[Milsurplus] X-Ray Damage.. more

[Bob Camp]

Hi

If the element is a PZT material, it needs to be polarized (polled)  
before it will work correctly. Oddly enough the ceramic pucks in a 455  
Kc filter work the same way. I still can't see how you could do it  
after you get out of the bulk state with normal materials. Normally  
you have to take the stuff above the Curie temperature to make the  
process "stick".

Bob


On Oct 27, 2007, at 12:07 AM, J Forster wrote:

> Bob Camp wrote:
>
>> Hi
>>
>> I must have missed the first post in the thread. The fact that they
>> are microphones was something I missed.
>
> Yup. The thread started with a post about known good, commercial  
> (Sure)
> crystal mikes that tested good being zapped during shipment.
>
>> A lot of microphone elements are parabolic in their force to
>> electricity characteristic. At "zero" they do not produce a useful
>> response. To make them work you "polarize" the element with a high
>> voltage. It's  a one time process, and normally heat is also  
>> involved.
>> Sounds like yours got a bit to much ....
>
> Crystal mikes are NOT electret mikes. The crystal is cut with a wet  
> string
> saw from a crystal. There is no 'polarization' process and certainly  
> not
> during shipment.
>
> Best,
> -John
>
>>
>>
>> I'm a little surprised that they do the polarization after mount
>> though. I alway assumed they did it to the bulk material .....
>>
>> Bob
>
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