National Physical Laboratory

Non-toxic phantoms for SAR measurements

Recipes for non-toxic head and body phantoms based on Polysorbate 20 or Polysorbate 80 mixed with water and salt for frequencies between 0.03 GHz and 6 GHz, as required for measuring the specific absorption rate (SAR) of RF energy in the body arising from transmitters.

Head Phantom for experimental dosimetry
Head Phantom for
experimental dosimetry

The phantoms are translucent, low viscosity, have low temperature coefficients, and were found to have stable complex permittivity for periods up to six years, making them suitable for use with commercial SAR measurement systems. Relaxing the required tolerance for the real permittivity and conductivity from ± 5 % to ± 10 % was found to approximately double the frequency bandwidth for which the phantoms were within specification, and to increase the life.

Head and body phantoms based on Polysorbate 20 (trade name TWEEN 20) or Polysorbate 80 (TWEEN 80) mixed with deionised water and salt have been developed for the frequency range 0.03 GHz to 6 GHz. Table 1 gives the percentage (by weight) of each of the ingredients to achieve the target properties specified in standards [1, 2] at a temperature of 22 °C. An additional 0.3 % (by weight) of Germaben II E is added to the final mix in order to prevent mould growing. These phantoms are translucent, non-toxic, have low viscosity, which makes them suitable for use with commercial SAR measurement systems. An important consideration for the phantoms is the dependence of the electrical properties on temperature, since this affects the measurement uncertainties. For these mixes this is typically a 1.5 % change in conductivity per degree, but a 3 % per degree change is observed with the mixes for frequencies of 0.45 GHz or lower.

Phantom Target properties from [1, 2] Ingredients, by weight
Frequency (GHz) Type ε' σ
S/m
Water % Polysorbate 20 % Polysorbate 80 % NaCL %
0.03 Head 55.0 0.75 50.43 47.37 0 2.19
0.15 Head 52.3 0.76 53.03 45.17 0 1.79
0.30 Head 45.3 0.87 50.43 47.37 0 2.19
0.45 Head 43.5 0.87 50.81 47.59 0 1.60
0.90 Head 41.5 0.97 52.87 46.10 0 1.03
1.80 Head 40.0 1.40 55.40 44.22 0 0.38
1.90 Head 40.0 1.40 55.24 44.57 0 0.19
2.45 Head 39.2 1.80 55.75 45.25 0 0.00
5.80 Head 35.3 5.27 62.70 0.00 37.30 0.00
0.15 Body 61.9 0.81 70.73 28.33 0 0.93
0.30 Body 58.2 0.92 70.32 28.70 0 0.98
0.45 Body 56.7 0.94 71.10 28.00 0 0.90
0.90 Body 55.0 1.05 71.30 28.00 0 0.70
1.80 Body 53.3 1.52 71.50 28.00 0 0.50
1.90 Body 53.3 1.52 71.61 28.00 0 0.39
2.45 Body 52.7 1.95 71.70 28.00 0 0.30
5.80 Body 48.2 6.00 80.00 0.00 20.0 0.00

References

[1] Draft Recommended Practice for Determining the Peak Spatial-Average Specific Absorption Rate (SAR) in the Human Head from Wireless Communications Devices: Measurement Techniques
IEEE Standard P1528™/D1.0, 2009

[2] Evaluating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields, Additional Information for Evaluating Compliance of Mobile and Portable Devices with FCC Limits for Human Exposure to Radiofrequency Emissions
Supplement C (Edition 01-01) to OET Bulletin 65 (Edition 97-01)

Last Updated: 2 Aug 2018
Created: 11 Sep 2012

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