<s>
Wireless	B-Application
power	I-Application
transfer	I-Application
(	O
WPT	O
)	O
,	O
wireless	B-Application
power	I-Application
transmission	I-Application
,	O
wireless	B-Application
energy	I-Application
transmission	I-Application
(	O
WET	O
)	O
,	O
or	O
electromagnetic	O
power	O
transfer	O
is	O
the	O
transmission	O
of	O
electrical	O
energy	O
without	O
wires	O
as	O
a	O
physical	O
link	O
.	O
</s>
<s>
In	O
a	O
wireless	B-Application
power	I-Application
transmission	I-Application
system	O
,	O
a	O
transmitter	O
device	O
,	O
driven	O
by	O
electric	O
power	O
from	O
a	O
power	O
source	O
,	O
generates	O
a	O
time-varying	O
electromagnetic	O
field	O
,	O
which	O
transmits	O
power	O
across	O
space	O
to	O
a	O
receiver	O
device	O
,	O
which	O
extracts	O
power	O
from	O
the	O
field	O
and	O
supplies	O
it	O
to	O
an	O
electrical	O
load	O
.	O
</s>
<s>
The	O
technology	O
of	O
wireless	B-Application
power	I-Application
transmission	I-Application
can	O
eliminate	O
the	O
use	O
of	O
the	O
wires	O
and	O
batteries	O
,	O
thus	O
increasing	O
the	O
mobility	O
,	O
convenience	O
,	O
and	O
safety	O
of	O
an	O
electronic	O
device	O
for	O
all	O
users	O
.	O
</s>
<s>
Wireless	B-Application
power	I-Application
transfer	I-Application
is	O
useful	O
to	O
power	O
electrical	O
devices	O
where	O
interconnecting	O
wires	O
are	O
inconvenient	O
,	O
hazardous	O
,	O
or	O
are	O
not	O
possible	O
.	O
</s>
<s>
Wireless	B-Application
power	I-Application
techniques	O
mainly	O
fall	O
into	O
two	O
categories	O
,	O
near	B-Algorithm
field	I-Algorithm
and	O
far-field	B-Algorithm
.	O
</s>
<s>
In	O
near	B-Algorithm
field	I-Algorithm
or	O
non-radiative	O
techniques	O
,	O
power	O
is	O
transferred	O
over	O
short	O
distances	O
by	O
magnetic	O
fields	O
using	O
inductive	O
coupling	O
between	O
coils	O
of	O
wire	O
,	O
or	O
by	O
electric	O
fields	O
using	O
capacitive	O
coupling	O
between	O
metal	O
electrodes	O
.	O
</s>
<s>
Inductive	O
coupling	O
is	O
the	O
most	O
widely	O
used	O
wireless	O
technology	O
;	O
its	O
applications	O
include	O
charging	O
handheld	O
devices	O
like	O
phones	O
and	O
electric	O
toothbrushes	O
,	O
RFID	B-Application
tags	I-Application
,	O
induction	O
cooking	O
,	O
and	O
wirelessly	O
charging	O
or	O
continuous	O
wireless	B-Application
power	I-Application
transfer	I-Application
in	O
implantable	O
medical	O
devices	O
like	O
artificial	B-Device
cardiac	I-Device
pacemakers	I-Device
,	O
or	O
electric	O
vehicles	O
.	O
</s>
<s>
In	O
far-field	B-Algorithm
or	O
radiative	O
techniques	O
,	O
also	O
called	O
power	B-Application
beaming	I-Application
,	O
power	O
is	O
transferred	O
by	O
beams	O
of	O
electromagnetic	O
radiation	O
,	O
like	O
microwaves	O
or	O
laser	O
beams	O
.	O
</s>
<s>
An	O
important	O
issue	O
associated	O
with	O
all	O
wireless	B-Application
power	I-Application
systems	O
is	O
limiting	O
the	O
exposure	O
of	O
people	O
and	O
other	O
living	O
beings	O
to	O
potentially	O
injurious	O
electromagnetic	O
fields	O
.	O
</s>
<s>
Wireless	B-Application
power	I-Application
transfer	I-Application
is	O
a	O
generic	O
term	O
for	O
a	O
number	O
of	O
different	O
technologies	O
for	O
transmitting	O
energy	O
by	O
means	O
of	O
electromagnetic	O
