We're talking about something in the 220 pF - 10 nF range, depending on what speeds and slew rates and such.
So yes, it might definitely be interesting to see how such a cap would stack up against off-the-shelf parts...
For ease of discussion, lets say a 1 nF cap... How much would one need and where would you easily obtain it? Preferably with non-crazy shipping cost to Europe. Or samples would be great too.
Edit: And to prevent misunderstandings ... this diy teflon cap would be purely to compare it to say a polypropylene, mainly just for the fun of it. It's a hobby after all. Not as the primary candidate for this design.
Hello Mrflibble
OK it is late here and I'm a little punch drunk. Here is a first pass assessment.
First to calculate size, teflon dielectric constant 2.1, polypropylene 2.3 so teflon maybe going to be 10 % bigger plate area if gap is the same. I use
C = 1 x 10e-9 F desired capacitance
e0 = 8.854 x 10e-12 F/m electric constant
er = 2.1 permittivity relative of PTFE
g = 0.001 inch or 2.54 x 10e-5 plate gap in meters
A = plate area in m
2 to be calculated
so C = (e0 x er) x A/g
or A = 0.000537825 m
2 or 5.37825 cm
2 this is do able, the first time I ran through this calc. I ended up with half a square meter for 1nF and thought that can't be right. please check as I am tired and making mistakes now.
There are multiple sources for copper foil 0.001 inch thick and teflon same thickness, let me continue to search for the best. Some additional notes: teflon sheet at 0.001 inch thick is listed in various places as having dielectric strength of 500 to 2000 V per 'mil' which I think means 1 thou inch thickness. Holy shit-snacks we can tie these caps across the mains! Also it is produced by 'skiving' which I think is the process where a very big solid log of teflon is put in a lathe and a thin sheet is shaved off by a very sharp cutter. Does not seem like good way to me, but what do I know
Prices are looking reasonable, more later. These materials can be purchased by one individual in some quantity and then after cutting and subdividing with a paper cutter sent to other experimenters using ordinary envelope and mail service for economy.
Suggest to me the best form factor/topology, alternating rectangular plates for a rectangular package or rolled up into a cylinder. I fear rectangular might act like a patch antenna but I know nothing!
Looking at conrad hoffman's page there doesn't appear to be a great advantage to teflon over polyprop in adsorption still it is fun to experiment. I am almost 'having a volt nut' now, just don't want it to happen in my pants
goodnight my friends, going to bed