I would like to determine the specific absorption rate (SAR) of a given antenna in a cube made of a given material. The known parameters of the antenna and the material are:
- Gain (G)
- Transmitted Power (Pt)
- Permittivity (eps'r and eps''r)
- Impedance (eta)
- Elect. Conductivity (sigma)
- Density (rho)
- Distance between the Antenna and the Cube (d)
My approach is to use the electrical definition of the SAR-Value:
- SAR = (sigma * E2) / (2 * rho)
As the power density S is given by
- S = E2 / eta = (Pt * G) / (4 * pi * d2)
the SAR-Formula can be rearranged to
- SAR = (sigma * eta * S) / (2 * rho)
However, as I compare my theoretical approach with a similar simulation by CST, I get a difference of around 30%. Therefore, I would like to ask if I made a mistake or if there are better approaches.
Abd-Alhameed, R.A., Excell, P.S. and Mangoud, M.A., 2005. Computation of specific absorption rate in the human body due to base-station antennas using a hybrid formulation. IEEE Transactions on Electromagnetic Compatibility, 47(2), pp.374-381.
Johannes Grund
You are making a fundamental mistake.
Point SAR = (sigma * Ed^2) / (2 * rho), where Ed is the peak electric field strength developed at a particular location inside biological tissue layer due to external incident r.m.s electric field (Ei) strength.
But, Power density (S) = Ei^2 / eta = (Pt * G) / (4 * pi * d^2)
Hence, you can not find a direct relationship between SAR and incident electric field(Ei)/power density(S).
SAR depends upon permittivity & loss tangent of biological tissue layers, Shape of biological object, Strength, polarization and direction of arrival of incident wave, tissue material density etc.
Hope it helps.
Regards,
Ardhendu Kundu
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