<s>
Surface	O
acoustic	O
wave	O
gas	O
sensor	O
or	O
surface	O
acoustic	O
wave	O
(	O
SAW	O
)	O
sensors	O
consist	O
of	O
an	O
input	O
transducer	B-Algorithm
,	O
a	O
chemically	O
adsorbent	O
polymer	B-Language
film	O
,	O
and	O
an	O
output	O
transducer	B-Algorithm
on	O
a	O
piezoelectric	O
substrate	O
,	O
which	O
is	O
typically	O
quartz	B-General_Concept
.	O
</s>
<s>
The	O
input	O
transducer	B-Algorithm
launches	O
an	O
acoustic	O
wave	O
that	O
travels	O
through	O
the	O
chemical	O
film	O
and	O
is	O
detected	O
by	O
the	O
output	O
transducer	B-Algorithm
.	O
</s>
<s>
Three	O
of	O
the	O
four	O
channels	O
have	O
a	O
polymer	B-Language
deposited	O
on	O
the	O
substrate	O
between	O
the	O
transmitter	O
and	O
receiver	O
.	O
</s>
<s>
The	O
purpose	O
of	O
the	O
polymers	B-Language
is	O
to	O
adsorb	O
chemicals	O
of	O
interest	O
,	O
with	O
different	O
polymers	B-Language
having	O
different	O
affinities	O
for	O
various	O
chemicals	O
.	O
</s>
<s>
When	O
a	O
target	O
chemical	O
is	O
adsorbed	O
,	O
the	O
mass	O
of	O
the	O
associated	O
polymer	B-Language
increases	O
,	O
causing	O
a	O
slight	O
change	O
in	O
phase	O
of	O
the	O
acoustic	O
signal	O
relative	O
to	O
the	O
reference	O
(	O
fourth	O
)	O
channel	O
,	O
which	O
has	O
no	O
polymer	B-Language
.	O
</s>
<s>
The	O
SAW	O
device	O
,	O
containing	O
the	O
transducers	B-Algorithm
and	O
ASICs	O
,	O
is	O
bonded	O
to	O
a	O
piece	O
of	O
quartz	B-General_Concept
glass	O
,	O
which	O
is	O
placed	O
in	O
a	O
leadless	O
chip	O
carrier	O
(	O
LCC	O
)	O
.	O
</s>
<s>
The	O
Microwave	B-Algorithm
chemistry	I-Algorithm
sensor	I-Algorithm
can	O
detect	O
several	O
chemical	O
materials	O
including	O
:	O
</s>
