대역 저지 공간 필터와 착용형 흡수체 응용을 위한 광대역 주파수 선택적 표면 설계

Abstract

Frequency selective surfaces (FSSs) are electromagnetic spatial filters designed to pass or block particular frequency bands of interest. For example, a band-stop FSS is reflective for the propagation of electromagnetic waves at a certain frequency. Because of their frequency selective characteristics, research into FSSs has been widely conducted for various applications such as microwave absorbers, artificial magnetic conductors, and concealment technology. In general, FSSs are realized by utilizing a periodic conducting sheet on a substrate. However, metallic materials have inherent disadvantages such as their susceptibility to oxidization, corrosion, and difficulty functioning at high-power (arcing, breakdown, and heating). In addition, those FSSs have a drawback of narrowband operation. To overcome these limitations, all-dielectric and all-textile FSSs with broadband characteristics are proposed. The all-dielectric FSS is outlined in further detail in Chapter 3. The unit cell of the FSS consists of a thick upper hexagonal prism part and a thin lower hexagonal prism part for monolithic construction. The proposed FSS has a planar array of hexagonal ceramic prisms like a honeycomb structure. The proposed FSS has three resonant dips. These are combined to establish a -10 dB fractional bandwidth (FBW) with a broad stop-band of 31.8 % (center frequency of 9.75 GHz). To demonstrate the resonant characteristic modes, cylindrical cavity mode analysis based on cylindrical wave functions is used. Finally, to overcome the large height of the FSS proposed in Chapter 3, a wearable metamaterial microwave absorber (WMMA) as an all-textile FSS is proposed. The WMMA is composed of two square ring resonators with different sizes, a backing ground plane, and a felt substrate. All conductive materials were fabricated using conductive textiles. The grid array of different square ring resonators provides a broad absorption band due to two neighboring resonance peaks. The measured results exhibit two absorptivity peaks greater than 90% and a full bandwidth at half maximum (FWHM) of 18.9% at 9.475 GHz. In addition, the proposed WMMA has a high absorptivity regardless of the polarization angle of the EM waves and the deformation effect. The proposed WMMA has a thickness of 1 mm. Therefore, it is suitable for low-profile wearable absorber applications.