In some prehistoric age of my youth, I would separate the aluminum foil 
from the paper that was the wrapper on a stick of gum.  Then I would 
take the aluminum foil and squeeze/crush it near my ear.  A marvelous 
"tin cry" would be heard.

Other musings.  What about relatively pure defect-free materials such as 
carbon-nanotubes in an epoxy matrix -- preferably somewhat flexible like 
a  urethane, so the matrix will not exhibit cracking sounds.  If the 
matrix is heavily loaded, the TCE, and elasticity should be controlled 
by the carbon nano-tubes, but maybe not so subject to ratchet effects?

Also along the fused quartz speculations -- what about crystal 
structures that grow in needle shapes for springs.  A good crystal would 
have very few dislocation sites to slip and ratchet.  One image that 
comes to mind is the titanium oxide in rutilated quartz.  (Please bear 
in mind that this may be a totally inappropriate material, but the 
concept of crystalline needles for a spring sure has an appeal.

I recall that silicon can form some very high-Q mechanical structures in 
MEMs devices such as oscillator control in place of quartz.  The quality 
of silicon crystals is very high for use in electronics as the defects 
have very detrimental results to the electronic properties.  Used wafers 
are often available from novelty surplus stores.  Scribed along cleavage 
plane lines would yield very good edges without microfractures that 
would also be bad for springs formed from any material

And finally one of the very interesting material classes  are the 
Metglas materials   Here you have a metal alloy that is very close to 
being fully amorphous.  Very springy and glass-like.  Dave, did you 
experiment with any Metglas materials for your vertical seismometer 
experiments?

Regards,
Charles R. Patton


On 8/15/2011 4:54 PM, Brett Nordgren wrote:
> Randall,
>
> What amount of dither do you think would be adequate?  I suppose it 
> could best be expressed as variation in the spring strain, or in 
> whatever other way you suggest.
>
> Thanks,
> Brett
>
> At 06:47 PM 8/15/2011, you wrote
>
> 
>
>>   I see this process as a potential energy function that is very much 
>> like the vertical seismometer, except turned upside down.  Extending 
>> the spring and then releasing, it does not return to a perfectly 
>> defined equilibrium point; i.e., it finds a new very slightly 
>> different places to come to rest because of the 'ratchety' nature of 
>> the restoring force at the very low levels.  Much of my experimental 
>> work is consistent with this 'heretical' viewpoint, and I think it is 
>> the very reason, Brett, you would do well to try and do some low 
>> level dithering of your instrument.  Allan Coleman's approach seems 
>> to accomplish this by means of his passive leveling arrangement.
>
>
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