Dynamic F-number and shading weights determined by element directivity for PAM

The time exposure acoustics (TEA) beamformer for passive acoustic mapping (PAM) has been demonstrated with potential for real-time monitoring via sparse-matrix, GPU-running etc., methods. However, TEA-based PAM methods generally have insufficient clutter suppression capability due to linearly assumed weighting coefficients, and whole-aperture realigned data reconstruction for the generation of the side/grating lobes. The F-number is a convenient way to determine the available data in the aperture domain and therefore reject the side/grating lobes. Nevertheless, the standard of an optimal F-number into PAM beamformer is unclear. To concern that, a strategy is proposed based on a soft-baffle Element Directivity (ED) model (related to the conformal nature of the receiving array) for Dynamic F-number and Shading Weight (DFSW). This approach maintains and shapes the top hyperbola part of the realigned receiving wavefront in the pixelwise aperture domain, that was investigated into TEA based PAM (TEA and coherent TEA (CTEA)). Final results from TEA and the proposed methods (ED TEA, ED CTEA) illustrated that the DFSW strategy developed from ED model mainly improves the image quality (FWHM, CNR) in the near-field, which is explained and verified by simulated and experimental data.