Rapid and accurate broadband absorption cross-section measurement of human bodies in a reverberation chamber (original) (raw)
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The electromagnetic absorption cross-section (ACS) averaged over polarisation and angle-ofincidence of 60 ungrounded adult subjects was measured at microwave frequencies of 1-12 GHz in a reverberation chamber. Average ACS is important in non-ionising dosimetry and exposure studies, and is closely related to the whole-body averaged specific absorption rate (WBSAR). The average ACS was measured with a statistical uncertainty of less than 3 % and high frequency resolution for individuals with a range of body shapes and sizes allowing the statistical distribution of WBSAR over a real population with individual internal and external morphologies to be determined. The average ACS of all subjects was found to vary from 0.15 to 0.4 m 2 ; for an individual subject it falls with frequency over 1-6 GHz, and then rises slowly over 6-12 GHz range in which few other studies have been conducted. Average ACS and WBSAR are then used as a surrogate for worst-case ACS/WBSAR in order to study their variability across a real population compared to literature results from simulations using numerical phantoms with a limited range of anatomies. Correlations with body morphological parameters such as height, mass and waist circumference have been investigated: the strongest correlation is with body surface area (BSA) at all frequencies above 1 GHz, however direct proportionality to BSA is not established until above 5 GHz. When average ACS is normalised to BSA, the resulting absorption efficiency shows a negative correlation with the estimated thickness of subcutaneous body fat. Surrogate models and statistical analysis of the measurement data are presented and compared to similar models from the literature. The overall dispersion of measured average WBSAR of the sample of the UK population studied is consistent with the dispersion of simulated worst-case WBSAR across multiple numerical phantom families. The statistical results allow the calibration of human exposure assessments made with particular phantoms to a population with individual morphologies.
Experimental Assessment of Specific Absorption Rate Using Room Electromagnetics
IEEE Transactions on Electromagnetic Compatibility, 2000
A closed room environment is viewed as a lossy cavity, characterized by possibly a line-of-sight component and diffuse scattering parts from walls and internal obstacles. A theory used in acoustics and reverberation chambers is applied for the electromagnetic case, and main issues related to measurement systems, antennas characteristics, diffuse energy properties, and human exposure are investigated. The goal of this paper aims first toward validation of the assessment of the reverberation time in an environment using a virtual multiple-input-multiple-output channel system. Second, the reverberation time in an adjacent room is investigated, and hence, a measurement-based method is readily developed to assess the absorption cross section and the whole-body specific absorption rate of humans at 2.3 GHz in a realistic closed environment.
Whole-Body Averaged Specific Absorption Rate Estimation using a Personal, Distributed Exposimeter
IEEE Antennas and Wireless Propagation Letters, 2014
For the first time, a body area network (BAN) is used to construct a personal, distributed exposimeter (PDE), which can measure the whole-body averaged specific absorption rate ( ) in real life, together with the incident power density ( ). The BAN consists of four textile antennas with integrated radio frequency receiver nodes tuned to the Global System for Mobile Communications (GSM) 900 downlink band. Calibration measurements at 942.5 MHz, using a human subject, are performed in an anechoic chamber. These are combined with numerical simulations to estimate both and from the averaged received power on the PDE. The PDE has 50% prediction intervals of 3 dB on and 3.3 dB on the , caused by the presence of the human body, whereas the best single textile antenna in our measurements exhibits 's of 7.1 dB on and 5 dB on . Measurements using the PDE are carried out in Ghent, Belgium, during which a median W m and W are measured.
Assessment of Electromagnetic Absorption towards Human Head Using Specific Absorption Rate
Bulletin of Electrical Engineering and Informatics, 2018
This paper presents a compact square slot patch antenna characterstics for wireless body area network (WBANs) applications.The assessment of the effects of electromagnetic energy (EM) on the human head is necessary because the sensitivity of human head to high radiation level. Although, structuring of low EM antennas is a major problem in the improvement of portable device and reducing the size of of the antenna is a major concern. However, performance of antenna reduces when antenna operates near human body which is lossy and complex in nature. The proposed antenna operates at 5.8GHz of the ISM Band for WBAN applications. The antenna has been designed and simulated with two different types of multilayer human head phantoms to characterize the antenna near the human head.The multilayer head phantom is constructed by five layers tissues head model using CST Microwave studio. Therefore, antenna with spherical phantom has the highest SAR value 0.206 W/Kg, while antenna with cubical pha...
Physics in Medicine and Biology, 2010
In this paper we propose an identification of morphological factors that may impact the Whole Body Specific Absorption Rate (WBSAR). The study is conducted for the case of an exposure to a front plane wave at the 2100MHz frequency carrier. This study is based on the development of different regression models for estimating the WBSAR as a function of morphological factors morphology. For this manner, a database of twelve anatomical human models (phantoms) has been considered. Also, eighteen supplementary phantoms obtained using morphing technique were generated to build the requested relation. The paper presents three models based on external morphological factors like the Body Surface Area (BSA), the Body Mass Index (BMI) or the body mass. These models show good results for families obtained by morphing technique on the estimation of the WBSAR (< 10%) but still less accurate (30%) when applied for different original phantoms. This study stresses the importance of the internal morphological factors such as muscle and fat proportions in the characterization of the WBSAR. The regression models are then improved using internal morphological factors with an estimation error around 10% on the WBSAR. Finally, this study is suited for establishing the statistical distribution of the WBSAR for a given population characterized by its morphology.
