The Need for Standards
Low Frequency (Qi)
High Frequency (Magnetic Resonance)
6.78 MHz / 13.56 MHz
Max transfer range
Yes, at different power levels
Low & limited, 30W max
Broad & versatile, 20W to 20kW+
Limited to 80%
High: up to 95%
Standard Wireless Power Technologies: Inductive vs. Resonant
Just what do we mean by “inductive” and “resonant” technologies? Here are the main differences between the two.
Inductive technology, which is a closely coupled solution, is the type of compliance used by Qi. This technology transfers power using low-frequency resonant tanks (100-205kHz) over very short distances (mostly anything under 10mm).
In 2009, the first standard for Qi had a 5W power requirement (“Low Power”). In 2015, that was increased to 15W capability (“Medium Power”). This year, Qi is hoping for over 100W (“High Power”). Those are currently in testing and should be rolled out later this year.
The other wireless power technology, resonant, is considered a loosely coupled solution. Primarily championed by the AirFuel Alliance, this technology uses a high-frequency resonant tank (6.78MHz) to transmit power over long distances (multitudes of feet). Resonant technology offers the ability to charge multiple devices at the same time, with a capability of up to 22W for upcoming systems. There are also up to 20kW magnetic resonance techonogies enabled by companies such as WiTricity in the USA.