<s>
Resonant	B-Architecture
inductive	I-Architecture
coupling	I-Architecture
or	O
magnetic	B-Architecture
phase	I-Architecture
synchronous	I-Architecture
coupling	I-Architecture
is	O
a	O
phenomenon	O
with	O
inductive	O
coupling	O
in	O
which	O
the	O
coupling	O
becomes	O
stronger	O
when	O
the	O
"	O
secondary	O
"	O
(	O
load-bearing	O
)	O
side	O
of	O
the	O
loosely	O
coupled	O
coil	O
resonates	O
.	O
</s>
<s>
A	O
resonant	O
transformer	B-Algorithm
of	O
this	O
type	O
is	O
often	O
used	O
in	O
analog	O
circuitry	O
as	O
a	O
bandpass	O
filter	O
.	O
</s>
<s>
Resonant	B-Architecture
inductive	I-Architecture
coupling	I-Architecture
is	O
also	O
used	O
in	O
wireless	B-Application
power	I-Application
systems	O
for	O
portable	O
computers	O
,	O
phones	O
,	O
and	O
vehicles	O
.	O
</s>
<s>
Various	O
resonant	B-Architecture
coupling	I-Architecture
systems	O
in	O
use	O
or	O
are	O
under	O
development	O
for	O
short	O
range	O
(	O
up	O
to	O
2	O
meters	O
)	O
wireless	B-Application
electricity	I-Application
systems	O
to	O
power	O
laptops	O
,	O
tablets	O
,	O
smartphones	O
,	O
robot	O
vacuums	O
,	O
implanted	O
medical	O
devices	O
,	O
and	O
vehicles	O
like	O
electric	O
cars	O
,	O
SCMaglev	O
trains	O
and	O
automated	O
guided	O
vehicles	O
.	O
</s>
<s>
Data	O
transmission	O
such	O
as	O
with	O
passive	B-Application
RFID	I-Application
tags	O
(	O
for	O
example	O
in	O
a	O
passport	B-Protocol
)	O
and	O
contactless	O
smart	O
cards	O
.	O
</s>
<s>
Resonant	O
transformer	B-Algorithm
of	O
CCFL	O
inverter	O
that	O
powers	O
a	O
cold-cathode	O
fluorescent	O
lamp	O
.	O
</s>
<s>
Couple	O
the	O
stages	O
of	O
a	O
superheterodyne	O
receiver	O
,	O
where	O
the	O
selectivity	O
of	O
the	O
receiver	O
is	O
provided	O
by	O
tuned	B-Algorithm
transformers	I-Algorithm
in	I-Algorithm
the	I-Algorithm
intermediate-frequency	I-Algorithm
amplifiers	I-Algorithm
.	O
</s>
<s>
High	O
voltage	O
(	O
one	O
million	O
volt	O
)	O
sources	O
for	O
X-ray	B-Library
production	O
.	O
</s>
<s>
The	O
Tesla	O
coil	O
is	O
a	O
resonant	O
transformer	B-Algorithm
circuit	O
used	O
to	O
generate	O
very	O
high	O
voltages	O
,	O
and	O
is	O
able	O
to	O
provide	O
much	O
higher	O
current	O
than	O
high	O
voltage	O
electrostatic	B-Algorithm
machines	I-Algorithm
such	O
as	O
the	O
Van	O
de	O
Graaff	O
generator	O
.	O
</s>
<s>
However	O
,	O
this	O
type	O
of	O
system	O
radiates	O
most	O
of	O
its	O
energy	O
into	O
empty	O
space	O
,	O
unlike	O
modern	O
wireless	B-Application
power	I-Application
systems	O
which	O
waste	O
very	O
little	O
energy	O
.	O
</s>
<s>
Resonant	O
transformers	B-Algorithm
are	O
widely	O
used	O
in	O
radio	O
circuits	O
as	O
bandpass	O
filters	O
,	O
and	O
in	O
switching	O
power	O
supplies	O
.	O
</s>
<s>
In	O
1894	O
Nikola	O
Tesla	O
used	O
resonant	B-Architecture
inductive	I-Architecture
coupling	I-Architecture
,	O
also	O
known	O
as	O
"	O
electro-dynamic	O
induction	O
"	O
to	O
wirelessly	O
light	O
up	O
phosphorescent	O
and	O
incandescent	O
lamps	O
at	O
the	O
35	O
South	O
Fifth	O
Avenue	O
laboratory	O
,	O
and	O
later	O
at	O
the	O
46	O
E	O
.	O
Houston	O
Street	O
laboratory	O
in	O
New	O
York	O
City	O
.	O
</s>
<s>
In	O
1897	O
he	O
patented	O
a	O
device	O
called	O
the	O
high-voltage	O
,	O
resonant	O
transformer	B-Algorithm
