Authors: Chiara Peletti, Long Li, Mohamed Abdel-Mageed & Raj Mittra
Source: FERMAT, Volume 9, Communications 8, May Jun., 2015
Abstract: Rapid growth in the use of a wide variety of wireless communication devices has also engendered concerns about health effects of electromagnetic radiation on humans. This, in turn, has prompted the need to reduce the Specific Absorption Ratio (SAR) in mobile devices, e.g., smartphones, and has caught the attention of the mobile phone industry which has been constantly searching, albeit unsuccessfully, for a practical solution to the SAR problem. Unfortunately, coming up with an approach for SAR reduction for the new mobile terminals, one that meets the bandwidth, efficiency, size and cost requirements. This paper presents an approach, based on the combined use of graphene-type absorbing cards (R-cards) and metal sheets in a mobile handset, to reduce the SAR below the allowable limits. The paper performs a study to determine the size and position of the card that helps reduce the SAR levels below the specified limits, without unduly sacrificing the antenna efficiency. The paper begins with a representative antenna design for the handset, which meets the coverage specifications of various frequency bands (LTE: 750 MHz, 2.1/2.6GHz; and GSM: 800/900 MHz, 1.8/1.9 GHz). Next, it evaluates the SAR levels generated by these antennas when placed in the proximity of the human head. Following this we insert the R-card at various locations in the vicinity of the antenna and study the effects of the card on both the SAR level as well as the efficiency of the antenna. We also investigate the use of metasurfaces, e.g., high impedance surfaces or HISs, for the same purpose. The study shows that a surface which combines the salutary features of both the R-cards and metasurfaces is perhaps the most desirable solution to the SAR-reduction problem with only a little compromise of the efficiency
Keywords: Mobile antennas, Specific Absorption Rate (SAR), Graphene-based R-card
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Wideband SAR Reduction for Smart Mobile Antennas for Next Generation Wireless Communication Systems