CommonMode EMI Calculator
The fields that couple from a circuit board trace directly to cables attached to the circuit board can induce commonmode currents on these cables resulting in radiated emissions. Electricfield coupling is proportional to the magnitude of the voltage on the trace. Magnetic field coupling is proportional to the current flowing in the trace. For a given board geometry, a closedform expression for the maximum emissions due to these coupling mechanisms is described in [1, 2].
 Assumptions:

 The board is not within a well shielded enclosure. (There's a different calculator for this case.)
 There is at least one cable attached to the board and the cable length is much greater than the board dimensions.
 The board is located approximately one meter above a ground plane (as in a CISPR or FCC radiated emissions test).
Important Note: This algorithm was revised in January 2014. The new algorithm does not ask for the source impedance. The voltage input by the user is the signal voltage, not the opencircuit source voltage. The signal current is the signal voltage divided by the load impedance. The new algorithm is described in [3].
[1] C. Su and T. Hubing, "Improvements to a Method for Estimating the Maximum Radiated Emissions From PCBs With Cables," IEEE Trans. on Electromagnetic Compatibility, vol. 53, no. 4, Nov. 2011, pp. 10871091.
[2] C. Su and T. Hubing, "Imbalance Difference Model for CommonMode Radiation from Printed Circuit Boards," IEEE Trans. on Electromagnetic Compatibility, vol. 53, no. 1, Feb. 2011, pp. 150156.
[3] C. Zhu and T. Hubing, "Maximum Radiated Emission Calculator: CommonMode EMI Algorithm," CVEL13051, Dec. 23, 2013.
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