fields	O
.	O
</s>
<s>
In	O
general	O
a	O
wireless	B-Application
power	I-Application
system	O
consists	O
of	O
a	O
"	O
transmitter	O
"	O
device	O
connected	O
to	O
a	O
source	O
of	O
power	O
such	O
as	O
a	O
mains	O
power	O
line	O
,	O
which	O
converts	O
the	O
power	O
to	O
a	O
time-varying	O
electromagnetic	O
field	O
,	O
and	O
one	O
or	O
more	O
"	O
receiver	O
"	O
devices	O
which	O
receive	O
the	O
power	O
and	O
convert	O
it	O
back	O
to	O
DC	O
or	O
AC	O
electric	O
current	O
which	O
is	O
used	O
by	O
an	O
electrical	O
load	O
.	O
</s>
<s>
Wireless	B-Application
power	I-Application
uses	O
the	O
same	O
fields	O
and	O
waves	O
as	O
wireless	O
communication	O
devices	O
like	O
radio	O
,	O
another	O
familiar	O
technology	O
that	O
involves	O
electrical	O
energy	O
transmitted	O
without	O
wires	O
by	O
electromagnetic	O
fields	O
,	O
used	O
in	O
cellphones	O
,	O
radio	O
and	O
television	O
broadcasting	O
,	O
and	O
WiFi	O
.	O
</s>
<s>
In	O
contrast	O
,	O
with	O
wireless	B-Application
power	I-Application
transfer	I-Application
the	O
amount	O
of	O
energy	O
received	O
is	O
the	O
important	O
thing	O
,	O
so	O
the	O
efficiency	O
(	O
fraction	O
of	O
transmitted	O
energy	O
that	O
is	O
received	O
)	O
is	O
the	O
more	O
significant	O
parameter	O
.	O
</s>
<s>
For	O
this	O
reason	O
,	O
wireless	B-Application
power	I-Application
technologies	O
are	O
likely	O
to	O
be	O
more	O
limited	O
by	O
distance	O
than	O
wireless	O
communication	O
technologies	O
.	O
</s>
<s>
Wireless	B-Application
power	I-Application
transfer	I-Application
may	O
be	O
used	O
to	O
power	O
up	O
wireless	O
information	O
transmitters	O
or	O
receivers	O
.	O
</s>
<s>
These	O
are	O
the	O
different	O
wireless	B-Application
power	I-Application
technologies	O
:	O
</s>
<s>
Resonant	B-Architecture
inductive	I-Architecture
coupling	I-Architecture
Mid	O
-	O
Low	O
kHz	O
–	O
GHz	O
Tuned	O
wire	O
coils	O
,	O
lumped	O
element	O
resonators	O
Charging	O
portable	O
devices	O
(	O
Qi	O
)	O
,	O
biomedical	O
implants	O
,	O
electric	O
vehicles	O
,	O
powering	O
buses	O
,	O
trains	O
,	O
MAGLEV	O
,	O
RFID	B-Application
,	O
smartcards	O
.	O
</s>
<s>
Near-field	B-Algorithm
or	O
nonradiative	O
region	O
–	O
This	O
means	O
the	O
area	O
within	O
about	O
1	O
wavelength	O
( λ	O
)	O
of	O
the	O
antenna	O
.	O
</s>
<s>
Resonance	B-Application
,	O
such	O
as	O
resonant	B-Architecture
inductive	I-Architecture
coupling	I-Architecture
,	O
can	O
increase	O
the	O
coupling	O
between	O
the	O
antennas	O
greatly	O
,	O
allowing	O
efficient	O
transmission	O
at	O
somewhat	O
greater	O
distances	O
,	O
although	O
the	O
fields	O
still	O
decrease	O
exponentially	O
.	O
</s>
<s>
Therefore	O
the	O
range	O
of	O
near-field	B-Algorithm
devices	O
is	O
conventionally	O
divided	O
into	O
two	O
categories	O
:	O
Short	O
range	O
–	O
up	O
to	O
about	O
one	O
antenna	O
diameter	O
:	O
Drange	O
≤	O
Dant	O
.	O
</s>
<s>
"	O
strongly	O
...	O
coupled	O
magnetic	O
resonance	B-Application
can	O
work	O
over	O
the	O
mid-range	O
distance	O
,	O
defined	O
as	O
several	O
times	O
the	O
resonator	O
size.	O
"	O
</s>
<s>
Agbinya	O
(	O
2012	O
)	O
Wireless	B-Application
Power	I-Application
Transfer	I-Application
,	O
p	O
.	O
40	O
This	O
is	O
