In Ramm’s second edition on refraction coefficient the author shares his recipe for creating materials with a desired refraction coefficient and solves the many-body wave scattering problem for many small impedance bodies. Technical problems are described which, when solved, make this theory practically applicable. It also provides physical and mathematical arguments for the possibility to produce such particles. Inverse scattering with non-over-determined scattering data is discussed. Revised and expanded, this new edition includes three new chapters: the discussion of technological problems to be solved for immediate applicability for creating materials with a desired refraction coefficient; symmetry properties of the solutions to the Helmholtz equation and new results on symmetry properties in harmonic analysis; and theorems in inverse scattering. Key Features Presents a method for creating materials with a desired refraction coefficient Includes a process for creating wave-focusing materials Highlights inverse problems of finding the potential from the non-over-determined scattering data Provides an overview of symmetry properties in scattering theory