EMI suppression for high-speed PCB

This paper studies two popular examples of high-speed Printed Circuit Board (PCB), portable embedded devices and industrial computers, through measurement of 10-m semi-anechoic chamber in ChungHwa Telecom Labs, and proposes some simple but practical remedies to reduce their Electromagnetic Interference (EMI). In the first example, EMI of portable embedded devices can be simply prevented by an iron case rather than an aluminum alloy case. Besides, this paper develops iron shielding sheets to further suppress EMI of critical on-board ICs. The measurement result verifies the suppression effect of iron shielding sheets is much better than that of rubber microwave absorbing patches. In the second example, EMI of industrial computers can be effectively blocked by the well-made chassis. In addition, the shunt capacitor can further suppress dominant EMI from the pulse regenerator, but its suppression effect at some spectrum is limited. To overcome this limitation, this paper proposes and verifies the copper foil is the best alternate.