An electrically frequency tunable absorber with no absorption frequency limit

ABSTRACT We propose an electrically frequency tunable absorber (EFTA) with varactor diodes, which can provide good absorption properties even in much higher frequency bands than conventional EFTAs. In general, conventional EFTAs cannot guarantee high absorption rate beyond a certain frequency limited by high capacitance of commercial varactor diodes. In this letter, however, we suggest a simple but fairly effective way to overcome the high frequency limit by intentionally inserting parasitic capacitance introduced from multiple slits. The parasitic capacitance connected to the varactor diodes in series can decrease overall capacitance to an optimum value. Consequently, we not only can maintain good absorption rate in a very high frequency region, but also freely select a target absorption frequency band by modifying the number of slits. Experiments for normal and oblique incidence have been carried out to validate the proposed method. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:145–148, 2017