N. Kuster

University of Zurich, Zürich, Zurich, Switzerland

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Publications (155)173.06 Total impact

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    ABSTRACT: In this study, human exposure to close-range wireless power transfer (WPT) systems operating in the frequency range 0.1–10 MHz with coil diameters up to 150 mm are investigated. Approximation formulae, which include scaling factors derived from numerical simulations that take variations of complex human anatomies into consideration, are proposed to conservatively estimate human exposure with respect to the most authoritative exposure guidelines. The approximation has been verified for two precommercial prototype WPT systems, the first of which, a 5-W system operating at 100 kHz, has been evaluated in this study; the second system been verified was reported in a separate study and operates at 6.78 MHz with a nominal current of 5.4 A$_{rm bf rms}$. Based on the results obtained, the optimal operational frequency range for WPT with respect to compliance with exposure safety guidelines is revealed to be ca. 1–2.5 MHz. In summary, this study provides novel and insightful information for the design of an exposure-compliant close-range magnetic resonant WPT system.
    IEEE Transactions on Electromagnetic Compatibility 10/2014; 56(5):1027-1034. · 1.35 Impact Factor
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    ABSTRACT: In this paper, fetal exposure to uniform magnetic fields (MF) with different polarizations is quantified at 50 Hz. Numerical computations were performed on high-resolution pregnant models at 3, 7, and 9 months of gestational age (GA), that distinguish a high number of fetal tissues. Fetal whole-body and tissue-specific induced electric fields (E) and current densities (J) were analyzed as a function of both the extremely low frequency magnetic field (ELF-MF) polarization and GA. Additionally, the induced field variation due to changes in fetal position was analyzed by means of two new pregnant models. The uncertainty budget due to the grid resolution was also calculated. Finally, the compliance of the fetal exposure to the ICNIRP Guidelines was checked. A fetal exposure matrix was built at 50 Hz, which could be used to further investigate possible interaction mechanisms between ELF-MF and the associated health risk. Some specific findings were: (1) the induced fields increased with GA; (2) the maxima E were found in skin and fat tissues at each GA; (3) fetal tissue-specific exposure was modified as a function of GA and polarization; (4) the change of the fetal position in the womb significantly modified the induced E in some fetal tissues; (5) the induced fields were in compliance with ICNIRP Guidelines and the results were quite below the permitted threshold limit. Bioelectromagnetics. 2014;9999:1–18. © 2014 Wiley Periodicals, Inc.
    Bioelectromagnetics 09/2014; · 1.86 Impact Factor
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    ABSTRACT: The influence of electromagnetic fields on the health of humans and animals is still an intensively discussed and scientifically investigated issue (Prakt Tierarzt 11:15-20, 2003; Umwelt Medizin Gesellschaft 17:326-332, 2004; J Toxicol Environment Health, Part B 12:572-597, 2009). We are surrounded by numerous electromagnetic fields of variable strength, coming from electronic equipment and its power cords, from high-voltage power lines and from antennas for radio, television and mobile communication. Particularly the latter cause's controversy, as everyone likes to have good mobile reception at anytime and anywhere, whereas nobody wants to have such a basestation antenna in their proximity.
    BMC Veterinary Research 06/2014; 10(1):136. · 1.74 Impact Factor
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    ABSTRACT: In view of the ever expanding research and development in the wireless area, recent advances and topical applications of a computational electromagnetics (CEM) platform are highlighted within this paper. In particular related to the simulation and optimization of complex industrial scenarios, CEM tools must provide outstanding performance with respect to user-friendliness, accuracy, robustness and computation speed. On the basis of optimizing a wireless power transfer system in interaction with a human body, the capabilities of the investigated CEM platform are demonstrated. The outlined feature range encompasses numerical/experimental body phantoms, LF and RF solvers as well as the latest achievements in GPU high performance computing (HPC).
