1993

Linjama, Jukka

Measurement of energy flow in acoustical and vibrational fields is usually based on the detection of one linear field quantity (e.g. sound pressure) and its spatial gradient, two transducers being used for the measurement. This report first reviews the quantities which can be obtained from the measurement of acoustical intensity with a two-microphone probe: intensity and the energy densities. A set of 'field descriptors', relative quantities giving a measure of propagating (active) character of the waves in the sound field, is proposed. As a main contribution, analogous, but approximate quantities for structural intensity (far field of bending waves) are then given. These energetic quantities are based entirely on the transversal velocity measured and the gradient of that velocity, and are thus available when the two-transducer method of bending wave intensity is used. Examples of the energy densities and field descriptors measured in an aluminium plate are presented, and proposals for further work are given.