Читать книгу Introduction To Modern Planar Transmission Lines - Anand K. Verma - Страница 254

Figure (5.17b) shows the matched DNG slab without any conductor backing. In this case, the impedance matching of the DNG slab is also obtained for the condition μ_r = ε_r. The transmissivity of a normally incident wave is given by equation (5.5.48b). A thicker DNG slab is taken (d >> d_min) to reduce the transmissivity T almost to a negligible value.

Both arrangements can be simulated using the Drude–Lorentz model discussed in chapter 6. We have discussed only the case of a single‐layered DNG absorber. It has a limited bandwidth, as μ_r = ε_r is obtained at one frequency. However, several thin layers of the lossy DNG could be stacked to get a wideband absorber. The multiple resonance DNG slabs provide multiband absorber also [J.32–J.35].

The metamaterials have several other characteristics and applications. For instance, the DNG medium could be tailored to hide an object from the incident waves. It leads to the concept of cloaking. The cloak to hide any object is designed using the concept of the transformation electromagnetics [J.36]. The graded anisotropic refractive index between zero and unity is obtained through transformation electromagnetics. The metamaterials are used from microwave to optical frequency ranges, including the THz band [B.16]. Chapter 21 discusses realization and some applications of metamaterial in planar technology.