Stacked Piezoelectric elements

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Hi,

 

If I have several piezoeletric disc with a resonant (thickness) frequency of 125 kHz and stack them on top of each other, the overall resonant frequency seems to drop (but their individual resonant frequency ought to remain the same.)

 

So, the question: If want to achieve a lower working, i.e., use them at a lower frequency than their individual resonant frequency - is it than a good way/good practice to stack them? Or, is there a better way? (of course best would be to buy one with the right resonant frequency - but, I'm on a low (i.e., no)) budget here.)

 

Allt the best!

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The resonant frequency is a mechanical thing - so, if you alter the mechanics, it should be expected that the resonance will change ?

 

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You SHOULD be able to shift the  resonant frequency downward by adding shunt capacitance. On the negative side, this will also lower the output sound intensity because the disk size is closely matched to the frequency. Sound intensity decrease may be quite large.

 

The resonant frequency does depend on the medium in which the resonator is placed. That is why piezo elements intended for use on boats (fish finders and such) do NOT work well in air. In air, these devices are resonant at a much higher frequency than is optimum for sound output. 

 

So, the short answer is that you should either use them at the design frequency or find other devices that work at the frequency you need.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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What frequency is the OP interested in, maybe a Freak has some that can be sent to the OP.

 

Jim

I have some 25kHz units that are used, have some epoxy on the back of them, but still usable.

What is the application?

 

 

 

 

 

 

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What's the application?  I'd think you want to stay away from the resonant frequency: make sure your input signal is bandlimited well below the resonant frequency.

Also, the resonant frequency is going to drop with any additional mass you attach.