[sdiy] Sonic qualities of parts..

[Neil Johnson]

Hi,

"Paul Perry" <pfperry at melbpc.org.au>
> They are also magnificently microphonic.
> One of the electronic mags ran a project for an "engine repair" stethoscope,
> using one glued to the end of a screwdriver as a microphone for listening to
> suspicious car sounds.

Both the voltage-dependence and microphony are due to the piezoelectric properties of the ceramic dielectric.  In the former, the applied electric field distorts the physical dimensions of the capacitor, reducing the capacitance.  In the latter it is acting as a crystal microphone.

Neil


--
http://www.njohnson.co.uk

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