    2013 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting; 07/2013
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    ABSTRACT: The strong reactive near-field wireless power transmission (WPT) systems induce electric fields in the body tissue of persons in their close vicinity. This may pose potential direct health hazards or indirect risks via interference with medical implants. In this paper, the safety guidelines and the fundamental coupling mechanisms of the human body with the electromagnetic near fields of WPT are reviewed as well as the methodology and the instrumentation for the demonstration of the safety of such systems operating between 100 kHz and 50 MHz. Based on this review, the advantages and shortcomings of state-of-the-art numerical and experimental techniques are discussed and applied to a generic WPT operating at 8 MHz. Finally, current research needs are identified which include: 1) the extension of safety guidelines for coverage of persons with implants; 2) more computationally efficient full-wave solvers; 3) higher quality human models which cover different population groups and include improved models of nerve tissue; 4) experimental dosimetric methods for the WPT frequency range; and 5) product standards to demonstrate safety of specific WPT.
    Proceedings of the IEEE 06/2013; 101(6):1482-1493. · 5.47 Impact Factor
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    ABSTRACT: In the design of a mobile device antenna, a closely positioned speaker is often found to cause severe degradation of antenna performance. Besides antenna frequency shift and bandwidth reduction, a frequently encountered negative impact from a miniature speaker is the significant loss of antenna radiation efficiency. In this study, the mechanical structure of a miniature speaker is numerically investigated with respect to its resonance characteristics in mobile phone frequency range and the interaction with a nearby antenna. The simulation results of a realistic speaker structure show that the fundamental mechanism behind speaker-related antenna radiation loss is the enhancement of non-radiatimg near-field energy due to a resonating speaker. An optimum antenna-speaker-integrated design relies on the avoidance of such speaker resonance.
    Antennas and Propagation (Eu- CAP), 2013 7th European Conference on; 04/2013
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    ABSTRACT: Microwave ablation (MWA) is a minimally-invasive modality used in the treatment of non-resectable tumours. In this paper, a comparison between different types of coaxial antennas and arrays is carried out in the interest of studying their ability to ablate liver tissue. It is found that double-slot coaxial antennas create a more localised heating near their tip compared to single-slot ones. Additionally, when it comes to arrays, triangular configurations create nearly spherical ablation zones, whereas square configurations rather flat zones. The study is extended to the modelling of clinically-relevant cases; the contribution of different tissue properties in determining the ablation zone is investigated. It is found that malignant tissues can be heated faster, and to a larger extend, and they do not experience a maximum-dimension plateau for increasing heating durations, contrary to healthy ones.
    Antennas and Propagation (EuCAP), 2013 7th European Conference on; 04/2013
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    ABSTRACT: OBJECTIVE: To examine the potential sensitivity of adolescents to radiofrequency electromagnetic field (RF EMF) exposures, such as those emitted by mobile phones. METHODS: In a double-blind, randomized, crossover design, 22 adolescents aged 11-13years (12 males) underwent three experimental sessions in which they were exposed to mobile phone-like RF EMF signals at two different intensities, and a sham session. During exposure cognitive tasks were performed and waking EEG was recorded at three time-points subsequent to exposure (0, 30 and 60min). RESULTS: No clear significant effects of RF EMF exposure were found on the waking EEG or cognitive performance. CONCLUSIONS: Overall, the current study was unable to demonstrate exposure-related effects previously observed on the waking EEG in adults, and also provides further support for a lack of an influence of mobile phone-like exposure on cognitive performance. SIGNIFICANCE: Adolescents do not appear to be more sensitive than adults to mobile phone RF EMF emissions.
    Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 02/2013; · 3.12 Impact Factor
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    ABSTRACT: Compliance with the established exposure limits for the electric field (E-field) induced in the human brain due to low-frequency magnetic field (B-field) induction is demonstrated by numerical dosimetry. The objective of this study is to investigate the dependency of dosimetric compliance assessments on the applied methodology and segmentations. The dependency of the discretization uncertainty (i.e., staircasing and field singularity) on the spatially averaged peak E-field values is first determined using canonical and anatomical models. Because spatial averaging with a grid size of 0.5 mm or smaller sufficiently reduces the impact of artifacts regardless of tissue size, it is a superior approach to other proposed methods such as the 99th percentile or smearing of conductivity contrast. Through a canonical model, it is demonstrated that under the same uniform B-field exposure condition, the peak spatially averaged E-fields in a heterogeneous model can be significantly underestimated by a homogeneous model. The frequency scaling technique is found to introduce substantial error if the relative change in tissue conductivity is significant in the investigated frequency range. Lastly, the peak induced E-fields in the brain tissues of five high-resolution anatomically realistic models exposed to a uniform B-field at ICNIRP and IEEE reference levels in the frequency range of 10 Hz to 100 kHz show that the reference levels are not always compliant with the basic restrictions. Based on the results of this study, a revision is recommended for the guidelines/standards to achieve technically sound exposure limits that can be applied without ambiguity. Bioelectromagnetics. © 2013 Wiley Periodicals, Inc.
