Black Body Approach: Parametric Version

In this chapter, we use simple models for acoustical waves (Section 3.1) [59], [61], [63], [64], [59], for water surface waves (Section 3.2) [62], [59], [61], [50], and for electromagnetic waves (Section 3.3) [65]. On the basis of these models, we consider the new concept of parametric "black body" with conceptual possibility of designing an active absorbing (nonreflecting) coatings in the form of a thin layer with small-scale stratification and fast temporal modulation of parameters. Algorithms for spatial-temporal modulation of the controlled-layer structure are studied in detail for a one-dimensional boundary-value problem. These algorithms do not require wave-field measurements, which eliminate self-excitation problem, that is the characteristic of traditional active systems. The majority of the considered algorithms of parametric control transforms the low-frequency incident wave to high-frequency waves of the technological band for which the waveguiding medium inside the layer is assumed to be opaque (absorbing). The efficient conditions of use are found for all the algorithms. It is shown that the absorbing layer can be as thin as desired with respect to the minimum spatial scale of the incident wave ensuring efficient absorption in a wide frequency interval (starting from zero frequency) that is bounded from above only by a finite space-time resolution of the parameter-control operations. The structure of a threedimensional parametric "black" coating, whose efficiency is independent of the angle of incidence of an incoming wave is developed on the basis of the studied one-dimensional problems. The general solutions of the problem of diffraction of incident waves from such coatings are obtained. These solutions are analyzed in detail for the case of a disk-shaped element.