Role of interactions between hardware units and card-cage structural members in the coupling of on-board EMI fields to currents on the outer surfaces of the card-cage structure

This paper presents an investigation of an EMI condition where electromagnetic interactions between conducting components of hardware units and card-cage structural members provide an efficient means of coupling the EMI fields generated on printed wiring boards (PWBs) to the outer surfaces of a single-shelf metallic card-cage. Experimental and computational results are presented. Far-field measurements at the 8th harmonic peak indicate that disconnecting the guard traces on the PWBs and shorting together the structural members of the card-cage at their midspan resulted in a cumulative reduction of ~7dB in the radiated field levels of the single-shelf EUT. These laboratory observations are generally confirmed and in practical quantitative agreement with the results of 3D EM field computational simulations. The findings of this investigation suggest that manipulating the dominant field mechanism(s) between EMI sources and the members of the card-cage can be an effective method of controlling near and far field emissions of the populated card-cage