Theoretical Evaluation of the Power Transmitted to the Body as a Function of Angle of Incidence and Polarization at Frequencies >6 GHz and its Relevance for Standardization

Theodoros Samaras and Niels Kuster, Bioelectromagnetics 2019, Volume 40, Issue 2, February 2019, pp. 136–139, online 25 January 2019; doi: 10.1002/bem.22170

Emerging wireless applications, including upcoming 5G telecommunications networks, are expected to make wide use of the millimeter wave (MMW) spectrum (30–300 GHz). In this frequency range, existing guidelines from the International Commission on Non-Ionizing Radiation Protection (ICNIRP)1 and IEEE2 are currently under revision. A major advantage of the new guidelines is that, not only are the limits (reference levels) for incident power density defined, but also a limit for the power density transmitted to the tissues – also referred to as the basic restriction or the dosimetric reference limit – is introduced. The objective of this study was to investigate different polarizations and angles of incidence to determine a conservative transmission factor for the incident power density level. For transverse-magnetic polarization, the optimal angles for mean and maximum transmittance values of all tissue models result in energy coupling at oblique incidence angles that can be much larger than that for normal incidence, with transmittance factors up to 70% or 40% higher than those assumed in the proposed guidelines for 10 GHz or 30 GHz, respectively.

The scientific and technical impact of the study can be summarized as:
  • The reference levels proposed in the guidelines are not conservative with respect to the basic restrictions
  • The coupling at an oblique incidence angle can be much larger than for normal incidence, increasing the transmittance factor to 0.95
  • Evaluation of only the normal component with respect to the surface may result in greatly underestimated exposures, by as much as a factor >10
  • The potential for underestimation as a function of the reference levels in the close near-field of transmitters is the subject of a follow-up study

1. ICNIRP. 1998. Guidelines for Limiting Exposure to Time-Varying Electric, Magnetic, and Electromagnetic fields (up to 300 GHz). Health Phys 74:494–521.
2. IEEE. 2005. C95.1—IEEE Standard for Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3 kHz to 300 GHz (New York: IEEE).