EMI control performance of the absorbing material for application on flexible cables

Common mode signals on flexible cables often cause unwanted EMI. Common mode currents can be controlled by applying electromagnetic absorbing materials to the flexible cables. This work presents a set of specially designed test apparatuses that allow the performance of absorbing materials to be estimated for three typical structures known to radiate: monopole antennas, loop antennas, and transmission lines. Two materials are compared for each of the apparatuses, and the resulting common mode and EMI metrics are presented. The amount and placement of absorbing material was optimized based on reduction of EMI and impact on signal integrity. The better-performing materials were further tested in the actual hardware (television), showing a lower reduction in EMI (of about 3 dB) compared to the test apparatuses. The possible reason for reduced performance is that the flexible cable may not be the only source of radiation in the more complex real system.