How It All Started with mmWaves

The story of millimeter wave (mmWave) in International Electromagnetic Commission (IEC) standardization originally began when the Federal Communications Commission (FCC) in the United States announced the use of mmWave spectrum for 5G services in July 2016. However, from the human electromagnetic fields (EMF) exposure’s point of view, since the radiocommuncation technologies had used only frequencies below 6 GHz until then, there were no standardized EMF exposure assessment methods available for the mmWave spectrum [1].

The human exposure to EMF is subject to exposure limits defined by government regulations, mostly referring to the guidelines issued by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) [2], or nearly identical guidelines issued by Institute of Electrical and Electronics Engineers Standards Association (IEEE SA). Meanwhile, IEC and IEEE SA are jointly in charge of international standards on measurement and calculation methods to assess human exposure to EMF.

This article describes the significant effort that Samsung’s global regulation team has made especially in chairing and contributing to the IEC/IEEE, which jointly developed the international standards.

Exposure Parameters for Assessment of Human Exposure

Earlier generations of mobile devices using below 6 GHz frequency bands assess compliance for human exposure to EMF by applying specific absorption rate (SAR) as assessment parameter. SAR is a measure of the rate at which energy is absorbed per unit mass by a human body when exposed to a radio frequency (RF) electromagnetic field. Simply speaking, if the measured SAR of a mobile device is below the SAR limit defined by a national regulation, then the mobile device is compliant and allowed to be placed on the market.Earlier generations of mobile devices using below 6 GHz frequency bands assess compliance for human exposure to EMF by applying specific absorption rate (SAR) as assessment parameter. SAR is a measure of the rate at which energy is absorbed per unit mass by a human body when exposed to a radio frequency (RF) electromagnetic field. Simply speaking, if the measured SAR of a mobile device is below the SAR limit defined by a national regulation, then the mobile device is compliant and allowed to be placed on the market.

However, for mobile devices using frequency bands above 6 GHz, power density (PD) should be applied instead of SAR. This is due to the shorter wavelengths for which the energy is absorbed already in a few millimetres from the skin surface and not penetrating deeper into the tissue as for longer wavelengths. The PD is a measure of rate at which energy is impinging the exposed surface, e.g., human skin, averaged over a certain averaging area. This essentially meant that we could no longer use familiar SAR measurement methods for mobile devices using above 6GHz frequency bands, especially mmWaves. In other words, new assessment methods were inevitably required to launch it in the market on time.

First Steps in Standardization for Power Density Assessment

From the beginning, it was clear that there was such an urgent market need for the PD assessment methods. Therefore, Samsung drove to make new standards and IEC decided to hurry. Then, by first collecting state of the art information on the possible assessment methods, a technical report was published as IEC technical report (TR) 63170 in 2018. This is a typical approach in IEC standardization since TR is not a normative document and reaching consensus is therefore faster among many different stakeholders.

In addition, the level of details required from international standards (IS) is so much higher that TR route was seen much faster. And, it indeed was. The TR work started in early 2017 and technical content was mostly finished by the end of the year, while the editorial finalization and publication took the first half of 2018.

Meanwhile, during the course of the TR development, it became clear that totally new methods were required in evaluation of PD at these frequencies and at the small distances from the RF sources such as mmWaves mobile devices. Measurement probes needed to be extremely thin and even then they disturbed the near-field of the source so that measurements would lead to non-reliable results in terms of compliance. It was seen that measurements needed to be conducted at further distance, but not too far! Computational methods were found to enable “back-propagation” methods; measurements could be conducted at suitable distance and electromagnetic waves were then computed at closer distances to the source.

Figure 1.  IEC standardization timeline of EMF exposure

Final Goal: International Standards

As soon as the TR was technically finalized, IEC and IEEE SA officially decided to form joint working group (JWG) to jointly develop the IS as a normative document. Knowing the abovementioned technical issues, it was decided to develop two standards: one for the measurement methods and the other for the computational methods. These would during the development become “sister standards,” under the same standard series, and be cross-referencing each other. Therefore, the development timelines also needed to be synchronized so that they could be published at the same time.

Samsung’s global regulation team decided to lead the standard task, and accordingly dedicated time and efforts to this extremely important task by proposing to take leadership in chairing the IEC/IEEE JWG for the measurement standard. With hindsight, this probably was a very clever investment to development of these very important PD standards, thus enabling the future fluent market access with regards to human exposure to EMF from mobile device using above 6 GHz frequency bands.

After kicking off in early 2018, there were enormous 50 meetings held alone during the active development years from 2018 to 2020, meaning roughly one meeting every three weeks for the period of three years consecutively! And, of course this was added with similar numbers of JWG meetings for computational methods. This all describes the enormous amount of work spent for an international working group with over 90 members spread around the world. Moreover, COVID-19 pandemic started in 2020 caused its own disturbance to the then so familiar workflow with face-to-face meetings, but remote work and online-only meetings were quickly adopted, thus leading to likely even higher productivity.

Looking back, the technical problems were solved relatively smoothly after all, even if there are always arguments between different stakeholders. On the other hand, the synchronisation with the “sister working group” for the computational standards and syncing the bureaucracies of the two standard organizations, i.e., IEC and IEEE SA, has taken its own toll at times.

But, what is most important and what are the results of the hard work that Samsung can be proud of is the fact that the two international standards, namely, the IEC/IEEE IS 63195-1 for the measurement procedure of power density and IEC/IEEE IS 63195-2 for the computational methods, have now finally been published [3, 4] !!!

But It Ain’t Over Yet …

Now, the international standards for PD have been published, and at the same time, a new compliance parameter of ICNIRP 2020 Guidelines, i.e., absorbed power density (APD), was defined.

In the IEC standardization’s point of view, the new goal is coming in front of us to prepare for 5G-Advanced and 6G from 6 GHz up to sub-Terahertz (sub-THz) frequency bands in the coming decade. While PD is measured or computed in free space, APD is defined just inside the surface of exposed area while considering realistic assessment’s point of view. This APD parameter enables more accurate assessment of exposure as being direct proxy of tissue heating and taking also into account possible reflections between transmitting device and the human body surface.

As a first step, Samsung’s global regulation team is once again driving to develop new measurement methods for APD in IEC, while starting to develop IEC Publicly Available Specification (PAS) on the conversion of the SAR to the APD. As a starting point, this is strategically based on existing SAR measurement technologies and is therefore limited to only frequencies up to 10 GHz. This is an important first step since many regulators are adopting APD as compliance parameter in these frequencies. A following, much bigger, task is to develop international standards for APD covering the whole frequency range from 6 GHz to 300 GHz. While measurement probe technology will still need a lot of miniaturisation and development to respond to very small wavelengths in these frequencies without too much perturbation of the fields, it is likely that computational methods will be in the key role. For example, computational techniques taking measured PD as input and then modelling the behaviour of the EM field in presence of the human body and the transmitting device could be the key technology for regulatory acceptance. We are already very excited to expect to make history again with the standardization of EMF exposure for the upcoming 6G world.