or	O
"	O
Tesla	O
coil.	O
"	O
</s>
<s>
Transferring	O
electrical	O
energy	O
from	O
the	O
primary	O
coil	O
to	O
the	O
secondary	O
coil	O
by	O
resonant	O
induction	O
,	O
a	O
Tesla	O
coil	O
is	O
capable	O
of	O
producing	O
very	O
high	O
voltages	O
at	O
high	B-Algorithm
frequency	I-Algorithm
.	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	O
and	O
artificial	O
hearts	O
.	O
</s>
<s>
Wireless	B-Application
electric	I-Application
energy	I-Application
transfer	I-Application
for	O
experimentally	O
powering	O
electric	O
automobiles	O
and	O
buses	O
is	O
a	O
higher	O
power	O
application	O
(	O
>10kW	O
)	O
of	O
resonant	O
inductive	O
energy	O
transfer	O
.	O
</s>
<s>
In	O
1998	O
,	O
RFID	B-Application
tags	I-Application
were	O
patented	O
that	O
were	O
powered	O
in	O
this	O
way	O
.	O
</s>
<s>
In	O
November	O
2006	O
,	O
Marin	O
Soljačić	O
and	O
other	O
researchers	O
at	O
the	O
Massachusetts	O
Institute	O
of	O
Technology	O
applied	O
this	O
near	B-Algorithm
field	I-Algorithm
behavior	O
to	O
wireless	B-Application
power	I-Application
transmission	I-Application
,	O
based	O
on	O
strongly-coupled	O
resonators	O
.	O
</s>
<s>
In	O
a	O
theoretical	O
analysis	O
,	O
they	O
demonstrate	O
that	O
,	O
by	O
designing	O
electromagnetic	O
resonators	O
that	O
suffer	O
minimal	O
loss	O
due	O
to	O
radiation	O
and	O
absorption	O
and	O
have	O
a	O
near	B-Algorithm
field	I-Algorithm
with	O
mid-range	O
extent	O
(	O
namely	O
a	O
few	O
times	O
the	O
resonator	O
size	O
)	O
,	O
mid-range	O
efficient	O
wireless	O
energy-transfer	O
is	O
possible	O
.	O
</s>
<s>
The	O
reason	O
is	O
that	O
,	O
if	O
two	O
such	O
resonant	O
circuits	O
tuned	O
to	O
the	O
same	O
frequency	O
are	O
within	O
a	O
fraction	O
of	O
a	O
wavelength	O
,	O
their	O
near	B-Algorithm
fields	I-Algorithm
(	O
consisting	O
of	O
'	O
evanescent	O
waves	O
 '	O
)	O
couple	O
by	O
means	O
of	O
evanescent	O
wave	O
coupling	O
.	O
</s>
<s>
In	O
2011	O
,	O
they	O
succeeded	O
in	O
powering	O
while	O
driving	O
(	O
CWD:charge	O
while	O
driving	O
)	O
across	O
a	O
large	O
gap	O
by	O
the	O
JR	O
Tokai	O
proprietary	O
9.8kHz	O
phase	O
synchronization	O
technology	O
developed	O
based	O
on	O
technology	O
similar	O
to	O
AGV	O
's	O
wireless	B-Application
power	I-Application
scheme	O
.	O
</s>
<s>
Non-resonant	O
coupled	O
inductors	O
,	O
such	O
as	O
typical	O
transformers	B-Algorithm
,	O
work	O
on	O
the	O
principle	O
of	O
a	O
primary	O
coil	O
generating	O
a	O
magnetic	O
field	O
and	O
a	O
secondary	O
coil	O
subtending	O
as	O
much	O
as	O
possible	O
of	O
that	O
field	O
so	O
that	O
the	O
power	O
passing	O
through	O
the	O
secondary	O
is	O
as	O
close	O
as	O
possible	O
to	O
that	O
of	O
the	O
primary	O
.	O
</s>
<s>
If	O
resonant	B-Architecture
coupling	I-Architecture
is	O
used	O
,	O
the	O
secondary	O
coil	O
is	O
capacitive	O
loaded	O
so	O
as	O
to	O
form	O
a	O
tuned	O
LC	O
circuit	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>
This	O
process	O
occurs	O
in	O
a	O
resonant	O
transformer	B-Algorithm
,	O
an	O
electrical	O
component	O
which	O
transformer	B-Algorithm
consists	O
of	O
high	O
Q	O
coil	O
wound	O
on	O
the	O
same	O
core	O
with	O
a	O
capacitor	O
connected	O
across	O
a	O
coil	O
to	O
make	O
a	O
coupled	O
LC	O
circuit	O
