Читать книгу Introduction To Modern Planar Transmission Lines - Anand K. Verma - Страница 250

The classical Salisbury absorber, shown in Fig (5.16a), is a narrow band resonant type absorber. The absorbing resistive screen has resistive 377Ω/sq impedance so that it is matched to free space. A metallic sheet (electric‐wall) placed behind the absorbing screen at a distance λ₀/4 creates the magnetic‐wall, i.e. the high impedance surface (HIS) at the plane of the resistive screen. The equivalent transmission line model of free space shows the absorbing screen as a 377Ω load followed by an open‐circuited termination corresponding to the magnetic‐wall. The concept of magnetic‐wall is discussed in the subsection (7.2.2) of chapter 7. At the magnetic‐wall, the total tangential components of the incident and reflected waves provide a high‐intensity electric field, i.e. . However, the total tangential component of the magnetic field is zero, i.e. . The total electric field induces a current on the resistive screen placed at the magnetic‐wall. The absorbed incident RF power is dissipated. Salisbury absorbing sheet is narrowband, thick, and bulky. By placing several absorbing resistive screens above the conducting plane, over a distance λ₀, a broadband absorber, known as Jaumann absorber, is obtained [B.15]. Again, it is a thick and bulky absorber. The metasurface provides an alternate arrangement for creating the high impedance surface to develop a thin and compact absorber. The realization of the metasurface is discussed in section (22.5) of chapter 22.

Figure 5.16 Composite surface absorber.