Which proximity sensor can be implemented from inside of a metal body or casing?

[jahanvi]

I'm in search of a proximity sensor that can work efficiently in a range of 10 cm or more, with high response speed. Most important requirement is- it should detect the presence of human body through metal casing.

 

[Nanren888]

Basically the news is bad. Your only hope is to explain more about the scenario in the hope that something very controlled about the scenario allows you an option.
How thick is the casting? Is it allowed to be purpose designed? Changed?
Is the rest of the scenarion controlled, empty or uncontrolled and infinitely variable?
Noisy? static? dynamic?
.
Why?
Why not put something outside?
optical window?
.
Clearly I am guessing at things that might help.
Any details?

 

[Harald Kapp]

Metal casing is opaque to electromagnetic radiation, therefore light and radar are not applicable.

Ultrasonic sensor may work, but the metal casing is a strong hurdle as it will reflect most of the sound energy.
Capacitive sensing may also work if the whole metal casing is (can be) used as an electrode, but 10 cm are a challenge for capacitive sensors.

The easiest way is an opening in the casing for the sensor to operate. Maybe camouflaged by a plastic cover matching the color of the casing.

 

[(*steve*)]

Charge the metal box up to a potential that can jump 10 cm. then detect the sound of a scream. the sound should penetrate the box.

 

[Minder]

What metal are we talking about?
For example, there are proximity sensors to detect piston position in pneumatic cylinders, they cannot be used in hydraulic cylinders as these posses a steel cylinder instead of the aluminum of pneumatic.
I have several and they are very small units.
IOW, ferrous metal cannot be used.
.M

 

[Nanren888]

Can the human be taught to do a Sheldon Cooper knock on the box?
.
Anyway, it's tough to realistically suggest how without a few more details.
.
With an extremely well defined environment that is otherwise static:
Whole box is an antenna, senses field change?
Whole box electrode, capacitive sensing?
.
Box is, or has a port, transparent to ...
ultrasonics: sense field, general, or directive
radar?
Light?
.
Box has additions to the outside with wires, other communication. into box:
Many options.
.
Is the casting ferrous? Iron, steel or aluminium, other?
.
Is the human cooperative?

 

[dave9]

It's a shame we don't have a way to make holes in metal yet, but I have hope for future generations.

 

[Bluejets]

Must be possible, I've seen Superman do it on tv.