Steve Iskra

FACTORS INFLUENCING UNCERTAINTY IN MEASUREMENT OF ELECTRIC FIELDS CLOSE TO THE BODY IN PERSONAL RF DOSIMETRY

This paper provides an insight into factors that can influence uncertainty in measurements at 900 MHz of electric fields close to the body for use in personal dosimetry. Computational simulations using the finite difference time domain method were used to determine the total electric field near the surface of the torso of heterogeneous (adult and child) human body models for a set of exposure scenarios that simulated both spatially constant and randomly varying incident fields. Modelling has shown that a properly responding isotropic electric field dosemeter mounted between 10 and 50 mm of the torso will on average underestimate the incident field strength by up to 6.45 dB. In the worst case (i.e. spatially constant field), the standard deviation or uncertainty reached 6.42 dB. Uncertainty was reduced to <2.17 dB by combining the simultaneous outputs of a pair of body-worn dosemeters (mounted front and rear of torso).

Effects of 2G and 3G mobile phones on performance and electrophysiology in adolescents, young adults and older adults.

OBJECTIVE This study examined sensory and cognitive processing in adolescents, young adults and older adults, when exposed to 2nd (2G) and 3rd (3G) generation mobile phone signals. METHODS Tests employed were the auditory 3-stimulus oddball and the N-back. Forty-one 13-15 year olds, forty-two 19-40 year olds and twenty 55-70 year olds were tested using a double-blind cross-over design, where each participant received Sham, 2G and 3G exposures, separated by at least 4 days. RESULTS 3-Stimulus oddball task: Behavioural: accuracy and reaction time of responses to targets were not affected by exposure. Electrophysiological: augmented N1 was found in the 2G condition (independent of age group). N-back task: Behavioural: the combined groups performed less accurately during the 3G exposure (compared to Sham), with post hoc tests finding this effect separately in the adolescents only. Electrophysiological: delayed ERD/ERS responses of the alpha power were found in both 3G and 2G conditions (compared to Sham; independent of age group). CONCLUSION Employing tasks tailored to each individuals ability level, this study provides support for an effect of acute 2G and 3G exposure on human cognitive function. SIGNIFICANCE The subtlety of mobile phone effect on cognition in our study suggests that it is important to account for individual differences in future mobile phone research.

MONTE CARLO SIMULATIONS OF THE ELECTRIC FIELD CLOSE TO THE BODY IN REALISTIC ENVIRONMENTS FOR APPLICATION IN PERSONAL RADIOFREQUENCY DOSIMETRY

Personal dosemeters can play an important role in epidemiological studies and in radiofrequency safety programmes. In this study, a Monte Carlo approach is used in conjunction with the finite difference time domain method to obtain distributions of the electric field strength close to a human body model in simulated realistic environments. The field is a proxy for the response of an ideal body-worn electric field dosemeter. A set of eight environments were modelled based on the statistics of Rayleigh, Rice and log-normal fading to simulate outdoor and indoor multipath exposures at 450, 900 and 2100 MHz. Results indicate that a dosemeter mounted randomly within 10-50 mm of the adult or child body model (torso region) will on average underestimate the spatially averaged value of the incident electric field strength by a factor of 0.52 to 0.74 over the frequencies of 450, 900 and 2100 MHz. The uncertainty in results, assessed at the 95 % confidence level (between the 2.5th and 97.5th percentiles) was largest at 2100 MHz and smallest at 450 MHz.

Potential GPRS 900/180-MHz and WCDMA 1900-MHz Interference to Medical Devices

This study compared the potential for interference to medical devices from radio frequency (RF) fields radiated by GSM 900/1800-MHz, general packet radio service (GPRS) 900/1800-MHz, and wideband code division multiple access (WCDMA) 1900-MHz handsets. The study used a balanced half-wave dipole antenna, which was energized with a signal at the standard power level for each technology, and then brought towards the medical device while noting the distance at which interference became apparent. Additional testing was performed with signals that comply with the requirements of the international immunity standard to RF fields, IEC 61000-4-3. The testing provides a sense of the overall interference impact that GPRS and WCDMA (frequency division duplex) may have, relative to current mobile technologies, and to the internationally recognized standard for radiated RF immunity. Ten medical devices were tested: two pulse oximeters, a blood pressure monitor, a patient monitor, a humidifier, three models of cardiac defibrillator, and two models of infusion pump. Our conclusion from this and a related study on consumer devices is that WCDMA handsets are unlikely to be a significant interference threat to medical electronics at typical separation distances.

