Peak Spatial-average Specific Absorption Rate Research Articles

Development of a Numerical Tablet Model in WLAN Band for SAR Study

This research proposes a numerical model for a tablet in the wireless local area network band for specific absorption rate (SAR) study. The design criteria, such as the tablet size, operating frequencies, antenna position, and target 1-g peak spatial-average SAR (psSAR) values in the flat phantom, are determined based on the SAR test reports of tablets distributed in South Korea from 2013 to 2017. An internal antenna is designed in a tablet platform to operate in dual bands of 2,450 MHz and 5,500 MHz. The numerical results illustrate that the 1-g psSAR values of the proposed numerical tablet model are within ±10% of the target values. Moreover, the return loss of the designed tablet model is larger than 10 dB, regardless of flat phantom, while its radiation efficiency is higher than 90% in free space.

Reduction in Human Interaction with Magnetic Resonant Coupling WPT Systems with Grounded Loop

Wireless power transfer (WPT) systems have attracted considerable attention in relation to providing a reliable and convenient power supply. Among the challenges in this area are maintaining the performance of the WPT system with the presence of a human body and minimizing the induced physical quantities in the human body. This study proposes a magnetic resonant coupling WPT (MRC-WPT) system that utilizes a resonator with a grounded loop to mitigate its interaction with a human body and achieve a high-efficiency power transfer at a short range. Our proposed system is based on a grounded loop to reduce the leakage of the electric field, resulting in less interaction with the human body. As a result, a transmission efficiency higher than 70% is achieved at a transmission distance of approximately 25 cm. Under the maximum-efficiency conditions of the WPT system, the use of a resonator with a grounded loop reduces the induced electric field, the peak spatial-average specific absorption rate (psSAR), and the whole-body averaged SAR by 43.6%, 69.7%, and 65.6%, respectively. The maximum permissible input power values for the proposed WPT systems are 40 and 33.5 kW, as prescribed in the International Commission of Non-Ionizing Radiation Protection (ICNIRP) guidelines to comply with the limits for local and whole-body average SAR.

Compliance Assessment of the Epithelial or Absorbed Power Density Below 10 GHz Using SAR Measurement Systems.

The introduction of new dosimetric quantities, in particular, epithelial or absorbed power density for frequencies above 6 GHz, in exposure guidelines and safety standards requires the development of new experimental assessment procedures for compliance testing. In this study, we propose to approximate the peak spatial-average absorbed power density (psSab ) using the same measured data and algorithms that are used for determining the peak spatial-average specific absorption rate psSAR, which is currently limited to frequencies up to 10 GHz. The uncertainty component for the transformation of psSAR to psSab was evaluated as less than 0.55 dB (13.5%) for any source as close as from the tissue simulating media. The approach is easy to implement and allows determining compliance with the basic restrictions of the latest safety guidelines. In the next project, we will expand dosimetric probes, phantoms, and procedures for frequencies above 10 GHz. © 2021 Bioelectromagnetics Society.

Brain EM Exposure for Voice Calls of Mobile Phones in Wireless Communication Environment of Seoul, Korea

The aim of this paper is to present the measurement results of the transmitted (Tx) power levels of mobile phones in currently operating wireless communication networks in Seoul in 2015 and 2017 and the calculation results of the specific absorption rate (SAR) in the brain for voice calls while holding a mobile phone against the user’s ear when operating at the measured mean power level. The Tx power levels of mobile phones using Code Division Multiple Access (CDMA) 2000, Wide CDMA (WCDMA), and Long-Term Evolution (LTE) networks were compared for the three main mobile network operators in South Korea. The actual mean Tx power level was less than 0.5% of the maximum power for the CDMA2000 and WCDMA networks. In the LTE networks, however, an extremely wide gap in Tx power was observed between the operators; two of the operators showed a mean power of less than 0.1% of the maximum, whereas the other showed mean powers of the three bands within the range of 0.8%–20% of the maximum power. The measurement results suggest that the SAR in the user’s brain is strongly dependent on the year the phone was used, the user-subscribed mobile operator, and the proportion of time connected to the network/technology. The maximum 1-g peak spatial-average SAR (psSAR) level at the mean Tx power in an LTE network was 4.8 mW/kg (for a child head model). A maximum gap of 25 dB in the psSAR was observed between all networks considered.

