Marcus Stiemer

Simulation based analysis of field correlation and ergodicity of a reverberation chamber

The electromagnetic fields in an electromagnetic reverberation chamber (ERC) with a rotating mode stirrer are numerically determined for each stirrer position via a finite element (FE) simulation. With these results both a correlation analysis according to the present engineering standard is performed and the spatial variation of the field averaged over all stirrer positions is computed. Thus, it is studied how far the notions of correlation and ergodicity of the chamber are related. With an efficient FE simulation at hand, further studies comprising loaded chambers and geometry optimization for electromagnetic compatibility testing will become possible.

On the validity and statistical significance of HEMP test standards

Critical electronic devices, i.e. units whose operation is essential, must be able to work even when exposed to extreme electromagnetic signals, such as High Altitude Nuclear Electromagnetic Pulses (HEMP). As a consequence, field tests with HEMP simulators are mandatory. In this paper, several statistical approaches to assess the quality of HEMP field tests are presented and compared to the test protocol specified by a German standard [1]. The proposed schemes are based on acceptance sampling and confidence intervals and improve the significance of the derived conclusions. In addition, more advanced techniques are discussed.

Numerical Optimization of Current Parameters in Combined Electromagnetic-Classical Forming Processes

A method for the virtual process design of combined quasi-static and electromagnetic forming processes based on a thorough process simulation is developed. Its flexibility is demonstrated by means of an identification problem for process parameters yielding a minimum bottom edge radius in round cup forming. Particularly, an optimum double exponential current pulse is identified. This class of pulses is parameterized as an example for pulses with mono-directed current employed to reduce the wear of the tool coil.

On the quality of a real open area test site

The quality of a real open area test site is affected by many factors, e.g., constructive elements carrying antennas, their power supply, the electric properties of the ground, or surrounding scattering sources. To quantitatively determine the influence of all factors that make a real test site differ from an ideal one, numerical simulation is employed here. Hence, it will become possible to arrange a test site so that all requirements for antenna calibration and electromagnetic compatibility testing according to engineering standards are granted.

Gene Expression Analysis in Human Peripheral Blood Cells after 900 MHz RF-EMF Short-Term Exposure

Radiofrequency electromagnetic fields (RF-EMF) are a basic requirement of modern wireless communication technology. Statutory thresholds of RF-EMF are established to limit relevant additional heat supply in human tissue. Nevertheless, to date, questions concerning nonthermal biological effects have yet to be fully addressed. New versions of microarrays (8 × 60K v2) provide a higher resolution of whole genome gene expression to display adaptive processes in cells after irradiation. In this ex vivo/in vitro study, we irradiated peripheral blood cells from five donors with a continuous wave of 900 MHz RF-EMF for 0, 30, 60 and 90 min. Gene expression changes (P ≤ 0.05 and ≥twofold differences above or below the room temperature control exposed samples) were evaluated with microarray analysis. The results were compared with data from room temperature + 2°C samples. Verification of microarray results was performed using bioinformatic analyses and qRT-PCR. We registered a lack of an EMF-specific gene expression response after applying the false discovery rate adjustment (FDR), using a high-stringency approach. Low-stringency analysis revealed 483 statistically significant deregulated transcripts in all RF-EMF groups relative to the room temperature exposed samples without an association with their corresponding room temperature + 2°C controls. Nevertheless, these transcripts must be regarded as statistical artefacts due to the absence of a targeted biological response, including enrichment and network analyses administered to microarray expressed gene subset profiles. Correspondingly, 14 most promising candidate transcripts examined by qRT-PCR displayed an absence of correlation with respect to the microarray results. In conclusion, these findings indicate that 900 MHz EMF exposure establishing an average specific absorption rate of 9.3 W/kg to whole blood cells is insufficient to induce nonthermal effects in gene expression during short-time exposure up to 90 min.

oFEM: An object oriented finite element package for Matlab

We introduce oFEM, an efficient and flexible finite element environment for Matlab. The proposed code is fast due to vectorization and scalable in terms of computation time. It further offers interfaces to pre and post processing tools, to import meshes and export computed data. A strict object oriented approach makes it flexible, easily extensible and applicable to a broad range of applications.

Constructive adjustment of characteristic parameters of a mode-stirred reverberation chamber for EMC tests and power spectroscopy

The purpose of this work is to develop a knowledge base which allows for the assessment of the influence of individual construction parameters on a mode stirred chambers performance in its particular area of application. With this knowledge, it would be possible to adapt a chamber for a particular purpose, e.g. to use the chamber for electromagnetic compatibility test procedures or for power spectroscopic measurements. The scattering parameters as well as the field strength and the distribution of the electric field are employed to quantify the influencing construction parameters of the chamber. In addition, a concept for a 3D positioning system is presented which can be used to accurately measure the electric field in the chamber. This is necessary in order to be able to make statistical statements about the electric field distribution.

Application of generalized linear models to evaluate nuclear EMP tests

High Altitude Nuclear Electromagnetic Pulses (HEMP) are among most extreme external signals that can interfere with an electric device. To ensure the survival of vital components even in case of a HEMP event, several procedures have been designed to test DUTs in a lab environment. As a consequence, field tests with HEMP simulators are mandatory. A valid estimation of the level which will cause a failure of the DUT due to the external HEMP (either generated artificially or by a real life HEMP event) will allow engineers to fix better field levels for HEMP susceptibility tests and to avoid overtesting. This paper will apply binary regression models such as as logit or probit on the results of HEMP tests from the literature and estimate an more applicable test level as a first step. Concluding, additional possibilities of the regression models are discussed.

Finite element simulation of the frequency-dependent polarization of biological cells

The impact of electromagnetic fields on biological tissue is increasingly gaining relevance for electromagnetic compatibility considerations. To estimate such effects, the determination of the electromagnetic exposition on the cellular level is essential. Hence, a new method for the finite element simulation of biological cells in electrolyte solution based on the electro-quasistatic approximation to Maxwells equations is presented here. By non-overlapping iterative domain decomposition (IDD), a more efficient and accurate incorporation of surface charge relaxation on material interfaces is achieved than by former methods. IDD does not only lead to an efficient consideration of the interface coupling of electrical flux- and current densities, but also overcomes numerical problems related to size differences of individual cell components. A completely parallel treatment of the resulting subdomains will enable the simulation of large cell systems in the future. The approach is validated in the case of a time-harmonic external field. Further, numerical errors and convergence properties are analyzed.

Determination of Extremal Points and Weighted Discrete Minimal Riesz Energy with Interior Point Methods

The asymptotic approximation of continuous minimal s-Riesz energy by the discrete minimal energy of systems of n points on regular sets in \(\mathbb{R}^{3}\) is studied. For this purpose an optimization framework for the numerical solution of the corresponding Gaus variational problem based on an interior point method is developed. Moreover, numerical results for ellipsoids and tori are presented.