supplies and coil arrays can be used to provide
greater orientation flexibility. The challenge,
however, is cost of those complex systems and
challenges with backwards compatibility. Over
time, the technology and use case will improve.
For now, this is the main shortcoming of Qi.
AirFuel Resonant’s major promise is use case.
AirFuel utilizes loosely coupled technology,
which means that multiple devices can charge
from a single transmit coil simultaneously;
orientation and distance (up to ~50 mm) is flexible;
power levels can scale reasonably above
50W; and device charging can be invisible and
more intuitive (i.e., embedding transmitters under
the counter versus visibly embedding in or
on the counter).
For AirFuel to succeed, it needs adoption and
scale. Superior technology and use case may
win over customers in the long term, but there’s
a significant uphill climb given Qi’s current market
Proprietary NFMC has the most flexible use
case because it’s proprietary. Everything from
multiple-device charging with high power and
unique environmental constraints down to
low-power, low-cost 1:1 systems with no data
transfer is open for adoption of NFMC.
RF provides an extremely compelling use case.
Whereas Qi offers millimetres of separation
and AirFuel offers centimetres of separation,
RF offers metres of separation. To date, longdistance
RF power transfer still isn’t expected
to deliver much more than 1W of power, but it
has the potential to be extremely valuable for
low-power applications that rely on positional
flexibility and metres of separation.
Ultrasound’s use case is less well known due to
the limited technical information available. Most
likely, the use case is somewhat similar to RF’s
in that it has the potential to deliver low power
over metres of distance.
SAFETY AND REGULATORY
Qi is implicitly safe due to magnetics and closeproximity
coupling. It’s achieved regulatory
approval in all major consumer markets and
has limited issues with interference due to low
frequency (~200 kHz), minimal radiation, and
known shielding techniques.
AirFuel is also implicitly safe for similar reasons
to Qi, but is challenged a bit more on interference
related issues due to higher frequency
of operation (6.78 MHz) and generally larger
transmitter antennas (for orientation flexibility).
Multiple AirFuel systems have achieved worldwide
regulatory approval, but regulatory is not
a “given” (by reason of EMI/EMC issues, not
safety issues) and should be carefully designed.
Proprietary NFMC can’t receive a blanket statement
because every system is unique. NFMC
(the same type of physics used by Qi and Air-
Fuel) is generally safe. Designers must carefully
consider EMI/EMC for each proprietary product
RF over distance hasn’t achieved regulatory
approval. The power required in the transmitter
to deliver usable power to devices multiple
metres away is significant. In other words, current
systems will need to be improved in order
to provide enough power with low-enough
emissions and high-enough efficiency to pass
regulatory requirements. This is a significant
challenge since power reduces exponentially
as it radiates away from a source due to the
inverse-square properties of EM waves.
Ultrasound technology at low power is safe, but
can it deliver meaningful amounts of power at
metres of distance? Again, the laws of physics
are stacked against ultrasound technology, and
the technology is too early stage for meaningful
data to be publicly available. However, proponents
of this technology are surely working on
Jacob Babcock is co-founder and CEO of Nu-
Current, a leading wireless power system and
magnetics solution provider.
This article first appeared
Find Wireless Charging
28 DesignNews NOVEMBER 2017 www.eedesignnewseurope.com