For this part, I have used this tutorial
and haven't changed anything. The weak part in my system was the antenna: thinner than the one adviced and not in a ring shape, because I then put it inside the baguette. Note: I recently used a coke can as an antenna and it worked even better than with a cable.
If you followed the tutorial. You should have connected the Arduino to your computer and run the Adruino code they give. Instead of this code you can use mine. It is the same except that I have commented all the serial communication we don't need, it will just send the distance information.
Run it and on the Arduino application and watch the datas you receive. To do that click on the button up right. Be sure they match the distance of you hand from the antenna. At some point the values are inverted, this is normal and this is also something to improve.