Les objets de numerunique

Invisibility cloak
31/03/2025

Purpose

The initial request was given by a lawyer wanting to prevent his clients from being distracted by their smartphones, asking if numerunique could provide a jammer. Since jamming is illegal, numerunique suggested a conductive fabric case that acts as a Faraday cage.

A conductive fabric

A conductive fabric is easily found. Here's how we tested it.
The wood is a well-known insulator. On the left of the picture below, you see a multimeter set to detect conduction and detecting none.

Now the probes are put on the fabric, the red LED is lit, it beeps (though this isn't visible in the picture) and displays a negligible voltage.

Computer-aided design software is not always needed. Below is the handmade sketch that helped compute the size of the required fabric.

Making of

Making the intended case is easy:

  1. Sew a hem on each end
  2. Prepare the folding
  3. Sew it
  4. Turn it inside out

Hems

Folding

Sewing

Final

Instructions for use

It is quite straightforward:

Side effect

The intended purpose is fulfilled: in its Faraday case, the smartphone can't be reached. The lawyer can lecture his client without being interrupted by an unwanted call.

Yet there is an interesting side effect. This case acts as an invisibility cloak, an actual one.


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