Comparisons of computed mobile phone induced SAR in the SAM phantom to that in anatomically correct models of the human head

The specific absorption rates (SAR) determined computationally in the specific anthropomorphic mannequin (SAM) and anatomically correct models of the human head when exposed to a mobile phone model are compared as part of a study organized by IEEE Standards Coordinating Committee 34, Sub-Committee 2, and Working Group 2, and carried out by an international task force comprising 14 government, academic, and industrial research institutions. The detailed study protocol defined the computational head and mobile phone models. The participants used different finite-difference time-domain software and independently positioned the mobile phone and head models in accordance with the protocol. The results show that when the pinna SAR is calculated separately from the head SAR, SAM produced a higher SAR in the head than the anatomically correct head models. Also the larger (adult) head produced a statistically significant higher peak SAR for both the 1- and 10-g averages than did the smaller (child) head for all conditions of frequency and position.     

Is the SAM phantom conservative for SAR evaluation of all phone designs?

The specific anthropomorphic mannequin (SAM) phantom was designed to provide a conservative estimation of the actual peak spatial specific absorption rate (SAR) of the electromagnetic field radiated from mobile phones. However, most researches on the SAM phantom have been based on early phone models. Therefore, we numerically analyze the SAM phantom to determine whether it is sufficiently conservative for various types of mobile phone models. The peak spatial 1‐ and 10‐g averaged SAR values of the SAM phantom are numerically compared with those of four anatomical head models at different ages for 12 different mobile phone models (a total of 240 different configurations of mobile phones, head models, frequencies, positions, and sides of the head). The results demonstrate that the SAM phantom provides a conservative estimation of the SAR for only mobile phones with an antenna on top of the phone body and does not ensure such estimation for other types of phones, including those equipped with integrated antennas in the microphone position, which currently occupy the largest market share.     

EEG electrode caps can reduce SAR induced in the head by GSM900 mobile phones

This paper investigates the influence of EEG electrode caps on specific absorption rate (SAR) in the head from a GSM900 mobile phone (217-Hz modulation, peak power output 2 W). SAR measurements were recorded in an anthropomorphic phantom using a precision robotic system. Peak 10 g average SAR in the whole head and in just the temporal region was compared for three phantom arrangements; no cap, 64-electrode "Electro-Cap," and 64-electrode "Quick-Cap". Relative to the "no cap" arrangement, the Electro-Cap and Quick-Cap caused a peak SAR (10 g) reduction of 14% and 18% respectively in both the whole head and in the temporal region. Additional computational modeling confirmed that SAR (10 g) is reduced by the presence of electrode leads and that the extent of the effect varies according to the orientation of the leads with respect to the radiofrequency (RF) source. The modeling also indicated that the nonconductive shell between the electrodes and simulated head material does not significantly alter the electrode lead shielding effect. The observed SAR reductions are not likely to be sufficiently large to have accounted for null EEG findings in the past but should nonetheless be noted in studies aiming to measure and report human brain activity under similar exposure conditions.     

Study on SARs in Head Models With Different Shapes by Age Using SAM Model for Mobile Phone Exposure at 835 MHz

Four head models with the outer shapes of different ages were established using the specific anthropomorphic mannequin (SAM) model of IEEE Standard 1528. The criteria of head height, face length, head length, and head breadth by age were applied to build the models. We assumed that the shells of all the head models have the same dielectric properties with the head-equivalent tissue in order to simulate a real pressed ear. The cheek and tilt positions of three bar-type phone models were used, and the positioning processes against each head model were described in detail. Antenna input impedances of the phones under the test positions and specific absorption rate (SAR) distributions in the head models were computed using the finite-difference time-domain (FDTD) technique. Spatial peak SARs averaging over 1 and 10 g were compared for fixed input and radiated powers of all the phones. The effect of the dielectric properties in a younger head model on SAR result was analyzed. First, input resistance of the phone antennas in the cheek position gradually increased when head size grew with age, but those for the tilt position showed a slight decrease. Second, for a fixed input power, the head models by age changed peak 1- and 10-g SARs by approximately 15%. The electromagnetic absorption depths in the head models in the same test position were about the same, but the head-averaged SAR was higher in the younger model because of the smaller head volume. Third, for a fixed radiated power, the peak SARs got relatively lower in the smaller head model and higher in the larger head model, compared with those for the fixed input power since the smaller head model needs lower input power. Fourth, it was shown that simultaneous change in the conductivity and permittivity of head tissue within 20%-30% did not have a significant influence on energy absorption.     

