Real-world Shelf-Life Study of Tissue Equivalent Liquids for SAR evaluation

SAR assessment, as defined by the IEEE-1528 standard, has been the standard for defining the safe exposure of the RF radiations and usage limits for wireless devices. The Tissue Equivalent Liquids (TELs) are essential parts of the SAR assessment system, as they mimic the human body's dielectric properties at their specific frequencies and allow for testing of the range of the wireless devices as per specified procedures. Since, the TELs are artificially synthesized compositions, they also need to meet the regulatory requirements of labelling the product and undergo shelf-life assessment for estimating the usable product life. In this paper, we present the real-world shelf-life study of few TEL compositions of different frequency range. The dielectric properties of these TELs at their respective frequency values/range are assessed and compared for over a period of 18 months, at different intervals, while keeping the TELs stored as per IEEE specified storage conditions i.e. temperature between 18°C and 25°C (within $\pm 1\ {{}^{\circ}\mathrm{C}}$) with RH between 40%-60%.