N. Kuster

University of Zurich, Zürich, Zurich, Switzerland

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Publications (147)150.67 Total impact

  • [Show abstract] [Hide abstract]
    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. · 1.86 Impact Factor
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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: 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: 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; · 2.02 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
  • S. Kuhn, N. 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. · 1.33 Impact Factor
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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 01/2013; 101(6):1482-1493. · 6.91 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. · 3.73 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. · 1.33 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: The study of magnetic stimulation of the human brain has been an on-going research topic since the 1980s. To achieve a better understanding of the cerebral stimulation, it is necessary to estimate the spatial distribution and peak magnitude of the induced electric field in the brain. By utilizing a high resolution anatomical model and a numerical technique based on quasi-static approximation, this study provides a state-of-theart estimation of the in situ electric field distribution in an adult brain when undergoing transcranial magnetic stimulation. Coil designs such as figure-8 and 4-leaf-clover are employed in the analysis. It is demonstrated that the brain regions which are more likely to be stimulated by the respective coil design can be better estimated by employing a realistic anatomical model than a homogeneous model. It is revealed that the location of the maximum in situ electric field does not necessarily coincide with the location of the maximum magnetic flux (directly below the coil). Instead, the site of stimulation is significantly influenced by the design of the coil and the coil position.
    Electromagnetic Compatibility (APEMC), 2012 Asia-Pacific Symposium on; 05/2012
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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. · 2.70 Impact Factor
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    ABSTRACT: The objective of this study was to investigate the cost and time effectiveness of virtual prototyping when applied to the optimization of antenna system design for mobile phones, compared to traditional development approaches. For the proposed evaluation, an enhanced commercial FDTD-based electromagnetic simulation platform, powered with GPU hardware acceleration and distributed network parallelization, was applied. Advanced genetic algorithms (GAs) were used to obtain robust antenna designs, targeting a multi-goal optimum within a minimum number of simulations. Various antenna structures, including folded monopoles, planar-inverted F, and folded-inverted-conformal antennas were considered. An optimized structure was developed in less than 24 hours, indicating the superiority of virtual prototyping over traditional design and optimization procedures for reducing costs, improving quality, and, particularly, in reducing development time.
    IEEE Antennas and Propagation Magazine 02/2012; · 1.18 Impact Factor
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    ABSTRACT: AbstractA novel approach for parallelization of the finite‐difference time‐domain (FDTD) method based on open computing language (OpenCL) and the message passing interface (MPI) was presented. Because of the portability of OpenCL, the developed code targets not only distributed shared memory computer clusters based on multicore central processing units but also clusters accelerated by graphics processing units. Subsequently, this article shows the results of numerical tests to evaluate the hybrid MPI‐OpenCL FDTD solver in electromagnetic simulations. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:785–789, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26610
    Microwave and Optical Technology Letters 01/2012; 54(3). · 0.59 Impact Factor
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    ABSTRACT: The study of magnetic stimulation of the human brain has been an on-going research topic since the 1980s. To achieve a better understanding of the cerebral stimulation, it is necessary to estimate the spatial distribution and peak magnitude of the induced electric field in the brain. By utilizing a high resolution anatomical model and a numerical technique based on quasi-static approximation, this study provides a state-of-the-art estimation of the in situ electric field distribution in an adult brain when undergoing transcranial magnetic stimulation. Coil designs such as figure-8 and 4-leaf-clover are employed in the analysis. It is demonstrated that the brain regions which are more likely to be stimulated by the respective coil design can be better estimated by employing a realistic anatomical model than a homogeneous model. It is revealed that the location of the maximum in situ electric field does not necessarily coincide with the location of the maximum magnetic flux (directly below the coil). Instead, the site of stimulation is significantly influenced by the design of the coil and the coil position.
    01/2012;
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    ABSTRACT: The performance of a GPS antenna (inverted-F) design is investigated when the tracking device is placed on flat torso and dog-shaped phantoms. A prototype of the device is constructed to validate the proposed antenna design in free space condition with both measurement and simulation. Following that, the effects of body loading to the antenna are examined through numerical simulations to achieve an optimum orientation of the device with respect to the actual operating condition (with body loading). The results from this study indicate that the radiation/reception characteristics of a small GPS antenna can be very different between free space and body loading conditions. In order to achieve the best antenna performance, the body loading effect should be closely examined.
    Antennas and Propagation (EUCAP), 2012 6th European Conference on; 01/2012

Publication Stats

2k Citations
150.67 Total Impact Points

Institutions

  • 2000–2013
    • University of Zurich
      • Institute of Veterinary Pharmakology and Toxicology
      Zürich, Zurich, Switzerland
  • 1992–2013
    • Eawag: Das Wasserforschungs-Institut des ETH-Bereichs
      Duebendorf, Zurich, Switzerland
  • 1989–2013
    • 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
  • 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
  • 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