User Manual

Determination of Probe Conversion Factors for 150MHz
Since at this time there exists no experimental method in determining E-field probe
conversion factors for frequencies below 800MHz, the following procedure was carried
out to give an approximation of the probe conversion factors for 150MHz.
The accuracy of the system was determined based on the two calibrated test frequencies
of 900 and 1800MHz, using validation dipoles as supplied by the manufacturer. The
measured results were found to be within the specified tolerances. For conversion factors
outside these two frequencies a linear extrapolation was performed as per the
manufacturer’s recommendations. In order to determine the accuracy of the conversion
factors, 300 and 450MHz dipoles were constructed in accordance with IEEE Std. P1528.
The two dipoles were then characterized for SAR using the appropriate head simulating
fluid for the given frequencies in a planar phantom as prescribed in IEEE Std. P1528.
The table below indicates the analytical target values for each dipole with the associated
measured results.
Frequency
(MHz)
Analytical SAR
@ 1W input
averaged over
1 gram
Measured SAR
@ 1W input
averaged over
1 gram
Delta
∆∆
Fluid Parameters
ε
r
=45.3
300 3.0 3.51 17.0%
σ=0.87
ε
r
=43.5
450 4.9 5.77 17.8%
σ=0.87
The extrapolated head conversion factors determined for 300 and 450MHz resulted in
SAR values being 17.0% and 17.8% greater than expected for each frequency
respectively. It is assumed that as this extrapolation is extended down to 150MHz, the
resulting SAR will again be overestimated by at least 17%.
The body conversion factors were determined based on a combination of the obtained
data from the validations, and numerical modeling results from an identical probe from
the same manufacturer.
The following two pages show examples of the conversion factors that were derived
through numerical modeling for a probe of similar properties.