Brain SAR of average male Korean child to adult models for mobile phone exposure assessment

This paper aims to implement average head models of Korean males and investigate age-related differences in the brain for exposure from radiation from mobile phones. Four male head models composed of a total of 69 structures were developed through a statistical investigation of the anatomical morphology for the age groups of 6, 9, 15 and 20–24 years in age, which are named KR-6, KR-9, KR-15, and KR-22 herein. Three numerical bar phone models with a dual-band built-in antenna were applied to calculate the specific absorption rate (SAR) in the brain; the body lengths of models Mavg and Mlong have the mean value and upper 5th percentile value of commercial bar phone models, respectively, with an antenna at the bottom, whereas Mrev has an antenna on top of the phone body, which is the same as in Mavg but rotated 180°. The cheek and tilt positions were employed for SAR simulations. As a result, a higher peak spatial-average SAR (psSAR) was observed in the brain for the child groups of KR-6 and KR-9 than for the adult groups of KR-15 and KR-22. In most configurations, the position-averaged psSAR10 g in the child brain was 62% (Mlong, 835 MHz), 61% (Mavg, 835 MHz), 102% (Mlong, 1850 MHz), 108% (Mavg, 1850 MHz), and 125% (Mrev, 1850 MHz) higher than in the adult brain. The higher frequency of 1850 MHz showed a wider difference in the brain psSAR between the child and adult groups owing to the shorter penetration depth. When a long phone with an antenna at the bottom operates at a higher frequency, it significantly reduces the brain exposure.

SAR thresholds for electromagnetic exposure using functional thermal dose limits

Background and purpose: To protect against any potential adverse effects to human health from localised exposure to radio frequency (100 kHz–3 GHz) electromagnetic fields (RF EMF), international health organisations have defined basic restrictions on specific absorption rate (SAR) in tissues. These exposure restrictions incorporate safety factors which are generally conservative so that exposures that exceed the basic restrictions are not necessarily harmful. The magnitude of safety margin for various exposure scenarios is unknown. This shortcoming becomes more critical for medical applications where the safety guidelines are required to be relaxed. The purpose of this study was to quantify the magnitude of the safety factor included in the current basic restrictions for various exposure scenarios under localised exposure to RF EMF.Materials and methods: For each exposure scenario, we used the lowest thermal dose (TD) required to induce acute local tissue damage reported in literature, calculated the corresponding TD-functional SAR limits (SARTDFL) and related these limits to the existing basic restrictions, thereby estimating the respective safety factor.Results: The margin of safety factor in the current basic restrictions on 10 g peak spatial average SAR (psSAR10g) for muscle is large and can reach up to 31.2.Conclusions: Our analysis provides clear instructions for calculation of SARTDFL and consequently quantification of the incorporated safety factor in the current basic restrictions. This research can form the basis for further discussion on establishing the guidelines dedicated to a specific exposure scenario, i.e. exposure-specific SAR limits, rather than the current generic guidelines.

Large scale study on the variation of RF energy absorption in the head & brain regions of adults and children and evaluation of the SAM phantom conservativeness

This paper presents the results of two computational large scale studies using highly realistic exposure scenarios, MRI based human head and hand models, and two mobile phone models. The objectives are (i) to study the relevance of age when people are exposed to RF by comparing adult and child heads and (ii) to analyze and discuss the conservativeness of the SAM phantom for all age groups. Representative use conditions were simulated using detailed CAD models of two mobile phones operating between 900 MHz and 1950 MHz including configurations with the hand holding the phone, which were not considered in most previous studies. The peak spatial-average specific absorption rate (psSAR) in the head and the pinna tissues is assessed using anatomically accurate head and hand models.The first of the two mentioned studies involved nine head-, four hand- and two phone-models, the second study included six head-, four hand- and three simplified phone-models (over 400 configurations in total). In addition, both studies also evaluated the exposure using the SAM phantom. Results show no systematic differences between psSAR induced in the adult and child heads. The exposure level and its variation for different age groups may be different for particular phones, but no correlation between psSAR and model age was found. The psSAR from all exposure conditions was compared to the corresponding configurations using SAM, which was found to be conservative in the large majority of cases.

