ABSTRACT
Stealth technology advances in radar-absorbing materials (RAMs) continue to grow rapidly. Barium hexaferrite is the best candidate for RAMs applications. Manganese dioxide (MnO2) is a transition metal with high dielectric loss and can be used as a booster for changing polarization and reducing reflection loss. The advantages of BaFe12O19 and MnO2 can be combined in a core-shell BaFe12O19@MnO2 composite to improve the material's performance. MnO2 composition, temperature, hydrothermal holding time, and sample thickness all have an impact on the core-shell structure. In this study, a core-shell BaFe12O19@MnO2 composite is synthesized in two stages: molten salt synthesis to produce BaFe12O19 as the core and hydrothermal synthesis to synthesize MnO2 as the shell. In the hydrothermal synthesis, BaFe12O19 and KMnO4 were mixed in deionized water using different mass ratios of BaFe12O19 to KMnO4 (1 : 0.25, 1 : 0.5, 1 : 0.75, and 1 : 1). The main goal of the analysis was to figure out how well the hydrothermal synthesis method worked at different temperatures (140 °C, 160 °C, and 180 °C) and holding times (9 h, 12 h, and 15 h). The composite material was subjected to characterization using a vector network analyzer, specifically at thicknesses of 1.5 mm, 2 mm, 2.5 mm, and 3 mm. The hydrothermal temperature and composition ratio of BaFe12O19 : MnO2 are the most influential parameters in reducing reflection loss. Accurate control of the parameters makes a BaFe12O19@MnO2 core-shell composite structure with a lot of sheets. The structure is capable of absorbing 99.99% of electromagnetic waves up to a sample thickness of 1.5 mm. The novelty of this study is its ability to achieve maximal absorptions on a sample with minimal thickness through precise parametric control. This characteristic makes it highly suitable for practical applications, such as performing as an anti-radar coating material. BaFe12O19@MnO2 demonstrates performance as a reliable electromagnetic wave absorber material with simple fabrication, producing absorption at C and X band frequencies.
ABSTRACT
In this study, fabrication of Pr15-xDyxFe77B8 (at.%) alloys with x = 0, 1, 2, and 3 compositions was performed with a mini vacuum arc melting furnace. The alloys were successively annealed in an inert atmosphere for microstructure homogenization. All alloys exhibit the typical characteristics of a permanent magnet. The coercivity gradually increases with increasing atomic fraction of Dy. The heat treatment applied to the samples changed the properties from those of a permanent magnet to those of a microwave absorber. The reflection loss (RL) value evaluated by a Vector Network Analyzer (VNA) shows broadband absorption characteristics in the full 8 GHz-12 GHz frequency range. The RL and bandwidth increase with the addition of the Dy substitute. The as-cast and annealed Pr15- xDyxFe77B8 alloy with the x = 1 composition shows superior absorption, starting from the 8 GHz frequency and increasing progressively, reaching less than -17 dB or an absorption of more than 85.0 % at a peak frequency of 10.5 GHz, after which it weakens to -6 dB at a frequency close to 12 GHz. Heat-treated samples were characterized by absorption with two almost overlapping absorption peaks at frequencies of 9.5 GHz and 11.5 GHz, leading to very broadband absorption across the full frequency range (8-12 GHz). It is concluded that permanent magnetic materials could be converted into radar absorbing materials (RAM). RAM based on heat-treated rare earth permanent magnet has broadband absorption characteristics.