Passive proximity detection using metal plate-capacity

Question

For some specific product, we need to create a proximity sensor of 50-100cm using a capacity sensing .(no PIR, no infra,no ultrasonic)

Reading on the net, haven't provide me what i needed .

So, i am trying to get some direction on how do you calculate the plate surface area and thickness, in relation to the maximum distance of detection of a human body .

The software probably much easier, although i will also need to find a way so that it can awake the controller only on detection .

Is there something like that, or is this a very wrong direction ?

thanks .

Answer 1

Have you looked at this: https://en.wikipedia.org/wiki/Capacitive_sensing there are some references at the bottom that should lead you to the correct formulas.

Capacitive sensing works based on capacity CHANGE due to the presence of another conductor. For 50 - 100 cm I think you would need a large plate (also 50 cm in diameter at least ?), also the object needs to be large and (somewhat) conductive to get a decent amount of change in capacitance. The main problem I see is the distance. On a smartphone's touchscreen your finger is only a few mm away so the sensing conductor can be small. That is not so in your application.

I work at a company where we make a distance sensor based on radar, it has no problem detecting objects at 50 - 100 cm. It is still in development though and not cheap.