Large-Scale Nanofiber Manufacturing| Top-Level Electromagnetic Design of Multishell ResonantCavity for Microspherical Microwave Structural Absorbers

Prof. Meng Fanbin from Southwest Jiaotong University: Top-Level Electromagnetic Design of Multi-shell Resonant Cavity for Microspherical Microwave Structural Absorbers

With the rapid development of modern electronics and communication technologies, the importance of microwave absorption materials for broadband absorption and lightweight requirements has become increasingly prominent. To address the evolving detection systems and expanding communication frequency bands, researchers have developed various microwave absorption materials aimed at achieving broadband absorption and lightweight goals. Current research on existing microwave absorption materials primarily focuses on micro/nano morphology regulation and lossy medium composition. Although micro/nano absorbers exhibit excellent absorption performance, optimizing nano-absorbers still faces significant challenges in practical applications.

Recently, Prof. Meng Fanbin’s team at Southwest Jiaotong University published their latest research titled "Top-Level Electromagnetic Design of Multi-shell Resonant Cavity for Microspherical Microwave Structural Absorbers" in the journal Small Structures. Through electromagnetic simulation, controllable fabrication, and numerical analysis, the researchers proposed a comprehensive spherical broadband absorber design by leveraging the advantages of continuous multilayer structures and micro/nano morphology regulation. Using controllable multi-axial electrospinning technology and broadband electromagnetic wave absorption design principles derived from simulations, they successfully prepared graphene-based aerogel microspheres (GAMs) with multi-layered core-shell structures. By adjusting shell structural parameters, optimizing multilayer shell design, regulating micro/nano morphology, and implementing interfacial engineering of nanomaterials, the electromagnetic attenuation behavior and impedance matching performance of the aerogel microspheres were significantly improved.

Figure 1: Electromagnetic design and simulation of graphene-based multilayer aerogel microspheres.

The team first established equivalent electromagnetic models for various multi-shell aerogel microspheres through simulations, analyzing the influence of different shell structures on electromagnetic wave absorption performance. The results showed that tuning shell parameters and multi-shell design could optimize impedance matching and wave attenuation. Based on the simulations, they fabricated aerogel microspheres with different shell structures, including hollow GAMs (HGAMs) and multi-shell GAMs (MGAMs).

Figure 2: Schematic preparation process and microstructures of multi-shell aerogel microspheres.

Figure 3: Microwave absorption performance of multi-shell aerogel microspheres.

Based on electromagnetic simulation and multilayer matching principles, the strategy for regulating graphene-based aerogel microspheres (GAMs) to achieve broadband high-efficiency absorption can be divided into four modes: shell parameter regulation (Mode I), double/multilayer design (Mode II), micro/nano structure or composition regulation (Mode III), and collective effect regulation (Mode IV).Using multi-axial electrospinning technology and directional freezing methods, the research team successfully prepared GAMs with tunable structural parameters, including hollow GAMs (HGAMs), double-layer GAMs (DGAMs), triple-layer GAMs (MGAMs), and triple-layer GAMs with cavities (HMGAMs). By adjusting the outer flow rate and electrostatic voltage, they precisely controlled the cavity size and found that the inner cavity dimensions significantly influenced electromagnetic performance.Experiments demonstrated that regulating hollow cavity size notably affected electromagnetic wave absorption performance. As shown in Figure 3, HGAMs-3 with the largest hollow resonant cavity achieved an effective absorption bandwidth (EAB) of 8.1 GHz at a thickness of 3.3 mm, with a minimum reflection loss (RL) of -34.8 dB, covering most of the X-band and the entire Ku-band. Additionally, the introduction of transparent layers and multi-shell designs significantly optimized the material's impedance matching and frequency response, further enhancing broadband absorption performance.Regulation of micro/nano structures, such as the assembly of RGO sheets and the incorporation of magnetic Fe₃O₄ nanoparticles, effectively enhanced conductive loss and dielectric polarization, optimizing the material's electromagnetic wave absorption capability.

Figure 4: Simulated electric field and volumetric loss density responses of single- vs. double-layer aerogel microsphere arrays.

Furthermore, through bowtie tests and electromagnetic simulations, the research team thoroughly investigated the collective absorption performance and attenuation mechanisms of GAMs.Experimental results showed that hollow GAMs exhibited ultra-broadband absorption performance in double-layer arrays, covering the 3 GHz to 18 GHz frequency range, with distinct multi-peak resonance phenomena. Thickness matching and collective resonance effects jointly contributed to the generation of multiple peaks, particularly at 4.3 GHz and above 18 GHz, corresponding to λ/4 or 3λ/4 resonances. The theoretical absorption performance of HGAMs-4 demonstrated moderate intensity and the widest EAB, with actual test results surpassing most reported broadband absorption materials.Electromagnetic simulations revealed that transparent layers and hollow cavity designs significantly improved electric field distribution and attenuation modes. The hollow cavities facilitated transmission coupling between microspheres, while the outer lossy shells enhanced the attenuation performance of the central microspheres. The study also found that double-layer stacking substantially improved electric field distribution and loss density, exhibiting two attenuation mechanisms: continuous mode and island mode.The results indicate that by adjusting free-space parameters (e.g., transparent layers or hollow cavities), different synergistic attenuation mechanisms can be constructed to further enhance electromagnetic wave absorption performance. The methods and design principles proposed in this study provide essential guidance for developing advanced broadband electromagnetic wave absorption materials. Further optimization of shell structures and nanomaterial interface design is expected to broaden absorption bandwidth and improve efficiency, promoting the application of aerogel microspheres in electromagnetic wave absorption, stealth technology, wireless communication, and other fields.