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Would adding layers to the capacitor of a proximity sensor from lets say 1 (A) to 4 layers (B) help with increasing the capacitance and at the same time the distance that can be sensed with a proximity sensor?

Simple capacitor vs multi-layer capacitor

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  • \$\begingroup\$ What signal does the finger carry? Stray line signal , RF from PCB?. Is it a ground loop or bridging 2 electrodes on a differential signal on board thru the surface dielectric or air? So is your detector sensing the emitter being shunted by the finger to gnd or bridged between vertical plates. \$\endgroup\$ Jul 31, 2020 at 12:48
  • \$\begingroup\$ Remember adding a large C in series to a small C in finger to plate does nothing to increase C sensitivity. But shunting a signal could with a smaller source capacitance. << 10 pF \$\endgroup\$ Jul 31, 2020 at 12:51
  • \$\begingroup\$ Use a Schmitt trigger relaxation Oscillator with 10M feedback and x pF to gnd. oscillator. Then maybe keep electrodes far apart so hand can bridge them from gnd on PCB so you from 0.5m away might be detected and observe frequency rise as you get closer. inverse squared sensitivity \$\endgroup\$ Jul 31, 2020 at 13:07

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Unfortunately, this won't work. In order to increase the sensitivity, you'd have to increase the area of near contact between the capacitor plate and your hand. Since all the plates you've drawn are connected to the same node, there's no electric field between them...only between the top plate and the finger. Reducing the thickness of the insulator would proportionally increase the capacitance.

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  • \$\begingroup\$ Would interleaving the 4 plates by another 4 grounded plates help? \$\endgroup\$
    – Pat
    Jul 31, 2020 at 12:26
  • \$\begingroup\$ What's your theory? How would it help? \$\endgroup\$
    – Transistor
    Jul 31, 2020 at 12:30
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    \$\begingroup\$ The sensor works by measuring the capacitance from the plate to your body. That is determined primarily by the capacitance between the plate and the finger touching the insulator, which in turn is proportional to the area of near contact and the dielectric constant, and inversely proportional to the distance (which is determined by the thickness of the dielectric). Adding interleaved plates to ground would increase the total capacitance, but the change in capacitance between touching and not touching would be the same; it would just be a smaller percentage of the total capacitance. \$\endgroup\$ Jul 31, 2020 at 12:52
  • \$\begingroup\$ I should note that flexible interleaved plates with spongy, compressible dielectric could be made into a pressure sensor, but I don't think that's what you're going for here. \$\endgroup\$ Jul 31, 2020 at 12:53

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