Response to “Children Absorb Higher Doses of Radio Frequency Electromagnetic Radiation From Mobile Phones Than Adults” and “Yes the Children Are More Exposed to Radiofrequency Energy From Mobile Telephones Than Adults”

This is a response to two critical comments on our 2014 paper in the IEEE Access. That paper reviewed numerical dosimetry/modeling studies on the exposure [in terms of specific absorption rate (SAR)] to the user of a mobile phone to radiofrequency energy, and possible differences in exposure to children versus adults. The main focus was on the peak spatial average SAR (psSAR) in the head, which is the relevant quantity for assessing compliance with national and international exposure limits for mobile phones. Morris et al . criticized this paper for not accurately presenting the conclusions of the studies that it reviewed, despite the fact that these conclusions were summarized in this paper by quoting the original authors. However, their critique reflects a simple misreading of our paper and confusion about different metrics of exposure. A second critique, by Gandhi, noted age- and gender-related differences in the absorption of RF energy in the head. We agree with his comments, if they are interpreted as referring to the psSAR in the brain (which is different from the psSAR for the head as a whole and is not used for compliance assessment). This response briefly reviews major factors that limit the relevance of numerical dosimetry/modeling studies under tightly controlled conditions used for compliance assessment to real-world exposures to users of mobile phones.

SAR Comparison of SAM Phantom and Anatomical Head Models for a Typical Bar-Type Phone Model

The current IEEE 1528 and IEC 62209-1 standards specify a simplified physical model of the human head to provide conservative measurement procedures of the peak spatial-average specific absorption rate (SAR) of a mobile phone. This means that the evaluated SAR in a specific anthropomorphic mannequin (SAM) head model should be higher than in the heads of a significant majority of users under normal operational conditions. In this paper, the conservativeness of the SAM is investigated by numerically comparing the SAR in the SAM with those in four anatomical head models at different ages for exposure from a typical bar-type mobile phone. A numerical bar-type phone model with an internal antenna at the bottom of the phone body was implemented at 835 and 1850 MHz. This model provides an SAR pattern and levels similar with the commercial bar phones released in Korea. For two standard test positions, spatial peak 1- and 10-g SARs were calculated for both the SAM phantom and anatomical head models. The SARs were also calculated when the antenna is located on top of the phone. The results show that the SAM phantom provides a conservative evaluation for a phone model with the antenna on the top. However, when the antenna is located at the bottom, the hotspot in the SAM occurred farther from the antenna feed point, and, thus, produced lower 1- and 10-g SAR results compared with the anatomical models.

High Resolution Numerical Modelling of In-Vehicle Mobile Calls

The scenario of making a mobile phone call inside a vehicle is numerically modeled using a high resolution FDTD gridding; solved by a 3-D full-wave electromagnetic simulation software on a high performance workstation machine with Tesla GPU accelerator. The simulated mobile call inside a vehicle involved; a high resolution human head with shoulder phantom (VH_Head_Model 9), high resolution realistic hand model (posable right-hand), realistic mobile phone handset CAD-models with different antenna types and a vehicle CAD-model (big-sedan Camaro-brand). The impact of the in-vehicle mobile calls on the electromagnetic interaction of the handset antenna and human is anticipated at different operating frequencies, i.e., GSM-900 and GSM-1800, and different handset positions with respect to head, i.e., cheek and tilt-position. A significant degradation in the handset antenna performance was observed due to the presence of the vehicle body while making a mobile call inside. Nevertheless, no change in the peak spatial-average specific absorption rate in head tissues was detected while making a mobile call inside vehicle, as compared with the specific absorption rate due to the mobile call in free-space.

Uncertainty evaluation in numerical modeling of complex devices

Numerical simulation is an efficient tool for exploring and understanding the physics of complex devices, e.g. mobile phones. For meaningful results, it is important to evaluate the uncertainty of the numerical simulation. Uncertainty quantification in specific absorption rate (SAR) calculation using a full computer-aided design (CAD) mobile phone model is a challenging task. Since a typical SAR numerical simulation is computationally expensive, the traditional Monte Carlo (MC) simulation method proves inadequate. The unscented transformation (UT) is an alternative and numerically efficient method herein investigated to evaluate the uncertainty in the SAR calculation using the realistic models of two commercially available mobile phones. The electromagnetic simulation process is modeled as a nonlinear mapping with the uncertainty in the inputs e.g. the relative permittivity values of the mobile phone material properties, inducing an uncertainty in the output, e.g. the peak spatial-average SAR value.The numerical simulation results demonstrate that UT may be a potential candidate for the uncertainty quantification in SAR calculations since only a few simulations are necessary to obtain results similar to those obtained after hundreds or thousands of MC simulations.