Quantification of electromagnetic absorption in humans from body-mounted communication transceivers
IEEE Transactions on Vehicular Technology, 2000
We have used a new millimeter-resolution MRIbased model of the human body to calculate the electromagnetic absorption in the head and neck for three experimental Yagi antennas suggested for the handheld transceivers of a proposed 6-GHz personal communication network (PCN) system. The SAR distributions are obtained with a resolution of 1.974 x 1.974 x 1.5 mm for the transceivers that are held against the ears and tilted forward by 33". The finite-difference time-domain technique is used to calculate the EM fields and SAR's for the transceiver, antenna, and head and neck coupled region that is divided into 158 x 84 x 188 or nearly 2.5 million cells. The highlights of the numerical calculations are verified by means of a head-shaped experimental model made of tissue-equivalent materials simulating the electrical properties (E~, a) of skull, brain, muscle, eyes, and ears developed for use at 6 GHz. Because of the proximity to the antenna, the highest SAR's are obtained for the upper part of the ear. For a planned radiated power of 0.6 W, the peak SAR's averaged over any 1 g of tissue defined as a tissue volume in the shape of a cube are on the order of 0.5-1.0 Wkg for two of the proposed antennas and considerably higher (2.06 Wkg) for the third antenna using a narrower offaxis reflector. Low SAR's for the first two antennas are likely due to the shielding provided by the relatively wider strip reflector plates used for these antennas.
International Journal of Antennas and Propagation, 2013
The safety aspects of the exposure of people to uniform plane waves in the frequency range from 900 MHz to 5 GHz are analyzed. Starting from a human body model available in the literature, representing a man in resting state, two new anatomical models are considered, representing different phases of the respiratory activity: tidal breath and deep breath. These models have been used to evaluate the whole body Specific Absorption Rate (SAR) and the 10-g averaged and 1-g averaged SAR. The analysis is performed using a parallel implementation of the finite difference time domain method. A uniform plane wave, with vertical polarization, is used as an incident field since this is the canonical exposure situation used in safety guidelines. Results show that if the incident electromagnetic field is compliant with the reference levels promulgated by the International Commission on Non-Ionizing Radiation Protection and by IEEE, the computed SAR values are lower than the corresponding basic restrictions, as expected. On the other side, when the Federal Communications Commission reference levels are considered, 1-g SAR values exceeding the basic restrictions for exposure at 4 GHz and above are obtained. Furthermore, results show that the whole body SAR values increase passing from the resting state model to the deep breath model, for all the considered frequencies.
Dependence of the RF field absorption on the human body dimensions
2009
In this paper, the dependence of radio-frequency (RF) field absorption on human body dimensions is investigated. The resonance properties of an ellipsoidal homogeneous human model have been investigated in frequency range from 10 MHz to 500 MHz with assistance of CST Microwave Studio program environment. In the article, the simulation of RF field absorption in the ellipsoidal body model has been performed for three various body heights, as well as three widths for a given body height.
Estimation Formulas for the Specific Absorption Rate in Humans Exposed to Base-Station Antennas
IEEE Transactions on Electromagnetic Compatibility, 2000
The demonstration of compliance with guidelines for human exposure to base-station antennas can be a time consuming process or often results in overly conservative estimates. To alleviate this burden and reduce the overestimation, approximation formulas for the whole-body average specific absorption rate (SAR) and the peak spatial SAR of human bodies using readily available basic antenna parameters have been developed and validated in this study. The formulas can be used for adults standing in the radiating near field of base-station antennas operating between 300 MHz and 5 GHz, at distances larger than 200 mm. It is shown that the 95th-percentile absorption for the human population can be well approximated by the absorption mechanism and statistical data of weight, height, and body-mass index of the human population. The validation was performed numerically using three anatomical human models (Duke, Ella, and Thelonious) exposed to 12 generic base-station antennas in the frequency range 300 MHz to 5 GHz at six distances between 10 mm and 3 m. From the 432 evaluated configurations, the estimation formulas for adult models are proven to be conservative in predicting the SAR exposure values of the two adults, but as expected not of the child.
SARwb-meter in diffuse fields, calibrated in a reverberation room
2015
A whole-body absorption meter, calibrated for simultaneous on-body measurements of the incident power density (Sinc) and whole-body averaged specific absorption rate (SARwb) in diffuse fields, is proposed. The meter consists of an on-body, textile antenna tuned to the GSM 900 DL band and is worn by a subject who is exposed to diffuse fields at 942.5 MHz in a reverberation chamber. The set-up allows for measurements of both the subject’s absorption cross section (0.32 m2), using measurements of the reverberation time, and the antenna aperture (2.8-3.3 cm2) of an on-body antenna. This antenna can thus be used for a simultaneous on-body measurement of the SARwb and the Sinc.