<s>
Terahertz	B-Architecture
radiation	I-Architecture
also	O
known	O
as	O
submillimeter	B-Architecture
radiation	I-Architecture
,	O
terahertz	B-Architecture
waves	I-Architecture
,	O
tremendously	B-Architecture
high	I-Architecture
frequency	I-Architecture
(	O
THF	O
)	O
,	O
T-rays	B-Architecture
,	O
T-waves	O
,	O
T-light	B-Architecture
,	O
T-lux	O
or	O
THz	O
–	O
consists	O
of	O
electromagnetic	O
waves	O
within	O
the	O
ITU-designated	O
band	B-Algorithm
of	I-Algorithm
frequencies	I-Algorithm
from	O
0.3	O
to	O
3terahertz	O
(	O
THz	O
)	O
,	O
although	O
the	O
upper	O
boundary	O
is	O
somewhat	O
arbitrary	O
and	O
is	O
considered	O
by	O
some	O
sources	O
as	O
30THz	O
.	O
</s>
<s>
Wavelengths	O
of	O
radiation	O
in	O
the	O
terahertz	B-Architecture
band	I-Architecture
correspondingly	O
range	O
from	O
1mm	O
to	O
0.1mm	O
=	O
100µm	O
.	O
</s>
<s>
Because	O
terahertz	B-Architecture
radiation	I-Architecture
begins	O
at	O
a	O
wavelength	O
of	O
around	O
1millimeter	O
and	O
proceeds	O
into	O
shorter	O
wavelengths	O
,	O
it	O
is	O
sometimes	O
known	O
as	O
the	O
submillimeter	B-Architecture
band	I-Architecture
,	O
and	O
its	O
radiation	O
as	O
submillimeter	B-Architecture
waves	I-Architecture
,	O
especially	O
in	O
astronomy	O
.	O
</s>
<s>
Terahertz	B-Architecture
radiation	I-Architecture
is	O
strongly	O
absorbed	O
by	O
the	O
gases	O
of	O
the	O
atmosphere	O
,	O
and	O
in	O
air	O
is	O
attenuated	O
to	O
zero	O
within	O
a	O
few	O
meters	O
,	O
so	O
it	O
is	O
not	O
practical	O
for	O
terrestrial	O
radio	O
communication	O
.	O
</s>
<s>
THz	O
beams	O
transmitted	O
through	O
materials	O
can	O
be	O
used	O
for	O
material	O
characterization	O
,	O
layer	O
inspection	O
,	O
relief	O
measurement	O
,	O
and	O
as	O
a	O
lower-energy	O
alternative	O
to	O
X-rays	B-Library
for	O
producing	O
high	O
resolution	O
images	O
of	O
the	O
interior	O
of	O
solid	O
objects	O
.	O
</s>
<s>
Terahertz	B-Architecture
radiation	I-Architecture
occupies	O
a	O
middle	O
ground	O
where	O
the	O
ranges	O
of	O
microwaves	O
and	O
infrared	O
light	O
waves	O
overlap	O
,	O
known	O
as	O
the	O
“	O
terahertz	O
gap	O
”	O
;	O
it	O
is	O
called	O
a	O
“	O
gap	O
”	O
because	O
the	O
technology	O
for	O
its	O
generation	O
and	O
manipulation	O
is	O
still	O
in	O
its	O
infancy	O
.	O
</s>
<s>
The	O
generation	O
and	O
modulation	B-Application
of	O
electromagnetic	O
waves	O
in	O
this	O
frequency	O
range	O
ceases	O
to	O
be	O
possible	O
by	O
the	O
conventional	O
electronic	O
devices	O
used	O
to	O
generate	O
radio	O
waves	O
and	O
microwaves	O
,	O
requiring	O
the	O
development	O
of	O
new	O
devices	O
and	O
techniques	O
.	O
</s>
<s>
Terahertz	B-Architecture
radiation	I-Architecture
falls	O
in	O
between	O
infrared	O
radiation	O
and	O
microwave	O
radiation	O
in	O
the	O
electromagnetic	O
spectrum	O
,	O
and	O
it	O
shares	O
some	O
properties	O
with	O
each	O
of	O
these	O
.	O
</s>
<s>
Terahertz	B-Architecture
radiation	I-Architecture
travels	O
in	O
a	O
line	O
of	O
sight	O
and	O
is	O
non-ionizing	O
.	O
</s>
<s>
Like	O
microwaves	O
,	O
terahertz	B-Architecture
radiation	I-Architecture
can	O
penetrate	O
a	O
wide	O
variety	O
of	O
non-conducting	O
materials	O
;	O
clothing	O
,	O
paper	O
,	O
cardboard	O
,	O
wood	O
,	O
masonry	O
,	O
plastic	O
and	O
ceramics	O
.	O
</s>
<s>
Like	O
infrared	O
,	O
terahertz	B-Architecture
radiation	I-Architecture
has	O
limited	O
penetration	O
through	O
fog	O
and	O
clouds	O
and	O
cannot	O
penetrate	O
liquid	O
water	O
or	O
metal	O
.	O
</s>
<s>
Terahertz	B-Architecture
radiation	I-Architecture
can	O
penetrate	O
some	O
distance	O
through	O
body	O
tissue	O
like	O
x-rays	B-Library
,	O
but	O
unlike	O
them	O
is	O
non-ionizing	O
,	O
so	O
it	O
is	O
of	O
interest	O
as	O
a	O
replacement	O
for	O
medical	O
X-rays	B-Library
.	O
</s>
<s>
Due	O
to	O
its	O
longer	O
wavelength	O
,	O
images	O
made	O
using	O
terahertz	B-Architecture
waves	I-Architecture
have	O
lower	O
resolution	O
than	O
X-rays	B-Library
and	O
need	O
to	O
be	O
enhanced	O
(	O
see	O
figure	O
at	O
right	O
)	O
.	O
</s>
<s>
The	O
earth	O
's	O
atmosphere	O
is	O
a	O
strong	O
absorber	O
of	O
terahertz	B-Architecture
radiation	I-Architecture
,	O
so	O
the	O
range	O
of	O
terahertz	B-Architecture
radiation	I-Architecture
in	O
air	O
is	O
limited	O
to	O
tens	O
of	O
meters	O
,	O
making	O
it	O
unsuitable	O
for	O
long-distance	O
communications	O
.	O
</s>
<s>
However	O
,	O
at	O
distances	O
of	O
~	O
10meters	O
the	O
band	O
may	O
still	O
allow	O
many	O
useful	O
applications	O
in	O
imaging	O
and	O
construction	O
of	O
high	O
bandwidth	O
wireless	B-General_Concept
networking	I-General_Concept
systems	O
,	O
especially	O
indoor	O
systems	O
.	O
</s>
<s>
In	O
addition	O
,	O
producing	O
and	O
detecting	O
coherent	O
terahertz	B-Architecture
radiation	I-Architecture
remains	O
technically	O
challenging	O
,	O
though	O
inexpensive	O
commercial	O
sources	O
now	O
exist	O
in	O
the	O
0.31.0THz	O
range	O
(	O
the	O
lower	O
part	O
of	O
the	O
spectrum	O
)	O
,	O
including	O
gyrotrons	B-Algorithm
,	O
backward	B-Algorithm
wave	I-Algorithm
oscillators	I-Algorithm
,	O
and	O
resonant-tunneling	B-Algorithm
diodes	I-Algorithm
.	O
</s>
