From: John Woodgate
Subject: Re: Ceramic Capacitors
Date: Thu, 26 Sep 2002 15:49:14 +0100
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Thu, 26 Sep 2002 16:42:09 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Fred Bloggs
wrote (in <3D93011B.email@example.com>) about 'Ceramic Capacitors', on
Thu, 26 Sep 2002:
>> I just found out that ceramic capacitors can exibit a piezoelectric effect
>> that in presence of mechanical vibrations on a board, can produce electrical
>> noise on a line that the capacitor is suppose to decouple...
>> The phenomenon may not be negligeable on big size surface mount caps.
>> The paper said "some" ceramic capacitor..
>Can you cite this paper? And I am perplexed by the statement that NP0
>dielectric does not exhibit piezoelectric effects since it is the same
>material in a blend of N-egative and P-ositive tempco to yield 0.
Maybe the piezo coefficients of the materials are also opposite. Or
maybe it's just that the molecule orientation is more nearly random in
Actually, I've recently been discussing NPO with AVX, who pointed out
that it shows mechanical resonances at high radio frequencies, and
indeed I found signs of resonances in one particular part at 270 and 540
MHz. The mechanical resonances are presumably a manifestation of piezo
action. They are not very pronounced in this particular part.
At present, I don't see a way of vibrating the part at 270 MHz to see if
it generates as well. (;-)
>> Does anyone have any information on precisely what kind of ceramic capacitor
>> would particularly exibit this behavior ? ( NPO, X7R, X5R, Y5V, Z5U ... ? )
>> Searches onthe net didn't bring anything relevant.
>Even if it does, the bulk component continues to exhibit capacitance
>which will attenuate the voltage greatly- probably because of the large
>effective output impedance of the small region producing the emf.
Well, some of the highest-k parts certainly generate tens of millivolts
from the sort of accidental knock that a component gets in handling a
Given sufficient provocation, and sample capacitors, I'll measure with
an impact hammer. I find the Izod tester tends to reduce the
capacitance, some times to near zero. (;-)
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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