Vitas Anderson

ERRATUM: "A COMPREHENSIVE TISSUE PROPERTIES DATABASE PROVIDED FOR THE THERMAL ASSESSMENT OF A HUMAN AT REST"

Accurate numerical calculation of the thermal profile in humans requires reliable estimates of the following five tissue properties: specific heat capacity (c), thermal conductivity (k), blood perf...

SAR versus Sinc: What is the appropriate RF exposure metric in the range 1–10 GHz? Part I: Using planar body models

This is the first of two articles addressing the most appropriate crossover frequency at which incident power flux density (S(inc)) replaces the spatial peak value of the specific energy absorption rate (SAR) averaged over 1 or 10 g (i.e., peak 1 or 10 g SAR) as the basic restriction for protecting against radiofrequency (RF) heating effects in the 1-10 GHz range. Our general approach has been to compare the degree of correlation between these basic restrictions and the peak induced tissue temperature rise (DeltaT) for a representative range of population/exposure scenarios. In this article we particularly address the effect of human population diversity in the thickness of body tissue layers at eight different sites of the body. We used a Monte Carlo approach to specify 32000 models (400 models for each of 8 body sites for 10 frequencies) which were representative of tissue thicknesses for age (18-74 years) and sex at the eight body sites. Histogram distributions of S(inc) and peak 1 and 10 g SAR corresponding to a peak 1 degrees C temperature rise were obtained from RF and thermal analyses of 1D multiplanar models exposed to a normally incident plane wave ranging from 1 to 10 GHz in thermo-neutral environmental conditions. Examination of the distribution spread of the histograms indicated that peak SAR was a better predictor of peak tissue temperature rise across the entire 1-10 GHz frequency range than S(inc), as indicated by the smaller spread in its histogram distributions, and that peak 10 g SAR was a slightly better predictor than peak 1 g SAR. However, this result must be weighed against partly conflicting indications from complex body modeling in the second article of this series, which incorporates near-field effects and the influence of complex body geometries.

SAR versus VAR, and the size and shape that provide the most appropriate RF exposure metric in the range of 0.5-6 GHz.

Basic restrictions for protecting against localized tissue heating induced from exposure to radiofrequency (RF) fields are typically specified as the specific energy absorption rate (SAR), which is mass averaged in recognition of the thermal diffusion properties of tissues. This article seeks to determine the most appropriate averaging mass (1, 3, 5, 7, or 10 g) and averaging shape (cube or sphere). We also consider an alternative metric, volumetric energy absorption rate (VAR), which uses volume averaging (over 1, 3, 5, 7, and 10 cm(3) ; cube and sphere). The SAR and VAR averaging approaches were compared by considering which was a better predictor of tissue temperature rise (ΔT) induced by near- and far-field RF exposures (0.5-6 GHz), calculated in a detailed human body model. For the exposure scenarios that we examined, VAR is better correlated with ΔT than SAR, though not at a statistically significant level for most of the metric types we studied. However, as VAR offers substantive advantages in ease of assessment we recommend this metric over SAR. Averaging over a cube or a sphere provides equivalent levels of correlation with ΔT, and so we recommend choosing the averaging shape on the basis of which is easier to assess. The optimal averaging volume is 10 cm(3) for VAR, and the optimal mass is 10 g for SAR. The correlation between VAR or SAR and ΔT diminishes substantially at 6 GHz, where incident power flux density may be a better exposure metric.

