Donor–acceptor modified ixiolite structural ceramics for millimeter-wave broadband metamaterial devices

Abstract

Low-loss microwave dielectric ceramics (MWDCs) are key components for passive devices in the microwave/millimeter-wave band, and in particular the tunable dielectric properties are significant for the development of ceramic-based dielectric metamaterials. Herein, a donor–acceptor modified ixiolite structural ZnTiNb₂O₈ system with (Cr_0.5Nb_0.5)⁴⁺ substitution (ZTN-CNx, x = 0–0.15) was first prepared to construct a low-loss broadband metamaterial device. The modulation effect of (Cr_0.5Nb_0.5)⁴⁺ on the crystal structure and the influence on the dielectric constant (ε_r), Q × f value and temperature coefficient of resonant frequency (τ_f) were reasonably demonstrated by combining various testing methods with complex chemical bond theory. Compared with pure ZnTiNb₂O₈, the ZTN-CN0.1 ceramic achieved a nearly 45% increase in the Q × f value without excessive deterioration of other dielectric parameters. Finally, based on the coupling of magnetic dipole and electric dipole, a millimeter-wave broadband metamaterial reflector based on the ZTN-CNx ceramic resonant unit cell was designed. The theoretical insertion loss could reach 0.035 dB in free space by adjusting the sturcture, and the millimeter-wave operating bandwidth was greater than 2 GHz (reflectivity >95%), which could also be verified in waveguides and highlighted the potential prospects for broadband passive devices in wireless communication and anti-electromagnetic interference (anti-EMI) fields in the millimeter-wave band.