[time-nuts] optically excite a quartz crystal?

[Bob Camp]

Hi

One of the reasons for going to plated electrodes was to control the damping on the resonator. You control plating thickness fairly tightly for this reason. A great big lump of iron on your vibrating area does indeed damp it. 

Bob

On Apr 21, 2014, at 9:29 AM, Mike Feher <mfeher at eozinc.com> wrote:

> Agree there are some like that, but, only a few. A large spring loaded plate
> is not going to dampen a piece of quartz vibrating in the MHz range at all.
> Granted, the sealed, and metalized construction is a better one, but it is
> mostly done to minimize shock and impurities. - Mike 
> 
> Mike B. Feher, EOZ Inc.
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 732-886-5960 office
> 908-902-3831 cell
> 
> 
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Bob Camp
> Sent: Monday, April 21, 2014 9:17 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] optically excite a quartz crystal?
> 
> Hi
> 
> If you look closely at most of them, the plates are not flat. They are
> higher on the edges than in the center. There's a gap in the middle. If you
> don't have the gap, the blank is constrained by the big heavy plate. That
> damps the resonance and lowers the Q.
> 
> Bob
> 
> On Apr 21, 2014, at 9:00 AM, Chuck Harris <cfharris at erols.com> wrote:
> 
>> I'm puzzling over this statement.  The FT-243's I have seen have a 
>> spring that squishes the quartz blank between the electrodes.  They 
>> aren't plated onto the quartz, but they are still in intimate 
>> mechanical and electrical contact.
>> 
>> -Chuck Harris
>> 
>> Bob Camp wrote:
>>> Hi
>>> 
>>> The WWII era FT-243 is one example of a crystal that has the active 
>>> portion of the electrodes separated from the resonator by an air gap. 
>>> There are lots of similar holders from that era that do pretty much 
>>> the same thing. Non-contacting electrodes are not very new.
>>> 
>>> Bob
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