Ceramic capacitor value changes drastically with DC bias

[Nico Coesel]

They are not very good at very low frequencies, sub-Hertz and such.

I use them in a design for detecting pressing a 'button' through
metal. If that isn't sub-Hertz... and the signal is pretty decent.
Maybe they work better if you stick them on a medium (plastic) which
can be warped a bit by the sound pressure.

 

[tm]

Piezo elements are too expensive I presume?

--

Take apart one of those piezo butane lighters and get a whole stack of them.

 

[Joerg]

Piezo elements are too expensive I presume?

Not suitable for my app. I need something really low in impedance. Thing
is, there is no market for that and nobody wants Z5U ceramic if they
don't have to. So they don't make very small ones much anymore. It's one
of those cases where hitching a ride as an off-label user can turn into
a white-knuckle ride.

 

[Jasen Betts]

Not suitable for my app. I need something really low in impedance. Thing
is, there is no market for that and nobody wants Z5U ceramic if they
don't have to. So they don't make very small ones much anymore. It's one
of those cases where hitching a ride as an off-label user can turn into
a white-knuckle ride.

How do you figure that a smaller capacitor will have a lower impedance?

Z=j/C.2.pi.f

 

[Joerg]

How do you figure that a smaller capacitor will have a lower impedance?

Z=j/C.2.pi.f

It has to be small because it's basically got to fit inside a <0.010"
diameter hole. The problem is that normally nobody makes caps with low
grade ceramic material for this size.