1 Department of Electrical Engineering, Technical University of Denmark 2 Acoustic Technology, Department of Electrical Engineering, Technical University of Denmark 3 Institut National des Sciences Appliquees de Lyon
In conventional near-field acoustic holography (NAH) it is not possible to distinguish between sound from the two sides of the array, thus, it is a requirement that all the sources are confined to only one side and radiate into a free field. When this requirement cannot be fulfilled, sound field separation techniques make it possible to distinguish between outgoing and incoming waves from the two sides, and thus NAH can be applied. In this paper, a separation method based on the measurement of the particle velocity in two layers and another method based on the measurement of the pressure and the velocity in a single layer are proposed. The two methods use an equivalent source formulation with separate transfer matrices for the outgoing and incoming waves, so that the sound from the two sides of the array can be modeled independently. A weighting scheme is proposed to account for the distance between the equivalent sources and measurement surfaces and for the difference in magnitude between pressure and velocity. Experimental and numerical studies have been conducted to examine the methods. The double layer velocity method seems to be more robust to noise and flanking sound than the combined pressure-velocity method, although it requires an additional measurement surface. On the whole, the separation methods can be useful when the disturbance of the incoming field is significant. Otherwise the direct reconstruction is more accurate and straightforward. © 2012 Acoustical Society of America.
Acoustical Society of America. Journal, 2012, Vol 132, Issue 6
Acoustic field measurement; Acoustic fields; Acoustic holography; Transfer matrix method; Velocity; Velocity control; Numerical methods; Double layers; Equivalent source; Field separation; Flanking sounds; Free fields; Nearfield Acoustic Holography; Particle velocities; Particle velocity measurement; Pressure-velocity; Separation methods; Single layer; Sound pressures; Transfer matrixes; Weighting scheme
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