Ultra-wideband electromagnetic wave absorption in mmWave using dual-loss engineered M-type hexaferrite: A wave cancellation approach

The development of broadband, high-performance electromagnetic (EM) wave absorbers in the millimeter-wave (mmWave) band requires optimizing both magnetic and dielectric losses, presenting significant challenges. Here, we report an ultra-wideband EM wave absorber for the mmWave band based on Strontium M-type ferrite (SrM) with dual-loss characteristics. SrM was synthesized via a non-stoichiometric sol–gel method with controlled iron (Fe) deficiencies to induce both dielectric and magnetic losses. The high magnetic anisotropy of SrM results in strong magnetic losses through ferromagnetic resonance (FMR) near 50 GHz, while Fe deficiencies induce local charge imbalances, leading to significant dielectric losses. EM wave characterization reveals that the dual-loss SrM absorber with an Fe/Sr ratio of 10 (SF10) exhibits an effective absorption bandwidth (EAB) of 26.95 GHz, covering the Q- and V-bands at a thickness of 0.5 mm. To elucidate the ultra-wideband absorption mechanism of the SF10 absorber, its EM parameters were analyzed using wave cancellation theory. The results demonstrate that the dual-loss characteristics reduce the amplitude difference between surface- and backplate-reflected waves and bring the phase difference close to π, enabling ultra-wide EAB through wave cancellation. These findings establish fundamental design principles for broadband EM wave absorbers.