In sonar applications one use different ceramics for emission and
reception depending on their characteristics.

The US NAVY propose a standard as follows:

PZT 4 -> "hard"
PZT 8 -> "very hard"

are suitable for emission in submarine acoustic field

PZT 5 -> "soft"

are suitable for reception.

In the case of "hard" type ceramics, they exhibit a high quality factor
(Q) (low losses), and good electromechanical coupling coefficient.
In the case of "soft" ceramics, the dielectric coefficient are bigger
than in "hard"-type ceramics.

For a microphone application, piezoceramics are probably not the best
candidates in term of efficiency due the bad adaptation of the
mechanical impedance (in the air the acoustic wave can be seen as a
large displacement and a low force and piezoceramics are more suitable
in fluid like water where -compare to air- the acoustic wave produce a
small displacement and a higher force which is good for piezoceramics.
However, some microphones using piezoelectric ceramics have been
reported so I wish you good luck...

Lionel

Le Touze Christophe wrote:
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> Among the different kinds of micromachined silicon microphones
> dedicated to human speech, we are interested in the
> piezoelectric type using thin film PZT (lead zirconate titanate)
> piezo-electric ceramic.
>     But it seems that PZT films on Si-wafer are mainly used as force
> sensors, ultrasonic micro-actuators, acoustic imaging or sonar
> transducers.
>     Is there any particular reason to explain this?
>
>     Please send me any suggestion on that subject.
>  Thank you !
>    Christophe LE TOUZE.
>
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--
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Lionel BUCHAILLOT
Microsystemes Silicium
Silicon Microsystems
IEMN Departement ISEN
Cite Scientifique
Avenue Poincare - B.P. 69
59652 VILLENEUVE D'ASCQ Cedex
FRANCE

E-mail : buchaillot@isen.iemn.univ-lille1.fr

Phone : +33 3 20 19 78 38
Fax : +33 3 20 19 78 84
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