A method of reducing the number of ferrite tiles in an absorber lined chamber

Anechoic chambers are used for both emission and immunity testing but the ferrite tiles used to line the inside of the chamber are extremely expensive. This paper describes a method of reducing the number of tiles, whilst ensuring a reliable test environment. The quality of a chamber is assessed by the magnitude of the difference between the normalised site attenuation (NSA) inside the chamber, and the theoretical NSA of free space. The chamber being acceptable if this is less than 4 dB at all frequencies in the range of interest. A genetic algorithm is used to optimise the layout of tiles with only 80% of the chamber walls covered. Transmission line matrix (TLM) modelling is used to determine the NSA in the chamber. Measurements provided for comparison show that the optimised tile layout with 80% coverage gives results as good as a fully lined chamber