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For example, is there any material I can place over a capacitive sensor, or the finger or conductor approaching it, so that the sensor will no longer activate?

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  • \$\begingroup\$ How much space do you have to work with? You can use a thick sheet of any non-conductive material to disable a capacitive sensor. However, depending on the sensitivity of the sensor, this may be inappropriate. \$\endgroup\$ – uint128_t Dec 31 '15 at 17:20
  • \$\begingroup\$ There is very little limit on space, but simple spacing must not be the solution. In other words any thick sheet of non-conductive material could disable the sensor simply by obstructing any conductive material from getting close enough to the sensor, but that isn't appropriate. The case is of the capacitive sensor buttons on the PS4 which are oversensitive. The standard "internet fix" is to dismantle the console and deliberately scratch the gold pad to reduce its sensitivity, but I am wondering if applying a material to the outside could deaden the spurious capacitance which trips it. \$\endgroup\$ – Mark Green Dec 31 '15 at 17:33
  • \$\begingroup\$ Try wearing gloves. \$\endgroup\$ – Ecnerwal Dec 31 '15 at 18:27
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A capacitive touch sensor sort of forms a parallel plate capacitor with your appendages. As capacitance increases above a threshold, the sensor triggers. So, let us examine the capacitance of a parallel plate capacitor and see what we can do to reduce it:

$$ C = \frac{k \epsilon_0 A}{d} $$

where \$ \epsilon_0\$ is the permittivity of space, a constant; \$ k\$ is the relative permittivity of the dielectric, dependent on the material between the two plates; \$A\$ is the area of the plates; and \$d\$ is the distance between them.

You can increase \$d\$ by a little bit by adding some material, but as you said in your comment, this alone is not enough.

\$A\$ is tricky to change; you don't want to modify the sensor, and your fingers aren't going to shrink.

It seems the obvious solution, then, is to reduce \$k\$. Unfortunately, as far as I am aware, \$k \simeq 1\$ for air, and all solids have \$k>1\$.

So, it seems like this is not possible.

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Interpose a conductor - a sheet of copper, or tinfoil - between finger and capacitive touch sensor - and ground the conductor. (It must be insulated from the capacitive sensor, of course).

Your finger will form capacitance to the ground plane but not the sensor behind it.

This assumes the sensor reacts to changes in capacitance, not absolute value, otherwise it will simply see a large constant capacitance to ground...

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