Structural surface intensity: An alternative approach in vibration analysis and diagnosis

The physical meaning of structure-borne sound intensity is discussed. The relationships which express the intensity on a free surface are evaluated in terms of measurable physical quantities. Five such independent quantities, three strains and two velocities, have to be simultaneously detected and processed in an appropriate way in order to get intensity readings. Formulae are presented for both the active and the reactive intensities, and for the intensity spectra. A technique is proposed, based on use of conventional transducers, which can be applied to practical surface intensity measurements. The accuracy of such a technique is discussed, and various possibilities for expressing the measurement readings are examined. A particular measurement is described and the results given of the surface intensity distribution obtained by conventional equipment at several points of an elevator drive mechanism.