. An analysis of the differences in the computed fields resulting from a neglect of the permittivity was carried out. On this basis, an estimation of the impact of the displacement current on the simulated low-frequency electromagnetic fields in the human body is obtained.

Efficient calculation of current densities in the human body induced by arbitrarily shaped, low-frequency magnetic field sources

In this paper, we extend the scalar-potential finite-difference (SPFD) approach in order to consider arbitrarily shaped time-harmonic field sources. The SPFD approach is commonly used to compute the currents induced by an externally applied magnetic field in regions with weak, heterogeneous conductivities such as, e.g., the human body. We present the extended scalar-potential finite-difference (Ex-SPFD) approach as a two step algorithm. In the first step, the excitation is computed by solving the magnetoquasistatic curl-curl equation on a coarse grid that is well adapted for the field sources. In the second step, the magnetic vector potential is prolongated onto a finer grid and a divergence correction inside the conductor is applied. Using the Maxwell-grid-equations (MGEs) of the finite integration technique, a geometric discretization scheme for Maxwells equations, this new approach has been implemented in a parallel environment in order to account for the memory-demanding high-resolution anatomy models used for the calculation of induced currents inside the human body. We demonstrate the validity and the improved numerical performance of the new approach for a test case. Finally, an application example of a human exposed to a realistic electromagnetic field source is presented.

Local grid refinement for low-frequency current computations in 3-D human anatomy models

The calculation of current densities in voxel-based high-resolution anatomy models allows insight in the current distribution inside the human body. The geometric complexity of the human body requires a very high resolution in order to properly resolve small organs. We present a local grid refinement scheme for low-frequency current calculations, allowing to finely resolve areas of particular interest. Using a Lagrange-multiplier approach, the whole model including the fine and coarse grid domains can be computed with only one solution of an algebraic system of equations. The presented approach is validated and tested on numerical examples

Using Domain Decomposition Techniques for the Calculation of Low Frequency Electric Current Densities in High Resolution 3D Human Anatomy Models

Purpose – Improved numerical calculation techniques for low‐frequency current density distributions within high‐resolution anatomy models caused by ambient electric or magnetic fields or direct contact to potential drops using the finite integration technique (FIT).Design/methodology/approach – The methodology of calculating low‐frequency electromagnetic fields within high‐resolution anatomy models using the FIT is extended by a local grid refinement scheme using a non‐matching‐grid formulation domain. Furthermore, distributed computing techniques are presented. Several numerical examples are analyzed using these techniques.Findings – Numerical simulations of low‐frequency current density distributions may now be performed with a higher accuracy due to an increased local grid resolution in the areas of interest in the human body voxel models when using the presented techniques.Originality/value – The local subgridding approach is introduced to reduce the number of unknowns in the very large‐scale linear a...

Transient calculation of the induced currents inside the brain during magnetic stimulation

Purpose – Transient calculation of currents in brain tissue induced during a transcranial magnetic stimulation treatment.Design/methodology/approach – Because of the short pulses used in this technique a time‐harmonic approximation is no longer valid, and transient effects have to be considered. We have performed a Fourier analysis of the induced currents calculated in a high‐resolution model of the brain using the extended scalar potential finite differences (Ex‐SPFD) approach.Findings – The peak induced currents in the transient development of the pulse are higher by a factor of approximately seven than the time harmonic solutions at the fundamental frequency. Furthermore, an analysis of the impact of the conductivity dispersion revealed an increase in the peak induced currents by 17.3 percent for white matter and by 20.8 percent for gray matter.Originality/value – Using the numerically efficient Ex‐SPFD approach, along with a high performance cluster, the current densities inside the brain can be calcu...

Large-Scale Calculations of Low-Frequency Induced Currents in High-Resolution Human Body Models.

We present large-scale computations of currents induced in the human body, arising from an external low-frequency magnetic field. Using the Ex-SPFD approach, a two-step algorithm for the efficient calculation of induced currents in inhomogeneous, low-conductive materials, models consisting of hundred millions of unknowns are used. The high model resolution allows a detailed analysis of the induced currents, even in small organs like in the eye

Picosecond turn-on dynamics of vertical-cavity surface-emitting lasers

This work presents experimental studies of the turn-on emission dynamics of a state-of-the-art selectively oxidized VCSEL with 14 /spl mu/m aperture size. These studies provide a comprehensive analysis on picosecond time scales with simultaneous 2D spatial resolution, polarization resolution, and resolution of the spectral distribution of the transverse modes.

Spatio-temporal turn-on dynamics of VCSELs

We present 2D-spatially and picosecond-resolved measurements of VCSEL emission, unveiling their rich dynamics, manifesting itself in temporal changes of the modal, polarization and spatial characteristics.