As new classes of electronic devices like phones or wireless chargers are introduced to the market — especially those devices that use radio frequency electromagnetic fields — it’s critical to verify that these new devices are safe when used by people with medical implants.
The limits for safe exposure of the human body to electromagnetic fields are well understood. In the USA, the FCC has set limits for the strength of electromagnetic fields that may be generated by electronic equipment and the FCC enforces the compliance with their certification program. Products that carry the FCC mark will not expose your body to harmful electromagnetic fields. The FCC has an excellent website and FAQ devoted to this subject. Other countries have similar regulations, certification procedures, and safety marks.
People who wear implantable electronic devices such as pace makers, defibrillators and deep-brain stimulators will not only be interested in the effect of electromagnetic fields on the human body, but also in the potential effect of electromagnetic fields on their implants.
To this end, a recent study published in the International Journal of Environmental Research and Public Health, the compatibility of a Qi wireless charger and cardiovascular implantable electronic devices (CIEDs) was assessed. The aim of this study was to assess the electromagnetic compatibility between CIEDs and the magnetic field of a common wireless charging technology. To do so, the voltage induced in CIEDs by an A13-type Qi wireless charger fields were measured and compared with the performance limits set by ISO 14117. In order to carry this out, a measuring circuit was developed that can be connected with unipolar or bipolar pacemaker leads. The measuring system was positioned at the four most common implantation sites in a torso phantom filled with physiological saline solution.
The study found that the induced field is well below the limits set by ISO 14117, even at two cm from the Qi transmitter coil (that is the location with the highest the induced field strength). The field strength drops off dramatically with increasing distance. At the more realistic distance of 10 cm, the induced field is only 2% of the field at 2 cm.
While this was not the first such study, it was particularly thorough and corroborates the findings of previous studies that determined Qi wireless charging does not interfere with CIEDs.
Human Safety — the relationship between frequency and power:
The top design factors that determine safety margins are the system’s operating frequency, the power that the system consumes, and the use of magnetic shielding in the product. As operating frequency increases the resulting electromagnetic field’s potential to interfere with other electronic devices increases (see e.g. the article on PlanetAnalog.com on “Design Considerations in Modern Wireless Power Transfer Systems: Frequency of Operation”). Similarly, as power consumption increases, the electromagnetic field strength increases and with it, the potential to interfere with other electronic devices.
Why is Qi wireless charging safe?
Qi-compatible products run at a low operating frequency (100 kHz to 200 kHz), and consequently, can deliver high power while remaining well within safe limits. Typical Qi transmitters (chargers) deliver up to 15 watts in a configuration where the transmitter coil and receiver coil are aligned and in close proximity. With this configuration, the field strength declines rapidly with distance, much more rapidly than with, for example, Wi-Fi base stations. This configuration significantly reduces the potential for interference with other electronic devices.
The Qi technology has been in high-volume production since 2010, and there are now hundreds of product types and hundreds of millions of users worldwide. With this market maturity comes a wealth of data that independently confirms the safety of products that use the Qi standard.