    Bioelectromagnetics 02/2013; · 1.86 Impact Factor
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    ABSTRACT: Although IARC clarifies radiofrequency electromagnetic fields (RF-EMF) as possible human carcinogen, the debate on its health impact continues due to the inconsistent results. Genotoxic effect has been considered as a golden standard to determine if an environmental factor is a carcinogen, but the currently available data for RF-EMF remain controversial. As an environmental stimulus, the effect of RF-EMF on cellular DNA may be subtle. Therefore, more sensitive method and systematic research strategy are warranted to evaluate its genotoxicity. To determine whether RF-EMF does induce DNA damage and if the effect is cell-type dependent by adopting a more sensitive method γH2AX foci formation; and to investigate the biological consequences if RF-EMF does increase γH2AX foci formation. Six different types of cells were intermittently exposed to GSM 1800 MHz RF-EMF at a specific absorption rate of 3.0 W/kg for 1 h or 24 h, then subjected to immunostaining with anti-γH2AX antibody. The biological consequences in γH2AX-elevated cell type were further explored with comet and TUNEL assays, flow cytometry, and cell growth assay. Exposure to RF-EMF for 24 h significantly induced γH2AX foci formation in Chinese hamster lung cells and Human skin fibroblasts (HSFs), but not the other cells. However, RF-EMF-elevated γH2AX foci formation in HSF cells did not result in detectable DNA fragmentation, sustainable cell cycle arrest, cell proliferation or viability change. RF-EMF exposure slightly but not significantly increased the cellular ROS level. RF-EMF induces DNA damage in a cell type-dependent manner, but the elevated γH2AX foci formation in HSF cells does not result in significant cellular dysfunctions.
    PLoS ONE 01/2013; 8(1):e54906. · 3.53 Impact Factor
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    ABSTRACT: Exposure to radiofrequency (RF) electromagnetic fields (EMF) is continuously increasing worldwide. Yet, conflicting results of a possible genotoxic effect of RF EMF continue to be discussed. In the present study, a possible genotoxic effect of RF EMF (GSM, 1,800 MHz) in human lymphocytes was investigated by a collaboration of six independent institutes (institutes a, b, c, d, e, h). Peripheral blood of 20 healthy, nonsmoking volunteers of two age groups (10 volunteers 16-20 years old and 10 volunteers 50-65 years old) was taken, stimulated and intermittently exposed to three specific absorption rates (SARs) of RF EMF (0.2 W/kg, 2 W/kg, 10 W/kg) and sham for 28 h (institute a). The exposures were performed in a setup with strictly controlled conditions of temperature and dose, and randomly and automatically determined waveguide SARs, which were designed and periodically maintained by ITIS (institute h). Four genotoxicity tests with different end points were conducted (institute a): chromosome aberration test (five types of structural aberrations), micronucleus test, sister chromatid exchange test and the alkaline comet assay (Olive tail moment and % DNA). To demonstrate the validity of the study, positive controls were implemented. The genotoxicity end points were evaluated independently by three laboratories blind to SAR information (institute c = laboratory 1; institute d = laboratory 2; institute e = laboratory 3). Statistical analysis was carried out by institute b. Methods of primary statistical analysis and rules to adjust for multiple testing were specified in a statistical analysis plan based on a data review before unblinding. A linear trend test based on a linear mixed model was used for outcomes of comet assay and exact permutation test for linear trend for all other outcomes. It was ascertained that only outcomes with a significant SAR trend found by at least two of three analyzing laboratories indicated a substantiated suspicion of an exposure effect. On the basis of these specifications, none of the nine end points tested for SAR trend showed a significant and reproducible exposure effect. Highly significant differences between sham exposures and positive controls were detected by each analyzing laboratory, thus validating the study. In conclusion, the results show no evidence of a genotoxic effect induced by RF EMF (GSM, 1,800 MHz).
