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Most convenient coating for piezoelectric disc ?


Externet

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Hi all.

A piezoelectric disc sensing soundwaves in its surrounding air needs to be protected from corrosive gases in order to avoid deterioration.

 

What type of coating/encapsulation would conduct sound with the least attenuation ?

Fluid as grease, soft as silicone, medium as vinyl, hard as epoxy ?

With no air gap between the coating and the sensing element ?

Thick or thin layer ?

Flexible or rigid material ?

Rough or smooth surface ?

Other considerations ?

 

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Those piezo disks rely on flexural modes, don't they? Then any adhering coating should show low losses, which would eliminate the liquids - they are bad as a chemical barrier anyway.

 

I vote for the plastic bag not touching the piezo element.

 

If the protection must be on the disk, then of a thin, hermetic and elastic material. Metals seem ruled out, alas, as the disks need electrodes, but a ceramic coating like SiO2 or Si3N4 offers an excellent protection. Its deposition needs a high temperature, fine for the piezo ceramics, but which restricts the electrode metals - small worry since the metals that protect against corrosion are the refractory ones.

 

You usual semiconductor process engineer can tell that quickly.

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