# ring-capacitor design

I created a simple design, based on the fundamentals of a parallel plate capacitor. Making a co-axial/tubular design:

Front view:

The "Air gap" is there to allow current flow in one-direction, from connector to end adjacent to the air gap.

I'm curious of the following:

1. Does the connectors(to the exterior circuit) effect's the capacitance($$\C\$$) of the design?

I only see the area between the plates being reduces based on the "width" of the connectors.

1. As the capacitor charges/discharges (interacting with the exterior circuit) would the flow of current out/in via the connectors cause any effect to the plates and the electrostatic field($$\E_s\$$) between them?

As for calculating the capacitance I believe this equation is still valid:

$$\C= \frac{2\pi k\varepsilon_0}{ln(\frac{b}{a})} \$$

• The "air gap" is not necessary. There's no reason not to let current flow both ways from the terminal. – Dave Tweed Apr 13 '19 at 16:53
• I have to ask, why would you design a capacitor like this? It seems unnecessarily large. – Hearth Apr 13 '19 at 16:53
• @DaveTweed It helps me imagine the current flow in one direction starting from the connector and looping around(if we consider the postivee plate) till the air-gap end, either in CW/CCW direction depending on the state(charge/discharge). – mai Apr 13 '19 at 18:13
• @Hearth Using this ring-like design with another component to conserve #-of parts for a project, rather not have a capacitor compartment. The hollow gap will have a non-conductive piece that serves another purpose in a system. – mai Apr 13 '19 at 18:15
• @M.Isaac Note that your air gap effectively doubles the capacitor's ESR and ESL while giving you no benefit. – Hearth Apr 13 '19 at 18:32

## 2 Answers

If the "connectors" are made of a conductive material then they become just part of each plate. They will not change the capacitance of the structure unless the thickness of the dielectric is different beneath the connector (hard to tell from your drawing).

As Dave Tweed said, the air gap serves no electrical purpose.

Of course, current flowing through the connectors is going to change the electric field between the plates. That's how capacitors work. The current flowing into one plate must be balanced by an equal current flowing out of the other plate. The relative voltage of the plate with current flowing into it will increase, with respect to the other plate.

• I agree with everything covered. I wanted to comment on the air gap point: It helps me imagine the direction of current path, with this design we can imagine the flow to be either CW/CCW in one direction, if I were to remove the gap, the current flow would be in both direction simultaneously(CW+CCW). I'll edit the question on that point. – mai Apr 13 '19 at 18:23

Using a split single layer cylindrical capacitor is similar to a foil capacitor with no continuous connection in a single loop.

The biggest difference is you have only 1 revolution of surface area to create this capacitance.

https://phys.libretexts.org/Bookshelves/University_Physics/Book%3A_University_Physics_(OpenStax)/Map%3A_University_Physics_II_-_Thermodynamics%2C_Electricity%2C_and_Magnetism_(OpenStax)/8%3A_Capacitance/8.1%3A_Capacitors_and_Capacitance