S. Al-Sowayan,  Improved Mutual Inductance of Rogowski Coil Using Hexagonal Core.   journal   = {International Journal of Electrical and Computer Engineering}, [online]. World Academy of Science, Engineering and Technology.
    January 2014, vol. 86(2). 293 - 296
    [viewed 11 August 2020]. Available from: https://publications.waset.org/pdf/9997534.