For the selection of the absorber material several things must be considered; the frequency range that have to be covered (including the requirements regarding chamber performance), the size of the place of installation as well as the respective costs. You can choose ferrite, pyramid or hybrid absorbers.
The following differences between the absorber types must be taken into account:
Reflectivity over a defined frequency range
Dimensions (length) and consequently the space required
An important advantage of ferrite absorbers is the fact that, despite their small thickness, they offer very good reflection attenuation characteristics starting already from a frequency of 30 MHz, thus being perfectly suitable for the use in smaller rooms. The biggest disadvantage however, is the relatively high price as well as the limitation of frequencies up to 1 GHz. Ferrite absorbers should be considered in all the cases where pyramid absorbers cannot be used due to limited space. An extension of the frequency range up to 18 GHz can be achieved by using a combination of ferrite absorbers with short pyramid absorbers (see hybrid absorbers).