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Simulation with NFML structure with single directional pipe: (a) physical structure (center pipe dimension: l = 192.1 mm and d = 27.8 mm; directional pipe dimension: l = 78.4 mm and d = 10 mm); (b) at the bottom of the NFML structure, the transparent cylinder indicates the microphone; (c) sound pressure distribution at 3014.6 Hz and (d) RMS sound intensity streamline at 3014.6 Hz.
