I am planning to build a rogowski coil but not the conventional one, which is a circular loop. Below is the example of a rogowski coil so you have the big picture of my question. In the picture, the current conducting wire (with current Ip) is encircled by a big circular loop rogowski coil. The cross sectional area of the winding itself can be a circle, rectangle, or oval. For this variations of cross sectional area, I know how to calculate the mutual inductance. However, what if the shape of the big loop is rectangular? How to calculate the mutual inductance? I hope you all can help me figure this out.