Approximation of aging effect on dielectric tissue properties for SAR assessment of mobile telephones

In electromagnetic dosimetry of children heads for mobile telephones, the dielectric properties of biological tissues for adults are so far being used due to the lack of the ones of children. In this paper, we derived an empirical formula according to Lichtenecker's exponential law for the complex permittivity of various tissues as a function of the hydrated rate or the total body water (TBW). We first examined its validity using the data measured by Peyman et al. for rats, and then applied the formula to the dielectric properties of 7-year-old and 3-year-old child head models by means of the relationship between the TBW and the age. With the dielectric properties for children derived in such an approach, we analyzed numerically the spatial peak specific absorption rate (SAR) for a 900-MHz mobile telephone in adult and child head models. As a result, we found that the dielectric properties for children do not affect significantly the 1- or 10- g averaged spatial peak SAR as well as the penetration depth. The finding could be qualitatively explained as cancellation of the increased conductivity and decreased electric field penetrating into the tissue because of the same degree of increase between the conductivity and permittivity in children compared to adults. Even in an extreme case, the age effect on the spatial peak SAR of dielectric properties is still within 10%.     

Bandwidth, SAR, and efficiency of internal mobile phone antennas

This paper presents a thorough investigation into the effects of several phone chassis-related parameters-length, width, thickness, and distance between the head and phone-on the bandwidth, efficiency, and specific absorption rate (SAR) characteristics of internal mobile phone antennas. The studied antenna-chassis combinations are located beside an anatomical head model in a position of actual handset use. The effect of the user's hand is also studied with two different hand models. The main part of the study is based on FDTD simulations, but also experimental results, which support the computationally obtained conclusions, are given. The presented analysis provides novel and useful information for future design of mobile handset antennas. The results show the general trends of bandwidth, SAR, and efficiency with different chassis parameters. The results also reveal a connection between these three performance parameters: an increase in SARs and a decrease in radiation efficiency occur compared to the general trend when the bandwidth reaches its maximum. This happens when the resonant frequency of the chassis equals that of the antenna.     

Performance of shorted microstrip patch antennas for mobilecommunications handsets at 1800 MHz

We have investigated the application of two different types of novel shorted-patch antennas for mobile communications handsets at 1800 MHz. A single shorted-patch and a stacked shorted-patch antenna offering improved bandwidth are compared with data for a λ/4 monopole. The finite-difference time-domain (FDTD) technique was used to calculate antenna characteristics such as impedance and radiation patterns for two cases: on a handset and on a handset near a (2.5-mm voxel) heterogeneous head model in an actual position of phone use. We also obtained specific absorption rate (SAR) distributions and calculated the spatial peak 1-g SAR values. In addition, the effect on SAR and antenna characteristics of including a block model of the hand was assessed. Similar performance is achieved from the single or stacked shorted-patch antenna with the latter providing greater bandwidth, 8.2% versus 9.4% with the head and hand included. Both antennas reduce the l-g spatial peak SAR value in the head by 70% relative to the monopole. The presence of the hand reduces the efficiency of all three antenna types by approximately 10%     

Specific Absorption Rate Values of Handsets in Cheek Position at 835 MHz as a Function of Scaled Specific Anthropomorphic Mannequin Models

A specific anthropomorphic mannequin (SAM) model was used to investigate the relation between local specific absorption rate (SAR) and head size. The model was scaled to 80 to 100% sized models at intervals of 5%. We assumed that the shell of the SAM model has the same properties as the head‐equivalent tissue. Five handsets with a monopole antenna operating at 835 MHz were placed in the approximate cheek position against the scaled SAM models. The handsets had different antenna lengths, antenna positions, body sizes, and external materials. SAR distributions in the scaled SAM models were computed using the finite‐difference time‐domain method. We found that a larger head causes a distinct increase in the spatial peak 1‐voxel SAR, while head size did not significantly change the peak 1‐g averaged‐SAR and 10‐g averaged‐SAR values for the same power level delivered to the antenna.     