The numerical modelling studies performed at the Gazi Biophysics Laboratory

In recent years humans are more exposed to human-made electromagnetic (EM) fields than natural fields with developing technologies. Especially, widespread use of wireless communication technologies in all areas of daily life and getting closer to sensitive organs like brain caused an increase in possible risks and worries about human health. For this reason, the potential health effects from the use of mobile phones has been studied intensively in scientific field. Specific Absorption Rate (SAR) with the dose limits are used to prevent possible health effects of Radio Frequency (RF) radiation. Due to lack of SAR value measurement on human or animal tissues directly or in a lab environment, the value of the dose from exposure to the EM Field was determined from measurements of phantoms filled with tissue equivalent liquid or can be made by using a computer simulation environment. The Numerical Modelling studies performed at the Gazi Biophysics Laboratory are reviewed in this paper: 1. Simulations of human head for mobile phone (CP) usage: In this study, the effects of 835 MHz and 900 MHz RFR exposures on human head while using CP were investigated. The effects of CP usage on SAR were calculated by SEMCAD X software which uses FDTD method in details. Some parameters as the different head dimensions and dielectric properties of the head (adult and child), positions of the mobile phone (cheek and tilt), and rectangular metal frame spectacles as a widely used metallic accessory were considered. With this aim, dose values in the tissue for 10 g peak spatial-average SAR value were calculated. At both of the frequencies of 835 MHz and 900 MHz, higher SAR values were obtained in the cheek positions than the tilt positions for conditions of with or without metal frame spectacles. 2. Simulations of “in vivo” experimental set-up: 2.1.Numerical simulations were performed on a simplified model of mouse contained in a square shaped glass cage and Generic Mobile Phone located 1 cm below the cage. 10 g peak spatial average SARs at 900 MHz in the head and trunk was determined respectively. 2.2.Numerical simulations were performed on a simplified model of rat located from the horn antenna as an RF source. 10 g peak spatial average SARs at 900 and 1800 MHz in the head was determined. 3. Simulations of “in vitro” experimental set-up: In vitro exposure system was consist of a horn antenna and 24-well micro titer plates. Quad Ridged Guide Horn antenna was used for a radio frequency field source. 24 well microtiter plates centered on 1 mm above the horn antenna. Numerical models for the DMEM medium inside a 24 well microtiter plates were used to assess peak SAR values averaged over 10 g of tissue at 2.1 GHz.

Dosimetry evaluation of a cylindrical waveguide chamber for unrestrained small rodents at 1.9 GHz

An exposure system, consisting of four identical cylindrical waveguide chambers, was developed for studying the effects of radiofrequency (RF) energy on laboratory mice at a frequency of 1.9 GHz. The chamber was characterized for RF dose rate as a function of animal body mass and dose rate variations due to animal movement in the cage. Dose rates were quantified in terms of whole-body average (WBA) specific absorption rate (SAR), brain average (BA) SAR and peak spatial-average (PSA) SAR using measurement and computational methods. Measurements were conducted on mouse cadavers in a multitude of possible postures and positions to evaluate the variations of WBA-SAR and its upper and lower bounds, while computations utilizing the finite-difference time-domain method together with a heterogeneous mouse model were performed to determine variations in BA-SAR and the ratio of PSA-SAR to WBA-SAR. Measured WBA-SAR variations were found to be within the ranges of 9-23.5 W/kg and 5.2-13.8 W/kg per 1 W incident power for 20 and 40 g mice, respectively. Computed BA-SAR variations were within the ranges of 3.2-10.1 W/kg and 3.3-9.2 W/kg per 1 W incident power for 25 and 30 g mouse models, respectively. Ratios of PSA-SAR to WBA-SAR, averaged over 0.5 mg and 5 mg tissue volumes, were observed to be within the ranges of 6-15 and 4-10, respectively.

Influence of the Hand on the Specific Absorption Rate in the Head

The influence of the user's hand holding a mobile phone to the ear on the peak spatial-average Specific Absorption Rate (psSAR) averaged over any 1 g and 10 g of tissue in the head is investigated. This study is motivated by recent reports that found substantial increases in psSAR by the presence of the hand in some cases. Current measurement standards prescribe the measurement of SAR in a head phantom without a hand present. The mechanisms of interaction between the hand and mobile phone models are studied. Simulations and measurements at 900 and 1800 MHz have been conducted to complement the understanding of the hand grip parameters leading to higher SAR in the head. Numerical simulations were conducted on four mobile phone models, and parameters such as the palm-phone distance and hand position were varied. Measurements of 46 commercial mobile phones were made, and the maximum psSAR with different hand positions and palm-phone distances was recorded. Both simulations and measurements have found increases in the psSAR in the head of at least 2.5 dB due to the presence of the hand. Furthermore, the psSAR is sensitive to the hand grip, i.e., the variations can exceed 3 dB.

