<s>
A	O
piezoelectric	B-Algorithm
sensor	I-Algorithm
is	O
a	O
device	O
that	O
uses	O
the	O
piezoelectric	O
effect	O
to	O
measure	O
changes	O
in	O
pressure	O
,	O
acceleration	O
,	O
temperature	O
,	O
strain	O
,	O
or	O
force	O
by	O
converting	O
them	O
to	O
an	O
electrical	O
charge	O
.	O
</s>
<s>
Piezoelectric	B-Algorithm
sensors	I-Algorithm
are	O
versatile	O
tools	O
for	O
the	O
measurement	O
of	O
various	O
processes	O
.	O
</s>
<s>
The	O
sensors	O
are	O
either	O
directly	O
mounted	O
into	O
additional	O
holes	O
into	O
the	O
cylinder	O
head	O
or	O
the	O
spark/glow	O
plug	O
is	O
equipped	O
with	O
a	O
built-in	O
miniature	O
piezoelectric	B-Algorithm
sensor	I-Algorithm
.	O
</s>
<s>
Even	O
though	O
piezoelectric	B-Algorithm
sensors	I-Algorithm
are	O
electromechanical	O
systems	O
that	O
react	O
to	O
compression	O
,	O
the	O
sensing	O
elements	O
show	O
almost	O
zero	O
deflection	O
.	O
</s>
<s>
This	O
gives	O
piezoelectric	B-Algorithm
sensors	I-Algorithm
ruggedness	O
,	O
an	O
extremely	O
high	O
natural	O
frequency	O
and	O
an	O
excellent	O
linearity	O
over	O
a	O
wide	O
amplitude	B-Application
range	O
.	O
</s>
<s>
One	O
disadvantage	O
of	O
piezoelectric	B-Algorithm
sensors	I-Algorithm
is	O
that	O
they	O
cannot	O
be	O
used	O
for	O
truly	O
static	O
measurements	O
.	O
</s>
<s>
The	O
main	O
effect	O
on	O
the	O
piezoelectric	O
effect	O
is	O
that	O
with	O
increasing	O
pressure	O
loads	O
and	O
temperature	O
,	O
the	O
sensitivity	O
reduces	O
due	O
to	O
twin	B-Application
formation	I-Application
.	O
</s>
<s>
While	O
quartz	B-General_Concept
sensors	O
must	O
be	O
cooled	O
during	O
measurements	O
at	O
temperatures	O
above	O
,	O
special	O
types	O
of	O
crystals	O
like	O
GaPO4	O
gallium	O
phosphate	O
show	O
no	O
twin	B-Application
formation	I-Application
up	O
to	O
the	O
melting	O
point	O
of	O
the	O
material	O
itself	O
.	O
</s>
<s>
However	O
,	O
it	O
is	O
not	O
true	O
that	O
piezoelectric	B-Algorithm
sensors	I-Algorithm
can	O
only	O
be	O
used	O
for	O
very	O
fast	O
processes	O
or	O
at	O
ambient	O
conditions	O
.	O
</s>
<s>
Piezoelectric	B-Algorithm
sensors	I-Algorithm
can	O
also	O
be	O
used	O
to	O
determine	O
aromas	O
in	O
the	O
air	O
by	O
simultaneously	O
measuring	O
resonance	O
and	O
capacitance	O
.	O
</s>
<s>
Computer	O
controlled	O
electronics	O
vastly	O
increase	O
the	O
range	O
of	O
potential	O
applications	O
for	O
piezoelectric	B-Algorithm
sensors	I-Algorithm
.	O
</s>
<s>
Piezoelectric	B-Algorithm
sensors	I-Algorithm
are	O
also	O
seen	O
in	O
nature	O
.	O
</s>
<s>
A	O
piezoelectric	O
transducer	B-Algorithm
has	O
very	O
high	O
DC	O
output	O
impedance	O
and	O
can	O
be	O
modeled	O
as	O
a	O
proportional	O
voltage	O
source	O
and	O
filter	B-Architecture
network	I-Architecture
.	O
</s>
<s>
C0	O
represents	O
the	O
static	O
capacitance	O
of	O
the	O
transducer	B-Algorithm
,	O
resulting	O
from	O
an	O
inertial	O
mass	O
of	O
infinite	O
size	O
.	O
</s>
<s>
Ri	O
is	O
the	O
insulation	O
leakage	O
resistance	O
of	O
the	O
transducer	B-Algorithm
element	O
.	O
</s>
<s>
Three	O
main	O
groups	O
of	O
materials	O
are	O
used	O
for	O
piezoelectric	B-Algorithm
sensors	I-Algorithm
:	O
piezoelectric	O
ceramics	O
,	O
single	O
crystal	B-General_Concept
materials	I-General_Concept
and	O
thin	O
film	O
piezoelectric	O
materials	O
.	O
</s>
<s>
The	O
ceramic	O
materials	O
(	O
such	O
as	O
PZT	O
ceramic	O
)	O
have	O
a	O
piezoelectric	O
constant/sensitivity	O
that	O
is	O
roughly	O
two	O
orders	O
of	O
magnitude	O
higher	O
than	O
those	O
of	O
the	O
natural	O
single	O
crystal	B-General_Concept
materials	I-General_Concept
and	O
can	O
be	O
produced	O
by	O
inexpensive	O
sintering	O
processes	O
.	O
</s>
<s>
The	O
less-sensitive	O
,	O
natural	O
,	O
single-crystal	O
materials	O
(	O
gallium	O
phosphate	O
,	O
quartz	B-General_Concept
,	O
tourmaline	O
)	O
have	O
a	O
higher	O
–	O
when	O
carefully	O
handled	O
,	O
almost	O
unlimited	O
–	O
long	O
term	O
stability	O
.	O
</s>
<s>
Thin	O
film	O
piezoelectric	O
materials	O
can	O
be	O
manufactured	O
utilizing	O
sputtering	O
,	O
CVD	O
(	O
chemical	B-Algorithm
vapour	I-Algorithm
deposition	I-Algorithm
)	O
,	O
ALD	O
(	O
atomic	O
layer	O
epitaxy	O
)	O
etc	O
.	O
</s>
