International intercomparison of specific absorption rates in a flat absorbing phantom in the near-field of dipole antennas

This paper reports the results of an international intercomparison of the specific absorption rates (SARs) measured in a flat-bottomed container (flat phantom), filled with human head tissue simulant fluid, placed in the near-field of custom-built dipole antennas operating at 900 and 1800 MHz, respectively. These tests of the reliability of experimental SAR measurements have been conducted as part of a verification of the ways in which wireless phones are tested and certified for compliance with safety standards. The measurements are made using small electric-field probes scanned in the simulant fluid in the phantom to record the spatial SAR distribution. The intercomparison involved a standard flat phantom, antennas, power meters, and RF components being circulated among 15 different governmental and industrial laboratories. At the conclusion of each laboratory's measurements, the following results were communicated to the coordinators: Spatial SAR scans at 900 and 1800 MHz and 1 and 10 g maximum spatial SAR averages for cubic volumes at 900 and 1800 MHz. The overall results, given as mean standard deviation, are the following: at 900 MHz, 1 g average 7.850.76; 10 g average 5.160.45; at 1800 MHz, 1 g average 18.44/spl plusmn/1.65; 10 g average 10.14/spl plusmn/0.85, all measured in units of watt per kilogram, per watt of radiated power.     

Specific absorption rates in a flat phantom in the near-field of dipole antennas

National and international regulatory bodies require compliance testing procedures for hand-held wireless telephones. The IEEE has promulgated a compliance verification procedure (P1528) to be followed in verifying whether a wireless phone is compliant with international standards. Manufacturers are required to assess the maximum near-field exposures that phones might produce in the head of a user. A recent intercomparison of the testing procedure has involved the cooperation of 15 government and industrial laboratories. These laboratories measured the 1- and 10-cm/sup 3/ cubic volume-averaged specific absorption rates (SARs) in a flat phantom filled with a standardized lossy dielectric fluid. The phantom absorber was placed in the near field of a custom dipole antenna. In support of this effort, we have performed a theoretical analysis of the expected SARs in the measurement system, which has allowed comparison with experiment. We have also been able to compare the 1and 10-cm/sup 3/ volume-averaged SARs for cubic and maximum SAR volumes. There is generally good agreement between experimental and theoretical SAR spatial patterns, and SARs averaged over 1- and 10-cm/sup 3/ cubic volumes. The 1- and 10-cm/sup 3/ average SARs in the shapes giving maximum SARs are about 35% larger compared to cubic volumes.     

Methodology to interpolate and extrapolate SAR measurements in avolume in dosimetric experiment

There has been an explosive growth in the area of wireless communication. Over the world, hundreds of millions of subscribers are using mobile phones. International and national organizations have recommended limits for the protection of mobile phone users and standards are going to be established to certify the compliance of mobile phones with these limits. To ensure this conformity, numerical and experimental dosimetric analyzes are essential to evaluate the electric fields inside the user's head. These fields can not be measured near the mobile phone- the phantom interferes where they are a maximum and the use of interpolation and extrapolation is then necessary to evaluate the electric field components. This paper describes the interpolation and extrapolation methodologies, of the experimental sampled data in three dimensions, of the power absorbed in the whole volume of the head phantom. A new method to interpolate and extrapolate SAR measurements is presented. This technique, which is very fast and not very expensive in terms of required memory, is compared with other interpolation techniques which use splines or wavelets     

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.     

An automated SAR measurement system for compliance testing ofpersonal wireless devices

An automated specific absorption rate (SAR) measurement system has been developed for compliance testing of personal wireless devices. Unlike other systems, this system uses a model with a lossy ear-shaped protrusion and the accuracy of this experimental setup has been checked by comparing the peak 1-g SARs for ten cellular telephones, five each at 835 and 1900 MHz, with the results obtained using a 15-tissue anatomically based model with the finite-difference time-domain (FDTD) numerical electromagnetic technique. The SAR measurement system uses a three-dimensional (3-D) stepper motor to move a Narda Model 8021 E-field probe to measure the SAR distribution inside a head-shaped tissue-simulant phantom near the radiating device. The head and neck part of the model with an ear-shaped protrusion of 3 mm thickness is made of a lossy outer shell of 5-7 mm thickness of epoxy laced with KCl solution. The phantom is filled with appropriate frequency-specific fluids with measured electrical properties (dielectric constant and conductivity) that are close to the average for gray and white matters of the brain at the center frequencies of interest (835 and 1900 MHz). The implantable E-field probe is calibrated using the FDTD-calculated SAR variations for a slab model at two commonly used frequencies, 835 and 1900 MHz and is checked to have good isotropic characteristics (±0.23 dB) and a wide dynamic range (0.01-10 W/kg). The system is validated using a 223-mm-diameter sphere model. Peak 1-g SAR's for ten telephones using different antennas are within ±1 dB of those obtained using the FDTD numerical method for the anatomical model of the head and neck region     

