In my project, I am developing a capacitive sensor based system which attempts to identify if two real world objects(*) get in contact with each other. I have done my homework (some) on Capacitive sensing and I am able to detect simple touch events either via classic charge/discharging-timer or oscillator 555 IC approaches. However, I still don't know exactly which object is in contact with which, and in my project, it is important that I determine this information.

So, the question I have is directly related to capacitance but in a somewhat general framework:

What can be said about two objects touching when it comes to their capacitance?

  • Are two objects put in contact sharing the same level of capacitance?
  • At the very least locally speaking, would it be such that if measured by sensors located on either side (the touching object, and the object being touched), we would read similar capacitance or at the very least relatable figures?
  • If not the actual level of Cap, would the "capacitance profiles" (dC/dt) be similar or relatable?

I would be interested to hear what people know (or think) on this subject and would appreciate any reference or link on existing research taking me in the "right" direction. Thank you.

*: real world objects would be (for example, but not limited to) a metal rod, and a sheet of conductive foil. For this conversation, I aim to remain realistic and so we are NOT talking about a piece of wood and a cut of fabric, but focus on reasonably conductive elements made primarily of metal.


If two objects are insulators, I don't think we can talk about capacitance at all. If the two objects are conductors, when they come in contact, there would be an electrical connection (short circuit) and in this case the capacitance is zero. That's what happens when a capacitor gets damaged - it's plates come in contact and it stops being a capacitor.

  • \$\begingroup\$ well and good, you are answering a question, but you are not answering my question. If two real world objects (plse note we are not talking about two capacitors here), for example two metal poles, both connected to cap sensors went to get in contact, would they then read the same capacitance? Intuitively, one would be able to say that two touching object form (only temporarily) a single object, and therefore, two sensors attached to the now single object would return the same data... but this is intuition and reality has its ways, especially with conductance and capacitance... \$\endgroup\$ – Jeruinsky Dec 11 '18 at 18:20
  • \$\begingroup\$ Of course, I should add that when it comes to measuring real world object capacitances, it is self-capacitance which is in scope, as opposed to mutual capacitance (self capacitance classically defined as the ratio of the change in an electric charge dQ to the corresponding change in its electric potential dV). \$\endgroup\$ – Jeruinsky Dec 11 '18 at 18:54
  • \$\begingroup\$ so that's it, no more interest than this, no one with any thoughts? no remarks from any of the big shots? (the Andy aka's, the Chris Stratton's of this space...). \$\endgroup\$ – Jeruinsky Dec 14 '18 at 11:35

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