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Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
If a parallel plate capacitor is constructed using layers of different dielectrics the greatest electric field gradient (V/m) will be across the dielectric with the lowest dielectric constant. So in the microwave glass case above, glass was actually the dominant dielectric.
PVA is a terrible choice unless you can prevent the absorbtion of atmospheric moisture.
If the application justifies it, you may consider ceramic dielectric high voltage capacitors e.g. 20x 1nF 20kV in series = 50pF 400kV = £10.01
It seems as though you are using high voltage dc ? If so then any dielectric that gives the desired voltage and capacitance will do, provided that the dc leakage is low. Low dielectric loss materials such as polystyrene and polyetheylene can be used but are not required.
If you are considering submerging your capacitor in oil, then just use oil as the dielectric. Much better than a solid dielectric, especially for development and/or repairs.
Registered Member #61406
Joined: Thu Jan 05 2017, 11:31PM
Location:
Posts: 268
Sorry Suliman I think I didn't understand you, are you saying that two different deiletic constants don't average out to something between, the way I understand you is the constant would have been 5 for glass.
Edit I understand why you would think that, if there is a conductive layer between the two dielectric it would be two capacitor in series, but without the conductive medium it is average out, the above 450-k at 1mm 1-k at 14mm Equal about 40-k,with the area and four plates in total equal 4nF,which the multimeter read as well.
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Mylar sheets for capacitors
