The impedance theory of scattering (which was proposed by the author-see Acoust. Phys. 52, No. 5 (2006)) is used as the basis for studying the extremum properties of the absorption and scattering sound powers of arbitrary elastic bodies in an arbitrary acoustic medium. Impedance-type conditions are obtained for the surfaces of a best absorber, a perfect scatterer, and a so-called Macdonald body. The absorbing and scattering properties of these objects are studied in comparison with the Kirchhoff black body. Illustrative examples are presented.
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