Noise pollution impact on people physical and mental health and causes indirect socio-economical problems. The social issue has longed to be resolved in modern time since conventional materials such as acoustic sponge and porous materials have poor performance in low frequency regions (<500Hz). Metamaterials are newly developed to overcome the Mass law limitation, whereas having other intrinsic limitations, such as narrow working frequency band. This study investigates the potential of achieving broadband sound attenuation by composite structure of membrane type acoustic metamaterial. Different acoustic phenomenon, including total reflection, total absorption and Willis coupling, were manipulated by modifying these composites. Hybridized Membrane Resonator (HMR) tube system and Off-centred Decorated Membrane Resonator (ODMR) were constructed for the study of Willis coupling and asymmetric resonance pattern coupling. Progressive change of Willis Coupling coefficient from W= 0 to 2.5 was demonstrated through fine tuning the effective parameters of the resonator. New Locally Resonant Sonic Material (LRSM), composed by membrane and perforated panel, with subwavelength dimension and high TL in low frequency region was proposed. Experimental data demonstrated that the new material had non-Mass law behaviour and dependence on hole dimension, number of layers and inter-layer separation instead. Based on the discussion of the observed acoustic features, additional components, namely side HMR and M-layer, were introduced, resulting in much better sound attenuating performance of existing devices without increasing their size. Through additional absorption and reflection, significant increment of transmission loss was observed. Broadband 0.1 transmission coefficient with 15mm overall thickness by composite membrane type acoustic metamaterial is presented. Further discussion is needed to transform the developed device into acoustic products such as earmuffs and sound-proof panels.

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Noise pollution impact on people physical and mental health and causes indirect socio-economical problems. The social issue has longed to be resolved in modern time since conventional materials such as acoustic sponge and porous materials have poor performance in low frequency regions (<500Hz). Metamaterials are newly developed to overcome the Mass law limitation, whereas having other intrinsic limitations, such as narrow working frequency band. This study investigates the potential of achieving broadband sound attenuation by composite structure of membrane type acoustic metamaterial. Different acoustic phenomenon, including total reflection, total absorption and Willis coupling, were manipulated by modifying these composites. Hybridized Membrane Resonator (HMR) tube system and Off-centred Decorated Membrane Resonator (ODMR) were constructed for the study of Willis coupling and asymmetric resonance pattern coupling. Progressive change of Willis Coupling coefficient from W= 0 to 2.5 was demonstrated through fine tuning the effective parameters of the resonator. New Locally Resonant Sonic Material (LRSM), composed by membrane and perforated panel, with subwavelength dimension and high TL in low frequency region was proposed. Experimental data demonstrated that the new material had non-Mass law behaviour and dependence on hole dimension, number of layers and inter-layer separation instead. Based on the discussion of the observed acoustic features, additional components, namely side HMR and M-layer, were introduced, resulting in much better sound attenuating performance of existing devices without increasing their size. Through additional absorption and reflection, significant increment of transmission loss was observed. Broadband 0.1 transmission coefficient with 15mm overall thickness by composite membrane type acoustic metamaterial is presented. Further discussion is needed to transform the developed device into acoustic products such as earmuffs and sound-proof panels.