Numerical Exposure Assessments of Communication Systems at Higher Frequencies

There are well‐established assessment guidelines for devices that operate under 10 GHz to keep the exposure levels under the basic limits and to minimize the public concern about over exposures. New emerging technologies are focusing on using frequency bands in mmW region (30–100 GHz), which is a part of radio frequency (RF) spectrum. The possible use of these higher frequency bands imposes new challenges in terms of EM exposure assessment. The mmW radiations are non‐ionizing and the major concern is heating of tissues at these frequencies. Due to lack of availability of assessment methods, governments currently rely on standards that developed before the exponential increase in use of wireless communication devices. Due to the shallow penetration depth in biological materials at mmW frequencies, most of the energy is absorbed within few millimeters of the skin. This makes challenging for conventional E‐field probe to estimate EM absorption on skin surface. Therefore, SAR levels were found significantly higher in comparison with those at microwave frequencies with same incident power density (IPD). International guidelines providing agencies recommend using power density (PD) as a basic restriction limit to reduce the excessive exposure at higher frequencies (above 10 GHz). But devices operating in near‐ or far‐field do not take account for field distribution or power absorption in the tissues, they only consider density of power travelling towards the tissue. Therefore, PD may not likely be useful as SAR or temperature for assessing safety at higher frequencies. In order to control over exposure at mmWs, numerical SAR assessment is performed on human head‐equivalent cube models (HHECM) and human eye‐equivalent cube models (HEECM) between 2 and 30 GHz in order to find out how SAR can be used as useful in limiting the over exposure at mmWs. For this purpose, EM wave penetration depth is used to identify the absorption levels with the help of SAR inside the body from the surface.