Health hazards of wireless power transfer.
GPHY makes sure to comply with all international standards on electrical safety, electromagnetic compatibility and the impact of radiation on the human body. In this blog, we will explore these standards and the impacts of electromagnetic radiation on humans.
Wireless power transfer is an area with great potential that will come on top of recent technological revolutions such as the Internet of Things and artificial intelligence. Despite extensive work for some companies to market wireless transfer products, there are still questions regarding the safety and health of these products. So let's do a review and update on the different wireless power transfer standards and how these fit together around international and national standards. It goes without saying that a growing number of multimedia and digital equipment are changing the landscape of equipment as well as the emissions in the electromagnetic spectrum that surround us. For wireless transfer, the two standards developed are Qi, based on magnetic induction and integrated in most cell phones, and AirFuel Alliance, based on resonant magnetic coupling. GPHY believes that AirFuel is the standard that will truly meet the needs of consumers and permanently change the way we charge our devices on a daily basis. To learn more about the differences between the standards, see the blog here.
Generally speaking, the electromagnetic waves around us are randomly oriented and composed of an electric and magnetic field.
These two types of field are generally related in the far field as shown in Figure 1, but this is not the case in the near field (generally for distances less than the wavelength). Thus, in the case of wireless power transfer, the two fields are considered near field and must be considered separately, as they have different impacts on the environment around them and on the humans.
For wireless power transfer, the magnetic field is the most important factor. Figure 2 shows the different types of waves in the electromagnetic spectrum and we recognize the visible part, which is light. Planck's law states that the higher the frequency, the greater the power of the photons, so gamma rays and x-rays are more dangerous than infrared and microwaves for example.
It is therefore the frequency that explains the difference between what are called ionizing waves and non-ionizing ones. Ionizing waves are those which manage to change the signature of our cells, our DNA or cause cancer like ultraviolet rays. In the case of wireless power transfer, the low frequencies used are non-ionizing waves and of the order of 100,000,000 weaker than ionizing ones. So there is no chance that the non-ionizing waves used for wireless energy transfer could impact the signature of our cells. In this case, two potential dangers can be observed for the human body, namely the heating of biological tissues and the currents induced in the nervous system. For the heating of biological tissues, a limit is established for the specific absorption rate SAR in terms of energy (watts) absorbed per mass of tissue (kg). Thus, this defines how much electromagnetic radiation heats a part of the human body. As regards the induced current, it is in relation to the nerve stimulation SN that the limit of the internal electric field in the body is fixed in electric potential (volt) over the distance (meter). An example of natural nerve stimulation in the body is the reflex. [Health Canada, Safety Code 6]
Around the world, various entities are involved in setting limits on RF exposures. The International Commission on Protection against Non-Ionizing Radiation (ICNIRP) is an NPO establishing and bringing together limits, scientific research and guidelines for non-ionizing radiation. The World Health Organization WHO is the second point of reference for setting international standards. The majority of countries use the same limits given the compilation of the results of scientific research on the subject. For example, in Canada, Health Canada sets the limits in safety code 6. Note that safety criteria and factors are already planned on this subject and are of the order of 50x.
Now that the table has been set for the limits against regulatory entities, how can we compare various technologies such as Wi-Fi, Bluetooth, Qi wireless power transfer and Airfuel. The main difference is the frequency used by these systems. For example, Wi-Fi and Bluetooth use frequencies of 2.4GHz and 5GHz while wireless power transfer uses frequencies from 100 to 300KHz (Qi) and 6.78MHz (AirFuel). In this case, it is impossible to compare the emitted levels in terms of electromagnetic power, because absorption by biological tissues varies with frequency.
Thus, in the case of technologies such as Wi-Fi and Bluetooth, it is the SAR limit that dominates and that defines the total heating of a cell phone that would be worn close to the ear during a call or worn in a trouser pocket. This limit is 1.6 W/kg for the head and torso while it is 4W/kg for the rest of the body. Typically a cellular device causes an SAR between 0.9W/kg and 1.15W/kg when worn on the head during a call. It is important to remember that these values have a safety factor of 50x. For Airfuel, SAR is also the dominant one, as the boundary transition is between 1-2 MHz. In the case of wireless Qi power transfer, it is rather nerve stimulation that limits exposure to radio frequencies. [Industry Canada]
In conclusion, all products meeting the requirements of regulatory entities are therefore automatically in accordance with the most recent research and requirements in the field of radio frequencies. Thus, with the Airfuel standard, the frequency and powers chosen have been designed to ensure that the products which comply with it are safe. For GPHY, the value of responsibility is paramount and the products developed must meet the highest standards at this level. For more information, we recommend that you consult the following sources: WHO, ICNIRP, Santé Canada, IEEE ou FCC.
Report ITU-R SM.2392-0 (08/2016), Applications of wireless power transmission via radio frequency beam