Enhanced sound attenuation using radially gradient sonic crystals with cladded resonators

This study investigates the sound attenuation characteristics of a radially gradient sonic crystal (RGSC) by analyzing two distinct configurations: one incorporating rigid resonators and the other featuring cladded resonators. Unlike conventional sonic crystals (SCs), the proposed RGSC structure is designed for radial wave propagation, making it effective for near-field applications. The inclusion of jute-felt cladding on the resonators enhances attenuation by increasing absorption at higher frequencies, addressing a key limitation of rigid-resonator-based SCs. A combination of finite element (FE) simulations and experimental measurements is used to analyze the insertion loss (IL) spectra of the RGSC. The results demonstrate that the resonance-induced bandgaps dominate attenuation in the lower frequency range (500–1400 Hz), while Bragg scattering effects govern higher frequencies. Notably, experimental findings confirm a significant improvement in attenuation due to cladding, particularly in the 3150–6400 Hz range. Furthermore, attenuation levels are experimentally analyzed at different measurement locations behind the RGSC. While attenuation is highest near the center, the inclusion of jute cladding improves performance even at outer locations, leading to effective broadband noise reduction. These findings suggest that RGSCs with cladded resonators can be highly effective for machinery enclosures, industrial applications, and urban noise control requiring omnidirectional noise mitigation.