Digital Wavefront Reconstruction for Acoustical Applications.
PENNSYLVANIA STATE UNIV UNIVERSITY PARK APPLIED RESEARCH LAB
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The work presented is an extension of research in acoustical holography as a tool for sound source location this research being centered on digital processing and computer graphics imaging. Holographic images of plates vibrating below coincidence frequency show radiation from regions of discontinuity and not from other regions. Digitally reconstructed images from acoustic holograms show the radiating part far-field component of the pressure at the source location. The image may be interpreted as a monopole distribution which would generate the same far field as did the original source distribution. A near-field scan records the entire field and yields an image which is proportional to the surface velocity of the plate. It shows the modal pattern of the plate vibration. The holographic far-field image is approximately equivalent to the near-field image with the high wave numbers filtered out. Since the far field contains spatial frequencies only up to 1lambda, image resolution is limited by the acoustic wavelength i.e., the ideal image is convolved with an Airy pattern.
- Acoustic Detection and Detectors