Elastic Waves in Solids, Volume 2

1Radiation of Elastic Waves

Acoustic waves emitted by sources of finite dimensions diverge, so that acoustic pressure and power density decrease with the distance from the transmitter. Understanding the radiation of sources is therefore essential to predict the acoustic field emitted by transducers used for medical diagnosis or in sonar systems, as well as in defect detectors in metallurgy or in other instruments and sensors.

The chapter is divided into three sections. In the first section, we study the acoustic radiation in a perfect fluid by a vibrating plane surface, then by a focused transducer. In the harmonic case and in a medium where the acoustic wave is defined by a scalar quantity such as the velocity potential or the acoustic pressure, the results are similar to those of the scalar theory of diffraction in optics. One specificity of acoustics is the use of short impulse waves or wave trains of varying durations. By drastically reducing the interferences between the waves emitted by the different points of the source, the conditions of the impulse diffraction, presented at the end of this section, are very different from those observed for time-harmonic waves. In the second section, we analyze the radiation of bulk elastic waves and Rayleigh waves in isotropic or anisotropic solids. With the exception of the explosive sources used in the field of oil exploration, these sources are most often located on the solid surface. The modeling of a seismic or a thermoelastic ...