FDTD-derived correlation of maximum temperature increase and peak SAR in child and adult head models due to dipole antenna

This paper investigates the correlation between the peak specific absorption rate (SAR) and the maximum temperature increase in head models of adults and children due to a dipole antenna. Much attention is paid to the effect of variation of electrical and thermal constants on the correlation for the child models, since these constants of child tissues are different from those of adult tissues. For investigating these correlations thoroughly, a total of 1400 situations are considered for the following six models: 3-year-old child, 7-year-old child, and adult models developed at the Nagoya Institute of Technology and the Osaka the University. The numerical results are analyzed on the basis of statistics. We find that the maximum temperature increases in the head can be estimated linearly in terms of peak SAR averaged over 1- or 10-g of tissue. In particular, no clear difference is observed between the adult and child models in terms of the slopes correlating the maximum temperature increase with the peak SAR. Also, the effect of electrical and thermal constants of tissue on these correlation is found to be marginal. Further, we discuss possible maximum temperature increases in the head and brain for SAR limits prescribed in safety guidelines. For the adult model developed at the Osaka Univ., these are found to be 0.26/spl deg/C and 0.10/spl deg/C at the SAR value of 1.6 W/kg for 1-g cubic tissue and 0.59/spl deg/C and 0.21/spl deg/C at the SAR value of 2.0 W/kg for 10-g cubic tissue. Similarly, for the 3-year-old child model at Osaka Univ., these are 0.23/spl deg/C and 0.11/spl deg/C for the value of 1-g SAR and 0.53/spl deg/C and 0.20/spl deg/C for the value of 10-g SAR.     

Experimental tests of SAR reduction on mobile phone using EBG structures

Experimental tests of specific absorption rate (SAR) reduction on a mobile phone have been performed. To protect a human head from exposure to electromagnetic fields and comply with exposure guidelines, the electromagnetic bandgap (EBG) structures are inserted in a commercial personal communication services (PCS) mobile phone. The measured results demonstrate the movement of a hot spot and the reduction of SAR in the human head.     

Correlation of maximum temperature increase and peak SAR in the human head due to handset antennas

This paper attempts to correlate the maximum temperature increase in the head and brain with the peak specific absorption rate (SAR) value due to handset antennas. The rationale for this study is that physiological effects and damage to humans through electromagnetic-wave exposure are induced by temperature increases, while the safety standards are regulated in terms of the local peak SAR. For investigating these correlations thoroughly, the total of 660 situations is considered. The numerical results are analyzed on the basis of statistics. We find that the maximum temperature increases in the head and brain can be estimated in terms of peak SARs averaged over 1 and 10 g of tissue in these regions. These correlations are less affected by the positions, polarizations, and frequencies of a dipole antenna. Also, they are reasonably valid for different antennas and head models. Further, we discuss possible maximum temperature increases in the head and brain for the SAR values prescribed in the safety standards. They are found to be 0.31/spl deg/C and 0.13/spl deg/C for the Federal Communications Commission Standard (1.6 W/kg for 1 g of tissue), while 0.60/spl deg/C and 0.25/spl deg/C for the International Commission on Non-Ionizing Radiation Protection Standard (2.0 W/kg for 10 g of tissue).     

