<s>
Electromagnetic	B-Algorithm
acoustic	I-Algorithm
transducer	I-Algorithm
(	O
EMAT	B-Algorithm
)	O
is	O
a	O
transducer	B-Algorithm
for	O
non-contact	O
acoustic	O
wave	O
generation	O
and	O
reception	O
in	O
conducting	O
materials	O
.	O
</s>
<s>
Due	O
to	O
this	O
couplant-free	O
feature	O
,	O
EMATs	B-Algorithm
are	O
particularly	O
useful	O
in	O
harsh	O
,	O
i.e.	O
,	O
hot	O
,	O
cold	O
,	O
clean	O
,	O
or	O
dry	O
environments	O
.	O
</s>
<s>
EMATs	B-Algorithm
are	O
suitable	O
to	O
generate	O
all	O
kinds	O
of	O
waves	O
in	O
metallic	O
and/or	O
magnetostrictive	O
materials	O
.	O
</s>
<s>
After	O
decades	O
of	O
research	O
and	O
development	O
,	O
EMAT	B-Algorithm
has	O
found	O
its	O
applications	O
in	O
many	O
industries	O
such	O
as	O
primary	O
metal	O
manufacturing	O
and	O
processing	O
,	O
automotive	O
,	O
railroad	O
,	O
pipeline	O
,	O
boiler	O
and	O
pressure	O
vessel	O
industries	O
,	O
in	O
which	O
they	O
are	O
typically	O
used	O
for	O
nondestructive	O
testing	O
(	O
NDT	O
)	O
of	O
metallic	O
structures	O
.	O
</s>
<s>
There	O
are	O
two	O
basic	O
components	O
in	O
an	O
EMAT	B-Algorithm
transducer	B-Algorithm
.	O
</s>
<s>
In	O
EMAT	B-Algorithm
terminology	O
,	O
this	O
field	O
is	O
called	O
bias	O
magnetic	O
field	O
.	O
</s>
<s>
The	O
electric	O
coil	O
is	O
driven	O
with	O
an	O
alternating	O
current	O
(	O
AC	O
)	O
electric	O
signal	O
at	O
ultrasonic	B-Application
frequency	O
,	O
typically	O
in	O
the	O
range	O
from	O
20kHz	O
to	O
10MHz	O
.	O
</s>
<s>
When	O
the	O
test	O
material	O
is	O
close	O
to	O
the	O
EMAT	B-Algorithm
,	O
ultrasonic	B-Application
waves	O
are	O
generated	O
in	O
the	O
test	O
material	O
through	O
the	O
interaction	O
of	O
the	O
two	O
magnetic	O
fields	O
.	O
</s>
<s>
The	O
distribution	O
of	O
Lorentz	O
force	O
is	O
primarily	O
controlled	O
by	O
the	O
design	O
of	O
magnet	O
and	O
design	O
of	O
the	O
electric	O
coil	O
,	O
and	O
is	O
affected	O
by	O
the	O
properties	O
of	O
the	O
test	O
material	O
,	O
the	O
relative	O
position	O
between	O
the	O
transducer	B-Algorithm
and	O
the	O
test	O
part	O
,	O
and	O
the	O
excitation	O
signal	O
for	O
the	O
transducer	B-Algorithm
.	O
</s>
<s>
A	O
majority	O
of	O
successful	O
EMAT	B-Algorithm
applications	O
are	O
based	O
on	O
the	O
Lorentz	O
force	O
mechanism	O
.	O
</s>
<s>
The	O
AC	O
current	O
in	O
the	O
electric	O
coil	O
induces	O
an	O
AC	O
magnetic	O
field	O
and	O
thus	O
produces	O
magnetostriction	O
at	O
ultrasonic	B-Application
frequency	O
in	O
the	O
material	O
.	O
</s>
<s>
The	O
disturbances	O
caused	O
by	O
magnetostriction	O
then	O
propagate	O
in	O
the	O
material	O
as	O
an	O
ultrasound	B-Application
wave	O
.	O
</s>
<s>
As	O
an	O
ultrasonic	B-Application
testing	O
(	O
UT	O
)	O
method	O
,	O
EMAT	B-Algorithm
has	O
all	O
the	O
advantages	O
of	O
UT	O
compared	O
to	O
other	O
NDT	O
methods	O
.	O
</s>
<s>
Just	O
like	O
piezoelectric	O
UT	O
probes	O
,	O
EMAT	B-Algorithm
probes	O
can	O
be	O
used	O
in	O
pulse-echo	O
,	O
pitch-catch	O
,	O
and	O
through-transmission	O
configurations	O
.	O
</s>
<s>
EMAT	B-Algorithm
probes	O
can	O
also	O
be	O
assembled	O
into	O
phased	O
array	O
probes	O
,	O
delivering	O
focusing	O
and	O
beam	O
steering	O
capabilities	O
.	O
</s>
<s>
Compared	O
to	O
piezoelectric	O
transducers	B-Algorithm
,	O
EMAT	B-Algorithm
probes	O
have	O
the	O
following	O
advantages	O
:	O
</s>
<s>
Based	O
