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Design >> Analog Design >> Question on mutual capacitance change on other neighboring conductors
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Message started by neoflash on Jul 30^th, 2017, 10:49am

Title: Question on mutual capacitance change on other neighboring conductors
Post by neoflash on Jul 30^th, 2017, 10:49am

I am looking for articles or textbooks that can explain the impact of 3rd conductor on mutual capacitance on two conductors.

For example, for many capacitance sensing scheme, the mutual C between sensor and object will change linearly with distance if no other conductors nearby. However, if there is other conductor close to sensor, the mutual C drops much faster with distance.

If any material helps understand this better, I would really appreciate it.

Title: Re: Question on mutual capacitance change on other neighboring conductors
Post by Maks on Jul 31^st, 2017, 9:36am

Capacitance change (inversely) linearly with distance only for a parallel-plate capacitor, or - for any capacitor if the change (of the distance) is small.

In general, introduction of a third body (a conductor with fixed voltage -
i.e. not floating) close to the "plates" of a capacitor will reduce the capacitance between the plates.

I never heard of a statement that the rate of capacitance change is faster in the presence of a third body.

I don't think you will find a detailed theoretical discussion of this thing in the literature. People do simulate capacitance, but it is not considered a cutting edge research, in general. And if it is a cutting edge research for some companies (like capacitive touch sensors) - they would keep this as a trade secret, not publishing the results.

Max