Hello,

I've been reading about piezo-ceramic disks and their use as contact microphones but can't figure out nor find anywhere how do they behave at most sound frequencies.

I see that their self-resonance frequency gets higher as their brass disk diameter increases, but exactly what does this mean in terms of audio recording?

Does the ratio between ceramic and brass disk diameter affect their performance somehow (like if brass disk diameter stays the same but ceramic disk diameter increases, their sensitivity and/or frequency range increases)?

Also, I've read that apparently their brass disk diameter gives the lowest frequency cutoff, with diameter increasing the frequency cutoff lowers, and this should stand true also if a larger surface/sheet is bound to the brass disk.

How large of a sheet should I need to lower a common piezo transducer cutoff frequency to say 50 Hz ? (or how can I roughly calculate this, just to get an idea if it's reasonable or not, I don't need anything exact).

Also since I guess that both the glued sheet material, thickness and stiffness affect the piezo transducer sensitivity, which kind of compromise should I choose not to compromise sensitivity too much? Something like heavy tinfoil, a 0.1mm steel sheet or even something as thick as 0.5mm steel?

Thank you

Allison

 

Have you seen this reference yet? Might help.

 

Have you seen this reference yet? Might help.

Thanks wayneh, it was indeed an interesting read but unfortunately didn't contain enough info to answer my questions.

 

The resonant frequency of a piezo disc depends, inter alia, on the vibration mode. This article, in particular around pages 10-14, may be of interest. For low resonant frequencies the bending mode would probably be used. Adding sheet material to a disc would increase the mass and tend to reduce the resonant frequency, but would also stiffen it and so reduce the bending mode sensitivity dramatically, which isn't what you want.

 

A lot of information here :

----> http://emerald.tufts.edu/programs/mma/emid/piezo.pdf

----> http://www.piezotech.fr/fr/5-technique-piezoelectric-eap-electroactive-polymer/

And big sheets ----> https://www.alibaba.com/product-detail/Piezo-Film-Sheet_60238867579.html