the	O
range	O
over	O
which	O
resonant	O
capacitive	O
or	O
inductive	O
coupling	O
can	O
transfer	O
practical	O
amounts	O
of	O
power	O
.	O
</s>
<s>
Far-field	B-Algorithm
or	O
radiative	O
region	O
–	O
Beyond	O
about	O
1	O
wavelength	O
( λ	O
)	O
of	O
the	O
antenna	O
,	O
the	O
electric	O
and	O
magnetic	O
fields	O
are	O
perpendicular	O
to	O
each	O
other	O
and	O
propagate	O
as	O
an	O
electromagnetic	O
wave	O
;	O
examples	O
are	O
radio	O
waves	O
,	O
microwaves	O
,	O
or	O
light	O
waves	O
.	O
</s>
<s>
Therefore	O
the	O
near-field	B-Algorithm
devices	O
above	O
,	O
which	O
use	O
lower	O
frequencies	O
,	O
radiate	O
almost	O
none	O
of	O
their	O
energy	O
as	O
electromagnetic	O
radiation	O
.	O
</s>
<s>
At	O
large	O
relative	O
distance	O
,	O
the	O
near-field	B-Algorithm
components	O
of	O
electric	O
and	O
magnetic	O
fields	O
are	O
approximately	O
quasi-static	O
oscillating	O
dipole	O
fields	O
.	O
</s>
<s>
The	O
transmitter	O
and	O
receiver	O
coils	O
together	O
form	O
a	O
transformer	B-Algorithm
(	O
see	O
diagram	O
)	O
.	O
</s>
<s>
The	O
induced	O
alternating	O
current	O
may	O
either	O
drive	O
the	O
load	O
directly	O
,	O
or	O
be	O
rectified	B-Algorithm
to	O
direct	O
current	O
(	O
DC	O
)	O
by	O
a	O
rectifier	B-Algorithm
in	O
the	O
receiver	O
,	O
which	O
drives	O
the	O
load	O
.	O
</s>
<s>
Inductive	O
coupling	O
is	O
the	O
oldest	O
and	O
most	O
widely	O
used	O
wireless	B-Application
power	I-Application
technology	O
,	O
and	O
virtually	O
the	O
only	O
one	O
so	O
far	O
which	O
is	O
used	O
in	O
commercial	O
products	O
.	O
</s>
<s>
It	O
is	O
used	O
in	O
inductive	B-Application
charging	I-Application
stands	O
for	O
cordless	O
appliances	O
used	O
in	O
wet	O
environments	O
such	O
as	O
electric	O
toothbrushes	O
and	O
shavers	O
,	O
to	O
reduce	O
the	O
risk	O
of	O
electric	O
shock	O
.	O
</s>
<s>
Another	O
application	O
area	O
is	O
"	O
transcutaneous	O
"	O
recharging	O
of	O
biomedical	O
prosthetic	O
devices	O
implanted	O
in	O
the	O
human	O
body	O
,	O
such	O
as	O
cardiac	B-Device
pacemakers	I-Device
and	O
insulin	O
pumps	O
,	O
to	O
avoid	O
having	O
wires	O
passing	O
through	O
the	O
skin	O
.	O
</s>
<s>
However	O
the	O
fastest	O
growing	O
use	O
is	O
wireless	B-Application
charging	I-Application
pads	O
to	O
recharge	O
mobile	O
and	O
handheld	O
wireless	O
devices	O
such	O
as	O
laptop	B-Device
and	O
tablet	B-Device
computers	I-Device
,	O
computer	B-Device
mouse	I-Device
,	O
cellphones	O
,	O
digital	B-Application
media	I-Application
players	I-Application
,	O
and	O
video	B-Device
game	I-Device
controllers	I-Device
.	O
</s>
<s>
In	O
most	O
modern	O
inductive	O
systems	O
resonant	B-Architecture
inductive	I-Architecture
coupling	I-Architecture
(	O
described	O
below	O
)	O
is	O
used	O
,	O
in	O
which	O
the	O
efficiency	O
is	O
increased	O
by	O
using	O
resonant	O
circuits	O
.	O
</s>
<s>
Resonant	B-Architecture
inductive	I-Architecture
coupling	I-Architecture
(	O
electrodynamic	O
coupling	O
,	O
strongly	O
coupled	O
magnetic	O
resonance	B-Application
)	O
is	O
a	O
form	O
of	O
inductive	O
coupling	O
in	O
which	O
power	O
is	O
transferred	O
by	O
magnetic	O
fields	O
(	O
B	O
,	O
green	O
)	O
between	O
two	O
resonant	O
circuits	O
(	O
tuned	O
