Hi So if we could just get that 180 mm blank line up and running, you could get some pretty good 1 MHz crystals. Of course that also involves minor issues like a 200+ mm diameter cold weld package and all the processing gear ….
Bob > On Jun 26, 2016, at 6:40 AM, Bernd Neubig <bneu...@t-online.de> wrote: > > Bob Camp: >> Every paper I have ever read on the intrinsic Q of quartz makes the claim >> that Q * F is a constant ( Q goes up as frequency goes down). Unless blank >> diameter gets in the way, this has been true for any >crystals I have ever >> used. Q does change as overtone changes, but that is not related to the Q of >> the material. A given blank design may (or may not) be limited by the Q of >> the quartz at any specific >frequency. That is a function of a lot of >> things. >> The material’s properties set a maximum Q you can achieve no matter how good >> your blank design is and how big the blank. Done properly, the best 5 MHz >> resonator you can do *will* have 2X the Q of >the best 10 MHz resonator. > > Indeed there is an physical limitation for the Q of piezoelectric resonators, > which is given by phonon interactions etc. For quartz this limit is given > approximately by Q*f = 15E12. See attached graph (sorry, in German). The real > crystal Q is determined by a couple of other factors like > - damping caused by the suspension (which for circular plano-parallel > thickness shear resonators like AT and SC is the larger, the larger the > thickness to diameter ratio is. The impact of the suspension can be reduced > e.g. by contouring the crystal (beveling, plano-convex or bi-convex shape) > - damping by the surrounding gas (dominating in low-frequency tuning-fork > type crystals, important for low- frequency AT-cut crystals, less important > for high frequency crystals > - damping effect due to stress and losses between crystal blank and electrodes > - mode of vibration: fundamental is worse than overtones, partly because the > electrode losses apply only to two outer interfaces of the vibration sublayers > rule of thumb for ATs with f in Hz: fundamental mode: Q*f about 1E12, 3rd > overtone Q*f about 2E12 ... 4E12, 5th and higher overtone 4E12 to 8E12. > for SC-cut 3rd or 5th overtone with optimized design Q*f can go up to > 13E12, e.g. Q of a good 10 MHz 3rd is about 1.1 mio to 1.3 mio, a good 100 > MHz 5th has a q of 120 000 to 135 000 > - in tuning fork crystals (which are all evacuated) Q*F is about 0.6E12 to > 1.5E12 > Rule of thumb means: these are typical averages , there are exceptions > > BTW: This does not apply to the sapphire DIELECTRIC resonators or other kinds > of resonators like DRO etc.. Those are different animals. > > Have fun > > Bernd > DK1AG > > > <Qtimesf.gif>_______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
