Applicability evaluation of the field reconstruction method based on boundary integral equations for practical uses (original) (raw)
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IEICE Communications Express
This paper presents an inverse method to reconstruct an antennaexcited electric field distribution of a dielectric object from measured field data, for the purpose of noninvasive SAR evaluation in the human phantom. The proposed method is a hybrid method combining the Boundary Integral Equation (BIE) and Finite Element Method (FEM). The BIE for the electromagnetic (EM) fields and equivalent currents of a radiating source are discretized using the method of moments (MoM) while EM fields in the scatterer and its surroundings are discretized using the FEM. The effectiveness of the method is tested numerically and experimentally using a dipole and a dielectric cuboid at 2.5 GHz. The numerical reconstruction achieves acceptably good agreement with that of reference as a whole. However, it is found from the experiment that the method is considerably sensitive to the measurement error. The factors that may have contributed to the errors are shortly discussed.
Accuracy of SAR Reconstruction in Human Phantoms From Surface Field Values
IEEE Transactions on Magnetics, 2000
This paper describes and discusses the use of the boundary element method to reconstruct the induced current density and specific absorption rate (SAR) distribution within a phantom of arbitrary shape, starting from field values on its external surface. The accuracy of the proposed approach is evaluated by comparison with the results given by other techniques in the solution of the whole electromagnetic problem, including also the sources. The influence of the parameters which could affect the reconstruction accuracy is deepened. The encouraging results obtained can open the way to a noninvasive experimental-computational procedure for the SAR evaluation.
IEEE Transactions on Electromagnetic Compatibility
In this article, we reconstruct the internal electric field due to a dipole antenna embedded in a dielectric phantom for developing a noninvasive specific absorption rate (SAR) measurement system. The reconstruction method is based on the surface equivalent theorem and boundary conditions, which relate the external field radiated from the embedded antenna to equivalent electromagnetic surface currents on the human body. The electric field data sampled at spatial points on a surface enclosing the phantom are used in the inverse calculation. All field integrals are discretized and numerically solved to obtain the electromagnetic currents on the phantom's surface. The internal electric field distribution and SAR value in a phantom can be calculated from the reconstructed surface currents if the electric properties of the phantom are known. The validity of the method was demonstrated numerically and experimentally using a dipole antenna embedded in the lossy rectangular phantom, which has a dielectric constant close to human skin tissue at 2.5 GHz. Comparison with forward numerical simulations has shown that the surface current and electric field distribution can be predicted with great precision. Carefully performing the experiments using a self-made phantom validated our numerical demonstration and provided satisfactory reconstruction results. Index Terms-Antenna measurements, biomedical telemetry, electromagnetic fields, inverse problems, specific absorption rate (SAR). I. INTRODUCTION R ECENTLY many kinds of wireless biomedical telemetry devices are deployed for disease prevention, diagnosis, monitoring, and even therapeutic functions. These devices are installed and operated at various locations. The wearable devices could be placed externally near the surface of the human body, contrary to implantable and ingestible devices that operate inside Manuscript
Progress In Electromagnetics Research, 2013
Contour reconstruction and accurate identification of dielectric objects placed on a conducting surface are the aims of the millimeter-wave Synthetic Aperture Radar (SAR) imaging processing system presented in this paper. The method uses multiple frequencies, multiple receivers and one transmitter in a portal-based configuration in order to generate the SAR image. Then, the information in the image is used to estimate the contour of the body under test together with the permittivity of the dielectric region. The results presented in this paper are based on synthetic scattered electromagnetic field data generated using an accurate Finite-Difference Frequency-Domain (FDFD)-based model and inversion based on a fast SAR inversion algorithm. Representative examples showing the good behavior of the method in terms of detection accuracy are provided.
E-field distribution modeling in a homogeneous phantom for a rapid SAR measurement
2003 IEEE International Symposium on Electromagnetic Compatibility, 2003. EMC '03., 2003
Specific Absorption Rate (SAR) designates the electromagnetic power density deposited per unit mass of biological tissue. SAR measurements are required to assess the compliance of mobile phones with existing standards and recommendations. The use of homogeneous phantoms leads to a relatively simple distribution of the electric field. Several ways of determining the decrease of the electric field in function of depth are here explored. The choice of a pseudo propagation constant allows to drastically reduce the number of E-field measurement points needed for the SAR calculation. The measurement time is then reduced to less than a minute, while the standard way takes about 10 minutes for a complete measurement of almost thousand E-field data points.
IEEE Transactions on Electromagnetic Compatibility, 2000
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.
