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Formulation and properties of Liquid Phantoms, 1 MHz to 10GHz

Loader, B G; Gregory, A P; Mouthaan, R (2018) Formulation and properties of Liquid Phantoms, 1 MHz to 10GHz. NPL Report. TQE 9

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Measurements of the Specific Absorption Rate (SAR) of energy at radio and microwave frequencies are performed in homogeneous liquid phantoms, which have similar electrical properties to the human tissues of interest. This report reviews the target properties for these phantoms given in existing standards, describes methods for measuring the permittivity and conductivity of phantoms, and presents recipes for making liquids having these properties for the frequency range 1 MHz to 10 GHz. For frequencies between 6 GHz and 10 GHz existing standards do not specify target properties, so these were obtained from human tissue properties, and verified by computer simulations of the human head. Methods for measurement at frequencies below 30 MHz are presented, although simple liquid phantoms cannot provide an accurate match at these frequencies as the required real permittivity exceeds that of de-ionised water. The RF permittivity and conductivity of three liquid phantoms is measured at MHz frequencies by using a 44-mm coaxial sensor and a discontinuous-inner-conductor coaxial cell. Electrode polarisation is observed to be a cause of measurement error at frequencies up to 50 MHz. For two of the phantoms it is found that the conductivity at 64 MHz and 128 MHz, corresponding to the RF frequency for 1.5 Tesla and 3 Tesla Magnetic Resonance Imaging (MRI) respectively, does not differ significantly from the static value, so an inductive conductivity sensor that operates at 5 kHz can be used for measurement.

Item Type: Report/Guide (NPL Report)
NPL Report No.: TQE 9
Subjects: Electromagnetics > RF and Microwave
Divisions: Engineering, Materials & Electrical Science
Last Modified: 18 Jun 2018 10:56
URI: http://eprintspublications.npl.co.uk/id/eprint/7946

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