Specific absorption rate in the human head due to metal-frame glasses and ear Prosthesis

Abstract

The research in this thesis involves the investigation of the specific absorption rate (SAR) in a human head model exposed to electromagnetic fields. The SARs (1-g and 10-g) were compared inside various models of the human head. Investigation is aimed at the study of the effect of the use of a realistic implant retained prosthetic ear attached to the side of the head and metal-frame glasses. A set of dipole antennas operating at a common frequency of 900, 1800 and 2100 MHz were rotated to investigate the effect of frequency and polarization. Two situations were considered in the thesis; radiation at the front of the face, and at the side of the head. Initial studies were conducted using a simplified model of the head and metal object to minimize the duration of the simulation. Four types of simple geometrical head were used; brick, cylindrical, spherical and elliptical cylinders were simulated with and without the simple shape of the nose to investigate its possible effects. At the same time, a straight metal rod was initially employed to represent the metal-frame glasses. The parameters were further expanded to the different conductivities of the metal rod, the dimensions of a model of the head, the curvature of the rod and the radii of the rod. In the side radiation case, the investigation of the ear prosthesis was initiated by looking at the effect of different dielectric properties of the artificial ear. Moreover, the combined use of these metal objects with realistic shapes of both glasses and implant (ear) were investigated in detail using homogeneous and heterogeneous models of a human head. The results suggest that different sections of the implant resonate depending on the frequency and polarization, and furthermore, demonstrate that this real implant is a complex scattering element. The implant focuses and reflects the incident radio frequency (RF) energy. The nearby tissue of the head will also have a secondary dielectric loading effect. The relative enhancement on the SAR10g due to the implant was much smaller. The SAR distribution shows that the increase in the SAR due to the metallic implant is extremely local with regards to the implant. This explains the change in the SAR1g and the much smaller changes to the 10g SAR. However, the metal-frame glasses selected in this investigation had given a negative significant increment of SARs at any orientation of the dipole and frequency chosen. Overall, with regard to the ear prosthesis, exposure to 900 MHz from any device adjacent to the implant may cause harm. It also is suggested that patients with ear prostheses should not be exposed to any near-body communication at any frequency range, because there is evidence that metal implanted inside certain materials has different behavior from the same metal that has not been implanted in any material.