Low-frequency (10- 450 MHz) Coaxial SAR Calibration System
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NPL has developed a coaxial system for calibrating electric field probes in liquids with continuous frequency coverage from 100 kHz to 450 MHz, these probes are used in applications such as testing the compatibility of implanted medical devices with MRI and SAR assessments.
The system is based on a coaxial transmission line in which part of the inner conductor is replaced with a plastic cylinder filled with the liquid phantom, Calibration is achieved by comparing the rate of temperature rise in the phantom due to the RF energy with output voltage from the diode sensors of the electric field probe. This arrangement has the advantages that the temperature rise is linear with time over several minutes; the temperature probe is thermally isolated from the surroundings.
Operating frequency range:
100 kHz to 450 MHz
Liquid volume required for calibration
1.3 litres
Input return loss:
> 15 dB (100 kHz to 120 MHz)
> 3 dB (120 MHz to 450 MHz
SAR per watt input power
(with Head Simulating Liquid)(approx)
0.7 W/kg per W @ 30 MHz
0.9 W/kg per W @ 150 MHz
1.1 W/kg per watt @ 300 MHz
2.6 W/kg per watt at 380 MHz
Typical calibration uncertainties ± 10%
On-site installation and staff training for these systems is also available.