circuits	O
)	O
,	O
one	O
in	O
the	O
transmitter	O
and	O
one	O
in	O
the	O
receiver	O
(	O
see	O
diagram	O
,	O
right	O
)	O
.	O
</s>
<s>
The	O
resonance	B-Application
between	O
the	O
coils	O
can	O
greatly	O
increase	O
coupling	O
and	O
power	O
transfer	O
,	O
analogously	O
to	O
the	O
way	O
a	O
vibrating	O
tuning	O
fork	O
can	O
induce	O
sympathetic	O
vibration	O
in	O
a	O
distant	O
fork	O
tuned	O
to	O
the	O
same	O
pitch	O
.	O
</s>
<s>
Nikola	O
Tesla	O
first	O
discovered	O
resonant	B-Architecture
coupling	I-Architecture
during	O
his	O
pioneering	O
experiments	O
in	O
wireless	B-Application
power	I-Application
transfer	I-Application
around	O
the	O
turn	O
of	O
the	O
20th	O
century	O
,	O
but	O
the	O
possibilities	O
of	O
using	O
resonant	B-Architecture
coupling	I-Architecture
to	O
increase	O
transmission	O
range	O
has	O
only	O
recently	O
been	O
explored	O
.	O
</s>
<s>
The	O
concept	O
behind	O
resonant	B-Architecture
inductive	I-Architecture
coupling	I-Architecture
systems	O
is	O
that	O
high	O
Q	O
factor	O
resonators	O
exchange	O
energy	O
at	O
a	O
much	O
higher	O
rate	O
than	O
they	O
lose	O
energy	O
due	O
to	O
internal	O
damping	O
.	O
</s>
<s>
Therefore	O
,	O
by	O
using	O
resonance	B-Application
,	O
the	O
same	O
amount	O
of	O
power	O
can	O
be	O
transferred	O
at	O
greater	O
distances	O
,	O
using	O
the	O
much	O
weaker	O
magnetic	O
fields	O
out	O
in	O
the	O
peripheral	O
regions	O
(	O
"	O
tails	O
"	O
)	O
of	O
the	O
near	O
fields	O
.	O
</s>
<s>
Resonant	B-Architecture
inductive	I-Architecture
coupling	I-Architecture
can	O
achieve	O
high	O
efficiency	O
at	O
ranges	O
of	O
4	O
to	O
10	O
times	O
the	O
coil	O
diameter	O
(	O
Dant	O
)	O
.	O
</s>
<s>
A	O
drawback	O
of	O
resonant	B-Architecture
coupling	I-Architecture
theory	O
is	O
that	O
at	O
close	O
ranges	O
when	O
the	O
two	O
resonant	O
circuits	O
are	O
tightly	O
coupled	O
,	O
the	O
resonant	O
frequency	O
of	O
the	O
system	O
is	O
no	O
longer	O
constant	O
but	O
"	O
splits	O
"	O
into	O
two	O
resonant	O
peaks	O
,	O
so	O
the	O
maximum	O
power	O
transfer	O
no	O
longer	O
occurs	O
at	O
the	O
original	O
resonant	O
frequency	O
and	O
the	O
oscillator	O
frequency	O
must	O
be	O
tuned	O
to	O
the	O
new	O
resonance	B-Application
peak	O
.	O
</s>
<s>
Resonant	O
technology	O
is	O
currently	O
being	O
widely	O
incorporated	O
in	O
modern	O
inductive	O
wireless	B-Application
power	I-Application
systems	O
.	O
</s>
<s>
One	O
of	O
the	O
possibilities	O
envisioned	O
for	O
this	O
technology	O
is	O
area	O
wireless	B-Application
power	I-Application
coverage	O
.	O
</s>
<s>
An	O
environmental	O
and	O
economic	O
benefit	O
of	O
wirelessly	O
powering	O
small	O
devices	O
such	O
as	O
clocks	O
,	O
radios	O
,	O
music	O
players	O
and	O
remote	B-Protocol
controls	I-Protocol
is	O
that	O
it	O
could	O
drastically	O
reduce	O
the	O
6	O
billion	O
batteries	O
disposed	O
of	O
each	O
year	O
,	O
a	O
large	O
source	O
of	O
toxic	O
waste	O
and	O
groundwater	O
contamination	O
.	O
</s>
<s>
A	O
study	O
for	O
the	O
Swedish	O
military	O
found	O
that	O
85kHz	O
systems	O
for	O
dynamic	O
wireless	B-Application
power	I-Application
transfer	I-Application
for	O
vehicles	O
can	O
cause	O
electromagnetic	O
interference	O
