Thomas H. Burns
Graduate Program in Acoust., Penn State Univ., University Park, PA 16804
William Thompson, Jr.
Courtney B. Burroughs
Penn State Univ., University Park, PA 16802
The instantaneous acoustic intensity is a spatially dependent vector that describes the power flow through a point in space as a function of time. It consists of both active and reactive components. For time harmonic sources, both components oscillate in time. In the past, multiple reactive intensity vectors have been simultaneously displayed in the form of vector fields. Each vector represented the maximum value the reactive intensity obtained at that point in space; it did not represent a time average since the reactive intensity, unlike the active intensity, time-averages to zero. Although plots of the amplitude of the reactive intensity are useful for localization and field characterization, they do not contribute to an understanding of energy transfer in the time domain. A vector field suggests that each vector obtains its maximum value at the same time instant, which is not true. The purpose of this presentation is to clarify conventional interpretations of the reactive intensity. This will be accomplished by analyzing the expression for the instantaneous acoustic intensity, interpreting traditional reactive intensity vector field plots, and using this information to make conclusions concerning energy transfer in the time domain. [Work supported by International Jensen, Inc.]