ELE Times December 2016 Electronics News in India | Online Electronics Mag | Page 53

Wireless Power

Figure 1: Top: Concept behind WiTricity’s technology, including coils, electronics that control power
output and regulation, and wireless communication between the source and capture devices to
ensure the correct power output. Bottom: The technology supports charging through surfaces of
different materials (left); the wireless range may be extended using resonant repeaters (right).

Magnetic Resonance Widens the
Transmission Gap
Other options for wireless energy transfer
require precise device positioning on a
pad or holder, very close proximity to
(often resting directly on) the charging
source, and the source can only charge a
single device with a single coil. Now, the
engineers at WiTricity have leveraged the
power of magnetic resonance to rethink
these limitations.
Their system, dubbed “highly resonant
wireless power transfer”, relies on
oscillating time-varying magnetic fields
generated by alternating current passing

through a coil that functions as a power
source. A power amplifier connected to
this source coil controls the power levels
and operating frequency, driving the
magnetic field levels.
A capture device, which acts as a receiver
and captures the magnetic field, contains
another coil tuned to the same frequency
as the source (see Figure 1). The field
converts the magnetic energy back to
radio-frequency alternating current in the
receiver, which can then be used as a new
local power source after being rectified
and regulated by power electronics.
The notable difference between

Figure 2: Left: A capture resonator, a resonant repeater, and a source resonator. Center: A WiTricity
source resonator designed for consumer electronics applications. Right: An electric vehicle charging
wirelessly, parked above a charging pad.

ELE Times | 53 | December, 2016

WiTricity’s technology and other
approaches is the use of magnetic
resonance. With both coils tuned to the
same resonant frequency, the receiving
coil is able to capture maximum power
through the magnetic field with very low
losses, and power can be transmitted
without the source and capture device
sitting next to each other or being
perfectly aligned.
“One major advantage is the flexibility of
motion and positioning. The receiving coil
doesn’t have to be in direct contact with
the device; for instance, while driving your
car you could drop your phone i