at	O
a	O
radius	O
of	O
up	O
to	O
300	O
kilometers	O
.	O
</s>
<s>
Capacitive	O
coupling	O
has	O
recently	O
been	O
applied	O
to	O
charging	O
battery	O
powered	O
portable	O
devices	O
as	O
well	O
as	O
charging	O
or	O
continuous	O
wireless	B-Application
power	I-Application
transfer	I-Application
in	O
biomedical	O
implants	O
,	O
and	O
is	O
being	O
considered	O
as	O
a	O
means	O
of	O
transferring	O
power	O
between	O
substrate	O
layers	O
in	O
integrated	O
circuits	O
.	O
</s>
<s>
A	O
disadvantage	O
of	O
this	O
configuration	O
for	O
wireless	B-Application
charging	I-Application
is	O
that	O
the	O
two	O
plates	O
in	O
the	O
receiving	O
device	O
must	O
be	O
aligned	O
face	O
to	O
face	O
with	O
the	O
charger	O
plates	O
for	O
the	O
device	O
to	O
work	O
.	O
</s>
<s>
Resonance	B-Application
can	O
also	O
be	O
used	O
with	O
capacitive	O
coupling	O
to	O
extend	O
the	O
range	O
.	O
</s>
<s>
An	O
electrodynamic	O
wireless	B-Application
power	I-Application
transfer	I-Application
(	O
EWPT	O
)	O
system	O
utilizes	O
a	O
receiver	O
with	O
a	O
mechanically	O
resonating	O
or	O
rotating	O
permanent	O
magnet	O
.	O
</s>
<s>
For	O
coupled	O
resonators	O
with	O
same	O
resonant	O
frequencies	O
,	O
wireless	B-Application
power	I-Application
transfer	I-Application
between	O
the	O
transmitter	O
and	O
the	O
receiver	O
is	O
spread	O
over	O
three	O
regimes	O
–	O
under-coupled	O
,	O
critically	O
coupled	O
and	O
over-coupled	O
.	O
</s>
<s>
The	O
transmitter	O
armature	O
is	O
turned	O
either	O
by	O
or	O
as	O
the	O
rotor	O
of	O
an	O
electric	O
motor	O
,	O
and	O
its	O
magnetic	O
field	O
exerts	O
torque	B-General_Concept
on	O
the	O
receiver	O
armature	O
,	O
turning	O
it	O
.	O
</s>
<s>
Far	B-Algorithm
field	I-Algorithm
methods	O
achieve	O
longer	O
ranges	O
,	O
often	O
multiple	O
kilometer	O
ranges	O
,	O
where	O
the	O
distance	O
is	O
much	O
greater	O
than	O
the	O
diameter	O
of	O
the	O
device(s )	O
.	O
</s>
<s>
Airy	O
's	O
diffraction	O
limit	O
is	O
also	O
frequently	O
used	O
to	O
determine	O
an	O
approximate	O
spot	O
size	O
at	O
an	O
arbitrary	O
distance	O
from	O
the	O
aperture	B-General_Concept
.	O
</s>
<s>
The	O
Rayleigh	O
limit	O
(	O
also	O
known	O
as	O
the	O
Abbe	O
diffraction	O
limit	O
)	O
,	O
although	O
originally	O
applied	O
to	O
image	O
resolution	O
,	O
can	O
be	O
viewed	O
in	O
reverse	O
,	O
and	O
dictates	O
that	O
the	O
irradiance	O
(	O
or	O
intensity	O
)	O
of	O
any	O
electromagnetic	O
wave	O
(	O
such	O
as	O
a	O
microwave	O
or	O
laser	O
beam	O
)	O
will	O
be	O
reduced	O
as	O
the	O
beam	O
diverges	O
over	O
distance	O
at	O
a	O
minimum	O
rate	O
inversely	O
proportional	O
to	O
the	O
aperture	B-General_Concept
size	O
.	O
</s>
<s>
Microwave	O
power	B-Application
beaming	I-Application
can	O
be	O
more	O
efficient	O
than	O
lasers	O
,	O
and	O
is	O
less	O
prone	O
to	O
atmospheric	O
attenuation	O
caused	O
by	O
dust	O
or	O
aerosols	O
such	O
as	O
fog	O
.	O
</s>
<s>
Power	O
transmission	O
via	O
radio	O
waves	O
can	O
be	O
made	O
more	O
directional	O
,	O
allowing	O
longer-distance	O
power	B-Application
beaming	I-Application
,	O
with	O
shorter	O
wavelengths	O
of	O
electromagnetic	O
radiation	O
,	O
typically	O
in	O
the	O
microwave	O
