Broadband Planar Nearfield Acoustic Holography based on One-third-octave Band Analysis

By the combination of the one-third-octave band mean-square pressure and the phase of the pressure corresponding to a single frequency line, the source behavior over a broad frequency range can be identified with relatively fewer data to process.

PhD Candidate: Hefeng Zhou
Supervisors: prof. dr. Henk Nijmeijer, prof. dr. ir. Ines Lopez-Arteaga
Project Funding: China Scholarship Council (CSC)
Project Period: September 2012 - August 2016

Planar nearfield acoustic holography is usually based on narrow-band, single frequency analysis, which is time consuming when the source behavior over a broad frequency range is of interest, which is the case with many industrial sources. In the present paper a method, broadband planar nearfield acoustic holography based on one-third-octave band analysis (BPNAH), is developed, of which data concerning the complex band pressure on the hologram is obtained by the combination of the one-third-octave band mean-square pressure and the phase of the pressure corresponding to a single frequency line.

A numerical study shows that there is no noticeable difference between the quality of the reconstruction by BPNAH and the quality of the conventional reconstruction from the summation of one frequency by one frequency in the corresponding band in the presence of noise, especially for single source and identical multiple sources. Being weakly affected by phase uncertainty, this method is a simple, time-saving and robust technique and thus particularly adapted to industrial studies.

Step 1: Rayleigh's first integral of each frequency sub-band
Step 2: Band mean-square pressure calculation
Step 3: Spatial window
Step 4: Zero-padding
Step 5: Fourier-based PNAH
Step 6: Quantitative evaluation