The Journal of the University of Duhok, 2020
Exposure human tissue to electromagnetic radiation (EM) from radio wireless frequencies causes many negative health effects. The assessment of the absorbed EM by human tissue depends on the Specific Absorption Rate (SAR) factor. In this paper, a square patch antenna (SPA) is designed to be a source of EM radiation, and optimized to operate at several applicable frequencies, such as GSM 1800, IEEE 802.11 WLAN standard 2.4 GHz and 5.3 GHz bands, and 3.2 GHz WiMAX band. The radiated EM by the SPA antenna is evaluated in a 3D human head model or Specific Anthropomorphic Model (SAM), which consists of two layers, the outer shell (1.5 mm thickness) and filled with tissue simulating liquid (TSL). The investigation involved four aspects, first the distance between the SAM and the EM source has been moved between 0 mm to 50 mm, second for the specific distances (0 mm, 15 mm, 30 mm, and 45 mm) the frequency of EM source has been changed among 1.8 GHz, 2.4 GHz, 3.2 GHz, and 5.3 GHz. Third, the tilt angle (θ) between the SAM and the antenna has been shifted from 0 0 to 90 0. Finally, the antenna encasement (2 mm thickness plastic material) was removed and the procedure in the first step is repeated to investigate the effect of encasement on the SAR reducing. The results reveal that there is an inversely proportional relation between SAR and distance, SAR and tilt angle. Besides, the antenna encasement has a large impact on attenuating SAR value, while the SAR is directly proportional to frequency. All SAR evaluations were performed by CST-2014 Microwave studio simulator which is built on the Finite-Difference-Time-Domain (FDTD) principle. All calculations are achieved over 1 g and 10 g of mass tissue averaging and according to IEEE/IEC 62704-1 standards.
IET Microwaves, Antennas & Propagation, 2015
Permittivity of the dielectric objects is calculated using the scattered fields from objects and the incident fields in the investigation domain. In practical applications, calculation of incident fields over closely placed discrete points is a challenging task. In this study, a simple method to calculate incident fields using equivalent sources is proposed. These equivalent sources are modelled from the measured incident fields around the dielectric objects. From these sources, permittivity of the dielectric objects is calculated on experimental data set by employing contrast source inversion technique. Further, the accuracy of the proposed method is studied on synthetic data by approximating the pyramidal horn antenna fields with line and equivalent sources.
Use of the finite-difference time-domain method for calculating EM absorption in man models
IEEE Transactions on Biomedical Engineering, 1988
The finite-difference time-domain (FDTD) method is used to calculate the detailed specific absorption rate (SAR) within the human body. SAR distributions are calculated using incident frequencies of 100 and 350 MHz for three different cases: 1) a homogeneous man model in free space, 2) an inhomogeneous man model in free space, and 3) an inhomogeneous man model standing on a ground plane. These various cases are used to evaluate the advantage of inhomogeneous models over homogeneous models, and grounded models versus free space models. Finally, comparison is made between the results obtained here and those obtained experimentally or with the method of moments (MOM).
Estimation of whole-body SAR from electromagnetic fields using personal exposure meters
Bioelectromagnetics, 2009
In this article, personal electromagnetic field measurements are converted into whole-body specific absorption rates for exposure of the general public. Whole-body SAR values calculated from personal exposure meter data are compared for different human spheroid phantoms: the highest SAR values (at 950 MHz) are obtained for the 1-year-old child (99th percentile of 17.9 mW/kg for electric field strength of 0.36 V/m), followed by the 5-year-old child, 10-year-old child, average woman, and average man. For the 1-year-old child, whole-body SAR values due to 9 different radiofrequency sources (FM, DAB, TETRA, TV, GSM900 DL, GSM1800 DL, DECT, UMTS DL, WiFi) are determined for 15 different scenarios. An SAR matrix for 15 different exposure scenarios and 9 sources is provided with the personal field exposure matrix. Highest 95th percentiles of the wholebody SAR are equal to 7.9 mW/kg (0.36 V/m, GSM900 DL), 5.8 mW/kg (0.26 V/m, DAB/TV), and 7.1 mW/kg (0.41 V/m, DECT) for the 1-year-old child, with a maximal total whole-body SAR of 11.5 mW/kg (0.48 V/m) due to all 9 sources. All values are below the basic restriction of 0.08 W/kg for the general public. 95th percentiles of whole-body SAR per V/m are equal to 60.1, 87.9, and 42.7 mW/ kg for GSM900, DAB/TV, and DECT sources, respectively. Functions of the SAR versus measured electric fields are provided for the different phantoms and frequencies, enabling epidemiological and dosimetric studies to make an analysis in combination with both electric field and actual whole-body SAR.