Boosting the performance of low-cost eco-friendly pyramidal absorbers with a Salisbury screen

Instead of using expensive highly performing conventional pyramidal absorbers, in some cases, the use of absorbers based on very cheap eco-friendly materials is an attractive alternative. The authors introduce a novel technique to improve the absorption bandwidth of these intrinsically low-quality absorbers by adding a Salisbury screen at the base of the pyramidal absorber, which adds two extra design parameters. The first is the resistive sheet surface impedance, and the second is the resonance frequency of the Salisbury screen. By tuning these two parameters, better impedance matching can be obtained. This is verified with the help of a transmission line model, full-wave simulations, and measurements. The method is applied to two different lower-quality absorbers found in the literature. In the first absorber, the operating bandwidth is increased at the lower frequency side by 40%, and in the second one, this is about 90%. Finally, a prototype of an eco-friendly combined absorber is designed and fabricated. The measurement validates the expected behaviour.