[time-nuts] Super stable BVA Quartz resonators... BVA??

Bernd T-Online BNeubig at t-online.de
Sat Dec 8 03:27:28 EST 2007

Hal Murray wrote:
  > Why is the top domed?  I assume flat would be easier to manufacture.
> Why is it not symmetrical?  If the top is domed, why not the bottom too?
For a plano-parallel qaurtz resonator the diameter must be at least 60 
times larger than the thickness, otherwise the vibration amplitude would 
be too high at the edges, and the suspension would damp teh vibration 
hence the Q would be lowered. For a 10 MHz 3rd overtone SC-cut you would 
need a crystal of 40 to 50 mm diameter!
By making a convex contour, the vibration is trapped in the center of 
the plate, and therefore the Q keeps high (and other parameters improve 
Bi-convex contours are more difficult to manufacture, as it is required 
that the symmetry axis of the upper and lower contour must coincide. 
Also other parameters become worse. For the BVA the manufacturability 
would also be much worse as it already is.



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