.	O
</s>
<s>
The	O
most	O
basic	O
resonant	B-Architecture
inductive	I-Architecture
coupling	I-Architecture
consists	O
of	O
one	O
drive	O
coil	O
on	O
the	O
primary	O
side	O
and	O
one	O
resonance	O
circuit	O
on	O
the	O
secondary	O
side	O
.	O
</s>
<s>
The	O
resonant	B-Architecture
inductive	I-Architecture
coupling	I-Architecture
is	O
the	O
near	B-Algorithm
field	I-Algorithm
wireless	B-Application
transmission	I-Application
of	I-Application
electrical	I-Application
energy	I-Application
between	O
magnetically	O
coupled	O
coils	O
,	O
which	O
is	O
part	O
of	O
a	O
resonant	O
circuit	O
tuned	O
to	O
resonate	O
at	O
the	O
same	O
frequency	O
as	O
the	O
driving	O
frequency	O
.	O
</s>
<s>
In	O
the	O
transformer	B-Algorithm
,	O
only	O
part	O
of	O
the	O
flux	O
generated	O
by	O
current	O
through	O
the	O
primary	O
coil	O
is	O
coupled	O
to	O
the	O
secondary	O
coil	O
and	O
vice	O
versa	O
.	O
</s>
<s>
The	O
coupling	O
coefficient	O
,	O
,	O
is	O
defined	O
as	O
the	O
ratio	O
of	O
transformer	B-Algorithm
open-circuit	O
voltage	O
ratio	O
to	O
the	O
ratio	O
that	O
would	O
be	O
obtained	O
if	O
all	O
the	O
flux	O
coupled	O
from	O
one	O
coil	O
to	O
the	O
other	O
.	O
</s>
<s>
Tight	O
coupling	O
is	O
when	O
the	O
coupling	O
coefficient	O
is	O
around	O
1	O
as	O
with	O
conventional	O
iron-core	O
transformers	B-Algorithm
.	O
</s>
<s>
In	O
Tesla	O
coils	O
around	O
0.2	O
is	O
used	O
,	O
and	O
at	O
greater	O
distances	O
,	O
for	O
example	O
for	O
inductive	O
wireless	B-Application
power	I-Application
transmission	I-Application
,	O
it	O
may	O
be	O
lower	O
than	O
0.01	O
.	O
</s>
<s>
However	O
,	O
if	O
in	O
the	O
state	O
of	O
resonant	B-Architecture
coupling	I-Architecture
,	O
higher	O
voltage	O
is	O
generated	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
the	O
type	O
on	O
the	O
left	O
figure	O
,	O
the	O
general	O
principle	O
is	O
that	O
if	O
a	O
given	O
oscillating	O
amount	O
of	O
energy	O
(	O
for	O
example	O
a	O
pulse	O
or	O
a	O
series	O
of	O
pulses	O
)	O
is	O
placed	O
into	O
a	O
primary	O
coil	O
which	O
is	O
capacitively	O
loaded	O
,	O
the	O
coil	O
will	O
'	O
ring	B-Algorithm
 '	O
,	O
and	O
form	O
an	O
oscillating	O
magnetic	O
field	O
.	O
</s>
<s>
Resonant	O
transfer	O
works	O
by	O
making	O
a	O
coil	O
ring	B-Algorithm
with	O
an	O
oscillating	O
current	O
.	O
</s>
<s>
The	O
fields	O
used	O
are	O
predominantly	O
non-radiative	O
,	O
near	B-Algorithm
fields	I-Algorithm
(	O
sometimes	O
called	O
evanescent	O
waves	O
)	O
,	O
as	O
all	O
hardware	O
is	O
kept	O
well	O
within	O
the	O
1/4	O
wavelength	O
distance	O
they	O
radiate	O
little	O
energy	O
from	O
the	O
transmitter	O
to	O
infinity	O
.	O
</s>
<s>
Unlike	O
the	O
multiple-layer	O
secondary	O
of	O
a	O
non-resonant	O
transformer	B-Algorithm
,	O
coils	O
for	O
this	O
purpose	O
are	O
often	O
single	O
layer	O
solenoids	B-Algorithm
(	O
to	O
minimise	O
skin	O
effect	O
and	O
give	O
improved	O
Q	O
)	O
in	O
parallel	O
with	O
a	O
suitable	O
capacitor	O
.	O
</s>
<s>
To	O
remove	O
energy	O
from	O
the	O
secondary	O
coil	O
,	O
different	O
methods	O
can	O
be	O
used	O
,	O
the	O
AC	O
can	O
be	O
used	O
directly	O
or	O
rectified	B-Algorithm
and	O
a	O
regulator	O
circuit	O
can	O
be	O
used	O
to	O
generate	O
DC	O
voltage	O
.	O
</s>