range	O
.	O
</s>
<s>
Power	B-Application
beaming	I-Application
using	O
microwaves	O
has	O
been	O
proposed	O
for	O
the	O
transmission	O
of	O
energy	O
from	O
orbiting	O
solar	O
power	O
satellites	O
to	O
Earth	O
and	O
the	O
beaming	O
of	O
power	O
to	O
spacecraft	O
leaving	O
orbit	O
has	O
been	O
considered	O
.	O
</s>
<s>
Power	B-Application
beaming	I-Application
by	O
microwaves	O
has	O
the	O
difficulty	O
that	O
,	O
for	O
most	O
space	O
applications	O
,	O
the	O
required	O
aperture	B-General_Concept
sizes	O
are	O
very	O
large	O
due	O
to	O
diffraction	O
limiting	O
antenna	O
directionality	O
.	O
</s>
<s>
Following	O
World	O
War	O
II	O
,	O
which	O
saw	O
the	O
development	O
of	O
high-power	O
microwave	O
emitters	O
known	O
as	O
cavity	B-Device
magnetrons	I-Device
,	O
the	O
idea	O
of	O
using	O
microwaves	O
to	O
transfer	O
power	O
was	O
researched	O
.	O
</s>
<s>
Japanese	O
researcher	O
Hidetsugu	O
Yagi	O
also	O
investigated	O
wireless	B-Application
energy	I-Application
transmission	I-Application
using	O
a	O
directional	O
array	O
antenna	O
that	O
he	O
designed	O
.	O
</s>
<s>
In	O
2013	O
,	O
inventor	O
Hatem	O
Zeine	O
demonstrated	O
how	O
wireless	B-Application
power	I-Application
transmission	I-Application
using	O
phased	O
array	O
antennas	O
can	O
deliver	O
electrical	O
power	O
up	O
to	O
30	O
feet	O
.	O
</s>
<s>
In	O
2017	O
,	O
the	O
Federal	O
Communications	O
Commission	O
(	O
FCC	O
)	O
certified	O
the	O
first	O
mid-field	O
radio	O
frequency	O
(	O
RF	O
)	O
transmitter	O
of	O
wireless	B-Application
power	I-Application
.	O
</s>
<s>
In	O
2021	O
the	O
FCC	O
granted	O
a	O
license	O
to	O
a	O
over-the-air	O
(	O
OTA	O
)	O
wireless	B-Application
charging	I-Application
system	O
that	O
combines	O
near-field	B-Algorithm
and	O
far-field	B-Algorithm
methods	O
by	O
using	O
a	O
frequency	O
of	O
about	O
900MHz	O
.	O
</s>
<s>
Due	O
to	O
the	O
radiated	O
power	O
of	O
about	O
1	O
W	O
this	O
system	O
is	O
intended	O
for	O
small	O
IoT	B-Operating_System
devices	O
as	O
various	O
sensors	O
,	O
trackers	O
,	O
detectors	O
and	O
monitors	O
.	O
</s>
<s>
This	O
mechanism	O
is	O
generally	O
known	O
as	O
'	O
power	B-Application
beaming	I-Application
 '	O
because	O
the	O
power	O
is	O
beamed	O
at	O
a	O
receiver	O
that	O
can	O
convert	O
it	O
to	O
electrical	O
energy	O
.	O
</s>
<s>
Wireless	B-Application
energy	I-Application
transfer	I-Application
systems	O
using	O
lasers	O
for	O
consumer	O
space	O
have	O
to	O
satisfy	O
laser	O
safety	O
requirements	O
standardized	O
under	O
IEC	O
60825	O
.	O
</s>
<s>
The	O
first	O
wireless	B-Application
power	I-Application
system	O
using	O
lasers	O
for	O
consumer	O
applications	O
was	O
demonstrated	O
in	O
2018	O
,	O
capable	O
of	O
delivering	O
power	O
to	O
stationary	O
and	O
moving	O
devices	O
across	O
a	O
room	O
.	O
</s>
<s>
This	O
wireless	B-Application
power	I-Application
system	O
complies	O
with	O
safety	O
regulations	O
according	O
to	O
IEC	O
60825	O
standard	O
.	O
</s>
<s>
In	O
the	O
context	O
of	O
wireless	B-Application
power	I-Application
,	O
energy	O
harvesting	O
,	O
also	O
called	O
power	O
harvesting	O
or	O
energy	O
scavenging	O
,	O
is	O
the	O
conversion	O
of	O
ambient	O
energy	O
from	O
