Scan-Based Near-Field Acoustical Holography on Partially Correlated Sources

• Main Author: Gardner, Michael D.
• Format: Others
• Published: BYU ScholarsArchive 2009
• Subjects: near; field; acoustics; acoustical; holography; partially; correlated; sources; reference; microphones; virtual; coherence; jet; noise; military; aircraft; length; spatial; variation; partial; decomposition; discrete; continuous; numerical; physical; Astrophysics and Astronomy; Physics
• Online Access: https://scholarsarchive.byu.edu/etd/1909; https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=2908&context=etd

Scan-based near-field acoustical holography (NAH) is applied to partially correlated sources. Partial field decomposition via the virtual coherence method is used to implement the scan-based NAH. The background and theory of these methods are developed. Multiple stationary reference microphones are required for the partial field decomposition. Guidelines for reference microphone placement in the literature thus far have been limited. Improved guidelines for reference microphones are given after the results of two sets of experiments. The first set involves discrete, partially correlated sources, both physical and numerical. The second set of experiments is strictly numerical and involves continuous sources. Fewer microphones are required for partially correlated sources as compared to completely uncorrelated sources. Reference microphone number is found to be more critical to reducing holography reconstruction errors than is placement or location. For the continuous results, an appropriate figure of merit is created: reference microphones per coherence length. Based upon the definition of coherence length, two reference microphones per coherence length are required to minimize reconstruction error. Further practical reference microphone guidelines are given. These guidelines are to assist in preparing for a full-scale application of scan-based near-field acoustical holography to a military aircraft jet.