I bought a pair of cheap house shoes and removed all the unnecessary stuff with an exacto (I'll put on the much warmer felted shoes instead).



Next cut a an approx 3mm deep circle out of the sole under your heel. It must have the size of your inductive coil. Don't make it too deep, because the the transmitted power will suffer a lot if the distance gets bigger!



If you try to keep the ring you cut out intact, you can glue it back on later (after making it as thin as possible) so, noone will even notice that there're coils inside.



Drill two holes through the sole, for the wires leading from the coil to the rectifier IC.



On the inside of the sole cut a rectangular whole in the size of the PCB for the rectifier. Make it as deep as possible, so the wearer won't feel it when walking.



Desolder the coil from the pcb, insert the coil inot the sole, insert the ic Into the other side of the sole and solder the wires back on (I made two cuts, so i could push the wires into the sole, to make them completely invisible).



If you took care while cutting the hole for the pcb you can use the cutout and put it back onto the ic.



First i tried to build the heating element myself by using wire, but it either got too hot or didn't warm up at all. So I decided to get some heated scarfs from the local super market (about 5€ per piece...). They contained small patches of thin hair like wire which are connected to a power source and get warm. Exactly what i needed.



I soldered the leads to the pcb and glued the patch onto the sole.



With everything attached, I ran a first test by putting the shoes onto the source coil: the heating element got warm after a few seconds:-)





