Use large metal sheets to detect body


I would be thankful for some input on this, and advice on where to read up on it.

This is for an art installation.

I have two thin metal sheets around 0.5x1.5 meters. They have been part of a large satellite dish. I think it is aluminium. Have to check though.

I would like use them to detect if a human body is nearby, around 1 or 2 meters. They will be hanging flat horizontally in the ceiling of a room. Optimally I want to be able to detect as soon as someone is entering the room.

I know I could use a PIR for this but I want to use the actual objects, the metal sheets.

I have read up a bit on capacitive sensors but the tutorials are mostly for touch screens and the such. I have tried out the CapSense library also, with just a basic circuit.

Although I do not know the technical solution I imagine that it could be really simple. The plates have been used as antennas (a satellite dish), so it should be possible to use them like that again. Right?

Thanks a lot for your help,


If you hang well insulated plates parallel to each other, forming a capacitor, the presence of a person or conductive object between the plates would change the capacitance.

On the other hand, the naked plates would be excellent antennas picking up all sorts of interesting electrical impulses, from lights, motors, power lines, radio stations, etc.

1 Like

What other metal is near by? Electrical wires? Electric lights? A suspended ceiling with steel framing?
What do you consider a person? A 2 year old child or a 6 ft. 300 lb adult?

You can use the two plates as a capacitor to control the frequency of an RF oscillator and monitor for change in frequency as the person changes the dielectric constant of the space between the plates.

1 Like

Thanks. Yes, there will be a lot of things that can (will) interfere. All of the above actually.

I would like to detect presence of persons from 2 years and up.

I think I can access and RF oscillator.

Thinking about it, what if I put a hidden plate on the floor?

You need to BUILD the RF oscillator and use the plates as frequency determining device.

1 Like

Might as well put a PIR sensor on the (hanging) plate. :grin:

1 Like

The cheap radar sensors work quite well and can be hidden,
but unfortunately not behind the metal plates. :grinning:

1 Like

I googled up some schematics, seems doable. Next step is to understand.

This is what made me think it was a possible way to go:

Go for it!

1 Like

PIR is boooring :slight_smile:

Maybe you have an idea for another way to use the plates for this purpose?

You got my idea. I wonder if you skipped all the science and math classes in school?

1 Like

I did skip a lot of classes, regret it badly.

Ill try to step on another mine then -

What if I use the plates as a giant microphone membrane?

What type of microphone?

1 Like

Alright, probably not possible. I was thinking crazy amplified piezo.

Hi @brodbord.

What if I use this sensor to detect human presence?

See page 10.

RV - mineirin

1 Like

One approach is to use anything that works to detect people, but tell them "the metal plates are doing it".

1 Like

I am now thinking I should do the opposite, use the panels to block the path of a sensor. That could give same effect and the plates are actually being used.

Maybe in combination with the capacitor/rf oscillator method, where the latter will be used for retrieving a more organic signal that I will translate to sound (art).

Is there a tutorial out there where I could build a small prototype trying out the capacitor/rf oscillator solution?

The first step is to get your material hung on insulating cords or what ever and measure the capacitance between the two plates. There are some DVM that may do that. Then you will know what else will be needed to reach, perhaps, a 4 mHz frequency.

1 Like

Amen to that. :roll_eyes: