Computational Study on Quasi-Ordered Acoustic Crystals in Double-Plate Configurations: Optimization-Guided Defect Engineering for Frequency-Selective Enhanced Wave Attenuation

Periodic phononic crystals inevitably increase weight in double-plate configurations (DPCs), limiting practical applications. This computational study proposes quasi-ordered scatterer arrangements for finite DPCs to achieve enhanced low-frequency wave attenuation via sparse defect engineering. The DPC comprises two parallel plates enclosing optimized multi-geometry scatterers—cylindrical, Ctype, and slot-type shells—whose distribution is determined by Finite Element Analysis coupled with an Adaptive Single-Objective (ASO) algorithm. Remarkably, DPC confinement amplifies individual scatterer effects, enabling arrangements sparser than Romero's free-space configurations to deliver superior broadband attenuation across predetermined low-frequency ranges. The optimization reveals that selective removal of just a few scatterers critically determines performance, yielding significant weight reduction while improving sound-proofing properties. This framework demonstrates that DPC fundamentally transforms acoustic interaction mechanisms, offering new possibilities for lightweight phononic systems where minimal material usage achieves maximal wave control. The computational predictions provide foundational insights for future experimental validation.