HFSS15: Calculating the SAR

The specific absorption rate (SAR) is a measure of the amount of electromagnetic energy absorbed in a lossy dielectric material. The SAR is a basic scalar field quantity that can be plotted on surfaces or within objects in HFSS.

HFSS uses the following equation to calculate the SAR: s * E²/(2r).

where

• s = the material’s conductivity. This is defined as: s_bulk+we₀e_rtgd

• r = the mass density of the dielectric material in mass/unit volume.

There are two types of SAR Field Overlay plots available in HFSS: local SAR, and average SAR. When calculating the local SAR, HFSS uses the equation above to calculate the SAR at each mesh point on an overlay plot. HFSS interpolates the values between the mesh points across the plot.

When plotting the average SAR, for each mesh point on the plot, HFSS reports the SAR averaged over a volume that surrounds that point. The volume is determined by the settings for the material’s mass density and mass of the material surrounding each mesh point set in the Specific Absorption Rate Setting dialog box. The volume will not cross object boundaries.

The Certification SAR quantity provided in the Fields Calculator is an efficient way to determine the peak spatial-average SAR. When computing the certification SAR, HFSS assumes the peak spatial-average SAR is located on an object surface. HFSS therefore searches for the peak local SAR on the surfaces, and creates an averaging volume around that location, completely inside the object with an axis normal to the surface at the location of the peak value of the local SAR.