Conceptual design of a nonreciprocal bandstop filter using metamaterial Thue-Morse multiferroic superlattices

A novel nonreciprocal bandstop filter (NBF) using metamaterial Thue-Morse multiferroic superlattices (MTMMS) is presented, where the multiferroic domains with polarization and magnetization simultaneous are arranged along x-axis according to the iterative rule of the Thue-Morse sequence. The dispersion relation is obtained by the transfer matrix method and indicates that the band gaps for the forward wave (FW) and the backward wave (BW) are not symmetrical. Transmission spectrum is utilized to illustrate the band gaps clearly. Two band gaps in the frequency ranges of ω = 20.9 - 23.03 GHz and ω = 63.98 - 64.41GHz can be observed in the MTMMS with the sequence of l=2 for the FW. However, the band gaps for the BW appear in the frequency ranges of ω = 19.49 - 21.92 GHz and ω = 63.12 - 63.98 GHz. The maximum bandwidth of 2.1GHz and an obvious nonreciprocity with respect to the FW and BW can be obtained in this case. The S-parameters can verify this property further. In addition, the NBSF is easy to integrate into practical systems since its size of forming stable band gaps is about one centimeter.