Diffraction Effects of Baffles on Acoustic Directivity Patterns.
PENNSYLVANIA STATE UNIV UNIVERSITY PARK APPLIED RESEARCH LAB
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The acoustic diffraction phenomena which occur at the edges of a baffle is investigated both experimentally and theoretically. Various sharp-edged and cylindrical-edged baffles were constructed in which geometry, impedance, and structural resonances were controlled. Data were obtained as a function of incident pressure, angle of incidence, and frequency, using two transducers, one in the far field and one on the baffle surface. Also investigated is the effect of placing small scattering barriers at the edge of rigid baffle surfaces. The Geometrical Theory of Diffraction is used to develop a theoretical model for the calculation of patterns. Both Sommerfeld and Malyuzhinets diffraction coefficients are discussed along with the utilization of a transition region function to remove singularities. Patterns obtained with rigid baffle surfaces exhibited ripples in the insonified region while soft baffles gave rise to a smooth bell-shaped directivity pattern with highly attenuated diffraction fields. Asymmetric patterns resulted when a transducer was positioned close to one edge of a finite baffle. The good agreement obtained between theory and experiment confirms the validity of the Geometrical Theory of Diffraction. Author