A PCB-based electrically tunable absorber with an expanded absorption frequency band

A printed circuit board (PCB) based electrically tunable absorber (ETA) providing good absorption rate at much higher frequencies than conventional ones is proposed. In conventional ETAs, the highest absorption frequency is mainly limited by very large capacitance of commercial varactors. In order to overcome the high-frequency limit, small parasitic capacitance is intentionally introduced by narrow slits inserted in a rectangular metallic patch printed on top of a substrate. Hence, overall capacitance of the proposed ETA can be remarkably reduced according to series connection between the capacitance from the slits and varactors. Consequently, we can continuously scan absorption frequencies in any target frequency band with almost no high-frequency limitation. In addition, by changing the number of slits, we can unrestrictedly select any target absorption frequency band. Good agreement between simulation and experiment proves the validity of our approach.