Experimental Demonstration of Novel Hybrid Microwave Absorbing Coatings Using Particle-Size-Controlled Hard–Soft Ferrite

The development of a thin and broadband microwave absorber using the microwave absorbing material (MAM) alone is a very challenging task for the researchers and industries. Therefore, a technique for developing a novel hybrid microwave absorbing coating (MAC) using particle-size-controlled hard-soft ferrites with optimized compositions is described and experimentally validated. The novelty of this paper is the possibility of enhancing and tuning the reflection loss (RL) properties of traditional MAMs by simply adjusting their particle size. The main target of this paper is to obtain wideband absorption corresponding to RL ≤ -10 dB and a lower coating thickness (≤ 2 mm). First, ferrite nanoparticles are synthesized and subsequently grown into distinct shapes and sizes by giving judicious heat treatment using a “bottom up” nanofabrication approach. Furthermore, these distinctly shaped and sized particles, i.e., spherical and flaky (20-30 nm), hexagonal (80-100 nm), and pyramidal (200-250 nm), are blended with one another in different proportions (1:1:1, 2:1:1, 1:2:1, and 1:1:2). An extensive morphological and electromagnetic (EM) characterization is carried out. An efficient theoretical and empirical model is used to investigate the EM properties of the heterogeneous MAC with respect to frequency and particle size. A fabricated MAC possesses an RL of -33.5 dB at 10.8 GHz with -10 dB absorption bandwidth of 4.2 GHz (covering the entire X-band region). Moreover, the ferrite layer coating thickness is only 2 mm. A good correlation between theoretical and measured results demonstrates the potential of the adopted approach for various practical EM applications.