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 ?

 

A plastic bag round the whole sensor ?

Maybe quartz/graphene nanocoating? just going for broke there.

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.