[time-nuts] Better quartz crystals with single isotope ?

Bill Hawkins bill.iaxs at pobox.com
Mon Apr 23 00:21:45 EDT 2018


Good questions.

The one that bothers me is the magnetic levitation required to compare
the standard to anything. You can't put other materials inside the
vacuum bell with the standard. I looked up the paper, but it's behind a
$40 pay-wall.

Electromagnets will levitate permanent magnets, but the effect is not
stable, with the free magnet sliding out of the field. 
Diamagnetic materials will be stable, but the effect is so weak it would
require superconducting electromagnets. Quartz, as it happens, is
diamagnetic.

Now the problem is to apply identical levitation to dissimilar
materials. This would seem to require identical superconducting magnets
and identical levitated platforms. Identical currents can flow in the
levitating magnets simply by connecting them in series. In order for the
platforms to be identically levitated, they have to be an identical
distance from the levitating magnet. Measuring that to the required
precision could be a challenge.

Machining physical parts can be done to 10 E-6. That's not enough, so
the mechanism will require calibration. I suppose they could compare it
to the present platinum standard. Then there's the question of
calibration interval, and what to use as the standard. Counting
oscillations of atoms would be so much easier.

I think Rick's three points make this a non-starter. It's a case of
experts in metrology not having enough expertise in quarts resonators.

In answer to why they can't use 10 grams, the comparison has to be 100
times more accurate than that for 1000 grams.

Hope I haven't strayed too far off topic, and wasted my time.

Bill Hawkins


-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Richard
(Rick) Karlquist
Sent: Sunday, April 22, 2018 4:11 PM
To: Discussion of precise time and frequency measurement; Bob kb8tq
Subject: Re: [time-nuts] Better quartz crystals with single isotope ?

On 4/22/2018 10:20 AM, Bob kb8tq wrote:

>> Do we know anybody in the quartz business who needs a really cool 
>> research project ?
> 
> You could put it on the list with the 1 Kg quartz resonator proposal
...
> 
> https://tf.nist.gov/general/pdf/2638.pdf 
> <https://tf.nist.gov/general/pdf/2638.pdf>
> 
> Also an offshoot of people thinking about the implications of all this
as it relates to resonators.
> 
> 
> Bob
> 

The cited article "must be true" because of its authors, I guess, but it
makes no sense to me.  They seem to be assuming that the resonant
frequency is inversely proportional to mass?  We all know three things:

1.  Frequency is inversely proportional to thickness.  Not mass.

2.  Frequency aging is affected by stress relaxation in well built
resonators.  The old idea that mass is gradually evaporating from the
resonator to the enclosure (glass enclosures) or mass is gradually
evaporating from the enclosure (metal enclosures) to depositing on the
resonator is simply obsolete in terms of current technology.
Thus again frequency is not a proxy for mass.

3. Resonators can "jump" in frequency without jumping in mass.

Given these facts, I am lost as how this is supposed to work.
Surely, the authors are well aware of the 3 items above.

Also, why does the resonator have to be a whole kilogram anyway.
If it weighed exactly 10 grams, couldn't you still compare it to a
kilogram using 100:1 leverage?

Can anyone straighten me out?

Rick
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