A Structured Basis to Determine Equivalent Dielectric Properties of Homogeneous Phantom Liquid Representing Multilayer Biological Tissues for SAR Measurement
Ardhendu Kundu
,
Kaushik Patra
,
Bhaskar Gupta
and
Amirul Islam Mallick
In today's era of wireless communication, interaction of electromagnetic energy and living biological systems is unavoidable - both in far field and in near field of the radiating antenna. Consequent basic safety limits on radiation levels are enforced through Specific Absorption Rate (SAR) limits. Practical measurement and validation of these SAR values require the deployment of phantom models containing tissue equivalent dielectric liquids - these liquids are conventionally single layer and homogeneous in nature. However, structured basis to formulate these custom made homogeneous phantom liquids representing arbitrary combinations of stacked tissue layers has not been properly reported in literature. To address the issue, this paper develops and illustrates a novel structured technique to define equivalent permittivity and loss tangent of homogeneous phantom liquid representing arbitrary combinations of stacked tissue layers - both in far field and in near field exposure scenarios. Electric field distribution and later on point SAR distribution inside different tissue layers have been attempted to replicate as closely as possible using equivalent homogeneous phantom liquid with properly tuned permittivity and loss tangent values. The fitting procedure involves minimization of the absolute/normalized maximum difference (of electric field and point SAR) between the original multilayer tissue and the modelled single layer homogeneous equivalent. This generalized technique is applied to two distinct multilayer (four layers are considered) biological models at 2.45 GHz where one is composed of four layers of equal thicknesses while the other one has four layers with unequal thicknesses. Moreover, the proposed technique has been tested and validated in the two abovementioned multilayer biological models for both far field (plane wave irradiation) and near field (in close proximity to antenna) exposure scenarios. This technique is quite successful in achieving equivalent dielectric liquids in which original point SAR data and its overall distribution across different layers can be realistically replicated while attempting point wise matching at several spatial points. In some cases, the original electric field/point SAR values are achieved with reduced precision near layer interfaces with significant dielectric contrast. Thus, the proposed technique can significantly contribute to accurately measure, validate and reflect the true spatial SAR distributions in original multilayer biological models using the derived homogeneous tissue equivalent phantom liquids.
