Sound intensity in the near field above a vibrating flat plate

This paper presents results from theoretical and experimental studies of sound intensity in the near field above a 1000 x 500 x 1.2-mm flat steel plate, The plate was vibrated at its center by a non-contacting magnetic exciter driven by a pink-noise signal, Root-mean-square vibration velocities were determined from measurements by a small accelerometer at 33.3-mm increments in a square grid pattern, Normal components of the measured vibration velocity, determined from 1/12th-octave-band analyses, were expanded as a two-dimensional Fourier series to give the x and y components in the wave-number domain of the structural bending waves, Sound intensity vectors, in planes parallel to the surface of the plate, were computed from the product of calculated sound pressures and calculated acoustic particle velocity vectors, Sound pressures and particle velocities represented the superposition of contributions from all structural bending waves in the vibrating plate, Sound intensities were measured at 33.3-mm increments in several planes above the surface of the plate, Measured and calculated contours of sound intensity level showed good agreement for the vibration mode with the greatest response, The predicted recirculation of sound power flow near the surface of the plate was confirmed by the measured sound-intensity-level contours. (C) 1997 Institute of Noise Control Engineering. [S0736-2501(97)00405-0].