Effects of ear-connection modeling on the electromagnetic-energyabsorption in a human-head phantom exposed to a dipole antenna field at835 MHz

Specific absorption rate (SAR) compliance measurements for wireless personal devices are usually performed in anatomically correct phantoms. The phantoms have a lossless spacer to model the external ear (pinna). The use of a lossless spacer has been questioned. The purpose of this paper was to study the effects of the lossy pinna by E-field and numerical assessments validated with thermal measurements. The measurements were performed in a box with a rectangular well simulating a pinna compressed during phone usage. Various openings were created in the septum separating the box and the well to simulate the connection between the head and pinna. A balanced half-wave dipole was used as the RF source. The results of this study lead to the conclusion that for SAR values averaged over 1 gram, within our current probe resolution, complicated lossy pinna structures are not necessary     

Novel Specific Absorption Rate (SAR) Measurement Method Using a Flat Solid Phantom

A novel specific absorption rate (SAR) measurement method is presented that employs a flat solid phantom with multiple embedded E-field probes. A radio device under test traverses over them during the scanning process. The solid phantom provides stable dielectric properties and easy handling, while the multiple E-field probes contribute to shortening the time for measuring the SAR distribution. This method can also be used as an alternative to that employing flat phantoms filled with liquid. Based on the numerical approach, the measurement system configuration is designed to obtain the SAR distributions with an error of within 10% at 900 and 1950 MHz, focusing on the following points: dimensions of the flat solid phantom, size of the E-field probe, and distance between the E-field probes. The experimental setup for the frequency of 1950 MHz confirms that the proposed measurement method obtains the average SARs over 10 and 1 g with an error of within 10% compared to the computed values.     

A four-shell diffusion phantom of the head for electrical impedance tomography

A four-shell head phantom has been built and characterized. Its structure is similar to that of nonhomogeneous concentric shell domains used by numerical solvers that better approximate current distribution than phantoms currently used to validate electrical impedance tomography systems. Each shell represents a head tissue, namely, skin, skull, cerebrospinal fluid, and brain. A novel technique, which employs a volume conductive impermeable film, has been implemented to prevent ion diffusion between different agar regions without affecting current distribution inside the phantom. Comparisons between simulations and phantom measurements performed over four days are given to prove both the adherence to the model in the frequency range between 10 kHz and 1 MHz and its long-term stability.     

International intercomparison of horn gain at X-band

An international intercomparison of horn gain and polarization measurements at X-band has previously been completed. There were seven participating laboratories with the National Institute of Standards and Technology serving as the pilot laboratory. Two X-band pyramidal standard gain horns with a nominal gain of 22 dB served as the traveling standards. Quantities measured included on-axis fixed frequency gain at 8, 10, and 12 GHz, swept frequency gain between 8-12 GHz and polarization characteristics at the three fixed frequencies. All laboratories performed the fixed frequency-gain measurements. The swept-frequency and polarization measurements were optional, with four laboratories performing swept-frequency measurements and three laboratories measuring polarization. The results of the gain measurements generally agreed within the reported uncertainties which were of the order of 0.1 dB or less     

有耗介质中单极天线的场分布和SAR图

用一段刚性同轴线制作的微细单极天线在医疗上已得到广泛应用。本文给出了单极天线在有耗介质中的近场分布的数值解，进而在有耗介质中测定了温度分布和ＳＡＲ图，利用近场分布计算的ＳＡＲ图和测定的ＳＡＲ图基本相符。     

IEC62209-2中的SAR评估方法

介绍了靠近身体使用的无线通信设备SAR评估方法适用范围、测量系统规格;详细解读SAR评估规程,包括人体组织模拟液和系统准备、待测设备准备、电池一次充电进行多次SAR测量的方法、待测设备相对于模型的位置布置、测试频率、要执行的测量、测试步骤、多频段同时发射的待测设备的测量以及后处理。     

A novel low SAR water-based mobile handset antenna

The effect of mobile phones on human health is becoming a serious concern in the last decade. This paper suggests a novel water-based cellular phone antenna for reducing the electromagnetic wave radiation toward human head. Two antennas are considered: a single band PIFA operating at 1.8 GHz, and a dual band PIFA operating at 900 MHz and 1.8 GHz. The specific absorption rate (SAR) is decreased up to 0.6 W/kg by limiting the propagation of near electromagnetic fields toward the human head and therefore reducing the current density distribution. The reduction of SAR is carried out by introducing an U-edge wall made of an absorbing water material at each corner of the ground plane.     

