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I want to design a capacitive proximity sensor to detect human presence at a distance of 10-15 cm.
Now I made my research on this type of sensor but everything that i found doesn't tell me about the size of such sensor, Can anyone help on how to calculate the size of the sensor?
The sensor Shape is circulaire and there is no constraint on it's size but the smaller the better.
I'm using a capacitive sensor because the system that i'm working on isn't fixed in one place, it is portable, so i don't need it to detect any object i only want it to detect human presence and the best option that i found is capacitive sensor which doesn't detect any object but only grounded objects, but if there is any better option that would be great.

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  • \$\begingroup\$ Capacitive sensors detect objects by measuring the change in an electric field caused by an object. They will detect non-grounded as well as grounded objects. \$\endgroup\$ – CHendrix Mar 22 '17 at 11:58
  • \$\begingroup\$ If you're using one electrode, you need a grounded object to change the electric field, non grounded object doesn't have any effect in this case. \$\endgroup\$ – L. Lt. Mar 22 '17 at 12:12
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The range is directly related to the size of the sensor. The bigger the sensor, the bigger the range.

We've been making capacitive sensors at work, directly on PCBs. In my experience, you can sense presence at a distance of 75% of the sensor diameter. So if you want to sense presence at 10cm to 15cm, I'd start with a sensor diameter of at least 20cm.

The range in which a probe is useful is a function of the size of the sensing area. The greater the area, the larger the range. The driver electronics are designed for a certain amount of capacitance at the probe. Therefore, a smaller probe must be considerably closer to the target to achieve the desired amount of capacitance. The electronics are adjustable during calibration but there is a limit to the range of adjustment. In general, the maximum gap at which a probe is useful is approximately 40% of the sensing area diameter. Standard calibrations usually keep the gap considerably less than that.

http://www.lionprecision.com/tech-library/technotes/cap-0020-sensor-theory.html

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