FDTD computation of temperature rise in the human head for portabletelephones

Temperature rises in the human head for portable telephones were computed with an anatomically based head model at 900 MHz and 1.5 GHz. The specific absorption rate (SAR) in the human head was determined using the finite-difference time-domain (FDTD) method, while a bioheat equation was numerically solved also using the FDTD method. The portable telephone was modeled by a quarter-wavelength monopole antenna on a dielectric covered metal box. The source geometries considered were the telephone barely touching the ear and the telephone pressing the ear, both having a vertical alignment at the side of the head. The antenna output power was set to be consistent with the portable telephones of today: 0.6 W at 900 MHz and 0.27 W at 1.5 GHz. Computed results show that a phone time of 6-7 min yields a temperature rise of approximately 90% of the steady-state value. Application of the ANSZ/IEEE safety guidelines restricting the 1-g-averaged spatial peak SAR to 1.6 W/kg results in the maximum temperature rise in the brain of 0.06°C, and application of the ICNIRP/Japan safety guidelines restricting the 10-g-averaged spatial peak SAR to 2 W/kg results in the maximum temperature rise in the brain of 0.11°C, both at 900 MHz and 1.5 GHz     

人体受到电磁辐射的仿真研究

基于可变网络的时域有限差分法,仿真了暴露于900MHz移动通信基站天线远区场中的人体和移动电话天线近区场中的人体头部电磁模型中产生的比吸收率分布,分析了基站天线和手机天线辐射对人体的影响。以理想点源天线作为基站天线,在人体正前方入射频率为900MHz的正弦平面波,仿真结果显示,人体在基站天线照射下的平均SAR值符合国际卫生部标准;以900MHz单频PIAF天线作为手机天线置于高仿真人体头部1cm处,仿真结果与环保标准比较,人体头部受到的照射剂量远低于安全标准。     

Evaluation of the SAR induced in a multilayer biological structure and comparison with SAR in homogeneous tissues

Wireless systems usage has evolved, for instance, with the recent increase in the use of a hands-free kit, the mobile phone is used more and more in a body-worn position. Therefore, to check the compliance to the international limits, new methods have to be developed. In this study, we analyze the relevance of using the equivalent head liquid for the biological structure of organs that are different from that of the head. This paper compares the Specific Absorption Rate (SAR) values assessed using simulations in a flat phantom filled with the liquid used to test the compliance of mobile phone close to the head to those values obtained using a multilayer model representing the tissues of the trunk. The multilayer structures are derived from the anatomical analysis of the visible human model and corresponding to reasonable positions of a handset in a body-worn configuration. The employed sources are half-wavelength dipoles placed at different distances from those structures and operating at frequencies between 300 MHz and 6 GHz.     

Temperature increase in the human head due to a dipole antenna at microwave frequencies

The temperature increases in a human head due to electromagnetic (EM) wave exposure from a dipole antenna are investigated in the frequency range of 900 MHz to 2.45 GHz. The maximum temperature increases in the head and brain are compared with the values of 10/spl deg/C and 3.5/spl deg/C (found in literature pertaining to microwave-induced physiological damage). In particular, the estimation scheme for maximum temperature increases of the head and brain tissues is discussed in terms of a peak average specific absorption rate (SAR) as prescribed in safety standards. The rationale for this attempt is that maximum temperature increases and peak average SARs have not been well correlated yet. For this purpose, the SAR in the head model is initially calculated by the finite-difference time-domain method. The temperature increase in the model is then calculated by substituting the SAR into the bioheat equation. Numerical results demonstrate that the temperature increase distribution in the head is largely dependent on the frequency of EM waves. This is mainly because of the frequency dependency of the SAR distribution. Similarly, maximum temperature increases in the head and brain are significantly affected by the frequency and polarization of the EM wave. The maximum temperature increases in the head (excluding auricles) and brain are determined through linear extrapolation of the peak average SAR in these regions. According to this scheme, it is found that the peak SAR averaged over 1 g of tissue in the head should be approximately 65 W/kg to achieve the maximum temperature increase of 10/spl deg/C induced in the head excluding auricles. This corresponds to a factor of about 40 compared to the FCC standard. On the other hand, the peak SAR for 10 g of tissue should be around 40 W/kg, which implies a factor of about 20 compared to the ICNIRP standard.     

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

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.      