    Radiation Research 01/2013; · 2.70 Impact Factor
  • Sven Kuhn, Niels Kuster
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    ABSTRACT: Mobile phones present the strongest source of radiofrequency electromagnetic held exposure to the human head. Mobile phones are routinely assessed with respect to safety by specihc absorption rate measurements at maximum output power. The difference of the exposure due to power control during normal usage was evaluated. A mobile measurement system to assess the effect of the power control in real networks was developed. It presents a realistic load to the phone and is able to measure the output power and band synchronously for the GSM900, DCS1800, and UMTS1950 bands. The system has a dynamic range of 60 dB and a measurement uncertainty of <;1 dB for GSM and <;1.5 dB for UMTS. Using the system, three mobile phones were evaluated in the three Swiss networks in urban and rural areas. The phones were tested in dual system (GSM and UMTS) and GSM only modes. The results show a small change of the mean output power in GSM mode (from -2 to -10 dB) compared to 30-dB power control dynamic range. The mean output power in UMTS was a factor >100 lower than GSM. In urban areas, UMTS was generally available and preferably used by the phones with rare fall backs to GSM. In the suburban/rural area, UMTS was hardly available or used by the phones.
    IEEE Transactions on Electromagnetic Compatibility 01/2013; 55(2):275-287. · 1.35 Impact Factor
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    ABSTRACT: The ICES Technical Committee 34 of IEEE has developed a set of standards for the evaluation of the compliance of wireless devices with exposure limits for electromagnetic fields using the finite-difference time-domain numerical method. This study describes the methodology for the validation of the simulation software and the assessment of the numerical uncertainty of the simulation results.
    Antennas and Propagation (EuCAP), 2013 7th European Conference on; 01/2013
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    ABSTRACT: This study provides recommendations for scientifically sound methods of evaluating compliance of wireless power transfer systems with respect to human electromagnetic exposure limits. Methods for both numerical analysis and measurements are discussed. An exposure assessment of a representative wireless power transfer system, under a limited set of operating conditions, is provided in order to estimate the maximum SAR levels. The system operates at low MHz frequencies and it achieves power transfer via near field coupling between two resonant coils located within a few meters of each other. Numerical modeling of the system next to each of four high-resolution anatomical models shows that the local and whole-body SAR limits are generally reached when the transmit coil currents are 0.5 ARMS - 1.2 ARMS at 8 MHz for the maximal-exposure orientation of the coil and 10-mm distance to the body. For the same coil configurations, the exposure can vary by more than 3 dB for different human models. A simplified experimental setup for the exposure evaluation of wireless power transfer systems is also described.
    IEEE Transactions on Electromagnetic Compatibility 01/2013; 55(2):265-274. · 1.35 Impact Factor
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    ABSTRACT: Diode detectors present inside electromagnetic field probes are typically calibrated for linearity using continuous sinusoidal waveforms (CW). In this paper, it is shown that CW linearization is not adequate for the measurement of complex wireless communication signals with high peak-to-average power ratios. While previous analog and digital communication signals (1G and 2G) can be more easily corrected for linearity, newer 3G and 4G communication protocols employ complex modulations with stochastic signal envelopes. As a result, proper linearization depends on the diode response and signal characteristics, and large errors results if CW linearization is used. The errors introduced when measuring such signals with probes employing CW linearization are quantified in this paper. A numerical model of the diode response is provided and validated against measurements. Errors due to CW linearization can exceed 2 dB, whereas linearity errors within 0.4 dB are attainable using the proposed calibration procedures for even increased dynamic ranges.
    IEEE Transactions on Electromagnetic Compatibility 12/2012; 54(6):1195-1204. · 1.35 Impact Factor
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    ABSTRACT: In light of the ever expanding research field of electromagnetic related studies, a simulation platform which is capable of solving multidisciplinary electromagnetic problems is indispensable. While dealing with challenging wireless product design or electromagnetic exposure safety assessment, numerical simulation can often provide insightful information which cannot be achievable by the current measurement techniques. The aim of this paper is to review the applications of numerical techniques in various electromagnetic-related research fields and to reveal the distinct advantages of employing state-of-the-art computational approaches.