Novel Specific Absorption Rate (SAR) Estimation Method Based on 2-D Scanned Electric Fields

This paper presents two methods that accurately estimate the specific absorption rate (SAR) distribution and spatial averaged SAR in a phantom exposed to electromagnetic waves from a wireless device. These methods theoretically estimate the SAR value from a 2-D scanned electric field (E-field) by basically applying the equivalence theorem. The validity of the proposed methods is investigated based on calculated and measured results. The estimated spatial averaged SAR over a 1-g or 10-g mass shows a difference of less than a few percent compared to the original SAR value. Furthermore, the proposed methods have the potential to measure the 3-D SAR distribution in several tens of seconds or a few minutes when used in combination with a 2-D probe array.      

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.     

Method for accurate measurement of complex permittivity of tissueequivalent liquids

A microwave method for determining the electrical properties of lossy liquids is presented. The method is optimised for measuring the complex permittivity of human tissue equivalent liquids typically used together with human head phantoms in SAR (specific absorption rate) measurements. The method presented has a considerably better performance than conventional methods     

An Algorithm for Predicting the Change in SAR in a Human Phantom Due to Deviations in Its Complex Permittivity

The aim of this study is to determine a robust prediction algorithm that can be used to correct the measured specific absorption rate (SAR) in a homogeneous phantom when its complex permittivity deviates from standardized reference values. Results are analyzed over a frequency range of 30–6000 MHz. Both measurements and numerical simulations are presented. Several antenna sizes and distances to the phantom are investigated so as to study a large range of SAR distributions. It is demonstrated that the prediction algorithm, while developed using dipole antennas, also works well for mobile telephone models. Employing the prediction algorithm reduces the SAR measurement uncertainty, thereby improving the reproducibility of SAR compliance assessment between laboratories. Another benefit of the algorithm is that it enables the use of broadband tissue-equivalent liquids, whose dielectric parameters are not currently within the tight tolerances of existing standards. The use of broadband liquids reduces the cost of SAR measurement. The method presented in this paper is of benefit to the IEEE 1528 and IEC 62209 measurement standards.      

Measurements of the RF Power Absorption in Spheroidal Human and Animal Phantoms Exposed to the Near Field of a Dipole Source

Experimental results for the average specific absorption rate (SAR) in scaled spheroidal phantoms of human and animal models exposed to near-field radiation are presented. Prolate spheroidal phantoms filled with saline solution simulating muscle tissue were used to measure average SAR values in different models. To control the exposure conditions, simple sources of known radiation characteristics, namely, short electric dipoles, were used. The accuracy of the experimental procedure was evaluated by making several average SAR measuremens at large distances (0.6 ?) from the dipole. The results obtained are found to be in good agreement with those available in the Radiofrequency Radiation Dosimetry Handbook [2]. Near-field SAR measurements for different models are presented as a function of the distance from the source. It is shown that even for the complex radiation fields in the near zone of the source, the average SAR below the resonance frequency can be explained in tenns of the magnitude and direction of the incident fields in the same way that the plane wave absorption characteristics are explained.     

Thermal Properties of Tissue Equivalent Phantom Materials

Thermal conductivity, specific heat, density, and thermal diffusivity were determined for standard RF and microwave phantom materials. Thermal conductivity data for seven phantom materials of varying aluminum content were analyzed using mixture theories. With the thermal diffusivity values obtained, worst case errors in SAR determination due to thermal conduction for adipose-muscle planar phantoms were estimated.     

Effect of amplitude modulation of the CDMA IS-95 signal on SAR measurements

Miniature probes employed for specific absorption rate (SAR) measurements are typically calibrated using a sinusoidal waveform (SW), even though they may be employed to measure a wide variety of communication signals with complex waveforms. This paper shows that the compression produced by the nonlinear response of the probe versus SAR, due to its diode detector, may introduce a significant overestimation of the SAR produced by CDMA IS-95 waveforms when the diode detector operates well into the compression region. This finding is demonstrated theoretically, verified numerically and experimentally, and physically interpreted. The effect is typically small and may be neglected in many practical circumstances involving low-power RF energy emitters, such as mobile phones or two-way dispatch radios.     

Comparison of finite-difference time-domain SAR calculations withmeasurements in a heterogeneous model of man

A finite-difference time-domain technique was used to calculate the specific absorption rate (SAR) at various sites in a heterogeneous block model of man. The block model represented a close approximation to a full-scale heterogeneous phantom model. Both models were comprised of a skeleton, brain, lungs, and muscle. Measurements were conducted in the phantom model using an implantable electric-field probe and a computer-controlled data acquisition system. The calculation and measurement of SAR distributions were compared primarily in the head (including the neck) and chest. To obtain the necessary spatial resolution with the computer model, the head and neck were modeled with approximately 105,000 cells, while 86,000 cells were used to configure the chest. Planewave fields, polarized in the E orientation, were utilized to irradiate the models at an exposure frequency of 350 MHz. Reasonable correlation existed between the calculations and measurements.