Solid-borne sound intensity: A personal perspective

Numerous facets of this still exotic subject are illuminated. A few historical remarks illustrate that the field of solid-borne sound intensity is much more intricate and less developed than its fluid-borne counterpart. Nevertheless, taking advantage of both magnitude and direction of the intensity vector resulted, for instance, in a successful measuring method for the localization of sound bridges. In this case the generic complexity is substantially reduced by the assumption of bending waves on thin plates. The usual restriction to measurements at the surface of a solid is uncritical for 'acoustically thin' bodies. In other cases, however, one either contents oneself with the quantities measured at the surface ('surface intensity') or tries to extrapolate the experimental information from the surface to the interior. Hence, theoretical work and numerical simulations are indispensable companions in the development of reliable measurement techniques. The concept of a 'universal' sensor for solid-borne sound in combination with special graphic presentations like circle-arrow plots might foster practical applications. Among the theoretical issues briefly touched upon are 'reactive intensity', energy-related the or ems, Lamb and Bloch waves (with a glance at the COMSOL software), redirection of energy flow, and the interaction of fluid-borne and solid-borne sound in porous media.