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Introduction

The effects of RF radiation from cell phones, implanted medical transmitters, and MRI systems in or near human tissue is an ongoing area of concern for manufacturers, regulatory bodies, and users of such devices. RF energy can cause heating in the tissue, which is quantified by the specific absorption rate (SAR) of the electromagnetic energy and the resulting rise in temperature in the tissue. For designers of such systems, it has become standard practice and almost essential to carry out calculations on new devices to ensure that they generate an SAR level below the limits set by the IEEE and other regulatory bodies.

The FDTD (finite-difference time-domain) modeling technique is the preferred method for making SAR calculations. This differential formulation allows users to divide the model space into very small cells, which in SAR applications allows excellent resolution of tissue in the human body. Other computational methods are unable to model the tissue structure to a resolution that is accurate enough for such calculations.

Remcom's XFDTD is an FDTD-based 3-D electromagnetic solver that is used by manufacturers of cell phones, implantable RF transmitters, and MRI devices to compute SAR values in their new products. In addition to SAR measurement capabilities, the Bio-Pro version of XFDTD also features an optional temperature rise module, which allows users to determine the effect of the SAR on human tissue.

To complement XFDTD, Remcom also offers HiFi human and animal models and the VariPose modeling package. With VariPose, the human body can be repositioned to produce an FDTD human body mesh model. Tissue resolutions of 10, 5, 3, 2, and 1 mm are available from the VariPose models. XFDTD is then capable of discretizing selected areas (or the whole model space) into smaller cell sizes by use of adaptive meshing.

XFDTD can also be used to determine the performance of an antenna under design, both as a stand-alone device and in situ in the human body. Antenna efficiency, VSWR, S-parameters, impedance, far-zone gain pattern, near-zone fields, partial patterns, and antenna diversity are some of the measurements available to antenna designers.

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•Application Note: Calculating SAR And Temperature Change In Human Tissue Using The FDTD Method