Modeling the Effect of Adverse Environmental Conditions and Clothing on Temperature Rise in a Human Body Exposed to Radio Frequency Electromagnetic Fields

This study considers the computationally determined thermal profile of a fully clothed, finely discretized, heterogeneous human body model, subject to the maximum allowable reference level for a 1-GHz radio frequency electromagnetic field for a worker, and also subject to adverse environmental conditions, including high humidity and high ambient temperature. An initial observation is that while electromagnetic fields at the occupational safety limit will contribute an additional thermal load to the tissues, and subsequently, cause an elevated temperature, the magnitude of this effect is far outweighed by that due to the conditions including the ambient temperature, relative humidity, and the type of clothing worn. It is envisaged that the computational modeling approach outlined in this paper will be suitably modified in future studies to evaluate the thermal response of a body at elevated metabolic rates, and for different body shapes and sizes including children and pregnant women.

Simulation of Pulsed ELF Magnetic Fields Generated by GSM Mobile Phone Handsets for Human Electromagnetic Bioeffects Research

Human provocation studies that investigate the effects of Global System for Mobiles (GSM) communication systems on the brain have focused on Radio Frequency (RF) exposure. We wish to further extend such study by investigating the effect of both RF and Extremely Low Frequency (ELF) field exposure, the latter generated by the GSM handset’s battery switching. The use of a commercial handset as an exposure source for such investigations is problematic for a number of reasons and therefore a simulated exposure source, capable of producing both RF and ELF components of exposure, is desirable. As a first step in developing such a source, we have quantified and characterized the ELF field from several commercial handsets (the RF characteristics being already well understood). Through experimental measurement we deduce that these fields can be sufficiently simulated by a 9 mm radius loop residing 10 mm beneath the front surface of the handset device and carrying enough current to generate peak fields of 25 μT at the surface of the handset.

Characterization of pulsed ELF magnetic fields generated by GSM mobile phone handsets

Human provocation studies that investigate the effects of Global System for Mobiles (GSM) communication systems on the brain have focused on RF exposure. We wish to further extend such study by investigating the effect of both RF and ELF magnetic field exposure, the latter being emitted by the GSM handset’s battery switching. The use of a commercial handset as an exposure source for such investigations is problematic and therefore a simulated exposure source, capable of producing both RF and ELF components of exposure, is desirable. As a first step in developing such a source, we have quantified and characterized the ELF radiation from several commercial handsets (the RF characteristics being already well understood). Here we present experimental results where, field distribution, and pulse waveform characteristics at ELF frequencies are measured. Finally, an equivalent source suitable for reproducing the ELF component of human exposure to GSM handset radiation is proposed.

Evaluation of potential GPRS 900/1800-MHz and WCDMA 1900-MHz interference to consumer electronics

This study assessed the potential for interference to consumer electronics from radio frequency (RF) fields radiated by general packet radio service (GPRS) 900/1800-MHz and wideband code division multiple access (WCDMA) 1900-MHz handsets. The study was enhanced by additional testing with fields that were characteristic of radio transmissions from GSM 900/1800-MHz handsets and 900/1800-MHz fields that comply with the requirements of the international immunity standard to RF fields, IEC 61000-4-3. Four examples of consumer electronics were tested-a television, radio, CD player, and telephone. Generally, each device exhibited some form of interference at most of the test field levels (1, 3, 10, and 30 V/m). GPRS/GSM 1800-MHz and WCDMA signals never caused interference to any device at 1 V/m. The IEC 61000-4-3-specified test signal consistently produced more audio/visual interference than GPRS- or GSM-type signals at the same test frequency and carrier field strength level. Audio/visual interference produced by WCDMA signals was generally lower than that produced by GPRS. These results, combined with the inherently lower maximum output power of WCDMA, indicate that WCDMA will usually pose a lower risk of interference compared with GPRS for similar separation distances between handsets and common items of consumer electronics.

Effect of adverse environmental conditions and protective clothing on temperature rise in a human body exposed to radiofrequency electromagnetic fields

This study considers the computationally determined thermal profile of a finely discretized, heterogeneous human body model, simulating a radiofrequency electromagnetic field (RF-EMF) worker wearing protective clothing subject to RF-EMF exposure, and subject to various environmental conditions including high ambient temperature and high humidity, with full thermoregulatory mechanisms in place. How the human body responds in various scenarios was investigated, and the information was used to consider safety limits in current international RF-EMF safety guidelines and standards. It was found that different environmental conditions had minimal impact on the magnitude of the thermal response due to RF-EMF exposure, and that the current safety factor of 10 applied in international RF-EMF safety guidelines and standards for RF-EMF workers is generally conservative, though it is only narrowly so when workers are subjected to the most adverse environmental conditions. Bioelectromagnetics. 38:356-363, 2017.

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.