My facilities here allow me to design a coil with trace width and trace spacing both 10 mils. I will not be able to get a spiral coil and instead can get a rectangular coil. Will the rectangular coil work? I had used the webench tool to design a coil till a distance of 7cm. But the webench tool has coil trace width and spacing as 4 mils. Could you please give the back end calculations so that I can keep the inductance and coil diameter same and adjust the other parameters while i design a coil with trace width and spacing of 10mils.