Implications from Broadband Microwave Absorption of Metal-modified SiC Fiber Mats.

Understanding the physical requirements for broad bandwidth is vital for the design of high efficiency microwave absorber. Our recent works on SiC fibres mats based absorbers imply that metal modification (e.g. Fe or Hf) could benefit their bandwidth effectively. For verification, we fabricated Co/SiC fiber mat via a similar electrospinning process and subsequent pyrolysis at 1400 oC in Ar atmosphere. The results indicate that after Co modification the SiC fiber mats show elevated permittivity and tangent loss. With proper amount of Co adding, the mats could exhibit a wide bandwidth of around 8 GHz (ranging from 10 to18 GHz) for effective absorption (reflection loss less than -10 dB) at 2.8 mm thickness. This is similar to our previous findings, confirming that metal modification could be an effective approach to extend the bandwidth of SiC mats absorber. Explanations can be found through theoretical analysis with quarter wavelength (λ/4) cancellation theory. It suggests that the declining permittivity (with the increase of frequency) is key to keep the wavelength in material (λm) nearly unchanged within a frequency range. As a result, in this range the λ/4 cancellation could be still satisfied without changing thickness, which could explain the reasons for the broad bandwidth of metal modified SiC fiber mats. With this model, it is further predicted that the effective absorption bandwidth could be even extended to be around 12 GHz with appropriate tangent loss. It should be emphasized that the implications obtained in this study could be also applicable to other dielectric absorbers. The requirement on permittivity and the proposed approach could serve as guidelines to achieve wide bandwidth on dielectric absorber replying on λ/4 cancellation principle.