Localized Dissipative Coupling for Transmission-Window Suppression in Open-Duct Phononic Crystals

Transmission windows between resonance gaps restrict the useful bandwidth of open duct phononic crystals. We numerically compare two prescribed locations for an equal porous volume: compact blocks at the cavity roofs and an insert in an independent inter-cavity bridge. In the lossless-air-wall two-dimensional pressure-acoustic model, bridge placement increases the five-cell continuous 10 dB attenuation span from 0.51 to 0.67 kHz, a 32% increase relative to this cavity-top baseline. Matched 0.25 Hz scans give window minimum transmission losses of 0.61 and 15 dB, respectively. Direct constitutive integration at 1150 Hz gives porous dissipation fractions of 0.016 and 0.42 of incident power. Mesh and frequency refinement quantify numerical sensitivity. Separate three-dimensional wall-loss calculations give an 8.5 dB placement benefit at 1150 Hz and lower rejection at adjacent sampled frequencies; they do not establish a continuous three-dimensional bandwidth. Two-dimensional hydraulic screening predicts pressure drops of 0.033–0.17 Pa at mean velocities of 0.10–0.50 m s−1. The comparison identifies a geometry-specific effect of dissipation placement under a fixed material budget. Insert characterization, mounting effects and experimental performance remain to be established.