Search

Your search keyword '"Rennings, Andreas"' showing total 227 results
Start Over Author "Rennings, Andreas"
227 results on '"Rennings, Andreas"'

1. The Importance of Subcellular Structures to the Modeling of Biological Cells in the Context of Computational Bioelectromagnetics Simulations

Author

Jerbic, Kevin, Svejda, Jan Taro, Sievert, Benedikt, Rennings, Andreas, Fröhlich, Jürg, and Erni, Daniel

Subjects
Physics - Applied Physics
Abstract

Numerical investigation of the interaction of electromagnetic fields with eukaryotic cells requires specifically adapted computer models. Virtual microdosimetry, used to investigate exposure, requires volumetric cell models, which are numerically challenging. For this reason, a method is presented here to determine the current and power densities occurring in single cells and their distinct compartments in a spatially accurate manner as a first step towards multicellular models within the microstructure of tissue layers. To achieve this, 3D models of the electromagnetic exposure of generic eukaryotic cells of different shape (i.e. spherical and ellipsoidal) and internal complexity (i.e. different organelles) are performed in a virtual, FEM-based capacitor experiment in the frequency range from 10 Hz to 100 GHz. In this context, the spectral response of the current and power distribution within the cell compartments is investigated and any effects that occur are attributed either to the dispersive material properties of these compartments or to the geometric characteristics of the cell model investigated in each case. In these investigations, the cell is represented as an anisotropic body with an internal distributed membrane system of low conductivity that mimics the endoplasmic reticulum in a simplified manner. This will be used to determine which details of the cell interior need to be modeled, how the electric field and the current density will be distributed in this region, and where the electromagnetic energy is absorbed in the microstructure regarding electromagnetic microdosimetry. Results show that for 5G frequencies, membranes make a significant contribution to the absorption losses., Comment: 22 pages, 10 figures | Updates: [v1] initial upload; [v2] COPYRIGHT NOTICE added after publication of the manuscript

Published
2022
Full Text
View/download PDF

3. Limits of effective material properties in the context of an electromagnetic tissue model

Author

Jerbic, Kevin, Neumann, Kevin, Svejda, Jan Taro, Sievert, Benedikt, Rennings, Andreas, and Erni, Daniel

Subjects
Physics - Applied Physics
Abstract

Most calibration schemes for reflection-based tissue spectroscopy in the mm-wave/THz-frequency range are based on homogenized, frequency-dependent tissue models where macroscopic material parameters have either been determined by measurement or calculated using effective material theory. However, as the resolution of measurement at these frequencies captures the underlying microstructure of the tissue, here we will investigate the validity limits of such effective material models over a wide frequency range (10 MHz - 200 GHz) . Embedded in a parameterizable virtual workbench, we implemented a numerical homogenization method using a hierarchical multiscale approach to capture both the dispersive and tensorial electromagnetic properties of the tissue, and determined at which frequency this homogenized model deviated from a full-wave electromagnetic reference model within the framework of a Monte Carlo analysis. Simulations were carried out using a generic hypodermal tissue that emulated the morphology of the microstructure. Results showed that the validity limit occurred at surprisingly low frequencies and thus contradicted the traditional usage of homogenized tissue models. The reasons for this are explained in detail and thus it is shown how both the lower "allowed" and upper "forbidden" frequency ranges can be used for frequency-selective classification/identification of specific material and structural properties employing a supervised machine-learning approach. Using the implemented classifier, we developed a method to identify specific frequency bands in the forbidden frequency range to optimize the reliability of material classification., Comment: 19 pages, 22 figures | Updates: [v1] initial upload; [v2] typos corrected, acknowledgements added, Fig. 18 extended; [v3] minor correction Fig. 11 [v4] Appendix: 3D Reference Simulation (major change) [v5] COPYRIGHT NOTICE added after publication of the manuscript

Published
2020
Full Text
View/download PDF

10. Investigating the influence of dielectric pads in 7T magnetic resonance imaging – simulated and experimental assessment

Author

Garcia Maíra M., Chaim Khallil T., Otaduy Maria C. G., Rennings Andreas, Erni Daniel, Vatanchi Maryam, and Zylka Waldemar

Subjects
7t mri, dielectric pads, experiment, electromagnetic simulation, dipole rf coil, phantom, b1, homogeneity, sar, mri safety, Medicine
Abstract

Dipole radiofrequency (RF) elements have been successfully used to compose multi-channel RF coils for ultrahigh fields (UHF) magnetic resonance imaging (MRI). As magnetic components of RF fields (B1) can be very inhomogeneous at UHF (B0≥7T), dielectric pads with high dielectric constants were proposed to improve the B1 efficiency and homogeneity [1]. Dielectric pads can be used as a passive B1 shimmimg technique thanks to inducing a strong secondary magnetic field in their vicinity. The use of such dielectric pads affect not only the B1 field but also the electric field. This in turn affects the specific absorption rate (SAR) and consequently the temperature distribution inside the patient’s body. To study these effects, a 29 cm-long transmission dipole RF coil element terminated by two meander was used for 7T MRI [2]. Using a cylindrical agarose-gel phantom, numerical and experimental results were analyzed with respect to homogeneity and amplitude of the magnetic and electric fields generated by the RF element in various configurations with and without dielectric pads. Calculated and measured B1 results were cross-checked and found to be in good agreement. When using dielectric pads B1 homogeneity and magnitude increase in regions where it was previously weak or insufficient. Calculations suggest that SAR distribution will change when using the pads.