the	O
environment	O
to	O
electric	O
power	O
,	O
mainly	O
to	O
power	O
small	O
autonomous	O
wireless	O
electronic	O
devices	O
.	O
</s>
<s>
Although	O
the	O
efficiency	O
of	O
conversion	O
is	O
usually	O
low	O
and	O
the	O
power	O
gathered	O
often	O
minuscule	O
(	O
milliwatts	O
or	O
microwatts	O
)	O
,	O
it	O
can	O
be	O
adequate	O
to	O
run	O
or	O
recharge	O
small	O
micropower	O
wireless	O
devices	O
such	O
as	O
remote	B-Application
sensors	I-Application
,	O
which	O
are	O
proliferating	O
in	O
many	O
fields	O
.	O
</s>
<s>
Around	O
1884	O
John	O
Henry	O
Poynting	O
defined	O
the	O
Poynting	O
vector	O
and	O
gave	O
Poynting	O
's	O
theorem	O
,	O
which	O
describe	O
the	O
flow	O
of	O
power	O
across	O
an	O
area	O
within	O
electromagnetic	O
radiation	O
and	O
allow	O
for	O
a	O
correct	O
analysis	O
of	O
wireless	B-Application
power	I-Application
transfer	I-Application
systems	O
.	O
</s>
<s>
After	O
1890	O
,	O
inventor	O
Nikola	O
Tesla	O
experimented	O
with	O
transmitting	O
power	O
by	O
inductive	O
and	O
capacitive	O
coupling	O
using	O
spark-excited	O
radio	O
frequency	O
resonant	O
transformers	B-Algorithm
,	O
now	O
called	O
Tesla	O
coils	O
,	O
which	O
generated	O
high	O
AC	O
voltages	O
.	O
</s>
<s>
Early	O
on	O
he	O
attempted	O
to	O
develop	O
a	O
wireless	O
lighting	O
system	O
based	O
on	O
near-field	B-Algorithm
inductive	O
and	O
capacitive	O
coupling	O
and	O
conducted	O
a	O
series	O
of	O
public	O
demonstrations	O
where	O
he	O
lit	O
Geissler	O
tubes	O
and	O
even	O
incandescent	O
light	O
bulbs	O
from	O
across	O
a	O
stage	O
.	O
</s>
<s>
He	O
found	O
he	O
could	O
increase	O
the	O
distance	O
at	O
which	O
he	O
could	O
light	O
a	O
lamp	O
by	O
using	O
a	O
receiving	O
LC	O
circuit	O
tuned	O
to	O
resonance	B-Application
with	O
the	O
transmitter	O
's	O
LC	O
circuit	O
.	O
</s>
<s>
using	O
resonant	B-Architecture
inductive	I-Architecture
coupling	I-Architecture
.	O
</s>
<s>
Tesla	O
failed	O
to	O
make	O
a	O
commercial	O
product	O
out	O
of	O
his	O
findings	O
but	O
his	O
resonant	B-Architecture
inductive	I-Architecture
coupling	I-Architecture
method	O
is	O
now	O
widely	O
used	O
in	O
electronics	O
and	O
is	O
currently	O
being	O
applied	O
to	O
short-range	O
wireless	B-Application
power	I-Application
systems	O
.	O
</s>
<s>
Tesla	O
went	O
on	O
to	O
develop	O
a	O
wireless	B-Application
power	I-Application
distribution	O
system	O
that	O
he	O
hoped	O
would	O
be	O
capable	O
of	O
transmitting	O
power	O
long	O
distance	O
directly	O
into	O
homes	O
and	O
factories	O
.	O
</s>
<s>
Tesla	O
thought	O
this	O
would	O
allow	O
alternating	O
current	O
to	O
be	O
received	O
with	O
a	O
similar	O
capacitive	O
antenna	O
tuned	O
to	O
resonance	B-Application
with	O
it	O
at	O
any	O
point	O
on	O
Earth	O
with	O
very	O
little	O
power	O
loss	O
.	O
</s>
<s>
In	O
1901	O
,	O
at	O
Shoreham	O
,	O
New	O
York	O
he	O
attempted	O
to	O
construct	O
a	O
large	O
high-voltage	O
wireless	B-Application
power	I-Application
station	O
,	O
now	O
called	O
Wardenclyffe	O
Tower	O
,	O
but	O
by	O
1904	O
investment	O
dried	O
up	O
and	O
the	O
facility	O
was	O
never	O
completed	O
.	O
</s>
<s>
Inductive	O
power	O
transfer	O
between	O
nearby	O
wire	O
coils	O
was	O
the	O
