SAR calculations in an anatomically realistic model of the head for mobile communication transceivers at 900 MHz and 1.8 GHz

Abstract

A new mathematical model of the head has been constructed from a set of serial MRI slices from one subject. Finite-difference time-domain (FDTD) calculations of the specific energy absorption rate (SAR) have been performed on this model with a 2 mm resolution for a generic mobile communication transceiver represented by a quarter-wavelength monopole on a metal box. The antenna was mounted either at the centre or corner of the top face of the box. The frequencies considered were 900 MHz and 1.8 GHz. Three irradiation geometries were considered, a vertical handset in front of the eye and vertical and horizontal orientations at the side of the ear. The effect of a hand grasping the handset was considered. The head model was scaled to represent the head of an infant and a subset of calculations was performed to verify that the SAR deposited in the infant head did not exceed that in the adult. Results are also presented for a half-wavelength dipole. The maximum SAR values produced by the generic transceiver for the horizontal orientation at the side of the head which is the most typical position, averaged over 10 g of tissue at 900 MHz and 1.8 GHz, are 2.1 and 3.0 W kg(-1) per W of radiated power. The corresponding values over 1 g of tissue are 2.3 and 4.8 W kg(-1) per W at 900 MHz and 1.8 GHz. However, if one were to consider all possible operational conditions, the placement of the transceiver in front of the eye will give 3.1 and 4.6 W kg(-1) per W averaged over 10 g of tissue and 4.7 and 7.7 W kg(-1) per W over 1 g of tissue at 900 MHz and 1.8 GHz, respectively.

Implications for SAR when using a symmetric phantom exposed to RF radiation using the FDTD method

“…It should be noted that the Brooks head has closed eyelids and the results in this paper are calculated with the eyelids kept closed. Hirata showed [3] that opening the eyelid increased the average SAR in the eye by 15% at 5.0GHz. The size of the Yee cell was 2mm, equal to the resolution of the head.…”

“…A rigorous Finite-Difference Time-Domain (FDTD) model is used. In recent years some work has been written up regarding mobile phones positioned near the ear [1][2][3][4]. The head has also been irradiated from in front of the eye using realistic mobile phone models [3][4][5].…”

“…Bernardi [8] considered the eyes to be particularly sensitive organs due to their proximity to the surface of the head and the their relatively low levels of blood flow when compared to other regions of the body. Dimbylow [3] also stresses the vulnerability of the eyes as they have a tendency to accumulate damage and cellular debris. EM modeling is computationally expensive; it is therefore advantageous to use symmetry which can reduce computational costs.…”

A study of changes to specific absorption rates in the human eye close to perfectly conducting spectacles within the radio frequency range 1.5 to 3.0 GHz

“…In recent years some work has been written up regarding mobile phones positioned near the ear [4]- [7]. The head has also been irradiated from in front of the eye using realistic mobile phone models [6]- [8]. This is topical as such hand held devices held to the front of and away from the head may soon become popular.…”

“…Bernardi [11] considered the eyes to be particularly sensitive organs due to their proximity to the surface of the head and the relatively low levels of blood flow when compared to other regions of the body. Dimbylow [6] also stresses the vulnerability of the eyes as they have a tendency to accumulate damage and cellular debris. In the same area Cooper [12], modeled a geometric head, and Bernardi [13] investigated an anatomical head, irradiated by simple dipoles positioned near metallic walls.…”