ABSTRACT
Due to their infinite energy, plane waves are not immediately appropriate for applications in US-NDT. Yet, as solutions of homogeneous wave equations, they may be superimposed with different amplitudes into arbitrary propagation directions: We obtain a spatial spectrum of plane waves that is literally a spatial spectrum because the propagation directions of the respective plane waves are given by the Fourier vector K as conjugate vector to R! Transducer radiation fields and Gaussian beams may be adequately described by these spectra (Chapters 14 and 12). Formally, we find the spatial plane wave spectrum by Fourier transforming the reduced wave equations with respect to two Cartesian coordinates; consequently, the resulting two-dimensional inverse Fourier integral has to be interpreted accordingly. To avoid unnecessary algebraic ballast, we will first deal with scalar acoustic wave spectra.