Dual-band planar inverted F antenna for GSM/DCS mobile phones

A compact dual-band planar inverted F antenna suitable for the application as a global system for mobile communication/digital communication system (GSM/DCS) dual-band mobile phone internal antenna is proposed and implemented. The proposed antenna has three resonant elements, two meandered metallic strips of slightly different lengths and one nearly-rectangular patch, which are printed on a supporting FR4 substrate and arranged in a compact configuration. These three resonant elements share a common shorting pin, and for the GSM (890-960 MHz) operation, the proposed antenna is operated with the two meandered strips both resonated as a quarter-wavelength structure, leading to a wide bandwidth formed by two resonant modes. For the upper band of the proposed antenna, three resonant modes are generated, two from the second higher-order modes of the two meandered strips and one from the nearly-rectangular patch, leading to a wide bandwidth covering the DCS band (1710-1880 MHz). The antenna design and experimental results are presented.     

Temperature increase in human eyes due to near-field and far-field exposures at 900 MHz, 1.5 GHz, and 1.9 GHz

This work investigates the effect of frequency, polarization, and angle of incidence of an electromagnetic (EM) wave on the specific absorption rate (SAR) and maximum temperature increase in the human eye at 900 MHz, 1.5 GHz, and 1.9 GHz. In particular, the temperature increase in the eye is compared for near-field and far-field exposures. The difference of a maximum temperature increase in the lens is also discussed between the head models of an adult and children. Throughout the investigations, our attention is paid to a maximum temperature increase in the lens for SAR values prescribed in safety standards. For the results of our investigation, the SAR and temperature increase in the eye are found to be largely dependent on the separation between the eye and a source, and the frequency, polarization, and angle of incidence of the EM wave. The maximum temperature increase (0.303/spl deg/C-0.349/spl deg/C) in the lens of the adult for the SAR value of 2.0 W/kg for the eye tissue (about 10 g) is marginally affected by the above-mentioned factors. No clear difference of a maximum temperature increase in the lens at the SAR limit is observed between the adult and children models.     

Correlation between maximum temperature increase and peak SAR with different average schemes and masses

This paper investigates the correlation between maximum temperature increases and peak spatial-average specific absorption rates (SARs), calculated by different average schemes and masses. For evaluating the effect of mass on the correlation properly, a three-dimensional Green's function is presented. From our computational investigation, no best average mass for peak spatial-average SAR exist from the aspect of the correlation with maximum temperature increase. This is attributed to the frequency dependent penetration depth of EM waves. Maximum temperature increase in the head including the pinna is reasonably correlated with peak spatial-average SARs for most average schemes and masses considered in this paper. Maximum temperature increase in the head only (excluding the pinna) is reasonably correlated with peak 10-g SARs for the average schemes considered in this paper. The rationale for this result is explained using the Green's function. The point to be stressed here is that the slope correlating them is largely dependent on the average scheme and mass. Additionally, good agreement is observed in the slopes obtained by using two head models, which have been developed at Osaka University and Nagoya Institute of Technology. However, weak correlation is observed for the brain, which is caused by the difference of the positions where peak SAR and maximum temperature increase appear. The 95th percentile values of the slope correlating maximum temperature increases in the head or brain and peak spatial-average SAR are quantified for different average schemes and masses.     

EM interaction of handset antennas and a human in personalcommunications

In personal communications, the electromagnetic interaction between handset-mounted antennas and the nearby biological tissue is a key consideration. This paper presents a thorough investigation of this antenna-tissue interaction using the finite-difference time-domain (FDTD) electromagnetic simulation approach with detailed models of real-life antennas on a transceiver handset. The monopole, side-mounted planar inverted F, top-mounted bent inverted F, and back-mounted planar inverted F antennas are selected as representative examples of external and internal configurations. Detailed models of the human head and hand are implemented to investigate the effects of the tissue location and physical model on the antenna performance. Experimental results are provided which support the computationally obtained conclusions. The specific absorption rate (SAR) in the tissue is examined for several different antenna/handset configurations. It is found that for a head-handset separation of 2 cm, the SAR in the head has a peak value between 0.9 and 3.8 mW/g and an average value between 0.06 and 0.10 mW/g for 1 W of power delivered to the antenna. Additionally, the head and hand absorb between 48 and 68% of the power delivered to the antenna