Theoretical and Experimental Study of Phononic Crystal Structures for Acoustic Wave Filtering and Energy Harvesting in Nigerian Infrastructure Applications

Background: Phononic crystals are periodic elastic structures that exhibit acoustic bandgaps analogous to electronic bandgaps in semiconductors, with applications in vibration isolation, noise filtering, and acoustic energy harvesting. Their design for Nigerian infrastructure vibration conditions represents an unexplored application domain. Aim: This study theoretically designed and experimentally validated phononic crystal structures for acoustic wave filtering and energy harvesting applications in Nigerian road and railway infrastructure contexts. Methods: Finite element simulations using COMSOL Multiphysics computed band structures and transmission characteristics of phononic crystal plate and pillar array designs. Fabricated aluminium and steel phononic crystal prototypes were characterised using laser Doppler vibrometry and acoustic impedance tube measurements. Piezoelectric energy harvesting from acoustic bandgap edge states was evaluated experimentally. Vibration source characterisation was performed on Lagos-Ibadan expressway and Abuja light rail infrastructure. Results: Phononic crystal plates achieved bandgap attenuation of 42 dB in the 200 to 800 Hz frequency range matching dominant infrastructure vibration spectra. Defect-mode resonance enhanced piezoelectric energy harvesting power density to 86 microwatts per cm2 at 15 Hz vibration. Bandgap frequency was tunable by 38% through pillar geometry modification. Conclusion: Phononic crystal structures are effective for both vibration filtering and energy harvesting from Nigerian infrastructure vibrations. Embedding piezoelectric phononic crystal arrays in bridge decks and railway sleepers is proposed as a self-powered structural monitoring power source. Keywords: phononic crystal, acoustic bandgap, energy harvesting, vibration filtering, Nigerian infrastructure.