Characteristic Mode Analysis and New Ground Approach At a Heat-sink for Reducing EM Radiation

Abstract

A heat-sink has been widely used to cool down the heat generated from an electronic device, but it can bring unwanted electromagnetic radiation which may cause EMI problems. We propose a systematic method to reduce the electromagnetic radiation by using the multiple grounding technique based on the grounding criteria and the theory of characteristic mode analysis. Our proposed method provides the insight to find the specific grounding positions which can be effectively reduced the radiation from the heat-sink. Numerical experiments are accomplished to validate this approach.

Fig. 1. The surface current distribution and geometry of theinvestigated 2-D conductive plate at 2.8 GHz

Fig. 2. A comparison of the radiated power referred to non-grounded and grounded plates

Fig. 3. A comparison of the radiated power referred to non-grounded and two grounded plates

Fig. 4. The geometry of 2-D flat-type heat-sink

Fig. 5. The variation with frequency of characteristic angles,

Fig. 6. The variation with frequency of modal weighting

Fig. 7. The surface current distribution with magnitudesand arrow plots about the selected modes and thedetermined positions of multiple grounding at 3frequencies

Fig. 8. The picture of testing the radiated power from theheat-sink in FEKO. The hemisphere surrounding theheat-sink describes the Far-field boundary forcalculating the radiated power, and it has beenresized for showing on the paper

Fig. 9. A comparison of the radiated power referred to non-grounded and six grounded heat-sinks

Table 1. Conditions of each parameter for resonance

Table 2. The modes and modal weighting coefficients at the resonant frequencies

Table 3. The characteristic currents of approximating the total current J at each frequency

Table 4. The characteristic modes and its current distri-bution which have top 3 dominant modal weighting coefficients at each frequency between Non-grounded and Grounded cases (the number in ( ) indicates the value of nβ ) ※ nJ and n￠J are different modes, although they have the same index ‘n’.