Cost-effective anechoic linings for compact screened rooms

In order to reduce cavity resonances and field distortions during EMC tests inside screened enclosures, some form of anechoic treatment is necessary. A rather expensive technique which is becoming very popular is the complete lining ofthe enclosure walls with ferrite tiles. This mostly enables to perform compliant immunity tests (better than 6 dB field uniformity according to IEC 1000-4-3 draft) and diagnostic emission tests up to 1 GHz. For higher frequencies, the ferrite tiles have to be complemented with a specially adjusted matched absorber. A cheaper technique has now been developed which also enables fully compliant immunity tests from 80 MHz upwards, but has no high-frequency limitation such as ferrite tiles. It consists of an optimised resistive absorber lining of 50 cm thickness. Excellent results have been obtained in screened enclosures using this absorber.