<s>
Time	B-Algorithm
Reversal	I-Algorithm
Signal	I-Algorithm
Processing	I-Algorithm
has	O
three	O
main	O
uses	O
:	O
creating	O
an	O
optimal	O
carrier	O
signal	O
for	O
communication	O
,	O
reconstructing	O
a	O
source	O
event	O
,	O
and	O
focusing	O
high-energy	O
waves	O
to	O
a	O
point	O
in	O
space	O
.	O
</s>
<s>
A	O
Time	B-Algorithm
Reversal	I-Algorithm
Mirror	I-Algorithm
(	O
TRM	O
)	O
is	O
a	O
device	O
that	O
can	O
focus	O
waves	O
using	O
the	O
time	O
reversal	O
method	O
.	O
</s>
<s>
TRMs	O
are	O
also	O
known	O
as	O
time	B-Algorithm
reversal	I-Algorithm
mirror	I-Algorithm
arrays	B-Algorithm
since	O
they	O
are	O
usually	O
arrays	B-Algorithm
of	O
transducers	B-Algorithm
.	O
</s>
<s>
They	O
are	O
also	O
used	O
in	O
the	O
ultrasonic	B-Application
domain	O
.	O
</s>
<s>
Yet	O
another	O
variation	O
is	O
to	O
use	O
a	O
single	O
transducer	B-Algorithm
and	O
an	O
ergodic	O
cavity	O
.	O
</s>
<s>
This	O
property	O
can	O
be	O
exploited	O
by	O
using	O
a	O
single	O
transducer	B-Algorithm
and	O
recording	O
for	O
a	O
long	O
time	O
to	O
get	O
as	O
many	O
reflections	O
as	O
possible	O
.	O
</s>
<s>
very	O
lossy	O
or	O
noisy	O
media	O
)	O
,	O
but	O
many	O
very	O
useful	O
ones	O
are	O
approximately	O
so	O
,	O
including	O
sound	O
waves	O
in	O
water	O
or	O
air	O
,	O
ultrasonic	B-Application
waves	O
in	O
human	O
bodies	O
,	O
and	O
electromagnetic	O
waves	O
in	O
free	O
space	O
.	O
</s>
<s>
His	O
team	O
has	O
done	O
numerous	O
experiments	O
with	O
ultrasonic	B-Application
TRMs	O
.	O
</s>
<s>
An	O
interesting	O
experiment	O
involved	O
a	O
single	O
source	O
transducer	B-Algorithm
,	O
a	O
96-element	O
TRM	O
,	O
and	O
2000	O
thin	O
steel	O
rods	O
located	O
between	O
the	O
source	O
and	O
the	O
array	O
.	O
</s>
<s>
Their	O
efforts	O
are	O
focused	O
on	O
radar	B-Application
systems	I-Application
,	O
and	O
trying	O
to	O
improve	O
detection	O
and	O
imaging	O
schemes	O
in	O
highly	O
cluttered	O
environments	O
,	O
where	O
Time	O
Reversal	O
techniques	O
seem	O
to	O
provide	O
the	O
greatest	O
benefit	O
.	O
</s>
<s>
The	O
beauty	O
of	O
time	B-Algorithm
reversal	I-Algorithm
signal	I-Algorithm
processing	I-Algorithm
is	O
that	O
one	O
need	O
not	O
know	O
any	O
details	O
of	O
the	O
channel	O
.	O
</s>
<s>
An	O
attractive	O
aspect	O
of	O
time	B-Algorithm
reversal	I-Algorithm
signal	I-Algorithm
processing	I-Algorithm
is	O
the	O
fact	O
that	O
it	O
makes	O
use	O
of	O
multipath	O
propagation	O
.	O
</s>
<s>
The	O
key	O
would	O
be	O
composed	O
of	O
the	O
locations	O
of	O
two	O
transducers	B-Algorithm
.	O
</s>
