Computer simulation study of the penetration of pulsed 30, 60 and 90 GHz radiation into the human ear.

There is increasing interest in applications which use the 30 to 90 GHz frequency range, including automotive radar, 5 G cellular networks and wireless local area links. This study investigated pulsed 30-90 GHz radiation penetration into the human ear canal and tympanic membrane using computational phantoms. Modelling involved 100 ps and 20 ps pulsed excitation at three angles: direct (orthogonal), 30° anterior, and 45° superior to the ear canal. The incident power flux density (PD) estimation was normalised to the International Commission on Non-Ionizing Radiation Protection (1998) standard for general population exposure of 10 Wm and occupational exposure of 50 Wm. The PD, specific absorption rate (SAR) and temperature rise within the tympanic membrane was highly dependent on the incident angle of the radiation and frequency. Using a 30 GHz pulse directed orthogonally into the ear canal, the PD in the tympanic membrane was 0.2% of the original maximal signal intensity. The corresponding PD at 90 GHz was 13.8%. A temperature rise of 0.032° C (+20%, -50%) was noted within the tympanic membrane using the equivalent of an occupational standard exposure at 90 GHz. The central area of the tympanic membrane is exposed in a preferential way and local effects on small regions cannot be excluded. The authors strongly advocate further research into the effects of radiation above 60 GHz on the structures of the ear to assist the process of setting standards.