Martin Zang

Numerical schemes for high-resolution dosimetry simulations of automotive low frequency Inductive Power Transfer systems

This paper deals with the simulation of human exposure to magneto-quasistatic fields of Inductive Power Transfer (IPT) systems. Since the applicability of direct eddy current field solvers for such problems becomes disputable when the scale and/or the resolution of geometries increase, both the Scaled-Frequency FDTD method and the Scalar-Potential Finite Difference (SPFD) approach are extended and used here. Numerical examples for the verification of the procedures and an application including shielding effects in nearby conductive structures are presented. The results are compared to the limits recommended by the International Commission on Non-Ionizing Radiation Protection (ICNIRP).

A Co-Simulation Scalar-Potential Finite Difference Method for the Numerical Analysis of Human Exposure to Magneto-Quasi-Static Fields

A two-step approach for the simulation of the exposure of a human body to magneto-quasi-static fields is presented. The co-simulation scalar-potential finite difference method is a calculation scheme, where a distribution of the magnetic vector potential inside the biological tissues is derived from a free space magnetic source field simulation using a tree-cotree gauging algorithm. With the obtained magnetic vector potential, the electric field strength inside the voxel representation of the biological tissues is calculated solving a high-dimensional discrete Poisson equation on a high-performance workstation with multiple graphics processing units (GPUs). An exposure scenario, including an inductive power transfer system, a car model, and an anatomical human body voxel model, is simulated using this approach, and the results are compared with a monolithic scaled-frequency finite difference time domain simulation. The maximum body-internal electric field strength (voxel average) is determined and compared with basic restrictions recommended by the International Commission on Non-Ionizing Radiation Protection.

Numerical Computation of Temperature Elevation in Human Skin Due to Electromagnetic Exposure in the THz Frequency Range

The ongoing development of new applications in the terahertz (THz) frequency range, such as wireless communication systems, full-body scanners, or other imaging procedures for biological and medical techniques, rapidly increases the number of persons who are potentially exposed to the electromagnetic radiation of those devices. Studies of thermal effects in humans caused by electromagnetic (EM) exposure with frequencies in the THz frequency range can rarely be found in the literature. In this paper, a method for the numerical computation of a potential thermal response in human skin due to EM fields between 0.1 and 10 THz is introduced. The method starts with the development of adequate simulation models for EM fields with penetration depths less than 1 mm. In a further step, it covers the provision of absolutely needed dielectric tissue parameters with help of the “effective medium theory,” since material properties above 100 GHz are not listed in the commonly consulted databases. The absorbed power in EM exposed human skin models of different complexity is calculated and subsequently used as heat source for temperature simulations. Spatial and time-dependent temperature profiles in the tissue are analyzed for transient and continuous exposures.

Numerical Verification of the Applicability of the Effective Medium Theory With Respect to Dielectric Properties of Biological Tissue

Especially in the THz region, little data is available regarding material properties based on measurements. It has been argued that the effective medium theory could provide a useful tool to estimate material data needed for electromagnetic field computations. In this paper, two numerical approaches are presented to test the applicability of the effective medium theory (EMT) with special regard to mm- and sub-mm-wavelengths. One approach is based on the well-known free-space method and the other one on a power loss evaluation scheme. Within the scope of application of the free-space method, the usability of the EMT is proven for two sets of dielectric tissue parameters on a longitudinally homogeneous and transversely structured sample. Moreover, power loss evaluation is a suitable method to show the applicability of the EMT. Analysis of layered models at 1-10 THz confirms that the EMT is a suitable tool to develop equivalent homogenized models with maximum errors for the dissipated powers of about 1%. In a more realistic example for a physiological fluid with spherical inclusions, the EMT yields an error of less than 1%.

Simulation of Inductive Power Transfer Systems Exposing a Human Body With Two-Step Scaled-Frequency FDTD Methods

For the simulation of the human exposure to magnetoquasi-static fields of inductive power transfer (IPT) systems two domain decomposition methods—the coupled scaled-frequency finite-difference time-domain (SF-FDTD) method and the co-simulation SF-FDTD method—are presented in this paper. Using both Huygens’ principle and the SF-FDTD method, a two-step approach is developed resulting in two different simulation schemes, the coupled SF-FDTD method and the co-simulation SF-FDTD method, respectively. These two-step schemes are able to replace high-dimensional monolithic exposure simulation models by problems of smaller size with less computer memory demand. An exposure scenario, including an IPT system, a car, and a high-resolution human body voxel model, is modeled and simulated using both methods. A full-scale monolithic SF-FDTD simulation is used as reference and its results—i.e., the body-internal electric field strengths—are compared with the results of the presented two-step methods. The maximum of the body-internal electric field strength (voxel average) is determined and compared to basic restrictions given by the international commission on nonionizing radiation protection.

A co-simulation Scalar-Potential Finite Difference (SPFD) approach for the simulation of human exposure to magneto-quasistatic fields

For the simulation of human exposure to magneto-quasistatic fields the applicability of direct eddy current solvers becomes disputable with increasing scale and/or resolution of geometries. As an alternative, the Scalar-Potential Finite Difference (SPFD) approach is extended here using a tree-cotree generated vector potential.

Waveguide simulation approach for transmission analysis of reinforced concrete wall structures

The determination of electromagnetic wall transmittance of buildings is important for mobile communications and with reference to safety issues for (intentional) electromagnetic interference (EMI/IEMI) problems. Thus, the knowledge of the inhomogeneous wall structure is significant for the transmittance analysis. Here, a reinforced concrete wall with a double rebar steel grid is considered. In most numerical simulation software tools, the calculation of a perpendicular field incidence is much easier than for oblique angles of incidence. To model obliquely incident waves in a finite space, field propagation features of a rectangular waveguide are used with an inserted representative sample of the inhomogeneous wall. Operation of the waveguide with the TE10-eigenmode is decomposable into two obliquely propagating waves allowing to compute the transmission factor for an obliquely incident uniform plane wave at reduced computational time and costs. This method is extended to provide for higher frequencies in the MHz range by using suitable higher eigenmodes (TE20, TE30, ...) and to overcome the problem of neglecting grid periodicities of the rebar steel grid. Some of the numerical results achieved with the waveguide model are compared with results based on a model of a free Gaussian beam.