By: Ryan McCaughey, PhD

The 5G moto mod will allow the moto z3 to become the first commercial 5G smartphone in the US. 5G, the fifth generation of cellular mobile communications, promises faster data rates, reduced latency, higher system capacity, and massive device connectivity. The February 2019 FCC filing[i] for the Motorola add-on reveals a unique feature to limit radiation exposure from 5G and sheds light on how 5G phones are tested for RF exposure compliance.

Inconsistent test methodologies

5G includes new radio technologies using frequencies below 6 GHz and above 24 GHz (in the RF spectrum known as millimeter wave). However, the FCC’s SAR (Specific Absorption Rate) compliance protocol only applies to frequencies up to 6 GHz. SAR is a measure of how much RF power from the phone or wireless device is absorbed in human tissue and the SAR test requires making measurements in head and body phantoms filled with tissue simulating media.

Above 6 GHz the FCC adopts a Maximum Permissible Exposure (MPE) restriction that limits the power density of a transmitting antenna. However, power density can only be accurately measured in the “far-field”, i.e., greater than 2 wavelengths from the source (for the 5G moto mod operating at 28 GHz, that equates to about an inch from the phone). So MPE testing cannot reliably predict exposure when a phone is held next to the head or body. Nor does it provide any information about how much RF is actually absorbed by the body. In fact, there are no human head or body simulating phantoms present in the test.

Impractical to measure

The 5G moto mod has four millimeter wave 5G modules, each of which consists of an array of 4 antennas each capable of creating 16 unique RF beam patterns so that the module can “steer” the transmitted signal in the direction for optimal connectivity. This beamforming technology significantly increases the number of exposure test cases. The FCC claims it is “impractical to measure every beam” because it would be too time-consuming. Therefore, they allow a computer simulation of each beam’s power density to identify the worst-case scenario, then that beam configuration and location are measured in the lab.

There are inherent limitations of numerical simulation of electromagnetic fields – the results rarely match a real-world measurement because it is impossible to accurately model complex systems.

The simulation of the moto mod makes unrealistic assumptions about the device being used floating in “free-space” away from any real-world objects, including human hands, heads and bodies. The FCC report acknowledges but dismisses a significant divergence between simulated and real-world measurements. For example, Figure 6.3.5-5 shows very different power density distributions and Table 6.3.5-9 shows a 50x difference between the measured and simulated power densities.[ii] Yet this time-saving methodology is approved for minimizing the RF exposure scenarios that should be tested.


Limiting 5G Radiation Exposure

The FCC filings for the 5G moto mod also detail a unique feature for limiting the exposure from the millimeter wave 5G radios: “The control mechanism is a simple one in which, if proximity detectors indicate the potential presence of the user within a roughly conical region in front of the module where power density may approach the MPE limit, that module is disabled from use by the modem. This terminates and prevents transmission from the module in question.”  Each 5G module has a thermal proximity sensor designed to detect human body heat (see Figure 5-1)[iii].


If the sensor comes within 5 inches of a human head, hand or body at 91 Fahrenheit, the 5G transmitter is deactivated. This feature implies that close proximity to millimeter wave radiation, even if it is below the MPE limit, is a concern to Motorola and/or the FCC.

Biological effects of 5G

Because 5G is such a new technology there are limited studies on the biological effects of exposure to millimeter wave RF. However, preliminary research shows it can increase skin temperature; alter gene expression; promote cellular proliferation and synthesis of proteins linked with oxidative stress, inflammatory and metabolic processes; generate ocular damage, and affect neuro-muscular dynamics.[iv] Studies even predict that because of their size and shape, sweat glands will act as antennas for millimeter wave radiation, that could result in physiological and neurological stress.[v]