Statistically optimized near field acoustic holography using an array of pressure-velocity probes

Abstract

Statistically optimized near field acoustic holography (SONAH) differs from conventional near field acoustic holography (NAH) by avoiding spatial Fourier transforms; the processing is done directly in the spatial domain. The main advantage of SONAH compared with NAH is that the usual requirement of a measurement aperture that extends well beyond the source can be relaxed. Both NAH and SONAH are based on the assumption that all sources are on one side of the measurement plane whereas the other side is source free. An extension of the SONAH procedure based on measurement with a double layer array of pressure microphones has been suggested. The double layer technique makes it possible to distinguish between sources on the two sides of the array and thus suppress the influence of extraneous noise coming from the “wrong” side. It has also recently been demonstrated that there are significant advantages in NAH based on an array of acoustic particle velocity transducers (in a single layer) compared with NAH based on an array of pressure microphones. This investigation combines the two ideas and examines SONAH based on an array of pressure-velocity intensity probes through computer simulations as well as experimentally.

Experimental validation of acoustic intensity bandwidth extension by phase unwrapping

“…Measurement of active acoustic intensity has numerous applications, including obtaining radiated sound power, 1 noise source identification, 2 sound field reconstruction, 3,4 and determining building sound insulation. 5 A limitation of using multimicrophone intensity probes 6 to characterize broadband sources and fields has been a requirement of repeating the measurement with a number of microphone spacings to overcome the significant bias errors 7 associated with the traditional quadspectrum-based intensity method.…”

Laser method of sound emission control from vibrating surfaces of noise road barriers

“…Intensity sound probes [2][3][4][5][6][7], their arrays and based on them near-field acoustic cameras [8], acoustic holography [9][10][11], or beamforming [12][13][14] are examples of such methods. Each of them can be also adapted as complementary tool for presented method verification.…”

Single layer planar near-field acoustic holography for compact sources and a parallel reflector

“…From a data-acquisition point of view, it is a common practice to measure pressure or particle velocity in two closely spaced surfaces, or to measure Cauchy data in a single layer. Among these two categories, some studies formulate the problem with inverse boundary element and Helmholtz equation least-squares methods via the singular value decomposition [3,4,5,6,7,8], while others use the spherical wave superposition method [9,10,11], the equivalent source method [12,13,14,15,16,17] or the statistically optimized NAH method [18,19,20,21,22,23]. There is also a recent application of the equivalent source method in which the (double-layer) measurements completely cover the source region, allowing acoustic visualization of the field in small cavities [24].…”