EMC & Circuit Protection continued from page 15
that the floating heatsink had high emissions at low frequencies, declining as frequency increased until peaking up again at its first resonance of 5.32GHz. Direct bonding at all four corners had a very dramatic effect in reducing the emissions below 600MHz, but reduced the resonance frequency from 5.32 to 2.0GHz. Direct bonding at all four corners plus in the middle of each side of the heatsink – making 8 equally spaced RF-bonds in all – reduced the emissions significantly up to 2.5GHz, and caused the resonant frequency to increase to 3.75GHz. Increasing the number of equally- spaced bonds to 16 reduced the emissions significantly all the way up to 4GHz, with the first resonance now shifted further up, to 4.7GHz. The level of emissions at frequencies below 2GHz is now very low indeed.
Figure 9 shows experiments that varied the bond resistance, starting with the direct corner-bonding of Figure 8, and then increasing the bond resistance. Figure 9 shows that all of the resistance values used dampened down the first resonance, but the higher the resistance the worse the emissions became at low frequencies. Resistive bonding might be a useful technique when it was not practical to obtain a first (lowest) resonance above the highest frequency of concern – certain product designs may have to trade off between emission levels at resonant frequencies and the levels at low frequencies.
Paul created the simulation, ran it, and emailed me the data for Figures 6, 7, 8 and 9 during a couple of hours on his laptop at home one evening. How long it would have taken to get this kind of design insight by making prototypes and testing them? Several days, at least! Modern electronic design is so complex and fast-paced that it requires the use of field solvers to save time and cost during design and development, delivering products to customers with less risk of time-to-market delays, and consequently lower corporate financial risks.
www.cherryclough.com
www.emcstandards.co.uk
References (1)
Figure 9: Variations in E-field emissions as the RF-bonding resistance is varied
Figure 8: Variations in E-field emissions as heatsink RF-bonding is varied
“The Physical Basis of EMC”, Keith Armstrong,
i) As a free article:
https://www.emcstandards.co.uk/the-physical-basis-of-emc; ii) As training course notes:
https://www.emcstandards.co.uk/the-physical-basis-of-si-pi-and-emc, iiI) As a paperback:
https://www.emcstandards.co.uk/the-physical-basis-of-emc2
16 September 2024 Components in Electronics
www.cieonline.co.uk
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