on	O
the	O
transduction	B-Algorithm
mechanism	O
of	O
EMAT	B-Algorithm
,	O
couplant	O
is	O
not	O
required	O
.	O
</s>
<s>
This	O
makes	O
EMAT	B-Algorithm
ideal	O
for	O
inspections	O
at	O
temperatures	O
below	O
the	O
freezing	O
point	O
and	O
above	O
the	O
evaporation	O
point	O
of	O
liquid	O
couplants	O
.	O
</s>
<s>
EMAT	B-Algorithm
is	O
a	O
non-contact	O
method	O
.	O
</s>
<s>
Although	O
proximity	O
is	O
preferred	O
,	O
a	O
physical	O
contact	O
between	O
the	O
transducer	B-Algorithm
and	O
the	O
specimen	O
under	O
test	O
is	O
not	O
required	O
.	O
</s>
<s>
Since	O
no	O
couplant	O
is	O
needed	O
,	O
the	O
EMAT	B-Algorithm
inspection	O
can	O
be	O
performed	O
in	O
a	O
dry	O
environment	O
.	O
</s>
<s>
With	O
contact-based	O
piezoelectric	O
transducers	B-Algorithm
,	O
the	O
test	O
surface	O
has	O
to	O
be	O
machined	O
smoothly	O
to	O
ensure	O
coupling	O
.	O
</s>
<s>
Using	O
EMAT	B-Algorithm
,	O
the	O
requirements	O
to	O
surface	O
smoothness	O
are	O
less	O
stringent	O
;	O
the	O
only	O
requirement	O
is	O
to	O
remove	O
loose	O
scale	O
and	O
the	O
like	O
.	O
</s>
<s>
Using	O
piezoelectric	O
transducer	B-Algorithm
,	O
the	O
wave	O
propagation	O
angle	O
in	O
the	O
test	O
part	O
is	O
affected	O
by	O
Snell	O
's	O
law	O
.	O
</s>
<s>
Using	O
piezoelectric	O
transducers	B-Algorithm
,	O
SH	O
wave	O
is	O
difficult	O
to	O
couple	O
to	O
the	O
test	O
part	O
.	O
</s>
<s>
EMAT	B-Algorithm
provide	O
a	O
convenient	O
means	O
of	O
generating	O
SH	O
bulk	O
wave	O
and	O
SH	O
guided	O
waves	O
.	O
</s>
<s>
The	O
disadvantages	O
of	O
EMAT	B-Algorithm
compared	O
to	O
piezoelectric	O
UT	O
can	O
be	O
summarised	O
as	O
follows	O
:	O
</s>
<s>
Low	O
transduction	B-Algorithm
efficiency	O
.	O
</s>
<s>
EMAT	B-Algorithm
transducers	B-Algorithm
typically	O
produce	O
raw	O
signal	O
of	O
lower	O
power	O
than	O
piezoelectric	O
transducers	B-Algorithm
.	O
</s>
<s>
NDT	O
of	O
plastic	O
and	O
ceramic	O
material	O
is	O
not	O
suitable	O
or	O
at	O
least	O
not	O
convenient	O
using	O
EMAT	B-Algorithm
.	O
</s>
<s>
Although	O
there	O
are	O
EMAT	B-Algorithm
transducers	B-Algorithm
as	O
small	O
as	O
a	O
penny	O
,	O
commonly	O
used	O
transducers	B-Algorithm
are	O
large	O
in	O
size	O
.	O
</s>
<s>
Low-profile	O
EMAT	B-Algorithm
problems	O
are	O
still	O
under	O
research	O
and	O
development	O
.	O
</s>
<s>
Due	O
to	O
the	O
size	O
constraints	O
,	O
EMAT	B-Algorithm
phased	O
array	O
is	O
also	O
difficult	O
to	O
be	O
made	O
from	O
very	O
small	O
elements	O
.	O
</s>
<s>
EMAT	B-Algorithm
has	O
been	O
used	O
in	O
a	O
broad	O
range	O
of	O
applications	O
and	O
has	O
the	O
potential	O
to	O
be	O
used	O
in	O
many	O
others	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
above-mentioned	O
applications	O
,	O
which	O
fall	O
under	O
the	O
category	O
of	O
nondestructive	O
testing	O
,	O
EMATs	B-Algorithm
have	O
been	O
used	O
in	O
research	O
for	O
ultrasonic	B-Application
communication	O
,	O
where	O
they	O
generate	O
and	O
receive	O
an	O
acoustic	O
signal	O
in	O
a	O
metallic	O
structure	O
.	O
</s>
<s>
Ultrasonic	B-Application
communication	O
is	O
particularly	O
useful	O
in	O
areas	O
where	O
radio	O
frequency	O
can	O
not	O
be	O
used	O
.	O
</s>
<s>
The	O
use	O
of	O
EMATs	B-Algorithm
is	O
also	O
under	O
study	O
for	O
biomedical	O
applications	O
,	O
in	O
particular	O
for	O
electromagnetic	O
acoustic	O
imaging	O
.	O
</s>
