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Registered Member #2115
Joined: Fri May 08 2009, 01:17PM
Location: Singapore
Posts: 46
I have noticed that for many dielectric plastic films, the breakdown electric field strength is greater as the film thickness decreases. eg.
Would it then make sense to partition a dielectric into small segments, with a conductive layer (eg. metallization) between segments? Theoretically this would allow for higher effective breakdown electric fields... does this make sense?
Of course, the minimum thickness possible would be determined by manufacturing processes.
Although the thin-ness of such a design would be prohibitive to the average hobbyist, is this the idea behind how metallized film caps are designed?
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
According to what the document says, failure is due to corona at the surface when higher voltage is used in the test melting the plastic. I don't think then that stacking thin films and conductors will help much, as when high voltage is applied corona at the surface will occur in the same way.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
kiat wrote ...
I have noticed that for many dielectric plastic films, the breakdown electric field strength is greater as the film thickness decreases. eg.
Would it then make sense to partition a dielectric into small segments, with a conductive layer (eg. metallization) between segments? Theoretically this would allow for higher effective breakdown electric fields... does this make sense?
Of course, the minimum thickness possible would be determined by manufacturing processes.
Although the thin-ness of such a design would be prohibitive to the average hobbyist, is this the idea behind how metallized film caps are designed?
Yes
But the big manufacturers can get to really thin films, with sputtered metallisation for the intermediate layers
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Sputtering isn't beyond the capabilities of the amateur, although aluminium is notoriously difficult to sputter (I assume this is the reason that most vacuum chambers used for semiconductor manufacture are machined from aluminium. (certainly all the systems I've worked on).
Aluminium can be applied using chemical vapour deposition, though, and, I imagine by other processes as well. This article suggests that CVD gives better results that evaporation deposition:
Amateur telescope builders tend to use evaporation of aluminium for coating mirrors after grinding them.
Copper, on the other hand, is really easy to sputter, which is why it tends to be avoided in the construction of these types of systems, and is generally shielded from ions when it's use can't be avoided. While it is considerably more expensive than aluminium, it may have cost advantages in an amateur setup, as you wouldn't need a lot for a few capacitors. I've no idea how successful this aproach would be, though.
Registered Member #3343
Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311
Ya..
Dielectrics in serie with the electrodes to allow a resultant high voltage in the paccage are the same circuit of several capacitors connected in serie...
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Capacitor question