Published
2020
Full Text
View/download PDF

12. Toward Mobile Integrated Electronic Systems at THz Frequencies

Author

Hillger, Philipp, van Delden, Marcel, Thanthrige, Udaya Sampath Miriya, Ahmed, Aya Mostafa, Wittemeier, Jonathan, Arzi, Khaled, Andree, Marcel, Sievert, Benedikt, Prost, Werner, Rennings, Andreas, Erni, Daniel, Musch, Thomas, Weimann, Nils, Sezgin, Aydin, Pohl, Nils, and Pfeiffer, Ullrich R.

Published
2020
Full Text
View/download PDF

13. Circular Polarization of Periodic Leaky-Wave Antennas with Axial Asymmetry: Theoretical Proof and Experimental Demonstration

Author

Otto, Simon, Chen, Zhichao, Al-Bassam, Amar, Rennings, Andreas, Solbach, Klaus, and Caloz, Christophe

Subjects
Physics - Classical Physics, Physics - Optics
Abstract

The paper includes two contributions. First, it proves that the series and shunt radiation components, corresponding to longitudinal and transversal electric fields, respectively, are always in phase quadrature in axially asymmetric periodic leaky-wave antennas (LWAs), so that these antennas are inherently elliptically polarized. This fact is theoretically proven and experimentally illustrated by two case-study examples, a composite right/left-handed (CRLH) LWA and a series-fed patch (SFP) LWA. Second, it shows (for the case of the SFP LWA) that the axial ratio is controlled and minimized by the degree of axial asymmetry., Comment: IEEE Transactions on Antennas and Propagation, Vol. 62, No. 4, April 2014

Published
2013
Full Text
View/download PDF

19. Towards Continuous Real-Time Plant and Insect Monitoring by Miniaturized THz Systems

Author

Sheikh, Fawad, primary, Prokscha, Andreas, additional, Batra, Aman, additional, Lessy, Dien, additional, Salah, Baha, additional, Sievert, Benedikt, additional, Degen, Marvin, additional, Rennings, Andreas, additional, Jalali, Mandana, additional, Svejda, Jan Taro, additional, Alibeigloo, Pooya, additional, Preuss, Christian, additional, Mutlu, Enes, additional, Kress, Robin, additional, Clochiatti, Simone, additional, Kolpatzeck, Kevin, additional, Kubiczek, Tobias, additional, Ullmann, Ingrid, additional, Root, Konstantin, additional, Brix, Fabian, additional, Krämer, Ute, additional, Vossiek, Martin, additional, Balzer, Jan C., additional, Weimann, Nils G., additional, Kaiser, Thomas, additional, and Erni, Daniel, additional

Published
2023
Full Text
View/download PDF

22. An Efficient Analysis of Scattering From Randomly Distributed Obstacles Using an Accurate Recursive Aggregated Centered T-Matrix Algorithm

Author

Degen, Marvin, Jandieri, Vakhtang, Sievert, Benedikt, Svejda, Jan Taro, Rennings, Andreas, and Erni, Daniel

Abstract

An efficient recursive aggregated centered transition matrix (T-matrix) algorithm (RACTMA) to analyze electromagnetic scattering from many randomly distributed obstacles is derived. The algorithm is based on the scatterer-centered T-matrix formalism and is accelerated using the aggregation concept—unlike other approaches—without violating the addition theorems. An analytical derivation for the T-matrix of multiple cylinders together with the details of the computational complexity are given. Scattering by more than 3000 noncircular elements is numerically studied, and the results for the scattered fields are compared with those obtained by a well-established recursive T-matrix algorithm and, to demonstrate a proper convergence, the results are also compared with a commercial finite element method (FEM)-based full-wave solver. The results show a perfect agreement and demonstrate a high computational efficiency of the proposed semianalytical formalism for normal and oblique incidences. The optical theorem and the reciprocity relationship are fully satisfied confirming the accuracy and numerical stability of the approach.

