Fe-SiC Composite Constituted Multilayer Gradient Perforated Microwave Absorbing Structure for Stealth Applications

Abstract

Microwave absorbers are advanced electromagnetic structures that can competently deplete the incident electromagnetic (EM) wave, and widely utilized for stealth and electromagnetic interference mitigation applications. There have been enormous strides in the broadening of absorption bandwidth (BW) using thin and lightweight functional materials. Apart from functional materials, the shape and loading of the absorber are equally responsible for attenuating the EM wave. There are various potential structures capable of altering the equivalent EM properties of the material to achieve excellent absorption BW [1]-[2]. The simultaneous achievement of wide absorption bandwidth and lower coating thickness of the absorber layer is a very challenging task. In this work, an effort is made towards the design of thin and broadband triple-layer absorber by incorporating gradient air perforation into the absorbing sheets constituted of iron (Fe)-silicon carbide (SiC) composites synthesized by robust top-down fabrication technique. The gradient air perforation prompts viable absorption BW if the period and diameter of perforations are equivalent to the wavelength.Fe-SiC composites in distinct compositions (i.e., FS1, FS2, FS3, FS4, FS5, FS6, and FS7) have been utilized in the development of microwave absorber. The composites have been developed using a top-down fabrication technique accomplished via a high-energy planetary ball mill (Model: Insmart device, MBM-07, India). The milling process has been initiated by loading stainless steel containers with hard 20 mm and 10 mm diameter steel balls. The powder to ball weight ratio (PBR) of 1:10 was taken with the rotor speed to 400rpm. The EM properties of the composite were measured in the range of 8.2 to 12.4 GHz (i.e., X-band) using a waveguide-based microwave measurement technique. Further, Jaya’s-Grey Wolf based hybrid multiobjective optimization technique has been utilized for the modelling of a perforated multi-layered absorber using the measured EM parameters. The mathematical model of air perforation is integrated with the transmission line equations such that the developed structure appears like a gradient perforated triple-layer structure. The fitness function of maximum BW below -10dB with minimum thickness is organized in the hybrid optimization algorithm. An optimal sample has been fabricated using epoxy coating and drilling techniques based on the optimal design variables obtained using the algorithm.The schematic of 3D topology and fabricated porotype of perforated absorber constituted of Fe-SiC composites is shown in Figs. 1 (a) and (b), respectively. Fig. 2 shows the reflection coefficient curve (RC) of single-layer absorber at their optimal thicknesses. Among all Fe-SiC composite database, FS-7 composite achieves a minimum RC value of -24.7dB at 11.1 GHz at an optimal thickness of 1.7mm, covering an absorption BW of 3.1 GHz below -10dB threshold in X-band. Furthermore, FS-4 composite exhibits an absorption BW of 1.7GHz with a minimum RC value of -10.9 dB at 9.3 GHz at an optimal thickness of 1.7 mm. However, FS-3 composite achieves a minimum RC value of -9dB at 8.2 GHz demonstrating no absorption BW.In the proposed gradient structure, the hybrid optimization algorithm chooses composite FS-4 for layer 1 with an optimal thickness of 0.4 mm backed with a perfect electrical conductor. Consecutively, layers 2 and 3 (i.e., air absorber interface) are structured using FS-7 and FS-3 composites with an optimal thickness of 0.9 mm and 0.3 mm, respectively. The optimum air perforation diameter is 6 mm, 5mm, 4mm for FS-3, FS-7, and FS-4, respectively with a period of 20 mm.The magneto-dielectric properties of composite FS-3 are high as compared to FS-4 and FS-7 composites. Due to the larger diameter of air perforation, the effective magneto-dielectric properties are supervised to act as an impedance matching layer. A 1.6 mm multilayer structure (without hole) is compared with the proposed structure as shown in Fig. 2 (b). Due to gradient air perforation in the layered structure, the EM parameters are altered, which leads to the shift of resonance frequency. The obtained result reveals a better -10 dB absorption BW of 3.4 GHz with a minimum RC of -19.9 dB at 10.8 GHz. An exceptional microwave absorption is achieved in terms of peak RC and BW with a substantial reduction in the total coating thickness of 1.6 mm in comparison to a single-layer absorber. Moreover, due to perforation, the weight of the structure is also reduced. The gradient impedance alignment within the structure improves the other mechanisms of absorption, such as phase cancellation, internal reflection, and frequency dispersion within the structure which results in improved absorption BW. **