[daugusto (OP)]

Hi, guys,
For some time now I´ve been researching a feasible way for the ordinary Joe to build a propellantless thruster, which, anyway, I wouldn´t have the courage to put in the market.
But the best answer seems to be the Lafforgue´s asymmetrical capacitor, shown to really work by J L Naudin, but requiring a very high-k material to produce considerable thrust.

According to the solver, titanium dioxide would be enough for that purpose, considering average Joe has no access to a significant amount of barium titanate.

Now, does the "insulating capacity" of a dieletric have to do with its thickness, or would a simple epoxy-based coating layer on the two electrodes, for example, do the job?

There will probably be no ready answers, but I would appreciate any comments. Also, for all purposes, regardless of any discussion on if this thruster works or not, what I want to build is a capacitor by definition.

More on the project can be found by searching "Lafforgue solver"

[alancalverd]

What capacitance and working voltage do you want?

[daugusto (OP)]

Working voltage will be some 500000V, and capacitance is not directly calculated but will fall in the pF range.

[alancalverd]

Polypropylene is the industry standard at 500 kV

[daugusto (OP)]

Thanks.

But does the permittivity of the dielectric increase with thickness, or would a thin layer of any dielectric chosen be the same as the complete gap between one electrode and the other?

The second option seems to be true, but I would like the opinion of someone who knows better than me.

[chiralSPO]

My understanding is that the breakdown depends on the strength of the field (V/m). So a material with a breakdown limit of 10⁷ V/m will need to be at least 1 mm thick to successfully separate plates that have 10000 V between them (I am assuming that the plates are touching the opposite sides of the dielectric layer).

If titanium dioxide is the material you're after, you're in luck! Titanium dioxide is in pretty much everything white, from paint to powdered sugar. You can harvest TiO2 from powdered sugar by dissolving it in hot water and running through a coffee filter. Rinse the TiO2 with high-proof alcohol or rubbing alcohol and allow them to air dry, then scrape them off the coffee filter. Making a layer of TiO2 between your electrodes might be a little tricky, but where there's a will there's a way. (you may also be able to buy some TiO2 online, but that's less fun)

[alancalverd]

Permittivity is a property of the bulk material and is independent of thickness.  Capacitance depends on the reciprocal of thickness.

C = εε₀A/d

Thus the capacitance is limited by the dielectric breakdown strength of the material (volt/mm).

[daugusto (OP)]

Oh, "dielectric stregth" now makes sense to me...

Guys, I think you´ve given me all I need.

chiralSPO,

I´ve been so concerned with how I´ll bend a 0.5mm alluminium sheet on the shape of the capacitor that i´ll have to skip the fun step

Hope to be able to share results not long from now.

Thank you very much from São Paulo!

[alysdexia]

Permittivity is a property of the bulk material and is independent of thickness.  Capacitance depends on the reciprocal of thickness.

C = εε₀A/d

Thus the capacitance is limited by the dielectric breakdown strength of the material (volt/mm).

By thickness (densitude) you mean depth.  Permittivity is indeed a function of lattice and bigger materials yield defects of worse permittivity than films.