Toward practical activation of nonreciprocal metasurfaces: dual control and design framework

Abstract This paper presents an actively controllable nonreciprocal metasurface based on a ferrite–patch structure with PIN diodes for dynamic control. Two activation methods are investigated: (a) phase control, which enables a 30° transmission-phase shift while maintaining nonreciprocal behavior, and (b) ON–OFF control, which switches the response by altering the propagation path. The phase-control metasurface is analyzed using transmission-line theory, full-wave simulation, and experiments, showing good agreement across methods. The ON–OFF design is optimized to suppress bidirectional transmission when ON. Experimental results confirm strong nonreciprocity, though slight frequency shifts arise from FR4 variability, and a back-fitted simulation improves consistency. The proposed dual-control framework provides a compact and low-cost approach to reconfigurable nonreciprocal surfaces that retain the use of permanent magnets for ferrite bias and are applicable to microwave wireless systems, including adaptive isolation, interference control, and tunable shielding. The results demonstrate the feasibility of compact, reconfigurable nonreciprocal metasurfaces using simple biasing circuits and offer design insights for frequency-stable implementations.