Evaluation of hematopoietic system effects after in vitro radiofrequency radiation exposure in rats

Purpose: This study was designed to investigate the effect of a 900-MHz continuous-wave (CW) radiofrequency radiation (RFR) exposure on the hematopoietic system in the rat. Materials and methods: Rat long bones (femur and tibia) were divided into two groups: Sham-exposed and radiofrequency (RF)-exposed. The mean Specific energy Absorption Rate (SAR) at 900-MHz averaged over the bone marrow (calculated by the finite-difference-time-domain ( fdtD) method) was 2 W/kg at 16.7 W root mean square (rms) forward power into a Transverse Electromagnetic (TEM) cell. The bones, placed in a Petri dish containing media, were kept in the TEM cell for 30 min duration of sham or RF exposure. After exposure, the bone marrow cells were extracted and the following end points were tested: (a) Proliferation rate of whole bone marrow cells, (b) maturation rate of erythrocytes, (c) proliferation rate of lymphocytes, and (d) DNA damage (strand breaks/alkali labile sites) of lymphocytes. Results: Our data did not indicate any significant change in the proliferation rate of bone marrow cells and lymphocytes, erythrocyte maturation rate and DNA damage of lymphocytes. Conclusion: Our findings revealed no effect on the hematopoietic system in rats for 900 MHz CW RF exposure at the 2 W/kg localised SAR limit value recommended by the International Commission for Non-Ionising Radiation Protection (ICNIRP) for public exposures.

A genotoxic analysis of the hematopoietic system after mobile phone type radiation exposure in rats.

Abstract Purpose: In our earlier study we reported that 900 MHz continuous wave (CW) radiofrequency radiation (RFR) exposure (2 W/kg specific absorption rate [SAR]) had no significant effect on the hematopoietic system of rats. In this paper we extend the scope of the previous study by testing for possible effects at: (i) different SAR levels; (ii) both 900 and 1800 MHz, and; (iii) both CW and pulse modulated (PM) RFR. Materials and methods: Excised long bones from rats were placed in medium and RFR exposed in (i) a Transverse Electromagnetic (TEM) cell or (ii) a waveguide. Finite-difference time-domain (FDTD) numerical analyses were used to estimate forward power needed to produce nominal SAR levels of 2/10 and 2.5/12.4 W/kg in the bone marrow. After exposure, the lymphoblasts were extracted and assayed for proliferation rate, and genotoxicity. Results: Our data did not indicate any significant change in these end points for any combination of CW/PM exposure at 900/1800 MHz at SAR levels of nominally 2/10 W/kg or 2.5/12.4 W/kg. Conclusions: No significant changes were observed in the hematopoietic system of rats after the exposure of CW/PM wave 900 MHz/1800 MHz RF radiations at different SAR values.

Nonlinear dynamics of charged particles interacting with combined ac-dc electromagnetic fields

A nonlinear Lorenz model describing interactions between charged particles and combined ac-dc electromagnetic fields is studied for various combinations of frequencies, field strengths and relative angle (θ) between the ac and dc magnetic fields. Strong directional effects on the magnitude and location of resonant particle motion are observed when θ is varied and the regular resonance windows in the aligned field (θ = 0) and linear version of the model studied previously by Durney etaal., break up to form irregular and less well pronounced regions of large and small particle displacements when nonlinearities are taken into account. The length of time takne to achieve resonant behaviour also becomes larger and more variable when nonlinearities are present. The possible relevance of these effects to interactions between electromagnetic fields and biological media is briefly discussed.

Significant RF-EMF and thermal levels observed in a computational model of a person with a tibial plate for grounded 40 MHz exposure

Using numerical modeling, a worst-case scenario is considered when a person with a metallic implant is exposed to a radiofrequency (RF) electromagnetic field (EMF). An adult male standing on a conductive ground plane was exposed to a 40 MHz vertically polarized plane wave field, close to whole-body resonance where maximal induced current flows are expected in the legs. A metal plate (50-300 mm long) was attached to the tibia in the left leg. The findings from this study re-emphasize the need to ensure compliance with limb current reference levels for exposures near whole-body resonance, and not just rely on compliance with ambient electric (E) and magnetic (H) field reference levels. Moreover, we emphasize this recommendation for someone with a tibial plate, as failure to comply may result in significant tissue damage (increases in the localized temperature of 5-10 °C were suggested by the modeling for an incident E-field of 61.4 V/m root mean square (rms)). It was determined that the occupational reference level for limb current (100 mA rms), as stipulated in the 1998 guidelines of the International Commission on Non-Ionizing Radiation Protection (ICNIRP), is satisfied if the plane wave incident E-field levels are no more than 29.8 V/m rms without an implant and 23.4 V/m rms for the model with a 300 mm implant.

