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