earliest	O
wireless	B-Application
power	I-Application
technology	O
to	O
be	O
developed	O
,	O
existing	O
since	O
the	O
transformer	B-Algorithm
was	O
developed	O
in	O
the	O
1800s	O
.	O
</s>
<s>
With	O
the	O
advent	O
of	O
cordless	O
devices	O
,	O
induction	B-Application
charging	I-Application
stands	O
have	O
been	O
developed	O
for	O
appliances	O
used	O
in	O
wet	O
environments	O
,	O
like	O
electric	O
toothbrushes	O
and	O
electric	O
razors	O
,	O
to	O
eliminate	O
the	O
hazard	O
of	O
electric	O
shock	O
.	O
</s>
<s>
In	O
the	O
early	O
1960s	O
resonant	O
inductive	O
wireless	B-Application
energy	I-Application
transfer	I-Application
was	O
used	O
successfully	O
in	O
implantable	O
medical	O
devices	O
including	O
such	O
devices	O
as	O
pacemakers	B-Device
and	O
artificial	O
hearts	O
.	O
</s>
<s>
The	O
first	O
passive	B-Application
RFID	I-Application
(	O
Radio	B-Application
Frequency	I-Application
Identification	I-Application
)	O
technologies	O
were	O
invented	O
by	O
Mario	O
Cardullo	O
(	O
1973	O
)	O
and	O
Koelle	O
et	O
al	O
.	O
</s>
<s>
The	O
proliferation	O
of	O
portable	O
wireless	O
communication	O
devices	O
such	O
as	O
mobile	O
phones	O
,	O
tablet	B-Device
,	O
and	O
laptop	B-Device
computers	I-Device
in	O
recent	O
decades	O
is	O
currently	O
driving	O
the	O
development	O
of	O
mid-range	O
wireless	O
powering	O
and	O
charging	O
technology	O
to	O
eliminate	O
the	O
need	O
for	O
these	O
devices	O
to	O
be	O
tethered	O
to	O
wall	O
plugs	O
during	O
charging	O
.	O
</s>
<s>
The	O
Wireless	B-Application
Power	I-Application
Consortium	O
was	O
established	O
in	O
2008	O
to	O
develop	O
interoperable	O
standards	O
across	O
manufacturers	O
.	O
</s>
<s>
In	O
2007	O
,	O
a	O
team	O
led	O
by	O
Marin	O
Soljačić	O
at	O
MIT	O
used	O
a	O
dual	O
resonance	B-Application
transmitter	O
with	O
a	O
25cm	O
diameter	O
secondary	O
tuned	O
to	O
10MHz	O
to	O
transfer	O
60	O
W	O
of	O
power	O
to	O
a	O
similar	O
dual	O
resonance	B-Application
receiver	O
over	O
a	O
distance	O
of	O
(	O
eight	O
times	O
the	O
transmitter	O
coil	O
diameter	O
)	O
at	O
around	O
40%	O
efficiency	O
.	O
</s>
<s>
In	O
2008	O
the	O
team	O
of	O
Greg	O
Leyh	O
and	O
Mike	O
Kennan	O
of	O
Nevada	O
Lightning	O
Lab	O
used	O
a	O
grounded	O
dual	O
resonance	B-Application
transmitter	O
with	O
a	O
57cm	O
diameter	O
secondary	O
tuned	O
to	O
60kHz	O
and	O
a	O
similar	O
grounded	O
dual	O
resonance	B-Application
receiver	O
to	O
transfer	O
power	O
through	O
coupled	O
electric	O
fields	O
with	O
an	O
earth	O
current	O
return	O
circuit	O
over	O
a	O
distance	O
of	O
.	O
</s>
<s>
Before	O
World	O
War	O
II	O
,	O
little	O
progress	O
was	O
made	O
in	O
wireless	B-Application
power	I-Application
transmission	I-Application
.	O
</s>
<s>
The	O
development	O
of	O
microwave	O
technology	O
during	O
World	O
War	O
II	O
,	O
such	O
as	O
the	O
klystron	O
and	O
magnetron	B-Device
tubes	O
and	O
parabolic	O
antennas	O
,	O
made	O
radiative	O
(	O
far-field	B-Algorithm
)	O
methods	O
practical	O
for	O
the	O
first	O
time	O
,	O
and	O
the	O
first	O
long-distance	O
wireless	B-Application
power	I-Application
transmission	I-Application
was	O
achieved	O
in	O
the	O
1960s	O
by	O
William	O
C	O
.	O
Brown	O
.	O
</s>