    Antennas and Propagation (APS/URSI), 2012 IEEE International Symposium on; 07/2012
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    ABSTRACT: The objective of this study is to investigate the near field coupling between a miniature loudspeaker and a nearby antenna. The analysis focuses on the loudspeaker voice coil radio frequency resonance characteristics and antenna radiation efficiency degradation due to the presence of the loudspeaker. Both measurement and simulation results are given to assess the impact of a loudspeaker when it is placed in close proximity with a monopole antenna mounted on a printed circuit board. This study leads to a better understanding to achieve optimum antenna loudspeaker integrated module design for mobile devices.
    Antennas and Propagation (APS/URSI), 2012 IEEE International Symposium on; 07/2012
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    ABSTRACT: To avoid potentially adverse health effects, the International Commission on Non-Ionizing Radiation Protection (ICNIRP) has defined reference levels for time varying magnetic fields. Restrictions on the electric fields induced in the human body are provided based on biological response data for peripheral nerve stimulation and the induction of phosphenes. Numerical modeling is commonly used to assess the induced electric fields for various exposure configurations. The objective of this study was to assess the variations of the electric fields induced in children and adults and to compare the exposure at reference levels with the basic restrictions as function of anatomy. We used the scalar potential finite element method to calculate the induced electric fields in six children and two adults when exposed to uniform magnetic fields polarized in three orthogonal directions. We found that the induced electric fields are within the ICNIRP basic restrictions in nearly all cases. In PNS tissues, we found electric fields up to 95% (upper uncertainty limit due to discretization errors, k = 2) of the ICNIRP basic restrictions for exposures at the general public reference levels. For occupational reference levels, we found an over-exposure of maximum 79% (k = 2) in PNS tissues. We further found that the ICNIRP recommendations on spatial averaging in 2 × 2 × 2 mm³ contiguous tissue volumes and removal of peak values by the 99th percentile cause the results to depend strongly on the grid discretization step (i.e. an uncertainty of more than 50% at 2 mm) and the number of distinguished tissues in the anatomical models. The computational results obtained by various research institutes should be robust for different discretization settings and various anatomical models. Therefore, we recommend considering alternative routines for small anatomical structures such as non-contiguous averaging without taking the 99th percentile in future guidelines leading to consistent suppression of peak values amongst different simulation settings and anatomical models. The peak electric fields depend on the local tissue distribution in the various anatomical models, and we could not find a correlation with the size of the anatomy. Therefore, we recommend extending the evaluation using a sufficient set of anatomies including other than standing postures to assess the worst-case exposure setting and correspondence to the basic restrictions.
    Physics in Medicine and Biology 03/2012; 57(7):1815-29. · 2.92 Impact Factor

Publication Stats

2k Citations
173.06 Total Impact Points


  • 2003–2013
    • University of Zurich
      • Institute of Veterinary Pharmakology and Toxicology
      Zürich, Zurich, Switzerland
  • 1993–2013
    • ETH Zurich
      • • The Foundation for Research on Information Technologies in Society (IT'IS)
      • • Integrated Systems Laboratory
      • • Electromagnetic Fields and Microwave Electronics Laboratory
      Zürich, ZH, Switzerland
  • 1992–2013
    • Eawag: Das Wasserforschungs-Institut des ETH-Bereichs
      Duebendorf, Zurich, Switzerland
  • 2010–2012
    • Erasmus MC
      • Department of Radiotherapy
      Rotterdam, South Holland, Netherlands
    • U.S. Food and Drug Administration
      • Center for Devices and Radiological Health
      Washington, D. C., DC, United States
  • 2011
    • University of Alabama at Birmingham
      • Department of Medicine
      Birmingham, AL, United States
    • University of São Paulo
      • Department of Radiology (FM)
      San Paulo, São Paulo, Brazil
  • 2000–2009
    • Zurich Instruments AG
      Zürich, Zurich, Switzerland
  • 2006–2007
    • Aristotle University of Thessaloniki
      • • Division of Physics (PHYS)
      • • Department of Physics, Analytical and Environmental Chemistry
      Saloníki, Central Macedonia, Greece
  • 2005
    • Fraunhofer Institute for Toxicology and Experimental Medicine ITEM
      Hanover, Lower Saxony, Germany
  • 1996
    • Deutsche Telekom
      Hamburg, Hamburg, Germany
  • 1994
    • University of Colorado
      • Department of Psychiatry
      Denver, CO, United States