ELE Times December 2016 Electronics News in India | Online Electronics Mag | Page 54

Wireless Power
saving and allowed us to virtually test our
concepts before building the real device.”

a suite of simulation apps around it that
would allow any of our
engineers—whether they knew how to
use COMSOL or not—to quickly test and
validate designs even if they didn’t
understand the entire model.”

Keeping a safe distance, right up close

Figure 3: Simulation results showing the
magnetic field levels (top) and power dissipated
(bottom) in a source resonator for consumer
electronics applications.

He created simulations with different
setups for each application, and included
electromagnetically relevant components
such as coil windings, specially shaped
ferrites and metal surfaces used to guide
the electromagnetic field, plates for
shielding sensitive electronics, and large
objects that might perturb the field, such
as a car chassis.
Then he ran a multiphysics study to
analyze the resulting electromagnetic and
thermal performance as a function of
power drawn by the devices, coil
displacements, and the effects of
perturbing objects (see Figure 3, top).
He extracted circuit parameters from the
results to guide the design of the
electronics, as well as predictions of
power dissipation and thermal loading on
different components (see Figure 3,
bottom). The team adjusted their designs
accordingly, determining the viable range
of coil displacements and power levels as
a function of size, weight, and thermal
constraints.
“The simulation allowed us to disentangle
various effects that we couldn’t isolate just
by testing, like power dissipation and heat
transfer,” Kurs remarked. “The flexibility of
COMSOL was particularly useful; we built

Since such devices are near to or in
contact with people’s bodies, electronics
manufacturers must adhere to safety
limits on the elec-tromagnetic fields
emitted by their products. The magnetic
fields needed for WiTricity’s wireless
transfer are usually fairly weak, but each
new application needs be checked for
compliance.
To make sure that the field levels and
resulting body temperatures would meet
regulations, the team ran several more
COMSOL simulations to study different
body tissues in close proximity to the
device. Their models calculated the
electric field based on the operating
frequency of the charging system, and
confirmed that the results were well
within FCC safety guidelines (see Figure 4).

changing wireless power transfer
technology, WiTricity is on the board of
the Alliance for Wireless Power (A4WP),
an organization dedicated to building a
“global wireless ecosystem” and creating
standards for wireless charging. Another
board member, Intel, has licensed
WiTricity’s technology to develop a
wireless desk desktop system. The A4WP
is an innovative group comprising leading
companies that are ushering in a new way
of thinking about wireless power: they are
imagining a future where everyday
surfaces—desks, cup holders, and even
your kitchen countertop—become zones
for charging the electronic devices we
depend on so much.

Andre Kurs, co-founder, WiTricity.
Figure 4: COMSOL simulation showing the
specific absorption rate (SAR) in a hand above a
charging cell phone. SAR is a measurement of
electromagnetic energy absorbed and turned
into heat. Results are in dB relative to the FCC
limit (a value of zero represents the limit).

Rethinking a growing industry for
wireless charging
Witricity’s designs based on magnetic
resonance are a major improvement over
other wireless charging methods, allowing
reliable wireless power transfer in a
flexible, consumer-friendly product.
Thanks to their simulation work in
COMSOL Multiphysics, the WiTricity team
optimized their designs for better
efficiency and longer ranges before
building costly prototypes.
In addition to being frontrunners in game-

ELE Times | 54 | December, 2016