IEI-EMF provocation case studies: A novel approach to testing sensitive individuals: IEI-EMF Provocation Case Studies

The etiology of Idiopathic Environmental Intolerance attributed to Electromagnetic Fields (IEI-EMF) is controversial. While the majority of studies have indicated that there is no relationship between EMF exposure and symptoms reported by IEI-EMF sufferers, concerns about methodological issues have been raised. Addressing these concerns, the present experiment was designed as a series of individual case studies to determine whether there is a relationship between radiofrequency-electromagnetic field (RF-EMF) exposure and an IEI-EMF individuals self-reported symptoms. Three participants aged 44-64 were tested during a series of sham and active exposure trials (2 open-label trials; 12 randomized, double-blind, counterbalanced trials), where symptom severity and exposure detection were scored using 100 mm visual analogue scales. The RF-EMF exposure was a 902-928 MHz spread spectrum digitally modulated signal with an average radiated power output of 1 W (0.3 W/m2 incident power density at the participant). In the double-blind trials, no significant difference in symptom severity or exposure detection was found for any of the participants between the two conditions. Belief of exposure strongly predicted symptom severity score for all participants. Despite accounting for several possible limitations, the present experiment failed to show a relationship between RF-EMF exposure and an IEI-EMF individuals symptoms. Bioelectromagnetics. 39:132-143, 2018.

Estimating uncertainty in calculated ambient RF field levels for hazard assessments

Just as for measured evaluations, the calculation of ambient levels of radiofrequency (RF) electric and magnetic fields for hazard assessments can entail random uncertainty, the extent of which depends on: how well the method of analysis approximates the governing electromagnetic equations (i.e. Maxwells equations); how closely the modeled object represents its real counterpart in form and composition, and; computational round off error. While uncertainty estimates are commonly required for RF measurements, they are rarely provided for calculated assessments. In this paper, a process for calculating uncertainty for calculated assessments is proposed. It incorporates a series of validation tests which are used to gauge the uncertainty in the computational technique and round off error. The comparator in the validation tests must be independent of the technique (e.g. measurement of antenna gain) and may vary for different types of analyses (e.g. full wave solutions vs ray tracing methods). Variational targets are set for the validation tests, and the uncertainty estimate for computational uncertainty diminishes as more tests are passed. Once determined in this way, the standard uncertainty for computational technique is then combined in a multiplicative model with standard uncertainties for other influence quantities such as forward power to the antenna and field scattering effects of nearby objects. By using the proposed approach, it will be possible to provide systematic corrections and uncertainty estimates for calculated assessments as they are for RF measurements, thereby allowing meaningful comparisons between them.

Assessment of guidelines for limiting exposures to emf using methods of probabilistic risk analysis.

Allowable limits of human exposure to radiofrequency fields commonly include a “factor of safety,” typically between 10 to 50, which is somewhat arbitrary. The broad objective in our work is to assess radiofrequency exposure limits, hazard thresholds, and safety factors using methods of probabilistic risk analysis. We focus our analysis on the variables affecting peak radiofrequency specific energy absorption rate (SAR) values in the brain from digital mobile telephones operating at approximately 900 MHz. As SAR is defined as a product of positive random variables, it is not unreasonable to assume that SAR has a lognormal distribution. Our analysis of component SAR variables such as conductivity and permittivity of grey brain matter and radiated field strengths using experimental and numerical modeling data strongly supports our hypothesis that SAR values are distributed lognormally. It then follows that the probability that the SAR exceeds a certain threshold can be derived directly and is shown to be very low for handset SARs relative to presently allowable standard limits.