Specific Absorption Rates of Anatomically Realistic Human Models Exposed to RF Electromagnetic Fields From Mobile Phones Used in Elevators

This paper presents a detailed numerical investigation to determine whether or not an increased specific absorption rate (SAR) in an adult using a mobile phone inside an elevator due to the multireflections of electromagnetic fields from the walls exceed the RF-exposure guidelines. A fully realistic heterogeneous human body model and an actual elevator size were employed. The nonuniform mesh finite-difference time-domain technique and a supercomputer were employed to obtain the SAR and other important parameters. The mobile phone was modeled as a lambda/2 dipole antenna placed at a distance of 16 mm from the head. For computations, operating frequencies of 900, 1500, and 2000 MHz with transmitting power of 250 mW were used. Computed results show that the peak spatial-average 10-g SAR depends on the position of the passenger and the antenna against the elevator walls. We observed a substantial increase in the whole-body average SAR and peak 10-g SAR values of the passenger in the elevator over their respective free-space values. However, the maximum values obtained do meet the basic restrictions described in the international RF safety guidelines. For example, the maximum values of the whole-body average and peak spatial-average SAR were 4.4% and 78% of the international RF safety guideline, respectively.

Dependence of the Occupational Exposure to Mobile Phone Base Stations on the Properties of the Antenna and the Human Body

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This study assesses human exposure in the close vicinity of mobile phone base station antennas by finite-difference time-domain simulations. The peak spatial average specific absorption rate (SAR) and the whole-body average SAR are analyzed in three different anatomical models (55–101 kg) with respect to the basic restrictions for occupational exposure. The models are at distances between 0.5 and 4 m from various antenna types operating at frequencies ranging from 450 to 2140 MHz. The validity of the simulations is confirmed by an analysis of the impact of the mesh resolution on local and whole-body average SAR and by experimental validation of the numerical models. The results demonstrate that the whole-body absorption generally determines the maximum permissible antenna output power for collinear array antennas. Local exposure depends on various effects that fluctuate strongly among individuals. In particular for short antennas, the peak spatial average SAR can be more restrictive than the whole-body absorption because they may only expose a fraction of the body. Therefore, compliance must be demonstrated for both quantities. </para>

Correlation Between Peak Spatial-Average SAR and Temperature Increase Due to Antennas Attached to Human Trunk

This paper discusses the correlation between peak spatial-average specific absorption rate (SAR) and maximum temperature increase for antennas attached to the human trunk. Frequency bands considered are 150, 400, and 900 MHz, which are assigned for occupational communications. This problem is throughly investigated with the aid of Green's function. In particular, the effect of variation of thermal constants on the temperature increase is revealed by using one-dimensional model. Computational results suggests that one of the most dominant factors which affect the correlation between peak SAR and maximum temperature increase is blood flow in tissues. This is confirmed by considering a three-dimensional realistic human body model. Uncertainties caused by the calculation of peak SAR and the difference in the body model shape are also quantified.

Testing the effectiveness of small radiation shields for mobile phones.

Nine small radiation shields made to adhere to the case of mobile phones were tested at 914 and 1880 MHz. Five popular products were tested because advertisements typically claim they are up to 99% effective in blocking radio frequency (RF) radiation emitted from mobile phones. Also, four other conceptually unusual products were tested because advertisements typically claim they emit oscillations that counteract the RF radiation from mobile phones. Each shield was tested on the same mobile phone, and measurements were made to compare the absorption of RF energy in the head with and without each shield attached to the phone. The phone was positioned against a head model, and an automated measurement process was used to determine specific absorption rate (SAR) in the same way it is used at Motorola to test the compliance of mobile phones with respect to human exposure limits. The location of the peak SAR was not observed to change with any of the shields attached to the phone, and the 1 g, peak spatial average SAR did not change by any statistically significant amount. These results indicate the small shields are ineffective in reducing the exposure of the head to RF energy emitted by a mobile phone.