Published
2023
Full Text
View/download PDF

27. THz Measurements, Antennas, and Simulations: From the Past to the Future

Author

Sheikh, Fawad, primary, Prokscha, Andreas, additional, Eckhardt, Johannes M., additional, Doeker, Tobias, additional, Abbasi, Naveed A., additional, Gomez-Ponce, Jorge, additional, Sievert, Benedikt, additional, Svejda, Jan Taro, additional, Rennings, Andreas, additional, Barowski, Jan, additional, Schulz, Christian, additional, Rolfes, Ilona, additional, Erni, Daniel, additional, Molisch, Andreas F., additional, Kurner, Thomas, additional, and Kaiser, Thomas, additional

Published
2023
Full Text
View/download PDF

30. Towards Continuous Real-Time Plant and Insect Monitoring by Miniaturized THz Systems

Author

Sheikh, Fawad, Prokscha, Andreas, Batra, Aman, Lessy, Dien, Salah, Baha, Sievert, Benedikt, Degen, Marvin, Rennings, Andreas, Jalali, Mandana, Svejda, Jan Taro, Alibeigloo, Pooya, Preuß, Christian, Mutlu, Enes, Kreß, Robin, Clochiatti, Simone, Kolpatzeck, Kevin, Kubiczek, Tobias, Ullmann, Ingrid, Root, Konstantin, Brix, Fabian, Krämer, Ute, Vossiek, Martin, Balzer, Jan C., Weimann, Nils, Kaiser, Thomas, and Erni, Daniel

Subjects
Elektrotechnik
Abstract

in press, CA Sheikh In this paper, new concepts for continuous 24/7 real-time monitoring of plants and insects with miniaturized terahertz (THz) systems are described and experimentally tested. Thus, for the first time, small-scale insights into the instantaneous plant health but also in their long-term growth can be obtained. Using such compact THz systems, e.g. water uptake, insect infestation and the behavior of pollinators (i.e. honey bees) and pests can be measured dynamically and non-invasively at virtually any position in the close biotope surrounding them. In addition to general understanding, this can be used to optimize crop yield and reduce resource consumption as well as for identifying characteristics of insect-plant interactions induced by potential environmental stressors. Given such holistic a approach, the proposed concepts may provide a significant advancement in environmental monitoring technology.

Published
2023

44. InP-Based THz Beam Steering Leaky-Wave Antenna

Author

Lu, Peng, primary, Haddad, Thomas, additional, Sievert, Benedikt, additional, Khani, Besher, additional, Makhlouf, Sumer, additional, Dulme, Sebastian, additional, Estevez, Jose Fernandez, additional, Rennings, Andreas, additional, Erni, Daniel, additional, Pfeiffer, Ullrich, additional, and Stohr, Andreas, additional

Published
2021
Full Text
View/download PDF

46. A Simple Superposition Formulation to Predict the Underwater Electric Potential Signature of Naval Vessels

Author

Thiel, Christian, Broecheler, Claas, Ludwar, Frank, Rennings, Andreas, and Erni, Jens Doose and Daniel

Subjects
ICCP, UEP superposition, SACP, underwater electric potential, UEP prediction
Abstract

The underwater electric potential (UEP) signature is an electric signal, which can be exploited by naval mines to be utilized as a possible trigger indicator and may cause severe damage to the vessel and the onboard crew. Hence, knowing the UEP signature as exactly as possible can help to evaluate a possible risk of the vessel being detected by naval mines or if the UEP signature is within a noncritical region. As the UEP signature differs for changes of the corrosion protection system, the UEP signature is usually unknown for new conditions. In this work, we present a simple mathematical formulation to predict the UEP signature based on the mere use of a single reference UEP signature, and the corresponding currents, which are excited by the impressed current cathodic protection (ICCP) system. With this methodology, deviations below 10 % between the maximum of the simulated UEP signature and the predicted UEP signature can be achieved, even in the presence of the nonlinear corrosion process. Furthermore, a corrosion protective coating of the propellers can significantly reduce the influence of the nonlinear corrosion process on the total UEP signature to improve the prediction accuracy of the superposition formulation as presented in this work.

Published
2020
Full Text
View/download PDF

47. Compact Metamaterial-based Coil Element for Combined ¹H/²³Na MRI at 7T

Author

Svejda, Jan Taro, Rennings, Andreas, and Erni, Daniel

Subjects
Physics::Medical Physics, Elektrotechnik
Abstract

High static magnetic flux densities in the field of magnetic resonance imaging (MRI) allow X-nuclei-based imaging and spectroscopy as well as the utilization of electromagnetic metamaterials. A compact dual-tuned coil element based on a metamaterial transmission line which achieves a quarter-wave resonance at the two distinct operating frequencies of the hydrogen and sodium nuclei is presented. In addition, first combined ¹ H/²³Na MRI measurement results from a structured phantom are shown and discussed. CA Svejda, Rennings, Erni

Published
2020

Catalog

Books, media, physical & digital resources
See catalog results