Abstract
An angular spectrum approach can be used to obtain high-resolution measurements of the acoustic plane wave reflection and transmission coefficients corresponding to a given planar sample of material. Such an approach involves exciting the sample with a compact broadband source located in the near field and then scanning the resulting reflected or transmitted field on a plane parallel to the sample surface. Fourier transforms in both space and time then yield a description of the acoustic field in terms of its angular spectrum, or expansion into time-harmonic plane waves propagating throughout a range of frequencies and angles. To demonstrate this method, measurements made on a thick aluminum plate submerged in water are shown. In this case the reflection and transmission coefficients are intricately structured, with individual features corresponding to different symmetric and antisymmetric guided wave modes propagating within the plate. The coincidence effect, by which the plate is nearly transparent acoustically at just those frequency-angle pairs that excite guided waves, is clearly seen in the measurements. Measurements made on other materials, as well as possible extensions to this method, will also be discussed. [Research supported by ONR.]
Published Version
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