Electronic – Are there crystals that are tolerant of high pressure


Are there crystals that are tolerant of high pressure?

Or do they all have an open space in their case?

A customer wants to use our product in a submarine, immersed in high pressure oil.

I thought we'd be OK using SMD crystals, based on this Wikipedia article and based on reading the reference from the US Dept of the Navy.

Instead, under pressure, the top of the case of the crystal imploded.

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(Picture of imploded SMD crystal after high pressure oil immersion test.)

Obviously, there's an air pocket in there.

It was suggested that we pot the crystal in epoxy. But I have some doubts that that would work: The pressure cracked the ceramic body of the SMD crystal; I doubt that epoxy can withstand what ceramic couldn't.

(Can a kind soul with 300 reputation points create a "high pressure" tag and add it to this post, please?)

Best Answer

I've used solid ceramic resonators in high-pressure environments (inside oil-filled canisters at 120m below sea-level) without any trouble.
Of course as Majenko has already alluded to they're typically not quite as precise as a crystal usually is, but they quite happily clocked my PICs and were accurate enough to allow my serial comms at a few 100k-baud.

I did consider encapsulating a standard crystal in epoxy as suggested bu others, but my concern was that although many epoxies are generally tougher and harder to break than a crystal, I didn't think they would provide much protection.
My thinking was that the reason epoxy is tough & hard-to-break is that it is able to flex or deform somehow by some small amount before breaking. But this would be transferring force to the crystal - exactly what I was trying to avoid.

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