EMI shielding effectiveness in conductively coated plastics

May 14th, 2014, Published in Articles: EngineerIT

 

Conductively coated plastics are becoming increasingly popular for EMI shielding. Vacuum metallising is a cost effective way to get fast turnaround in small quantities. Commonly, shapes can be complex, making it impossible to get absolutely uniform coatings. The article covers comparative shielding effectiveness (SE) tests on various configurations, primarily to assess the impact of selected voids in the coating.

emi-shielding-may2014Testing was performed at Environ Labs, based in Bloomington, Minnesota, using accepted shielding effectiveness methods. We used a 252 cm coated panel, configured as described in the individual tests. The panels were grounded at the perimeter using good quality EMI gasketing. An aluminum panel was first tested, and is used as a baseline; therefore, the SE of all coated panels are shown relative to the aluminum panel.

Our findings were that small voids in the samples had little impact on the shielding effectiveness. Additional small holes, as might be placed in an array for ventilation purposes, also had minimal impact. Larger holes showed shielding degradation especially at higher frequencies.

This validates our position that SE is primarily driven by larger openings created by seams and by wires (data and power) penetrating the shield.

We’ll start with a comparison of four samples and continue with a wrap-up… (more)

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